The influence of chemical and thermal treatment on the point of zero charge of hydrous zirconium oxide
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Two zirconia samples were prepared by precipitation from aqueous zirconium oxychloride and zirconyl sulfate solutions with potassium hydroxide. The prepared zirconia samples were amorphous. The pH(pzc) values of the zirconia samples, determined in NaCl and NaNO3 solutions, were 6.6 +/- 0.1 and 6.9 +/- 0.1, respectively. After prolonged hydration of zirconia in doubly distilled water, the pH(pzc) decreased to 4.7 +/- 0.3. Crystallization into tetragonal (metastable) + monoclinic zirconia appeared at 691 K. Above 873 K, the tetragonal metastable phase changes to a monoclinic phase. It was shown that crystallite sizes of zirconia treated at 673-1273 K increased from 9.5 to 40.5 nm, respectively. The increase in temperature from 385 to 1070 K increased the pH(pzc) of zirconia samples from 6.6 to 9.0, respectively.