PHYSICAL PROPERTIES OF SOME HIGH-TEMPERATURE REFRACTORY COMPOSITIONS

In the course of an investigation that involved a study of pyrochemical reactions, it was necessary to develop a refractory that could be used satisfactorily at temperatures in the range of 1800° to 2200°C. It was found that calcined magnesia (96%, MgO) or electrically fused magnesia (98% MgO) could be bonded adequately by mixing sized aggregates with 2.5%, by weight of calcined sea‐water magnesia and wetting with a 24° Bé. solution of magnesium chloride Large shapes of these compositions fired at 1450°C. were satisfactory for use in the required temperature range. A small‐scale study OF the properties of various refractory bodies showed that compositions containing relatively pure limestone or dolomite readily hydrated in water even after firing to 2100°C. and were unsuitable for refractory use. The addition of silica, alumina, zirconia, chromic oxide, or combinations of these oxides to dolomite or limestone resulted in a refractory stable against hydration. The inversion of zirconia was reduced appreciably by the addition of 5% magnesia. Bodies containing BaO·ZrO2 and CaO·ZrO2 were found to be stable after firing to 2100°C. with no inversion up to 1200°C. and with a coefficient of expansion less than that of electrically fused magnesia. Small‐ and large‐scale tests of an MgO·Cr2O3 spinel composition showed this material to be highly refractory with a low coefficient of expansion; the compound, however, dissociates and loses Cr2O3 above 1700°C. While the small‐scale tests disclosed a number of compositions which show promise as high‐temperature refractories, their full evaluation for use on a large scale was not made.