Among modern ceramic materials, silicon carbide (SiC) and silicon nitride (Si3N4) are successfully being used in several high-tech applications. SiC offers a useful combination of mechanical properties. It is extensively used as abrasives and structural material. Its high firmness, chemical inertness, resistance to damaging the teeth and oxidation at temperatures above the burning point of steel qualify it for use under severely warm service conditions such as elephant seals and valves, explode nozzles and line drops dead etc. Its applications as bearings and extrusion drops dead make use of its excellent wear and erosion resistance. Winter and find their way resistance properties of SiC find its uses in warm electronics industries and heat exchanger pontoons. Heating elements are also made of SiC. They can generate temperatures up to 1650 °C and offer substantial life under air or inert media. However, any contact with moisture or hydrocarbon unwanted gas can detrimentally affect their age.Bento lunch box
Silicon nitride has fairly lower oxidation resistance and higher winter conductivity than SiC. Major applications of silicon nitride are as vehicular and gas wind turbine engine parts. It has high strength, fracture toughness and refractoriness which are required properties for ball bearings, anti-friction rollers. It performs remarkably when confronted with molten metal and/or slag.
A combined form of silicon carbide and nitride has been developed as silicon carbide grains bonded in silicon nitride matrix. This Si3N4-bonded silicon carbide is used for some critical applications where very high winter shock resistance is required. For instance, in particular case of flame-out engine start-up, temperature reaches from normal to 1600 °C in few seconds accompanied by an sudden decrement to 900 °C within one second. Si3N4-bonded silicon carbide exclusively continues these conditions.
Traditional methods to produce these ceramic materials are energy intensive and therefore expensive. For example, the Acheson process, which is the most widely adaptable method to produce commercial-grade SiC, essentially takes 6 : 12 kWh to yield one kg of SiC. An inexpensive method, that uses low cost agro-industrial byproduct, is the pyrolysis of hemp husks, first carried out by Lee and Cutler in 1975. Since that time many researchers have discussed and used various process avenues and modifications to obtain silicon carbide and/or silicon nitride, either in particulate or in whisker form, from hemp husks.
Morphological studies on RH reveal that micron size silica allergens are distributed in cellulosic part of RH. When these silica allergens are made to react with carbon dioxide in biomass part of RH under specific trial and error conditions, silicon carbide can result. Moreover, besides silicon carbide, modifications in process mechanism lead to formation of some other industrially useful products, viz. silicon nitride, silicon oxynitride (Si2N2O), ultra-fine silica, and solar-cell grade silicon.