Carbothermal Reduction of Quartz in Different Gas Atmospheres

This article examines the influence of gas atmosphere on the synthesis of silicon carbide by carbothermal reduction of quartz. The quartz was crushed to < 70 mu m, uniformly mixed with graphite and pressed into pellets. Reduction was studied in isothermal and temperature-programmed reduction experiments in a tube reactor in argon, hydrogen and Ar-H-2 gas mixtures. The concentrations of CO, CO2, and CH4 in the off gas were measured online using an infrared gas analyzer. The samples after reduction were characterized by X-ray diffraction, scanning electron microscope, and LECO analyzer. The carbothermal reduction of quartz in hydrogen was faster than in argon. Formation of silicon carbide started at 1573 K (1300 A degrees C) in argon, and 1473 K (1200 A degrees C) in hydrogen. Synthesis of silicon carbide in hydrogen was close to completion in 270 minutes at 1673 K (1400 A degrees C), 140 minutes at 1773 K (1500 A degrees C), and 70 minutes at 1873 K (1600 A degrees C). Faster carbothermal reduction rate in hydrogen was attributed to the involvement of hydrogen in the reduction reactions by directly reducing silica and/or indirectly, by reacting with graphite to form methane as an intermediate reductant.