Thermodynamic Modeling of Phase Equilibria in the WO₃‐Zn System

Abstract

There are no alloys in the W‐Zn binary system. The combustion process in the WO3‐Zn powder mixture gives mainly metallic tungsten and zinc oxide. The ZnO in the product can be easily leached (e.g., with HCl), so that from stoichiometric quantities of reagents, one can obtain W powder of good purity. Here we investigated the phase equilibria for the WO3‐Zn system in the temperature range of 900‐1500 K. The inert component (Ar) was introduced into the system to change the pressure within the range of 0.1‐0.5 MPa. When the pressure is constant, the quantity of tungsten dioxide in the equilibrium mixture of components increases with rise in temperature, while the fraction of the zinc oxide decreases. The fraction of metallic tungsten in the mixture also decreases with temperature increase and becomes near zero at 1500 K and 0.1 MPa. Up to 1100 K, the output of tungsten is close to the limiting (stoichiometric) value in the whole considered pressure range (0.1‐0.5 MPa).