Investigating the Structure & Properties of Metal Alloys Project.pdf · above; however, now they...

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Investigating the Structure & Properties of Metal Alloys NUCu 150-3 Fe-Cu steel alloy A Curriculum Project developed by Stephanie Zaucha from Deerfield High School for Northwestern University’s Nanoscale Science & Engineering Center through the 2006 Research Experience for Teachers Program Optical micrograph – 1000X Metal alloy visible on microscale SEM image – 4000X Metal alloy visible on microscale LEAP image Metal atoms visible on nanoscale

Transcript of Investigating the Structure & Properties of Metal Alloys Project.pdf · above; however, now they...

Page 1: Investigating the Structure & Properties of Metal Alloys Project.pdf · above; however, now they have the ability to characterize both the structure and chemistry of alloys and their

Investigating the Structure & Properties of Metal Alloys

NUCu 150-3 Fe-Cu steel alloy

A Curriculum Project developed by Stephanie Zaucha from Deerfield High School for Northwestern University’s

Nanoscale Science & Engineering Center through the 2006 Research Experience for Teachers Program

Optical micrograph – 1000X Metal alloy visible on microscale

SEM image – 4000X Metal alloy visible on microscale

LEAP image Metal atoms visible on nanoscale

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Curriculum Outline – Guiding Questions

Question One: What is the internal structure of a metal? What does it look like? (The properties of metals are dependent on their crystal structure, and the defects in the structure that can exist.)

a) LAB: The Crystal Structure of Metals b) Follow-up Assignment: Steel Webquest - Part 1

Question Two: What is a metal alloy? How is it made? (Alloys are a combination of two or more metals, which have enhanced properties as a result of their combination.)

c) LAB: Synthesis of an Inexpensive Alloy

Question Three: How are the properties of a metal affected by various heat treatments? (The metal crystal structure can be altered by processing treatments to make them more useful in various applications.)

d) LAB: Investigating the Effects of Various Heat Treatments on the Properties of a Metal e) Follow-up Assignment: Steel Webquest - Part 2

Question Four: How can scientists visualize and study the altered properties of metals? (The metal crystal structure can be observed at the macro, micro, and nanoscale.)

f) ACTIVITY: A Journey Through Size and Scale g) ACTIVITY: Visualizing Metals on the Nanoscale

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Curriculum Project Introduction

Developed by: Stephanie Zaucha Graduate Student Mentor: R. Prakash Kolli Principle Investigator: Dr. David N. Seidman Background Scientists have greatly extended the array of materials available for human use. Chemists have learned to modify the properties of matter by physically blending or chemically combining two or more substances. An alloy is a solid solution composed of two or more metals, or of a metal(s) with one or more nonmetals. Metals and alloys are virtually everywhere in our daily lives. Alloys are used to make aircraft engines, automobiles, bridges, buildings and even paper clips. The alloys bronze, brass, and pewter have been used for centuries. The properties exhibited by various metals are directly related to their internal micro and nano structure. When discussing a metal’s atomic structure (in nanometers – nm), metal ions are held together by metallic bonds in which each positive metal ion is attracted to the negatively charged delocalized electrons. Positive ions in a metal can be packed together to form different crystal structures depending on how the ions are layered. When discussing a metal’s microstructure (in micrometers - µm), a grain represents the small crystals that grow around a nucleus in all directions when a molten metal is cooled. Where one grain meets another at the edge is called a grain boundary. However, dislocations can be present, which are defects in the metal lattice structure where a few ions in a layer are missing, causing the neighboring layers to be displaced slightly to minimize the strain. The more grain boundaries there are the more difficult it is for the dislocations to move and for the metal to change shape. The result is that the metal is stiffer and harder. It is also stronger. Most alloys are created to change the elemental metals' physical properties, such as conductivity, density, ductility, hardness, luster, malleability, melting point, tensile strength, and/or chemical properties, such as resistance to corrosion. Alloys often exhibit increased strength and hardness. Precipitation hardening is a process that can be used to affect the physical properties of an alloy, such as steel, by introducing copper-rich precipitates. Various treatments can be used such as cold-working, or heat treatment followed by quenching and tempering a metal. As a result of such treatments, an alloy can demonstrate increased strength and toughness due to the precipitates being formed within its complex microstructure. Many mechanical properties of a precipitation hardened alloy can be analyzed on a macroscopic scale using Tensile testing, Charpy V-notch, and Vickers Hardness analyses. In the 1930’s, scientists only had the ability to characterize large (macro) properties of metals as described above; however, now they have the ability to characterize both the structure and chemistry of alloys and their precipitates on a three-dimensional nanoscale. A nanometer is a billionth of a meter, or 10-9 m. This is advantageous to study in light of historical events that involved material failure, such as the 1912 sinking of the Titanic, the 1987 Challenger Disaster, and most recently the 1996 U.S.S. Cole Bombing. The applications of being able to visualize materials on the nanoscale are immense. All modern industries rely on materials to create new products and technologies. By better understanding the atomic-scale structure of these materials and improving their properties to better fit our desired uses for them, we will only continue to make advances in product science and technology.

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Motivation for Curriculum Project In the 1930’s, scientists only had the ability to characterize large (macro) properties of metals; now with improved technology they have the ability to characterize the microstructure and nanostructure. This is advantageous to study in light of historical events that involved material failure, such as the sinking of the Titanic in 1912 and more recently, the October 12th, 2000 USS Cole Bombing. Scientists are studying various steel alloys in an effort to identify those that are stronger, tougher, and more explosion-resistant without introducing brittleness. Students can also investigate the properties of alloys to better understand how the materials that make up their daily world are studied and improved. As a result, there is historical relevance as well as current applications for studying the properties of steel as a material. The Seidman Group at Northwestern University’s Center for Atom-Probe Tomography is being partially funded by the Office of Naval Research for this very reason. The following article can be shared with students, or assigned as a reading, to introduce the necessity for studying metal alloys in today’s society. McGuinness, P. E. (2006). Redesigning the United States Navy with the atom probe. Scanning the Industry, 28(3), 189. Retrieved August 2, 2006, from

http://www.scanning.org/scanabstracts/SCANNING06/28189.pdf Connection to Curriculum Learning about the crystal structure and properties of metals and chemical bonding are key concepts for any introductory chemistry course. In addition, the ability to describe and manipulate the notion of scale is a core understanding in math and science. This curriculum project, Investigating the Structure and Properties of Metal Alloys, builds upon students’ knowledge of metals and chemical bonding to introduce relevant applications regarding metal alloys and nanoscale technology. Learning Goal & Objectives The main goal of this curriculum project is to provide students with an opportunity to learn more about the field of materials science and engineering through hands-on experiences with metal alloys. Students will develop an understanding of the relationship between the structure and composition of metals and their observable macroscopic and nanoscale properties. They will discover how these properties determine applications, and gain an appreciation of the historical impact of metals and the role they will play in the future. This goal will be met as a result of addressing four guiding questions, each with its own specific set of objectives. Question One: What is the internal structure of a metal? What does it look like?

At the end of the activity & webquest, students will be able to… identify the type of bonding present between metal ions, identify the basic crystal structures that metal atoms form, describe the role of delocalized electrons & positive metal ions in creating a lattice structure, describe imperfections in the crystal structure, including vacancies & dislocations, and illustrate how grains, grain boundaries, and dislocations appear in a metal’s microstructure.

Question Two: What is a metal alloy? How is it made?

At the end of the lab, students will be able to… define what an alloy is and how it is made, explain why alloying a metal is favorable or not, and identify commonly used alloys and in what industries they are used.

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Question Three: How are the properties of a metal affected by various heat treatments? At the end of the lab & webquest, students will be able to… describe the effects of cold-working and heat treating on the resulting strength of a metal, explain differences in observed strength between elemental and alloyed metals, and evaluate why the properties of the metals are dependent upon their structure.

Question Four: How can scientists visualize and study the altered properties of metals?

At the conclusion of these activities, students will be able to… differentiate between exponential & standard notation, determine the length scale between objects of very different sizes, understand the invisibility of the nanoscale to the unaided eye, discuss visual images of atoms, molecules, and cells and their relative sizes, and predict what the internal structure of a metal looks like at the micro and nano scales.

Standards Addressed As a result of the various labs and activities with the curriculum project, the student understandings described below are addressed. This includes standards as articulated both in the National Science Education Standards (listed first) and the Illinois States Learning Goals (listed second). Inquiry Process CONTENT STANDARD A - Science as Inquiry As a result of activities in grades 9-12, all students should develop understanding of:

• Abilities necessary to do scientific inquiry • Understandings about scientific inquiry

STATE GOAL 11: Understand the processes of scientific inquiry and technological design to investigate questions, conduct experiments and solve problems. 11.A.4a Formulate hypotheses referencing prior research and knowledge. 11.A.4b Conduct controlled experiments or simulations to test hypotheses. 11.A.4c Collect, organize and analyze data accurately and precisely. 11.A.4d Apply statistical methods to the data to reach and support conclusions. 11.A.4f Using available technology, report, display and defend to an audience conclusions drawn from investigations. Science Content CONTENT STANDARD B – Physical Science As a result of activities in grades 9-12, all students should develop understanding of:

• Structure and properties of matter STATE GOAL 12: Understand the fundamental concepts, principles and interconnections of the life, physical and earth/space sciences. 12.C.4b Analyze and explain the atomic and nuclear structure of matter. 12.C.5b Analyze the properties of materials (e.g., mass, boiling point, melting point, hardness) in relation to their physical and/or chemical structures.

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The Nature of Scientific Research CONTENT STANDARD E – Science & Technology As a result of activities in grades 9-12, all students should develop understanding of:

• Understandings about science and technology CONTENT STANDARD F – Science in Personal & Social Perspectives As a result of activities in grades 9-12, all students should develop understanding of:

• Science and technology in local, national, and global challenges

CONTENT STANDARD G – History & Nature of Science As a result of activities in grades 9-12, all students should develop understanding of:

• Science as a human endeavor • Nature of scientific knowledge

STATE GOAL 13: Understand the relationships among science, technology and society in historical and contemporary contexts. 13.A.4c Describe how scientific knowledge, explanations and technological designs may change with new information over time (e.g., the understanding of DNA, the design of computers).

References An Introduction to the Nanoscale: Surface Area and Volume. Materials World Modules. Supported by a

National Science Foundation grant to Northwestern University, 2004. http://www.materialsworldmodules.org/modules/m_description.htm

Callister, W. D., Materials Science and Engineering, and Introduction; 6th ed., Wiley Publishing, 2003. Exploring the Nanoworld. University of Wisconsin-Madison Materials Science & Nanotechnology

Modules. http://mrsec.wisc.edu/Edetc/modules/MiddleSchool/PygmyShrew/index.html Illinois State Board of Education. Illinois Learning Standards.

http://www.isbe.state.il.us/ils/ Isheim, D., Kolli, K. P., Fine, M., Seidman, D. N., An Atom-Probe Tomographic Study of the Temporal

Evolution of the Nanostructure of Fe-Cu Based High-Strength Low-Carbon Steels; ACTAMAT Journal, 35-40, 2006.

Metals! They’re Everywhere! A MAST Module. Materials Science & Technology 1995. Developed in

part at the Materials Science & Technology Workshop held at the University of Illinois at Urbana-Champaign during 1993-95. http://matse1.mse.uiuc.edu/home.html

Molecular Expressions: Science, Optics, and You

http://micro.magnet.fsu.edu/primer/java/scienceopticsu/powersof10/ Nanoscale Activities. University of Wisconsin-Madison Internships in Public Science Education (IPSE).

http://mrsec.wisc.edu/Edetc/IPSE/educators/index.html

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NASA Explores

http://media.nasaexplores.com/lessons/01-032/9-12_1.pdf National Research Council. National Science Education Standards. Washington, DC: National Academy

Press (1996). What is Steel? WebQuest. Derek Denby (Head of Science at Leggott Sixth Form College).

http://www.schoolscience.co.uk/content/5/chemistry/steel/index.html Other Resources Scale of Things PDF

http://www.sc.doe.gov/bes/Scale_of_Things_07OCT03.pdf Virtual SEM Simulation

http://micro.magnet.fsu.edu/primer/java/electronmicroscopy/magnify1/index.html Education Center for National Nanotechnology Initiative

http://www.nano.gov/html/edu/home_edu.html

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Investigating the Internal Structure of Metals

Introduction

Did you know that metals account for about two thirds of all the elements and about 24% of the mass of the planet? They are all around us in such forms as steel structures, copper wires, aluminum foil, and gold jewelry. Metals are widely used because of their favorable properties such as strength, ductility, high melting point, thermal and electrical conductivity, and toughness. These properties also offer clues as to the structure of metals. As with all elements, metals are composed of atoms. The strength of metals suggests that these atoms are held together by strong bonds. These bonds must also allow atoms to move; otherwise how could metals be hammered into sheets or drawn into wires?

A reasonable model would be one in which atoms are held together by strong, but delocalized, bonds. Such bonds could be formed between metal atoms that have low electronegativities and do not attract their valence electrons strongly. This would allow the outermost electrons to be shared by all the surrounding atoms, resulting in positive ions (cations) surrounded by a sea of electrons, or an “electron cloud.”

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Because these valence electrons are shared by all the atoms, they are not considered to be associated with any one atom. This is very different from ionic or covalent bonds, where electrons are held by one or two atoms. The metallic bond is therefore strong and uniform. Above their melting point, metals are liquids, and their atoms are randomly arranged and relatively free to move. However, when cooled below their melting point, metals rearrange to form ordered, crystalline structures. Objectives At the conclusion of this lab, you will be able to…

identify the basic crystal structures that metal atoms form, and describe imperfections in the crystal structure of metals, including vacancies & dislocations.

Advance Preparation

Please answer the following questions in complete sentences in your lab notebook:

1. Identify three objects / items that you rely on everyday that is constructed out of metal. 2. Describe the bonding that occurs between atoms in a metal, using the terms valence electron,

metal cation, shared, and electron cloud in your response.

3. How do metallic bonds differ from ionic or covalent bonds?

- Metal cation

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Procedure You will be visiting 2 different stations in this investigation of the internal structure of metals. Be sure to record all sketches and data in your lab notebook. Please wait until the groups have finished before moving to the second station. Station 1 – The Crystal Structure of Metals

1. Each of the Styrofoam balls will represent an atom and the toothpick will represent bonds. Attach 10 of the balls together with toothpicks to form a triangle with four balls at the base. This will form the first layer of the packing model. Draw a diagram of the arrangement of the atoms in your lab notebook.

2. Attach 6 of the balls together with toothpicks to form a triangle with 3 balls at the base. This will

form the second layer of the packing model. Draw a diagram of the arrangement of the atoms in your lab notebook.

3. Form another triangle of Styrofoam balls like the one created in step one with the remaining 10

balls.

4. Place the second layer on top of the first one with atoms of the second layer nesting in the hollows between the atoms of the first layer. This creates the closest possible packing of atoms.

5. The third layer can be placed on top of the second layer in one of two positions. It can be placed so

that its atoms are directly over those in layer one. This gives what we call an ABABAB arrangement that corresponds to hexagonal close packed, or HCP. The third layer can also be placed on top of the second layer so that its atoms are not directly over those in the first layer. This gives what we call an ABCABC arrangement that corresponds to a face-centered cubic arrangement, or FCC. Try both arrangements with your layers. Be sure to make and label a sketch that will help you remember these arrangements of atoms.

6. Lastly, attach 4 of the balls together with toothpicks to form a square. Make two such squares.

Sandwiched between these layers will be one atom. Your model should look like a cube, with an atom in the center. Draw a diagram of this structure from the side view in your lab notebook. This is a body-centered cubic, or BCC arrangement.

7. Before disassembling your models, answer the first set of analysis questions in your lab notebook.

Use your structures to help you! Have your instructor initial below when your team has finished.

8. Be sure to gently disassemble your structures and clean up your lab area before moving to the next

station.

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Station 2 – The Particle Model of Metals Please keep the Petri dish flat on the table so the Bb’s do not spill out.

1. The Bb's represent the atoms in a metal. If you move the Petri dish back and forth the atoms move. This simulates the movement of atoms in a metal when it is heated. First move the dish back and forth somewhat rapidly to represent heating. Then slow the motion down and gradually stop to simulate the formation of the crystal (such as cooling the metal over time in the air, a process called “annealing”).

2. Once you stop, make a sketch in your lab notebook showing how the Bb's are arranged. You do

not have to draw all the Bb's – just sketch the general arrangement of the atoms.

3. Then make a sketch showing the arrangement of Bb's around an empty space. When this happens in the metal it is called a vacancy. In a real crystal when atoms are out of line it is called a dislocation. Be sure to sketch any vacancies or dislocations you observe.

4. Move the dish back and forth somewhat rapidly, again simulating the heating of the metal.

Heating the metal increases the atoms more kinetic energy. This time, stop the movement rapidly. This is like plunging the metal into a beaker of cold water (called “quenching”). Make a sketch in your lab notebook showing the general arrangement of the atoms, noting any vacancies or dislocations you observe.

5. For the last simulation, imagine that the metal you are observing on the atomic level is a bobby

pin. Shake the Bb’s as to simulate what it is like to a) heat the metal, b) cool quick, and then c) heat again,but not as hot (called “tempering”). Draw what the bobby pin now looks like on the atomic level, again noting any vacancies or dislocations you observe.

6. Now answer the second set of analysis questions in your lab notebook. Use your Bb model to help

you! Have your instructor initial below when your team has finished.

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Analysis Please respond in complete sentences.

After completing Station 1 -

1. Which packing arrangement(s), FCC, HCP, or BCC appear to be the most densely packed in any given area?

2. What is the difference in FCC and HCP arrangements? Feel free to describe in words, or sketch!

3. About how small would an atom have to be to fit in an interstitial hole in an FCC, HCP, or BCC crystal structure? (Predict answer as what fraction of an atom – 1/2? 1/3? 1/5? 1/8?)

After completing Station 2 - 1. Are the Bb's arranged perfectly at the end of each simulation? Would you expect atoms to be

perfectly arranged? Explain why or why not.

2. Describe how the arrangement of the Bb's are different between each of the three heating/cooling methods. Are there more or less empty spaces, i.e., places where a Bb is missing, or other defects?

To be completed on your own-

1. In both the FCC and HCP crystal structure arrangements, atoms in layer 2 were nestled in between the spaces of those atoms in layer 1. Based on what you know about metals and bonding, why would this be how the atoms arrange themselves?

2. What properties might the atomic arrangement affect in a metal? Why would this be?

3. Summarize the purpose of the two station activities by responding to the objectives listed at the beginning of the lab.

Read the handout provided on “The Crystal Structure of Metals” before answering the questions below.

4. What is a unit cell?

5. How many are atoms in BCC, FCC and HCP unit cells?

6. Identify one property that varies with crystal structure, and a metal example.

7. What is a grain? How can you change grain size?

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The Crystal Structure of Metals

Crystals To form the strongest metallic bonds, metals are packed together as closely as possible. Several packing arrangements are possible. Instead of atoms, imagine marbles that need to be packed in a box. The marbles would be placed on the bottom of the box in neat orderly rows and then a second layer begun. The second layer of marbles cannot be placed directly on top of the other marbles and so the rows of marbles in this layer move into the spaces between marbles in the first layer. The first layer of marbles can be designated as A and the second layer as B giving the two layers a designation of AB.

Layer "A"

Layer “B”

AB packing

Notice that layer B spheres fit in the holes in the A layer. Packing marbles in the third layer requires a decision. Again rows of atoms will nest in the hollows between atoms in the second layer but two possibilities exist. If the rows of marbles are packed so they are directly over the first layer (A) then the arrangement could be described as ABA. Such a packing arrangement with alternating layers would be designated as ABABAB. This ABAB arrangement is called hexagonal close packing (HCP).

If the rows of atoms are packed in this third layer so that they do not lie over atoms in either the A or B layer, then the third layer is called C. This packing sequence would be designated ABCABC, and is also known as face-centered cubic (FCC). Both arrangements give the closest possible packing of spheres leaving only about a fourth of the available space empty.

The smallest repeating array of atoms in a crystal is called a unit cell. In the FCC arrangement, there are eight atoms at corners of the unit cell and one atom centered in each of the faces. The atom in the face is shared with the adjacent cell. FCC unit cells consist of four atoms, eight eighths at the corners and six halves in the faces.

A third common packing arrangement in metals, the body-centered cubic (BCC) unit cell has atoms at each of the eight corners of a cube plus one atom in the center of the cube. Because each of the corner atoms is the corner of another cube, the corner atoms in each unit cell will be shared among eight unit cells. The BCC unit cell consists of a net total of two atoms, the one in the center and eight eighths from the corners.

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The illustrations below show the FCC and BCC unit cells. Unit cell structures determine some of the properties of metals. For example, FCC structures are more likely to be ductile than BCC or HCP.

Body Centered Cubic Face Centered Cubic The table below shows the stable room temperature crystal structures for several elemental metals. Crystal Structure for some Metals (at room temperature) Aluminum............ FCC Nickel.................. FCC Cadmium............. HCP Niobium............... BCC Chromium............ BCC Platinum............... FCC Cobalt................. HCP Silver.................. FCC Copper................ FCC Titanium............... HCP Gold................... FCC Vanadium............. BCC Iron.................... BCC Zinc.................... HCP Lead................... FCC Zirconium............. HCP Magnesium........... HCP As atoms of melted metal begin to pack together to form a crystal lattice at the freezing point, groups of these atoms form tiny crystals. These tiny crystals increase in size by the progressive addition of atoms. The resulting solid is not one crystal but actually many smaller crystals, called grains. These grains grow until they impinge upon adjacent growing crystals. The interface formed between them is called a grain boundary. Grains are sometimes large enough to be visible under an ordinary light microscope or even to the unaided eye. The spangles that are seen on newly galvanized metals are grains. The pictures below show a typical view of a metal surface with many grains, or crystals.

Grains and Grain Boundaries for Steel

Optical micrograph – 1000X Steel visible on microscale

SEM image – 4000X Steel visible on microscale

Illustration of grains & grain boundaries

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Crystal Defects Metallic crystals are not perfect. Sometimes there are empty spaces called vacancies, where an atom is missing. Another common defect in metals are dislocations, which are lines of defective bonding. Below you will see a cross section of an edge dislocation, which extends into the page. Note how the plane in the center ends within the crystal.

These and other imperfections, as well as the existence of grains and grain boundaries, determine many of the mechanical properties of metals. When a stress is applied to a metal, dislocations are generated and move, allowing the metal to deform.

“Metals! They’re Everywhere!” A MAST Module. Materials Science & Technology 1995.

Steel micrograph and SEM image courtesy of S. Zaucha, working at Northwestern University.

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A B

The Crystal Structure of Metals – TEACHER NOTES

Major Concepts Students will have the opportunity to learn more about the basic crystal structures that metal atoms form. To maximize the bonding, atoms in metals pack together as closely as possible. Several packing arrangements exist such as face centered cubic (FCC), hexagonal closest packing (HCP), and body centered cubic (BCC). However, metallic crystals are not perfect. Sometimes there are empty spaces, vacancies, where an atom should be. There are also small mismatches, dislocations, in the rows of atoms. Therefore, the properties of metals are very dependent on their crystal structure. Defects in the crystal structure of metals control many of their properties including hardness and ductility. Level This lab is appropriate for both regular level and honors high school chemistry, grades 9-12. Expected Student Background It is expected that students have an introductory understanding of bonding based on the structure of the atom. Time The lab can be completed in a 50-minute class period.

Safety No safety precautions need to be taken to complete this activity. Materials

Station 1 – materials needed per station -35 Styrofoam balls, about 1.5" diameter -24 toothpicks (round)

Station 2 – materials needed per station

-Plastic Petri Dish -Bb's

Teacher Background The information in the introduction to the lab, as well as in the student handout should provide decent background on the concept of metallic bonding and the crystal structure of metals. However, jumping ahead to the next activity and completing the webquest before the students would be beneficial as well. Before class, it would be beneficial for the teacher to have a completed models constructed with the layers painted different colors to help the students visualize the three types of packing arrangements. To paint the Styrofoam balls, use water-based paint diluted slightly and add a small amount of detergent. Below are the arrangements for the triangles the students are to construct.

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Assessing Laboratory Learning

Ask students to identify what crystal structure is represented in a model presented to the class, or in a picture on a quiz or test. Students should describe defining characteristics that helped them correctly identify the structure.

Ask students to describe what a vacancy or dislocation is in a metal crystal and how it can affect the properties of the metal.

Answers to Questions Advance Preparation

Please answer the following questions in complete sentences in your lab notebook: 1. Identify three objects / items that you rely on everyday that is constructed out of metal.

Answers will vary. 2. Describe the bonding that occurs between atoms in a metal, using the terms valence electron, metal cation, shared, and electron cloud in your response.

The valence electrons (outermost electrons) of a metal atom are delocalized and shared by neighboring atoms in the crystal. The positive metal cations are therefore surrounded by what is described as an electron cloud.

3. How do metallic bonds differ from ionic or covalent bonds? Because these valence electrons are shared by all the atoms, they are not considered to be associated with any one atom. This is very different from ionic or covalent bonds, where electrons are held by one or two atoms.

Analysis After completing Station 1 -

1. Which packing arrangement(s), FCC, HCP, or BCC appear to be the most densely packed in any given area?

Actually, FCC and HCP packing arrangements have the same atomic density. They each have approximately 26% empty space.

2. What is the difference in FCC and HCP arrangements? Feel free to describe in words, or sketch! FCC has an ABC arrangement while HCP is ABA.

3. About how small would an atom have to be to fit in an interstitial hole in an FCC, HCP, or BCC crystal structure? (Predict answer as what fraction of an atom – 1/2? 1/3? 1/5? 1/8?)

Depending on the type of hole, an interstitial atom should be approximately one third the size of the atom which makes up the crystal structure in order to "fit" well.

After completing Station 2 - 1. Are the Bb's arranged perfectly at the end of each simulation? Would you expect atoms to be

perfectly arranged? Explain why or why not. It is unlikely that the atoms are perfectly arranged. Some disorder is expected.

2. Describe how the arrangement of the Bb's are different between each of the three heating/cooling methods. Are there more or less empty spaces, i.e., places where a Bb is missing, or other defects?

More defects exist at higher temperatures (when the Petri dish was shaken rapidly).

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To be completed on your own- 1. In both the FCC and HCP crystal structure arrangements, atoms in layer 2 were nestled in between

the spaces of those atoms in layer 1. Based on what you know about metals and bonding, why would this be how the atoms arrange themselves?

To maximize the bonding, atoms in metals pack together as closely as possible. 2. What properties might the atomic arrangement affect in a metal? Why would this be?

Strength, ductility and/or toughness -defects in the crystal structure of metals can affect their properties.

3. Summarize the purpose of the two station activities by responding to the objectives listed at the beginning of the lab.

a) Several packing arrangements exist such as face centered cubic (FCC), hexagonal closest packing (HCP), and body centered cubic (BCC).

b) Metallic crystals are not perfect. Sometimes there are empty spaces, vacancies, where an atom should be. There are also small mismatches, dislocations, in the rows of atoms. Defects in the crystal structure of metals control many of their properties including hardness and ductility.

Read the handout provided on “The Crystal Structure of Metals” before answering the questions below.

4. What is a unit cell? The smallest repeating array of atoms in a crystal is called a unit cell.

5. How many atoms are in BCC and FCC unit cells? The BCC unit cell consists of a net total of two atoms, the one in the center and eight eighths from the corners. The FCC unit cell consists of four atoms, eight eighths at the corners and six halves in the faces.

6. Identify one property that varies with crystal structure, and a metal example. FCC structures are more likely to be ductile; for example, gold, copper, and silver are all FCC arrangements.

7. What is a grain? How can you change grain size? As metal cools, the resulting solid is not one crystal but actually many smaller crystals, called grains. Grain sizes can change when a stress is applied to a metal, as dislocations are generated and move, allowing the metal to deform.

References Metals! They’re Everywhere! A MAST Module. Materials Science & Technology 1995. Developed in

part at the Materials Science & Technology Workshop held at the University of Illinois at Urbana-Champaign during 1993-95. http://matse1.mse.uiuc.edu/home.html

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What is Steel? – A Webquest Investigating the Structure, Bonding, and Treatment of Metal Alloys

Introduction Your task is to use a new resource as a source of information continuing your investigation of the structure and properties of metal alloys. After entering the website, take a few minutes to become familiar with its resources in the top left corner, such as the index and summary buttons. Once you begin, however, please use the page arrow button at the top right corner of the page to advance page by page – you wouldn’t want to miss anything. You can also select the “Contents” button at the top left hand corner to find the pages by topic as well. Feel free to sketch anything in the margins that will be helpful to you in describing what you’ve learned! Objectives At the conclusion of this webquest, you will be able to…

identify the type of bonding present between metal ions, describe the role of delocalized electrons and positive metal ions in creating a crystal lattice

structure, illustrate how grains, grain boundaries, and dislocations appear in a metal’s microstructure, compare and contrast the various treatments for steel alloys, and synthesize how the microstructure and resulting properties of an alloy change(s) in response

to the treatment of the metal.

PART ONE - Structure of & Bonding in Steel (pages 2-6) KEY TERMS TO UNDERSTAND: metallic bonds, delocalized electrons, electron cloud, metal lattice, alloy, crystal structure, dislocations, grains, grain boundary What is Steel? (page 1)

1. How can the properties of an alloy, like steel, be modified?

2. Why is steel used so universally? Metallic Bonds (page 2)

3. What types of bonds hold ions together in metals? _________________________________ 4. Use your mouse to roll over the highlighted terms in Picture 1.1. Then read the text under “A

cloud of electrons.” Using your new knowledge from the picture and text, explain how bonds are created between metal ions.

Microstructure of a steel alloy

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5. Describe the two properties of metals you read about. Why can we do this to metals?

Click on the Summary button in the top left hand corner. Did you take away the main ideas from this section?

Why are metals good conductors of heat & electricity? (page 3)

6. Check out the animations (Pictures 1.3, 1.4, and 1.5) on page 3. Why are metals good conductors of heat & electricity? Be sure to discuss both ionic vibrations and free electrons in your explanation!

Alloys (page 4)

7. What element(s) is a steel alloy made of?

8. How are alloys formed?

Click on the Summary button in the top left hand corner. Did you take away the main ideas from this section?

The Crystal Structure of Metals (page 5)

9. List the three different ways that positive ions in a metal can be packed together.

a) __________________________________________________ b) __________________________________________________

c) __________________________________________________

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10. How is the layering in the hexagonal close packed (HCP) system similar to a face centered cubic packed (FCC) system? How is the layering different?

Click on the Summary button in the top left hand corner. Did you take away the main ideas from this section?

Dislocations in the Crystal Structure (page 6)

11. What is a dislocation in a crystal lattice? (Use Picture 1.11 to visualize your definition as well!) 12. Examine Pictures 1.12 and 1.13 before explaining what a grain and

grain boundary is. Then label the picture on the right.

13. What instrument do you think one would use to examine the grain boundaries in steel? At what magnification?

14. Why is it favorable to have more grain boundaries in a material?

Click on the Summary button in the top left hand corner. Did you take away the main ideas from this section?

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PART TWO – Treatments for Steel Alloys (pages 7-11) KEY TERMS TO UNDERSTAND: cold working, annealing, hot working, quenching, tempering, alloying Why are metals treated further after casting? (page 7)

1. After reading this introduction, why are metals treated further after casting? Cold working (page 8)

2. What does cold working produce within a metal structure that leads to it becoming “work hardened,” or stronger?

Annealing, hot working, & quenching (page 9)

3. What happens when a metal is annealed?

4. How is hot working a metal different than cold working a metal?

5. Complete the following table after reading the information provided about quenching:

What is “quenching”? When is quenching used? What does quenching do to steel?

Click on the Summary button in the top left hand corner.

Did you take away the main ideas from this section?

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Tempering (page 10) 6. What is the purpose of tempering a metal?

7. How is a metal tempered? Alloying (page 11)

8. Read about alloying metals and analyze Picture 2.7 after putting your cursor over the terms “slide” and “more easily.” How does alloying disrupt the crystal structure? Make a sketch to support your response.

9. Lists other elements that are typically added to iron alloys.

Click on the Summary button in the top left hand corner. Did you take away the main ideas from this section?

Special Steels – HSLA steels (page 12) 10. Describe the favorable properties of high-strength low-alloy (HSLA) steels.

11. Where does the strength of HSLA steels come from?

Metal alloy in a furnace

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Mechanical Properties of Steel (pages 18, 20)

12. Mechanical properties describe the ways in which a material behaves. We are most interested in tensile strength and hardness.

a) Describe how tensile strength is tested.

b) Describe how hardness is tested.

Tensile testing of a steel bar

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What is Steel? A WebQuest – TEACHER NOTES

Major Concepts Students will have the opportunity to explore their curiosities about metal alloys and their properties through this two part webquest; the major concepts addressed include identifying the metallic bonding that occurs between metal ions, describing the role of delocalized electrons and positive metal ions in creating a crystal lattice structure, and illustrating how grains, grain boundaries, and dislocations appear in a metal’s microstructure. In addition, students will be asked to compare and contrast the various treatments for steel alloys, as well as synthesize how the microstructure and resulting properties of an alloy change(s) in response to the treatment of the metal.

Level This lab is appropriate for both regular level and honors high school chemistry, grades 9-12.

Expected Student Background It is expected that students have defined what an alloy is and have an introductory understanding of bonding based on the structure of the atom. Students should be comfortable navigating the Internet as a resource to locate and process scientific information.

Time This activity should be completed in two parts, as identified in the activity itself. If done well, this activity can be very lengthy and time consuming. It is anticipated that if completed at one time, students would rush towards the end and not learn any new information to prepare them for the next lab. It is suggested that students begin part one of the webquest after completing Lab 1 and begin part two of the webquest after completing Lab 2. This can be completed inside and/or outside of class over a number of days.

Safety There are no safety hazards for this activity. Materials One computer per one – two student(s) (if completed in class)

Teacher Background The properties exhibited by various metals are directly related to their internal micro and atomic structure. When discussing a metal’s atomic structure, metal ions are held together by metallic bonds in which each positive metal ion is attracted to the negatively charged delocalized electrons. Positive ions in a metal can be packed together to form different crystal structures depending on how the ions are layered. When discussing a metal’s microstructure, a grain represents the small crystals that grow around a nucleus in all directions when a molten metal is cooled. Where one grain meets another at the edge is called a grain boundary. However, dislocations can be present, which are defects in the metal lattice structure where a few ions in a layer are missing, causing the neighboring layers to be displaced slightly to minimize the strain. The more grain boundaries there are the more difficult it is for the dislocations to move and for the metal to change shape. The result is that the metal is stiffer and harder. It is also stronger. Most alloys are created to change the elemental metals' physical properties, such as conductivity, density, ductility, hardness, luster, malleability, melting point, and tensile strength, and/or chemical properties,

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such as resistance to corrosion. Alloys often exhibit increased strength and hardness. Precipitation hardening is a process that can be used to affect the physical properties of an alloy, such as steel, by introducing copper-rich precipitates. Various treatments can be used such as cold-working, or heat treatment followed by quenching and tempering a metal. As a result of such treatments, an alloy can demonstrate increased strength and toughness due to the precipitates being formed within its complex microstructure. Many mechanical properties of a precipitation hardened alloy can be analyzed on a macroscopic scale using Tensile testing, Charpy V-notch, and Vickers Hardness analyses. Assessing Self-Guided Learning

Students’ packets can be collected and graded for accuracy after completion.

Give a reading quiz after completion of the packet to assess understanding of information. Students could be allowed to use their packet for assistance if needed, or more basic understanding questions could be asked if taken without use of their packets.

The following (more general) questions could be asked as an assessment of their “big picture” understanding:

o What is an alloy? How does it form? o In what industries / for what purposes are alloys used? o Where have you encountered alloys in your daily life? o How are scientists working to improve the quality of these materials? o What properties are desirable in these materials? o How is research done on these materials?

Answers to Questions PART ONE - Structure of & Bonding in Steel (pages 2-6) What is Steel? (page 1)

1. How can the properties of an alloy, like steel, be modified? (mechanical & heat treatment)

2. Why is steel used so universally? (a versatile material; can adjust its composition & internal structure to modify properties)

Metallic Bonds (page 2)

3. What types of bonds hold ions together in metals? (metallic bonds)

4. Use your mouse to roll over the highlighted terms in Picture 1.1. Then read the text under “A cloud of electrons.” Using your new knowledge from the picture and text, explain how bonds are created between metal ions.

(Metal ions are held together by metallic bonds. These bonds are created when at least one outermost electron from each atom are no longer bound to individual atoms. The free electrons become delocalized, forming a cloud of electrons that are free to move through the solid lattice structure. The bonding electrons no longer belong to any particular metal atom. Each positive metal ion is attracted to the negatively charged delocalized electrons. The negative electrons are in turn attracted towards the positive metal ions. It is these attractions that hold the structure together forming metallic bonds.)

5. Describe the two properties of metals you read about. Why can we do this to metals?

(Malleable: pressed into different shapes without breaking) (Ductile: drawn out into thin wires without breaking)

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(Possible because of the metallic bonding between ions – they are strong, but not directed between any particular ions).

Why are metals good conductors of heat & electricity? (page 3)

6. Check out the animations (Pictures 1.3, 1.4, and 1.5) on page 3. Why are metals good conductors of heat & electricity? Be sure to discuss both ionic vibrations and free electrons in your explanation!

(1) because of the ionic vibrations of the stationary positive ions in the lattice that increase with an addition of KE and 2) because of the free, delocalized electrons that increase in velocity with an addition of KE – allow both electrical conductivity and thermal conductivity. NOTE: solids have vibrational energy)

Alloys (page 4)

7. What element(s) is a steel alloy made of? (Mainly Fe, + C and other metals)

8. How are alloys formed? (atoms of other metals replace atoms of iron in the metal lattice structure).

The Crystal Structure of Metals (page 5)

9. List the three different ways that positive ions in a metal can be packed together. (hexagonal close packed, face centered cubic, body centered cubic)

10. How is the layering in the hexagonal close packed (HCP) system similar to a face centered cubic packed (FCC) system? How is the layering different?

(An HCP system is similar to a FCC system in that ions in both layers 1 & 2 arrange themselves in hexagons, where layer 2 ions will fall in the gaps of the layer 1 ions. They differ in layer 3: in HCP the ions in layer 3 lie above the ions in layer 1, whereas in FCC the ions in layer 3 lie above the gaps in the previous 2 layers.)

Dislocations in the Crystal Structure (page 6)

11. What is a dislocation in a crystal lattice? (Use Picture 1.11 to visualize your definition as well!) (It is a defect in the lattice structure in which a few ions in a layer are missing, causing the neighboring layers to be displaced slightly to minimize the strain.)

12. Examine Pictures 1.12 and 1.13 before explaining what a grain and grain boundary is. Label the picture on the right.

(A grain represents the small crystals that grow around a nucleus in all directions when a molten metal is cooled. Where one grain meets another at the edge is called a grain boundary.)

13. What instrument do you think one would use to examine the grain boundaries in steel? At what magnification?

(Microscope – optical microscope at 1000x) 14. Why is it favorable to have more grain boundaries in a material?

(The more grain boundaries there are the more difficult it is for the dislocations to move and for the metal to change shape. The result is that the metal is stiffer and harder. It is also stronger. This is favorable for those building things with the metal.)

PART TWO – Treatments for Steel Alloys (pages 7-11) Why are metals treated further after casting? (page 7)

1. After reading this introduction, why are metals treated further after casting? (to modify the microstructure)

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Cold working (page 8)

2. What does cold working produce within a metal structure that leads to it becoming “work hardened,” or stronger?

(produces additional dislocations within the structure. When two or more dislocations meet, the movement of one tends to interfere with the movement of the other. This increases the strength of the metal and also makes it stiffer.)

Annealing, hot working, & quenching (page 9)

3. What happens when a metal is annealed? (It is heated to a temperature of about half of its melting point. The grains within the structure re-crystallize into many fine grains. In the new structure dislocations can move more easily. The metal therefore becomes softer and more malleable and ductile.)

4. How is hot working a metal different than cold working a metal? (a hot worked metal is shaped at a temperature above its recrystallization temperature. Annealing takes place while the metal being worked rather than being a separate process.)

5. Complete the following table after reading the information provided about quenching:

What is “quenching”? When is quenching used? What does quenching do to steel?

Quenching describes the sudden immersion of a heated metal into cold water or oil. It is used to make the metal very hard.

Quenching is usually used with metals that are alloyed with small amounts of other metals. At high temperatures the alloying metals are dissolved in the base metal.

Quenching is an important process that is used in the production of steel cutting tools. Steel used for this purpose contains nearly 1% carbon. (This is a high carbon steel).

If the material is cooled slowly, the alloy elements have time to precipitate out separately. If the metal is quenched, however, the alloying metals are trapped within the crystal grains, which makes them harder. The precipitates also reduce the movement of dislocations which contributes to the hardness of the material.

Tempering (page 10)

6. What is the purpose of tempering a metal? (Quenched steel is hard, but brittle. Tempering makes a metal more malleable, even if some of the hardness has to be sacrificed.)

7. How is a metal tempered? (The quenched steel is heated again but this time to a temperature between 200 °C and 300 °C. When the metal reaches the tempering temperature, it is quenched again in cold water or oil. )

Alloying (page 11)

8. Read about alloying metals and analyze Picture 2.7 after putting your cursor over the terms “slide” and “more easily.” How does alloying disrupt the crystal structure? Make a sketch to support your response.

(In the alloy, some of the added ions may be larger than most of the ions making up the metal lattice. They disrupt the regular arrangement of ions and make it more difficult for the layers to slide over each other. This makes the alloy harder and less malleable and ductile than the pure metal (in which the layers slip over each other more easily).

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9. What other elements are typically added to iron alloys? (Co, Mn, Mo, Ni, Cr, Ti, W, V)

Special Steels – HSLA steels (page 12)

10. Describe the favorable properties of high-strength low-alloy (HSLA) steels. (much stronger and tougher than ordinary carbon steels, ductile, highly formable, weldable, highly resistant to corrosion - which is important since the structure may be in place for a long time.)

11. Where does the strength of HSLA steels come from? (their improved microstructure by alloying with other elements.)

Mechanical Properties of Steel (pages 18, 20)

12. Mechanical properties describe the ways in which a material behaves. We are most interested in tensile strength and hardness.

a) Describe how tensile strength is tested. (A tensile test is used to find out what happens when a material such as steel is stretched. A steel bar is placed in a device that pulls one end away from the other fixed end. The tensile strength is the maximum stress that the bar can withstand before breaking.)

b) Describe how hardness is tested. (The hardness of a material is a measure of how hard it is to change its shape. A hard material is difficult to scratch or dent, but it will scratch or dent a softer material. Brinell Hardness testing uses a spherical shaped indenter, while Vickers Hardness testing uses a diamond shaped indenter.)

References What is Steel? WebQuest. Derek Denby (Head of Science at Leggott Sixth Form College).

http://www.schoolscience.co.uk/content/5/chemistry/steel/index.html

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Synthesis of an Inexpensive Alloy Investigating the Intermolecular Forces between Metals

Introduction

Scientists have greatly extended the array of materials available for human use. Chemists have learned to modify the properties of matter by physically blending or chemically combining two or more substances. An alloy is a solid solution composed of two or more metals, or of a metal(s) with one or more nonmetals. Metals and alloys are virtually everywhere in our daily lives. Alloys are used to make aircraft engines, automobiles, bridges, buildings and even paper clips. The alloys bronze, brass, and pewter have been used for centuries.

Certain metals are appropriate for use in certain functions, while not suitable in others. Alloys may be used either to replace or to conserve more expensive metals. Most alloys are created to change the elemental metals' physical properties, such as conductivity, density, ductility, hardness, luster, malleability, melting point, and tensile strength, and/or chemical properties, such as resistance to corrosion. Alloys often exhibit increased strength and hardness. Stainless steel, for example, is iron alloyed with chromium and nickel. The strength of stainless steel makes it useful in tools. Alloys also have lower electrical and thermal conductivity than pure metals. For example, nichrome wire—made from an alloy of nickel, iron, and chromium becomes red-hot when a current is passed through it and can be used as the heating element of hair dryers, toasters, and space heater. Objectives At the conclusion of this lab, you will be able to…

define what an alloy is and how it is made, explain why alloying a metal is favorable or not, and identify commonly used alloys and in what industries they are used.

Advance Preparation

Please answer the following questions in complete sentences in your lab notebook:

1. What is an alloy? 2. What two physical properties of metals can be improved by alloying a metal? 3. You need to bring 3 pennies to lab tomorrow – check the date on your pennies and bring only

those minted before 1982. What is the composition of a penny minted before 1982? After 1982? (HINT: Use your resources to look up this information – remember to cite your resource!)

4. What advice would you give someone about to use a 3.0 M sodium hydroxide solution? Why? 5. What three end products will you observe and record in a data table?

Interesting Websites Visit the following websites for interesting facts and information on United States Currency:

Federal Reserve Bank of Atlanta (http://frbatlanta.org/publica/brochure/fundfac/html/coins.html) The United States Mint (http://www.usmint.gov/)

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Safety Safety goggles and lab aprons must be worn throughout the entire lab. 3M sodium hydroxide will be heated using a hot plate and can badly burn the skin. If any solution contacts your skin, immediately wash the affected area with cold water and notify your instructor. Procedure

1. Be sure to wear safety goggles throughout the entire lab.

2. Use a piece of steel wool to clean the surface of your three pennies. Rub both surfaces of each penny until it is shiny. Record the appearance of the pennies (before treatment) in your lab notebook.

3. Mass out approximately 0.5 grams of granulated zinc. Pour it into a 250 mL beaker.

4. Using a graduated cylinder, carefully add 15 mL of 3.0 M sodium hydroxide solution into the

250 mL beaker with the zinc. The cover the beaker with a watch glass.

5. Using the hot plate, gently heat the solution until it just begins to bubble. (The hot plates do not need to be turned up very high!) Turn the hot plate down and continue to gently heat the solution, without letting it boil.

Caution: Do not allow the solution to boil vigorously. Hot sodium hydroxide solution can badly burn the skin. If any solution contacts your skin, immediately wash the affected area with cold tap water and notify your instructor.

6. Using forceps, carefully add two clean copper pennies to the hot sodium hydroxide solution.

Do not drop the coins into the solution or it will cause a splash. Place the pennies so that they are not sitting on top of one another. Set the third penny aside as a control.

7. Replace the watch glass over the top of the beaker and allow the pennies to remain in the

gently bubbling solution for 2 -3 minutes. Observe and record any changes in the appearance of the coins. While the pennies are in the solution and one partner is observing, the other can fill two 100-mL beakers half full with distilled water.

8. When 2 -3 minutes have passed and no further changes are noted, turn off the hot plate. Then,

use forceps to remove the two pennies from the solution. Place them both in one of the beakers of distilled water.

9. Using forceps, remove the coins from the beaker of water. Rinse them under running tap

water, and dry the coins with a paper towel. Set one treated coin aside to be used later for comparisons.

10. Using crucible tongs, gently heat the other dry treated coin in the outer cone of a Bunsen

burner flame by passing it back and forth through the flame. Hold the coin vertically with the crucible tongs as demonstrated by your instructor. This should take only 10-20 seconds.

11. Continue heating the coin for three seconds after its appearance changes. Do not overheat it.

Immediately immerse the coin in the second beaker of distilled water. Record your observations in your lab notebook.

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HINT! Use your resources to look up this information – remember to

cite your resource!

12. Remove the coin from the beaker of water, and dry it with a paper towel.

13. Observe the appearance of the three pennies and record all observations in a neat data table in your lab notebook. What were the different “treatments” for each of your three pennies?

Clean-up When the beaker has sufficiently cooled, carefully pour the NaOH and zinc into the waste beaker

under the fume hood. Rinse the beaker with distilled water to be sure to get out all of the zinc. All materials should be washed using brushes, soap, and warm water.

Please clean your area thoroughly and dry your glassware, before locking your drawer.

Be sure that the balances and hot plates are turned off before leaving the lab.

Analysis Compare the colors of the three coins and consider what happened in each step of the procedure…

1. Bronze and brass are two materials you may be familiar with that are alloys.

a) What metal(s) is brass composed of?

b) What metal(s) is bronze composed of?

c) What material did you create in lab?

2. What actually happened to the atoms of Cu and Zn when the penny was put into the zinc and sodium hydroxide solution?

3. What happened at the molecular level when the penny was further heated directly in the flame? Draw, at the molecular level, what your final product looks like.

4. Why will the silver-colored pennies fade over time? Why are the gold-colored pennies not going to fade as fast?

5. Why were you asked to bring pennies minted before 1982? Be sure to explain the composition of each type of penny in your response.

6. Describe the ways in which alloys differ from their component elements.

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Synthesis of an Inexpensive Alloy – TEACHER NOTES

Major Concepts Students will have the opportunity to make an alloy – brass; the major concepts addressed include defining what an alloy is, understanding how alloys are made, describing the metallic bonding that occurs in an alloy, and recognizing the significance of alloying metals for use in various industries.

Level This lab is appropriate for both regular level and honors high school chemistry, grades 9-12.

Expected Student Background It is expected that students have defined what an alloy is and have an introductory understanding of bonding based on the structure of the atom. Students should be comfortable in the lab using hot plates, Bunsen burners, and concentrated chemical solutions.

Time The lab can be completed in a 50-minute class period.

Safety Safety goggles and lab aprons must be worn throughout the entire lab. 3M sodium hydroxide will be heated using a hot plate and can badly burn the skin. If any solution contacts the skin, students should be instructed to immediately wash the affected area with cold water and notify his/her instructor. In addition, care should be taken in using both the hot plates and Bunsen burners throughout the lab. Materials – needed per team

• Safety goggles • One 250-mL beaker • Two 100-mL beakers • One 25-mL graduated cylinder • Forceps • Crucible tongs • Beaker tongs • Watch glass

• Hot plate • Striker or matches • Bunsen burner • Three copper pennies • 0.5 g granulated zinc • 15.0 mL 3 M sodium hydroxide * • Distilled water • Steel wool **

*Instead of 3 M sodium hydroxide solution, 1 M zinc chloride solution can be used as well. If this option is used, be sure students mass out 2.0 - 2.5 grams of granulated zinc to begin and add 25 mL of the 1 M zinc chloride solution to the zinc metal.

**Instead of steel wool, a solution of sodium chloride (a small amount of NaCl) and vinegar (~20 mL) can be made to clean the pennies. Place the pennies into the solution and occasionally stir until they appear to be clean. Be sure students dry the pennies before moving on.

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Teacher Background Pennies before or after 1982 may be used. However, pennies minted after 1982 contain a higher percent of zinc (97.6% vs. 5%). For this reason, they are more likely to warp if overheated. The melting point of copper is 1,083 ºC, whereas zinc's melting point is much lower at 420 ºC. In the newer pennies, there may not be enough copper present to create the alloy brass.

In 1981, Congress authorized a change in the penny's composition, abandoning the 95 percent copper and 5 percent zinc alloy used for decades. In order to save expensive copper, penny coins, starting in 1982, were made instead of zinc with a thin layer of copper plated on the surface. The one-cent piece is now copper-plated zinc—97.6 percent zinc and 2.5 percent copper. The old and new pennies look virtually identical, but the new coin is about 19 percent lighter.

As a result of this lab, students will produce brass. Brass is an alloy of zinc and copper. The shiny brass color may make students think of the metal gold. The silvery product, formed first, is a type of brass with a relatively high concentration of zinc. The golden surface, formed after heating, is a brass with less than 35% zinc. The deposition process can be repeated by returning the golden penny to the zinc chloride solution, where it will again become silvery. After the lab, discuss with students the history of the penny’s composition. The following information can be shared in any format:

1859 – 1864

88% copper 12% nickel

1864 - 1909 Indian Head 95% copper 5% zinc alloy (Zn, Sn)

1909 - 1982 95% copper (2.95 g Cu)

5% zinc alloy (0.15 g Zn)

1982 - present

“Wheat penny” - Lincoln (front) Wheat (back) 2.4% copper

(0.06 g Cu)97.6% zinc

(2.46 g Zn)*Visit The United States Mint (http://www.usmint.gov/) for more information.

Assessing Laboratory Learning

A class discussion can include sharing historical information about the chemical makeup of the penny. After comparing results with neighboring teams, individual students (or lab teams) can turn in their responses for credit.

Ask students to draw a model of a brass alloy on an atomic scale and describe how metallic bonding occurs.

Ask students to find an example (by conducting research) of how alloying metals for use in industry has proven more favorable than using elemental metals, and share with the class.

Answers to Questions Advance Preparation

1. What is an alloy? An alloy is a solid solution composed of two or more metals.

2. What two physical properties of metals can be improved by alloying a metal? Alloys often exhibit increased strength and hardness.

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3. You need to bring 3 pennies to lab tomorrow – check the date on your pennies and bring only those minted before 1982. What is the composition of a penny minted before 1982? After 1982? (HINT: Use your resources to look up this information – remember to cite your resource!)

Before 1982: 95% Cu, 5% Zn alloy / After 1982: 2.4% Cu, 97.6% Zn 4. What advice would you give someone about to use a 3.0 M sodium hydroxide solution? Why?

Safety goggles and lab aprons must be worn. 3M sodium hydroxide can badly burn the skin. If any solution contacts the skin, immediately wash the affected area with cold water and notify your instructor.

5. What three end products will you observe and record in a data table? Penny (untreated); Penny treated with Zn and NaOH; Penny treated with Zn and NaOH and heated in a flame

Analysis Compare the colors of the three coins and consider what happened in each step of the procedure…

1. Bronze and brass are two materials you may be familiar with that are alloys. a) What metal(s) is brass composed of? Cu and Zn b) What metal(s) is bronze composed of? Cu and Sn c) What material did you create in lab? The students created brass by combining Cu & Zn

2. What actually happened to the atoms of Cu and Zn when the penny was put into the zinc and sodium hydroxide solution?

The atoms of Cu in the penny and Zn in the beaker were able to come into contact and create metallic bonds between the atoms. Atoms of Zn replace atoms of Cu in the solid structure.

3. What happened at the molecular level when the penny was further heated directly in the flame? Draw, at the molecular level, what your final product looks like.

The bonds between the atoms of Cu and Zn were strengthened by the heat – the addition of energy in the form of heat increased the movement of the delocalized electrons around the metal ions.

4. Why will the “silver” pennies fade over time? Why are the “gold” pennies not going to fade as fast?

The atoms of Zn are merely “wedged” between the atoms of Cu. Over time they will separate and the penny will appear copper again. The atoms of Cu and Zn exposed to the heat have stronger bonds now and will not separate as quickly.

5. Why were you asked to bring pennies minted before 1982? Be sure to explain the composition of each type of penny in your response.

Pennies minted before 1982 are 95% Cu and 5% Zn alloy. Pennies minted after 1982 are 2.4% Cu and 97.6% Zn. If the goal is to make an alloy – brass – then students need to start with the penny that is mostly copper in order to create an alloy with the zinc provided in class. The penny minted after 1982 is only copper-plated and does not have enough copper to create an alloy.

6. Describe the ways in which alloys differ from their component elements. Most alloys are used to change the metals' physical properties, such as conductivity, density, ductility, hardness, luster, malleability, melting point, and tensile strength, and/or chemical properties, such as resistance to corrosion. Alloys often exhibit increased strength and hardness.

References NASA Explores

http://media.nasaexplores.com/lessons/01-032/9-12_1.pdf

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Investigating the Effects of Various Heat Treatments on the Properties of a Metal

Introduction

Metals are used for many different purposes. Two hundred years ago, the town blacksmith produced nails, hammers, wheel rims, knives, and horseshoes from the same basic metal. In some applications, a metal must be able to bend easily without breaking, whereas in other cases the metal must resist bending. In industry today, metallurgists can produce these results by using different metals, alloying metals, and by processing metals. However, the substitution of a different metal or using a special alloy is often costly. Therefore processing a common metal is often the most cost efficient method of producing a metal that has the properties required in a specific application. Since the properties of a material are dependent upon its structure on the atomic level, altering its structure should alter its properties.

Common treatments include cold-working and heat treating metals, including annealing,

quenching, and tempering metals. Most metals respond to heat treatment, but the treatment temperatures are unique for different metals. Grains in metals tend to grow larger as the metal is heated. A grain can grow larger by atoms migrating from another grain that may eventually disappear. Dislocations cannot cross grain boundaries easily, so the size of grains determines how easily the dislocations can move. As expected, metals with small grains are stronger but they are less ductile. Objectives At the conclusion of this lab, you will be able to…

describe the effects of cold-working and heat treating on the resulting strength of a metal, explain differences in observed strength between elemental and alloyed metals, and evaluate why the properties of the metals are dependent upon their structure.

Advance Preparation

Please answer the following questions in complete sentences in your lab notebook:

1. Do you think an elemental metal (composed of atoms of only one element) or an alloyed metal (composed of atoms of two or more elements) will display more strength? Why? Make a sketch if needed!

2. In order to be better prepared for lab, create a chart summarizing the properties of each metal

to be studied. Be sure to include the element / alloy’s name, the composition of the material (100% of one element? Or varying percentages of a number of elements?), melting point in °C, and other pertinent characteristics to note. The six metals being studied in the lab are: aluminum, copper, brass, Monel nickel alloy, low carbon steel, and high carbon steel.

3. Hypothesize: Of the 6 metals tested, which will demonstrate the most number of bends to

break after heat treatment? Of the 4 types of treatments, which will affect the properties of the metals the most? Be sure to justify your predictions!

Safety Safety goggles and lab aprons must be worn throughout the entire lab. Take precautions to avoid burns or fire when using the Bunsen burners to heat and bend the metal. Remember, heated metals remain very hot for a long time. They should be set aside to cool and picked up/moved with caution. Use the heat protective forceps provided.

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Procedure Control Treatment -

1. Obtain 3 bobby pins. 2. Straighten one bobby pin. Then bend the straight end of the pin back and forth several times to

determine the number of bends to break it in two. Is it springy? Is it easier or harder to bend the more times you bend it? Record your observations in a data table in your lab notebook.

3. Repeat this treatment two more times. 4. Notice that it is more difficult to bend the metal at the same place the first few times. Imagine

what is happening at the atomic level within the bobby pin. Please make a sketch of what is occurring at the atomic level in your lab notebook.

Treatment 1: Annealing -

5. Obtain 3 bobby pins. 6. After lighting the Bunsen burner, carefully hold the bent end of the bobby pin in the hottest

part of the flame (using your forceps) until it glows red-hot (about 30 seconds). Then gradually remove the pin from the flame by pulling it straight up and out of the flame.

7. Allow the sample to cool gradually in the air for about three minutes. This process of strong heating and slow cooling is called annealing. Repeat with the other two bobby pins, using the same bending technique to make the trials as consistent as possible.

8. After they have cooled, bend the pins back and forth until they break and record the number of bends that it takes to break the metal in your lab notebook. Was it easy to bend, compared to the unheated pin?

Treatment 2: Quenching

9. Obtain 3 bobby pins. 10. Fill a 250 mL beaker with cold tap water. 11. Carefully hold the bent end of the bobby pin in the hottest part of the flame (using your

forceps) until it glows red-hot. 12. Then immediately plunge it into the beaker of water and swirl it around, under water,

vigorously for 30 seconds. This process of strong heating and quick cooling is called quenching.

13. Bend the pin back and forth until it breaks and record the number of bends that it takes to break the metal in your lab notebook. Was it easy to bend, compared to the other pins?

14. Repeat treatment 2 for the other two bobby pins. Treatment 3: Tempering

15. Obtain 3 bobby pins. 16. Heat and quench all three bobby pins as done in Treatment 2 described above. 17. Then reheat the pins until they glow with a dull redness (do not allow them to become red hot

as done before!) and remove them gradually from the flame as you did in the annealing process. Allow the sample to cool gradually in the air for about three minutes. This process of strong heating, quick cooling, and slow heating, slow cooling is called tempering.

18. Bend the pins back and forth until they break and record the number of bends that it takes to break the metal in your lab notebook. Was it easy to bend, compared to the other pins?

19. Now repeat the treatments described with other metals assigned to your team by your

instructor. Metal wires should be cut about 6 cm long. Remember to record data about the various trials.

20. When you are finished, be sure to clean up your lab area and return all metals to the middle lab table. Average your data for the multiple trials conducted and be prepared to share your findings with the class.

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Analysis

Please respond in complete sentences on a separate sheet of paper.

1. Briefly summarize the differences between the three heat treatments used on the metals in this lab.

2. Compare the effects of heat treatment on the observed strength of the metals tested. In general, what conclusion can you draw about the strength of metals after annealing? quenching? tempering?

3. Note that after heat treatment, changes to the metal appear invisible, but the strength was still affected. After tempering one of the metal samples, imagine what is happening at the atomic level to improve the metal’s strength. Sketch and describe what you envision happening to strengthen the metal.

4. Compare & contrast the various metals tested. Are they all affected the same way by the different heating and cooling methods? Feel free to create a chart, table, or graphic organizer to summarize your comparisons.

5. You have learned in class that alloyed metals are stronger. Evaluate your comparisons of the metals in question #4 above. Were the alloyed metals stronger than the elemental metals? Try to explain why this is, based on their differences in crystalline structure.

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The Effects of Processing Treatments on Metals

Mechanical Properties When small loads (stresses) are applied to metals they deform, and they return to their original shape when the load is released. Bending a sheet of steel is an example where the bonds are bent or stretched only a small percentage. This is called elastic deformation and involves temporary stretching or bending of bonds between atoms.

P

l b

When higher stresses are applied, permanent (plastic) deformation occurs. For example, when a paper clip is bent a large amount and then released, it will remain partially bent. This plastic deformation involves the breaking of bonds, often by the motion of dislocations. Dislocations move easily in metals, due to the delocalized bonding, but do not move easily in ceramics. This largely explains why metals are ductile, while ceramics are brittle.

If placed under too large of a stress, metals will mechanically fail, or fracture. This can also result over time from many small stresses. The most common reason (about 80%) for metal failure is fatigue. Through the application and release of small stresses (as many as millions of times) as the metal is used, small cracks in the metal are formed and grow slowly. Eventually the metal is permanently deformed or it breaks (fractures). In industry, molten metal is cooled to form the solid. The solid metal is then mechanically shaped to form a particular product. How these steps are carried out is very important because heat and plastic deformation can strongly affect the mechanical properties of a metal. Grain Size Effect: It has long been known that the properties of some metals could be changed by heat treating. Grains in metals tend to grow larger as the metal is heated. A grain can grow larger by atoms migrating from

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another grain that may eventually disappear. Dislocations cannot cross grain boundaries easily, so the size of grains determines how easily the dislocations can move. As expected, metals with small grains are stronger but they are less ductile. Quenching and Hardening: There are many ways in which metals can be heat treated. Annealing is a softening process in which metals are heated and then allowed to cool slowly. Most steels may be hardened by heating and quenching (cooling rapidly). This process was used quite early in the history of processing steel. In fact, it was believed that biological fluids made the best quenching liquids and urine was sometimes used. In some ancient civilizations, the red hot sword blades were sometimes plunged into the bodies of hapless prisoners! Today metals are quenched in water or oil. Actually, quenching in salt water solutions is faster, so the ancients were not entirely wrong. Quenching results in a metal that is very hard, but also brittle. Gently heating a hardened metal and allowing it to cool slowly will produce a metal that is still hard but also less brittle. This process is known as tempering. It results in many small Fe3C precipitates in the steel, which block dislocation motion which thereby provide the strengthening. This process of heating and quenching, resulting in precipitates, is often referred to as precipitation hardening. Cold Working: Because plastic deformation results from the movement of dislocations, metals can be strengthened by preventing this motion. When a metal is bent or shaped, dislocations are generated and move. As the number of dislocations in the crystal increases, they will get tangled or pinned and will not be able to move. This will strengthen the metal, making it harder to deform. This process is known as cold working. At higher temperatures the dislocations can rearrange, so little strengthening occurs. You can try this with a paper clip. Unbend the paper clip and bend one of the straight sections back and forth several times. Imagine what is occurring on the atomic level. Notice that it is more difficult to bend the metal at the same place. Dislocations have formed and become tangled, increasing the strength. The paper clip will eventually break at the bend. Cold working obviously only works to a certain extent! Too much deformation results in a tangle of dislocations that are unable to move, so the metal breaks instead. Heating removes the effects of cold-working. When cold worked metals are heated, recrystallization occurs. New grains form and grow to consume the cold worked portion. The new grains have fewer dislocations and the original properties are restored.

“Metals! They’re Everywhere!” A MAST Module. Materials Science & Technology 1995.

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Heat Treatment of Metals – TEACHER NOTES

Major Concepts Students will have the opportunity assess the strength of a variety of metals both before and after heat treatment; the major concepts addressed include explaining the differences in observed strength between elemental and alloyed metals and evaluating why the properties of the metals are dependent upon their structure. Level This lab is appropriate for both regular level and honors high school chemistry, grades 9-12.

Expected Student Background It is expected that students have defined what an alloy is and can visualize how metallic bonding between metal ions works at the atomic level. Students should be comfortable in the lab using Bunsen burners and conducting a controlled experiment with multiple trials.

Time The lab can be completed in a 50-minute class period, depending on how many metals each team is assigned to test. With more time, this lab could easily fill a 90-minute class period as well, with follow up data sharing between teams and a class discussion. This lab can be modified in a variety of ways to best fit your students’ needs, as described in the teacher background below.

Safety Safety goggles and lab aprons must be worn throughout the entire lab. Students must take precautions to avoid burns or fire when using the Bunsen burners to heat and bend the metal. Remember, heated metals remain very hot for a long time. They should be set aside to cool and picked up/moved with caution. Use the heat protective forceps provided. Materials –needed per team

• Safety goggles • Bunsen burner • Striker or matches • Heat-protective forceps • 250 mL beaker • 12 bobby pins • (Paper clips)* • Wire cutter

(16 or 18 gauge solid wire of the following metals)*

• Aluminum (Al) • Copper (Cu) • Brass (Cu, Zn alloy) • Monel (Ni, Cu alloy) • A low carbon steel alloy • A high carbon steel alloy

*Many of the quantities of metals will vary, depending on how many teams are studying each metal, and how many trials have been required by the instructor. The metals were ordered from McMaster-Carr Supply Company and can be ordered at http://www.mcmastercarr.com/

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Aluminum composition of material / MP wire diameter size of coil / # of feet cost order #

99% Al alloy (Alloy 1100) MP = 660.4°C

0.040”

¼ lb. / 169’

$6.51

8904K71

Additional information: -does not turn red like other metals before the point when it liquefies! Copper & Copper Alloys

composition of material / MP wire diameter size of coil / # of feet cost order # 99.9% Cu MP = 1083°C

0.040”

¼ lb. / 49’

$5.08

8873K15

Brass (Alloy 260) MP = 1680°C (alloy of 70% Cu & 30% Zn) (+ at most 0.07% Pb & 0.05% Fe)

0.040”

¼ lb. / 53’

$6.43

8864K62

Nickel alloy (Monel Alloy 400) MP = 1300-1350°C (alloy of 67% Ni & 30% Cu) (+ up to 2.5% Fe)

0.032”

¼ lb. / 81’

$14.60

8905K31

Additional information: -Monel Alloy 400 can only be hardened by cold-working the material. -Elemental nickel is used primarily as an alloying element to increase corrosion resistance of Fe and Cu alloys. Steel (“iron alloys”)

composition of material / MP wire diameter size of coil / # of feet cost order # Steel (1006-1008) black oxide MP = 1300-1500°C

0.041”

¼ lb. / 55’

$2.51

8870K13

Steel (1080-1090) MP = 1300-1500°C “music wire” – spring temper C steel

0.041”

¼ lb. / 55’

$3.13

9666K62

Additional information: -Do not want “zinc-galvanized” or any type of prepared, coated, or polished steels – will alter properties. -The lower the number of the steel, the less alloying there is. Ex: 1006 – 1008 steel is “mild” or a low Carbon steel. 1080-1090 steel has more alloying, and is therefore is a stronger steel. General Information on Materials – -The principle behind alloys is that whatever is insoluble in the elemental metal will precipitate out after heat treating, therefore increasing the strength of the metal. -Size of wire:

16 AWG (gauge) = 1.29 mm (0.058 in) 18 AWG (gauge) = 1.02 mm (0.040 in)

-Bunsen burner at ~ 1000°C

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Teacher Background Processing metals with heat followed by quenching and cold-working should harden them. However, strong heating and quenching will only affect steel. Some aluminum is precipitation hardened with small amounts of copper. Heating these alloys strongly will soften them by causing the copper to form large precipitate particles which have little hardening effect. Most aluminum wire, however, is soft. In general, annealing the wires should soften the metal allowing it to bend more easily and more times before breaking; it will lose its springiness and rigidity due to changes in the crystalline structure and is more ductile. The quenched wires should be harder and bend fewer times before breaking, being stronger, but more brittle. The tempered wire should bend more times than the quenched wire did before breaking. Quenching causes the metal to contract severely, causing deformations in the material as the outside of the material shrinks more quickly than the inside. Tempering removes the residual strain on the metal’s microstructure as a result of the severe quench, therefore, making it stronger. This lab can be used to discuss two variations of what was being studied:

1. Test different metals with the same heat treatment and compare how properties change This setup would require more time and materials. Can compare 6 known metals - Al, Cu, Brass, Monel, Low C, High C steel, plus two

other metals – bobby pins and paperclips (both steels) after heat treatment. However, be aware that the alloys are key here; will only see hardening in metals that

will have precipitates after heat treatment and therefore change the properties (need other elements in the metal to have precipitation!). If using all elemental metals, will not see hardening effects.

If short on time or materials, each group could also test one or two metals of the eight available and share results, instead of testing most or all of the metals over three trials.

2. Test one alloyed metal (steel) with different heat treatments & and compare how properties

change This setup would be much faster and require less materials. Each treatment changes the alloy – new microstructure therefore new properties Annealing (slow, air cool) will lead to weaker metal Quenching (quick cool) will lead to stronger, brittle metal Tempering (quick cool followed by slow cool) will lead to a stronger, less brittle metal

Discussion should take place about the potential sources of error in completing the lab. If lab teams test different metals, there is the possibility that their bending technique (rate of bending, force of bending) could differ. In addition, teams may heat the metals in different parts of the flame for varying amounts of time, or not move the metals to the beaker of water at the same rate for the quench. This discussion could play a significant role if using class averages and comparing data. Assessing Laboratory Learning

Students should compare data as a class and discuss what conclusions can be drawn. After comparing results with neighboring teams, individual students (or lab teams) can turn in their responses for credit.

Students can be asked to respond to the analysis questions individually first. Then they could be asked to read the supplement reading on Heat Treatments and discuss with a lab partner. After, students could revisit and revise their analysis question responses to then submit for a grade.

Ask students to compare and contrast the difference in structure and resulting strength of elemental metals and alloyed metals.

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Answers to Questions Advance Preparation

1. Do you think an elemental metal (composed of atoms of only one element) or an alloyed metal

(composed of atoms of two or more elements) will display more strength? Why? Make a sketch if needed!

An alloyed metal because alloys contain a number of elements that when heat treated (or “hardened”) will precipitate out, therefore strengthening the metal by blocking further movement of dislocations.

2. In order to be better prepared for lab, create a chart summarizing the properties of each metal

to be studied. Be sure to include the element / alloy’s name, the composition of the material (100% of one element? Or varying percentages of a number of elements?), melting point in °C, and other pertinent characteristics to note. The six metals being used are listed in the lab.

See the chart provided under “Materials.”

3. Hypothesize: Of the 6 metals tested, which will demonstrate the most number of bends to break after heat treatment? Of the 4 types of treatments, which will affect the properties of the metals the most? Be sure to justify your predictions!

Analysis

1. Briefly summarize the differences between the three heat treatments used on the metals in this lab.

Anneal- strong heat, slow cool; Quench- strong heat, quick cool; Temper- strong heat, quick cool, slow heat, slow cool

2. Compare the effects of heat treatment on the observed strength of the metals tested. In general,

what conclusion can you draw about the strength of metals after annealing? quenching? tempering?

In steel, the metal is weaker after annealing, stronger yet brittle after quenching, and stronger but less brittle after tempering.

3. Note that after heat treatment, changes to the metal appear invisible, but the strength was still affected. After tempering one of the metal samples, imagine what is happening at the atomic level to improve the metal’s strength. Sketch and describe what you envision happening to strengthen the metal.

The precipitates that form block dislocation movement in the microstructure of the metal.

4. Compare & contrast the various metals tested. Are they all affected the same way by the different heating and cooling methods? Feel free to create a chart, table, or graphic organizer to summarize your comparisons.

The metals are NOT affected in the same way by all treatments, For example, the nickel alloy can only be hardened by cold-working the metal, and not heat treatment. In addition, the alloys will be affected more significantly by the heat treatment than the elemental metals due to their composition.

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5. You have learned in class that alloyed metals are stronger. Evaluate your comparisons of the metals in question #4 above. Were the alloyed metals stronger than the elemental metals? Try to explain why this is, based on their differences in crystalline structure.

References Metals! They’re Everywhere! A MAST Module. Materials Science & Technology 1995. Developed in

part at the Materials Science & Technology Workshop held at the University of Illinois at Urbana-Champaign during 1993-95. http://matse1.mse.uiuc.edu/home.html

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From micro scale…

to macro scale.

A Journey Through Size and Scale

Introduction

Scientists examine things in particular ways using a combination of very sophisticated equipment, everyday instruments, and unlikely tools. Some phenomena that scientists want to observe are so tiny that they need a magnifying glass, or even a microscope to see them. Sometimes things are so far away that a powerful telescope must be used in order to see them. It is extremely important that one understands the magnitude of scale and can compare the relative sizes of objects being studied. Objectives At the conclusion of this activity, you will be able to…

differentiate between exponential & standard notation, determine the length scale between objects of very different sizes, utilize a chart created to recall visual representations relating to a wide range of lengths, & evaluate the smallness of the nano scale relative to the macro scale.

Part One – Ranking Objects By Relative Size As a team, your task is to predict how big different objects are compared to one another. Discuss the list of objects below with your team, and then rank the ten objects in order from largest to smallest.

dust mite diameter of the flu virus nucleus of a cell diameter of a human hair cluster of atoms thickness of a cell wall individual DNA strands red blood cell thickness of toenails diameter of a bacterium

Record your thoughts in the area below:

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Part Two – Relating Size and Scale

SCA

LE

exponential notation standard notation English

LENGTH equivalent in SI (metric) units

LENGTH example

gigameter (Gm) diameter of our sun

SOLA

R

SYST

EM

height of proposed cable for releasing objects into space

diameter of Earth

megameter (Mm)

distance from Lake Superior to the Gulf

of Mexico coast

width of Florida penisula

height of Mt. Everest

GLO

BA

L

five city blocks

hectometer (m)

101

10

ten

dekameter (dam) height of a house

100

1

one

meter (m) height of a

human

10-1

0.1

one tenth

decimeter (dm) width of your

hands

HU

MA

N

MIC

RO

micrometer (µm)

NA

NO

nanometer (nm)

ATO

MIC

Angstrom (Å)

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A Journey Through Size and Scale – TEACHER NOTES

Major Concepts In this activity, students will investigate size of objects using metric measurements to provide them with a sense of scale. It involves a review of metric prefixes as well as metric conversions and exponential vs. standard notation. This will enable students to grasp the concept of the size of objects at the macro-, micro-, and nano- scale. Level This lab is appropriate for regular level high school chemistry, grades 9-12.

Expected Student Background In order to study scale, students need to be familiar with the metric system and scientific notation. It would be very beneficial to review prefixes such as deci-, centi-, milli-, micro-, and nano- prior to this activity. The pre-assessment in this activity (Part One) is meant to help expose previous misconceptions about size and scale and identify what students already know. Time The activity can be completed in a 50-minute class period.

Safety No safety precautions need to be taken to complete this activity. Materials Classroom computer with Internet access LCD projector Copies of Handouts

This activity is planned for use with “The Universe Within: An Interactive Java Tutorial” - http://micro.magnet.fsu.edu/primer/java/scienceopticsu/powersof10/ The simulation allows viewers to move towards or away from objects by a scale factor of 10. In addition to providing strong visual images and a feel for relative scale, the simulation offers a great way to show students how to use scientific notation. However, this could activity also be modified for use with the Eames’ Power of Ten book and/or video, or the IMAX video Cosmic Voyage. Both explore scale in the universe, moving from the subatomic level to the ends of the known universe. Teacher Background

1. Students should first complete the pre-assessment, Part One: Ranking Objects by Relative Size. Students, in pairs or small groups, should rank the objects on this list from smallest to largest.

Part One – Ranking Objects By Relative Size Objects listed from largest to smallest: thickness of toenails (mm) dust mite (200 um) diameter of a human hair (60 um) red blood cell (5 um)

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nucleus of a cell (1 um) diameter of a bacterium (1 um) diameter of the flu virus (100 nm) thickness of a cell wall (10 nm) individual DNA strands (10 nm) cluster of atoms (1 nm)

2. With time, groups could compare their rankings with other groups, or as a class on the board. This

will initiate conversation about possible misconceptions regarding relative sizes of objects. Answers need not be provided at this point in time; however, it should be pointed out if groups are in disagreement, and why it is so important to understand size and scale.

3. Then teams are asked to associate a size value to the objects ranked. Students will receive a blank

chart in Part Two: Relating Size and Scale, on which to rank the objects according to size and assign each object a size value. Encourage them to use pencil! You will need to go over the headings in the chart to be sure students understand what they are being asked for. In addition, students should complete the remainder of the chart as well. This is an excellent learning opportunity to review the concepts of exponential and standard notation, English compared to SI units, and prefixes such as deci-, centi-, milli-, micro-, and nano-. The class can share afterwards, again pointing out possible misconceptions this time regarding scale.

4. Before providing answers, show the online simulation of the Universe Within. If a classroom

computer and projector is not available, students can see this independently on students computers or in a computer lab. Be sure to show this a number of times, as students will catch on that some of the objects described are what they were previously ranking before.

5. After having seen the simulation, small groups should return to Part Two: Relating Size and Scale

to rearrange the listed objects and their sizes so that they are accurately ranked according to the simulation. Discuss the sheet with the class to clarify misconceptions that still exist, using the table provided with the answers on the overhead.

References An Introduction to the Nanoscale: Surface Area and Volume. Materials World Modules. Supported by a

National Science Foundation grant to Northwestern University, 2004. http://www.materialsworldmodules.org/modules/m_description.htm

Molecular Expressions: Science, Optics, and You

http://micro.magnet.fsu.edu/primer/java/scienceopticsu/powersof10/

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Visualizing Metals on the Nanoscale

Introduction

How do scientists visualize and study the altered properties of metals? In the last lab, you heat treated a variety of metals to affect their mechanical properties, such as strength and ductility. Note however that after each treatment, changes to the metal appeared invisible from the outside, but evidence showed that the properties of many of the metals changed. At what scale were the properties affected? The answer is - the nanoscale.

Imagine a world where a medical device can maneuver like a tiny submarine through your capillaries, enter a cell to find a disease in its earliest stage, and stop the disease right there. Imagine that a tire on a car weighs a few ounces, and that the most powerful computer (which now takes up about eight large bookcases) will fit in the end of your pencil. Scientists and engineers are working toward this world right now, but the work is only in its infancy. Eventually, this new science – nanoscience – will greatly change our technological society. This nano-revolution is likely to transform most of the materials and devices we use today.

Studying the nanoscale means working with objects that are unimaginably small. The prefix nano- refers to 10-9. (A nanogram is 10-9 gram; a nanosecond is 10-9 second). This nano-revolution is first defined by its size. At the nanoscale, sizes are given in nanometers. It seems small, but how small is it? In order to find this out, one must understand the concept of scale. Scale means “a gradation of ranges of a quantity.” When the quantity is length, the ranges are often described by prefixes such as macro-, micro-, and nano-. The scale of the world we perceive day to day is the macroscale, or things we can see. The next smaller-scale environment is the microscale, or things we can see if we use a microscope. The nanoscale is smaller still, followed by the atomic scale. Most of us have a hard time conceptualizing abstract measurements that small. Think about this - a single human hair is normally 60,000 to 120,000 nanometers wide! Objectives At the conclusion of this activity, you will be able to…

understand the invisibility of the nanoscale to the unaided eye, discuss visual images of atoms, molecules, and cells and their relative sizes, and predict what the internal structure of a metal looks like at the micro and nano scales.

Procedure

Imagine you could get an inside view of the metal wires you worked with in lab. With the human eye, one can see metals on a macro scale. With the aid of an optical microscope (up to 1000X magnification) or a scanning electron microscope (SEM – up to 10,000X magnification), one can see metals on a micro scale. New instruments even allow one to see metals on a nano scale! Your task is to predict what you think a metal looks like at the macro-, micro- and nano- scale.

Take a moment to review what we have studied so far about the crystal structure of metals, metallic bonding, and the heat treatment of metals to affect their properties.

Before creating your prediction cards, make a sketch of your thoughts for each scale on a piece of

scratch paper. If you were able to see into the structure of the metal itself, what would you see?

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Now take some time to create your prediction cards; be sure to use pencil. Label each card as

macro-, micro-, or nano scale, and add any other information we need to understand your sketch. Feel free to shade the sketches with colored pencils or crayons as well, if that is what you think you would see.

Lastly, describe or label any structures we can see at each order of magnitude.

When you are finished, add your cards to the board under the appropriate column: macro-, micro-, or nano scale. You will be asked to compare your sketch to your peers’ and record your observations in your lab notebook.

Thought Questions

1. Was it easy or challenging to predict what a metal looks like at various scales? Explain your response.

2. How did your sketch(es) differ from those of your classmates? Describe any noticeable features that were different.

3. Why is it sometimes difficult to speculate what a material might look like at a different scale?

4. Now consider what may be happening at the nanoscale when a metal is heat treated.

a) After heat treatment, what is one mechanical property of the metal that was altered?

b) What evidence did you have of this at the macro scale?

c) What might be happening at the micro- or nano scale to cause this change? (Hint: Think about what makes alloys unique! What are they composed of?)

d) With technology today, can we see individual atoms in a metal? Explain your response.

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Visualizing Metals on the Nanoscale – TEACHER NOTES

Major Concepts In this activity, students will predict how the structure of a metal looks at the micro and nano scales. It involves a review of metric prefixes as well as metric conversions. This activity will enable students to understand why scientists study materials on various scales to assess their mechanical properties. Level This lab is appropriate for regular level high school chemistry, grades 9-12.

Expected Student Background In order to study scale, students need to be familiar with the metric system and scientific notation. It would be very beneficial to review prefixes such as deci-, centi-, milli-, micro-, and nano- prior to this activity. Time The activity can be completed in a 50-minute class period.

Safety No safety precautions need to be taken to complete this activity. Materials 3 notecards per student pencils, colored pencils, crayons Teacher Background Much of the learning opportunities in this activity come with teacher facilitation as students create their sketches and predictions of what a metal looks like internally. Some students will be challenged by this task and will need some guidance. Ask them to go back and find their sketches from the Crystal Structure of a Metal Lab; what did they observe? At what scale were those drawings? What structures were visible? Giving students a place to start is helpful. In addition, the lessons taken from this activity come from student and class discussion after comparing the predictions of their peers. Realizing that scale is difficult to visualize, students can learn a lot from assessing the predictions of others and trying to justify why the metal would appear the way it does. Most importantly, images of steel alloys on the micro and nano scales (provided on the following pages) should be share with students to provide them with an accurate image of what grain boundaries look like on the microscale and what metal atoms look like on the nanoscale. The precipitation that has occurred in this heat treated steel alloy is what increases the strength of the alloy. It should be pointed out that the precipitate structures present throughout the entire volume of metal atoms studied are a crucial feature of this structure on the nanoscale.

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Answers to Questions 1. Was it easy or challenging to predict what a metal looks like at various scales? Explain your

response.

2. How did your sketch(es) differ from those of your classmates? Describe any noticeable features that were different.

3. Why is it sometimes difficult to speculate what a material might look like at a different scale?

Sometimes we don’t have the appropriate instrumentation to visualize the material on another scale. For example, a microscope will not allow us to visualize atoms on the nanoscale, only grains on the microscale.

4. Now consider what may be happening at the nanoscale when a metal is heat treated.

a) After heat treatment, what is one mechanical property of the metal that was altered? Strength was affected

b) What evidence did you have of this at the macro scale? The metals time of bend to breaking was affected by the heat treatment.

c) What might be happening at the micro- or nano scale to cause this change? (Hint: Think about what makes alloys unique! What are they composed of?) The alloying elements in the metal bond together into a precipitate which strengthens the material (by blocking dislocation motion).

d) With technology today, can we see individual atoms in a metal? Explain your response. Yes!

References An Introduction to the Nanoscale: Surface Area and Volume. Materials World Modules. Supported by a

National Science Foundation grant to Northwestern University, 2004. http://www.materialsworldmodules.org/modules/m_description.htm

Molecular Expressions: Science, Optics, and You

http://micro.magnet.fsu.edu/primer/java/scienceopticsu/powersof10/

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Images of a Steel Alloy on the Microscale

Optical micrographs of a steel alloy at 1000X. The unit used to measure grains and grain boundaries at this scale is micrometers, µm.

SEM image @ 90X – cup/cone ductile fracture SEM image @ 3000X – cup/cone ductil fracture

The SEM images were obtained with a Scanning Electron Microscope at various magnifications, as indicated. The steel microstructure is still evaluated here using the micrometer.

SEM image @ 4000X – steel microstructure

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• Cu• Ni • Al • Mn• Si • Fe • C • Nb

Key to Element Colors

Images of a Steel Alloy on the Nanoscale

The images illustrate a small piece of steel (only 50 nm wide at the tip!) on the nanoscale, using in instrument called the LEAP (Local Electrode Atom Probe tomography). Precipitation hardening is evident in these samples of steel. The atoms of the main element, Fe, are illustrated in blue. The atoms of the alloying elements are color coded, as indicated in the key above. By studying the number density, average radius, and composition of these precipitates that formed as a result of heat treatment, scientists can evaluate the mechanical properties on a nanoscale.

Entire analyzed volume of ions (~8M atoms)

A Nb-C precipitate

Cu-rich precipitates

Cu-rich precipitates highlighted

Cu-rich cores of the precipitates are covered in a “shell” of Ni, Al, and Mn