materials processing: ceramics

silicate ceramics describe __Si +__O, shape is ___

1, 4, tetrahedron (not a unit cell)

silicate ceramics are ____ charged, if not neutral, what is its charge?

negatively, -4

crystalline silica has a ____ structure with ___ melting points

network, high (due to Si-O interatomic bonding)

Silica glasses are ____ (fused silica) with a high degree of atomic randomness and same basic unit (NOT UNIT CELL) as silica

noncrystalline solids

network formers ex: B2O3 and GeO2

oxides than can form glassy/polyhedral oxide structures (similar to SiO2)

network modifiers ex: CaO and Na2O

do not form polyhedral networks, but cations are still incorporated

intermediates ex: TiO2 and Al2O3

are not network formers but substitute for Si

addition of these modifiers and intermediates -→ lowers the ____ and _____ of a glass

melting point and viscosity

cation–vacancy and a cation–interstitial pair

frenkel defect

a cation vacancy–anion vacancy pair (found in AX materials)

Schottky defect

measure of a ceramic material’s ability to resist fracture when a crack is present

fracture toughness

The degree of ionic character of the interatomic bonds in ceramics depends on the difference of ____

electronegativity of atoms (higher diff = more electronegative)

Carbon atoms in graphite are ___ hybridized, but are ____ hybridized in diamond

sp2, sp3

a state for ionic compounds wherein there is the exact ratio of cations to anions as predicted by the chemical formula

stoichiometry

The structure of a grinding wheel depends on the ______

spacing of grits

The grade of a grinding wheel depends on the amount of _____ holding abrasive grains in the wheel.

bonding agent

Typically small amounts of material are removed at high speed during grinding to produce…

fine swarf

_____ of a grinding wheel occurs when the porosities on the wheel surfaces become filled or clogged with chips from the workpiece

loading

glass forming operations occur between what two temperatures?

working and softening

powder particles are pressed together until pores form between them, the more it is pressed the smaller the pores get

sintering

what is the goal of sintering?

reduce porosity → increase mechanical properties

uses heat to relieve internal stresses

annealing

enhances strength of glass by intentionally inducing compressive residual surface stresses

glass tempering

larger ratio of Rc/Ra = ____ coordination #

higher (anions have more cation neighbors)

AmBnXp-Type Crystal Structures have ____ and ____ crystal structure

more than one cation type, perovskite

how is electroneutrality established in negatively charged layered silica?

2nd planar sheet with an excess of cations to bond to 1st sheets excess of anions

bonding within 2 layered silicate sheets are

strong and intermediate ionic-covalent

bonding between adjacent layered silicate sheets are

loosely bound to one another by weak van der Waals forces

is the ratio of cations to anions altered by the formation of either a Frenkel or a Schottky defect?

NO

as porosity increases, ____ and _____ decrease

elastic modulus and flexural strength

Material processed by heat treatment to produce fine-grained polycrystalline structure

glass-ceramic

what is the critical cooling rate for glass-ceramic (minimum rate so that entire product is only glass ceramic)?

100 C/min

why are glass-ceramics used in fabrication? what are some of its properties?

ease of fabrication, strength and resistance to thermal shock

failure modes of a grinding wheel:

• ______ of individual particles

• ______ in individual particles

• ______ between particles

attricious wear, microcracks, bond fracture

below the strain point, fracture will occur before…

the onset of plastic deformation

Bonding of ceramics tends to be either totally _____ or totally _____ or a combination of the two

ionic, covalent

what influences ionic crystal structure? (list 2)

magnitude of charge on each ion, relative size of cation and anion

what shows a stable crystal structure?

all anions are in contact with the cation

c

rock salt, 6

identify the crystal structure and coordination number

cesium chloride, 8 (cation)

identify the crystal structure and coordination number, what type of atomic bonding is typically present here?

zinc blende, 4, covalent

AmXp-Type Crystal Structures have what notable properties, coordination number, and rc/ra ratio?

unequal charges on cation and anion, 8, 0.8

perovskite crystal structure

layers of covalently bonded carbon in hexagonal pattern, layers are held in a stack by ________ forces, who am i?

weak van der waals forces, graphite

repeating unit formula for layered silicates = _____

(Si2O5)^-2

are diamond and graphite considered a ceramic, polymer, or metal?

none, but sometimes graphite can be a ceramic

why do anions never have interstitial defects?

too large, too much strain

plane strain fracture toughness equation

temperature dependence of defects

identify the materials

A=aluminum oxide B=glass

identify the y axis, what is the xmax?

modulus of elasticity, 1

identify the y axis, what is xmax?

flexural strength, 0.55

Common applications for abrasives include ____, ____, ____, and _____

grinding, polishing, cutting, sharpening

Large number of cutting edges for abrasive particles, each removing very small amounts of material

grinding

the process of producing a true circle on a wheel that has become out of round

truing

the process of conditioning, producing sharp new edges on worn grains on the grinding surface of a wheel

dressing

dressing is necessary after the grinding wheel experiences ____ or becomes ____

attritious wear, loaded

what nucleating agent is typically added to shorten crystallization times?

TiO2

viscosity is ____ at ____ temperatures

higher, lower

does sintering involve melting?

no, occurs below the Tm

Which ceramic processing method involves compacting powders and heating them to improve strength?

powder processing and sintering

(T/F) Viscosity at the annealing point is lower than at the softening point, such that atomic diffusion occurs rapidly enough to relieve residual stresses within about 15 minutes at the annealing point.

false

(T/F) Viscosity is very high at the strain point, at which the material becomes so rigid that it will fracture before undergoing plastic deformation.

true

Which ceramic abrasive is known for being second only to diamond in hardness and is ideal for machining ferrous metals?

kaolinite

A=supercooled liquid B=crystalline solid