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Material Science

Ceramics

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Introduction to ceramics Ceramics are inorganic, non‑metallic

materials, which are processed and may be used at high temperatures.

They consist mainly of silicon chemically combined with non‑metallic elements such as oxygen, carbon and nitrogen and with metallic compounds

hard and brittle low tensile strengths high compressive strengths and the ability to retain th

is strength at high temperatures

Examples: cements, glasses, refractories and abrasives

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Types of ceramics:

Crystalline ceramics Amorphous ceramics Bonded ceramics

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Crystalline ceramics I These are widely used for cutting tools

and abrasives They may be single‑phase materials

such as aluminium oxide (corundum), or mixtures of such compounds

have a greater refractoriness than most metals (Tantalum carbide 3890 oC)

Hardness of some ceramic materials are very high (same as diamond)

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Crystalline ceramics II Glazed porcelain insulators are used for

electrical insulation purposes as supporting high‑ and medium‑voltage overhead electric cables

The hard glaze prevents the insulators from 'weathering'. Any dirt deposited on hard glazed porcelain is quickly washed away by rain as it cannot adhere to the smooth surface.

Unglazed ceramics are used for wire‑wound resistors and for heating elements.

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Crystalline ceramics III

Traditional shaping methods for ceramics consist of :

hand and machine moulding powder pressing the extrusion and rolling of a

plastic, clay‑water mixture

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Amorphous ceramics This group of for ceramic materials is not

crystalline and the molecules are not arranged in regular geometric patterns

This group of ceramic materials includes the 'glasses' as used for such applications as glazing, mirrors, optical lenses, reinforcement fibres GRP products and optical fibres for data transmission.

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Bonded ceramics This group includes the 'clay' products These are complex materials containing

both crystalline and amorphous constituents in which individual crystals are bonded together by a glassy matrix after 'firing‘

The uses of ceramic products from this group include electrical insulators and refractories for furnace linings.