Electrodeposition of Tungsten in ZnBr2-NaBr and ZnCl2-NaCl Melts.
Electrodeposition of Tungsten in ZnBr2-NaBr and ZnCl2-NaCl Melts.
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DOI：
10.1002/chin.199126012
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发表时间：
1991-07
期刊：
影响因子：
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通讯作者：
A. Katagiri;Masaaki Suzuki;Z. Takehara
中科院分区：
文献类型：
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作者：
A. Katagiri;Masaaki Suzuki;Z. Takehara
The electrodeposition of tungsten has been investigated in the molten salt systems ZnBr2-NaBr-WBr5 and ZnCI2-NaC1-WC16 at 450~ Voltammetric results showed that the reduction of tungsten species is an irreversible process. Electrodeposits were mixtures of a-and~-tungstens, the former being the thermodynamically stable phase, a-Tungsten exhibited the shape of cubic crystallites which tended to grow larger, whereas 13-tungsten always had a crystal size smaller than 1 ixm. The 13-tungsten was formed during the initial stage of electrodeposition, irrespective of the substrata material, and remained predominant at high current densities or in pulsed electrolysis. It is likely that the phase transition of 13-tungsten to a-tungsten occurs when the size of the [3-tungsten crystallites becomes larger than a critical value.The electrodeposition of refractory metals and their compounds has been investigated by several researchers using different kinds of molten salts (1-13). Senderoff and Mellors (7, 8) have obtained coherent deposits of tungsten from a fluoride melt at temperatures of 700-850~ Recently our research group has been interested in ZnBr2-NaBr melts (14-16), which have relatively low liquidus temperatures and exhibit a Lewis acid character similar to AICI~-NaC1 melts. Thus, we conducted electrolysis in ZnBr2-NaBr melts containing WO3 or WBrr, at temperatures of 350-450~ where a dense deposit of tungsten was obtained. From our results, we inferred that a stable tungsten species of low oxidation state is involved in the electrodeposition of tungsten. It seems important to study the electrochemical behavior of tungsten species in such melts and to elucidate the nature of the tungsten deposit obtained. It also seems worth trying to use a ZnC12-NaCI melt as the solvent electrolyte, since it has properties similar to those of the bromide system (17, 18). This paper describes an electrochemical study of the tungsten species in ZnBr2-NaBr and ZnC12-NaCI melts and an investigation of the crystal structure and morphology of tungsten deposits obtained in these melts.
