Thermal evolution of thin boehmite films

Using transmission electron microscopy, electron diffraction and resistance change measurements, we studied the process of thermal evolution of thin boehmite (a-Al2O3·H2O) films. It has been shown that the crystal lattice of boehmite decomposes at a temperature of 670 K, with simultaneous partial dehydration. Above 875 K crystallization of ?- Al2O3 occurs and the morphology of the film changes from fibrous to granular. Annealing of ?- Al2O3 at 1300 K results in its transformation into d- Al2O3. At temperatures of 1475 to 1575 K the transformation of d-Al2O3 into a- Al2O3 was observed. Depending on the temperature of annealing, thin a-Al2O3 films were composed of fine crystals or of large (micrometre) corundum crystals. The method of producing of the various aluminas in the form of thin films presented in this report makes investigation of the structure transitions in aluminium oxides by means of transmission electron microscopy possible, and such films can be also used as supports for transmission electron microscopy studies of the model metal-oxide supported catalysts.