APPLICATION OF METHANE AND MICRO SILICA FOR SILICON CARBIDE SYNTHESIS 

Abstract

A new direction in silicon carbide synthesis technology, which meets resource conservation requirements, is using large-tonnage artificial waste. Highly dispersed silicon carbide (SiC) powders were synthesized using microsilica as a silicon-based raw material. It is a finely dispersed, artificial waste from the production of metallurgical silicon and ferrosilicon and carbonaceous reducing agents containing natural gas, consisting of 94% of methane (CH₄(g)) and fine wastes of oil coke (С_pc(s)). The latter is formed at the blending stage in silicon or ferroalloys production. Silicon carbide was synthesized in a resistance furnace at temperatures of 1600–1900 °C. We have designed a special device to supply a part of the carbonaceous reducing agent in a gaseous state to the reaction zone of the furnace. Its design made it possible to realize the CH₄ carbon and hydrogen dissociation on the feed route to the resistance furnace. Experiments were carried out by varying the proportion of methane in the composition of the total carbonaceous reducing agent (petroleum coke and methane) to determine the optimal synthesis conditions and achieve the maximum yield of SiC. While maintaining the total amount of carbonaceous reducing agent required by the stoichiometric ratio to reduce silicon with carbon, the proportion of CH₄(g) increased from 0.15 to 0.60 of the total amount of carbon, and С_pc(s) decreased from 0.85 to 0.40, respectively. It is shown that lowering the petroleum coke proportion to 40% due to methane does not reduce the yield and quality of synthesized silicon carbide. Analysis of the chemical composition of the synthesized powders demonstrates the relatively high yield of silicon carbide, that is 69.2–72.8 wt.%, and the maximum value is reached at CH₄(g) = 0.30 and С_pc(s) = 0.70. The share of other impurities is free carbon (21.6–25.3 wt.%); silicon (0.8–1.3 wt.%) and impurities of metal oxides (1.8–3.4 wt.%). Electron microscopy found that the size of the synthesized particles ranges from several tens of nanometers to several hundred microns. The bulk of the particles has a dimension of fewer than 100 μm. Micro- and nanopowders of silicon carbide synthesized in this way belong to the 4H, 6H, and 3C polytypes confirmed by Raman spectroscopy and X-ray phase analysis. The proposed silicon carbide synthesis method will reduce production costs and open prospects for controlled regulation of this product's properties.