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Formation of ZrO2 by the Thermal Decomposition of Zirconium Salts

Hydrated zirconium salts containing Cl-, NO3- or SO_4^-2 were thermally treated up to 1300 degrees CThe thermal decomposition products were investigated using the X-ray diffraction (XRD), Fourier transform IR spectroscopy (FT-IR) and laser Raman spectroscopy. The thermal decomposition products of all three zirconium salts, characterized as amorphous material, showed a maximum of X-ray scattering at similar to 16 degrees and also in the corresponding FT-IR spectra a broad band at 450 cm^-1. With an increase of the heating temperature of all three salts (400 degrees C for ZrOCl_2 . 8H_2O, 400 degrees C for ZrO(NO_3)_2 . 2H_2O and 700 degrees C for Zr(SO_4)_2 . 4H_2O), the metastable t-ZrO_2 was formed, which disappeared on further heating to higher temperatures. The yield of t-ZrO_2, measured by XRD, depended on the nature of the starting salt, and the highest value was obtained for ZrOCl_2 . 8H_2O salt. The t-ZrO_2 phase formed from ZrOCl_2 . 8H_2O was thermally most unstable, while the presence of a small amount of t-ZrO_2 was observed in the thermal decomposition product obtained by heating Zr(SO_4)_2 . 4H_2O even at 1300 degrees C. Metastable t-ZrO_2, generated by the thermal decomposition of ZrOCl_2 . 8H_2O or ZrO(NO_3)_2 . 2H_2O salt, was highly sensitive to mechanical treatment, while metastable t-ZrO_2 formed from Zr(SO_2)_2 . 4H_2O was stable during the same process. The nature of the starting salt influenced the formation of metastable t-ZrO_2 ; however, when t-ZrO_2 was once formed, its stability depended on the anionic impurities that remained in the oxide material. [References: 38]

X-ray diffraction ; Phase transformation ; Raman spectrum ; Tetragonal ZrO2 ; Crystallization ; Stabilization ; Temperature ; Polymorphs

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