Fabrication of alumina sheets by extrusion

Abstract

Alumina suspensions for extrusion were prepared by adding methylcellulose and glycerol to a system of water, ammonium polyacrylic acid, and alumina powder. The effect of the additives on the rheology of the mixtures was evaluated. The mixtures which could be formed into a sheet of less than 100 μm in thickness showed Bingham flow characteristics. As the flow characteristics of the mixture, an empirical equation, P/k = A + B ln R, was obtained, where P is the extrusion pressure for forming alumina sheets, k is the apparent yield stress of the mixture, A and B are constants, and R is the extrusion ratio. The effect of methylcellulose and glycerol on the particle packing and the flexibility of alumina green sheets was discussed. A dense, translucent, alumina sheet of 80 μm thick was obtained after firing at 1400°C for 4 h.