Influence of pellet composition and structure on carbothermic reduction ofsilica

The melting zone in a cupola has temperatures greater than 1773 K and a red ucing atmosphere. This condition is suitable for the carbothermic reduction of silica. The key to the applicability of carbothermic reduction of silic a for ferroalloy production is rapid in situ production of SiC and its subs equent dissolution in the hot metal. The main objective of this investigati on was to study the kinetics of the carbothermic reduction process and dete rmine the optimum parameters for rapid and complete in situ conversion of s ilica to SiC. At temperatures above 1773 K, the key reactions in the carbot hermic reduction process are (1) SiO2 (s) + CO (g) = SiO (g) + CO2 (g), (2) SiO (g) + 2C (s) = SiC (s) + CO (g), (3) C (s) + CO2 (g) = 2CO (g). To mee t the objective of this study, conditions must be such that the surface rea ctions occurring at the carbon and silica surfaces are rate limiting and th e entire silica is converted to SiC. Pellet composition and structure in te rms of carbon to silica ratio, their particle sizes, and compaction pressur e that ensure surface reaction is rate controlling were determined. The gas -solid reaction kinetics was mathematically modeled in terms of the process parameters. The reaction kinetics improved by reducing both carbon and sil ica particle sizes, However, below a certain critical particle size, there was no significant improvement in the reaction kinetics. For complete conve rsion of SiO2 (s) to SiC (s), excess carbon and critical porosity are neces sary to ensure that the entire SiO (g) generated by Reaction [1] is consume d via Reaction [2] within the pellet.