ИСТИНА

The formation of fine-crystalline corundum from hydrargillite at 400C in supercritical water fluid (SCWF) at a pressure of 26.8 MPa in the presence of a-Al2O3 particles is investigated. It was found that the addition of fused a-Al2O3 particles into the reaction medium accelerates the formation of fine-crystalline corundum by the increase of the nucleation rate. The process is accompanied by both the build-up of fused corundum grains, and the generation of new corundum crystals from boehmite. It was found that the formation of new crystals depends on the distance between grains of additives. Depending on this distance, the newly formed crystals consist of two or three fractions with different average particle size. It is concluded that the build-up of fused corundum particles in the medium of SCWF occurs due to the uptake of corundum nuclei, formed in the surrounding layer of boehmite. Added particles of fused corundum with average size of 2.82 micrometers have the layer of a thickness of 17.47 microns from which the build-up occurs. Corundum nuclei formed at large distances from the growing particles become centers of growth of new corundum crystals of the smallest sizes. SCWF role is to increase the spatial and structural mobility of the reactants.