PREPARATION OF HETEROCOAGULATED COLLOIDAL SUSPENSIONS FOR FABRICATIONOF CERAMIC-MATRIX COMPOSITES BY ELECTROPHORETIC FILTRATION DEPOSITION

Nanosized mullite matrix precursors comprising individually a mixture of a boehmite sol (Remal A20) and either a hexagonal colloidal silica sal (Akzo-Nobel, Bindzil 30/220) ol one of a series of Aerosil amorpho us fumed silica powders in aqueous suspension, have been characterised in terms of particle size, particle size ratio, rheological behaviour ; and solids loading. Particle mobility measurements and TEM were empl oyed to determine the heterocoaguluted particles' net surface charge a nd the nanoscale alumina-silica particle interaction behaviour respect ively. The suspension finally chosen for further investigation was opt imised to obtain a heterocoagulated mullite precursor sol suitable Soi composite fabrication by electrophoretic filtration deposition. This technique, in conjunction with pressure filtration, is uf major techno logical relevance to the fabrication of ceramic matrix-composures; for ex-ample, the fabrication of multilayer alumina fibre reinforced mull ite composites with nanosized matrix grains. It has been shown that ni t aqueous colloidal suspension, comprising two different nanosized par ticle species (i.e. boehmite and silica) and exhibiting a solids loadi ng as high as 30 wt-% of heterocoagulated boehmite and silica particle s ui?der stable dispersion conditions, carl be prepared if the short, range particle-particle interactions are well controlled via homogeneo us hetero-coagulation of the constituent boehmite and silica coagulati on of the particles. (C) 1998 The Institute of Materials.