Control of pore morphology and mechanical strength of alumina ceramics produced by freeze-casting

Abstract

In this work, unidirectional and bidirectional freeze-casting techniques were employed to fabricate alumina monoliths using camphene as solvent. Monolith samples with aligned porosity were produced in unprecedented molds designed using materials with different thermal conductivities (technyl and copper) and varying the alumina monoliths concentrations (15, 20 and 25 % of solid load). The total porosity of the produced monoliths ranged within 50–70 % and it was observed that the different molds did not influence the total porosity of the material. The SEM images showed that the samples produced in the technyl/copper mold presented a change on the perpendicular alignment of the pores in the transition region from copper to technyl. The copper side exhibited more aligned structures forming continuous channels, that become less noticeable when closer to the transition region, reaching the technyl region where the dendrites were not well aligned. The monoliths prepared in the technyl mold showed a better mechanical resistance with values of 19.6; 23.34 and 34.2 MPa for 15, 20 and 25 % of the solid load, respectively.