Studies of the Stability of High Temperature Resistant Ceramic Coating Glasses

摘要

Chemical and physical mechanisms were studied which were believed responsible for the instabilities of the glassy phase of composite glass-metal systems when subjected to elevated temperatures over prolonged periods of time. Two prominent types of glass devitrification behavior were indicated by X-ray diffraction analysis of a series of glass-metal composite specimens which had been heat treated up to 200 hours at 870°C. (l) The cyclic development, disappearance and reappearance of various diffraction peaks which indicated considerable crystalline activity, (2) For certain, glasses the early development of diffraction peaks which persisted throughout the heat treating period. This behavior indicated an equilibrium between the products of devitrification and the residual glass.nA simple barium borosilicate glass was compared with a complex glass which was composed of 70 per cent by weight of the simple glass plus five modifying oxides. When identically heat treated, it was found that the simple glass devitrified more rapidly than the complex glass, although the same crystalline products were formed.nHeat treatments on composite glass-metal specimens with glasses intermediate in composition between the simple and complex glasses revealed that at temperatures of 8l5°C and 870°C all of the glasses devitrified in a short time. However, at 760CC some of these glasses resisted initial devitrification for over 50 hours.nSingle oxide additions of CaO, ZnO, Ti02, Bi203 and Ce02 to the simple glass all delayed to some extent the initial appearance of the devitrification products found in the simple glass. On firing to form the composite glass-metal specimens ceria crystals precipitated from the ceria containing glasses and these remained as a separate phase during subsequent heat treating.nAs determined by microscopic examination, ceria additions to the simple glass had two principal effects: (1) At lower heat treating temperatures an outside layer of crystalline ceria developed, (2) Relatively low temperature melting glasses were formed which permitted the development of recognizable crystalline modifications of silica and barium disilicate at lower heat treating temperatures than the original simple barium borosilicate glass required.