Dissolution of Yttrium Ions and Phase Transformation of 3Y‐TZP Powder in Aqueous Solution

In order to understand the reactions of yttria‐containing zirconia powder in aqueous solution, the dissolution behavior of yttrium and the formation of the monoclinic ( m ) phase of the Y‐TZP powder were investigated. The tests were conducted in aqueous solution at temperatures up to 95°C. The results showed that the reaction order of yttrium dissolution from the surface of TZP powder is 5‐9, and the activation energy is about 8.4 kJ/mol. However, the value of the reaction order is different from that (0.96‐1.20) of the formation of m ‐phase. However, the yttrium dissolution of the slurries with the addition of 2 mol% dispersant (D‐134) was reduced greatly to an extremely low (<2 ppm) level up to 24 h at the testing temperatures. The results also showed that the amounts of m ‐phase formation were nearly the same for the powders in the slurries with or without D‐134 addition. The decrease of yttrium content in the presence of D‐134 and the formation of the m ‐phase of the TZP powder were not closely related. The degradation mechanism, or the formation of m ‐phase, should not be directly related to the dissolution of yttrium ions from a zirconia surface.