Study On Preparation Of Tungsten Powder By Salt - Electrolysis Of NaCl - CaCl2 - CaWO4 System

Using tungstate prepared tungsten powder by the method of molten salt electrolysis, it can simplify the process of traditional manufacturing processes, while molten salt electrolysis method is a better purification techniques, the electrically active impurities larger than that of tungsten can be removed by pre-electrolysis, thereby it can producing high purity tungsten powder.Early Experimental studies have shown that tungsten powder can be obtained by electrolysis in NaCl-CaCl2-CaWO4system, but the system electrolytic processes has not yet to study in detail, the nature of this paper is to analyze the theoretical basis and test conditions through the tungsten powder prepared by molten salt electrolysis system,,the system properties such as solubility and conductivity were measured to study the mechanism for the electrode reaction, through the electrolysis of the morphology characterization, analysis the influence of experimental conditions on the results, then the test conditions were optimized, and strive to get the system under test conditions better for the molten salt electrolysis of tungsten powder and provide basic data.Used isothermal saturation method to study the temperature and the molten salt component mole ratio on the CaW04solubility, used X ray diffraction method to detect molten salt phase composition in the extremely cold sample. The results prove that the dissolve of CaW04in NaCl-CaCl2molten salt systems include two parts, physical and chemical dissolution of process. In the form of molecules dissolved in melt in physical process, and in the process of chemical Ca2Wo4dissociation of Ca2-and WO42-in the electrolytic experiment, WO42-will be decomposed into WO3and O2" first at the cathode surface, then the W6+in cathode discharge, WO3is gradually restore as W, process including the W6+â†'W4+â†'W.As one of the important physical and chemical parameters of molten salt,conductivity has important guiding significance on choosing the best electrolyte and electrolysis temperature. Effect of temperature and component mole ratio in molten salt on conductivity of NaCl-CaCl2-CaWO4system was investigated using CVCC method.Orthogonal experiment results indicated that the conductivity in molten salt,which increases with rise of temperature and increase of NaCl content,while the NaCl is the main factor.When NaCl:CaCl2=1:1, namely the system of minimum total melting point about1.81S/cm appeared the low end of its conductivity, and with the increase of NaCl and CaCl2, conductivity also increases.By orthogonal test method in NaCl-CaCl2system electrolytic CaW04, tungsten metal powder preparation experiment mainly graphite rod electrode materials, electrolytic process, the cathode discharge phenomenon, due to the effect of corrosion of the CaCl2on cathode, electrolyte after the end of the cathode surface will have a fracture phenomenon, make the graphite particles into molten salt, the cathode lead to partial test result showed in the WC and W2C and other impurities.After electrolysis the molten salt obviously divided into three layers:top layer thick for gray electrolyte layer, lower-middle-class black density of solid matter, this is mainly for deposition of tungsten powder, the bottom is white CaW04layer.Orthogonal design experiments on main technical conditions such as temperature, slot voltage and ratio of molten salt, gets the main factors influencing the current efficiency and obtain the optimum experiment conditions for: electrolytic temperature750℃-800℃, NaCl:CaCl2=4:6nearby, slot voltage of2.5-3.OV.And verified in a better condition experiments, the electrolytic product X ray diffraction analysis, energy spectrum analysis, and scanning electron microscopy (SEM) was taking pictures, show the product particle size below1um, more than98%purity, current efficiency is about82%,And under the condition of better explore the metal wire as cathode material electrolytic feasibility of tungsten powder, graphite cathode and the difference of copper cathode, comparative analysis for the use of NaCl-CaCl2-CaW04system of molten salt electrolytic preparation of tungsten powder, which provides theoretical basis and research direction.