A. THE STRUCTURE OF MATERIALS AND BINARY ALLOY SYSTEM

1.0 THE STRUCTURE OF MATERIALS AND PERIODIC TABLE OF THE ELEMENTS

1.1 The Structure Of Materials1. Differences in properties of various materials are due to the differences in the structures of materials.2. They are of atoms and molecules which are bond together by definite forces to form crystal structure

and microstructure.3. Crystal structures or crystals : atomic arrangements which have a repetitive pattern in all the

three dimensions of space.4. Molecules : are forms when two or more atoms combined chemically.5. Microstructure : is the appearance of the structure of a material under a microscope and

consists of phase structure and grain structure.6. All solid materials consist of a large number of particles called molecules that are bonded together to

form a bulk material. Each molecule is further composed of tiny particles called atoms. Individual properties of atoms and their arrangement in the molecule determine the properties of the materials.

1.1.1 Atoms atoms : is the basic unit of an element formed for all materials weather for solid,

gas or liquid. an atom of any element consists of the nucleus and the electrons the nucleus : is a stationary mass, situated at the center and carrying a positive

charge and it consists of protons and neutrons which proton carries a positive charge, while the neutron carries no charge

the electrons : revolve around the nucleus in definite orbits and carry a negative charge

the valence electrons : are the outer electrons and are least firmly bound to the atomic nucleus and revolve in the outer orbits

Fig 1 : The position of electron, nucleus and orbit in an atom

1.1.2 Elements elements : combination of two or more of one kind of atoms bonding together elements are pure substances incapable of further division and consisting of particles

formed entirely from one type of atom1.1.3 Mixtures

mixtures : various kinds of atoms combined together but not chemically1.1.4 Compounds (sebatian)

compounds : various kinds of atoms are combined in a definite proportion, which is expressed by a chemistry formula

1.2 Atomic Numbers, Atomic Masses and Atomic Orbits(i) Atomic Numbers

indicates the numbers of protons which are in its nucleus, and in a neutral atom the atomic number is also equal to the number of electrons

(ii) Atomic Masses and Atomic Weight Atomic Weight = atomic masses of an element

atomic masses of Hydrogen

Atomic Masses = atomic numbers = number of proton + number of neutron

(iii) Atomic Orbits Using the 2n2 formula to state the total of atoms in every orbit, where n is total of

orbit1st orbit, n = 1Total of atom = 2 (1)2 = 2

2nd orbit, n = 2Total of atom = 2 (2)2 = 8

3rd orbit, n = 3Total of atom = 2 (3)2 = 18

4th orbit, n = 4Total of atom = 2 (4)2 = 32

Element 1st orbit 2nd orbit 3rd orbitHydrogen, HOxygen, O

Chlorine, ClCarbon, C

1222

688

72

nucleus

electron

orbit/shell

valence electrons

Table 1

1.3 Periodic Table of the Elements1. It is a chart of list of elements which all the elements with same chemical properties in one line

as one group.2. The horizontal rows of elements on the periodic table called periods.  The vertical columns called

groups or families.3. Characteristics :

(i) 18 lines of boxes in vertical (ii) 7 lines of boxes in horizontal (iii) 8 groups start with group I until VIII (iv) arrange by atomic number start with Hydrogen (v) elements in same line horizontally has same total of orbits (vi) chemical properties of an atom depend on total of electron in outer orbit which called as

valency atom (vii) when electron are followed from group I to group III, metal properties of an element

become lessen but total of electron will increase and become the non-metal properties (viii) elements which has total of same electron in outer orbit are in the same group and also

has the same chemical properties (ix) elements in group I has 1 electron in outer orbit, elements in group II has 2 electron in

outer orbit (x) each period has same total of orbits

4. Usages :(i) to classified certain elements easier (ii) as a revision where elements reactive properties can be known (way to the right, the

reactive properties are lessen) (iii) all the information about the elements can be known specially its properties because they

are collected by groups(iv) elements in first group has same chemical properties (v) easier to acknowledge certain unknown element and also its properties and the usage (vi) easier to analyze and understand every reaction between the elements

by groups

by periods

* electron configuration = the distribution of all the electrons in an atom according to their atomic orbital.

1.4 Crystal Structures1. It is atomic arrangements which have a repetitive pattern in all the three dimensions of space

are called crystal structures or crystals.2. The crystals can be formed as metal or non-metal.3. Single crystals : are solid with unit cell formed stacked tightly together and polycrystalline

consists with large number of single crystals. 4. In atom solidification process, melting metal will act upon each other and will position themselves in

a periodic and regular geometric pattern in space called a space lattice. 5. There are 4 types well-known crystal structures and it was :

(i) simple cube (ii) body centered cubic/ BCC (iii) face centered cubic/ FCC (iv) hexagonal close packed/ HCP

N7

Nitrogen

14

2:5

Atom’s massAtom’s mass

SymbolSymbol

Element’s nameElement’s name

Electron configuration

Electron configuration

Atom’s noAtom’s no

Fig 3 : The Periodic Table of the elements

Fig 2 : Guide for elements in the Periodic Table

single crystal grains

grain boundaries

1.4.1 Simple Cube a unit cell with an atomic packing arrangement in which eight identical atoms

located at the corners of an imaginary cube contains only one atom per unit cell

e.g. natrium chloride (salt)

1.4.2 Body Centered Cubic (BCC) a unit cell with an atomic packing arrangement in which one atom is in contact

with eight identical atoms located at the corners of an imaginary cube contains two atoms per cell

e.g. chromium, tungsten, molybdenum, vanadium, sodium (natrium)

1.4.3 Face Centered Cubic (FCC) a unit cell with an atomic packing arrangement in which 12 atoms surround a

central atom contains four atoms per cell

e.g. silicon, nickel, cuprum, aurum, platinum

1.4.4 Hexagonal Closed Packed (HCP) a unit cell with an atomic packing arrangement in which 12 atoms surround a

central identical atom

e.g. magnesium, barium, zinc, cadmium, cobalt

Simple Cube8 atoms in corners x 1/8 = 1 atom

Face Centered Cubic (FCC)8 atoms in corners x 1/8 = 1 atom6 atoms in faces x ½ = 3 atomsTotal = 4 atoms

Hexagonal Closed Packed (HCP)12 atoms in corners x 1/6 = 2 atoms2 atoms in faces x 1/2 = 1 atom6 atoms in sides x 1/2 = 3 atomsTotal = 6 atoms

Fig 4 : Structure and grain boundaries

Body Centered Cubic (BCC)8 atoms in corners x 1/8 = 1 atom1 atom in center = 1 atomTotal = 2 atoms

Fig 5

Fig 6

Fig 7

Fig 8

1.5 Bonds in Solid1.5.1 Covalent Bonding

occurs when two atoms (same elements) have a tendency to accept electrons which are satisfied for both by sharing of electrons between the outer electron orbits of the two atoms

an example is found in the chlorine molecule- the outer orbit of each atom possesses seven electrons - each chlorine atom would like to gain an electron and form a stable octet- this can be done by sharing two electrons between pairs of chlorine

atoms- each atom contributes one electron for the sharing process.

Fig 9 : Covalent Bonding for Chlorine

1.5.2 Metallic Bonding occurs when two metal atoms have a tendency to give up their electrons

and shared with all atoms close to them and formed of an electron cloud that spreads throughout the solid metal.

the circle with the inner positive signs represent positive ion cores and the charge clouds around the ion cores represent the dispersed valence electrons

Fig 10 : Metallic Bonding

1.5.3 Ionic / Electrovalence Bonding exists between two unlike atoms that had a strong tendency to give up

electrons (a metal) close to an atom that has a strong tendency to accept electrons (a nonmetal) and allows a transfer of one or more electrons depending on the valence of the atoms

an example is natrium chloride (NaCl)- it shows reaction of atoms between natrium and chlorine- for ionic natrium chloride, electron from natrium atom transferred to

chlorine atom to form natrium chloride

Na Cl 2.8.1 2.8.7

BEFORE

Na Cl

2.8 AFTER 2.8.8

Cl2 molecules. Couple of sharing electrons.

Cl Cl

OR

Fig 9 : atoms arrangement for disordered solid solutions

Fig 11 : Ionic/ Electrovalence Bonding for NaCl

electron transferred from natrium to chlorine

2.0 SOLIDIFICATION OF METALS AND ALLOYS2.1 The Stages Of Grain Structures Formation1. Solidification process occurs along with the grain formation 2. Nucleus tips freely find their own way to much colder place 3. Causing the nucleus to grow and expanding 4. The expand will form the secondary dendrite arm with 90 to each other 5. This will continue until a structure called dendrite structure existed

2.2 The Differences Between Base Metal and Alloy1. Base metal

metal has same elements, extreme properties and cannot fulfill the need for engineering work

its characteristics :(i) malleable – can be shape to many form(ii) ductile – can be form to fine wire

2. Alloy a metal alloy : is a combination of two or more metals or a metal and a nonmetals

2.3 Solid Solutions 1. Solid solution : when two elements mix or dissolve in the solid state and formed as a single

phase.2. There are certain factors that effected the solid solution formation :

(a) relative size factor/similar size of the atoms (b) same electrochemical/ electronegativity properties (c) same atoms valency (d) same crystal structure

2.4 Types Of Solid Solutions2.4.1 Disordered Solid Solution

Solute and solvent atoms are randomly distributed on lattice sites

2.4.2 Ordered Solid Solution the atoms (solute and solvent) take up preferred positions and the solution

becomes ordered

2.4.3 Interstitial Solid Solution atoms of small atomic radius fit into the empty spaces or interstices of the

lattice structure of the solvent atoms

2.4.4 Intermetallic Compounds some compounds which are very similar in nature to chemical compounds

called intermetallic compounds made up of 2 or more elements producing a new phase with its own

composition, crystal structure and properties

2.5 Solidification For Base Metals And Alloys1. When certain metal heated constantly, it will reach a point where it will start to melt. 2. If this temperature continues, the metal will melt entirely and the constant melting temperature called

melting point.3. But the process is reverse while cooling state because the kinetic energy of the atoms or molecules

for liquid are lessen and the metal viscosity are increased.4. In liquid phase, atoms of the metal are in disordered position but when it begins to freeze, the atoms

will be arrange and systemize to certain geometry.5. All solid material formed either in amorphous or crystalline structure.6. Amorphous structure is form when atoms do not have the long-range repetitive pattern of

arrangement and the pattern breaks at different places.

Fig 12 : Formation of Grain Structure

nucleus formation dendriteformation

solidification end by the existent of

the grain

dendrite formation growth & the arm met to

form grain boundaries

Solute atomsSolvent atoms

Fig 14 : atoms arrangement for ordered solid solution

Solute atoms Solvent atoms

Fig 15 : atoms arrangement for interstitial solid solution

Solvent atoms Solute atoms

Fig 13 : Atoms arrangement for disordered solid solution

2.6 Coring Formation In Metal Solidification1. Alloys solidification starts with the dendrite skeletons formation.2. The growth of dendrite crystalline continues and enlarges when solidification temperature reducing.

It will continue to grow to every axes until they meet and united.3. The dendrite solidifications also known as the coring process.

Fig 16 : Dendrite skeleton

2.7 Terminologies In Phase Diagram1. Phase

a phase in a material in terms of its microstructure : is a region that differs in structure and/or composition from another region

2. Equilibrium Phase Diagram are graphical representations of what phases are present in a materials system at various

temperatures, pressures and compositions3. Composition

are percentage of certain materials contains purposely or not added to another material. With this it can cause changes in phases, the properties and the shape of the microstructures.

4. Liquidus the temperature at which liquid starts to solidify under equilibrium conditions.

5. Solidus the temperature which all liquid has completely solidified.

2.8 Binary Alloy System 1. Binary phase diagram : is a phase diagram in which there are only two components and a

mixture of two metals (a binary alloy).2. The area above the upper line in the diagram called the liquidus, corresponds to the region of stability

of the liquid phase, and the area below the lower line called solidus, represents the region of stability for the solid phase.

3. The region between the liquidus and solidus represents a two-phase region where both the liquid and solid phases co-exist.

4. Referred to figure 17, an alloy with X% nickel will solidifies as such :i. at temperature t1, the liquid will mixed with a solid solution which matches with point p at

solidus line. Therefore, the first solid solution crystalline form from pii. when the temperature decrease, the solid solution will change through absorption followed the

solidus line to point qiii. at temperature t2, the liquid, m in the state of equilibrium with the solid solutioniv. the solidification process of the alloy will be done at temperature t3 when the last drop of the

liquid, n, solidify, changing the solid solution crystalline to r

5. Figure 18 shows the phase equilibrium diagram for copper-nickel alloys and the diagram based on figure 17.

i. for 100% copper and 0% nickel (pure copper) there is a single solidification temperature of 1084C

ii. for an alloy of 80% copper and 20% nickel, solidification starts at 1190 C and is complete at 1135C. between the solidus and the liquidus is a solution of molten copper and nickel together with crystals of a solid solution of copper and nickel

iii. for an alloy of 80% nickel and 20% copper, solidification starts at 1410C and is complete by 1380C

iv. finally, for 100% nickel and 0% copper (pure nickel) solidification occurs at the single temperature of 1445C

v. below the solidus, the alloy consists entirely of crystals of copper and nickel in solid solution.

liquidus

solidus

1455

1084

t2

t1

t3

p

q

r

m

n

solid solution

tem

pera

ture

(o C

)

100% Cu X% Ni 100% % Ni

t1 – solidify temperature begins

t3 – solidify temperature ends

– liquid m and the solid solution are in equilibrium state

Fig 17 : Binary Alloy System for copper-nickel

Fig 18 : The phase equilibrium diagram for copper-nickel alloys