Characterization of Abrasion Powder Worn from Alumina Balls by Wet Milling and Its Phase Transformation during Heating

Abstract

Abrasion test of high and low purity alumina balls is conducted in different types of mills under wet condition. The abrasion powder produced by abrasion of high purity alumina balls gave extremely large value of specific surface area over 30m2/g. The powder includes α-Al(OH)3 of gibbsite type, while α-Al(OH)3 is not included in an abrasion powder worn from the low purity alumina one. A considerable amount of amorphous aluminum hydroxide is contained in both abrasion powders. The amount of aluminum hydroxide in the powder increased as the milling becomes moderate and as the balls' size is small. The aluminum hydroxide in the abrasion powder is transformed into a single phase of α-alumina without forming κ- and θ-alumina phases at a relatively low temperature of about 900°C. This is completely different from the phase transformation of an ordinary powder of α-Al(OH)3. The formation of α-alumina from abrasion powder at such low temperature is attributed to a seed-effect of fine α-alumina powder mixed uniformly in the abrasion powder. An abrasion powder worn in alcohol also enables us to sinter at comparatively low temperature.