Electrolysis: processes – compositions used therein – and methods – Electrolytic coating – Forming nonmetal coating
Patent
1997-10-07
2000-02-29
Gorgos, Kathryn
Electrolysis: processes, compositions used therein, and methods
Electrolytic coating
Forming nonmetal coating
205 50, 205124, B65D 7302, B65D 8542
Patent
active
060305177
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
(i) Field of the Invention
The present invention relates to a process for preparing a film of a metal oxide or of a metal hydroxide of an element of Groups IIB or IIIA of the Periodic Table, deposited on a substrate.
(ii) Description of the Related Art
Metal oxides, in thin-film form, are very important materials in various technological fields because of their optical, electrical and catalytic properties. Among their many applications, mention may be made, for example, of the use of zinc oxide for the preparation of transparent conducting electrodes in solar cells.
The metal oxide thin films are generally obtained by vacuum deposition techniques, such as sputtering or chemical vapor deposition, or by deposition in successive layers using molecular beam epitaxy (MBE). All these processes involve expensive equipment.
Another process for preparing thin films of oxides is the reactive chemical spraying technique which is carried out in an ordinary atmosphere, without a closed chamber. However, the deposition temperatures are very high, of the order of 400-500.degree. C.
Various studies have been undertaken in order to produce deposits electrolytically. For example, Jay A. Switzer, Electrochemical Synthesis of Ceramic Films and Powders, Am. Ceram. Soc. Bull. 66, [10] 1521-24 (1987), describes the preparation of an oxide film on the anode of an electrochemical cell by oxidation of a dissolved metal ion followed by hydrolysis and calcining, the process being illustrated by the preparation of thallium oxide. This process relies on increasing the oxidation state of the metal ion in solution, with the formation, and deposition on a substrate, of an insoluble oxide. However, this process can only be implemented in order to prepare the oxide of a metal which has at least two stable oxidation states in the reaction medium. J. A. Switzer (mentioned above) and R. T. Coyle, et al., (U.S. Pat. No. 4,882,014) furthermore describe the preparation of powders of metal oxides and hydroxides as ceramic precursors. These powders are formed by precipitation near the cathode of an electrochemical cell, this precipitation being caused by the reduction of nitrate ions. Next, these powders are dried and sintered at high temperature in order to obtain the ceramic materials. The deposits possibly formed on the cathode are scraped off and recovered in powder form. The intended objective is consequently the formation of a powder, and neither the direct formation of an oxide or hydroxide film on a substrate, nor its use as such are described. Furthermore, no mention is made of an oxygen reduction reaction for the formation of an oxide or hydroxide film.
SUMMARY AND OBJECTS OF THE INVENTION
The object of the present invention is to provide a process which does not have the drawbacks of the processes of the prior art, in order to obtain a film of a metal oxide or of a metal hydroxide on a substrate by an electrochemical route, said film exhibiting good mechanical integrity and good adhesion to the substrate.
The subject of the present invention is a process for depositing a film of a metal oxide or of a metal hydroxide of formula M(OH).sub.x A.sub.y, M representing at least one metallic species in the oxidation state i chosen from the elements in Groups IIB and IIIA of the Periodic Table, A being an anion whose number of charges is n, 0<x.ltoreq.i and x+ny=1, on a substrate in an electrochemical cell which includes an electrode consisting of said substrate, a counterelectrode, a reference electrode and an electrolyte consisting of a conducting solution of at least one salt of the metal M. The process is characterized in that oxygen is dissolved in the electrolyte and a cathode potential of less than the oxygen reduction potential and greater than the potential for deposition of the metal M in the electrolyte in question is imposed on the electrochemical cell.
When a potential as defined above is imposed on the electrochemical cell, this causes reduction of the oxygen and the formation of an oxide or hydrox
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Switzer, "Electrochemical Synthesis of Ceramic Films and Powders", Am. Ceram. Soc. Bull., 66 [10] 1521-24 (1987). No month available.
Lincot Daniel
Peulon Sophie
Centre National de la Recherche Scientifique
Gorgos Kathryn
Nicolas Wesley A.
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