Investigations on thermo-mechanical fabrication of micro-scale porous surface features

In this paper, we present the preliminary results of our investigations to fabricate porous micro-feature surface structure arrays on large surface areas for fuel cell and other heat/mass transfer applications. We hypothesized that micro-channels of around 200-400 μm height and width with porosity levels of 30-50% and with strong bonding to a thin substrate could be fabricated using hot powder compaction and/or hot roll powder compaction. We investigated the effects of compaction pressure, temperature, holding time, powder size and substrate conditions on the attainable porosity and channel size. Our feasibility study findings indicate that both pressure and temperature have significant effect on the porosity level. Suggested temperature levels are around 450 °C to ensure strong bonding among powders and between powders and the thin substrate. Minimum pressure level can be around 50 MPa, but it depends on the temperature levels. Roughened substrate surface condition is found to slightly assist in achieving strong bonds and high porosity. In order to have high porosity levels, uniform powder size is preferred. Although not tested extensively, hot compacted specimens up to 450 °C temperature levels are found to be not very strong. Hence, subsequent sintering is necessary.