In situ ellipsometric characterization of films formed by cathodic reduction of chromate

In the chlorate process, it is known that a small addition of chromate to the electrolyte increases the current efficiency at the cathode by hindering the electrochemical reduction of intermediately formed hypochlorite. This paper presents results from in situ ellipsometric studies of the formation...

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Bibliographic Details
Published in:	Electrochimica acta Vol. 42; no. 3; pp. 389 - 398
Main Authors:	Tidblad, A.Ahlberg, Martensson, J.
Format:	Journal Article
Language:	English
Published:	Oxford Elsevier Ltd 1997 Elsevier
Subjects:	Chemistry chlorate manufacture chromium hydroxide film Electrochemistry Electrodeposition Exact sciences and technology General and physical chemistry gold cathode in situ ellipsometry sodium hydroxide electrolyte Study of interfaces in situ ellipsometry sodium hydroxide electrolyte chromium hydroxide film gold cathode chlorate manufacture Gold Chromium III Hydroxides In situ Chlorates Transition metal Sodium Chromates Experimental study Ellipsometry Electrodes Chemical reduction Sodium Hydroxides Electrodeposition Kinetics Manufacturing Electrochemical reaction
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Summary:	In the chlorate process, it is known that a small addition of chromate to the electrolyte increases the current efficiency at the cathode by hindering the electrochemical reduction of intermediately formed hypochlorite. This paper presents results from in situ ellipsometric studies of the formation of the chromium(III) hydroxide film in an attempt to further elucidate the consequences to the cathode surface. The results obtained are in good agreement with findings from conventional electrochemical and surface analytical techniques. The thickness of the chromium(III) hydroxide layer obtained by cathodic reduction on evaporated gold electrodes is less than 4 nm after 2 h of film growth at − 1.0 and −0.6 V rel. SCE. At −1.0 V, the initial film growth is rate limited by the nucleation process. With 0.15 mM chromate, the film attains a maximum thickness within 2 h of growth. When the chromate concentration is 15 mM, the rate of film growth rapidly decreases, but continuous growth is still in progress after 2 h of exposure. The film grows homogeneously and there are neither structural rearrangements within the film during build-up, nor changes in the mechanism of film growth with time. Studies of deposition and dissolution of the film indicate that the mechanistic path is the same in both directions.
Bibliography:	ObjectType-Article-2 SourceType-Scholarly Journals-1 ObjectType-Feature-1 content type line 23
ISSN:	0013-4686 1873-3859
DOI:	10.1016/S0013-4686(96)00229-0