ENHANCED PACKING DENSITY AND SOLID LOADING OF AQUEOUS NANO-Y₂O₃ SUSPENSIONS BY PRE-TREATING THE STARTING POWDERS WITH PHOSPHORIC ACID

This work extensively investigated the preparation and dispersion of concentrated aqueous suspensions of H₃PO₄-treated nano-sized Y₂O₃ powder particles. For comparison purposes, the untreated Y₂O₃ powder was also studied. Compared to the untreated Y₂O₃ powder, the treated powder exhibited a narrower particle size distribution and enhanced homogeneity in particle dispersion. In the case of the untreated powder suspension, there was a rapid increase in the pH from 9.34 to 10.4 in a short dispersion time, whereas no variation in the pH was observed for the treated Y₂O₃ suspension during the hydrolysis tests. This was because the phosphate-based protection layer on the surfaces of the particles inhibited the hydrolysis of Y₂O₃ powders, thus enabling the formation of colloidally stable suspensions. TAC was employed as the dispersant in preparing both the treated and untreated Y₂O₃ suspensions. The treated Y₂O₃ suspension exhibited lower viscosity and maintained long-lasting stability for 6 h compared to the untreated one. It was determined that the use of H₃PO₄ at a dosage of 1 wt% allowed one to obtain suspensions with the lowest sedimentation volume and viscosity. A series of treated Y₂O₃ suspensions with solid loadings ranging from 20 vol% to 40 vol% were obtained, which were centrifugal slip cast into cylindrical shapes. The resulting cast green bodies from the 35 vol% treated Y₂O₃ suspensions exhibited a uniform and high packing density of 49.24%.