Structure And Properties Of Ceramics Flashcards
inorganic and nonmetallic materials
Ceramic
between metallic and non-metallic elements which the interatomic bonds are either totally ionic or predominantly ionic but having some covalent character
Ceramic
greek word keramikos, which means
Burnt stuff
crystal structures are generally more complex than those for metals
Ceramics
Two characteristics of the component ions on crystalline ceramic materials influence the crystal structure
magnitude of the electrical charge
sizes of the cations and anions
Why is it that some or the ceramics are predominantly ionic?
There crystal structure is electrically charged
Common ceramic materials are those in which there are equal numbers of cations and anions
AX Compound
Most common AX compound crystal structure
Rock salt
coordination number for both cations and anions is 6
Rock salt
coordination number is 8 for both ion types
Cesium chloride
AX structure is one in which the coordination number is 4
Zinc Blende
charges on the cations and anions are not the same
AmXp
Interstitial positions
Tetrahedral
Octahedral
Four atoms (three in one plane, and a single one in the adjacent plane) surround one type
Tetrahedral position
involves six ion spheres, three in each of the two planes
Octahedral position
AmBnXp types, which is found for magnesium aluminate or spinel (MgAl2O4)
Spinel structure
composed primarily of silicon and oxygen
Silicate
2 most common abundant element in Earth’s crust
Silica
Oxygen
most simple silicate material
Silicon dioxide or silica
three primary polymorphic crystalline forms of silica
Quartz
Cristobalite
Tridymite
Silica that exist as noncrystalline solid or glass having a high degree of atomic randomness, which is characteristic of the liquid
Fussed Silica or vitreous silica
oxides (B2O3, GeO2) may also form glassy structures
Network former
oxide additives
Network modifier
oxides, such as TiO2 and Al2O3, substitute for silicon and become part of and stabilize the network
Intermediate
addition _____________________ lowers the melting point and viscosity of a glass and makes it easier to form at lower temperatures
modifiers and intermediates
can be produced by the sharing of three oxygen ions in each of the tetrahedra
Layered silicate
ordinarily established by a second planar sheet structure having an excess of cations, which bond to these unbonded oxygen atoms from the Si2O5 sheet
Electroneutrality
basic structure is characteristic of the clays and other minerals
Sheet
Common clay mineral
Kaolinite
Common clay mineral
Kaolinite
made of a series of these double layers or sheets stacked parallel to each other and form small flat plates that are typically less than 1μm in diameter and nearly hexagonal
Crystal of kaolinite
Exist in 2 allopathic form
Carbon
Allopathic forms of carbon
Diamond
Graphite
metastable carbon polymorph at room temperature and atmospheric pressure
Diamond
variant of the zinc blende structure in which carbon atoms occupy all positions
Diamond
structure of diamond is appropriately called?
diamond cubic crystal structure
stable polymorph at ambient temperature and pressure
Graphite
used to designate the types and concentrations of atomic defects in ceramics
Defect structure
state that exists when there are equal numbers of positive and negative charges from the ions
Electroneutrality
defect involves a cation–vacancy and a cation–interstitial pair
Frenkel defect
defect found in AX materials is a cation vacancy–anion vacancy pair
Schottky defect
created by removing one cation and one anion from the interior of the crystal and then placing them both at an external surface. Because the magnitude of the negative charge on the cation i
Schottky defect
state for ionic compounds wherein there is the exact ratio of cations to anions as predicted by the chemical formula
Stoichiometry
there is any deviation from this exact ratio
Nonstoichiometric
occur for some ceramic materials in which two valence (or ionic) states exist for one of the ion types
nonstiochiometric
What are the solid solution that the impurity atom can form in thr ceramic material?
Interstitial
Substitutional
the ionic radius of the impurity must be relatively small in comparison to the anion
Interstitial
substitutes for the host ion to which it is most similar in an electrical sense
Substitutional
usually occurs by a vacancy mechanism in order to maintain charge neutrality in an ionic material
Diffusion
Vacancies
Occurs in pairs
Form nonstoichiometric compound
Created by substitutional impurities
One of the relatively simple ceramic phase diagrams
Aluminum oxide - chromium oxide
has the same form as the isomorphous copper–nickel phase diagram, consisting of single liquid-phase and single solid-phase regions separated by a two-phase solid–liquid region having the shape of a blade
Aluminum oxide - chromium oxide
it is frequently the case that the two components are compounds that share a common element
Binary-two component phase diagram
One eutectic and 2 eutectoid is found gor this system
Zirconium oxide - calcium oxide
zirconia material having a calcia content within the range cited
Partially stabilize zirconia
Principle constituent of ceramui refactories
Silica and alumina
consists of the formation and propagation of cracks through the cross section of material in a direction perpendicular to the applied load
Brittle fracture process
Crack growth in crystalline ceramics:
Transgranular
Intergranular
cracks propagate along specific crystallographic (or cleavage) planes, planes of high atomic density
Transgranular fracture
measure of a ceramic material’s ability to resist fracture when a crack is present
Fracture toughness
fracture of ceramic materials occur by the slow propagation of cracks, when stresses are static in nature
Static fracture
This type of fracture is especially sensitive to environmental conditions, specifically when moisture is present in the atmosphere.
Static fatigue
occurs at the crack tips
Stress corrosion process
involves examining the path of crack propagation, as well as microscopic features of the fracture surface.
Fractographic study
indicative of whether the ceramic piece was excessively weak or the in-service stress was greater than anticipated
Stress magnitude
crack surface that formed during the initial acceleration stage of propagation is flat and smooth
Mirror region
Surface features:
Mist
Hackle
faint annular region just outside the mirror
Mist
beyond the mist
Hackle
has an even rougher texture
Hackle
composed of a set of striations or lines that radiate away from the crack source in the direction of crack propagation
Hackle
arc shaped, and they provide information regarding stress distributions and directions of crack propagation
Wallner line
stress at fracture using this flexure test
Fractural strength
modulus of rupture, fracture strength, or bend strength, an important mechanical parameter for brittle ceramics
Fractural strength
occurs by the motion of dislocations.
Plastic deformation
Reasons why ceramics are brittle
Covalent bond is strong
Limited number of slip
Dislocation structure is complex
measure of a noncrystalline material’s resistance to deformation
Viscosity
For some ceramic fabrication techniques, the precursor material is in the form of
Powder
deleterious to the flexural strength for two reasons: (1) pores reduce the cross-sectional area across which a load is applied, and (2) they also act as stress concentrators—for an isolated spherical pore, an applied tensile stress is amplified by a factor of 2
Porosity
It is used to measure the hardness of the ceramic
Knoop and vicker technique
deformation as a result of exposure to stresses(usually compressive) at elevated temperatures
Creep
