Table Particle diameters of different

Commercial Y2O3 (99.99% pure, Huizhou Ruier Rare Chemical Hi-Tech Co. Ltd., Huizhou, China) powder was used as the starting material. The powder has a BET surface area of 31.5 m2/g. X-ray diffractometric (XRD) analysis indicated that the Y2O3 powder was a cubic-structured polymorph and the crystallite size calculated from Scherrer\'s equation is 19 nm. In a typical processing, 60 g starting Y2O3 powder was dispersed in ethyl alcohol with the addition of sulfuric VX-702 and 2 wt% of dispersant (ammonium salt of poly(methacrylic acid)), and then the suspensions were ball milled in polyurethane jars filled with ZrO2 balls for 8 h. The amounts of added sulfuric acid were expressed as a molar percentage of the Y2O3 powder basis (mol%). For comparison purpose, the starting Y2O3 powder without sulfuric acid addition was also ball-milled identically. The resultant suspensions were then dried at 110 °C, followed by sieving through a 200-mesh nylon sieve for pulverization. After sieving, the powder was calcined at 900–1200 °C for 4 h in furnace in a stagnant air condition. The green compacts were prepared by dry pressing at 100 MPa, followed by hydrostatical isostatic pressing under a pressure of 200 MPa.