Molten glass corrosion resistance of new Mo-Ru-Si compounds

摘要

In spite of a very promising potential for a large field of high temperature applications, MoSi{sub}2 shows only a limited resistance against molten glass corrosion. Efforts to improve the performance of MoSi{sub}2-based materials led to the investigation of the Mo-Ru-Si phase diagram. The isothermal section at 1673 K revealed five new intermetallics with original structures. The crystallographic study of two of them was made using standard and synchrotron X-ray measurements combined with KKR (Korringa-Kohn-Rostoker) calculations. The use of such total energy electronic structure calculations was helpful in order to localize accurately Mo and Ru in the new compound β-Mo{sub}26Ru{sub}47Si{sub}27. This compound crystallizes in P4/mmm space group with a = 9.2164(1) A, c = 2.88721(1) A, Dx = 9.69(1) g/cm{sup}3. The structure has been refined by the Rietveld method down to R{sub}p = 1.1%, R{sub}B = 12.0 %, R{sub}F = 8.7% for 6814 ob-served data and 271 independent reflections. Moreover, electrochemical techniques enabled the determination of the redox properties of the new intermetallic compounds. It has been shown that, in contact with molten glass at 1623 K, Mo-Ru-Si compounds were subjected to electrochemical reactions leading to the simultaneous oxidation of silicon and molybdenum. The progressive superficial depletion of Si and Mo resulted in the more or less rapid formation of a thick, porous and low adherent Ru-layer. Consequently, the results showed that Ru-additions had no positive effect on the molten glass corrosion resistance of MoSi{sub}2-based materials. The formation of a porous Ru-layer should even accelerate the degradation kinetics through galvanic coupling occurring between the superficial layer and the bulk material.