PHYSICO-CHEMICAL PROPERTIES OF ULTRADISPERSED POWDERS OF SILICON

Experimental investigations of ultradispersed silicon powder produced by mechanical grinding are conducted. The process of scaling powders using mechanochemical grinding was studied. It was found that the dimension of crystallites of the silicon powder determines their physical and chemical properties. Finely divided powders of silicon with a particle size ≤10 nm easily decompose water at room temperature into hydrogen and oxygen, they are easily oxidized by air oxygen and actively interact with hydroxides and acids with the release of significant amount of heat. The rate of saturation of micro- and ultradispersed powders with hydrogen at a constant rate of flow in the flow system depends on the temperature of the hydrogen hydrogenation process. It was found that the hydride formed at a low temperature (≤573 K) is in an equilibrium state when it is being hydrogenated in a flow reactor. The treated powder passes into a metastable state with the termination of the thermal action after hydrogenation. Hydrogen, entering the volume of micro- and ultradispersed silicon powder in the temperature range 373–723 K due to the diffusion process, can react not only with silicon atoms to form hydrides of the SiH₂ type, but also with hydrides of less active radicals of the type of Si₂H₄, Si₂H₆. The hydrogenation process has two distinct stages. It is shown that the temperature of the transition between the stages is determined by the dispersion of micro- and ultradispersed silicon powders and by the structure of hydrides on the particle surface. As a result, it is established that the optimum temperature of hydrogenation should be taken at a temperature of 623 K, at which the maximum mobility of silicon atoms is reached during the formation of hydride. Sharp decrease in the hydrogen content is observed at a temperature above 723 K for the Si₂H₄ (SiH₂).

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