Chapter 12 Flashcards
ceramics
means “burnt stuff,” indicating that desirable properties of these materials are normally achieved through a high-temperature heat treatment process called firing
cation
- metallic ionsare
- positively charged because they have given up their valence electrons to the nonmetallic ions
anion
negatively charged
rock salt crystal structure
- most common AX crystal structure
- coordination number for both cations and anions is 6
- two interpenetrating FCC lattices—one composed of the cations, the other of anions
cesium chloride crystal structure
- coordination number is 8
- anions are located at each of the corners of a cube, whereas the cube center is a single cation
zinc blende or sphalerite structure
- coordination number is 4
- all ions are tetrahedrally coordinated
tetrahedral position
four atoms (three in one plane, and a single one in the adjacent plane) surround one type
octahedral position
six ion spheres, three in each of the two planes
silicates
- materials composed primarily of silicon and oxygen, the two most abundant elements in Earth’s crust
- not considered ionic
silicon dioxide or silica (SiO2)
- most simple silicate material
- material is electrically neutral and all atoms have stable electronic structures
fused silica or vitreous silica
silica made to exist as a noncrystalline solid or glass having a high degree of atomic randomness, which is characteristic of the liquid
network formers
other oxides that form glassy structures
network modifiers
oxides that do not form polyhedral networks, their cations are incorporated within and modify the SiO4-4 network
intermediates
other oxides, such as TiO2 and Al2O3 although not network formers, substitute for silicon and become part of and stabilize the network
carbon
exists in two allotropic forms—diamond and graphite—as well as in the amorphous state
diamond
metastable carbon polymorph at room temperature and atmospheric pressure
graphite
- another polymorph of carbon
- furthermore, it is a stable polymorph at ambient temperature and pressure
delocalized
does not belong to a specific atom or bond
defect structure
designate the types and concentrations of atomic defects in ceramics
electroneutrality
state that exists when there are equal numbers of positive and negative charges from the ions
Frenkel defect
- type of defect involves a cation–vacancy and a cation–interstitial pair
- defect where cation leaves its normal position and moves into an interstitial site
Schottky defect
- type of defect found in AX materials & involves a cation vacancy–anion vacancy pair
- removing one cation and one anion from the interior of the crystal and then placing them both at an external surface
stoichiometry
state for ionic compounds wherein there is the exact
ratio of cations to anions as predicted by the chemical formula
stress raisers
points at which the magnitude of an applied tensile stress is amplified and no mechanism such as plastic deformation exists to slow down or divert such cracks
static fatigue or delayed fracture
fracture of ceramic materials will occur by the slow
propagation of cracks, when stresses are static in nature
mirror region
crack surface formed during initial stage of propagation, usually smooth and flat
mist region
crack surface formed during second stage of propagation, faint annular region just outside the mirror region
hackle region
crack surface formed during third stage of propagation, composed of a set of striations or lines that radiate away from the crack source in the direction of crack propagation
Wallner lines
arc shaped and provide information regarding stress distributions and directions of crack propagation
viscous flow
the rate of deformation is proportional to the applied stress
viscosity
measure of a noncrystalline material’s resistance to deformation
porosity
subsequent to compaction or forming of these powder particles into the desired shape, pores or void spaces exist between the powder particles
hardness tests for ceramics
- Vickers and Knoop techniques
- use indenters having pyramidal shapes
creep
occurs at higher temperature in ceramics
