Transition (active) phases of alumina were synthesized starting from sodium
aluminate solution prepared out of Bayer liquor. The neutralisation of
sodium aluminate solution was performed by sulphuric acid. Powder X-ray
diffraction (XRD), Fourier-transformed infrared spectroscopy (FT-IR),
scanning electron microscopy (SEM) and low-temperature nitrogen absorption
studies were employed to trace the formation of the transition phases of
alumina. The results show that the properties of the powders (phase
composition, morphology and specific surface area) are strongly influenced
by the initial pH value of the system, as well as by the duration of
neutralisation step. It is possible to obtain powders with heterogeneous
structure with dominant phase of bayerite, gibbsite or boehmit by tuning the
pH and concentration of the starting sodium aluminate solution. The
transition (active) phases of alumina (?- and ?-alumina) with high specific
surface area (264-373 m2/g) are formed through the thermal dehydratation of
aluminium hydroxide (bayerite and gibbsite) and aluminium oxyhydroxide
(boehmite or pseudoboehmite) at the temperature of 500?C. Namely, bayerite
and pseudoboehmite transforms to ?-phase of alumina upon heating, while
gibbsite transforms to ?-phase, maintaining the parent morphology.