NaCl-KCl熔盐Ta~(5+)在钨电极上的电化学还原机理
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摘要
以NaCl-KCl为电解质体系,K_2TaF_7为原料,利用循环伏安法、计时电位法和计时电流法研究温度为1 073K时钽离子在钨电极上的电化学过程。结果表明,在1 073K温度下49%(质量分数)KCl-51%(质量分数)NaCl-5%(质量分数)K_2TaF_7的熔盐体系中,钽离子在钨电极上还原是一步转移5个电子反应,即Ta2++5e-→Ta相对于铂电极析出电位为-1.6V;钽离子在钨电极析出过程中出现成核极化现象,该电化学还原是准可逆反应。并且通过循环伏安和计时电流可判断钽离子在钨电极上的还原过程是受离子扩散步骤控制,1 073K时Ta~(5+)在49%(质量分数)KCl-51%(质量分数)NaCl-5%(质量分数)K_2TaF_7熔盐中的扩散系数D=7.48806×10-5 cm2/s。
The electrochemical reduction mechanism of Ta~(5+)on the tungsten electrode at 1 073 K was studied through the methods of cyclic voltammetry,chronopotentiometry and chronoamperometry using NaCl-KCl and K_2TaF_7 as molten salt and raw material.The results showed that the electrochemical reduction of Ta~(5+)on the tungsten electrode is a five-electron transition process by one step in 49 wt%KCl-51 wt%NaCl-5 wt%K_2TaF_7 molten salt at 1 073 K.The electrode reaction is Ta2++ 5 e-→ Ta and the reduction potential of Ta~(5+)is at around-1.6 Von a tungsten electrode as compared with a platinum electrode.During depositing process,the nuclear polarization phenomenon is observed.The depositing process of Ta is an quasi-reversible reaction.Cyclic voltammetry and chronoamperometry indicated that the reduction of Ta~(5+)on tungsten electrodes process is controlled by the diffusion step of ions and the diffusion coefficient is calculated to be 7.48806×10-5 cm2/s in49 wt%KCl-51 wt%NaCl-5 wt%K_2TaF_7 molten salt at 1 073 K.
The electrochemical reduction mechanism of Ta~(5+)on the tungsten electrode at 1 073 K was studied through the methods of cyclic voltammetry,chronopotentiometry and chronoamperometry using NaCl-KCl and K_2TaF_7 as molten salt and raw material.The results showed that the electrochemical reduction of Ta~(5+)on the tungsten electrode is a five-electron transition process by one step in 49 wt%KCl-51 wt%NaCl-5 wt%K_2TaF_7 molten salt at 1 073 K.The electrode reaction is Ta2++ 5 e-→ Ta and the reduction potential of Ta~(5+)is at around-1.6 Von a tungsten electrode as compared with a platinum electrode.During depositing process,the nuclear polarization phenomenon is observed.The depositing process of Ta is an quasi-reversible reaction.Cyclic voltammetry and chronoamperometry indicated that the reduction of Ta~(5+)on tungsten electrodes process is controlled by the diffusion step of ions and the diffusion coefficient is calculated to be 7.48806×10-5 cm2/s in49 wt%KCl-51 wt%NaCl-5 wt%K_2TaF_7 molten salt at 1 073 K.
引文
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[2] Tu Chungen.The distribution of tantalum and niobium resources and supply and demand of raw materials[J].Rare Metals Letters,2004,23(12):10-12(in Chinese).涂春根.钽、铌资源的分布与原料的供需状况[J].稀有金属快报,2004,23(12):10-12.
[3] He Jilin.The development of world tantalum powder technology[J].Chinese Engineering Science,2001,3(12):85-89(in Chinese).何季麟.世界钽粉生产工艺的发展[J].中国工程科学,2001,3(12):85-89.
[4] Hu Zhongwu,Li Zhongkui,Zhang Tingjie.New developments and applications of tantalum and tantalum alloys[J].Rare Metals and Cemented Carbides,2003(3):34-36(in Chinese).胡忠武,李中奎,张廷杰.钽及钽合金的新发展和应用[J].稀有金属与硬质合金,2003(3):34-36.
[5] Yu Xiaoming,Tan Lili,Yang Ke.Application and research progress of tantalum as biomedical material[J].Material guide,2012,26(1):79-82(in Chinese).于晓明,谭丽丽,杨柯.钽金属的医学应用研究进展[J].材料导报,2012,26(1):79-82.
[6] Shi Xianbo,Zhao Lianyu,Yan Wei.Study on strengthening effect of tantalum in Fe-C-Ta alloy[J].J Iron Steel Res Int,2013,25(12):58-62(in Chinese).史显波,赵连玉,严伟.钽在Fe-C-Ta合金中的强化作用[J].钢铁研究学报,2013,25(12):58-62.
[7] Senderoff S,Mellors G W.Hexavalent fluorides of tantalum and niobium[J].Electroehem Soc,1965,112(6):1028-1029.
[8] lnman D,Sethi R S,Spencer R.The effects of complex ion formation and ionic adsorption on electrode reactions involving metals and metal ions in fused salts[J].Electroanal Chem,1971,29(1):137-147.
[9] Taxil P,Mahenc J.The preparation of corrosion-resistant layers by the electrolytic deposition of tantalum on nickel and stainless steel[J].Corr Sci,1981,21(1):31-40.
[10] Li Guoxun,Barhoum A,Lantelme F.Electrochemical reduction mechanism of tantalum in NaCl-KCl-K2TaF7molten salt[J].The Chinese Journal of Nonferrous Metals,1992,2(3):52-57(in Chinese).李国勋,Barhoum A,Lantelme F.钽在NaCl-KCl-K2TaF7熔体中的电化学还原机理[J].中国有色金属学报,1992,2(3):52-57.
[11] Idem,Nippon Kagaku Kaishi.Adsorption state of aromatic amines on palladium under hydrogenation and the hydrogenation mechanism[J].The Chemical Society of Japan,1975(2):255.
[12] Zhang Mingjie,Wang Zhaowen.Principle and application of electrochemistry of fused salts[M].Beijing:Chemical Industry Press,2006:231-238(in Chinese).张明杰,王兆文.熔盐电化学原理与应用[M].北京:化学工业出版社,2006:231-238.
[13] Chen Zeng,Zhang Milin,Han Wei,et al.Electrochemical reduction of Zr(Ⅳ)in the LiCl-KCl moltensalt[J].Rare Metal Materials and Engineering,2009,38(3):456-459.
[14] Bard A J,Faulkner L R.Electrochemical fundamentals and applications(2nd edition)[M].New York:John Wiley and Sons INC,2003:225-227.
[15] Li Mei,Sun Tingting,Liu Bin,et al.Elec-trochemical behavior of Dy(Ⅲ)and the selective formation of Dy-Ni intermetallic compounds in LiCl-KCl eutectic melts[J].Acta Physico-Chimica Sinica,2015,31(2):309-314.
[16] Barde A J,Faulkner L R.Electrochemical methods,fundamentals and applications[M].Beijing:Chemical Industry Press,2005:159.
[17] Paul M S Monck.Fundamentals of electroanalytical chemistry[M].Beijing:Chemical Industry Press,2001:100-101.
[18] Greef R,Peat R,Pletcher L M,et al.Instrumental methods in electrochemistry[M].London:Ellis Hrwood,1990:316-317.
[19] McDonald D D.Transient techniques in electrochemistry[M].New York:Plenum Press,1977:365-367.
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