Materials section 3

Ceramics are usually a _ of and _ elements.

compound, metallic, nonmetallic

Ceramic bonds are totally or partially _.

ionic

Generally, ceramics are:

hard, brittle, electrical and thermal insulators

Oxide structures have ____ anions that are much larger than _____ cations

oxygen, metal

Closed packed oxygen structure is usually an _ lattice.

FCC

In an oxide structure, cations are in the _ of the lattice.

holes

Charge neutrality:

netcharge in the oxide structure should be zero.

Stable structures:

maximize the number of nearest opposite charged neighbors

coordination number is increased with:

r cation/r anion

stoichiometry site selection:

if all of one type of site is full, the remainder have to go into other site types.

bond hybridization: the ____ can have impact

hybrid orbitals

ceramic density calculations:

p = (number of formula units within unit cell)(sum of atomic weights of all anions in the formula unit)/VcNa

glass structure is ___

amorphous

amorphous structure occurs by adding:

impurities

impurities interfere with formation of:

xtalline structure

diamond is ____ carbon

tetrahedral

diamond has a __ cubic structure

diamond

diamond is one of the _____/_____ materials known

strongest, hardest

diamond is also a __ and __

semiconductor, metastable

graphite has a ______ structure, with strong bonding within ______ layers and van der Waals between _______.

layered, planar, layers

both _ and __ defects can be observed in ceramics

interstitial, vacancy

defects: cation is out of place

frenkel

______ defect: a paired set of cation and anion vacancies

shottky

impurities must also satisfy _____

charge balance

ceramics are _.

brittle

_____ of ceramics can be enhanced by compressive stresses in the surface region.

fracture strength

the______ is usually 10x the tensile strength.

compressive strength

at room temp, ceramic behavior is usually ______, with _ failure.

elastic, brittle

the __ _____ bend test is often used to determine elastic modulus

3 point

in xtalline ceramics, is very difficult.

slip

in non-xtalline ceramics, there are no:

dislocations

in non-xtalline ceramics, materials deform by .

viscous flow

is a measure of a glassy material's resistance to deformation.

viscosity

xtalline materials:
xtallize at _____, have abrupt change in ____

melting temp, spec. vol.

glasses:
do not ___.
______ _____ varies smoothly with T

xtallize, spec. vol

viscosity relates __ and _.

shear stress, velocity gradient

viscosity is a measure of _ material's _ to deformation

non-xtalline, resistance

temps in glasses in terms of viscosity:
melting pt: P
working pt: __ P
softening pt: P
annealing pt: P
strain pt: P

100, 10^4, 4x10^7, 10^13, 3x10^14

sheet forming is a ______ draw

continuous

______: heat for approx. 15 min, and slowly cool

annealing

annealing removes _ caused by uneven

internal stress, cooling

: puts surface of glass part into compression

tempering

tempering ______ growth of cracks from surface _______

suppresses, scratches

___ glasses darken on exposure to light

photochromic

particulate forming: ______ and ______ used to reach desired particle size

milling, screening

mixing particles and water produces a _

slip

the last step of particulate forming is ______ and ________ the component

drying, firing

drying: ____ size and spacing __.

layer, decrease

vitrification: liquid glass forms from ____ and flows between ______ particles.

clay, SiO2

_________: used in both clay and non-clay compositions during particulate forming

sintering

sintering procedure:
produce ceramic and/or glass particles by
place particles in
____ at elevated T to reduce _____ ______

grinding, mold, press, pore size

4 categories of ceramics:

glasses, clay products, refractories, cements

3 fabrication techniques of ceramics: ____ forming, _______ forming, and _______

glass, particulate, cementation

heating treating is used to ____ stress from ____

alleviate, cooling

cement and concrete have a ______ reaction in cement that ______ over weeks/months

hydrolysis, hardens

A polymer is a built of small units called

macromolecule, mers

the small units in a polymer are successively _______- throughout the macromolecule ____

repeated, chain

the 4 covalent chain configurations for a polymer, in order of increasing strength:

linear, branched, network, cross-linnked

________: all monomer units are of the same type

homopolymer

_ are constructed of different mers

copolymers

molecular weight of a polymer: mass of a ______ of ______

mole, chains

the rotational degree of _______ in the bonds of the polymer chain _______ allows for a wide range of shapes, or ______, for the chain

freedom, backbone, conformations

linear polymer: ___ joining of mers. _____, long flexible chains. ______ and ______ bonds hold the chains together.

end-to-end, single, van der waals, hydrogen

branched polymer: ______ _____ chains connected to main chain, _____ chain packing _____, and thus reduced _______

side branch, reduced, capability, density

crosslinked polymers: _______ chains joined by side chains, _______ at elevated temperatures promotes ______, _____ atoms might be involved in cross linking bond

adjacent, synthesis, crosslinking, noncarbon

network polymers: ______ crosslinked, ____ functional mers can provide ______ ______ cross linking

highly, tri, three dimensional

tacticity: _______ of chain

stereoregularity

all R-groups are on the same side of the chain:

isotactic

R-groups on alternate sides of the chain:

syndiotactic

R-groups are randomized in position

atactic

thermoplastics _____ when heated. ___ bonding between chains is ______ and movement is ____. this process is __

soften, secondary, weakened, facilitated. reversible

thermosets become _______ when heated. ______- cross-linking bonds are formed.

permanently hard, covalent

moderate stiffness and strength, high ductility, high impact resistance, poor creep resistance , recyclable…. this is a thermo_____ polymer

plastic

high stiffness and strength, high creep resistance, low/moderate ductility, poor impact resistance, not recyclable. this is a thermo____ polymer

set

very low stiffness
low strength
very high elasticity
good impact resistance
not easily recycled

elastomer

xtalline: arrangement of units in a defined, arrangement. symmetry observed

well, spatial, translational

rate of cooling during solidification for PC. ____ is necessary for chains to move and align into an xtal structure.

time

mer complexity: less likely in complex structures, _ polymers xtallize relatively easily

xtallization, simple

chain configuration: _ _____polymers xtallize easily, ____ inhibit xtallization. _____ polymers are almost completely amorphous, _____ polymers can be both xtalline and amorphous

linear, branches, network, crosslinked

isomerism: ____, ______ polymers xtallize relatively easily

isotactic, syndiotactic

copolymers: ____ to xtallize if mer arrangements are more regular: ____ and ___ can xtallize easier than random and graft.

easier, alternating and block

more xtallinity means more:

density, strength, resistance to dissolution and softening

upper yield point: formation of a small ____, in contrast to metals, the ___ proceeds by __ of neck region throughout the whole length

neck, deformation, extension

microscopic picture: ______ in the neck region become and oriented along axis, causing localized of material. ___ proceeds by propagation of neck thru length

chains, aligned, strengthening. elongation

an amorphous polymer is _____ at low temps, ______ at intermediate temps, and _____ liquid at high temps.

glass, rubbery, viscous

deformation at low temps for polymers is _ ____when load is applied, and __.

instantaneous, reversible

at high T, deformation is ______ dependent and not _______.

time, reversible

at intermediate temps, behavior is ______. there is ____ elastic strain and viscous ______ dependent strain.

viscoelastic, instantaneous, time

viscoelastic behavior is determined by __

rate of strain

polymers have a _ fracture strength than metals

lower

__ fracture dominates for thermosetting polymers

brittle

thermoplastic polymers have ___ and _____ fractures, as well as a _ between both modes

brittle, ductile, transition

fracture in thermoplastics is due to _

crazing

crazing is

griffith cracks in metals

thermoplastic fracture has yielding, and the formation of ____

localized, microvoids

___ bridges support load across face

fibrillar

craze growth proceeds __ of fracture

absorption, energy

_ of voids and of bridges results in crack formation

coalescence, rupture

drawing the polymer prior to use, and chains in the ___ direction

stretches, aligns, stretching

drawing ___ the elastic modulus in stretching dir. and ___ the TS in the stretching dir., and ___ ductility.

increases, increases, decreases