Reduction of transformation temperature to alpha-alumina from ammonium aluminum carbonate hydroxide by grinding

Effect of dry and wet ball milling of ammonium aluminum carbonate hydroxide (AACH) on the transformation to alpha-alumina during heating was investigated, The dry grinding causes distortion of the AACH crystals, resulting in considerable reduction in the transformation temperature to alpha-alumina. This may be due to the easy nucleation of or-alumina during heating. In the heating the AACH ground under wet condition, significant reduction in the transformation temperature was recognized when high purity alumina balls were employed, while no noticeable change in the temperature was observed in case of zirconia balls. This is attributed to seed and dispersion effects of fine alpha-alumina powder worn from the alumina balls during grinding. alpha-alumina single phase appears in the AACH heated below 1000 degrees C after grinding with the alumina balls under wet condition. The ct-alumina powder formed from the ground and calcined AACH has a relatively large specific surface area and can be sintered at a lower temperature than that for the unground AACH.