Сверхкритические флюиды. Теория и практика
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2014, N3, pp. 36-54

Yu.D. Ivakin, M.N. Danchevskaya, G.P. Muravieva

Induced formation of corundum crystals in supercritical water fluid

The formation of fine-crystalline corundum from hydrargillite at 400 °C in supercritical water fluid (SCWF) at 26.8 MPa in the presence of corundum particles is investigated. It is found that the addition of fused corundum 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 added fused corundum grains, and the generation of new corundum crystals from boehmite. The formation of new crystals depends on the distance between the grains of the additive. Depending on this distance, the newly formed crystals consist of two or three fractions with different average particle sizes. It is concluded that the build-up of the fused corundum particles in the medium of SCWF occurs due to the uptake of corundum nuclei formed in the surrounding layer of boehmite. For the added particles of fused corundum with average size of 2.82 μm the layer from which the build-up occurs has a thickness of 17.47 μm. The corundum nuclei formed at large distances from the growing particles become the centers of the growth of new corundum crystals of the smallest sizes. The role of SCWF is to increase the spatial and structural mobility of the reactants.

Key words: fine-crystalline corundum, supercritical water fluid, solid phase transformation, induced nucleation, build-up of crystals

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