“Amorphous” Precursors of α-Al2O3: An Electron Optical Study

Basic aluminium chloride gels are thermally decomposed into X-ray amorphous products. Corundum begins to crystallize in them about 400 °C on certain conditions. Electron optical examinations on powders of corundum-forming gels and of their decomposition products show in an essential part aggregates of sheetlike components as powder particles. These have sharp electron diffraction patterns. The interpretation of diagrams proves the existence of two different structures with similar lattices, which are evidently related to those of diaspore and corundum. A defect structure is to be assumed for the corundum crystals formed.