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These materials show plastic deformations. Nevertheless, due to the inflexibility of the structure of the crystalline components there are few systems of slides for dislocations of movement and the deformation happens in very slow form. With the not crystalline (glassy) materials, the viscous fluency is the principal reason of the plastic deformation, and also it is very slow. Nonetheless, it is omitted in many applications of ceramic materials. They have high resistance to the compression and are capable of operating in high temperatures. Its great hardness makes them a material widely used like abrasive and as cutting tops of tools. The ceramic materials should be more resistant than metallic materials but its thin structure prevent from being slide, basic mechanism for a classic deformation. Ceramic materials like metals, have the same crystalline imperfections (small cracks and crevices), and all in it tends to concentrate efforts, so the metallic material fail by fracture. Its physical properties are: - Less weigh than metals, but more than the polymers. - Low electrical conductivity. - Low thermal conductivity. - Low thermal expansion and failure. The structure of ceramic crystals, which contain several atoms of different sizes, is the most complex of all structures of the materials. The bonds between these atoms are usually covalent (sharing electrons, hence the case of strong bonds) or ionic (primary bonds between oppositely charged ions, also a strong link). These links are much stronger than metallic bonds. Thus properties such as hardness or thermal and electrical resistance, are significantly higher in ceramics than in metals. The ceramics are available as a single crystal in polycrystalline form, for example, with many grains. The grain size has a major influence on the resistance and the properties of ceramics. The finer grain size (hence the term fine ceramics), the higher the resistance and toughness. The most important properties in ceramic materials are: - Color and Appearance: The color depends on the impurities (iron oxide) and additives that are used for the purpose of ornament in the building. - Density and porosity: they are all defined as similar to natural stones. The actual density is about 2g/cm3. - Absorption: is called the Specific Absorption% by weight of water absorbed on a dry piece. With it relates permeability. - The ability to receive low temperatures without suffering damage in the faces exposed to cold. - Mechanical resistance: the requirement usually refers to the compressive strength and modulus of elasticity magnitudes closely related to porosity. It likewise noted the acceptable tensile strength of ceramic material.
Article Source: http://www.bharatbhasha.net Article Url: http://www.bharatbhasha.net/technology.php/210919 Article Added on Thursday, February 4, 2010
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