Mats lecture 8 Flashcards
Ceramics and Glass
Ceramics usually are compounds that consist….?
two or more elements (they have different atomic radius)
What kind of bonds do ceramics have?
-They have covalent, ionic, or combined covalent/ionic bonding
What are some common ceramics (chemical formulas)
-CaF2
-MgO
-NaCl
-Al2O3
-SiO2
-Si3N4
-ZnS
-SiC
Describe what is happening in a ceramic crystal oxide structure
-Oxygen anions are larger than metal cations
-Close packed oxygen in a lattice (usually FCC)
-Cations fit into interstitial sites among oxygen ions
List the factors that determine crystal structure
- relative size of ions
- Maintenance of charge neutrality (net charge in ceramics should be zero)
Which structures do AX-type ceramic crystals typically have?
-either FCC or BCC unit cells
How many number of atoms are there in an AX-type ceramic
-Have the same number of “A” atoms as “X” atoms in the unit cell
What are the sizes of the “A” and “X” atoms?
-the “A” and “X” atoms are usually different sizes
In what locations do the smaller atoms sit in the unit cell?
-Smaller atoms sit in the interstitial locations
In what locations do the smaller atoms sit in the unit cell?
-Larger atoms sit in the regular atomic sites
List the three most common AX-type crystals
-The sodium chloride (rock salt) structure
-The zinc blende structure
-The cerium chloride structure
What kind of crystal structure does NaCl have?
-FCC
What kind of crystal structure does ZnS have?
-FCC
What kind of crystal structure does CsCl have?
-BCC
What is the definition of a Coordination number?
-The number of nearest neighbouring atoms for a particular atom
What are common examples of AX2 (fluorite) compounds?
-CaF2
-ZrO2
-CeO2
What happens in an Anti-fluorite Structure?
-Position of cations and anions are reversed
What is a ABX3 structure known as?
-Perovskite Structure
What is Quartz made of?
-Crystalline SiO2
Is Quartz strong?
-Yes
-Very strong (but brittle)
Describe the melting temperature of Quartz and what it is
-Very high melting temperature
-T=1750 degrees Celsius
What is window glass made of?
-Non crystalline SiO2
Is window glass strong?
-No
-Very weak (but still brittle at room temperature)
Describe the melting temperature of window glass and what it is
-Very low melting temperature
(T= 780 degrees Celsius)
-Becomes very ductile (viscous) at high temperature
