Week 6 Part 1 Ceramics Flashcards
What is a ceramic?
defined as synthesized inorganic, solid, crystalline, materials, excluding metals.
How do you differentiate between a ceramic and a metal?
the atomic bonding
What are the medical applications of ceramics? (4)
- joint replacement
- dental fillings
- bone grafts/cement
- eye
What are the 3 main characteristics of ceramics?
- excellent wear
- mechanical properties
- corrosion resistance
What is ionic bonding?
between a metal and nonmetal
What is the atomic bonding commonly found in ceramics?
ionic and covalent
What are the two factors that determine crystal structure?
- relative size of ions
- maintenance of charge neutrality
What is the relative size of ions? (in respect to determining crystal structure)
from the formation of stable structure - to maximize the number of oppositely charged ion neighbors
What is the maintenance of charge neutrality? (in respect to determining crystal structure)
the net charge should be zero - reflected from chemical formula
AX Crystal Structure
A = cation, X = anion
AmXp
m = charge of cation
p = charge of anion
m - p = 0 (neutral)
Common AX crystal structure, include coordination # and unit cell
Sodium Chloride
NaCl
m = 1, p = 1
coord. # = 6
unit cell = FCC
Ceramics that don’t have equal charge cations are at the ____________ of the cube with anions at the _______________.
center of the cube with anions at the corner
coordination number increases with what ratio
radius of cation over the radius of anion
Theoretical density of ceramic variables:
n’ , Ac, Aa, Vc, Na
n’ = # of formula units/unit cell
Ac = sum of atomic weight of all cations in formula unit
Aa = sum of atomic weight of all anions in formula unit
Vc = volume of unit cell
Na = avogadro’s number
What are the two point defects in a crystal structure?
- vacancies
- interstitials
What is a vacancy point defect? (cation and/or anions?)
a space in the structure where an atom should be but isn’t
- exists in ceramics for both cations and anions
What is an interstitial point defect? (cation and/or anions?)
an atom is shoved between other atoms when it shouldn’t be
- exists only for cations
- anions are too large relative to interstitial sites
What are the two defects in crystal structures?
- Schottky
- Frenkel
What is the Schottky defect?
where there are vacancies in both cation and anions in the correct ratio to maintain neutrality
What is the Frenkel defect?
when a vacancy and interstitial pair is created to maintain neutrality
The Schottky and Frenkel defects keep _________, but why?
neutrality or else they would cause an unstable structure.
What are impurities? (for anions)
when solute anions form mainly substitutional solutions since they are too large to fit easily in the interstitial space
What are impurities for cations?
they readily form both types: substitutional and interstitial
Ceramics are more _________ than metals. (mechanical property)
brittle
