Silicon carbide hardness range

A wide range of applications for hard, wear-resistant coatings of electroless nickel containing silicon carbide particles have been discussed by Weissenberger . The solution is basically for nickel-phosphorus coatings, but contains an addition of 5-15 g/1 silicon carbide. Hiibner and Ostermann have published a comparison between electroless nickel-silicon carbide, electrodeposited nickel-silicon carbide, and hard chromium engineering coatings. 

Silicon carbide is a man-made mineral which has high hardness, is generally chemically inert and can be obtained in the form of refractories and special components. Refractories made from silicon carbide can be obtained with a wide range of bond systems while specialized components have a few types of bond systems. 

Silicon carbide (SiC) is the most widely used nonoxide ceramic. Its major application is in abrasives because of its hardness (surpassed only by diamond, cubic boron nitride, and boron carbide). Silicon carbide does not occur in nature and therefore must be synthesized. It occurs in two crystalline forms the cubic P phase, which is formed in the range 1400-1800°C, and the hexagonal a phase, formed at >2000°C. 

A superfinishing abrasive stone is generally vitrified bonded and has a hardness range of HRH20-70. White aluminum oxide, silicon carbide, cubic boron nitride, or diamond abrasive is used. Abrasive sizes in the JIS 300- 500 range are used for coarse finishing, while JIS 600- 1500 abrasives are used for a fine finish (Matsui and Nakasato 1965, Onchi et al. 1995, Varghese et al. 1998). 

Hardness testing of the refractories is not an everyday procedure, yet it is very useful to remember that the hardness of self-bonded silicon carbide ceramics is in the range of 20-25 GPa, the hardness of nitride-bonded silicon carbide refractories is 16-20 GPa, and the hardness of alumina ceramics is 12-16 GPa, which is three to four times higher than with dense alumina silica dense refractories. 

The abrasives used for coatings are diamond, aluminum oxide (corundum), silicon carbide, boron carbide, boron nitride, emery, flint (quartz), and garnet. These range in hardness and cost. Typically the superabrasives, synthetic diamond and cubic boron nitride, do not compete easily with the standard abrasives. 

Silicon carbide is usually offered in a size range of 16—240 grit. It is angular in shape. Silicon carbide is an extremely hard sharp grain that is more Mable than aluminum oxide. It is used in blasting of extremely hard materials, and it is expensive. 

Diamondlike Carbides. Silicon and boron carbides form diamondlike carbides beryllium carbide, having a high degree of hardness, can also be included. These materials have electrical resistivity in the range of semiconductors (qv), and the bonding is largely covalent. Diamond itself may be considered a carbide of carbon because of its chemical structure, although its conductivity is low. 

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