Aptitude evaluation of alumina coated with aluminum borate crystals as filter material for molten aluminum

Abstract

We studied fabrication of improved alumina tube filter component coated with aluminum borate crystal 9Al₂O₃·2B₂O₃ (9A2B) for filtration of molten aluminum. The 9A2B crystals were not be formed by heating an Al₂O₃–B₂O₃–CaO glass frit. It was necessary to add Al₂O₃ material to the frit for forming the 9A2B crystals on alumina grain. XRD results showed that 9A2B crystals were formed at 1100°C and grown to 1200°C, and more grown into cooling down process from 1200 to 1000°C. As compared with the conventional tube filter coated with boric silicate glass, the alumina filter components had high strength until 1200°C, small thermal expansion, little pollution to molten aluminum, and little corrosion by not wetting to molten aluminum.