Silica Decomposition Using a Transferred Arc Process

Abstract

A novel process for silica decomposition consisting of transferring a thermal arc directly to a silica anode was investigated. The effects of current (150−250 A), plasma gas flow rate (10−20 L/min of Ar), and plasma gas composition (0−2.8% H2) on the rate of decomposition were examined. The decomposition rate ranged from 0.09 to 1.8 g/min and was determined to be heat-transfer-limited, with decomposition occurring below the arc root where the anode surface attained its boiling point. The decomposition rate was independent of plasma gas flow rate, suggesting that convective heat transfer was reduced significantly by the counterflow of decomposition products (SiO(g) and O2) from the surface. Increasing the current increased the decomposition rate because heat input to the anode because of electron flow and arc radiation increased. Adding H2 to the plasma gas increased the decomposition rate because of an increase in radiative heat transfer to the anode, a reduction in the theoretical energy requirement for decomposition, and a consumption of O2 which lowered the silica boiling point. The fumed silica produced had properties typical of commercial fumed silica products.

Silicon induced in situ hole formation in optical fibers

“…Several potential gas phase species could exist: The prevalent gaseous species formed is SiO as given by reaction (3) based on thermodynamic calculations for low oxygen partial pressures [12][13][14]. In addition, for silica in an inert atmosphere, Widjaja and Musgrave [13] state that at temperatures above 1100 K, the oxide film is found to decompose yielding SiO(g).…”

Recovery of Turkish Oil Shales by Electromagnetic Heating and Determination of the Dielectric Properties of Oil Shales by an Analytical Method

“…Decarbonation of dolomite begins at 777.7 °C . Silica decomposition in an inert atmosphere starts at 2800 °C and carbothermic reduction of silica starts around 1530 °C …”

“…27 Silica decomposition in an inert atmosphere starts at 2800 °C and carbothermic reduction of silica starts around 1530 °C. 28 Presence of clays and fine sands in the matrix favor increased rates of fuel formation. Rock minerals such as pyrite, calcite, and smectite also favor fuel-forming reactions.…”

Transferred Arc Production of Fumed Silica: Rheological Properties

“…Previous work by Addona and Munz (1999) demonstrated the technical feasibility of producing fumed silica using this method, but was unable to demonstrate the special rheological properties of the powder. The most important characteristic of fumed silica is the presence of hydroxyls on the surface of the partic1es, in the form of isolated hydroxyl groups, hydrogen-bonded hydroxyl groups and siloxane groups.…”