RESUMO
BACKGROUND: There are many studies on the effect of different experimental parameters on the tetragonal phase of zirconia, but it is unclear whether pH values have effects on the tetragonal phase in hydrothermal reactionOBJECTIVE: To prepare two zirconia systems via hydrothermal method and to regulate the tetragonal phase purity and control the grain size of zirconia (ZrO2) crystal by pH values.METHODS: Analytical reagents Zr(NO3)4?5H2O and Y(NO3)3?6H2O were adopted as reactors, and nano-sized neat ZrO2 and yttria-stabilized tetragonal ZrO2 polycrystal (Y-TZP) powders were synthesized using the hydrothermal method. X-ray diffraction was adopted to characterize the influence of pH values and pH regulators (NaOH solution and ammonium hydroxide/NaOH solution) on phase purity and grain size of tetragonal zirconia.RESULTS AND CONCLUSION: Pure zirconia samples with a grain size lower than 20 nm were obtained through the hydrothermal method, and samples with higher tetragonal phase content compared to monoclinic phase could be derived when the pH value was higher than 10. The optimal pH values for neat zirconia and Y-TZP were 13 and 12,respectively. Furthermore, the ammonium hydroxide/NaOH solution was more favorable to enhance the content of tetragonal zircona. Therefore, the control of pH values and rational choice of pH regulators can improve the tetragonal phase purity and grain size of zirconia.