Dense mullite ceramic bodies and process of manufacture

Claim 1

The process for converting a molecularly intermixed mixture of alumina (Al 2 O 3 ) and silica (SiO 2 ) to dense mullite bodies, said mixture having been formed by precipitating a gel composed essentially of aluminum and silicon hydroxides in substantially stoichiometric proportions to form mullite (Al 6 Si 2 O 13 ), and dehydrating said gel to obtain said mixture, comprising: a. having present in said mixture an amount of molecularly intermixed titania (TiO 2 ) of at least 0.25% but below 1.50% titania based on the weight of the mullite which can be formed therefrom; b. calcining said mixture at a temperature within the range from 900° to 1150° C. to convert said mixture to mullite in intimate association with titania, said calcined mullite being in the form of frangible aggregates of titania crystals and mullite crystals having an average crystalline size as determined by line broadening X-Ray diffraction measurement of less than 1500 Angstroms; c. grinding the calcined mixture until said aggregates are broken up and there is obtained a mixture of separated crystals of mullite and titania; d. forming the ground mixture into the shape of the desired mullite bodies; and e. heating said formed mullite bodies at an effective sintering temperature within the range from 1500° to 1700° C. to integrate said bodies, said heating at said effective sintering temperature being continued until said bodies have a density of at least 2.50 grams per cubic centimeter.