Colloidal processing of a mullite matrix material suitable for infiltrating woven fibre preforms using electrophoretic deposition

Commercially available alumina and silica precursors for the preparation of mullite ceramic via colloidal processing and viscous transient sintering have been identified, including fumed nanosize powders and colloidal suspensions. These materials were chosen due to the fact that they can be used in the form of a sol, as mullite matrix precursors, to infiltrate woven fibre preforms using electrophoretic deposition. The sintered density of the mullite matrices sintered for 2 h, at the upper temperature for fabricating SiC-fibre reinforced composites (1300 degrees C) is only approximate to 90% of theoretical. However, by exploiting a viscous flow densification mechanism, it is envisaged that hot-pressing can be used to produce fully dense mullite matrix composites at the required temperatures. Additionally, using a simple pressureless sintering route, almost fully dense (98% of theoretical density) monolithic mullite has been obtained from the pre-mullite powders. A very homogeneous and fine microstructure was achieved by sintering for 5 h at a temperature of approximate to 1450 degrees C. (C) 1996 Elsevier Science Lmited