The Basic Study On Fe-W Functionally Gradient Material Made By Electrodeposition In Molten Salt

Tungsten has very high melting point, strength, hardness and well-known chemical stability. Because of its high production costs, brittleness and bad machining property, the applied range of tungsten is confined extremely. In order to decrease the production costs of tungsten and widen the application area of tungsten, it is necessary that new methods of production tungsten and preparation technology of Fe-W gradient material should be researched. In the present work, the preparation technology of dense tungsten and Fe-W gradient material are studied by electrochemical method in ZnO-WO₃-Na₂WO₄ system.Differential thermal analysis, TGA, XRD, four parallel electrode method, rotating cylinder method as well as slide method have been appli(?)d to investigate respectively primary crystallization temperature, weight loss at high temperature, structure, conductivity, viscosity and surface tension in ZnO-WO₃-Na₂WO₄ system. It was found that primary crystallization temperature of the system is less than 750℃ in measuring range. Weight loss of the system at molten state is very small. The main phases in melts are Na₂W₂O₇, Na_2.4Zn_0.8W₂O₈ and Na₂WO₄. The relation between conductivity and temperature follows general rule of conductivity in molten salt. The conductivity of the system in melts is influenced by ratio of X_ZnO to X_WO3 and when concentration of Na₂WO₄ is invariable, the conductivity is maximal at the ratio being 1. In the range of the ratio of X_ZnO to X_WO3 being less than 1, substituting Na₂WO₄ for WO₃ decreases the viscosity of the system and being greater than 1, increases the viscosity. The surface tension of the system is reduced with temperature rise.Cyclic voltammetry, chronopotentiometry as well as chronoamperometry have applied to investigate the electrochemical mechanism of tungsten deposition in ZnO-WO₃-Na₂WO₄ system. It was found that the electrode process is a 6-electron transferred quasi-reversible process. The diffusion coefficient of tungsten ion was measured as 4.77 ×10^-7 cm².s^-1 at 920℃. The electrodeposition of tungsten is a process of three-dimensional progressive nucleation.The influence of composition, current density, current waveform, electrodepositing time and temperature on coating and current efficiency were researched. The optimal...