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First we will start with the definition of refractories and ceramics. Refractories and ceramics are non-metallic materials capable of maintaining physical and chemical stability at high temperatures. ...
The Making of Refractory Materials
Chart # 1
The first step in processing ceramics is crushing of the raw materials. ...
The second process of shaping ceramics is plastic forming. ...
Finally the third process in shaping ceramics is pressing. ...
Structure of Refractories Materials
A refractory is a type of ceramic so I’ll refer to ceramics once again. ... Consequently, the properties of ceramics are significantly higher than those for metals, particularly their hardness and thermal and electrical resistance.
Ceramics are available as a single crystal or in a polycrystalline form, consisting of many grains. ... The finer the grain size the higher the strength and toughness- hence the term fine ceramics.
Among the oldest raw material for ceramics is clay, a fine-grained sheet like structure, the most common being kaolinite. ...
Another major raw material for ceramics is flint and feldspar. ... The types of ceramics I’ll be talking about are carbides. ... Cerments are combinations of ceramics bonded with a metallic phase. Introduced in the 1960’s , they combine the high-temperature oxidation resistance of ceramics and the toughness, thermal-shock resistance, and ductility of metals. ... Cerments can be regarded as composite materials and can be used in various combinations of ceramics and metals bonded by powder-metallurgy techniques.
General Properties of Refractory Materials
Compared to metals, ceramics have the following relative characteristics: brittle, high strength and hardness at elevated temperatures, high elastic modulous, low toughness, low density, low thermal expansion, and low thermal and electrical conductivity. However , because of the wide variety of ceramic material composition and grain size, the mechanical and physical properties of ceramics vary significantly. For example, the electrical conductivity of ceramics can be modified from poor to good, which is the principle being semi-conductors.
Because of there sensitivity to flaws, defects, and cracks, the presence of different types of levels of impurities, and different methods of manufacturing, ceramics have a wide range of properties. ...
Although there are exceptions and unlike most metals and thermoplastics, ceramics generally lack impact toughness and thermal shock resistance because of their inherent lack of ductility. ... In addition to undergoing fatigue failure under cyclic loading, ceramics exhibit a phenomenon known as static fatigue. ... Some methods include:
a) Heat treatment and chemical tempering
b) Laser treatment of surfaces
c) Coating with ceramics with different thermal expansion coefficients
d) Surface finishing operations
Significant advances are being made in improving the toughness and the properties of ceramics which include; control of purity and structure, use of reinforcements, emphasis on design of advanced methods of stress analysis in ceramic components, and the processing of raw materials. ... Thermal conductivity of ceramics, as well as other materials, decreases with increasing temperature and porosity because air is a poor thermal conductor.
Approximate Word count = 2317
Approximate Pages = 9.3
(250 words per page double spaced)
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