Overview of materials Flashcards
Identify different classes of materials
ceramics metals hybrids glasses polymers elastomers
Give examples of uses of metals in automotive and aeronautical applications
Aeronautical fuselage wings gas turbine Automotive chassis body panels engine block and pistons
Give examples of uses of ceramics in automotive and aeronautical applications
Aeronautical coating on gas turbine blades sensors space shuttle tiles Automotive spark plugs sensors heat shields
Give examples of uses of polymers in automotive and aeronautical applications
Aeronautical interior cable insulation pump gears Automotive bumpers chemical tanks-brake fluid cable insulation
Give examples of uses of glasses in automotive and aeronautical applications
Aeronautical cockpit windows Automotive windscreen
Give examples of uses of elastomers in automotive and aeronautical applications
Aeronautical and Automotive tyres seals gaskets
Give examples of uses of hybrids in automotive and aeronautical applications
Aeronautical wings sound insulation padding Automotive sound insulation tyre sealant padding
Characteristics of metals
hard shiny good conductors of electricity and heat strong stiff ductile/malleable/formable able to bear loads resistant to shock
Define a lattice
It is a periodic array of points in space
Common crystal structures in metals
BCC - body centred cubic FCC - face centred cubic HCP - hexagonal close-packed
Define polymorphism
the ability of a solid substance to exist in more than one form of crystal structure
Define allotropy
the existence of two or more different physical forms of a chemical element
Define a unit cell
The smallest group of atoms which has the same symmetry as the crystal structure
Define a primitive unit cell
The smallest possible unit cell and contains only one atom
Describe an FCC lattice and give examples of FCC metals
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
Describe a BCC lattice and give examples of BCC metals
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
Describe an HCP lattice and give examples of HCP metals
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
Identify the two methods of calculating packing efficiency
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
What is the equation for calculating the packing efficiency?
packing efficiency = (number of atom per unit cell)(volume of one atom)/volume of the unit cell
Reduction in the mass of a fluid of known density tells us the volume. How can the density be calculated?
density = density(fluid) * m1/(m1-m2)
Define an alloy
It is a combination of two or more metals leading to more desirable properties
Identify the properties of Nickel based alloys
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
Define a superalloy
An alloy which is used in service close to its melting temperature
Why are nickel based alloys used in jet engines?
they have creep and corrosion resistance
Define creep resistance
slowing the movement of dislocation through the crystal structure
Identify common types of ceramics
- oxides
- complex
- carbides
- nitrides
- borides
Characteristics of ceramics
- 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
Equation for calculating ionic character
Ionic character = 1 - exp[-0.25(Xa-Xb)2]
How can the interaction between the cation and the anion affect the stability of a ceramic crystal structure
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)
Define the coordination number
The number of nearest neighbours
How is the atomic radius affected by the coordination number?
the atomic radius tends to increase as coordination number increases and decreases with ionic charge
