Dry-pressing behavior of silicone-coated alumina powders

The dry-press properties of commercial alumina powders coated with an adsorbed layer of siloxane-terminated silicone were tested. The adsorption reaction was characterized using Fourier transform infra-red (FTIR) spectroscopy. The solvent was removed by filtration. Compression and spring-back during dry pressing, and green strength after pressing were measured for the silicone-coated powders, and compared with those of poly (vinyl alcohol)-(PVA-) and paraffin-coated powders. Silicone was a better lubricant and binder than paraffin or PVA. The recovery of silicone-modified powders was greatest, indicating a lower friction coefficient. Green strengths of dry-pressed bars were compared using four-point bend flexure testing. Weibull moduli were calculated using the method of maximum likelihood. Dry-pressed bars made with silicone-coated powder yielded higher Weibull exponent m and characteristic stress σ0. When the silicone was polymerized after pressing, m and σ0 increased further.