Thermal decomposition of precipitated fine aluminium trihydroxide

Abstract

Fine (1.5 mum) aluminium trihydroxide (ATH), prepared from Bayer liquor, was subjected to dehydration at various temperatures up to 1400degreesC. The fine ATH was found to be gibbsitic in nature. XRD data indicated the formation of various transitional phases before becoming a stable alpha-Al2O3 phase. Boehmite phase formation, that is unlikely at such a fine particle level, started at around 250degreesC and completed its transformation at 400degreesC. Formation of boehmite phase was also observed with 0.25 and 1 mum sized particles. Beyond 400degreesC, various transitional phases were formed. At 500degreesC, chi-alumina formation was found; kappa-alumina phase transformation started at 900degreesC and completed at 1 000degreesC. Coarser particles (similar to100 m) also followed the similar trend. In the case of coarse ATH, alpha-Al3O2 transformation was found at around 1200degreesC, whereas for fine particles, alpha-Al2O3 transformation temperature was found to be 1400degreesC. 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 400degreesC. Lattice parameters and hkI values were calculated and reported. Determination of crystallite size, cell volume, number of atoms/unit cell and number of unit cell/crystal lite were also undertaken and reported.