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Reactions between refractory metals and silica at elevated temperature De Cleene, Michel Louis André

Abstract

An investigation was conducted on the reaction between silica glass and the refractory metals, Mo, V, Nb, Ta, Ti and Zr. The metals were heated to 1650°C under vacuum (5x10⁻⁴m.m. of Hg.) in contact with the silica. The interface was examined metallographically. The formation of compounds was examined by X-ray diffraction technique. A liquid layer was formed by reaction of the metals with silica. This reaction was responsible for bonding between the two phases. Vanadium and tantalum showed the best bonding characteristics. Niobium formed only a fair bond. In the case of molybdenum and titanium little adhesion occurred. Experimental observations and theoretical considerations indicated that in most cases the liquid was a low fusible silicate. The nature of the reaction was found to be essentially oxidation of the metal followed by solution of the oxides in the glass. Vanadium oxides are rapidly dissolved in silica causing extensive corrosion of the metal. The oxides of niobium and tantalum do not dissolve so rapidly. Only molybdenum showed good corrosion resistance under experimental conditions. The oxides found at room temperature were respectively VO₀․₉, Nb₂O₅, Ta₂O₅ and MoO₉. X-Ray data showed that tantalum - silica interface contained other species that could be silicon, silica, sub-oxides, silicides and crystallised silicates.

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