Modeling of the process of metallic tungsten fluorination
The most promising way to obtain wear-resistant coatings or the products made from refractory materials is the method based on the deposition of such materials from the gas-steam phase by reduction of their fluorides or chlorides. The first phase of this method is the obtaining of gaseous tungsten hexafluoride yielded by the reaction between fluorine gas and tungsten powder, which initiates at about 300°C. In this paper, a numerical calculation of the tungsten powder fluorination in a chemical reactor, whose working zone represented as a long channel of rectangular cross-section, is carried out. Passing through the active zone of the reactor, fluorine interacts with tungsten powder, and the process results in a tungsten hexafluoride formation. The aim of this work is to study the influence of the hydrodynamics and heat and mass transfer on the generation of gaseous hexafluoride of the metal. To clarify this effect, a numerical simulation of the system of three-dimensional Navier-Stokes equations and heat and mass transfer equations accounting for the presence of heterogeneous reaction on the lower face of working zone in the chemical reactor is implemented in this paper. In the problem considered, the fluid density is variable and depends only on the concentration of components in the mixture.