LU84236A1 - METHOD AND DEVICE FOR THE CONTINUOUS, HIGH-CURRENT DENSITY ELECTROLYTIC DEPOSITION OF A LAYER OF A ZINC-BASED ALLOY ON A WIRE, TUBE, BAR OR THE LIKE - Google Patents

Description

4 * 2

The present invention relates to a process for the electrolytic deposition, continuously and at high current density, of a layer of a zinc-based alloy on an element in the form of wire, tube, bar 5 or the like, according to which displaces this element in an electrolysis cell, opposite an insoluble anode, through an electrolyte containing zinc sulfate.

In the processes known up to now, in the literature for covering such an element with a metallic layer, there are essentially two very different techniques.

A first technique consists simply in passing the element through one or more baths containing the molten cover metals, ^ 5 as described for example in American patent No. 3,858,333 in the name of Thompson, while following a second In technical terms, the element is covered by successive electrolytic deposits of the covering metals on the element, as for example described in DOS 2,106,226 from Michelin et Cie or in Japanese patent application 81.00.297. from Showa Electric Wire and Cable Cy. . / f 4 '3

Such methods are generally very complex V * and expensive, inter alia by the fact that they require a relatively large number of steps for each of which a very rigorous control of the operating conditions is required.

One of the aims of the present invention consists in remedying the abovementioned drawbacks and in proposing an extremely simple and reliable process for an application on an industrial scale continuously and at high current density and without rejection of toxic effluents.

To this end, according to the invention, the pH of the electrolyte of the electrolysis cell is less than 2, a temperature of 40 to 70 ° C. and a concentration of 0.2 to 2 moles / liter of 15 zinc and 0.3 to 2 moles / liter of iron sulphate, = nickel and / or cobalt, depending on the nature of the alloy to be produced.

Advantageously, the pH is maintained in the electrolyte less than 1.2 and preferably less than 0.4.

According to an advantageous embodiment / a molar ratio M / Zn which is less than 1.5 is maintained in the electrolyte, for a pH lower than or at most equal to 1.2, 25 M being Ni , Fe or Co.

According to a particularly advantageous embodiment, the concentration of metal ions in the electrolyte is adjusted so as to obtain a zinc-nickel alloy containing 2 to 14% of nickel, a zinc-iron alloy containing 2 to 15% of iron or a zinc-cobalt alloy containing 2 to 12% cobalt. , / t <4 The invention also relates to a process for the continuous regeneration of the electrolyte of an electrolysis cell for the electrolytic deposition, at high current density, of a layer of an alloy 5 based of zinc on a sheet, in particular of the electrolyte tel.gue described above.

According to the invention, the pH is maintained in the electrolyte below 2 and at least part of this electrolyte is continuously extracted from the cell to regenerate this electrolyte by dissolving in this part, in ratios corresponding to the desired alloy, zinc, on the one hand, and nickel-plated iron and / or cobalt, on the other hand, depending on the nature of the alloy desired, the electrolyte thus regenerated 15 then being reintroduced, also continuously, in the electrolysis cell.

According to a particular embodiment of the invention, the zinc is introduced into the electrolyte to be regenerated in the metallic form.

According to a particularly advantageous embodiment of the invention, zinc and the other metal of the alloy to be produced and used for regeneration | of the electrolyte are introduced into separate quantities of electrolyte, these quantities then being combined before being reintroduced into the electrolysis cell, the ratio of these quantities being adjusted according to the desired ratio of metals in I the alloy to be produced in the cell, j Finally, the invention also relates to one; 30 installation for carrying out the electro / | trolysis and regeneration as described above.

! (5 'This installation is characterized in that it is equipped, for the continuous regeneration of the electrolyte, with a device connected to said electrolysis cell comprising a buffer tank / connected 5 directly to the cell by inlet and outlet pipes, and at least two dissolution reactors mounted in parallel on this tank and through each of which electrolyte can flow from the buffer tank, means being provided for regulating the relative flow rate of the electrolyte through these reactors depending on the ratio of metals in * the alloy to be produced in the cell.

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 of the invention with reference to the accompanying drawings.

FIG. 1 shows a block diagram of a first embodiment of the installation according to the invention.

FIG. 2 shows a block diagram of a second embodiment of the installation according to the invention.

In these two figures, the same reference numbers refer to identical or analogous elements.

The invention is above all aimed at optimizing the use of a sulfate electrolyte, in extraction electrolysis.

It relates more particularly to a process for the electrolytic deposition, continuously and at high current density, in particular from 20 to 300 A / dm, 2

and preferably from 30 to 200 A / dmy of a layer of a zinc-based alloy with a thickness varying preferably / between 1 and 12 on a wire-shaped element, / X

(I

6 "bar, tube or the like, for example made of steel or soft iron.

This is a process by which this element is moved in one or more electrolysis cells, opposite an insoluble anode, through an electrolyte containing zinc sulfate.

The cell may be of a conventional type or correspond to that which is the subject of patent in the United Kingdom No. 1,038,671, improved by a system for circulating one electrolyte. ÎO According to this process, the pH of the electrolyte of the electrolysis cell is less than 2, a temperature of 40 to 70 ° C and a concentration of 0.2 to 2 moles / liter of zinc sulfate and 0 , 3 to 2 moles / liter of an iron, nickel and / or cobalt sulfate, depending on the nature of the alloy to be produced. - The alloy can therefore be a zinc-, nickel, zinc-iron, zinc-cobalt alloy or even a zinc-nickel-iron, zinc-nickel-cobalt, zinc-iron-cobalt alloy or even a zinc alloy- iron-cobalt-nickel.

More particularly, a pH of less than 1.2 and preferably less than 0.8 is maintained in the electrolyte of the electrolysis cell, eg between a pH of 0 and 0.5.

One can, for example, use, at high current density, an electrolyte with an acidity greater than * 1 mole / liter, in particular of the order of 1.5 moles / liter.

The acidity in the electrolyte can be adjusted by the addition of sulfuric acid.

Advantageously, the relative concentration of metal ions in the electrolyte is adjusted so as to obtain a zinc-nickel alloy containing from 2 to 14% of nickel, a zinc-iron alloy containing 2 to 15% of iron or a zinc alloy. cobalt containing 2 to 12% / cobalt. fy 1.

7

Contrary to certain known methods, an electrolytic bath free of metal chlorides and also free of supporting electrolytes is used, so as to obtain a bath as pure as possible, thus making it possible to ensure the formation of a Electrolytic deposition on the element of a zinc alloy of very high homogeneity and purity, without it being necessary to take special precautions in this regard.

Since the electrolyte is free of chlorides, use may be made of an anode formed * of a lead-silver alloy, with a silver content, which is preferably 0.6 to 1.2%.

Furthermore, thanks to the fact that the electrolyte 15 has a very low pH, it is possible to maintain in the electrolyte a molar ratio M / Zn of less than 1.5, M being Ni, Fe or Co, this mistletoe therefore allows to reduce the relative quantity of the metal M used for the formation of a zinc alloy.

This can be an important characteristic of the electrolyte. '*

In order to allow operation with relatively high current densities, in particular up to. 2300 A / dm, as already indicated above, the relative speed of the electrolyte relative to the element to be covered is advantageously maintained at a value greater than lm / sec, and even at 2m / sec, this speed preferably being greater than 4m / sec for densities of 2 'current of the order of 200 to 300 A / dm, depending on the na- /

ολ ture of the element. AT

/// 8

In order to be able to carry out an electrolysis in a very acidic bath, at a pH up to 0 or even lower, there is associated with electrolysis a continuous regeneration of the electrolyte which is such as to stabilize the pH in the cells, the regeneration using this high acidity for the dissolution in the electrolyte to regenerate of the metals which are deposited at the cathode.

To ensure this regeneration of elec-10 trolyte, a pH of less than 2, and preferably less than 1.2, is maintained in it, and the electrolyte is extracted continuously from the cell to dissolve therein, in ratios corresponding to the desired alloy, zinc, on the one hand, and nickel, iron and / or cobalt, on the other hand, depending on the nature of the alloy desired, the electrolyte thus regenerated then being reintroduced, also continuously, into the electrolysis cell.

To avoid entrainment, in the electrolytic bath of the cell itself, of undissolved particles coming from this regeneration and thus preventing contamination of the electrodeposition on the sheet to be covered and also to allow adjustment. flexible in the regeneration process depending on the operating conditions of the cell, the addition of these metals takes place in separate quantities of electrolyte to be regenerated, outside the electrolysis cell, these quantities then being mixed again, before being reintroduced into the cell, at the time when all the 2q metals are completely dissolved and possibly, after settling of insoMdI.es impurities coming from / this regeneration. f 9 "

The fact of isolating adjustable quantities of electrolyte, to which metals to be dissolved for regeneration are then added separately, makes it possible to regulate the conditions of dissolution of these metals, independently of the circulation of the electrolyte in the cell electrolysis itself, and this while carrying out continuous electrolysis and regeneration perfectly suited to this electrolysis.

Advantageously, the zinc 10 is introduced into the electrolyte to be regenerated in metallic form, which excludes or minimizes contamination of the electrolyte bath.

Nickel and cobalt are advantageously introduced into the electrolyte in the form of carbonates, while iron is advantageously introduced in metallic form or in the form of ferric hydroxide or a combination of the two.

FIG. 1 shows a block diagram of a first embodiment of an installation for the electrolytic deposition, continuously and at high current density, * 1 of a layer of a zinc-based alloy on an element in the form of a wire, bar, tube or the like.

This installation comprises an electrolysis cell 1, in one or more 25 or more of these elements pass simultaneously opposite an insoluble anode through an electrolyte containing sulphate. zinc. This element or these elements, as well as the anode and the cathode, have not been shown in the figure, since it may be an electro-cell. lysis of any type known per se for this kind / of operations. / J.

7 10 The element therefore in fact acts as a * cathode, while the insoluble anode is preferably made of a lead-silver alloy, the silver content of which is between 0.6 and 5 1.2% .

This installation is characterized in that it is equipped with a device for continuous regeneration of the electrolyte, connected to the electrolysis cell 1.

10 This regeneration device comprises a buffer tank 2 connected directly, by an inlet pipe 3 and an outlet pipe 4, to the cell, and two dissolution reactors 5 and 6, mounted in parallel * * on the tank 2, means being provided for regulating the relative flow rate of the electrolyte through these reactors as a function of the ratio of metals in the alloy to be produced in cell 1.

These means are for example constituted by valves 7 and 8 provided respectively upstream of the reactors 5 and 6, which are connected by a supply pipe 9 and a return pipe 10 to the tank 2.

'* \

The tank 2 can possibly function as a decanter in the event that insoluble materials, originating from the dissolution of the metals in the reactors 5 and 6, are introduced into this tank through the return pipe 10,

The circulation between the cell 1 and the tank 2 is ensured by a pump 12, provided eg on the conduit 4, while the circulation between the tank 2 and the reactors 5 and 6 is obtained by a pump 13 provided eg on the conduit 9..

The operation of this installation can / can be described as follows: / h 11

As a result of the electrolysis reaction in cell 1, zinc and one or more other metals, intended to form an alloy with zinc, are deposited on the element (s) moving in the cell. This results in an exhaustion of the electrolyte in metal ions and an increase in the acidity of the bath. In regime, one aims to maintain in the bath a pH lower than 2 and preferably lower than 1.2, as already indicated above.

The electrolyte generally circulates in the cell at relative speeds of 1 to 4 m / sec or possibly more with respect to said element, depending on the desired current density, and is extracted from the cell by the inlet pipe 3 to be introduced into the reser-15 see buffer 2, in which a relatively stable pH, corresponding substantially to that desired in the cell, is maintained.

Part of the electrolyte in reservoir 2 is directed, via the supply line 8, to the two dissolution reactors 5 and 6, also called regenerators. In one of the reactors, for example the reactor * 5, the zinc necessary to compensate for the depletion of zinc is introduced into the electrolytic bath of cell 1, while in the other reactor, it is introduced. 25 duit the other metal intended to form an alloy with zinc in cell 1.

The relative flow rate of the electrolyte through these reactors 5 and 6 is regulated by the valves 7 and 8, so that the ratio of the quantities of dissolved metals 30, brought back by the return pipe 9 to the reservoir, corresponds to the concentration ratio of these metals necessary to obtain the desired alloy. / 12

The arrow 11 indicates an introduction of water into the 1-tank 2 to compensate for the water consumption during the electrolysis reaction.

As already indicated above, the zinc can be introduced in a metallic form, for example in the form of bars or ingots, into the reactor 5.

The electrochemical reactions on which the electrolysis and regeneration of the electrolyte are based, described above, will be described in more detail below, thus giving the preferred operating conditions for electroplating. of a zinc-nickel alloy, .. zinc-iron and zinc-cobalt.

1 ° Zinc-nickel.

A) composition of the electrolytic bath in cell 1: ZnSO 4: 0.5 to 2 moles / liter

NiSO ^: 0.2 to 2 moles / liter pH: 0 to 1.2 (by addition of H ^ SO ^) 20

b) operating parameters of the electrolysis cell: temperature: 40 to 70 ° C.

2 current density: 20 to 300 A / dm relative circulation speed of the electrolyte: 25 1 to 8 m / sec c) regeneration products introduced into the reactors /

5 and 6 -. rJ

Zn and NiC03. 2Ni (0H) o / V

30 ‘f.

13 <3) composition of the alloy obtained:? 2 to 14% of Ni e) electrochemical reactions; 5 - at the cathode: Zn ++ + 2e- * Zn

• H

Ni + 2e - => Ni - at the anode: 2H20 - ^ O + 4H + + 4th f) overall balance of electrolysis: 10 a Ni ++ + (1 - a) Zn ++ + 2e a Ni + (1 - a) Zn H20 ---> 1/2 o2 + 2H + + 2e a Ni ++ + (1 - a) Zn * 1-4- + H20-> o; Ni + (1 - a) Zn + 1/2 02 + 2H + 15 a represents the molar percentage of nickel in the deposit (in fraction of unit) g) regeneration: - for zinc: 20 (1 - a) Zn + (1 - a) 2H + -> (1 - a) Zn ++ + (1 - a) h2 - for nickel: basic nickel carbonate NiC03.2 Ni (OH) 2.

In an aqueous solution at pH 1, the dissolution of this product corresponds to the dissolution of NiO, after release of C0_ and release of ELOl _ + ^ a- + 2

a NiO H- a 2Π - »a Ni + a H O

- overall; (1 - a) Zn + a NiO + 2H ^ - * a Ni ++ + (1 - α) Zn ++ + 30 (1 - a) H: + a; EO / / 7 14 h) overall assessment of the electrolysis and regeneration process: aNi ++ + (l-ct) Zn ++ + H20—> aNi + (l-oc) Zn + 1/2 02 + ctH + (l-ct) Zn + aNiO + 2H "t-> oNi ++ - t (la) Zn +++ (la) H2 + aH20 5 (la) H20 - * (la) H2 + 1/2 (la) 02 2 ° Zinc-iron.

a) composition of the electrolytic bath in the cell 1: 10 ZnSO ^: 0.5 to 2 moles / liter

FeSO ^: 0.6 to 2 moles / liter * pH: 0 to 1.2 (by addition of I ^ SO ^) b) operating parameters of the electrolysis cell:

15 temperature: 40 to 70 ° C

2 | · Current density: 2 O at 300 A / dm relative circulation speed of the electrolyte: 1 to 8 m / sec 20 c) regeneration products introduced into the reactors j 5 and 6: '

Zn and.

Fe or Fe + Fe (0H) 2 25 d) composition of the alloy obtained: 2 to 15% of Fe ie) electrochemical reactions: I ++ S - at the cathode: Zn + 2e - = * · Zn j 30 Fe ++ + 2e- ^ Fe - at the anode: 2H20_ * 02 + 4H + + 4th /! t 15 vf) overall balance of electrolysis: aFe ++ + (la) Zn ++ + 2e— * aFe + (la) Zn H20 ------------------> 1/2 02 + 2H + + 2e 5 ctFe +++ (la) Zn +++ H ^ O— ^ aFe + (la) Zn + 1/2 02 + 2H + a represents the percentage of iron in the deposit (in fraction of unit).

10 g) regeneration: -for zinc: '(1 - a) Zn + (1 - a) 2h "Î ^> (1 - a) Zn ++ + (1 - â) -H2 -for iron (two possibilities) : a. iron powder 15 a Fe + 2aH -> aFe + aEt, giving overall the following diagram: aFe + (la) Zn + 2H * - »(la) Zn ++ + aFe ++ + H2 b. iron and goethite [Fe + 2Fe0.0H + 6H + -> 3Fe ++ + 4 ^ 0] 20

i K

h) overall assessment of the electrolysis and regeneration process: aFe +++ (la) Zn ++ + H20— ^ aFe + (la) Zn + 1/2 02 + 2H + aFe + (la) Zn + 2H + -> (1-a) Zn +++ aFe '+ + H'2 25 H20 -> 1/2 02 + H2 3 ° Zinc-cobalt.

a) composition of the electrolytic bath in the cell 1: 30, /

ZnSO ^: 0.3 to 2 moles / liter /

CoSO ^: O, 6 to 2 moles / liter Ai pH: 0 to 2 (by addition of H ^ SO ^ [D / 16 * b) operating parameters of the electrolysis cell: *

temperature: 40 to 70 ° C

2 current density: 2o at 300 A / dm relative circulation speed of the electrolyte: 5 1 to 8 m / sec c) regeneration products introduced into reactors 5 and 6:

Zn and CoC03.2Co (0H) 2 10 d) composition of the alloy obtained: 2 to 12% of Co e) electrochemical reaction: 15 - at the cathode: Zn ++ + 2e-i Zn ++

Co + 2e- ± Co - at the anode: 2H20_ ^ 02 + 4H + + 4th i 'f) overall balance of electrolysis: | 20 & Co ++ + (l-a) Zn ++ + 2e— ^ aCo + (l-a) Zn | H20 _! - * 1/2 02 + 2H + V 2e I aCo ++ + (l-a) Zn +++ H o-- »aCo + (l-a) Zn + 1/2 0 + 2H +

j <! - β Z

l! VS ! 25 a represents the molar percentage of cobalt in | the deposit (fractional unit) | i g) regeneration:! -for zinc: 30 (l-tt) zn + (l-a) 2H + -5 * (l-a) zn ++ + (l-cOEL / F Z j f 17 -for cobalt: basal cobalt carbonate CoC03.2Co (OH) 2 *

In an aqueous solution at pH 1, the dissolution of this product corresponds to the dissolution of CoO after release of CCt and release of H 0. * + 2 ++ 2 a CoO + α 2H-> a Co + a H20 - overall i aCoO + (la) Zn + 2H% cxCo +++ (la) Zn ++ + H20 + (l-cc) H ^ 10 h) overall assessment of the electrolysis and regeneration process:, aCo +++ (la) Zn +++ HO — f aCo + (la) Zn + 1/2 02 + 2H +

aCoO + (1-a) Zn + 2H -> aCo ++ + (l-a) Zn +++ aH20 + ’(l-a) H

15 (l-a) H20 -Ml-a) H2 + 1/2 (ι-to) C> 2

In conclusion, it can therefore be seen that, for these three types of alloys, there is, in terms of electrolysis, in addition to consumption of metal ions for the alloy to be produced, consumption in H „0, a production. + 2 H ions and release of oxygen.

In addition, in particular in the case of a -f + -H- zinc-nickel alloy, the Ni / Zn = a molar ratio is less than 1.5 and generally between 0.5 and 1.2 in the electrolytic bath.

The production of H ‘ions, discussed above, therefore leads to an acidification of the electrolytic bath in the cell. / J, 30 1.

18 ‘As already indicated above, an essential characteristic of the invention consists in using these H + ions produced to regenerate the electrolyte.

Thus, it is possible to maintain the pH in the electrolytic bath of the cell above a minimum value and, at the same time, to replace therein, the metal ions which have been extracted from this bath as a result of the electrolytic deposition , without the need for special means to form these ions.

! Metals or metal compounds used | * for regeneration in reactors 5 and 6 must preferably be easily soluble in acid baths without leaving insoluble traces, which may pollute the electrolytic bath. Thus, metals in the metallic state, such as zinc and iron, and carbonates or hydroxides of nickel, cobalt and iron are particularly suitable. A preference is given, for example, to basic carbonates of nickel and cobalt and to ferric hydroxide mixed optionally with particles. of metallic iron.

. In the case of the use of carbonates, the evolution of CO ^, mixes the solution and thus makes it possible to increase the homogeneity of the electrolyte in reactors 5 and 6.

The process of the invention is illustrated below by guelgues practical examples of embodiment.

Example 1.

In order to produce an electrolytic deposit of a zinc-nickel alloy on a steel wire with a diameter of 1 mm, an electrolysis of an electrolytic bath / containing 0.5 moles / liter of NiSOyi /! Ψ 19 and 0.7 tnole / liter of ZnS04, maintained at a pH of the order of 0.3 by addition of sulfuric acid, and at a temperature of the order of 50 ° C. The density of the extraction current was 30 A / dm. The voltage at the terminals of the cel-5 Iule was 4 Volts and the cathodic efficiency was 74%. The electrolyte circulation speed was 3 m / sec, while the wire speed, in the opposite direction to that of this circulation, was 1 m / sec.

The anodes used were lead-silver, with a silver content of 0.6%. For regeneration in reactors 5 and 6, metallic zinc and basic nickel carbonate were used.

The thickness of the deposit obtained was 4 ^.

The alloy obtained contained about 13% nickel.

The appearance of the deposit is a light gray, uniform and shiny.

Example 2.

A steel wire with a diameter of 3 mm was coated with a zinc-nickel alloy.

20 For this purpose, a bath of 1 mole / liter of ZnSO 4 and 0.8 ra ° l / liter of NiSO 4, maintained at a pH of 0.5, per l was used in the electrolysis cell. 'addition of H ^ SO ^ and at a temperature of 50 ° C.

The cathodic extraction current density was of the order of 50 A / dm. The voltage across the cell was 5.3 Volts and the cathode current efficiency was 74%. The circulation speed of the electrolyte / (20 was of the order of 3 m / sec, while the speed of movement of the wire in the opposite direction to that of the electrolyte was of the order of 6 m / sec .

For the regeneration in reactors 5 and 6, metallic zinc and basic nickel carbonate were used.

The electrolytic deposit obtained was formed by a nickel-zinc alloy containing 11% nickel and having a thickness of the order of 1 ^ ·· 10 The appearance of the deposit was a uniform light gray.

Example 3.

A steel wire with a diameter of 3.5 mm a. was coated with a zinc-nickel alloy.

The electrolytic bath used contained 2 moles / liter of ZnSO 4 and 2 moles / liter of NiSO 4 and was maintained at a pH of 0.2 by the addition of H 4 SO 4, and at a temperature of the order of 50 ° C.

2

The density of the cathode current was 150 A / dm.

The voltage across the cell was 12 Volts 2o and the efficiency of the cathode current was 74%.

The speed of the electrolyte was 4 m / sec, while that of the wire, in the opposite direction to that of the electrolyte, was 3.3 m / sec.

The anodes used were lead-silver, with a silver content of 0.6%.

The regeneration took place by the addition, to the electrolyte, of metallic zinc and basic nickel carbonate.

"The alloy contained 13% nickel and had a / 30 shiny gray appearance. // ï 21

Example 4.

t

A steel tube with an outside diameter of 5/8 inches and an inside diameter of 14.5 mm was coated internally and externally with a zinc-nickel alloy.

The electrolytic bath used contained 1 harbor / liter of NiSO 4, 1 mole / liter of ZnSO 4 and was maintained at a pH of 0.8 and at a temperature of the order of 50 ° C.

The density of the cathodic current was 50 A / dm.

The voltage across the cell was 5.3 Volts and the efficiency of the cathode current was 76%.

* »- The circulation speed of the electrolyte was 2 m / sec, while that of the tube, in the opposite direction to that of the electrolyte, was 1.2 m.

The anodes used were lead-silver, with a silver content of 0.6%.

The regeneration took place by the addition to the electrolyte of metallic zinc and basic nickel carbonate.

The alloy contained 10% nickel and had a uniform light gray appearance. The thickness of the deposit was of the order of 5 AL.

. These four tests were reproduced by simply replacing the NiSO. respectively by FeS0 „

and CoSO ^ to produce zinc-iron and zinc- / cobalt alloys. A J

î 22. For regeneration, in the case of the production of a zinc-iron alloy, we used metallic zinc and a mixture of iron and goethite! ! and also iron only.

J 5 In the case of the production of a zinc-cobalt alloy, the regeneration took place using metallic zinc and basic cobalt carbonate.

The other operating parameters and conditions were kept similar to those of these four examples for the preparation of a zinc-nickel alloy.

FIG. 2 shows a block diagram of a second embodiment of an installation for the continuous high density electrolytic deposition of a layer of a zinc-based alloy 15 on a shaped element of wire, bar, tube or the like.

In this embodiment, all of the electrolyte is continuously circulated through the closed circuit 15, in which there is provided a circulation pump 16, to achieve the circulation speed 20 necessary in the electrolysis cell 1 and thus making it possible to obtain a sufficiently high cathodic current density. Only a fraction of the electrolyte is subjected to the abovementioned regeneration in a device which comprises a buffer tank 2 this denier also serving as a dissolution reactor, to the same degree as the reactors 5 and 6 of the first embodiment shown in FIG. 1. This reservoir 2 is connected directly to the cell 1 by an inlet pipe 3 and an outlet pipe 4, a circulation pump 12 and a valve 17 for adjusting the flow rate being provided on this pipe 4. n \ sy 23

This helps to make traffic in? this separate circuit independent of circulation through the electrolysis cell itself, this mistletoe would have the advantage of being able to create, for example, in tank 2, thus acting as a dissolution reactor, the necessary conditions for dissolving the metals intended to the regeneration of the electrolytic bath.

From the description, and in particular from the practical examples given above, it follows that the method according to the invention has the advantage that a coating of an element in the form of a wire, bar, tube or the like is obtained by a alloy in a single operation, unlike this mistletoe is for example the case in known methods 15 according to which it is for example necessary to pass through a series of successive baths of covering metals, which are separated by washing baths, and by a final heat treatment.

According to this known technique, a coating is obtained formed from at least two successive layers between which a potential difference can form.

This can therefore give rise to material migration and thus to the formation in the coating of corrosion centers.

It is understood that the invention is not limited to the embodiments described above of the method and installation according to the inventicx ^^^ / 24 It is thus, for example, that, in certain cases, one could limit itself, for the regeneration of the electrolyte, to the addition to the buffer tank 2 of the metals necessary to compensate for the exhaustion of the.

5 bath in the electrolysis cell without making use of the closed circuit 15 of FIG. 2, so that all the electrolyte of the cell passes through this reservoir.

However, the possibility exists that, in such an embodiment, special precautions will have to be taken to prevent entrainment of the solid particles, originating from regeneration, in the electrolysis cell via line 4.

Furthermore, depending on the nature of the desired alloy or the operating conditions, one could provide either a single reactor or two or more of two reactors in parallel with the buffer tank 2, combined or not with a closed circuit of the same type as the circuit 15 of FIG. 2 to ensure circulation in the cell.

Finally, the following method and installation ‘" the invention applies to the coating of any type of wire, tube, bar or the like made of a material j electrically conductive. Π î

Claims (19)

1. Process for the electrolytic deposition, continuously and at high current density, of a layer of a zinc-based alloy, on an element in the form of a wire, bar, tube or the like, according to which this 5 is displaced element in an electrolysis cell, opposite an insoluble anode, through an electrolyte containing zinc sulphate, characterized in that a pH of less than 2 is maintained in the electrolyte of the electrolysis cell temperature from 40 to 70 ° C and a concentration of 0.2 to 2 moles / liter of zinc sulfate and 0.3 to 2 moles / liter of iron, nickel and / or cobalt sulfate depending on the nature of the alloy to be produced. 2. Method according to claim 1, characterized in that a pH of less than 1.2 and preferably less than 0.4 is maintained in the electrolyte. 3. Method according to either of Claims 1 or 2, characterized in that the pH in the electrolyte is adjusted by adding sulfuric acid. 4. Method according to claim 3, charac- * t 2o teriser in that it maintains in the electrolyte of the electrolysis cell a concentration of sulphurous acid greater than 1 mole / liter. " 5. Method according to any one of claims 1 to 4, characterized in that the concentration of metal ions in the electrolyte is adjusted so as to obtain a zinc-nickel alloy containing 2 to 14% of nickel, an alloy zinc-iron containing 2 to 15% iron or a zinc-cobalt alloy containing 2 to 12% / cobalt. f \ j 6. Method according to any one of the preceding claims, characterized in that an electrolytic bath substantially free of chlorides is used. 7. A method according to any one of the preceding re-vendications, characterized in that * in the electrolysis cell, an anode formed of a lead-silver alloy is used, the silver content of which is preferably 0, 6 to 1.2%. 8. Method according to any one of the preceding claims, characterized in that, in the electrolyte of the electrolysis cell, a molar ratio M / Zn of less than 1.5 is maintained, M being Ni , Fe or Co. 9. Process for the continuous electrolytic deposition at high current density of a layer of a zinc-based alloy on an element in the form of a wire, bar, tube or the like, according to which this element is disturbed in at least one electrolytic cell ev of an insoluble anode and through an electrolyte bath containing zinc sulphate, in particular method according to any of the preceding claims, characterized in that it is maintained in the electrolyte a pH inferral to 2 and that is extracted from the electrolyte of a continuous mess of the cell to regenerate it by dissolving therein, in ratios corresponding to the desired alloy. zinc, on the one hand, and nickel, iron and / or cobalr. on the other hand, depending on the nature of the desired alloy of the electrolyte thus regenerated, then being reintroduced, also continuously, into the cell electrolysis. / 30 ‘/ F 10. Method according to claim 9, characterized in that the zinc is introduced into the electrolyte to be regenerated in metallic form. 11. Method according to either of Claims 9 and 10, characterized in that nickel and cobalt are introduced into the electrolyte to be regenerated in the form of carbonates, while iron is introduced into the electrolyte to regenerate in metallic and / or ferric hydroxide form. 12. Method according to any one of claims 9 to 11, characterized in that the zinc and the other metal of the alloy to be produced and serving for the regeneration of the electrolyte are introduced in separate quantities of electrolyte, these quantities then being combined before being reintroduced into the electrolysis cell, the ratio of these quantities being adjusted as a function of the desired ratio of metals in the alloy to be produced in the cell. 13. Process for the electrolytic deposition, in continuous and at high current density, of a layer of a% t of a zinc-based alloy on an element in the form of wire, bar, tube or abalogue, such as described above or shown in the accompanying drawings. „14. Installation for the electrolytic deposition, continuously and at high current density, of a layer of a zinc-based alloy on an element in the form of wire, bar, tube or the like, comprising a cell electrolysis in which at least one element in the form of a wire, bar / tube or the like can move continuously, opposite an insoluble anode and through an electrolyte containing zinc sulphate, this installation being characterized in that it is equipped, for the J “regeneration, continuously, of the electrolyte, of a device connected to said electrolysis cell and comprising a buffer tank connected directly, by inlet and outlet pipes, on the 5 cell. 15. Installation according to claim 14, characterized in that it comprises at least one separate dissolution reactor connected to the buffer tank and through which electro-lyte from the buffer tank can flow. 16. Installation according to claim 15, characterized in that it comprises at least two dissolution reactors mounted in parallel on this tank and through each of which electrolyte can flow from the buffer tank, means being provided. to adjust the relative flow rate of the electrolyte through these reactors according to the ratio of metals in the alloy to be produced in; the cell. I 20 17.Installation according to any of the | Claims 14 to 16, characterized in that it comprises I a circulation circuit for the electrolyte closed on! j the mistletoe cell is independent of the regulatory system! abovementioned generation. 18. Installation for electrolytic deposition, continuously and at high current density, as described above or shown diagrammatically in the attached drawings. / \ f 30 L Ü 19. Element in the form of a wire, bar, tube or the like coated with a zinc-based alloy according to the method or by means of the installation as described above or shown in the accompanying drawings. Drawings: - plates ..... pages of which ...... / 4 - cover page - JfcL - description pages - £ L _____ pages of claims - short description Luxembourg, JUNE 1982 * Agent: A / Charles München * l »