1. Materials Engineering
Lecture 11:
Ceramics.
Glass

2. What is ceramics? Oxides: aMexOy(∙bMe’mOn)∙cNMeuOw∙dH2O
Nitrides: aMexNy(∙bMe’mNn)
Carbides: aMexCy
Silicides: aMexSiy
Generally, very hard, very tough, very brittle, refractory.

3. Ceramic materials

4. Chemical Bonds in ceramic materials
Si-O, Si-C, Si-N: purely covalent
Me-O, Me-C, Me-N, Me-Si: partly covalent
SiC
ZnS
Si3N4
SiO2
Al2O3
NaCl
MgO
CaF2
Material 12 18 30 51 63 67 73 89
% ionic bond
Even when a typical metal is bound to a typical non-metal, some orbital overlapping takes place => each ionic bond has some fraction of covalent.
Ceramics is built by covalent bonds and the ceramic properties are the result of covalent bonding

5. Crystal structure of ceramics
Metal structures are formed by non-directional metal bonds => they are dense (close packing)
Ceramic structures are formed by directional covalent bonds => these are loose and brittle

6. Ceramics and glass Ceramic materials are always crystalline
Glass materials are amorphous

7. Silicate ceramics Clay, sand, quartz, talс and others are silicates:
MekMe’lSipOq =
aMexOy(∙bMe’mOn)∙cNMeuOw
The main structural element of all silicates is SiO44- tetrahedron

8. Silica Silica: SiO2: 2.2 gr/cm3, m.p. 1575 - 1725ºC Polymorhism:
Crystobalite
Metastable (stable above 1470ºC)
Quartz: 2.65 g/cm3, HM=7, UV-transparent
Sand: dispersed quartz

9. Silicates Simple: forsterite (Mg2SiO4) and others;
Layered: talc, kaolinite and others.
Clay is a mixture of layered silicates

10. Carbon allotropy
Carbon is not ceramic. However it is technically close to ceramics.
Diamond
Graphite
Fullerene
Carbon nanotubes: the strongest known material in the Universe, very light, ductile, electric anisotropy (metal conductor along the tube, semiconductor across)

11. Defects in ceramics Due to defects ceramics can be: Cation conductive
Anion conductive
Electron conductive
Insulator
Two types of point defects are especially important: Schottky and Frenkel defects

12. Mechanical properties of ceramics
Brittle fracture
Testing: compression and bending
Elasticity (almost like of metals)  fracture (no plasticity)
Porosity is very important (influences on elasticity and strength)
Hardness (Knoop hardness, HK)
Creep at elevated temperatures
Viscose flow at elevated temperatures (and for glasses)

13. Glasses characterisitcs other B2O3 Al2O3 CaO Na2O SiO2 glasses
High m.p., low thermal expansion => glassware for high temperatures; UV-transparent
> 99.5
Fused silica (quartz)
Thermal shock and chemically resistant => chemical glassware 4 96
Vycor
Thermal shock and chemically resistant => ovenware 13
2.5
3.5 81
Borosilicate (pyrex)
Easily worked, durable => regular glass
4MgO 1 5 16 74
Soda-lime (container)
Easily drawn into fibers => glass-resin composites 10 15 55
Fiberglass
High density, high refraction index => optics
37PbO, 8K2O 54
Optical flint
Easily fabricated, strong, resists thermal shock => ovenware
6.5TiO2, 0.5As2O3
5.5 30 14
43.5
Glass-ceramic (pyroceram)

14. Refractory ceramics
Service temperature
Porosity, %
TiO2
CaO
Fe2O3
Cr2O3
MgO
SiO2
Al2O3
< 1587ºC
10-25
1-2
0-1
70-50
25-45
fireclay
< 1890ºC
18-25
1-4
10-45
90-50
Alumina fireclay
< 1650ºC 25
2.2
0.6
96.3
0.2
Silica 22
2.5
3.0
0.3
90.0
1.0
Periclase 21
2.0
8.2
73.0
5.0
9.0
Periclase – chrome ore
Other refractories: alumina, zirconia, carbides, SiC, graphite
Firing: raw materials contain large and fine particles (of different compositions). The large particles form a bonding phase (glassy or crystalline) and this phase is responsible for the strength of the brick.

15. Cements, Abrasives, Special ceramics
Portland cement (the most popular)
Cement + water  (setting) concrete
Preparation: clay + lime are fired at ~ 1440ºC  clinker
Clinker is ground + gypsum  portland cement
Portland cement is hydraulic (set by water)
Special cements are set by other materials
Abrasive ceramics (HK>1000): diamond, SiC, WC, corundum (Al2O3), silica sand
Special ceramics:
Piezoelectric (strain ~ electricity): BaTiO3, PZT (lead zirconate-titanate), PbTiO3, NaKNbO3
MEMS (microelectromechanical systems)
Optical fibers (high purity silica)
Ceramic bearings (Si3N4)

16. Glass production Press-and-blow technique Drawing Thermal processing:
annealing
Thermal tempering

17. Ceramic production Hydroplastic forming Slip casting Drying Firing
Powder pressing
Extrusion
Sintering

18. Musts of this lecture
Ceramics: composition and properties; classification
Ceramic structure and its influence on properties
Glass
Silicates
Defects in ceramics
Mechanical properties of ceramics
Refractories, cements, abrasives, special ceramics
Glass production
Ceramic production