Plasma Chemistry and Plasma Processing, Vol. 20, No. 4, 2000 Mathematical Modeling of Silica Anode Decomposition Tony Addona, 1 P. Proulx, 2 and R. J. Munz 1 Received September 1, 1999; revised March 1, 2000 The volatilization of quartz in a transferred arc plasma followed by quench and recondensation is a promising route to the production of fumed silica. In this work, an existing model of a transferred arc was modified and combined with a newly developed model of a molten silica anode to predict the behavior of a transferred arc evaporator as a function of current and plasma gas flow rate. The model predicts temperature, current, and flow fields in both the plasma and anode as well as evapor- ation rates. Although quantitative agreement with experimental results was not possible because of insufficient property data for silica at high temperature, the results were within an order of magnitude of those measured experimentally. The model developed is useful for the design and scaleup of this type of reactor. KEY WORDS: Thermal plasma; transferred arc; fumed silica; modeling. 1. INTRODUCTION The first step in the thermal plasma production of fumed silica [an ultrafine silica powder with unique properties (1) ] is the decomposition of a SiO 2 source (usually quartz) according to the following reaction: SiO 2 → SiO (g) C 1 2 O 2 (1) The energy required is supplied by a thermal plasma heat source and a reducing agent such as C, Si, or H 2 is also used to facilitate the decompo- sition. The silicon monoxide vapor [SiO (g) ] formed is then rapidly quenched using an oxidizing agent, such as air or steam, to induce fumed silica generation. Because of their high efficiency and potential for scale-up, dc arc torches have received the most attention as thermal plasma generators for this process. Previous systems using dc nontransferred arc torches have 1 Department of Chemical Engineering, McGill University, 3610 University Street, Montreal, Quebec, H3A 2B2. email: rmunz@chemeng.lan.mcgill 2 Department of Chemical Engineering, Universite ´ de Sherbrooke, Sherbrooke, Quebec. 521 0272-4324001200-0521$18.000  2000 Plenum Publishing Corporation