Influence of the slip composition on the properties of tape-cast alumina substrates

Tape-casting process was used to produce alumina (Al2O3) substrates in an aqueous system with poly(vinylalcohol) (PVA) and glycerine as binder and plasticizer, respectively. Various compositions of Al2O3 slips were prepared by dispersing the powder in water with ammonium polyacrylate (NH4PA), with subsequently additions of different amounts of PVA and glycerine. The influence of the slip composition on the rheological properties of the slips and the properties of the resultant green tapes were studied. In addition, the properties of the sintered tapes were investigated and related to those of the green tapes. PVA and glycerine did not affect the dispersion properties of the Al2O3 powder which were governed by the adsorbed NH4PA. Glycerine additions enhanced the flexibility of the green tapes but also produced a decrease in the tensile strength and in the drying shrinkage. The increase in the PVA content increased the tensile strength but resulted in a markedly decrease in the green density of the tapes. The slip composition 5 wt.% PVA–5 wt.% glycerine produced green tapes with sufficient tensile strength and flexibility which had higher green and sintered density and lower sintering shrinkage. Thus, this composition was adequate for the production of Al2O3 substrates by the tape-casting process.