Physical, mechanical, and thermal properties improvement of porous alumina 'substrate through dip-coating and re-sintering procedures

Dip-coating and re-sintering procedures were employed to improve the properties of porous alumina substrate produced through sponge replication technique. The sintering process induced defects to the porous substrate. Therefore, it was dip-coated with catalyst materials (SiC, Cr, and Ni) solutions and then re-sintered at 900-1250 degrees C in vacuum furnace. The oxidation of catalyst materials was not detected after re-sintering process. The porosity of plain substrate (90.2%) was significantly reduced (85.3-88.7%) after multiple dip-coating cycles and re-sintering process, mainly due to closed cells and healed defects. The bulk and flaky morphologies of SiC and Cr powders increased the tendency for clogged cell, whilst the fine size additive materials heal defects through liquid phase sintering (LPS) mechanism. This prompted increment of thermal conductivity for the dip-coated substrate from 0.344 W/mK for plain substrate to 1.064 W/mK. The compressive strength for the once coated substrate was higher compared to the tri-coated substrate. The catalyst-based coatings are important for better physical, mechanical, and thermal conductivity of porous alumina and found beneficial especially in high temperature applications. (C) 2016 Elsevier Ltd and Techna Group S.r.l. All rights reserved.