The properties of partially stabilized zirconia (PSZ) as porous ceramics were investigated with various relative humidities (RH) in terms of the curing behavior of the phenolic resin (PR). The PSZ powders with 5 wt.% of PR as a binder were stored in a constant chamber condition at a temperature of 50 oC and different humidity levels (25, 50, 75, and 95%) for 1 h before compaction. The green and the sintered density were gradually decreased with an increase in the humidity level. The porosity of specimens increased and the Young's modulus was decreased in response to a decrease of the sintered density. As the RH level increases, a rough surface and an irregular microstructure of the green body were observed because of the agglomerated particles, and the degree of curing for the PR was improved from 10.1% to 59.7%. The agglomerates were sufficiently hard to endure a compaction pressure owing to the curing of the PR, so the green density was decreased by the large volume of voids and the internal spaces. The curing behavior of PR with various RH was proved by the decomposition of hexamine as a curing agent using FT-IR, which was similar to the effect of temperature on the curing of the PR. It could be concluded that the formation of hard agglomerated particles generate a reduction of green density, and it can affect the properties of porous PSZ.

Keywords: Porous PSZ ceramics, Relative humidity (RH), Phenolic resin (PR), Curing behavior, Agglomerated particles.