1. CERAMICS MATERIALS Applications of ceramics refractories sensors
capacitors
the magnetic strip on a credit card
space shuttle protection from high temperature
addition to paints
found in bone and teeth
spark plugs
Ceramics exhibit good strength under compression and virtually no ductility
under tension. Ceramics are inorganic and non-metallic materials that are
commonly electrical and thermal insulators, brittle and composed of more than
one element (e.g., two in Al2O3)

2. DEFINITIONS
The word ceramic, derives its name from the Greek keramos, meaning "pottery", which in turn is derived from an older Sanskrit root, meaning "to burn". The Greeks used the term to mean "burnt stuff" or "burned earth". Thus the word was used to refer to a product obtained through the action of fire upon earthy materials
Ceramics make up one of three large classes of solid materials. The
other material classes include metals and polymers. The combination
of two or more of these materials together to produce a new material
whose properties would not be attainable by conventional means is
called a composite. Examples of composites include steel reinforced
concrete, steel belted tyres, glass or carbon fibre - reinforced plastics
(so called fibre-glass resins) used for boats, tennis rackets, skis, and
racing bikes.

3. CERAMIC GROUPING GLASSES CEMENTS ADVANCED CERAMICS GLASS STRUCTURAL
CLAY
PRODUCTS
WHITEWARES
FIRECLAY
SILICA
BASIC
SPECIAL

4. Ceramics can be classified based on chemical composition – oxides, carbides, nitrides, sulfides and fluorides. Or they can be grouped according to their major functions. Ceramics found in coatings – glazes, are ceramic coatings applied to glass objects and enamels are ceramic coatings applied to metallic objects.
Alumina (Al2O3):
Diamond (C):
Silica (SiO2):
Silicon carbide:
Silicon nitride (Si3N4):
Titanium oxide (TiO2):
Zirconia (ZrO2):

5. Function Application Examples Electrical Magnetic Optical Automotive
Capacitor dielectrics
Microwave dielectrics
Conductive oxides
Superconductors
Electronic packaging
Insulators
Solid-oxide fuel cells
Piezoelectronic
Electro-optical
BaTiO3, SrTiO3, Ta2O5,
Ba2Ti9O20, Al2O3 Ba(Mg1/3Ta2/3)O3, Ba(Zn1/3Ta2/3)O3, BaTi4O9,
In-doped SnO2 (ITO)
YBa2Cu3O7-x (YBCO)
Al2O3
Porcelain
ZrO2, LaCrO3
Pb(ZrxTi1-x)O3 (PZT)
PLZT, LiNbO3
Magnetic
Recording media
Ferrofluids, credit cards,
Circulators, isolators,
Inductors, magnets
γ-Fe2O3, CrO2(chrome cassettes)
Fe3O4
Nickel zinc ferrite
Manganese zinc ferrite
Optical
Fibre optics
Glasses
Lasers
Lighting
Doped SiO2
SiO2 based
Al2O3, yttrium aluminium garnate
Al2O3, glasses
Automotive
Oxygen sensors, fuel cells
Catalyst support
Spark plugs
Tires
Windshields/windows
ZrO2
Cordierite
SiO2
SiO2 based glasses

6. Mechanical/structural
Cutting tools
Composites
Abrasives
WC-Co cermets
Silicon-aluminium-oxynitride (Sialon), Al2O3
SiC, Al2O3, silica glass fibres
SiC,Al2O3, diamond,BN, ZrSiO4
Biomedical
Implants
Dentistry
Ultrasound imaging
Hydroxyapatite
Porcelain, Al2O3
PZT
Construction
Buildings
Concrete
Glass
Sanitaryware
Others
Defense
Armor materials
Sensors
Nuclear
Metal processing
PZT, B4C
SnO2
UO2
Al2O3, SiO2-based refractories
O2 sensors, casting molds
Chemical
Catalysis
Air, liquid filtration
Paints, rubber
Oxides (Al2O3,ZrO2,ZnO,TiO2)
Domestic
Tiles, sanitaryware
Whiteware, kitchenware,
Pottery, art, jewelry
Clay, Al2O3, SiO2-based and glass ceramics, diamond, ruby, cubic, zirconia

7. Properties of Ceramics
Material
Melting point (°C)
Thermal expansion coefficient (x10-6 cm/cm)/°C
Knoop Hardness (HK) (100 g)
Al2O3
2000
6.8
2100 BN
2732
0.57, -0.46
5000
SiC
2700
3.7
2500
Diamond
1.02
7000
Mullite
1810
4.5 _
TiO2
1840
8.8
Cubic ZrO2
10.5

8. Material D(g/cm3) T (psi) F (psi) C (psi) Y (psi) Ft (psi√in) Al2O3
3.98
30,000
80,000
400,000
56 x 106
5,000
SiC (sintered)
3.1
25,000
560,000
60 x 106
4,000
Si3N4 (rxn bonded)
2.5
20,000
35,000
150,000
30 x 106
3,000
Si3N4 (hot pressed)
3.2
130,000
500,000
45 x 106
Sialon
3.24
60,000
140,000
9,000
ZrO2 (partially stabilized)
5.8
65,000
100,000
270,000
10,000
ZrO2 (transformation toughened)
50,000
115,000
250,000
29 x 106
11,000
Tensile strength = T; Flexural strength = F; Young’s modulus = Y;
Compressive strength = C; Fracture toughness = Ft; Density = D.

9. Synthesis and processing of
ceramic powders
Consolidation into a dense,
monoclinic object using
sintering or firing
Synthesis of ceramic
powders
Ball milling, blending, spray drying
of powders using processing additives
Shaping of powders into useful
shapes (green ceramics) using pressing,
slip casting, tape casting
Final sintered ceramic product
Secondary processing (e.g. grinding,
cutting, polishing, electroding,
coating etc.)

10. DIFFERENT TECHNIQUES FOR PROCESSING OF ADVANCED CERAMICS
These techniques are used to convert properly processed powders into desirable shape to form the green ceramic (is a ceramic that has not yet been sintered.
Slip casting;
Compaction (uniaxial or isostatic);
Tape casting;
Extrusion;
Injection molding;
See Figure 15-2 on page 539 of Askeland and Phule

11. Characteristics of sintered ceramics
Important in sintered ceramics – grain size, grain size distribution, and the level and type of porosity.
Grains and grain boundaries: Ceramics with small grain size are stronger than coarse – grained ceramics. Finer grain size reduces stresses that develops at grain boundaries due to anisotropic expansion and contraction. Average grain size properly controlled produces magnetic, dielectric and optical properties.
Porosity: Pores represent defects in polycrystalline ceramics and are usually detrimental to the mechanical properties of bulk ceramics. Pores may be either interconnected or closed. The apparent porosity measures the interconnected pores and determine permeability or ease with which gases or fluids seep through ceramic components.
Apparent porosity = Ww – Wd / Ww – Ws x 100 (W = weight either after removal from water (s), dry (d) or suspended in water (s).
True porosity = ρ - B / ρ x (B = bulk density, ρ = true density or specific gravity of the ceramic material.

12. Example 15.1 on page 544:
Silicon carbide particles are compacted and fired at a high temperature to produce a strong ceramic shape. The specific gravity of SiC is 3.2 g/cm3. The ceramic shape is weighed when dry (360 g), after soaking in water (385 g) and while suspended in water (224 g). Calculate the apparent porosity, the true porosity, and the fraction of the pore volume that is closed.
Apparent porosity = Ww – Wd / Ww – Ws x 100 = 385 – 360 / 385 – 224 x 100 = 15.5%
Need bulk density to calculate true porosity;
Bulk density (B) = Wd / Ww - Ws = 360 / 385 – 224 = 2.24 g.cm-3
True porosity = ρ - B / ρ x 100 = 3.2 – 2.24 / 3.2 x 100 = 30%
Closed pore percentage = true porosity – apparent porosity;
= 30 – 15.5 = 14.5%
Therefore, fraction closed pores = 14.5 / 30 = 0.483

13. Inorganic Glasses
Non-crystalline materials especially based on silica (others are based on fluorides, sulfides and alloys). Define glass: a metastable material that has hardened and become rigid without crystallizing. Below the glass temperature the rate of volume contraction on cooling is reduced and material considered glass not undercooled liquid.
Undercooled
liquid
Glass
Crystalline Tg Tm
Density
When silica crystallizes on cooling, abrupt change in the density is observed

14. Silicate glasses are most widely used, fused silica made from pure silica has high melting point and the dimensional changes during heating and cooling are small. Oxides can be classified as glass formers (silica), intermediates (aluminium oxide) and modifiers (magnesium oxide) – cause glass to devitrify or crystallize as they break up the network structure.
Modified silicate glasses;
Modifiers break up the network of the silica. When Na2O is added Na+ ions enters the holes in the network while O2- ions becomes part of the network structure. The O:Si ratio becomes large and when it reaches 2.5 glass is difficult to form. Modifiers reduces melting points and viscosity of the silica making it possible to produce glass at lower temperatures.
Glass formers – B2O3, SiO2, GeO2, P2O5, V2O3
Intermediates – TiO2, ZnO, PbO2, Al2O3, BeO
Modifiers – Y2O3, MgO, CaO, PbO, Na2O

15. Glass manufacturing
At high temperatures and with viscosity controlled so that glass can be shaped without breaking.
Liquid range – sheet and plate glass produced when glass is in a molten state. Liquid tin used to form smooth surface on glass.
Working range – shapes for containers or light bulbs can be formed by pressing, drawing or blowing glass into molds. Glass is heated in the working range so that is formable but not runny.
Annealing range – annealed to reduce residual stresses during forming. Large glass castings are often annealed and slowly cooled to prevent cracking.
Tempered glass – quenching the surface of plate glass with air causing the surface layers to cool and contract. Used in car and home windows shelving for refrigerators, ovens, furnitures.
Laminated glass – consist of two annealed glass pieces with a polymer (polyvinylbutyral, PVB) in between used to make car wind shields.

16. Glass SiO2 Al2O3 CaO Na2O B2O3 MgO PbO Fused silica 99 vycorTM 96 4
PyrexTM 81 2 12
Glass jars 74 1 5 15
Window glass 72 10 14
Plate glass 73 13
Light bulbs 16
Fibers 54
Thermometer 6
Lead glass 67 17
Optical flint 50 19
Optical crown 70 8
E-glass fibers 55 20
S-glass fibers 65 25

17. Glass Composition – most glass are based on silica, modifiers such as Na2O (soda), CaO. Common commercial glass contains approximately 75% SiO2, 15%Na2O and 10% CaO = soda line glass. Borosilicate glass – contains 15% B2O3, used in lab glassware, glass ceramics and containers for high level radioactive waste.
Calcium aluminosilicate glass or E-glass (20% Al2O3, 12%MgO and 3%B2O3) – used for general purpose fiber for composite materials such as fiber glass.
Fused silica – gives best resistance to high temperature, thermal shock and chemical attack. Photochromic glass – darkened by the UV portion of sunlight used for sunglasses. Polychromatic glasses – sensitive to all light not just UV light.

18. Glass ceramics – are crystalline materials derived from amorphous glasses. Glass-ceramics have a substantial level of crystallinity (>70 – 99%). Formability and density of glass becomes important. Glass is crystallized using heterogeneous nucleation by such oxides such as TiO2 and ZrO2. In making glass ceramics – first step is to assure that no crystallization during cooling from the forming temperature.
Forming
Nucleation
Growth
Melting
Time
Temperature (°C)
1600
900
800
650
1250
liquidus
Softening
point
Annealing
-4 x 104
-107.6
Viscosity µ(poise)
Heat treatment profile for glass-ceramic fabrication.
Cooling must be rapid to avoid the start of crystallization. Isothermal and continuous cooling values for lunar glass. The rate of nucleation of precipitates is high at low temperatures, whereas rate of growth is high at higher temperatures

19. Nucleation of the crystalline phase is controlled in two ways; first the glass contains agents such as TiO2, that react with other oxides and form phases that provides the nucleation sites. Second heat treatment is designed to provide number of nuclei, the temperature should be relatively low in order to maximize the rate of nucleation.
Processing and Applications of clay products:
Clay products are traditional ceramics used for producing pipe, brick, cooking ware. Clay – kaolinite and water serve as the initial binder for the ceramic powders, which are typically silica. Feldspar, [(K,Na)2O.Al2O3.6SiO2 , is used as a flux (glass forming) agent during later heat treatment.

20. Forming techniques for clay products;
The powders, clay, flux and water are mixed and formed into shape. Dry or semi-dry mixtures are mechanically pressed into green shapes, isostatic pressing may be done, the powders are placed into a rubber mold and subjected to high pressures
Drying and Firing of Clay products;
During drying, excess moisture is removed and large dimensional changes occur. Temperature and humidity are controlled to provide uniform drying – minimizing stresses, distortion and cracking. Firing – produces rigidity and strength of the ceramic materials. During heating the clay dehydrates an vitrification or melting begins. Impurities and fluxing agent reacts with ceramic materials and clay producing low-melting point liquid phase at the grain surfaces.
Clay
Glassy bond
Liquid phase
formed
Firing time
The liquid helps eliminate porosity and after cooling changes to a rigid glass. The glassy phase provides ceramic bond and shrinkage

21. Refractories – components of equipments used in production, refining and handling of metals and glasses, for constructing heat treating furnaces. They must survive high temperatures without being corroded or weakened. Refractory bricks contain 20 to 25% apparent porosity to provide improved thermal insulation.
Acid refractories -
Base refractories -
Neutral refractories -

22. Compositions of typical refractories (weight percentage)
Refractory
SiO2
Al2O3
MgO
Fe2O3
Cr2O3
Acidic
Silica
95-97
Superduty firebrick
51-53
43-44
High-alumina firebrick
10-45
50-80
Basic
Magnesite
83-93
2-7
Olivine 43 57
Neutral
Chromite
3-13
12-30
10-20
12-25
30-50
Chromite-magnesite
2-8
20-24
30-39
9-12

23. Other ceramic materials
Cements:
A chemical reaction converts a liquid resin to a solid that joins the particles. CO2 gas acts as a catalyst to dehydrate sodium silicate to produce glassy material.
xNa2O.ySiO2.H2O + CO2 = glass
Coatings:
Thin films and Single crystals:
Fibers: