Overview of materials

Question 1

Identify different classes of materials

Answer 1

ceramics metals hybrids glasses polymers elastomers

Question 2

Give examples of uses of metals in automotive and aeronautical applications

Answer 2

Aeronautical fuselage wings gas turbine Automotive chassis body panels engine block and pistons

Question 3

Give examples of uses of ceramics in automotive and aeronautical applications

Answer 3

Aeronautical coating on gas turbine blades sensors space shuttle tiles Automotive spark plugs sensors heat shields

Question 4

Give examples of uses of polymers in automotive and aeronautical applications

Answer 4

Aeronautical interior cable insulation pump gears Automotive bumpers chemical tanks-brake fluid cable insulation

Question 5

Give examples of uses of glasses in automotive and aeronautical applications

Answer 5

Aeronautical cockpit windows Automotive windscreen

Question 6

Give examples of uses of elastomers in automotive and aeronautical applications

Answer 6

Aeronautical and Automotive tyres seals gaskets

Question 7

Give examples of uses of hybrids in automotive and aeronautical applications

Answer 7

Aeronautical wings sound insulation padding Automotive sound insulation tyre sealant padding

Question 8

Characteristics of metals

Answer 8

hard shiny good conductors of electricity and heat strong stiff ductile/malleable/formable able to bear loads resistant to shock

Question 9

Define a lattice

Answer 9

It is a periodic array of points in space

Question 10

Common crystal structures in metals

Answer 10

BCC - body centred cubic FCC - face centred cubic HCP - hexagonal close-packed

Question 11

Define polymorphism

Answer 11

the ability of a solid substance to exist in more than one form of crystal structure

Question 12

Define allotropy

Answer 12

the existence of two or more different physical forms of a chemical element

Question 13

Define a unit cell

Answer 13

The smallest group of atoms which has the same symmetry as the crystal structure

Question 14

Define a primitive unit cell

Answer 14

The smallest possible unit cell and contains only one atom

Question 15

Describe an FCC lattice and give examples of FCC metals

Answer 15

contains an atom at each corner of the cube one atom at the centre of each face 4 atoms in each conventional unit cell FCC metals: Al, Ca, Ni, Cu, Sr, Ag, Pt, Au, Pb

Question 16

Describe a BCC lattice and give examples of BCC metals

Answer 16

an atom at each corner of the cube one atom located in the centre of the cube 2 atoms in each conventional unit cell BCC metals: Li,Na,K,V,Cr,Mn,Fe,Mo,W

Question 17

Describe an HCP lattice and give examples of HCP metals

Answer 17

12 atoms located at the corners 2 at the top and bottom corners 3 located in a triangle 6 atoms in each conventional unit cell HCP metals: Mg,Ti,Co,Zn,Zr

Question 18

Identify the two methods of calculating packing efficiency

Answer 18

by inspection, determine the close-packed direction Pythagoras theorem: calculate lattice parameter and hence the volume of the cubic unit cell in terms of the atomic radius

Question 19

What is the equation for calculating the packing efficiency?

Answer 19

packing efficiency = (number of atom per unit cell)(volume of one atom)/volume of the unit cell

Question 20

Reduction in the mass of a fluid of known density tells us the volume. How can the density be calculated?

Answer 20

density = density(fluid) * m1/(m1-m2)

Question 21

Define an alloy

Answer 21

It is a combination of two or more metals leading to more desirable properties

Question 22

Identify the properties of Nickel based alloys

Answer 22

used in jet engines

heavy, density = 8900kg/m^3

high melting point = 1455 degrees

Young’s modulus = 207GPa

FCC up to the melting point

alloying for solution hardening, carbide formation and grain-boundary strengthening

Question 23

Define a superalloy

Answer 23

An alloy which is used in service close to its melting temperature

Question 24

Why are nickel based alloys used in jet engines?

Answer 24

they have creep and corrosion resistance

Question 25

Define creep resistance

Answer 25

slowing the movement of dislocation through the crystal structure

Question 26

Identify common types of ceramics

Answer 26

• oxides
• complex
• carbides
• nitrides
• borides

Question 27

Characteristics of ceramics

Answer 27

• hard
• not ductile
• brittle
• electrically insulating
• resistant to corrosion, weather,wear
• poor conductor of wear
• low impact strength
• low shock resistance
• high melting point
  
  • weak in tension,strong in compression

Question 28

Equation for calculating ionic character

Answer 28

Ionic character = 1 - exp[-0.25(X_a-X_b)²]

Question 29

How can the interaction between the cation and the anion affect the stability of a ceramic crystal structure

Answer 29

the cation must be in contact with the anions otherwise the structure is unstable

if the cation site is marginally too large, the cation will undergo a small displacement(up to 10*10^-10)

Question 30

Define the coordination number

Answer 30

The number of nearest neighbours

Question 31

How is the atomic radius affected by the coordination number?

Answer 31

the atomic radius tends to increase as coordination number increases and decreases with ionic charge