Influence of precipitation chemistry and ball-milling on the thermal behavior of zirconium hydroxide

Zirconium hydroxide precipitates, obtained by rapid precipitation at pH 2.5, 7.5, and 10.5, were ball-milled for up to 60 h and then heated inside a differential scanning calorimeter (DSC) at temperatures of up to 600 degrees C. Crystal phases produced after heating were analyzed by FTIR and laser Raman spectroscopy. It was found that without regard to the precipitation pH the first stage of ball-milling caused an increase of the crystallization temperature that resulted in the formation of pure t-ZrO2. The second stage of ball-milling caused a decrease of the crystallization temperature resulting in the formation of m-ZrO2. The ball-milling process also influenced the dependence of the crystallization enthalpy of zirconium hydroxide on the precipitation pH. In the case of zirconium hydroxide precipitated at pH 2.5, the ball-milling caused dehydration and an increase in its hygroscopy. The nature of these effects was discussed. The extension of FTIR spectra to the far infrared region made it possible to distinguish between t-ZrO2 and m-ZrO2 polymorphs by this technique. Also, the influence of laser power on the identification of ZrO2 polymorphs by Raman spectroscopy was elaborated.