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TOPIC 1 : MATERIAL STRUCTURE & BINARY ALLOY JF302/ 1/
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1.0 MATERIAL STRUCTURE & BINARY ALLOY
1.1 Atom Is the elementary particles that make up all the materials either in the form of solid, gas or
liquid. Atomic size is very small, however it has the weight and the properties of its own.
The atom consists of three basic particles as shown below :
Particle Charge
Proton Positive
Neutron Neutral
Elektron Negative
In terms of the charge, the atom is neutral because the proton has a charge opposite to the
electrons. The nucleus consists of protons and neutrons. While electrons rotate around it.
Arrangement of electrons in atoms is shown in Figure 1
Figure 1: Position of the electron, the atomic nuclei and orbital
1.2Elements
A combination of two or more atoms of same type. It is in original condition. Example:
the less relative metal such as gold and paltinium. Non-metals such as diamond, graphite,
and sulfur.
1.3 Mixture
A combination of two or more atoms of different types, but not chemically combined.
1.4 Compounds
A combination of two or more different atoms chemically joined. Example: Iron +
sulphide and heated, produce iron sulfide. Natural compounds are very stable because the
particles are rigidly held therein. So it will not be easily knocked down. Eg: Sodium
Chloride can be decomposed at a temperature of 800 C. Bonding that occurs is called
chemical bonds.
Nucleus which consist of
proton dan neutron
Electron
Shell / orbital 1
Orbital 2
Orbital 3
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1.4 Element Periodic Table
Consists of 109 elements. Vertical column in the named group. Sometimes called the
horizontal column. Periodic table has eight groups, from group I to VIII. Four groups
have special names, such as in Figure 1.3. This table has a middle block, known as the
transition elements.
Figure 1.3 : Element Periodic Table
N
7
Nitrogen
14
2:5
Atomic weight
Symbol
Name of element
Electron Configuration
Atomic number
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1.5The characteristic of Element Periodic Table
Chemical properties of an atom depends on the number of electrons in the outer shells of
atoms, called atomic valence . In this arrangement, the elements have the same number of
electrons in the outer shell will be included in the same group. This is why the elements
in the same group have similar chemical properties. Elements in group 1 had an electron
in the outer shell, the elements in group 2 has 2 electrons in the outer shell.
Each periodic with the same number of shells.
1.6 The Usage of Element Periodic Table
To facilitate the classification of an element. It also gives information about the elements,
especially the properties of the element as it is collected in order. Facilitate expect an
element that is still in the discovery and predicting the properties and usage. Easy to
analyze and understand a reaction between the elements.
1.7 Electron configuration (order of filling electrons in orbital)
Each shell can only be filled by a certain number of electrons only. If a shell has been
fully completed, other electrons to be filled into the next shell. Generally, the electrons
will occupy the shell closest to the nucleus prior to occupying other shell.
Fill the electrons in the shell closest to the nucleus first. This shell has the lowest energy (e-max = 2n
2). After that, the electrons are filled in the next
shell which is more powerful.
After the 18th elements, an exemption from this rule will apply. Where it should be in the order which been determined.
1.8Crystal
Solids can be classified into solid crystalline and amorphous solids. Crystalline or
crystalline solid consisting of atoms arranged in a three-dimensional repetitive pattern or
uniform. Crystals composed of metallic and nonmetallic. Single crystals with unit cell is
composed of solid and uniform polycrystalline crystal consists of many single crystals in
Figure 1.4 below
Details of single crystal
(butiran hablur tunggal)
Grain boundries (sempadan
ira @ bijian)
Rajah 1.4 : Structure and grain boundries
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In the solidification process of atomic, liquid metal will react with each other and
organize their respective positions in a uniform and orderly form. The compilation of this
orderly process called space lattices. Crystals can be seen by using the X - Ray
defractometer while the grain can be seen clearly using metallurgical microscope after the
process of grinding, polishing, etching. Four types of crystal structures that are often
found is the simple cubic (simple cube), body-centered cubic (BCC), face-centered cubic
(FCC) and hexagonal closed pact (HCP) as in Figure 1.5.
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Rajah 1.5 : Crystal structure
Examples of materials that crystallize in this form are: -
Simple cube = salt (Na Cl)
BCC = chromium, molibdenum, titanium and tungsten.
FCC = aluminium, kuprum, aurum and nickel.
HCP = berillium, magnesium and zinc. 1.9The types of bonding
There are three ways how an atom is bond :
Bonding Ion / ionic / elektrovalen
Covalent
Bonding metal / metal
a) Ionic Bonding (Elektrovalen / Ion)
This bonding occurs when one or more electrons transferred (donated) from one atom to
another atom. Atoms lose electrons become + ve ions (cations) and atom receive electron
become -ve ions (anions). Ionic bonding occurs due to the attraction of the ion with a
different charges.
As in Figure 1.7: The reaction between natrium and chlorine atoms. For natrium chloride
ion, electrons are transferred from natrium atoms to chlorine atoms to form natrium
chloride. Ions Na + Cl organized together with the large number of ions in crystals.
Elekton are transferred from Na to the Cl to form Na Cl.
Most of the mineral materials and ceramics are of ionic bonding.
Elektron transferred from
natrium to clorine
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Figure 1.7 : Ionic Bonding of Natrium Cloride b) Covalent bond
Terhasil daripada tarikan diantara elektron yang dikongsi ini dengan nukleus positif bagi
atom yang masuk kedalam ikatan.
Partnership of the elctron in order to ensure the outer electrons (valence electrons) are
always full as shown in Figure 1.8. Resulting from the attraction between electrons that
are shared by the positive nucleus of an atom into the bond. Usually, the material which
have a covalent bond are fragile. For an example, an electrical insulator (polymers and
ceramics)
Figure 1.8: Covalent Bonding (a) Clorine (b) Oxigen
c)Metal Bonding (Metallic)
Atomic arranged very close to each other. Each atom provides one @ more electrons
move throughout the metal crystals as shown in Figure 1.9. Electrons not only shared by
a few atoms only, but will be owned by all the atoms in it. These solids are bound by
attraction between metal ions and free electrons posiitif. It produces forces a strong bond.
For example : heated tungsten atom between 3400 C - 5000oC.
2.0 SOLIDIFICATION OF METALS AND ALLOYS
In previous topic, we have examined the structure of existing materials from atoms and
we have understand that the building or a combination of atoms of the structure is the
basis of the phase formation. This time we will try to understand how these phases
solidify form and combine to produce a grain that can be seen in the gross. For that, let us
together see how the solidification of metals and alloys occur.
2.1 The growth of crystal / Grain
Solidification process occurs with the growth of the nucleus (nukleas). Nucleus edges
(bucu-bucu nukleas) are free to choose their own path to a cooler place. This causes the
growth of nuclei and the development of the growing edges (perkembangan bucu). The
(a) Molecule of Cl2. One pair of electron
(b) Molecule of oxigen, O2.-Two
pairs of electron
Cl Cl O O
Figure 1.9: Metal Bonding (positive ion in a gas of electron)
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Radial arm (lengan jejari) is formed which will form the secondary arms (lengan
secondary) which is respectively 90 from one another. This continued until one
structure existing which been called dendrites, as shown in Figure 2.1 below.
The dendritic growth & arm met each other to form the grain boundaries. The
solidification ends with the formation of grains.
2.2 Pure Metal (Logam Tulin)
Logam yang mempunyai elemen-elemen yang sama, mempunyai sifat-sifat yang
melampau (extreme) dan tidak dapat memenuhi kehendak kerja kejuruteraan. Logam
tulin mempunyai cirri-
i. Mudah di tempa boleh di ketuk kepada berbagai bentuk. ii. Mulur boleh dijadikan wayar yang halus.
2.2 Alloy (Aloi/Pancalogam)
Gabungan/cantuman rapat antara 2 atau lebih komponen bahan ( unsur logam dan bukan
logam) dan wujud samada dalam keadaan pepejal atau cecair. Contoh : sedikit karbon
dicampurkan dengan besi akan menghasilkan keluli.
2.3 Solid Solution (Larutan Pepejal)
Atom atau molekul-molekul bahan telah menduduki kedudukan yang biasa dalam kekisi
hablur dan membentuk suatu fasa tunggal. Apabila pemejalan berlaku, atom-atom aloi
akan tersusun dengan teratur dan ia dipanggil ruang kekisi. Fasa ini mengekalkan
kelarutan zarah yang terdapat dalam keadaan cecair sama ada sebahagian atau
keseluruhannya.
Rajah 2.1: The formation of nucleas, dendrite structure and grain
boundries
The formation of
nucleus Dendrite Solidification ends with
the form of grains The dendrite growth &
arm met each other to
form grain boundries
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2.4 Types of Solid Solution (Jenis-jenis Larutan Pepejal)
Terdapat 2 jenis larutan pepejal iaitu :
i) Larutan Pepejal Gantian (Substitution Solid Solution)
Secara Rawak (random replacement)
Secara Teratur ( ii) Larutan Pepejal Celahan (Interstitial Solid Solution)
a) Substitution Solid Solution of Random Replacement (Larutan Pepejal Gantian Secara Rawak)
Atom zarah mengambil tempat atom utama secara rawak dan susunannya tidak teratur.
(Rajah 2.2)
b) Larutan Pepejal Gantian Secara Teratur Atom zarah mengambil tempat atom utama dan susunannya teratur seperti Rajah 2.3 di
bawah.
c) Interstitial Solid Solution (Larutan Pepejal Celahan) Atom zarah yang kecil mengisi ruang-ruang di antara atom-atom dalam kekisi. Ia berlaku
sekiranya atom logam tambahan ini adalah lebih kecil dari logam induknya. Larutan jenis
ini adalah lebih kuat kerana peranan atom logam yang lebih kecil akan memenuhi
ruangan-ruangan yang ada. Oleh yang demikian, kegelinciran dapat dielakkan dari
berlaku seperti Rajah 2.4 di bawah .
Atom Zarah
Atom Utama
Atom Zarah
Atom Utama
Rajah 2.2: Susunan atom bagi larutan pepejal gantian secara rawak
Rajah 2.3: Susunan atom bagi larutan pepejal gantian secara teratur
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2.6 Solidification (Pemejalan Bahan)
Apabila sesuatu logam dipanaskan dengan sekata, ia akan mencapai kepada satu takat
suhu dimana ia akan mula melebur. Sekiranya pemanasan pada suhu yang sekata ini
diteruskan, keseluruhan logam akan lebur. Suhu tetap peleburan ini dipanggil sebagai
titik lebur. Semasa penyejukkan keadaan yang sebaliknya berlaku. Tenaga kinetik bagi
atom-atom atau molekul bagi cecair tersebut berkurangan dan kelikatan logam semakin
bertambah. Di dalam keadaan cecair, atom-atom logam berada dalam keadaan rawak.
Tetapi apabila pembekuan berlaku, atomnya akan tersusun dengan teratur mengikut
geometri tertentu. Semua bahan pepejal terbentuk dalam keadaan amorfous (tidak
berhablur) atau crystalline (berhablur/kristal).
2.7 Formation of Metal Core in solidification (Pembentukan Teras Dalam Pemejalan Logam)
Pembekuan pancalogam dimulai dengan pembentukan awal rangka dendrit (dendritic
skeletons) seperti Rajah di bawah.
Rajah 2.5 : Susunan rangka dendrit
Pertumbuhan hablur-hablur dendrit ini akan berterusan dan membesar apabila suhu
pembekuan menurun. Pembesaran akan berlaku di setiap paksi-paksinya dan akhirnya
akan bercantum. Pembekuan dendrit ini juga dikenali sebagai teras (coring) di mana
hablurnya terdiri daripada atom-atom logam lain sebagai bendasing.
Atom Zarah
Atom Utama
Rajah 2.4: Susunan atom bagi larutan pepejal celahan
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2.8 Phase Balance Diagram Of Binary Alloy System (Rajah Keseimbangan Fasa
Bagi Sistem Aloi Perduaan)
Untuk memahami kandungan bahan dan struktur fasa. Ini bermakna satu bahagian
homogen (komponen) bahan yang boleh diasingkan secara fizikal dan mempunyai
kandungan kimia serta struktur yang teratur.
2.8.1 Phase (Fasa)
Merujuk kepada suatu bentuk struktur atau kawasan yang mempunyai sifat berlainan
jenis akibat dari perubahan atau memiliki sifat semulajadi yang berbeza. Ia dipisahkan
oleh garis-garis lengkung pendinginan atau sempadan fasa
2.8.2 Phase Balance Diagram (Rajah Keseimbangan Fasa)
Gambarajah fasa ialah peta sesuatu system dan ia menunjukkan fasa yang sepatutnya
wujud di bawah keadaan keseimbangan untuk sebarang gabungan rencaman dan suhu
tertentu. Gambarajah fasa digunakan secara meluas dan amat penting terutama untuk
memahami system logam dan aloi.
2.8.3 Composition (Komposisi)
Komposisi ialah peratus kandungan bahan-bahan tertentu yang sengaja atau tidak sengaja
dimasukkan ke dalam sesuatu bahan. Dengan kehadiran peratus komposisi bahan ini
boleh menyebabkan perubahan dalam fasa, sifat dan bentuk struktur mikro bahan.
2.8.4 Liquidus (Cecair)
Liquidus merujuk kepada garisan lintang yang memisahkan antara fasa cecair bahan
dengan fasa separa cecair bahan. Semasa proses pemejalan berlaku, zarah bahan yang
berada pada suhu lebur akan mula memejal apabila suhu diturunkan. Titik permulaan
proses pemejalan berlaku apabila melepasi garisan lintang liquidus.
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2.9 The process of solidification for pure metal and alloy according to the cooling
curve (Proses pemejalan Logam tulen dan aloi merujuk kepada Graf lengkung
Pendinginan)
1) Metal Cooling curve diagram (Graf lengkung pendinginan Logam Tulin)
Apabila logam disejukkan ke suhu beku, ia mengalami kesukaran untuk
membentuk hablur/nukleus.
Keadaan ini berlaku di antara 0.1 hingga 10C (Kawasan B hingga C)
Apabila nukleus mula terhasil, suhu akan meningkat ke titik suhu beku (Thermal arrest) yang sebenar (D) dan suhu tidak dibebaskan lagi.
Apabila pembentukan hablur tamat (E) suhu akan terbebas semula. 2) Alloy Cooling Curve diagram (Graf lengkung pendinginan Aloi)
Apabila penyejukan berlaku, haba dibebaskan hingga ke suhu beku dan unit-unit sel mula terbentuk.
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Apabila sampai pada titik beku (Thermal arrest), haba tidak lagi dibebaskan kerana digunakan untuk pembentukan hablur-hablur hingga selesai.
Selepas itu haba kembali dibebaskan (Equilibrium Freezing Temperature)
2.9 The phase balance diagram, which comprises of a few cooling curves for solid solution (Gambarajah Keseimbangan Fasa, terhasil dari gabungan graf lengkung pendinginan Larutan Pepejal)
Sistem pancalogam atau aloi ini lebih mudah dipelajari dengan merujuk kepada gambarajah keseimbangan fasa atau gambarajah juzuk aloi tersebut. Rajah keseimbangan ini berdasarkan kepada suhu dan peratusan kandungan aloi yang boleh membantu memahami dan meramalkan apakah perubahan struktur aloi yang berlaku sewaktu pemanasan dan penyejukkan untuk pembekuan. Rajah ini juga penting sebagai panduan bagi proses rawatan haba dan memperbaiki sifat-sifat kimia bahan tersebut. Di dalam kebanyakkan aloi perduaan (binary alloy) iaitu campuran diantara dua jenis logam, juzuk-juzuknya boleh larut antara satu sama lain dalam keadaan cecair.
Berikut adalah graf lengkung pendinginan sebenar bagi aloi @ pancalogam:- Keadaan sebenar ini menunjukkan nisbah yang wujud di antara titik mula pemejalan (Liquidus point) dan titik tamat pemejalan (Solidus point) yang disebut Freezing Range.
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Sekiranya lengkung ini diplotkan sebanyak 6 graf, hasilnya dapat dilihat seperti di bawah :-
The construction of phase balance diagram (Mekanisma pewujudan rajah keseimbangan fasa)
Contoh penafsiran graf keseimbangan fasa:
1455
1083
t2 t1
t3
p
q r
m n
Larutan pepejal
Su
hu
(o C
)
100% Cu X% Ni 100
% % Ni
t1 suhu pemejalan bermula
t3 suhu pemejalan berakhir
t2 cecair yang kerencaman m
berada dalam keadaan
keseimbangan dengan
larutan pepejal kerencaman.
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Rajah di atas menunjukkan suatu aloi yang mengandungi X % nikel akan memejal seperti
berikut :
i. Pada suhu t1, kerencaman cecair 1 akan berada dalam keadaan keseimbangan dengan larutan pepejal kerencaman yang sepadan kepada titik p pada garisan
solidus (garisan pepejalan). Oleh itu hablur larutan pepejal pertama membentuk
terdiri dari kerencaman p.
ii. Apabila suhu turun maka kerencaman larutan pepejal berkecenderung untuk berubah dengan cara resapan mengikut garisan pepejalan kepada titik q.
iii. Pada suhu t2, cecair yang kerencaman m berada dalam keadaan keseimbangan dengan larutan pepejal kerencaman.
Proses pemejalan aloi ini akan selesai pada suhu t3 apabila titisan terakhir cecair
kerencaman n, memejal, membaiki kerencaman hablur larutan pepejal kepada r.
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EXERCISE
1. Atom consist of nucleus and .................. A. Electron B. Proton C. Neutron D. Atomic number
2. Nukleus consist of............... and proton. A. Neutron B. Atomic number C. Electron D. Proton
3. Atomic Number is a the total of ...............in an atom. A. Proton B. Neutron C. Atomic number D. Electron
4. Atomic Mass Number is the total of the quantity of proton plus the quantity of........... A. Elektron B. Proton C. Neutron D. Nombor atom
5. Atomic number of Ferum is 26, so the oleh itu Atomic Mass Number of Ferum is ..........
A. 26 B. 52 C. 78 D. 104
6. Atomic number of Magnesium ialah 12, so the number of orbital is ........... A. 1 B. 2 C. 3 D. 4
7. The total number of electron at orbital no-3 not more than ........... A. 6 B. 12 C. 18 D. 24
8. Atomic number of Aluminium is 13, so the quantity of elektron at the last orbital is .............
A. 1 B. 2 C. 3 D. 4
9. One of the type of atomic bond is ............... A. mass B. Proton C. Elektron D. Metal
10. Solid solution consists of the substitutional type and................... A. reverse B. return C. Interstitial D. Middleness