Antioxidation Mechanism of Si-SiC Oxidation Inhibitor for Grain-oriented Silicon Steel

Abstract

Antioxidation mechanism of a newly developed oxidation inhibitor of refractory powder mixture composed of SiO₂, Si, SiC, synthetic mica, colloidal silica, surface active agent, and coking bond has been investigated.
During heating, Al₂O₃ is formed as a result of the decomposition by Si (metallic silicon) of mullite (3Al₂O₃·2SiO₂) contained in refractory powder. Furthermore, the fine SiC powder is oxidized and changes gradually to a protective cristobalite-SiO₂ (C-SiO₂) layer which acts as an excellent diffusion barrier to oxygen from atmosphere. The protective C-SiO₂ is not formed from the C-SiO₂ which is added in the oxidation inhibitor but is formed through the oxidation process of the SiC.
On the other hand, Al₂O₃ which is formed by the decomposition of mullite becomes Al₂O₃·SiO₂ in combination with SiO₂. On the steel surface, however, Al₂O₃ becomes highly protective FeO·Al₂O₃or 3FeO·Al₂O₃·3SiO₂ layer and, at the same time, it prevents the formation of a low melting point material such as fayalite (2FeO·SiO₂).
It has been clarified that this oxidation inhibitor exhibits the excellent antioxidability due to superposed effect of above-mentioned reactions.