Titanium-Containing Precipitates in Corundum of Brown Aluminous Abrasives after Heat-Treatments in Air

Abstract

The corundum grains of single crystal 60 to 80μm in size, which were prepared from commercial brown aluminous abrasives by removing their impurity phases, were heated in air at temperatures between 1, 200° and 1, 630°C for various hours. Phases of the precipitates given by the oxidation of Ti³⁺ ions in the corundum were examined by the X-ray diffraction method and by optical microscopy. Only rutile was found within the corundum crystals in any of the specimens, although β-Al₂TiO₅ is stable above about 1, 300°C. β-Al₂TiO₅ was found on the surfaces of the corundum crystals after long heat-treatments at high temperatures. The β-Al₂TiO₅ was given by the titanium moving out to the surfaces from the rutile which had precipitated within the corundum crystals. The cause of the fact that the rutile did not give β-Al₂TiO₅ within the corundum crystals was discussed. Formation of β-Al₂TiO₅ from a mixture of Al₂O₃ and TiO₂ powders was found to be supressed by the addition of a small amount of CuO. A trace of Cu was contained in the corundum grains.