MULLITE FORMATION, HIGH-TEMPERATURE PROPERTIES OF ANDALUSITE- ALUMINA BASED LCC AND ULCC

摘要

Mullite is an attractive bonding phase in alumina castable because of its high melting point (1850°C). It is also well-known that mullite contributes to good mechanical properties, low thermal conductivity, low thermal expansion and good chemical stability.The aim of this work is to investigate the mullite formation in the bond phase of andalusite-alumina based castables via the measurement of the high-temperature strengths of various ULCC and LCC. The influence of microsilica, andalusite fines and cement contents was described. It seems that a compromise in the microsilica and fine andalusite contents has to be found in order to have optimum hot strength properties. It is also shown that andalusite-alumina based castables are less sensitive to the addition of cement than alumina or bauxite based castables. A SEM analysis has showed the presence of an interface in the borders of the andalusite grains. A diffusion of CaO from the matrix toward the grains might limit the content of CaO in the matrix, increasing the high-temperature strength properties of the castables.