ARTIFICIAL SILLIMANITE AS A REFRACTORY1

Abstract

Alumina-silica mixtures were prepared by fusing quartz, china clay, fire clay, and alumina in the electric furnace. When alumina is less than 68%, crystalline sillimanite (3Al2O3.2SiO2) with glass is produced. This material is not very resistant to loads at high temperatures because of the early fusion and internal lubricating action of the glass surrounding the crystals. Above 68% alumina, crystalline corundum appears am1 the glass is practically absent. This latter composition is very resistant to high-temperature loads when ail interlocking, recrystallized bond is developed. This material is not affected materially by acid slags, but it cannot resist basic slags. However, the dense structure of a brick of material above 68% Al2O3 causes less slagging in a laboratory bath test than silica brick. The laboratory made sillimanite-corundum brick withstood higher temperatures than the best silica, magnesia, chrome, fire clay, or zirconia brick even though the cone of fusion of the former is less than that of MgO, Cr2O3 or ZrO2. More and better service tests with a large number of brick fired in large kilns is needed to follow up this laboratory work.