Etsuro Kato

Morphology of corundum crystallized by heating mixture of ≠-Al2O3 and AlF3

Abstract The morphology of corundum crystals, synthesized from a mixture of ≠-Al2O3 prepared from well-crystallized hydrated aluminum sulfate and reagent grade AlF3, was studied. The average size of the largest crystal was about 35 ≠m in diameter, which was obtained at 900°C for 20 h. The crystal size in diameter decreased and the thickness increased with elevating the heating temperatures from 900 to 1200°C. The crystal habit was composed of hexagonal {0001} faces, and of {10 1 2} and {10 12 } faces at the side of the hexagonal planes. A number of trigonal pyramids were observed on the {0001} planes of the corundum crystallized at lower heating temperatures.

Thermal changes in texture of aggregates of ultra-fine crystallites in hydrolysed zirconia particles

Abstract Zirconia particles of about 1000 × 1000 × 300 A in size, which were aggregates of rectangular shaped and regularly oriented ultra-fine crystallites of about 30 × 100 A, were prepared by hydrolysis from 0.1 moll-1 ZrOCl2 solution. Changes in the texture of the particles on heating were studied by electron microscopy. The growth of the crystallites occurred predominantly at peripheries of the particles at 500°C and in the whole particles at 600°C, resulting in crystallites of 160–360 A in diameter at 800°C. The voids which were present initially among the crystallites, coalesced and increased in size at temperatures up to 600°C, but diminished above 800°C. Single crystals and (100) twins were formed at 1000°C.