Silicon Tetrafluoride

Silicon Tetrafluoride

Introduction

The main purpose of this research paper is to make an evaluation of the hazards of silicon tetrafluoride on the industrial hygiene. The silicon tetrafluoride is obtained by reducing, hot, silica or silicon halides (SiCl 4, for example) by metals such as potassium (K), calcium (Ca), magnesium (Mg), zinc (Zn) or aluminum (Al). It can be also obtained by the electrolysis of fused silica, with electrodes of carbon (C). To obtain extremely pure silicon (required for the electronics industry), it involves silicon tetrachloride (SiCl 4) purified by distillation and then reduced by zinc. Silicon tetrafluoride thus obtained is refined by the technique of zone melting and contains less than 1 part per million (ppm) impurities. It can also be converted into tetrachloride corresponding hydride (silane, SiH 4), which is then decomposed by heating. Silicon is usually in the form of crystals dark gray, very hard (can scratch the glass), structurally similar to that of diamond. It can also take the appearance of a brown microcrystalline powder of amorphous appearance (Allchin, 1994). Its density is equal to 2.35, and it melts at about 1420 ° C. Pure silicon is a semiconductor; impure, it is a good conductor of electricity. The state Division of silicon influences on its reactivity. This is essentially a tetravalent element (it admits four neighbors). When cold, the compact silicon reacts vigorously with fluorine (F 2), forming silicon tetrafluoride (SiF 4) gas, it oxidizes easily, even hot, because it is covered with a protective film of silica.

Literature Review

Industry hygiene has become a very important problem. The problem of industry hygiene is increasing day by day. There are different reasons behind the increase in the industry hygiene. Just like the other factors silicon tetrafluoride is one of them. Silicon is the most abundant electropositive element of the earth's crust. It is a metalloid with a strong metallic luster and extremely brittle (Lumby, 1975). Usually, it is tetravalent in its compounds, but sometimes is divalent, and is markedly electropositive in its chemical behavior. Furthermore, silicon compounds are known pentacoordinados and six-coordinated. The prosperity of today's electronic industry is based on silicon technologies. In addition to crystalline silicon (c-Si), polycrystalline silicon (poly-Si) and hydrogenated amorphous silicon (a-Si:H) are employed in a variety of electronic devices. Elemental silicon oil and intermetallic compounds are used as alloy members to provide greater resistance to aluminum, magnesium, copper and other metals. Metallurgical silicon with a purity of 98-99% is used as feedstock in the manufacture of organosilicon compounds and silicone resins, elastomers and oils. Silicon chips are used in integrated circuits. Photovoltaic cells for direct conversion of solar energy into electricity using wafers cut from single crystals of electronic grade silicon (Owczarski, 1981). Silicon dioxide is used as raw material for producing elemental silicon and silicon carbide. Large crystals of silicon are used for piezoelectric crystals. Fused quartz sands are transformed into silicon glass used in laboratories and chemical plants as well as electrical insulators. It uses a colloidal dispersion of silica ...