1. Ceramic introduction

2. What is "ceramic"?
– from Greek meaning: "burnt earth"
– non-metal, inorganic
• Examples
– sand, stone
– porcelain (china), pottery
– brick, concrete
– glass
– cutting tools
– turbine engines
• Unique properties
– hard and strong in compression, brittle
– refractory (resistance to heat)
– electrical insulator (?)
– chemically stable
– special functions, e.g. optical

3. Types of ceramics
• Rocks and minerals
• Clays
– composed of Al2O3,SiO2 &
chemically bound water
– attributes: easy to form with
water addition
– applications: bricks, tiles,
porcelain, pottery, etc
• Glasses
– SiO2 based
– attributes: transparent to light;
easy to form
– applications: windows,
containers, lenses, etc
• Cements
– consisting of CaO, SiO2 & Al2O3
– attributes: form paste withwater and then harden
– applications: construction,road, concrete
• Engineering ceramics (advanced ceramics, high-performance ceramics, technical ceramics)
– e.g. Al2O3, SiC, Si3N4, ZrO2
– attributes: excellent physical, chemical or mechanical properties
– applications: heat engines, cutting tools, die material, superconductors

4. Engineering ceramics
• Aluminium oxide (Al2O3)
– cutting tool - increased cutting speed
– die inserts - better wear resistance
– bearings under low load - e.g. tiny sapphire spheres for watches (e.g. 19 jewel watch)
– abrasives - e.g. grinding wheel, grinding powder
– package material for Si chips
– laser generator
– crucible for metal casting
– refractory furnace lining
– reinforcing phase in MMC
• Aluminium nitride (AlN)
– good thermal conductivity
(> 200 W/mK)
– applications in electronic engineering when high thermal conductivity is needed
• Barium titanate (BaTiO3)
– high dielectric constant (up to 9500)
– used in capacitor (high charge-storage capability desirable)
• Beryllium oxide (BeO)
– high thermal conductivity (> 250 W/mK)
– applications similar to AlN

5. • Graphite (C)
– solid lubricants
– seals
– crucibles for molten metals
– heating element in an inert atmosphere: >2000°C
• Silicon carbide (SiC)
– heating element - up to 1500°C
– abrasives - e.g. grinding wheel, grinding powder
– dies for hot pressing
– reinforcing phase in MMC
– in heat engines – under development
• Boron carbide (B4C)
– low density (~2.5 g/cm3) and hard
– armor for helicopter and personnel
• Boron nitride (BN)
– hexagonal BN: good solid lubricant
– cubic BN: hard - e.g. as abrasives or for cutting tools
• Diamond (C)
– cutting tools
– abrasives
– jewelry
– coating films

6. • Silicon nitride (Si3N4)
– bearings under high load
– reinforcing phase in MMCs
– metal cutting tools
– in heat engines – under development
• Zirconium oxide (ZrO2)
– very low thermal conductivity (~1.8W/mK)
– thermal barrier coating - e.g. coating on the surface of superalloy gas turbine engine component (resulting in a temperature drop of ~300°C across the layer)
– heating element at >1800°C
• Glass ceramics
– ease of forming
– no porosity
– unique properties: e. g. transparency with tiny crystals; low thermal expansion
– example: LiAlSi2O6
• low thermal expansion
• low thermal conductivity
• good radiation ability
• good impact strength
• high hardness
• e.g. for cooker hob (flat separation between heating coil and cooking utensil)

7. Characteristics of ceramics
• Elastic modulus
– Al2O3 = ~390 GPa
– SiC = ~420 GPa
– diamond = >1000 GPa
– Comparison with metals
steel = ~200 GPa
Al = ~70 GPa)
• Strength – tensile
- Al2O3 = ~ MPa
- Si3N4 = up to MPa
- Comparison with metals
steels = >1000 MPa
Al alloys = MPa
– flexural
• Al2O3 = MPa
• SiC = MPa
• Si3N4 = MPa
• Fracture toughness
– ceramics = < 10 MPa m1/2
– metals = > MPa m1/2
• Ductility
– ceramics = nil in most cases
– metals = > 10-20%
• Density
– ceramics: 2-6 g/cm3
– metals
g/cm3 for light alloys
> 7 g/cm3 for many others

8. • Thermal conductivity
– diamond = ~900 W/mK
– graphite = ~100 W/mK
– SiC = > 100 W/mK
– Al2O3 = ~30-40 W/mK
– Si3N4 = ~15 W/mK
– ZrO2 = ~1.5 W/mK
– Comparison with metals
• Cu = ~ W/mK
• Al = ~ W/mK
• carbon steel = W/mK
• Thermal expansion coefficient
– SiC = 4.3 x 10-6 /K ( °C)
– Al2O3 = 8.6 x 10-6 /K ( °C)
– Si3N4 = 3.2 x 10-6 /K ( °C)
– Comparison with metals
• Cu = ~18 x 10-6 /K ( °C)
• Al = ~26 x 10-6 /K ( °C)
• carbon steel = ~13 x 10-6/K ( °C)

12. The ionic radii for K+ and O2- as 0. 138 and 0. 140 nm, respectively
The ionic radii for K+ and O2- as and nm, respectively. What would be the coordination number for each O2- ion?
Briefly describe the resulting crystal structure for K2O.
Explain why this is called the
antifluorite structure.