PHYSICAL-CHEMICAL ASSESSMENT OF SILICON CARBIDE – PRODUCT OF TECHNOGENIC SILICA RECOVERY BY FUME LIGNITE SEMI-COKE

Abstract

The paper describes the conducted physical-chemical certification of silicone carbide, obtained from fine-grained charge of two kinds, which contains microsilica formed at the production of silicon and high-silicon ferrosilicium, as well as semicoke from brown coal of Beresovskii deposit of Kansk-Achinsk basin. Microsilca of both kinds contains 93.41 – 95.33 % and 91.72 – 93.00 %, 63 % of SiO 2 ; 1.96 – 3.28 % and 0.56 – 1.18 % of С своб . ; 0.30 – 0.34 % and 0.18 – 0.20 % of Si своб . ; 1.25 – 1.45 % and 1.38 – 2.32 % of (CaO + Fe 2 O3 + MnO). Microsilica has a specific surface of 21 000 – 24 000 m 2 /kg and is inclined to aggregation with the formation of spherical units with the size of 200 – 800 nm. The units consist of spherical particles with a dimensional diapason from 30 to 100 nm. Brown-coal semicoke contains 94.05 % of carbon; 9.2 % of ash; 0.2 % of sulfur; 0.007 % of phosphorus and has a specific surface of 264 000 kg/m 2 . Phase and chemical compositions of silicone carbide, its specific surface, the size and the form of carbide particles have been studied. It has been established that in both cases predominate phase is silicon carbide of a cubical structure (β-SiC), but an accompanied one is a glassy phase, formed with lime silicate, magnesium and iron. At carburizing of charge, containing microsilca of the production of ferrosilicium, α-iron accompanies to silicon carbide. At the synthesis temperature of 1923 and 1973 K and the duration of 50 and 90 minutes polymorthic transformation of β-SiC into α-SiC II occurs. The content of silicon carbide in the products of carbonization is 82,52 – 84,90 %. The authors of the work have established the viability and optimal conditions of chemical enrichment of silicon carbide: influence of hydrochloric acid with the concentration of not less than 35 % at the temperature of 353 K, ratio of Т:Ж = 1:2, durability of 3 hours. The indexes of chemical enrichment have been defined: the content of silicon carbide in the products of enrichment is 90.42 – 91.10 %, removal of impurities of metal and iron oxides of 87 – 95 %. Silicon carbide appears as micropowder with the particles of wrong form with the dimensional range of 0.2 – 1.0 um with the specific surface of 8000 – 9000 m 2 /kg.