HOT-PRESSING OF ACICULAR MULLITE FINE POWDERS PREPARED BY HYDROTHERMAL CRYSTALLIZATION OF AMORPHOUS POWDERS HYDROLYZED MIXED ALKOXIDES.

In order to characterize the mullite powder prepared by hydrothermal crystallization of amorphous powder obtained by hydrolysis of mixed alkoxides (Al//2O//3/SiO//2 mol ratio equals 3/2), hot-pressing experiments were conducted in graphite at 1400 degree to 1600 degree C under 20 to 40 MPa for 0 to 30 min. Mullite ceramics hot-pressed at 1600 degree C under 40 MPa for 30 min had a bulk density of 3. 1 g/cm**3 for every powder. But below 1600 degree C, crystallized mullite powder gave less dense ceramics than the amorphous powder. Flexural strength was 195 MPa for mullite ceramics prepared by hot-pressing of powders crystallized hydrothermally at 600 degree C under 20 MPa for 24 h at 1600 degree C under 20 MPa for 30 min.