Processing of Nextel™ 720/mullite composition composite using electrophoretic deposition

A technique for electrophoretic deposition (EPD) of alumina, silica and alumina/silica mixtures has been developed. These matrices have been successfully infiltrated into electrically non-conducting 2D alumina fibre weaves. Surfactants based on carboxylic acid/amine combinations in ethanol were assessed. The objective was the co-deposition of alumina and silica at mullite ratio by tailoring electrophoretic mobilities. Aluminium and silicon contents were measured by inductively coupled plasma atomic emission spectrometry. The distribution of species within samples was monitored via elemental mapping in scanning electron microscopy (SEM). Fibres were heat treated in air at 1400°C to assess tolerance to proposed sintering temperatures. Sintering studies were carried out at 1400 and 1600°C on powder compacts containing alumina and silica in the mullite ratio. The effect of seeding the compacts with mullite was investigated with the aim of reducing the temperature required for mullite formation. Resultant composite green bodies are densely infiltrated with powder deposited within fibre tows. The ease of preparation of low volume content powder suspensions reduces slurry processing time in comparison to conventional routes. The infiltration time required is short. Intermediate amounts of a fine mullite type powder seeding encouraged mullite formation when compacts were sintered at 1400°C for 2 h. These findings indicate that a potentially economic electrophoretic composite manufacturing route, not restricted to single powder species or conductive fibre weaves, has been developed.