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CERAMICS

A ceramic is an inorganic and non-metallic solid made up of either metal or non- metal compounds that have been shaped and then hardened by heating to high temperatures. They are hard and brittle, composed of more than one element and commonly used for electrical and thermal insulators. Ceramic comes from the Greek word meaning ‘pottery’. The clay-based domestic wares, art objects and building products are familiar to us, but pottery is just one part of the ceramic world.

Crystal Structures of Ceramic Ceramics have a combination of stronger bonds called ionic and covalent bonds. Ionic bonds - occurs between a metal and nonmetal and involves the attraction of opposite charges when electrons are transferred from the metal to the nonmetal. Covalent bonds - occurs between two nonmetals and involves sharing of atoms. The strength of an ionic bond depends on the size of the charge on each ion and on the radius of each ion.

Ceramic bonds are mixed, 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 and oxygen or halogens as anions.

Properties of Ceramics Oxidation resistant Brittle Thermal Insulators Non- magnetic Electrical Insulators Chemically stable Hard

Ceramic Applications

Ceramic applications

In Aerospace Ceramics are being used in military aircraft, space shuttle and its equipment for many years. Its include thermal protection systems in rocket exhaust cones, insulating tiles for the space shuttle, engine components, and ceramic coatings that are embedded into the windshield glass of many airplanes. Ceramics fiber are used as heat shields for fire protection and thermal insulation in aircraft and space shuttles….

In Medical Developments in ceramic materials and product design are offering surgeons and patients new options for joint replacement surgery. Driven by the medical industry’s need for ever smaller yet more complex components, materials scientists today are making use of innovative processing techniques, including injection moulding, engineered coatings and ceramic-metal assemblies. The results include hand tools, valves, and implantable devices.

In Automotive Design and Manufacture Ceramics have increasingly being used in automotive design and manufacture as an alternative to metals… Ceramics make an ideal material for transducers and sensors. It also being used in fuel tank ultrasonic level sensor. Involve in the development of tyre pressure monitoring systems(TPMS)

In Technology Ceramics has improve the antenna performance used in gadgets. It being used together with metal material to build the insulating walls and switching gates of transistors.

In Alternative Energy and Power Generation Nuclear power plant need ceramic materials for fuel handling and durability under atomic bombarment.

Mechanical properties of ceramics

General Ceramics material in general is relatively brittle. Its tensile strength varies greatly from very low values of less than 0.69MPa to about 7x10^3MPa for whiskers of ceramics. Only a few ceramics have tensile strength above 172MPa. For compressive strength,it is about 5 to 10 times higher than tensile strength. Many ceramics are hard and have very low impact resistance.

Mechanism for the Deformation of Ceramic Material In covalent crystals and covalently bonded ceramics,the bonding between atoms is specific and directional. When covalent cystals are stressed to a sufficient extent,they exhibit brittle fracture.

Factors Affecting the Strength of Ceramic Material Pores in the brittle ceramic materials. Size and volume fraction of pores. Flaws in processed ceramic materials.