Abstract
Decomposition of coprecipitated (Cr-Al) hydroxides was studied with special emphasis on the crystallization and composition of the corundum type solid solution.
Temperature of crystallization of the corundum phase increased with increasing Al content. The corundum phase contained higher Cr/Al ratio than in the starting coprecipitate for all the compositions studied, though more Al was accommodated with increasing temperature.
It was shown that at least 1300°C is necessary to obtain a homogeneous solid solution with the Cr/Al ratio equivalent to that in the coprecipitate.
The comparison of the decomposition experiments for the aged and non-aged coprecipitates indicates that boehmite produced by the aging of coprecipitates accelerates the crystallization of the corundum phase.
Considerable compositional deviation of corundum phase from those in the available phase diagram is explained as due to the difficulty in getting an equilibrium state. This point of view is supported by the results of prolonged isothermal heating of coprecipitates.
