CORROSION OF CERAMIC SILICON CARBIDE IN HYDROFLUORIC ACID

Abstract

Silicon carbide usable in mechanical or electrical engineering is produced in various purity grades and exhibits a large number of crystal structure variants. As for use in the chemical field, it is commonly stated that it is highly resistant in acid media but not suitable for use in alkaline media. This paper discusses the resistance of compact silicon carbide to hydrofluoric acid. The compact silicon carbide has been prepared by sintering using the SSiC method with or without binders based on scandium oxide Sc₂O₃ and calcium fluoride CaF₂. The purest silicon carbide sample of cubic 3C structure sintered without a binder was almost insoluble in hydrofluoric acid. It has been shown, however, that pure silicon carbide is perfectly insoluble in hydrofluoric acid irrespective of the structure variants detected in the samples (3C, 4H, 6H, 15R). The corrosion stability of the compact ceramics is affected by the residual SiO₂ content (together with other impurities) in imperfect SiC preparations, and it is influenced by the choice and chemical properties of the chosen ceramic binder as well.

Keywords

• silicon carbide
• hydrofluoric acid
• corrosion resistance