Classification and Properties of Ceramic...
-
Upload
vuongthuan -
Category
Documents
-
view
214 -
download
1
Transcript of Classification and Properties of Ceramic...
Lec 27, Page 1/17
MME 131: Introduction to Metallurgy and Materials
Lecture 27
Classification and Properties of Ceramic Materials
AKMB Rashid Professor, MME Dept
BUET, Dhaka
Today’s Topics
1. What are ceramics?
2. Structure of ceramics
3. Classification of ceramics
4. Characteristics of generic ceramics
5. Typical properties
6. Manufacture of ceramics
Lec 27, Page 2/17
What Are Ceramics?
comes from the Greece word keramicos, which means burnt stuff
broadly classed as inorganic, non-metallic materials
usually a compound, or a combination of compounds, between metallic and nonmetallic elements
(mainly, O, N, C, B)
bonds are either totally ionic, or combination of ionic and covalent
Typical Characteristics of Ceramic Materials
brittle
Hard, wear-resistant, electrically and thermally insulating,
refractory, chemically stable, durable, non-magnetic.
BUT
These properties are not common to ALL ceramics !!
everlasting !!!
load bearing ??!!
Lec 27, Page 3/17
ZrO2 toughened Al2O3 (cutting tools)
YBa2Cu3O7 (superconductor)
(Ba,Sr)0.6Fe2O3 (magnet)
New “high-performance” ceramics
unusual properties (e.g., high toughness, conductive)
need to understand structure-property relation
Some exceptions
High melting point and high refractoriness (except glass)
Generally electrical and thermal insulators
Generally hard and strong with low plasticity
Low fracture toughness (brittle)
Chemically inert
Many are low cost (bricks)
Wide range of appearance
Common properties
Lec 27, Page 4/17
Some Property Check
Materials 1040 Soda- Silicon
Steel glass nitride
Density, kg m-3 7850 2480 3200
Modulus, GPa 210 74 310
UTS / MOR, MPa 500 50 300 – 850
Fracture Toughness, MPa m1/2 140 0.7 4.0
Softening / Melting Temp., K 1765 1000 2173
Ceramic Structure
More than one type of atoms (cations, anions).
Complex structures, based on BCC, FCC, and HCP.
Structures are named based on the first mineral that is discovered to have the structure. (e.g., rocksalt structure)
Have low packing density (because of large anions)
Na Cl Ti Ca O Rocksalt structure
Perovskite structure
Lec 27, Page 5/17
Based on SiO44- tetrahedron
Si-O bonding is largely covalent, but overall SiO4 block has charge of -4.
Various silicate structures are formed by different ways of arranging SiO4
4- blocks.
vertex (ring)
edge (chain)
face (sheet)
SiO44- tetrahedron
Silicate Structures
Silicate glass – pure SiO2
melts at a very high temperature
very brittle
high viscosity
Hard to fabricate
Crystalline silica
Soda-glass
Modifiers / breakers (e.g., Al, Na) are added to open up / break the network and reduce the melting point
Lec 27, Page 6/17
Defects in Ceramic Structure
Like metals, defects such as vacancies and substitutional atoms are present.
Slip is difficult in polycrystalline ceramics, so defects have little effect on strength.
But, defects have significant influence on electric properties.
Classification of Ceramics
very “traditional” (clay-based and silica-based ceramics used for construction and other applications)
but also are new HIGH-TECH ceramics
1. optical (transparency) (opto-electronics)
2. electronic (piezoelectric, sensor, superconductor)
3. thermo-mechanical (engine material)
4. wear-resisting (cutting tool)
In 1974, the U.S. market for the ceramic industry was
estimated at $20 million. Today, the U.S. market is estimated
to be over $500 billion
Lec 27, Page 7/17
Silicate Ceramics: presence of glassy phase in a porous structure
clay ceramics (with mullite – 3Al2O3.2SiO2) silica ceramics (with cordierite – 2MgO.2Al2O3.2SiO2)
Oxide Ceramics: dominant crystalline phase, with small glassy phase
single oxide (Al2O3), modified oxide (zirconia toughened alumina) mixed oxide (mullite, BaTiO3)
Non-oxide Ceramics: carbon, SiC, BN, TiB2, sialon
Glass-ceramics: partially crystallised glass
SiO2-Li2O, LAS, MAS
Classification based on COMPOSITION
Traditional Vitreous Ceramics clay-based products porcelain sanitary ware tiles bricks refractories
Glasses based on SiO2, with additions to reduce m.p. or give special properties containers households optical glasses
Natural Ceramics rocks & minerals, including ice; bones
Cement & Concrete a complex ceramics with many phases structural composite
High-performance Advanced Ceramics special ceramics having improved toughness, wear resistance, electrical properties, etc. cutting tool sensor grinding laser bearing superconductor
Classification based on APPLICATIONS
Lec 27, Page 8/17
Glasses
Any material that has solidified and become
rigid without forming a regular crystal
structure is known as glass.
Usually a term applied to ceramic materials
(although metals can be formed into glasses
as well).
There is no long range order, although the
silicate tetrahedra are still linked together.
Crystalline materials: crystallize at melting temp, Tm.
have abrupt change in sp. vol. at Tm.
Glasses: do not crystallize.
sp. vol. varies smoothly with T.
Glass transition temp., Tg.
“temperature at which glass becomes rigid enough to handle”
can also be load-bearing (e.g., car window, container glass,
vacuum equipment)
basically contains three types of ingredients:
(1) network former (SiO2, B2O3)
(2) network breaker (Na2O, K2O)
(3) network modifier (Al2O3)
generally brittle (can be toughened by physical process and by
varying the composition or the microstructure)
Corning Glass Museum
general “glass” commonly applied to silicate based ceramic materials.
Lec 27, Page 9/17
Soda-lime Glass 70% SiO2, 10% CaO, 15% Na2O, 5% MgO/Al2O3
Low melting/softening point, easily formed and shaped.
Windows, bottles, etc.
Borrosilicate Glass (Pyrex) 80% SiO2, 13% B2O3, 4% Na2O, 3% Al2O3
High temperature strength, low coefficient of thermal expansion, good thermal shock resistance.
Cooking and chemical glassware
LAS Glass-Ceramic 20% Li2O, 20% Al2O3, 60% SiO2, + TiO2 (nucleating agent)
Heat treatment cause glass to crystallise to form crystal/amorphous composite with greater creep resistance and very low coefficient of thermal expansion and excellent thermal shock resistance.
Cooker tops, ceramic composites
Traditional Vitreous Ceramics
pottery, porcelain, tiles, structural and refractory bricks are still made by processes very similar to those of 2000 years ago
fired products consist of a glassy phase (based on SiO2) which melts and “glues” together a complex polycrystalline multiphase (based on Al2O3) body.
formed into shape using clays in wet, plastic state, which is then dried and fired for crystallization and vitrification
Lec 27, Page 10/17
1. Plastic materials
Assist forming process (deform easily without rupture, retain the imposed shape)
Example: Clays, talk.
2. Fluxes
Promotes fusion during firing.
Aid viscous liquid formation; to produce a glassy matrix
Example: Feldspar, nepheline syenite, volcanic ash.
3. Fillers
Provides a rigid component to aid in forming and firing.
Confer some very important physical properties (eg.,thermal expansion)
Example: Silica, calcined clay, alumina, limestone, bone ash
Raw Materials
Ceramic Typical Typical Type Composition Uses Porcelain Electrical insulator China Made from clays, Tableware, Earthenware mixed with tiles, Pottery other inert materials art ware Bricks Construction, refractory uses
Earthenware
Stoneware
Porcelain
China
Pottery
Bricks
Lec 27, Page 11/17
High-performance Advanced Ceramics
Traditional ceramics are weak because they contains many pores and cracks; their elastic moduli are low because of glass phases present
Advanced ceramics exhibits superior mechanical, electrical, optical, and magnetic properties and corrosion or oxidation resistance.
electronic ceramics insulators, substrates, capacitors, varistors, actuators, sensors
optical ceramics windows, lasers; magnetic ceramics
engineering/structural ceramics have applications in mechanical engineering, chemical engineering, high-temperature technology, and in biomedical technology
special ceramics nuclear reactor materials, refractories
Engineering Ceramics
high performance of engineering ceramics are resulted due to:
1. full density with fewer microcracks and higher intrinsic modulus
2. high toughness (measured by fracture toughness, KIC)
resultant properties are comparable with those of metals, cermets, or even diamond
Lec 27, Page 12/17
Shroud ring and turbine blades
for helicopter engines (Si3N4)
Sealing rings and other
pump spares (SiC)
Cutting tools
(Al2O3, Si3N4, etc.)
Rotor (Alumina) Gears (Alumina)
Hip joint
Socket (Al2O3)
ball (ZrO2)
Lec 27, Page 13/17
Electronic Ceramics
shows unusual electrical properties
normally insulator, but can be made to
semiconductor or even superconductor by carefully
controlled addition of impurities (the process is
known as doping)
e.g., doping of Si with B or P
Ceramic Typical Typical Type Composition Uses
Alumina Al2O3, 3Al2O3.2SiO2 Electronic insulator
Dielectric ceramics BaTiO3 Capacitor
Piezoelectric ceramics SiO2, ZnS, GaAs Ultrasonic device, Strain gauge, microphone
Superconductors YBa2Cu3O7 Electromagnet, magnetic resonance imaging (MRI)
Ceramic
insulators
Magnetic
Levitation
Lec 27, Page 14/17
Cement and Concrete
used on an enormous scale in construction industries;
only brick and timber rival in volume (then steel)
very cheap – about one tenth the cost per volume
of steel
Concrete Culvert
cement is a combination of lime (CaO), silica (SiO2) and
alumina (Al2O3), which set when combined with water.
concrete is a mixture of sand and stone (aggregate)
held together by a cement (thus concrete is a ceramic-
ceramic composite)
Cement Typical Typical Type Composition Uses Portland cement CaO + SiO2 + Al2O3 Cast facing, walkways, etc. and as component of concrete, used for general construction
Lec 27, Page 15/17
Natural Ceramics
stone is the oldest construction materials and the most durable (Pyramid, 5000 years old)
behaves like any other ceramic in load-bearing conditions
ice is also a ceramic
manifestations include anything ranging from ice cubes through icebergs to the Arctic continent and the Antarctic ice cap (3 km thick, 1013 m3 vol.)
bone is also a ceramic
the mineral constituent of bone is hydroxyapatite (HA), Ca10(HPO4)6(OH)2. 43 mass % of human body is HA.
Ceramic Typical Typical Type Composition Uses Limestone (marble) Largely CaCO3 Sandstone Largely SiO2 Building construction Granite Aluminium silicate
Ice H2O Arctic engineering
Bone Ca10(HPO4)6(OH)2 HA for human bone
Lec 27, Page 16/17
Ceramic Composites
ceramics stiffness, hardness
toughness
Ceramic Composite Components Typical Uses Fibre glass Glass – polymer High-performance CFRP Carbon – polymer structures Cermet, ZTA WC – Co, ZrO2 – Al2O3 Cutting tools, dies Bone HA – collagen Animal structure
polymer / metal +
Ceramic composite
Lec 27, Page 17/17
Data for Ceramics
Thermal Young’s Modulus of Fracture Shock Materials Density Modulus Rupture Toughness Resistance Mg m-3 GPa MPa MPa m1/2 K Soda lime glass 2.48 74 50 0.7 84 Borrosilicate 2.23 65 55 0.8 280
Porcelain, pottery 2.3-2.5 70 45 1.0 220
Diamond 3.52 1050 - - 1000 Dense alumina 3.90 380 300-400 3-5 150 Silicon nitride 3.2 310 300-850 4 500 Zirconia 5.6 200 200-500 4-12 500 Sialon 3.2 300 500-830 5 510
Cement 2.4-2.5 30-50 7 0.2 <50
Ice 0.92 9.1 1.7 0.12 -
MME 131: Lecture 31 Part 2
Processing of Ceramic Materials
Next Class