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79 Cards in this Set

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Crystalline
atoms arranged in a regular periodic manner
- most metals, some ceramics
Non-Crystalline (glassy)
- no long range order
- atoms are randomly oriented (some ceramics
ceramics
compound between metal and non metal
composites
combination of different groups of materials where the properties are better than the individual material
Polymers structure
- consist of macro-moleculues with repeat unit
Properties: Metals
- excellent electrical conductor
- good thermal conductor
- ductile (will bend before breaking)
- relatively high strength
Moderate:
melting temp
elastic modulus
thermal expansion
Properties: ceramics
- Electrical insulator
- thermal insulator
- brittle (not ductile)
- High compression, weak tension
Large:
- melting temp
- elastic modulus
-Small thermal expansion
Properties: Polymers
- electrical insulator
- thermal insulator
- strong variable depending on chain
- light weight
-small melting temp
- small elastic modulus
- large thermal expansion
electropositive / electronegative
(+)
- atoms have a greater tendancy to lose electrons
(-)
- atoms have a greater tendancy to form a negative ion (anion)
covalent bonding
-: atoms achieve a filled outer orbital by sharing of electrons
Properties:
- strong bond
- high melting point
- electrons localized, cannot move freely through material = electric insulator
- bonding is direction, resists deformation
ionic bonding
- filled outer shells achieved by transfer of electrons
properties:
- strong bond
- no free electrons = electric insulator
- non-directional = electrostatic attraction
the more electronegative the non-metal...
the more electropositive the metal, the more ionic the bonding
(LiF totaly ionic)
metallic bonding
- outer electrons are only loosely bound due to sea of electrons
Properties:
- electrons are delocalized and can move freely = electron conductor
- planes of atoms can slide over each other = metals are easily deformed
- high electrical and thermal conductivity
vander waals bonding
In covalent moleculues, electrons not shared evenly between different atoms. Electric dipole causes vander waals attractions
fully close-packed
bonding is non-directional, atoms are the same size, there are no charge constraints, the densest possible structure (FCC, HCP, BCC)
atomic packing factor
Volume of atoms in a unit cell / total unit cell volume
FCC = .74
BCC = .68
HCP = .74
Theortical Density
p = (n*A)/(Vc*Na)

n = number of atoms associated with each unit cell
Vc = volume of uni cell
Na = avagadro's number
A = atomic weight
FCC (a?) cord#
face centered cubic

a = 2*R*sqrt(2)

cord # = 12
BCC (a?) cord#
body centered cubic

a = (4*R)/(sqrt(3))

cord# = 8
Planar Atomic Density
#atoms in plane / area of plane
Lattice parameter (a)
the length of unit cell
- : the equilibrium spacing of atoms, how close together the atoms want to come, if they go any closer they will repel, any further they will attract
SiO2, B2O3 are types of network
formers
Na2O, K2O, CaO are network...
modifiers
Tg
glass transition temp. glass does not melt but becomes softer and network is weaker
Intermediate Oxide
PbO

- : does not form glass alone, but sits in or between the network
Theoretical Density for ceramics (two diff atoms)
P = (Na*Aa + nb*Ab ) / (Vc * Na)
xrtl Structure NaCl
cord# = 6
rc/ra + .414 to .732

2 FCC structures
xrtl structure CsCl
cord# = 8
rc/ra = .732 to 1

BCC? no, two atoms in the center
ZnS xrtl structure
cord# = 4
rc/ra = .225 to .414
- all ions are tetrahedrally coordinated
Point Defects ( 0 dimensions)
- vacancy
- : abscence of an atom or ion

props:
- thermodynamically stable defects
- equilibrium defects
- as temp increases, concentration of vacancies increases
concentration of vacancy

Nv = Nexp(-Qv / kT)
Nv = # of vacant sites
N = # of total sites
Qv = energy requiered to create vacancy
K = boltzman's constant
T = absolute temp

- vacancy increase = density decrease
interstitial defect
extra ion or atom present

- conc. interstitial < conc. of vacancies
Frenkel defect (ceramic)
cation vacancy
- moves from vacancy to interstitial spot
Schottky defect
charge neutrality maintained by having one cation vacancy for every one anion vacancy
Substitiational (metal)
An atom replaces that of the regular metal that is about the same size, same xtal struc., higher valancy
Interstitial (metal)
an atom with a smaller atomic diameter fills the voids among host atoms
diffusion
material transport by atomic motion
interdiffusion
atoms of one metal diffuse into another
self-diffusion
atoms exchanged positions are the same type
conditions for diffusion
must be an empty (vacant) adjacent site
- atom must have sufficient energy to break bonds with neighbor atoms and cause slight lattice distortion
vacancy diffusion
atoms adjacent to vacant site jumps into it and so on
Interstitial diffusion
jump from interstitial site to another rapidly
- fast than vacancy diffusion
Ficks first law of diffusion

J = -D (dC/dX)
- diffusion is driven by a concentration gradient of diffusing species

J = flux of atoms
dC = concentration change
dX = change of position
D = diffusion coefficient
- conc. gradient does not change with time
ficks second law of diffusion

Cs-Cx / Cs-Co = erf( x/ (2sqrt(Dt))
Cx = conc at depth
Co = initial conc
Cs = const surface conc., set by atmosphere
D = diffusion coeff
x = depth
t = time
erf(z)
temp diffusion

D = Do*exp(-Qd / RT)
Do = temp independent (m^2 / s)
Qd = activation energy
R = gas constant (units pending)
T = abs temp
carburization (ficks second law)
increase the carbon content at the surface of a steel component by heat treating the component, more carbon at the surface. obtains a harder, more wear resistant surface
Hooke's Law ...
stress strain behavior
elastic deformation
deformation where stress and strain are proportional. plot is linear
E = dStress / dStrain
plastic deformation
perminant, non-recoverable deformation
yielding
when elastic deformation becomes plastic deformation
proportional limit (P)
represents the on set of plastic deformation on a microscopic level
yield strength (omega y)
the stress value corresponding to the strain offset
- magnitude is a measure of a metals resistance to plastic deformation
tensile strength
the stress value at the maximum on the stress-strain curve, represents the maximum stress that can be sustained by a structure in tension
- maintaining this stress fractures the material
ductility
a measure of the degree of plastic deformation that has been sustained at a fracture
brittle
low ductility = little or no plastic deformation
hardness
a measure of a materials resistance to localized plastic deformation
scratch test
if substance A can scratch B, A is considered harder
- scratchability
hardness test
uses indentor
- harder the material, deeper the indentor goes, the larger the indentation.
- measure width of indent to determine hardness
slip
permanant deformation, planes of atoms slide across one another, plastic deformation produced bu dislocation mothion
slip system
slip plane and slip direction

{ plane } <direction>
Burgess vector : characteristics of dislocation
vector that completes the circuit
b(FCC)
b(BCC)
b(HCP)
- a/2 <110>
- a/2 <111>
- a/3 <11 2bar 0>
resolved shear stress

tR = Ocos(phi)cos(lambda)
shear components that exist at all but parallel or perpendicularr alignment to the stress direction

phi - angle between the normal to the slip plane and the applied stress direction
lambda - angle between slip direction and
O(omega) - applied tress
yield strength
d = grain diamter
ky , omegao = constants for particular material
omega y = yield strength
glass: melting point - viscocity = 100P
glass is fluid enough to be considered liquid
glass: working point 10^4 P
glass is easily deformed
glass: softening point 4*10^7 P
max temp that a glass piece can be handled without alterations
glass : annealing point 10^13 P
atomic diffusion is sfficiently rapid that any stress maybe removed within 15 minutes
strain point 3*10^14 P
any temp below this point, fracture will occer before plastic deformation

Tg > strain point temp
float glass method
makes sheet glass
press and blows method
makes bottle shapes, put glob of molten glass in shape mod, press into mod, control temp, blow compressed air in so it takes shape of container
glass fibecs
spin molten glass and pull out small fibers
tempered glass
start with glass at high temp around softening point, blow with cold air so glass tries to contract, surface layer in compression, inside in tension
slip casting
- forming ceramic
- suspend clay and/or other non plastic materials in water and pour into a porous mold. the mold will absorb the water and leave behin the solid clay
solid casting
solid clay piece
drain slip casting
just the outline of the mold (pot)
uniaxial pressing
powder compacted in a metal die by pressure applied in a single direction, simple
isotatic pressing
powder material contained in a number envelope and the pressure is applied by a fluid with some magnitude in all directions
hot pressing
powder pressing and heat treatment performed simultaneously, used for materials that do not form liquid except at very high temp