1. Department of Chemical Engineering and Applied Chemistry, Aston University, Birmingham, B4 7ET, U.K.
2. Robinson Brothers Ltd., Phoenix Street, West Bromwich, B70 0AH, U.K.
3. U.K. Materials Technology Research Institute (A Pera Technology Company), Nottingham Road, Melton Mowbray, Leicestershire, LE13 0PB, U.K.
4. Materials and Engineering Research Institute, Sheffield Hallam University, Howard Street, Sheffield, S1 1WB, U.K.