The Basical Study On Fe-W Functionally Gradient Materials By Electrochemical Method In Salts

In order to decrease the production costs of tungsten and widen the application area oftungsten, it is necessary that preparation technology of Fe-W gradient material should beresearched.In the present work, the preparation technology of Fe-W Gradient material arestudded by electrochemical method in ZnO-WO₃-Na₂WO₄ system. First investigaterespectively primary crystal temperature, weight loss at high temperature, structure,conductivity and viscosity in ZnO-WO₃-Na₂WO₄ system. It was found that primary crystaltemperature of the system is less than 750℃in measuring range. Weight loss of thesystem 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 followsgeneral rule of conductivity in molten salt. The conductivity of the system in melts isinfluenced by ratio of X_ZnO to X_WO3 and when concentration of Na₂WO₄ is invariable, theconductivity is maximal at the ratio being 1. In the range of the ratio of X_ZnO to X_WO3 beingless than 1, substituting WO₃ for Na₂WO₄ decreases the viscosity of the system and beinggreater than 1, increases the viscosity.The influence of composing , current density, current cycle reverse time percentage,electrodeposition time, temperature on coating and current efficiency were researched. Theoptimal technological condition of producing dense tungsten by electrodeposition wasobtained. The composing of molten salt is X_Na2WO4:X_ZnO:X_WO3=0.6:0.2:0.2. Thetemperature of electrodeposition is about 920℃. The average current intensity is 60mA/cm.The current cycle reverse time percentage is t₁:t₂=1:2. The coating electrodepositionlayer is choiceness.The influence of temperature, current density as well as operation way on sectionpattern, concentration of tungsten in coating and on tungsten diffusion in basic body wasresearched. It was shown that the influence of temperature on the solid diffusion oftungsten in the Fe is greater than the current intensity. For making Fe-W gradient material,first, reverse current was supplied at fixed strength and time(Let the cathode dissolve, thedissolved parameter Q>100), then, normal cycle reverse electrodeposition was carried onunder the optimal technological condition. The gradient layer was made of Fe, W and asmall quantity of Fe2W and Fe7W6. The crystal growth of pure W layer occupied relativelygreat advantage in {200}orientation.