Oxidation of silicon carbide and the formation of silica polymorphs

Abstract

The oxidation of both single crystal and relatively pure polycrystalline silicon carbide, between 973 and 2053 K, resulted in the formation of cristobalite, quartz, or tridymite, which are the stable crystalline polymorphs of silica (SiO 2 ) at ambient pressure. The oxide scales were found to be pure SiO 2 with no contamination resulting from the oxidizing environment. The only variable affecting the occurrence of a specific polymorph was the oxidation temperature. Cristobalite was formed at temperatures ജ1673 K, tridymite between 1073 and 1573 K, and quartz formed at 973 K. The polymorphs were determined using electron diffraction in a transmission electron microscope. These results were further confirmed using infrared and Raman spectroscopies. Cristobalite was observed to grow in a spherulitic fashion from amorphous silica. This was not the case for tridymite and quartz, which appeared to grow as oriented crystalline films. The presence of a thin silicon oxycarbide interlayer was detected at the interface between the SiC substrate and the crystalline silica using x-ray photoelectron spectroscopy.

Crystallization kinetics for SiO2 formed during SiC fiber oxidation in steam

“…During SiC oxidation SiO 2 crystallization starts between 700 and 1400°C . The wide range in temperature is due to the extreme sensitivity of silica crystallization to impurities, and to H 2 O and other gases in the oxidizing environment .…”

Synthetic fayalite Fe2SiO4 by kinetically controlled reaction between hematite and silicon carbide

“…). The high‐temperature passive oxidation of silicon carbide is known to proceed via formation of amorphous silica which crystallizes to different polymorphs of silica (cristobalite, tridymite, and quartz) at higher temperatures and longer treatment time . It has also been reported that the reduction of fayalite in H 2 at temperatures below 1100°C yields metallic Fe co‐existing with amorphous silica .…”

Tailoring crystallinity and configuration of silica nanotubes by electron irradiation

“…It is well known that crystalline phases of SiO 2 such as quartz, tridymite, and cristobalite on SiC substrate is produced by the oxidation of SiC substrate at temperatures higher than 700°C [27]. At temperatures above 1200°C, the initially amorphous SiO 2 crystallizes, beginning at the oxideatmosphere interface, and then b-cristobalite crystals appear [28].…”

“…The structure of SiO 2 nanotube begins to show amorphization after as little as 20 s irradiation, is mostly amorphous after 1 min, and appears completely amorphous after 4 min under these beam irradiation conditions. Quartz and silica glass are stable, whereas a-cristobalite is unstable, at room temperature [27]. It is therefore relatively easy to amorphize cristobalite nanotubes by electron beam irradiation.…”