Electrolysis: processes – compositions used therein – and methods – Electrolytic coating – Coating moving substrate
Patent
1994-02-23
1997-06-17
Gorgos, Kathryn L.
Electrolysis: processes, compositions used therein, and methods
Electrolytic coating
Coating moving substrate
205101, 205270, 205316, 205261, 204232, 204237, 204263, 204266, C25D 300, C25D 320, C25D 1710, C25D 1716
Patent
active
056393601
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
This is a national stage application of PCT/8392/00022 FILED May 27, 1992.
The present invention relates to an electrode, preferably an insoluble electrode for an electrolytic cell. The invention relates also to plants and processes using such electrode for the plating or deplating of metal strips.
BACKGROUND OF THE INVENTION
Insoluble electrodes are commonly employed in processes for coating strips of metals by electrochemical routes, preferably of zinc-coated or galvanized steel strips, with the aid of metals or metal alloys, in accordance with which an electrolyte laden with salts of the coating metals is recycled between the cathodic metal strip to be coated and the insoluble anode.
Depending on the electrolyte used, for example sulphate- or chloride-based electrolytes, the use of this process generates gases at the anode, for example oxygen or chlorine, which partially undergo undesirable bonding with the coating metals or which, because of their high reactivity or their toxicity, have detrimental consequences during the use of the coating process or for the environment. These gases which arise at the anode mix with the electrolyte and can, consequently, cause undesired reactions and enter the environment, given that during the electrolytic coating of metal strips the electrolyte circuit on the strip cannot be separated from the atmosphere.
A process for coating galvanized steel strips with the aid of iron compounds or of alloys of the latter is known. To do this, a sulphate-based electrolyte laden with salts of coating metal is conducted in a closed circuit between the steel strip to be coated circulating endlessly and the insoluble anodes. Because of known electrochemical processes, iron precipitates in the form of iron compounds at the cathodic metal strip. Divalent oxygen is released at the anode, oxygen which comes into contact with the metal salts, more particularly because of the recycling of the electrolyte. This oxygen oxidizes a part of the divalent iron to trivalent iron, with the result that large quantities of iron oxide are produced, which soil the electrolytes and which must be separated from the circuit by making use of costly filtration processes.
Furthermore, the formation of Fe.sup.3+ reduces the cathodic efficiency of the current and deteriorates the adhesion of the deposited layer.
Finally, the use of salts of the coating metal, or the use of iron in corresponding dissolving plants and the replacement of other substances employed which are entrained together increase the cost of such a coating process very appreciably.
BRIEF DESCRIPTION OF THE INVENTION
To solve these problems, the applicants have developed a special electrode which is particularly useful in processes for electrochemical coating of metal strips, but which is also suitable in other processes such as processes for electrochemically removing a coating from a strip such as a steel strip.
The electrode according to the invention is placed in an enclosure defining a chamber and one wall of which is formed by a membrane allowing ions to pass through the latter, the said enclosure having a first opening for feeding the chamber with an electrolyte and a second opening for removing the electrolyte from the chamber.
The enclosure or the electrode is advantageously provided with means intended to ensure a minimum velocity of the electrolyte in the vicinity of the electrode, a velocity which is preferably higher than 0.1 m/s, in particular higher than 0.5 m/s.
Such means are, for example, baffles or fins directing the flow of electrolyte in the chamber or a part thereof.
In one embodiment, the baffles or fins extend from the vicinity of the first opening of the enclosure as far as the vicinity of the second opening of the enclosure, so as advantageously to divide the chamber into a number of separate compartments extending between the electrode and one wall of the chamber or enclosure, in particular the membrane.
In another embodiment, the said baffles or fins create an at least partially upward c
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May Hans Josef
Prum Norbert
Schnettler Roland
Gorgos Kathryn L.
May Hans Josef
Schnettler Roland
Sikel N.V.
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