LU84138A1 - METHOD AND DEVICE FOR THE CONTINUOUS, HIGH-CURRENT DENSITY ELECTROLYTIC DEPOSITION OF A LAYER OF A ZINC-BASED ALLOY ON SHEET - Google Patents

Description

2.4581 od

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Patent application dated .10 May. .1982 ..........

Designation of the Inventor (1) The undersigned .Mans i.e. u r. Ch a ries. M.u n c.h e n »advice in., Patents .. to .....................

Luxem bour g., ..... lia. «Bo ul ev a rd Pr in ce - H enr i ......................... .................................................. ....

acting as depositor - agent of the depositor - (2). 1 a., S.oci been ... anonynia ... di te ..; ..... Cocker.i 11 - $ amber. 9 ..... $ .. e.rai.ng ... in Belgium (3) of the invention concerning: "Process and. dispos i ti f for .the .... deposit é 1 e et ro.] y..t ique,.. continuously ....

. and high. density of..current, ... d.a layer .... d, a ... all.i.a.ge .... à..base de. zinc on sheet metal ".............................................. .................... .............................. ............................................- designates as inventor (s ): ^ ΓΝοιη and first names .Mo.nsie.ur ... Ren.é .... WI.NA.ND ... .................... .................................................. .......

Address ... 2.4 * ... avenue Jean XXIII., Rixensar.t .. ».... B..el.gique .................... .............

2. Surname and first names ............................................. .................................................. .......................................... ........ ...

Address ................................................. .................................................. ............................................. ..... ..........................

3. Surname and first names ............................................. .................................................. .................................................. ................

Address ................................................. ............................. ..................... .................................................. .....................................

He affirms the sincerity of the above indications and declares to assume full responsibility for them.

Luxembo.ur..g ................................, on ... June 4 ... .................................. 19.82- liMKELUXEWiBüiiRaiöii ^ EU PROFR.ETÊ IKÔUSTRlEtÛ “vLl, ^ -Épcsi> _.

(signature)> wif - /: ‘s ·» ° * (1) Nbnj, pré! prâ, '; iftrme, Sdfesse.

“} (2) Nar%. loan is addressed to the depositor.

"L I" i i

I DESCRIPTION MEMORY

filed in support of an application for

I PATENT OF INVENTION

formed by i | the so-called public limited company: t i | ! "Cockerill-Sambre" î! for: î "Method and device for the electrolytic deposition, continuously and at high current density, of a layer of a zinc-based alloy on a sheet".

| _. ---------------------------------------------------------- ----- 1 Inventors: Lucien RENARD.

| Alain WEYMEERSCH.

! t

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The subject of the present invention is a process for the continuous electrolytic deposition at a high current density of a layer of a zinc-based alloy on a sheet, in particular a sheet of steel, according to which moves this sheet in an electrolysis cell, in contact with a cathode and opposite an insoluble anode, through an electrolyte containing zinc sulfate.

In known methods of this kind hitherto in the literature, use is made of an electrolyte! of relatively complex composition requiring a | very rigorous control of the operating conditions for! obtain alloys of sufficient purity, with very good industrial yields.

This therefore risks presenting fairly serious technical problems for the application of these methods on an industrial scale.

t Thus, DE-PS 30 05 159, which relates to a process for the preparation of a zinc-nickel alloy,! 20 mentions a sulfate rain containing a relatively high amount of Na 2 SO 4, as a support electrolyte. 1 use of such a support electrolyte is ir.caspensable so that the electrolytic bath in the electrolysis cup is sufficiently conductive at a pH of at least 2i at which the bath must be marttened in practice , as indicated

In the examples shown in this publication.

| By ail_ = urs, DE-OS 30 11 911, which is | also relates to a process for preparing a! 30 zinc-nickel alloy relates to the use of SrSO, / I / 2 (i as a support electrolyte in an electrolytic bath, = whose pH is always greater than 2, as also illustrated by the concrete examples of application described in that -this.

In these two previous processes, in industrial practice, the current density cannot generally exceed 20 A / dm, as is moreover apparent once more from said illustrative examples.

One of the aims of the present invention is to overcome the abovementioned drawbacks and to propose one! extremely simple and reliable process for continuous industrial application with high density iü i | current tee and without rejection of toxic effluents.

! For this purpose, according to the invention, the electrolyte of the electrolysis cell 11 is kept: | a pH below 2, a temperature of 40 to 70 ° C and I a concentration of 0.2 to 2 moles / liter in zinc sulfate and 0.3 to 2 moles / liter in iron sulfate, nickel and / or cobalt, depending on the nature of the alloy j; 20 to be produced.

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

According to a preferred embodiment, an M / Zn molar ratio, which is less than 1.5, is maintained in the electrolyte, and this for a pH lower than or at most equal to 1.2, / J.

M being Ni, Fe or Co. IM

30 ! j 3 "f = i i j The invention also relates to a method I. for the continuous regeneration of the electrolyte of an electrolysis cell for the electrolytic deposition, at high current density, of a layer of a zinc-based alloy 5 on a sheet, in particular of the electrolyte, such. as 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, iron and / or cobalt, on the other hand, depending on the nature of the desired alloy, the electrolyte thus regenerated at 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, the zinc and the other metal of the alloy to be produced and used for the regeneration of the electrolyte are introduced in amounts: separate from the electrolyte, these quantities are then combined before being reintroduced into the electrolysis cell, the ratio of these quantities being adjusted according to the desired ratio of metals in the alloy to be produced in the cell.

Finally, the invention also relates to an installation for implementing the electrolysis and regeneration process as described above. // 4. .

This installation is characterized by the fact that - it is equipped, for the regeneration in ccr.tinu of the trolyte elec, with a device connected to the said ce elec trolysis unit comprising a buffer tank, connected directly to the cell by inlet and outlet pipes, and at least two dissolving reactors mounted in parallel on this tank and through each of which electrolyte can flow from the buffer tank, means being provided 10 to adjust the relative flow rate of the electrolyte through these reactors according to the ratio of these metals in the alloy to be produced in the cell.

Other details and particularities of the invention will emerge from the description given below, I by way of nonlimiting examples of each particular embodiment of the process of the invention with reference to the accompanying drawings.

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

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

In these two figures the same reference numbers relate to identical or similar 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 Λ / dm, of a layer of a zinc-based alloy of uru · thickness varying from preferably between 2 and 12 / on a sheet, /, for example a steel sheet. /// shoot ! '5 ï \ Ü

It is a process by which this sheet is moved in an electrolysis cell, in contact with a cathode and opposite an insoluble anode, through an electrolyte containing zinc sulfate. The cell can be a conventional type or correspond to that which is the subject of the patent in the United States of America No. 4,304,653

According to this process, the pH of the electrolysis cell is maintained at a pH below IQ 2, a temperature at 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 sulphate depending on the nature of the alloy to be produced, i The alloy can therefore be a zinc- i] nickel, zinc- iron, zinc-cobalt or even a ji alloy of zinc-nickel-iron, zinc-nickel-ccbalt, zinc-iron-cobalt or even a zinc-iron-cobalt-nickel alloy.

More particularly, a pH of less than 1.2 and preferably less than 0.4 is maintained in the electrolyte of the electrolysis cell, eg between a pH of 0 and 0.3.

One can, for example, use 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 controlled 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 12% of nickel, a zinc-iron alloy containing 2 to • 15% of iron or a zinc alloy. -cobalt containing 2 to 12% /! cobalt. / y t: 6

Contrary to certain known processes, 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 an electrolytic deposit. on the sheet of a zinc alloy of very high homogeneity and purity, without gu'il

It is necessary to take special precautions in this regard.

g 10 Since the electrolyte is free from chlorides, use may be made of an anode formed ij 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, can be maintained in the elect | -j - {-; | trolyte an M / Zn molar ratio of less than 1.5, 1 M being Ni, Fe or Co, this mistletoe therefore makes it possible to reduce the relative amount of the metal M used for | the formation of a zinc alloy.

! jf. „.

;! 20 This may be a feature

Important electrolyte.

In order to allow operation with relatively high current densities, in particular from 20 to 300 A / dm2, as already indicated above, the relative speed of the electrolyte relative to the steel strip is advantageously maintained. a value greater than 1 m / sec, this speed preferably being greater than 4 m / sec for current densities of the order of, y 300 A / dm2. ///

Xi 7

In order to be able to carry out an electrolysis in a very acid 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, regeneration using this high acidity for dissolution in the electrolyte to regenerate 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 prevent contamination of the electrolytic deposit on the sheet to be covered and also to allow a flexible adjustment of the regeneration process in function under 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, by the time all! ! -an metals are fully dissolved and possibly JU / I after settling of insoluble impurities from / I this regeneration.

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8

By isolating adjustable quantities of electrolyte, to which metals to be dissolved for regeneration are then added separately, it is possible to regulate the conditions for dissolving these metals, independently of the circulation of the electrolyte.

In the electrolysis cell 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, i * 1 this mistletoe excludes or minimizes contamination! of the electrolyte bath.

| Nickel and cobalt are advantageously introduced into the electrolyte in the form of | 15 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, of a layer of a zinc-based alloy on a sheet.

This installation comprises an electrolysis cell 1. In the laguelle there passes a sheet in contact with a cathode and opposite an anode 25 insoluble through an electrolyte containing zinc sulphate. This sheet, as well as the anode and the cathode, have not been shown in the figure, since it may be an electrolysis cell known per se for this type of operation. . A / - 1 / i.

9

The sheet 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.

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 to regulate 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 settling tank 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 for example on the conduit 4, while the circulation between the tank 2 and the reactors 5 and 6 is obtained by a pump 13 provided for example on the conduit 9. /

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

T

; 10 ί i i As a result of the electrolysis reaction • in cell 1, zinc and one or more others; metals, intended to form an alloy with zinc, se! deposit on the sheet moving in the cell.

! 5 This results in exhaustion of the electro-! lyte 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.

10 The electrolyte generally circulates in the cell at relative speeds of 1 to 4 m / sec or possibly more with respect to the sheet, depending on the desired current density, and is extracted from the cell by the inlet pipe 3 to be introduced into the reservoir-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 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, the other metal intended is introduced. 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 ^ / / 11

The arrow 11 induces an introduction of water into the 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 will be described in more detail below. on which the electrolysis and regeneration of the electrolyte, referred to above, are based, as well as the preferential operating conditions and this for the electrolytic deposition of a zinc-nickel alloy, | zinc-iron and zinc-cobalt, j 1 ° Zinc-nickel.

; 15 | a) composition of the electrolytic bath in cell 1:! ZnSO ^: 0.5 to 2 moles / liter; NiSO. : 0.2 to 2 moles / liter! 4 | 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: J 25 1 to 4 m / sec i - * c) regeneration products introduced into the reactors / 5 and 6: ^

Zn and NiC03. 2Ni (OB) 2 / L · \ I 12 d) composition of the alloy obtained: 2 to 12% of Ni e) electrochemical reactions: 5 - at the cathode: Zn ++ + 2e —Zn

Ni "*" "*" + 2e- 'Ni - at the anode: 2H20 -' · 02 + 4H + + 4th f) overall balance of electrolysis: 10 a Ni ++ + (1 - a) Zn ++ + 2e a Ni + (1 - a) Zn H20_______________ ____> 1/2 02 + 2H + + 2e

j | a Ni ++ + (1 - a) Zn ++ + Η20- ^ α Ni -ï- (1 - a) Zn + 1/2 02 + 2H

II

! 15 a represents the molar percentage of nickel in | the deposit (in fraction of a unit) | g) regeneration: -for zinc: 20 (1 - a) Zn + (1 - a) 2H + -i (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 evolution of CO2 and release of H2O;

a NiO + a 2H + --- o; Ni + a H O

- overall; (1 - a) Zn + a NiO + 2H ^ -> a Ni ++ - (1 - a) ZnT + +! 30 d - k 'H2 -fa H20 / / I 13 ί h) overall assessment of the electrolysis and regeneration process: aNi ++ + (1-a) Zn ++ + E ^ O— ^ aNi + (Ι-α,) Ζη + 1/2 c> 2 + ctH + (la) Zn + o: NiO + 2H + - ouI +++ (1-a) Zn +++ (1-a) H + aH 0 2 2 5 (1-a) H20 --—- - * (1-a) H2 + 1/2 (1-a) 02 2 ° Zinc-iron.

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

FeS04: 0.6 to 2 moles / liter pH: 0 to 1.2 (by addition of H_S0) b) operating parameters of the electrolysis cell:

15 temperature: 40 to 70 ° C

ί 2 J current density: 20 to 300 A / dm | relative circulation speed of the electrolyte:; 1 to 4 m / sec ί i | 20 c) regeneration products introduced into reactors ί 5 and 6:

Zn and

Fe or Fe + FefOH) ^ 25 d) composition of the alloy obtained: 2 to 15% of Fe v * P e) electrochemical reactions: | ++ | - at the cathode: Zn + 2e —- Zn I 30 Fe ++ + 2e - T Fe! - at the anode: 2H „0 __ + 4H + + 4th A / I / 14 f) overall balance of electrolysis: aFe ++ + (la) Zn ++ + 2e- ^ cc.Fe + (l-ct) Zn H20-- ---- -> 1/2 02 + 2H + + 2e 5 aFe +++ (la) Zn +++ H20 — SaFe + (la) Zn + 1/2 02 + 2H +

Ia represents the percentage of iron in the deposit (in fraction of a unit).

10 g) regeneration: -for zinc: (1 - a) Zn + (1 - a) 2H ^ - + (1 - a) Zn ++ + (1 - a) H2 J -for iron (two possibilities): a . iron powder I + -j ~ j- * I 15 a Fe + 2aH -? aFe + aH2 giving I overall the following diagram: ÎaFe + (l-a) Zn + 2H + - ^ (l-a) Zn ++ + aFe ++ + H2 b. iron and goethite a | [Fe + 2Fe0.0H + 6H + -> 3Fe ++ + 4Η20Ί 20 h) overall assessment of the electrolysis and regeneration process: aFe +++ (la) Zn ++ + H20 _ ,? aFe + (la) Zn + 1/2 02 + 2H + aFe + (lo :) 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 4 / CoS04: 0.6 to 2 moles / liter / pH: 0 to 2 (by addition of E ^ SO ^) / d /% 15

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: 5 1 to 4 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-Zn ++ _

Co + 2e-r-Co - at the anode: 2 ^ 0_j ^ 02 + 4H + + 4th f) overall balance of electrolysis: 20 aCo ++ + (l “a) zn ++ + 2e—> aCo + (la) Zn H O ------ ----------------- 1/2 0 + 2H + + 2e 1 2 ^; aCo ++ + (1 -a) Zn +++ H20 -> aCo + (l-a) Zn + 1/2 o2 + 2H + i “25 a represents the molar percentage of cobalt in. 'the deposit (in fraction of a unit) ig) regeneration: -for zinc: ^ • 30 (la) Zn + (la) 2H + - »(la) Zn ++ + (la) H9 /: / i 16 -for cobalt: basic cobalt carbonate] 'I CoC03.2Co (0H) 2 ·

In an aqueous solution at pH 1, the dissolution of this product corresponds to the dissolution of CoO after evolution of CO and release of H 0 ^ 4- ^ 4-4- ^ a CoO + a 2H -> a Co + a And, 0 - overall i aCoO + (1-ct) Zn + 2E + —s aCo'f ++ (lo;) Zn ++ + H20 + (la) H2 10 h) overall assessment of the electrolysis and re-generation process: aCo +++ (1 -a) Zn +++ HO— · aCo + (la) Zn + 1/2 02 + 2E +

IaCoO + (1-α) Ζη + 2H-- o: Co ++ + (1-a) Zn +++ aH20 -j- (la) H2 15 (la) H20 ------------—; ( la) H2 + 1/2 (1-a) 02 | In conclusion, it can therefore be seen that, for these three types of alloys, there is, at the level of electrolysis, 20 in addition to a consumption of metal ions for the alloy to be produced, a consumption in H20, production of H + ions and release of oxygen.

In addition, in particular in the case of a zinc-nickel alloy, the Ni / Zn = c: molar ratio is ir.fé-25 lower than 1.5 and generally between 0.8 and 1.2 in the electrolytic bath. .

The production of E + ions, of which question above, thus leads to an acidification of the electrrolytic bath in the cell.

30 /! i I 17 t ï; As already indicated above, a characteristic Ί '. The essential tick of the invention consists in using I these H ions produced to regenerate the electrolyte.

Thus, the pH in the electrolytic bath of the cell can be kept above an I value. minimum and, at the same time, replace therein, the metal ions, which have been extracted from this bath as a result of electrolytic deposition, without it being necessary to use special means to form these ions.

The 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 j is for example given to basic nickel carbonates \; 20 and cobalt and to the hydroxide hydroxide optionally mixed with particles of metallic iron.

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

The method of the invention is illustrated below, t I after by some practical examples of embodiment.

j

Example 1.

In order to produce an electrolytic deposit of a zinc-nickel alloy on a steel sheet, an electrolysis of an electrolytic bath - / containing 1.2 moles / liter of NiSO 4 and 1 mole / was carried out. liter / Jf / II.

118 of ZnSO 4, maintained at a pH of the order of 1 and at a temperature of the order of 50 ° C. The extraction current density was 100 A / dm ^, while the relative circulation speed of the electrolyte, with respect to the sheet, was 1 m / sec.

The anodes used were lead-silver, with a silver content of 1.2%.

The thickness of the deposit obtained was 5} JV

The pH of the electrolyte leaving the cell and • y} passing through line 3 to the buffer tank 2 was of the order of 0.8, while the pH of the electrolyte ^. used for dissolution. passing through the return line 10 had a pH of the order of 1.5. The alloy obtained contained about 8% nickel.

15 Example 2.

In the electrolysis cell, a bath of 0.5 moles / liter of ZnSO 4 and of 0.6 moles / liter of NiSO 4 was used, maintained at a pH of 1.2, by the addition of t ^ SO ^, and at a temperature of 50 ° C.

The density of the cathodic extraction current was of the order of 30 A / dm ^, while the circulation speed of the electrolyte was of the order of 1 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 5 ^ /.

/ f The appearance of the deposit was a uniform light gray.

/ 19!

Example 3.

; The electrolytic bath used contained! 2 moles / liter of ZnSO and 2 moles / liter of NiSO and 1 - 4 was maintained at a pH of 0, by the addition of I ^ SO ^, 5 and at a temperature of the order of 50 ° C.

’2 The density of the cathode current was 300 A / dm, while the relative speed of the electrolyte relative to the sheet to be protected by the alloy was 4 m / sec.

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

! The alloy contained 8% nickel and had a shiny, uniform gray appearance.

| 15 Example 4.

'The electrolytic bath used contained! 0.5 moles / liter of NiSO ^, 0.5 moles / liter of ZnSO ^ j and 1.5 moles / liter of ï ^ SO ^ and was maintained at a temperature of the order of 50 ° C .

| The density of the cathode current was 200 A / dm,! while the relative speed of the electrolyte with respect to the sheet to be covered by the alloy was! 4 m / sec.

The regeneration took place by the addition to the electrolyte of metallic zinc and basic nickel carbonate. The alloy contained 8% nickel and exhibited an as- | "'metallic gray pect.

! These four tests were reproduced by simply replacing the RiSO 4 respectively with FeEO 4, e +.

CoSO ^ to produce zinc-iron and zinc-coba alloys ^^^ / 20

For regeneration, in the case of the production of a zinc-iron alloy, use was made of metallic zinc and a mixture of iron and goethite and also of iron only.

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 have been 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 j continuous, high density electrolytic deposition! | current, a layer of a zinc-based alloy j 15 on a sheet.

1 In this embodiment, we do! continuously circulate all of the electrolyte through the closed circuit 15, in which a! circulation pump 16, in order to achieve the circulation speed \ 20 necessary in the electrolysis cell 1 and thus make it possible to obtain a sufficiently high cathode current density. Only a fraction of the electrolyte is subjected to the abovementioned regeneration in a device which includes a buffer tank 2 which also acts as a dissolution reactor, to the same degree as 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 / / i 21 [* This helps make circulation | in this separate circuit independent of circulation through I through the electrolysis cell itself, this mistletoe would therefore have the advantage of being able to create, for example, in • 5 the tank 2, thus acting as a dissolution reactor, the necessary conditions for dissolution of metals intended for the regeneration of the electrolytic bath.

It is understood that the invention is not limited to the embodiments described above of the method and installation according to the invention.

Thus, for example, in certain cases, it could be limited, for the regeneration of the electrolyte, to the addition to the buffer tank 2 to I of the metals necessary to compensate for the exhaustion of the; 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.

Finally, 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 30 of FIG. 2 to ensure circulation in the / cell. / 1 / f

Claims (18)

122 REVERDI CAT IONS 1. Process for the electrolytic deposition, continuously and at high current density, of a layer of a zinc-based alloy on a sheet, according to which this sheet is moved in an electrolytic cell , in contact with a cathode and next to a | insoluble anode, through an electrolyte containing! zinc sulphate, characterized in that a lower pH is maintained in the electrolyte of the electrolysis cell | at 2, a temperature of 40 to 70 ° C and a concentration T; 10 from 0.2 to 2 moles / liter of zinc sulphate and from 0.3 to> 2 moles / liter of an iron, nickel and / or H cobalt sulphate depending on the nature of the alloy to be produced. i 2. Method according to claim 1, ca acterized in that gu'on maintains in the electrolyte one; PH less than 1.2 and preferably less than 0.4. .i 3. Process according to either of the vl | Claims 1 or 2, characterized in that the pH in the electrolyte is adjusted by the addition of sulfuric acid. 3 :! 4. The process as claimed in claim 3, characterized in that a concentration of sulfuric acid greater than 1 mol / liter is maintained in the electrolyte of the electrolytic cell. 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 12% of nickel, a zinc-iron alloy containing 2 to 15 of iron or a zinc-cobalt alloy containing 2 to 12% / of cobalt. 30 (Jf jj II î «: t li 23 | i! 6. Process according to any one of the preceding claims, characterized in that I use an electrolytic bath substantially free of chlorides. 7. Method according to any one of the preceding claims, characterized in that an anode formed of a lead-silver alloy is used in the electrolysis cell, the silver content of which is preferably 0.6 to 1.2%. i | 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 electrolytic deposition, in 1. continuous and high current density, of a layer; of a zinc-based alloy on a sheet, according to- | which one moves this sheet in an electrolysis cell, in contact with a cathode and facing one; insoluble anode, through an electrolyte bath including zinc sulphate, in particular process according to any one of the preceding claims, characterized in that a pH of less than 2 is maintained in the electrolyte and that the electrolyte is continuously extracted from the cell in order to regenerate it by dissolving 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 desired alloy, i of the electrolyte thus regenerated then being reintroduced,>! also continuously, in the electrolysis cell. r / • ι il - \ 24 • I] t i! v 10. A method according to claim 9, characterized in that the zinc is introduced into the electrolyte to be regenerated in the medium form. 11. Method according to either of Claims 5 and 10, characterized in that the nickel and the cobalt are introduced into the electrolyte to be regenerated in the form of carbonates, while the iron is introduced into the electrolyte to regenerate in metalligue and / or ferrigue hydroxide form. 12. Method according to one guelcongue of I! claims 9 to 11, characterized in that it! zinc and the other metal of the alloy to be produced and used for the regeneration of the electrolyte are introduced into! separate guarantees of electrolyte, these guarantees being! 15 then reunited before being reintroduced into the cell; Electrolysis cell, the ratio of these guarantees being §; set according to the desired ratio of metals in the alloy to be produced in the cell. 13. Process for electrolytic deposition, in! 20 continuous and high current density, a layer of | zinc-based alloy on a sheet, such as described above or shown in the accompanying drawings. 14. Installation for the electrolytic deposition, I continuously and at high current density, of a layer:% I 25 of a zinc-based alloy on a sheet, comprising! , an electrolysis cell in the laguelle can move! a continuous sheet, in contact with a cathode and I opposite an insoluble anode, through an electrolyte containing zinc sulphate, this installation | 30 being characterized in that it is equipped, for the / he 25 J! Ί! lt; lï | "continuous regeneration of the electrolyte of a positive device connected to said electrolysis cell and comprising a buffer tank connected directly, by inlet and outlet pipes, to the! * 5 cell. 15. Installation according to claim | . . | j 14, characterized in that it comprises at least one | separate dissolution reactor connected to the buffer tank 1 and through which electrolyte from the buffer tank can flow. ^ 16. The method of claim 15, 1 characterized in that it comprises at least two dissolution reactors mounted in parallel on this tank and through each of which can circulate 15 electrolyte from the buffer tank, means being intended to adjust the relative flow rate |! of the electrolyte through these operating reactors | of the ratio of metals in the alloy to be produced in! the cell. ! i he 20 17. Method according to any one of | Claims 14 to 16, characterized in that it comprises a circulation circuit for the electrolyte closed on | the mistletoe cell is independent of the aforementioned ί regeneration device. ! * 25 18. Installation for electrolytic deposition! ; that, continuously and at high current density, such as described above or shown schematically in the attached drawings. i i Drawings: —Δ— plates | 30 2. £. pages of which —A— cover page § ____ â.4 ..... description pages I _________ li ... claims parts I ___ descriptive abbreviation I Luxembourg, \ q May 19B2 I The agent: / 0 /