Electrochemical behavior of boron in LiF-NaF-KF- melts

L.P. Polyakova, G.A. Bukatova, E.G. Polyakova, Erik Christensen, Jens H. Von Barner, Niels Bjerrum

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    Abstract

    The electrochemical reduction of B(III) to B(0) in KBF4-LiF-NaF-KF melts has been studied by voltammetric and chronopotentiometric methods, Glassy carbon, Pt, and Ag were used as working electrode materials. Only in the case of Ag was the reduction not complicated by interaction between boron and the electrode material. On a silver electrode B(III) was reduced to B(0) in a single irreversible step in the KBF4 concentration range up to 5.7 x 10(-2) mole percent (m/o). The cathodic half-wave potential was -1.34 V us, an Ag/AgCl reference electrode at 700 degrees C. The diffusion coefficient of BF4- at 700 degrees C was determined to be 2.06 X 10(-5) cm(2) s(-1). Further increase of the KBF4 concentration above 5.7 x 10(-2) m/o leads to a change in the reduction process. An ohmic resistance control becomes the limiting factor oi the boron electroreduction process. The ''apparent surface resistance'' changes from 3.0 to 21.6 Ohm cm(2) as the temperature decreases from 700 to 550 degrees C, respectively. Furthermore at KBF4 concentrations higher than 5.7 x 10(-2) m/o a second reduction peak and a corresponding anodic peak appeared on the voltammograms. These peaks were attributed to formation of alkali metal borides.
    Original languageEnglish
    JournalJournal of The Electrochemical Society
    Volume143
    Issue number10
    Pages (from-to)3178-3186
    ISSN0013-4651
    DOIs
    Publication statusPublished - 1996

    Bibliographical note

    Copyright The Electrochemical Society, Inc. [1996]. All rights reserved. Except as provided under U.S. copyright law, this work may not be reproduced, resold, distributed, or modified without the express permission of The Electrochemical Society (ECS).

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