Microfabrication of ceramics by colloidal isopressing

Colloidal isopressing involves formulating a slurry with a weakly attractive particle network that can be pre-consolidated to a high relative density by pressure filtration and still retain fluid-like characteristics. The pre-consolidated slurry is injected into an elastomeric mold and isopressed. Isopressing rapidly converts the slurry into an elastic body that can be removed from the mold without shape distortion. Not only is this process rapid, but since the water saturated compact produced by this method does not shrink during drying, it can also be converted into a green body without a long drying period.;It is demonstrated that micron-size surface features, such as the features on a one-dollar coin, and 5 mum wide channels with an aspect ratio of 2, can be rapidly produced on the surface of alumina powder compacts. The fracturing of thin vertical portions of a micro patterned surface during pressure release and demolding has been an obstacle to obtaining micron-sized features with high aspect ratios. The fabrication of such features is enabled by strengthening the saturated isopressed body. It is shown that concentration controlled gelation of a PVA-TyzorRTM TE additive effectively increases the strength of the elastic, isopressed body, saturated with water, while maintaining the low viscosity of the pre-consolidated slurry, which is required for transferring the pre-consolidated slurry into a rubber mold prior to isopressing.;Since differential strain recovery (different elastic expansion of the PDMS material relative to the consolidated powder compact) is one cause of stress that introduces cracks during pressure release, the strain recovery of the consolidated alumina body is investigated and it is found that cracks will not occur if the elastic moduli of the inclusions are larger than 3 GPa. Wax and Aluminum power mixtures were made as inclusions so that the elastic modulus is big enough to avoid crack during pressure release after isopressing and heat treatment and the inclusions could be easily melted and dissolved so that a cavity inside of the alumina body could be obtained.;Finally, the densification behavior of two different alumina powders (AKP-50 and TM-DAR) are studied and compared.