ABSTRACT
The ammoniated hydroxide later accompanies the silica component to form silicon hydroxide, and it is assumed that the two components are coprecipitated. Generally, ammonia solution is used as a precipitant in the mixed solution of two components. On its addition, the pH of the medium changes from acidic to neutral to basic. As a result, the solubility of the aluminum component decreases to initiate the formation of gelatinous aluminum hydroxide colloidal precipitates. Low and McPherson measured the unit cell parameter of mullite formed at different temperatures and plotted unit cell edge versus composition. The variation in cell volume versus cell edge finally showed the composition of mullite as a function of temperature. Colomban noted DTA traces of typical monolithic alumina gel and fine gel powder obtained from AlOBu using various alkoxides by hydrolysis conditions. DTA traces of these samples show that a high temperature exothermic peak corresponds to the formation of the a-alumina phase.
