LU85403A1 - PROCESS FOR FORMING A GLOSSY DEPOSIT OF METAL OR A METAL CONTAINING ALLOY ON A CONDUCTIVE SUBSTRATE - Google Patents

Description

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The present invention relates to a process for the formation of a substantially shiny deposit, of a metal or of an alloy containing this metal, on the surface of a conductive substrate, by electrolysis of an electrolyte based on -d a solution of a salt of this metal and optionally of at least one other metal intended to form said alloy.

Many methods are known for depositing nickel or a shiny nickel alloy on a sheet.

In general, these known methods have the drawback of requiring the presence of organic additives during electrolysis to obtain the gloss of the deposit.

These organic additives are incorporated at least partially into the deposit of nickel or a nickel alloy and it is found that they promote the subsequent corrosion of this metallic layer in its environment of use.

In addition, by the presence of inclusions of these organic additives in said layer, the latter has rather poor mechanical properties in the sense that the layer is hard and brittle and therefore not very ductile.

Furthermore, it is also known to form, in the absence of such additives, a shiny deposit of cobalt on steel.

However, up to now, in order to obtain this glossy deposit with good adhesion, very strict electrolytic conditions must be observed. Thus, the pH of the electrolyte bath is very critical, so that very serious problems exist * 0 - 3 - for the industrial application of a shiny cobalt without additives.

One of the essential aims of the present invention is to present a method enabling the abovementioned drawbacks to be remedied, that is to say obtaining a substantially shiny deposit of a metal or an alloy of this metal, in which the presence of organic additives is reduced to the strict minimum, so that it has no influence on chemical properties, such as corrosion resistance, mechanical properties, such as ductility.

To this end, according to the invention, the content of organic additive is lower in the electrolyte than that corresponding to a metallic deposit containing at most 1% of impurities due to the presence of this organic additive, and the electrolyte is subjected to a substantially constant and homogeneous movement in the immediate vicinity of the surface to be covered with the substrate, with a speed of at least 0.3 m / s relative to the substrate, so as to create a hydrodynamic regime d flow of the electrolyte such that the electrolysis conditions are homogeneous on a substantially microscopic scale over the entire surface to be covered with the substrate.

Advantageously, the electrolyte is substantially free from organic additives.

According to a particular embodiment of the invention, a speed of the electrolyte is maintained close to the surface to be covered with the substrate of between 0.5 and 5 m / s, preferably around 2.5 m / s.

‘According to a preferred form of the invention, the metal is chosen from the group formed by Co, Fe, Ni, Cr, Mn, Zn, possibly in association with Mo.

Other details and particularities of the invention will emerge from the description given below, by way of nonlimiting examples, of some particular embodiments of the method according to the invention.

In general, the present invention relates to a process for the formation of a substantially shiny deposit, of a metal or of an alloy containing this metal, on the surface of a conductive substrate, such as a sheet of steel or metal objects, has 5 very varied forms, such as door latches for example, by electrolysis of an electrolyte based on an aqueous solution of a salt of this metal and optionally at least at least one other metal intended to form said alloy.

These are mainly the metals chosen from the group formed by Co, Fe, Ni, Cr, Mn, Zn, optionally in association with Mo, such as a Ni-Mo alloy, rich in Mo ep.

This process is essentially characterized by the fact that an organic additive content is maintained in the electrolyte lower than that corresponding to a metal deposit 15 containing at most 1% of impurities due to the presence of this organic additive and that this electrolyte is subjected to a substantially constant and homogeneous movement in the immediate vicinity of the surface to be covered with the conductive substrate, with a speed of at least 0.3 m / s relative to the substrate.

This speed must be chosen so as to create in the immediate vicinity of this surface a hydrodynamic flow regime of the electrolyte which is such that the conditions of electrolysis, such as the concentrations and the pH of the electrolyte, are homogeneous on a substantially microscopic scale along the entire surface of the substrate to be covered.

It has been found that if these conditions are met, an appreciably shiny metallic deposit is obtained on the substrate. Thus, it is possible to vary the electrolysis conditions, between relatively wide limits, provided that they vary in the same way near the entire surface to be covered.

If the substrate is formed by a sheet, it is advantageous to make use of an electrolysis cell of the type described and represented in French patent 79.27.756.

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Advantageously, use is made of an electrolyte which is substantially free of organic additives, that is to say in which such an additive has not been intentionally added as is the case in most of the known methods including question above. 5 Thus in practice it could indeed be that, depending on the origin of the salts used in electrolysis, this electrolyte contains traces of organic additive.

More specifically, in the context of the present invention, the expression "free of organic additives" can mean that the electrolyte contains less dp: - 20 mg / l of sodium lauryl sulfate; - 5 mg / 1 of class I additive such as: benzene sulfonic, bisulfonic, trisulfonic acids and their derivatives, toluene sulfonic, bisulfonic acids and their derivatives, naphthalene sulfonic, bisulfonic, trisulfonic acids and their derivatives, saccharin, and any other additive of the same type; 20 - 5 mg / 1 of class II additive such as: - coumarin (with a restriction of less than 3 mg / 1) - formaldehyde and its derivatives, - carboxylic acids such as cystine and their derivatives, - pyridine and its derivatives, - butynediol, - quinoline and its derivatives, - nitrile derivatives, - thiourea and its derivatives, and any other additive of the same type; 30 - 0.1 g / 1 citric acid or formic acid.

It is admitted that with such additive contents, the chemical and mechanical properties of the metallic deposit - 6 - are not noticeably altered for most of the industrial applications envisaged. More particularly, in most cases, depending on the practical electrolysis conditions and the nature of the metal deposit, a speed of the electrolyte is maintained in the immediate vicinity of the surface to be covered with the substrate of between 0.5 and 5 m / s, preferably around 2.5 m / s.

Furthermore, it has been found that if the pH in the electrolyte is maintained between -1 and 8, and preferably between 1 and k, good results are obtained.

It is the same for the density of the cathode current which between 3 and 1000 amperes / dm2, and in particular between 5 and 100 amperes / dm2, makes it possible to obtain a very satisfactory glossy deposit with an industrially acceptable yield.

J5 The temperature of the electrolyte can be relatively low, of the order of 10 to 70 ° C and preferably between 15 and 35 ° C.

As regards the concentration of the metal or metals in the electrolyte, this is generally between 0.01 g / l ions and saturation.

The saturation concentration of a given metal can, if the metal deposit consists of an alloy, depend on the concentration of the other metal of this alloy.

The process according to the invention is particularly useful for the formation of a substantially shiny deposit of nickel or a nickel alloy, such as a nickel-molybdenum alloy on a steel substrate.

In this regard, for a deposit of pure nickel, tests were carried out under the following conditions: 30 - pH: 1.5 to 1.8, - relative speed of the electrolyte relative to the surface to be covered * - 7 - substrate greater than or equal to 1 m / s, - temperature between 20 and 35 ° C, - composition of the electrolytic bath: nickel chloride at substantially molar concentration, 5 - current density varying between 3 and 15 A / dm2 depending the relative velocity of the electrolyte.

Thus, the lowest current density was combined with the lowest relative flow velocity and the highest density was combined with the highest flow velocity. For a relative flow speed of 1 m / s, the current density was maintained at around 3 A / dm2 and for a speed of the order of 5 m / s, the current density was maintained at around of 15 A / dm2.

It has in fact been found that under these working conditions, the hydrogen formed at the cathode is discharged in a continuous and regular manner during all the electrolysis in the form of microscopic bubbles, therefore not disturbing the metallic deposit.

It was thus possible to obtain a shiny and very adherent deposit of nickel on a steel sheet up to 20 thicknesses of 20 μm.

The anode used was generally soluble, although an insoluble anode, for example carbon or even platinum, could also be used.

Other practical tests have been carried out for depositing a bright nickel-molybdenum alloy on a steel sheet using an anode which is insoluble in platinum.

| v From a solution containing order | from 110 to 160 g / 1 of Na ^ Cy 20 g / 1 of NH ^ CI, 1 to 40 g / 1 of NiSO ^ .7 and 5 g / 1 of Na ^ MoO ^ .2H ^ 0. at room temperature, on the order of 30 ° to 25 ° C., a nickel-molybdenum alloy, rich in molybdenum up to 50% molybdenum, glossy and adherent with thicknesses up to 25 μm, was deposited.

The cathodic current density - w - δ - varied from 5 to 30 A / dm2, while the speed of passage of the solution parallel to the cathode was 0.3 to 1 m / s.

Contrary to what was the case with nickel deposition, it has been found that very good results are obtained if the high current density is combined with the low displacement speeds of the electrolyte relative to the cathode.

Thus, for a current density of 30 A / dm2, it is preferable to maintain a speed of the electrolyte relative to the surface of the substrate to be covered, thus forming the cathode, of the order of 0.3 m / s .

Furthermore, a substantially shiny deposit of iron with a thickness of the order of 5 μm, on a copper sheet, was obtained from a molar iron fluoborate bath containing 10 g / l of NaCl, at a pH close to 0 and at a temperature of 55 to 60 ° C, with a current density of 20 to 30 A / dm2 for a stirring speed of 1.5 m / s.

From these various tests it therefore follows that it has been possible, quite unexpectedly, to obtain a substantially shiny deposit of a pure metal or an alloy on a surface of a conductive substrate by electrolysis of an electrolyte, without the need to add an organic additive thereto, if care is taken to create a determined relative speed of the electrolyte relative to the surface to be covered.

The other parameters of electrolysis, such as temperature, pH, concentration of metals to be deposited in. the electrolyte are generally less critical, so that the process is of marked interest for its application on an industrial scale.

It is understood that the invention is not limited to the concrete examples given above, but that the process can also be applied to the deposition, by electrolysis, of other metals, in particular Cr, Mn, Zn and Co.

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More particularly for cobalt, it has been found that, contrary to what is the case in the known processes for the formation of a bright deposit, the pH of the electrolyte bath is relatively uncritical, and can vary between 5 fairly wide boundaries.

This process can also be applied by means of any type of existing electrolytic cell provided that a sufficiently high and homogeneous relative speed of the electrolyte can be created there near the surfaces to be covered. . "

Claims (9)

1- Method for the formation of a substantially shiny deposit, of a metal or an alloy containing this metal, on the surface of a conductive substrate by electrolysis of an electrolyte 5 based on a solution of a salt of this metal and optionally of at least one other metal intended to form said alloy, characterized in that an organic additive content lower than that corresponding to a metallic deposit containing at most 1% is maintained in the electrolyte impurities due to the presence of this organic additive, and in that the electrolyte is subjected to a substantially constant and homogeneous movement in the immediate vicinity of the surface to be covered with the substrate, with a speed of at least minus 0.3 m / s relative to the substrate, so as to create a hydrodynamic flow regime of the electrolyte such that the electrolysis conditions are homogeneous on a substantially microscopic scale over the entire surface to be covered with the substrate. 2. Method according to claim 1, characterized in that the electrolyte is substantially free of organic additive. 3. Method according to claim 1, characterized in that maintains a speed of the electrolyte in the immediate vicinity of the surface to be covered with the substrate of between 0.5 and 5 m / s, preferably of the order of 2 , 5 m / s. 4. Method according to any one of claims 1 to 3, characterized in that the pH of the electrolyte is maintained between -1 and 8, preferably between 1 and 4. 5. Method according to any one of claims 1 to 4, characterized in that the density of the cathode current is maintained between 3 and 1000 amps / dm2, preferably between 5 to 100 amps / dm2. 6. Method according to any one of claims 1 to 5, characterized in that the temperature of the electrolyte on the surface to be covered with the substrate is maintained between - 11 - ft1 tw 10 and 70 ° C, preferably between 15 and 35 ° C. 7. Method according to any one of claims 1 to 6, characterized in that the metal is chosen from the group formed by Co, Fe, Ni, Cr, Mn, Zn, optionally in association with Mo. 8. Method according to any one of claims 1 to 7, characterized in that the electrolyte contains a sulfate and / or chloride of the above-mentioned metal or metals. 9. Method according to any one of claims 1 to 8, characterized in that the concentration of the metal or metals in the electrolyte is between 0.01 g / 1 ions and the saturation. ..sssinc: ......... ZL .. plor.cnes ..... of which ...... λ ........ cover page ....... .6 ...... page? ûf description .......; dp ....... / ..... abbreviated csscricv1 Luxembourg. the "f M Ist · The representative (• / se A.sJr: /./ϊ/.ν i '.: Λ · -! 1‘ liUÎL s u