Influence of pH value and solvent utilized in the sol–gel synthesis on properties of derived ZrO2 powders

ZrO2 precursor solutions were prepared by the sol–gel process. Zirconium n-propoxide (ZNP) was dissolved in methanol (MeOH), ethanol (EtOH) and propanol (PrOH) in acid medium (pH 0.5), and in PrOH at pH 5. Transparent solutions were obtained at pH 0.5, whereas a white solution was obtained at pH 5. Powders were obtained by gelificating and drying of the solutions at 100 °C in air atmosphere. Pellets were prepared by uniaxial pressing of these powders at 300 MPa. The samples were heat-treated up to a maximum temperature of 1350 °C. The structure and microstructure of the samples were analysed using X-ray diffraction and scanning electron microscopy and the hardness was measured by Vickers indentation. The type of alcohol used as ZNP solvent does not influence the final properties of the obtained powders. However, the pH of the medium in which the hydrolysis of ZNP was performed has a strong influence on the microstructure, morphology and sintering process of the prepared samples. The powders prepared at different pH have different colours, morphology and crystalline structure. The pellets prepared from the powders obtained at pH 5 present higher densification and hardness values.