Electrophoretic deposition infiltration of 2-D woven SiC fibre mats with mixed sols of mullite composition

Electrophoretic deposition (EPD) has been used to infiltrate a dual-component mixed sol of mullite composition into woven, electrically conducting SiC (Nicalon) fibre preforms. Both silica and alumina precursors had a near-equiaxed particle shape and their controlled colloidal mixing at an optimised pH (3.1) has lead to their extensive heterocoagulation on a nanometre scale. The mechanisms of particle migration in the EPD cell are not fully clear at this stage. It is suggested that both sol species migrate simultaneously as a 'composite' sol particle to the fibre mat serving as one electrode in the cell. Owing to the small particle size of the silica and alumina used, both components were able to infiltrate the spaces within the fibre tows. Good particle packing and a high solids-loading were achieved, producing a firm matrix deposit which adhered to the fibres. The maintenance of the stoichiometric mullite composition in the deposited material was confirmed by, XRD analysis of the deposited material heat-treated at 1350 degrees C for 5 h. The high-quality infiltrated fibre mats serve as preforms for the fabrication of mullite matrix composites. (C) 1997 Elsevier Science Limited.