Improved conversion of silica to silicon@ using electro-furnace - comprises addn. of small amt. of magnesium silicate which improves the conversion of evaporated silicon mon:oxide

摘要

Silicon is mfd. by the conversion of quartz in an electro-furnace using a fill of preforms of fine quartz and a fine grained carbon medium as well as coarse quartz. The conversion consists of a first stage in which a coke structure with open pores is formed by the formation of Sic by reduction of fine grained SiO2. The second stage occurs in the bottom of the furnace and consists of redn. of coarse quartz by SiC under the formation of gaseous Si-oxide. The feature is that Mg-silicate is added to the preforms in a quantity which measures a Si yield improvement of at least 5 wt.%, pref. 10-20 wt.%. The furnace is operated in such a way that Mg-silicate in the upper parts is converted almost completely into Mg-carbide, pref. at a temp. below the m.pt., which converts the Si-oxide which is generated in the preforms and rises in the furnace. Also claimed are the use of other silicates in the preforms which are converted into carbides in the furnace, and a process for the formation of the preforms. USE/ADVANTAGE - The process improves the conversion yield of the process significantly without resulting in a large contamination of the end prod. by Mg, as this escapes at the end of the process. The contamination level can be made very low by using low contamination starting prods. The processes are assumed to occur as follows: MgSiO3 + 4C = MgC2 + SiO + 2CO then : MgC2 + 2SiO = Mg + 2Si + 2CO. The liq. Si is rapidly converted to the carbide : Si + C = SiC. The Mg formed is gaseous and reacts easily with the C to form new carbide : Mg + 2C = MgC2.