Silicon grades

Comments Stat-Kon grades contain carbon fibre Lubricomp has PTFE. mg = moulding grade, CF = carbon fibres, GS glass spheres, AF = aramid fibres. Si = silicone. Grades PF-1008 (40%GF) PF-1006 FR/E (30%GF) also available. 

Regular grade silicon (99%) costs about 0.50/g. Silicon 99.9% pure costs about 50/lb hyperpure silicon may cost as much as 100/oz. 

Soft magnetic materials are characterized by high permeabiUty and low coercivity. There are sis principal groups of commercially important soft magnetic materials iron and low carbon steels, iron—siUcon alloys, iron—aluminum and iron—aluminum—silicon alloys, nickel—iron alloys, iron-cobalt alloys, and ferrites. In addition, iron-boron-based amorphous soft magnetic alloys are commercially available. Some have properties similar to the best grades of the permalloys whereas others exhibit core losses substantially below those of the oriented siUcon steels. Table 1 summarizes the properties of some of these materials. 

Iron—Aluminum and Iron—Aluminum—Silicon Alloys. The influence of aluminum on the physical and magnetic properties of iron is similar to that of silicon, ie, stabilization of the bcc phase, increased resistivity, decreased ductility, and decreased saturation magnetization, magnetocrystalline anisotropy, and magnetostriction. Whereas Si—Ee alloys are well estabHshed for electrical appHcations, the aluminum—iron alloys have not been studied commercially. However, small (up to ca 0.3%) amounts of A1 have been added to the nonoriented grades of siHcon steel, because the decrease in ductiHty is less with A1 than with Si. 

In the past, all grades of refined ferromanganese were made by various modifications of multistep silicon reduction processes. Depending on the carbon content desired in the product, a manganese ore and lime mixture was allowed to react with the silicon in silicomanganese or low carbon silicomanganese in an open, electric-arc furnace. The equilibrium reaction is... 

Molten silicon is not a semiconductor, and has no commercial use, although because of the high heat of fusion, it has been considered as a heat storage medium. The Hquid (molten) siUcon properties summarized in Table 6 are nevertheless of importance because these affect single-crystal growth, an operation through which essentially all semiconductor-grade siUcon must pass. 

Refining. In order to produce silicon that meets the requirements of the chemical, ie, siUcones, and primary aluminum markets, the siUcon produced in the arc furnace requires further purification. The quaUty of siUcon for the chemical siUcones industry is critical with respect to the levels of aluminum and calcium present, and the primary aluminum grade of siUcon requires low levels of calcium, iron, and phosphoms. The impurity requirements for the secondary aluminum market are not as stringent, so long as the siUcon content is >98.5%. 

The electronics market uses sihcon as trichlorosilane, which is decomposed with hydrogen at high temperatures to produce semiconductor-grade sihcon (see Silicon compounds). 

Silicon Tetrachloride. Most commercially available sihcon tetrachloride is made as a by-product of the production of alkylchlorosilanes and trichlorosilane and from the production of semiconductor-grade sihcon by thermal reduction of trichlorosilane. 

Silicate esters are used ia the production of coating and refractories and in some semiconductor manufacturing operations. A broad range of purity grades of silicon tetrachloride are available to meet the requirements of these different appHcations. 

Feasibility of the Silane Process for Producing Semiconductor Grade Silicon,]e.. Propulsion Laboratory Contract 954334, June 1979. 

Reduction/Reaction with Hydrogen. Tetraduorosilane reacts with hydrogen only above 2000°C. Tetrachlorosilane can be reduced by hydrogen at 1200°C. Tetraio do silane can be reduced to sihcon at 1000°C (165). Reduction of tetraduorosilane with potassium metal to sihcon was the first method used to prepare sihcon (see Silicon and silicon alloys). The reduction of sihcon tetrachloride by ziac metal led to the first semiconductor-grade sihcon (166,167). 

W. Ingle, R. Rosier, S. Thompson, and R. Chaney, Semiconductor-Grade Solar Silicon Purification Project NASA-CR-158868, Rept.-2257/12, Cape Canavral, Fla, 1979,... 

Silicon Reduction. The preparation of ferrovanadium by the reduction of vanadium concentrates with ferrosiUcon has been used but not extensively. It involves a two-stage process in which technical-grade vanadium pentoxide, ferrosiUcon, lime, and fluorspar are heated in an electric furnace to reduce the oxide an iron alloy containing ca 30 wt % vanadium but undesirable amounts of siUcon is produced. The siUcon content of the alloy is then decreased by the addition of more V2O5 and lime to effect the extraction of most of the siUcon into the slag phase. An alternative process involves the... 

Material Grade Chro-miu c m Carbon Silicon Sulfur Phos-phoms d, T- d N itrogen... 

Seal Face Combinations The dynamic of seal faces is better understood today. Seal-face combinations have come a long way in the past 8-10 years. Stellite is being phased out of the petroleum and petrochemical applications. Better grades of ceramic are available, cost of tungsten has come down, and relapping of tungsten are available near most industrial areas. Silicon carbide is being used in abrasive service. 

Some of the problems can be solved with specially selected oil grades. Another solution is synthetic oils, but cost is a problem particularly with silicone oils. Alternatives must be reviewed to match service life of the lubricant with lubrication requirements in the compressor. 

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