Effect of triethanolamine on the crystallization behavior and kinetics of nano t-ZrO₂ synthesized by microwave-assisted hydrothermal method

The effect of mineralizer triethanolamine (TEOA) on crystallization behavior of nano-ZrO₂ crystallites preparated by microwave-assisted hydrothermal was investigated using X-ray diffraction (XRD), scanning electron microscope (SEM), transmission electron microscope (TEM) and high resolution TEM (HRTEM). The isothermal crystallization kinetics of nano-ZrO₂ was studied, and the action mechanism of mineralizer TEOA was discussed. XRD and TEM results indicated that the product is a single tetragonal zirconia (t-ZrO₂), and the particle size is 25–30 nm. The addition of mineralizer triethanolamine can significantly improve the nucleation rate and crystallization rate of nano-ZrO₂. In order to obtain nano-ZrO₂ crystallites with uniform size and good crystallinity, the concentration of TEOA should not be less than 0.3 mol/L (M). There is a good linear relationship between ln[-ln(1-Xc)] and lnt when the concentration of TEOA is 0.3 M, 0.4 M, 0.5 M, indicating that Avrami equation can well describe the crystallization process of nano-ZrO₂ crystallites. The crystallization kinetics equations are described by ln[-ln(1-Xc)] = ln0.0005 + 2.25lnt, ln[-ln(1-Xc)] = ln0.025 + 1.28lnt, ln[-ln(1-Xc)] = ln0.4 + 0.57lnt, respectively. With the increase of the concentration of TEOA, the alkali separation of TEOA is carried out continuously, which aggravates the dissolution of colloid and makes the process of crystallization and nucleation easier. Meanwhile, alkoxide ammonium ion formed by alkali ionization can form an electric double layer structure on the surface of zirconia crystallites, thus promoting the dispersion of nano-zirconia powders.