1. CERAMICS Definition:  A compound of metallic and non-metallic elements prepared by the action of heat and subsequent cooling.  There are two general categories of ceramic;  Traditional ceramics – tiles, brick, sewer pipe, pottery  Industrial ceramics (engineering, high-tech, or fine ceramics) – turbine, semiconductors, cutting tools  The structure of ceramics is maybe crystalline or partly crystalline structure, or may be amorphous.  Generally atoms in ceramics are covalent or ionic bonded and the much stronger is metallic bonds.  The hardness and thermal and electrical resistance in ceramics are better than in metals.  The grain size influences the structure of ceramics (finer grain size has give higher strength and toughness).  The oldest materials to make ceramics is clay (fine-grained sheet like structure) i.e. kaolinite (a white clay of silicate of aluminum with alternating weakly bonded layers of silicon and aluminum ions).  The other common materials are flint (a rock composed of very fine grained SiO ₂ ) and feldspar (a group of crystalline minerals of aluminum silicate and potassium, calcium or sodium).  Porcelain is a white ceramic made of kaolin, quartz, and feldspar used mostly in kitchen appliance and bath ware.

2. Alumina  Also called corundum or emery  Most widely used  Used in pure form or as raw material  High hardness and moderate strength  Alumina + other oxides are used as refractory materials for high-temp applications  Suitable as electrical and thermal insulation, cutting tools/abrasives, etc.

3. Zirconia  Good toughness, good resistance to thermal shock, wear and corrosion  Have low friction coefficient  Used in hot extrusion die, grinding beads/dispersion media for aerospace coatings, etc.  Have thermal stability and low thermal conductivity

4. Carbides  Made of tungsten and titanium,silicon  Examples : Tungsten carbide (WC), titanum carbide (TiC), silicon carbide (SiC)

5. Nitrides  Cubic boron nitride (CBN)  Titanum nitride (TiN)  Silicon nitride (Si3N4)

6. Glass  Amorphous solid  Super-cooled liquid (cooled at a rate too high for crystal formation)  Content more than 50% silica (glass former)  Types of commercial glasses ¨ sodalime glass (most common), lead alkali glass, borosilicate glass, aluminosilicate glass, 96% silica glass, fused silica glass  Thermal classification - hard (greater heat, e.g., borosilicate) or soft glass (e.g., soda lime glass ¨ lampworking)

7. Glass ceramics  High crystalline microstructure  Stronger than glass  Shaped and then heat treated  Treatment process known as devitrification(recrystallization of glass)  Near zero coefficient of thermal expansion, high thermal shock resistance

8. Graphite  Crystalline form of carbon layered structure  Basal planes or sheets of close packed C atoms  Weak when sheared along the layers  Also known as lampblack (pigment  High electrical and thermal conductivity  Good resistance to thermal shock and high temperature

9. Types of graphite  Fibers - important use in reinforced plastics and composite materials  Foams - high service temperature, chemical inertness, low coefficient of thermal expansion and electrical properties  Carbon foams - graphitic or non-graphitic structures  Buckyballs - carbon molecules in the shape of soccer balls. Also called fullerents, chemicallyinert, and act like solid lubricant particles

10. Diamond  Diamond-Like Carbon (DLC) developed as diamond film coating  Can be coated with Ni, Cu, or Ti for improved performance  Cutting tools materials (single or polycrystalline)  Abrasive in grinding  Dressing of grinding wheels (abrasive sharpening)  Dies for wire drawing  Cutting tools and dies coating

11. Structural Properties Rock salt structure(AX)(NaCl )

12. Spinel structure(AB2X4)(MgAl2O4)

13. Crystal Structures  Ceramic bonds are mixed, ionic and covalent, with a proportion that depends on the particular ceramics. The ionic character is given by the difference of electronegativity between the cations (+) and anions (-). Covalent bonds involve sharing of valence electrons. Very ionic crystals usually involve cations which are alkalis or alkaline- earths (first two columns of the periodic table) and oxygen or halogens as anions.

14.  The building criteria for the crystal structure are two:  maintain neutrality  charge balance dictates chemical formula  achieve closest packing  the condition for minimum energy implies maximum attraction and minimum repulsion. This leads to contact, configurations where anions have the highest number of cation neighbors and viceversa.

15.  COMPLEX SILICATE STRUCTURES  The majority of ceramic materials, in particular those derived from clay, sand, or cement, contain the element silicon in the from of silicates.

16. Mechanical properties 

17. Application  Automotive:  Brake pads Ceramic materials retain their properties at elevated temperatures due to the strong ionic-covalent bonding.  Safety glass windshield Ceramic materials retain their properties at high pressure due to the strong ionic-covalent bonding.

18.  Medical (Bioceramics):  Dental restoration Ceramics materials has low reactivity towards acids and enzymes in the mouth due to its covalent bonding.  Bone implants Ceramics materials has low reactivity towards the fluid and chemical substance in human body due to its covalent bonding.