Electrochemical Dissolution of Tungsten Carbide in NaCl-KCl-Na 2 WO 4 Molten Salt
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TUNGSTEN is a significantly precious rare metal. It is widely utilized in military industrial complexes, metallurgy, aerospace, and other important fields due to the corresponding excellent physical and chemical properties.[1,2] Cemented carbides, also called hard metals, are the most important utilized products of tungsten currently. The main constituent is the tungsten carbide, which has hardness similar to diamonds. Tungsten carbide scrap recycling is an important factor in the global tungsten supply. The tungsten carbide scrap, due to the corresponding high tungsten content in comparison with the ore, is a valuable raw material.[3] At present, the zinc process is the main method of cemented carbide recovery in the world.[4] This is a treatment with molten zinc which is dissolved in the cobalt phase and consequently distilled off, leaving a spongy material which is easily crushed. This powder is added back into the manufacture of ready-to-press powder production. Due to this reason the zinc process
LIWEN ZHANG, ZUOREN NIE, XIAOLI XI, LIWEN MA, XIANGJUN XIAO, and MING LI are with the College of Material Science and Engineering, Beijing University of Technology, Beijing 100124, China. Contact e-mail: [email protected] Manuscript submitted February 28, 2017.
METALLURGICAL AND MATERIALS TRANSACTIONS B
does not change the original microstructure of tungsten carbide. Consequently, the recycled material quality by zinc processing has been decided prior to the zinc smelting furnace.[5] In contrast, the molten salt electrolysis demonstrates a unique advantage in terms of refractory metals preparation.[6,7] Several studies were conducted in molten salts to prepare tungsten from tungsten-containing compounds, such as the tungstate,[8–11] the tungsten sulfides,[12] the tungsten chlorides[11,13] and the tungsten oxides.[14–16] In the authors’ works, the tungsten carbide was utilized as a consumable anode, electrochemically dissolved in molten NaCl-KCl to supply tungsten ions, which were consequently discharged on the cathode and deposited as tungsten powders.[17,18] In this case, the tungsten was extracted from the tungsten carbide, whereas the properties of the tungsten powder, such as purity, fineness, and uniformity, could be controlled by the electrolysis condition changes. Although nanometer tungsten powders could be prepared by this method, several problems are still required to be studied, such as the current efficiency being quite low due to an active compound absence in the NaCl-KCl molten salt. In order to improve the dissolution rate and the current efficiency, it was necessary to discover a suitable active substance acting as a carrier of tungsten ions. On the other hand, the carbon produced from the tungsten carbide anode increased during electrolysis, whereas consequently the tungsten powders reacted with carbon
again, constituting the product impure. Also, that might lead to a short circuit after a long period of electrolysis. Therefore, the carbon effects avoidance is another challenge. In this work, the sodium t
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