Ambient Pressure-Dried Zirconia Xerogels and Aerogels Using Various Catalysts

The experimental results on the ambient pressure dried zirconia xerogels and aerogels using various catalysts are reported here. The catalysts (acid and base) have the major impact on the hydrolysis and polycondensation of the precursor solution. Therefore, zirconia xerogels and aerogels are synthesized using various catalysts such as ammonium hydroxide (NH₄OH), ammonium fluoride (NH₄F), hydrochloric acid (HCl), acetic acid (CH₃COOH), and citric acid (C₆H₈O₇) via ambient pressure drying. The influence of these catalysts on the physical and structural characteristics of zirconia is studied by measuring the bulk density, Fourier transform infrared (FTIR), thermo gravimetric-differential scanning calorimetric (TG-DSC), as well as X-ray diffraction analyses. During the synthesis, the molar ratio of ZrPro:PrOH:Acac.:H₂O:HMDZ is kept fixed to 1:27:0.39:3.6:3.3, respectively. Among all zirconia samples, xerogels catalyzed using ammonium fluoride and acetic acid are observed to be low dense (～0.67 g cc⁻¹). Moreover, the corresponding zirconia aerogels possess lower density (0.26 g cc⁻¹) than xerogels. FTIR spectra reveal the high peak intensity of C-H, Si-C, and Zr-O-Si chemical bonds in zirconia xerogels and aerogels manifesting their hydrophobic characteristics. The zirconia xerogels and aerogels retain their hydrophobicity up to around 400 °C as confirmed from the TG-DSC analysis. Further, the X-ray diffractogram indicates the amorphous nature of the zirconia xerogels and aerogels.