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

A technique for electrophoretic deposition (EPD) of alumina, silica and alu mina/silica mixtures has been developed. These matrices have been successfu lly infiltrated into electrically non-conducting 2D alumina fibre weaves. S urfactants based on carboxylic acid/amine combinations in ethanol were asse ssed. The objective was the co-deposition of alumina and silica at mullite ratio by tailoring electrophoretic mobilities. Aluminium and silicon conten ts were measured by inductively coupled plasma atomic emission spectrometry . The distribution of species within samples was monitored via elemental ma pping in scanning electron microscopy (SEM). Fibres were heat treated in ai r at 1400 degrees C to assess tolerance to proposed sintering temperatures. Sintering studies were carried out at 1400 and 1600 degrees C on powder co mpacts containing alumina and silica in the mullite ratio. The effect of se eding the compacts with mullite was investigated with the aim of reducing t he temperature required for mullite formation. Resultant composite green bo dies are densely infiltrated with powder deposited within fibre tows. The e ase 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 seed ing encouraged mullite formation when compacts were sintered at 1400 degree s C for 2 h. These findings indicate that a potentially economic electropho retic composite manufacturing route, not restricted to single powder specie s or conductive fibre weaves, has been developed. Crown Copyright (C) 2000 Published by Elsevier Science Ltd. All rights reserved.