MORPHOLOGICAL AND PHASE-CHANGES OF TRANSITION ALUMINAS DURING THEIR REHYDRATION

Transition aluminas (TA), obtained by fast (0.5-1 s) calcination of gibbsite in the temperature range 375-600-degrees-C, were rehydrated at 20, 70 and 90-degrees-C. The rehydration process was investigated using transmission electron microscopy, X-ray, and thermogravimetric-differential thermal analysis. During rehydration, the TAs react yielding aluminium hydroxides: pseudoboehmite, boehmite, and bayerite. The phase-composition changes are accompanied by changes in particle morphology. Using transmission electron microscopy, six stages of rehydration were found, with characteristic morphological changes occurring. The changes are responsible for connecting the particles into stable grains during the process of obtaining catalyst carriers or adsorbents from TA.