Generally they combine good corrosion resistance with ease of manufacture by

Generally they combine good corrosion resistance with

This preview shows page 16 - 18 out of 79 pages.

Generally they combine good corrosion resistance with ease of manufacture by moulding to shape and relatively low cost. Their properties can be matched to almost any design problem with the exception of high- temperature environments. Some of these materials can match the strength of alloy steels on a weight basis, and are now replacing metals for many traditional applications. Synthetic adhesives are also being used for the joining of metallic components even in highly stressed applications.
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~ Page 17 of 79 ~ NATURAL NON-METALS Below is a basic introduction to the applications for some of the materials found in this diverse group. 1. CERAMICS These are inorganic materials, originally just clay-based materials. They are produced by baking naturally occurring clays at high temperatures after moulding to shape. They tend to be brittle, relatively stiff, stronger in compression than tension, hard, chemically inert and bad conductors of electricity and heat. The non-glasses tend to have good heat and wear resistance and high-temperature strength. Specially selected clays are used to make heat-resistant bricks for furnace linings. Kaolin ‘china’ clays are used to make porcelain mouldings for high -voltage insulators and high- temperature-resistant cutting tool tips. Commercially produced ceramics comprising metal oxides, carbides and nitrides are also widely used for high-performance tool tips because of their extreme hardness, resistance to abrasion and their ability to work at high temperatures without softening. Unfortunately, ceramic materials are all brittle and often require to be bonded with other materials to form composites to improve their strength properties. Ceramics include: (i) GLASSES: Soda lime glasses, borosilicate glasses, pyroceramics. Glasses are hard-wearing, abrasion resistant materials with excellent weathering properties. They are used in electrical insulator applications, laboratory equipment, optical components in measuring instruments and, in the form of fibres to reinforce polymers. Glass is made by melting together the naturally occurring materials: silica (sand), limestone (calcium carbonate) and soda (sodium carbonate). (ii) DOMESTIC CERAMICS: Porcelain, vitreous china, earthenware, stoneware, cement. Examples of domestic ceramics and glasses abound in the home in the form of cups, plates and glasses. (iii) ENGINEERING CERAMICS: Alumina, carbides, nitrides. Because of their hardness and abrasion resistance, such ceramics are widely used as cutting tool tips. (iv) NATURAL CERAMICS: Rocks. 2. RUBBER This is used for hydraulic and compressed air hoses and seals. Naturally occurring latex is too soft for most engineering uses but is used widely for vehicle tyres when it is compounded with carbon black. 3. SILICON This is used as an alloying element and also for the manufacture of semiconductor devices.
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