The contamination of nickel surfaces during oxidation in fused silica reaction vessels

Abstract

In many experiments involving the high temperature oxidation of nickel in fused silica reaction vessels the final oxidation products have been found to include silica as β-cristobalite. Prior to oxidation the nickel was decarburized by exposure to oxygen followed by hydrogen reduction of the remaining oxide film. The silicon of the silica was transferred from the vessel walls to the specimen as silicon monoxide formed by the reduction of the silica by the carbon monoxide produced during the decarburization step. The silicon monoxide was reduced at the metal specimen by residual carbon to form silicon which then dissolved in the nickel. Detectable contamination of the surface took place during subsequent oxidation when the silicon was preferentially oxidized at the surface. The reaction of carbon monoxide with the silica tube was enhanced by devitrification caused by previous high temperature (> 700° C) treatment. Contamination could be avoided if the tube was never heated above 700° C and was minimized at 900° C by more complete decarburization of the specimen.