Obtaining a functional coating during the plasma-chemical synthesis of borides w-b systems on al₂o₃ substrate

Abstract

The article presents the results of studies of an experimental coating obtained in the process of plasma synthesis of tungsten borides and the reduction of metallic tungsten, from a mixture obtained on the basis of a scheelite concentrate and a boron-containing material. The coating was formed on an Al₂O₃ substrate. The paper describes a step-by-step process of formation of tungsten borides on the substrate surface and reduction of metallic tungsten from oxide, using a high-temperature synthesis unit — a plasma generator. The formation of a coating on a substrate consisting of reduced metallic tungsten and borides of the W–B system proceeds in one technological stage in the process of condensation from the vapor-drop phase. To conduct a series of experiments, a prototype of an indirect plasma torch was developed with the generation of an electric arc plasma flow with a specific power g 10⁴–10⁵ W/cm2. In the process of high-temperature plasma flow exposure to the complex structures of the mineral concentrate and tungsten oxide included in its composition, destructurization and subsequent sublimation of the mixture material in the form of a vapor-drop phase occur. The synthesis of tungsten borides occurs in the process of chemical transformations, when the dispersed material is removed from the heated plasma flow, the formation of nucleating phases and condensation from the vapor droplet phase on the substrate surface. The synthesis process is also accompanied by a significant sublimation of boron from the compounds, which leads to the reduction of metallic tungsten. The material obtained in the course of plasma synthesis forms the W–B system and structures, the physicochemical properties of which depend on the mixture composition, flux density, plasma pressure and temperature. The results of a chemical analysis of particles forming a W–B coating on the surface of an Al₂O₃ substrate in the form of a solid solution of dendrite crystals are presented. In the course of X-ray spectral microanalysis, the phase composition of coating samples was determined, the presence of tungsten borides W₂B₅, WB₂, W₂B, WB and metallic tungsten were revealed. The results of research work on obtaining coatings or films based on the W–B system, using mineral multi-component raw materials, can be useful in various science-intensive industries, in the hydrometallurgical or chemical industries.