Abstract
Recent work on sintering in the presence of a liquid phase has suggested that high temperature glassy bonds have greater possibilities. This whole work has been designed with bond materials which would produce east refractories, so that complex designs may be produced economically, The formation of bond will be guided roughly by the phase diagram, but may take place at a much lower temperature due to formation of eutectic mixtures by the minute traces of impurities whose presence may be difficult to determine. In this investigation an attempt has been made to follow the process of bond formation indirectly, in ethyl silicate, sodium silicate and potassium silicate bonded alumina and alumino-silicates, by following the thermal expansion characteristics, the refractoriness under load at high temperatures, and room temperature transverse bend strength developed during firing at different temperatures. The results have further been correlated with studies on microstructures and X-ray patterns. Above 1000°C the bond formed new compounds both crystalline and glassy. The silica bond produced a stable alumino-silicate compound, whereas the alkali silicates produced a glassy bond from which precipitation of microcrystalline phases occurred. Although some of the alkali silicates produced a room temperature bond for alumina equal to that of ethyl silicate, for sillimanite the ethyl silicate produced the best bond. Both the alumino-silicate compound and any precipitated phase were too fine to be definitely identified, but indirect evidence indicated their presence. At high temperatures the sodium silicate bond was best for alumina, and potassium silicate for sillimanite test pieces. The implications of the results from the viewpoint of the behaviour of fired and unfired refractories have been discussed and the probable reasons compared with the existing ideas.