Thermal decomposition of precipitated fine aluminium trihydroxide

Abstract

Fine (1.5 μm) aluminium trihydroxide (ATH), prepared from Bayer liquor, was subjected to dehydration at various temperatures up to 1400°C. The fine ATH was found to be gibbsitic in nature. XRD data indicated the formation of various transitional phases before becoming a stable α‐Al2O3 phase. Boehmite phase formation, that is unlikely at such a fine particle level, started at around 250°C and completed its transformation at 400°C. Formation of boehmite phase was also observed with 0.25 and 1 μm sized particles. Beyond 400°C, various transitional phases were formed. At 500°C, chi‐alumina formation was found; kappa‐alumina phase transformation started at 900°C and completed at 1000°C. Coarser particles (∼100 μm) also followed the similar trend. In the case of coarse ATH, α‐Al2O3 transformation was found at around 1200°C, whereas for fine particles, α‐Al2O3 transformation temperature was found to be 1400°C. FTIR spectra showed the presence of molecular water and Al–O bonds in gibbsitic material. Characteristic vibrations at 3098, 2099 and 1070 cm−1 were found for boehmite particles at 400°C. Lattice parameters and hkl values were calculated and reported. Determination of crystallite size, cell volume, number of atoms/unit cell and number of unit cell/crystallite were also undertaken and reported.