FR2526447A1 - METHOD AND DEVICE FOR THE CONTINUOUS, HIGH-CURRENT DENSITY ELECTROLYTIC DEPOSITION OF A LAYER OF A ZINC-BASED ALLOY - Google Patents

Abstract

THE INVENTION RELATES TO A PROCESS FOR THE ELECTROLYTIC DEPOSIT, IN CONTINUOUS AND AT HIGH CURRENT DENSITY, OF A LAYER OF A ZINC-BASED ALLOY, ON AN ELEMENT IN THE FORM OF A BAND, WIRE, BAR, TUBE OR ANALOGUE, ACCORDING TO WHICH THIS ELEMENT IS MOVED IN AN ELECTROLYSIS CELL, NEAR AN ANODE, THROUGH AN ELECTROLYTE CONTAINING ZINC SULPHATE, KEEPING IN THE ELECTROLYTE OF THE ELECTROLYSIS CELL 1 A LOWER PHASE AT 2, A TEMPERATURE OF 40 TO 70C AND A CONCENTRATION OF 0.2 TO 2 MOLESLITER OF ZINC SULPHATE AND 0.3 TO 2 MOLESLITER OF IRON, NICKEL AND OR COBALT SULPHATE DEPENDING ON THE NATURE OF THE COATING LAYER A PRODUCE.

Description

"Process and device for continuous and high electrolytic deposition

  current density, a layer of one

zinc-based alloy ".

  ________________________________________________________

  The subject of the present invention is a method

  for continuous, high-density electroplating

  current, of a layer of a zinc-based alloy on an element in the form of a strip, wire, tube, bar or the like, according to which this element is displaced in an electrolysis cell, opposite an anode through an electrolyte containing zinc sulfate. In the processes hitherto known in the literature for covering such an element with a metallic layer, there is essentially a distinction

two very different techniques.

  A first technique consists simply in passing the element through one or more baths containing the molten covering metals, as described for example in American patent NI 3,858,333 in the name of Thompson, while according to a second technique, one obtains the covering of the element 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.

  Such processes are generally very

  p J iced and expensive, inter alia by the fact that they require a relatively large number of stages for each of which a very rigorous control of the operating conditions is required. More particularly, in the processes

  known in the literature, for the recovery of

  strip-shaped elements, in particular steel plates,

  an electrolyte of relative composition is used-

  complex requiring very rigorous control of the operating conditions to obtain alloys

  of sufficient purity, with industrial yields

trially valid.

  This therefore risks presenting fairly serious technical problems for the application of these methods to

industrial scale.

  DE-PS 30 05 159, which relates to a process for the preparation of a zinc-nickel alloy,

  mentions a sulfate bath containing a quan-

  relatively large amount of Na 2504, as an electro-

  support lyte The use of such an electrolyte

  support is essential so that the electro-

  lytic in the electrolysis cell is sufficient

  sufficiently conductive at a p H of at least 2, at which the bath must be maintained in practice, as indicated

  in the examples described in this publication.

  Furthermore, DE-OS 30 11 911, which also relates to a process for the preparation of a zinc-nickel alloy, relates to the use of Sr So 4, as a support electrolyte in an electrolytic bath, the p H is always greater than 2, as also illustrated by the concrete examples of application described

In this one.

  In these prior processes, in industrial practice, the current density cannot generally exceed 20 A / dm, as is moreover apparent from a

  once more of said illustrative examples.

  One of the aims of the present invention consists in remedying the aforementioned drawbacks and in proposing a

  extremely simple and reliable process for an application

  continuous industrial scale and high density

  current tee and without rejection of toxic effluents.

  To this end, according to the invention, we main-

  holds in the electrolyte of the electrolysis cell a p H less than 2, a temperature of 40 to 700 C and a concentration of 0.2 to 2 moles / liter of zinc sulfate and of 0.3 to 2 moles / liter of iron, nickel and / or cobalt sulphate, depending on the nature of the alloy

to produce.

  Advantageously, the electro-

  lyte a p H less than 1.2 and preferably less

at 0.4.

  According to a preferred embodiment-

  tial, an M / Zn + molar ratio is maintained in the electrolyte which is less than 1.5 and this for a p H less than or at most equal to 1.2, M being Ni, Fe or Co, this ratio preferably being between 2 and 3 for the preparation of an alloy

Zn-Fe.

  The invention also relates to a method for the continuous regeneration of the electrolyte of an electrolytic cell for electrolytic deposition, at high current density, of a layer of a zinc-based alloy on an element. strip, wire,

  tube, bar or the like, especially electro-

lyte as described above.

  According to the invention, it is maintained in the elect

  trolyte a p H less than 2 and at least part of this electrolyte is extracted continuously 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 then being reintroduced, also continuously, into

the electrolysis cell.

  According to a particular embodiment of the invention, zinc is introduced into the electrolyte

  to regenerate in metallic form.

  According to a particular embodiment

  advantageously 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 into separate quantities of electrolyte, these quantities then being combined before being reintroduced in 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 a

  installation for implementing the elective process

  trolysis and regeneration as described above.

  This installation is characterized in that it is equipped, for the continuous regeneration of the electrolyte, with a device comprising a

  buffer tank connected directly, by hoses-

  incoming and outgoing terminals on the electrical cell

trolysis.

  Other details and peculiarities of the in-

  vention will emerge from the description given below,

  by way of nonlimiting examples of some particular embodiments of the process and of the installation

  according to the invention with reference to the accompanying drawings.

  Figure 1 shows a block diagram of a

  first embodiment of the following installation

before the invention.

  Figure 2 shows a block diagram of a second embodiment of the following installation

the invention.

  In these figures the same reference numbers

  rence relate to identical or similar elements

logues.

  The invention relates more particularly-

  ment to a process for electroplating, in con-

  continuous and high current density, especially from 20 to

2 2

  300 A / dm, and preferably 30 to 200 A / dm, of a layer of a zinc-based alloy with a thickness preferably varying between 1 and 12, / ï on an element

  in the form of a strip, wire, bar, tube or ana-

  log, made for example of steel or soft iron.

  It is a process by which this element is moved in one or more electrolysis cells, opposite an anode, through an electrolyte containing zinc sulfate. The cell can be of a conventional type or correspond to that which is the subject of the patent in the United Kingdom NO 1,038,671, improved by an electrolyte circulation system, especially if it is

  of elements in the form of wires, tubes or bars, for example.

  Furthermore, for covering strips, such as steel sheets, it is possible in particular to make

  use of a cell corresponding to the one making the

  draft of the patent in the United States of America NO 4 304 653.

  According to this process, the p H lower than 2, the temperature at 40 to 70 ° C. and a concentration of 0.2 to 2 moles / liter of zinc sulfate and 0, are maintained in the electrolyte of the electrolysis cell. 3 to 2 moles / liter of iron sulfate, nickel and / or

  cobalt, depending on the nature of the alloy to be produced -

  The alloy can therefore be a zinc alloy-

  nickel, zinc-iron, zinc-cobalt or a zinc-nickel-iron, zinc-nickel-cobalt, zinc-iron-cobalt alloy

  or even a zinc-iron-cobalt-nickel alloy.

  More particularly, a p H of less than 1.2 and preferably less than 0.8, p e is maintained in the electrolyte of the electrolysis cell.

p H of O 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

  regulated 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% of iron or a zinc-cobalt alloy. containing 2 to 12%

cobalt.

  Unlike some known processes, we

  uses an electrolytic bath free of metallic chlorides

  metallic and also free of supporting electrolytes, so as to obtain a bath as pure as possible, therefore making it possible to ensure the formation of an electrolytic deposit on the element of a zinc alloy of very high homogeneity and purity , without the need to take special precautions

in this regard.

  Since the electrolyte is free of chlorides, if an insoluble anode is used, use may be made of an anode formed of a lead-silver alloy, with a silver content which is preferably 0.6

at 1.2%.

  If, on the other hand, a soluble anode is used, it is based on zinc or consists of a

  alloy corresponding to the alloy of the coating

covering to be produced.

  Thus, if the anode consists of pure zinc, ions of the other metal are added to the electrolyte or

  other metals of the alloy to be formed.

  Furthermore, if the soluble anode is constituted

  killed by an alloy, the composition of the latter may be the same as or different from that of the layer of

covering to be produced.

  So if the anode is made of an alloy

  of different composition from that of the layer of re-

  garment to produce the composition of the electrolyte bath can be adapted by the addition of ions of the metal or metals. A soluble anode is particularly suitable for the formation of a covering layer in a

Zn-Fe alloy.

  Furthermore, thanks to the fact that the electrolyte

  has a very low p H, we can maintain in the elect

  trolyte an M / Zn molar ratio of less than 1.5, M is nickel or cobalt, and between 2 and 3, if M

  is iron, which therefore reduces the relative amount

  metal M used for the formation of a

zinc alloy.

  This can be a characteristic

the electrolyte.

  In order to allow operation with relatively high current densities, in particular up to 300 A / dm 2, as already indicated above, the relative speed of the electrolyte is advantageously maintained

  relative to the element to be covered at a higher value

  less than 1 m / sec, and even 2 m / sec, this speed

  may in certain special cases be

  less than 4 m / sec for current densities of the order of 200 to 300 A / dm, depending on the nature and

shape of the element to be covered.

  In order to be able to conduct an election

  trolysis in a very acidic bath, at a p H up to O or lower still, one associates with electrolysis a continuous regeneration of the electrolyte which is such as to stabilize the p H in the cells, the regeneration implementing this strong acidity for dissolution in

  the electrolyte to regenerate metals that have deposited

at the cathode.

  To ensure this regeneration of the elect

  trolyte, a p H of less than 2, and preferably less than 1.2, is maintained in the latter, 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, the electrolyte thus regenerated then being reintroduced, also continuously, into the cell

electrolysis.

  To avoid entrainment, in the electric bath

  trolytic of the cell itself, of particles not dis-

  bunkers from this regeneration and thus prevent contamination of the electrolytic deposit on the element to be covered and also to allow flexible adjustment of the regeneration process according to the operating conditions of the cell, the addition of these metals has

  held in separate amounts of electrolyte to reg-

  outside, outside the electrolysis cell, these

  tities being then mixed again, before being reintroduced into the cell, at the time when all the metals are completely dissolved and optionally after settling of insoluble impurities originating from this regeneration.

252644 Y

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

  continuous perfectly adapted to this electrolysis.

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

of the electrolyte bath.

  Nickel and cobalt are advantageous-

  ment introduced into the electrolyte in the form of carbonates, while iron is advantageously introduced in metallic form or in the form of hydroxide

ferric or a combination of both.

  For the formation of Zn-Fe alloys, depending on the operating conditions, it is useful and often necessary to take certain precautions to avoid a considerable reduction in the overall yield of the electrolysis as a result of the formation at the anode, at

from Fe + ions, Fe + ions.

  Thus, according to the invention, ammonium sulfate is added to the electrolyte to stabilize the + I

Fe ions in the form of complexes.

  In addition, at least part of the electrolyte is advantageously subjected to a reduction operation, so as to transform Fe ions into Fe ions. In this regard, it has been found that SQ 2 is

  particularly suitable as a reducing agent

  this makes it possible to form ions Fe and SQ 4 It can then

  be regenerated using an ion exchange resin.

  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 an element in strip, wire, bar, tube shape

or the like.

  This installation includes an electrolysis cell 1, in which one or more pass

  of these elements simultaneously opposite an anode

  soluble through an electrolyte containing zinc sulphate This element or these elements, as well as the anode and the cathode, have not been represented in the figure,

  since it can be an electro-

  lysis of any type known per se for this kind of operation. The element therefore in fact acts as a cathode, while if an insoluble anode is used, it is preferably made of a lead-silver alloy, the silver content of which is included.

between 0.6 and 1.2%.

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

electrolysis 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 adjust the relative flow rate of the electrolyte through

  to these reactors depending on 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 pipe

  9 and a return pipe 10 to the tank 2.

  The tank 2 can possibly do

  decanter function in the event that

  soluble, from the dissolution of metals in

  reactors 5 and 6 would be introduced in this reactor

serve by the return pipe 10.

  The circulation between cell 1 and the

  tank 2 is provided by a pump 12, provided p e.

  on the duct 4, while the circulation between the tank 2 and the reactors 5 and 6 is obtained by a

  pump 13 provided on the pipe 9.

  For the preparation of a Zn-Fe alloy, this installation may additionally include a reactor

  reduction 18 connected via con-

  picks 19 and 20 and a pump 21, adjustable flow rate,

on the buffer tank 2.

  A reducing agent, such as SQ 2, is then introduced into this reactor to transform Fe + ions

in Fe + ions.

  An ion exchange resin, for example in the form of a grid in the reactor 18,

  regenerates the reducing agent.

  The operation of this installation can be described as follows: As a result of the electrolysis reaction in cell 1, zinc and one or more other metals, intended to form an alloy with zinc, become

  deposit on the element (s) moving in the cell.

  This results in an exhaustion of the electro-

  lyte in metal ions and increased acidity

  dity of the bath In operation, the aim is to maintain in the bath a p H less than 2 and preferably less than

  1.2, as already mentioned above.

  The electrolyte generally circulates in the-

  cubicle at relative speeds of 1 to 4 m / sec or even

  how much more with respect to said element, depending on the density

  desired current, and is extracted from the cell by

  the inlet pipe 3 to be introduced into the tank

  see buffer 2, in which a relatively stable p H,

  substantially corresponding to that desired in the cell

lule, is maintained.

  Part of the electrolyte in reservoir 2 is directed, via the supply line 9, to the two

  dissolution reactors 5 and 6, also called regenerated-

  rators In one of the reactors, for example the reactor, the zinc necessary to compensate for the depletion of zinc is introduced into the electrolytic bath of

  cell 1, while in the other reactor, we introduce

  duit the other metal intended to form an alloy with

zinc in cell 1.

  The relative flow of the electrolyte through these reacts

  5 and 6 is regulated by valves 7 and 8, ma-

  so that the ratio of the quantities of dissolved metals, brought back by the return pipe to the tank, corresponds to the concentration ratio of

  these metals needed to obtain the desired alloy.

  The loche It indicates an introduction of water into the tank 2 to compensate for the water consumption

  during the electrolysis reaction.

  As already mentioned above, zinc can be introduced in a metallic form, for example

  in the form of bars or ingots, in reactor 5.

  During the formation of a Zn-Fe alloy, part of the electrolyte arriving in the buffer tank 2 is directed towards the reactor with a flow which is

  function of the concentration of Fe +++ ions in the elect

  trolyte. The electro-chemical reactions at the electrodes will be described in more detail below.

  on which electrolysis and regeneration are based

  ration of the electrolyte, of which question above, as well as the preferential operating conditions and this for the electrolytic deposition of a zinc-nickel alloy,

zinc-iron and zinc-cobalt.

10 Zinc-nickel.

  a) composition of the electrolytic bath in the cell 1 Zn SO 4: 0.5 to 2 moles / liter Ni SO 4: 0.2 to 2 moles / liter p H: O to 1.2 (by addition of H 2504) b) operating parameters of the electrolysis cell: temperature: 40 to 70 C current density: 20 to 300 A / dm relative circulation speed of the electrolyte: 1 to 8 m / sec c) regeneration products introduced into the reactors and 6: Zn and Ni CO 3 2 Ni (OH) 2 d) composition of the alloy obtained: 2 to 14% of Ni e) electrochemical reactions: at the cathode: Zn ++ + 2 e, Zn Ni ++ + À 2 e Ni 2 H + + 2 e H 2 at the anode: 2 H 20> 2 + 4 H + + 4 e

2 Zinc-iron.

  a) composition of the electrolytic bath in cell 1: Zn 504: 0.3 to 2 moles / liter eg SO 4: 0.6 to 2 moles / liter p H: O to 1.2 (by addition of H 2504)

  Optionally (NH 4) 2 So 4 0.5 to 1 mole / liter.

  b) operating parameters of the electrolysis cell: temperature: 40 to 70 C current density: 20 to 300 A / dmi relative circulation speed of the electrolyte: 1 to 8 m / sec c) composition of the alloy obtained : 2 to 15% Fe; A In insoluble anode (Pb-Ag 0.6% pe) 1) regeneration products introduced into the reactors and 6: Zn and Fe (possibly Fe + Fe (OH) 3) 2) electrochemical reactions: at the cathode Zn + 2 e Zn Fe ++ + 2 e Fe Fe + e Fe 2 H + + 2 e H 2 at the anode: 2 H 20 x O + 4 H + + 4 e Fe Fe + e 3) reduction of Fe +++ ions to Fe + ions: The ions Fe produced at the anode is reduced to Fe ++ ions, at the exit of the electrolysis cell 1, thanks to three mechanisms: a In the zinc reactor 5: Zn + 2 Fe +++ Zn + 2 Fe ++ or -Zn + 2 a Zn + H 2) H 2 + 2 Fe +++ __ 2 H + + 2 Fe ++ Zn + 2 Fe +++ Zn + 2 Fe ++ b In the iron reactor 6: Fe + 2 H) Fe + + H 2 2 + 2 Fe + 2 + 2 Fe ++ -, + H 2 Fe + 2 3 e C In the reduction reactor 17: 2 Fe +++ + SO + 2 HO -> 2 Fe ++ + H SO + 2 H +

2 2 2 4

  Depending on the operating conditions, the dimensioning of the three reactors is determined to maintain a constant composition in Fe ++, Zn + and

a low content of Fe +++ ions.

  B In soluble anode 1) anode: Zn-Fe alloy of the desired covering composition; or pure zinc

  iron ration in an annex reactor.

  2) electrochemical reactions: at the cathode: Fe ++ + 2 e Zn ++ + 2 e 2 H + + 2 e at the anode: Fe -_ Fe ++ Zn Zn ++ of the layer

with regenerated-

  Fe Zn 1 H 2 + 2 e + 2 e 3) reduction of Fe + ions to Fe ++: Thanks to the use of a soluble anode the formation of Fe +++ in this one does not occur and therefore in principle comes only from an oxidation

by air Fe ++ ions.

* This has the consequence that the amount of Fe formed in the electrolyte is relatively small and does not generally require the addition of a reducing agent of the type

SO 2 for example.

3 Zinc-cobalt.

  a) composition of the electrolytic bath in cell 1: Zn 504: 0.3 to 2 moles / liter Co 504: 0.6 to 2 moles / liter p H: O to 2 (by addition of H 2504) b) parameters operating procedures of the electrolysis cell: temperature: 40 to 70 C current density: 20 to 300 A / dm 2 relative circulation speed of the electrolyte: 1 to 8 m / sec c) regeneration products introduced into the reactors and 6: Zn and Co CO 3 2 Co (OH) 2 d) composition of the alloy obtained 2 to 12% of Co e) electrochemical reaction: at the cathode: Zn ++ + 2 e -Zn Co ++ + 2 e -Co 2 H + + 2 e H 2 at the anode 2 H 2 O + 4 H + 4 e In conclusion, we therefore note that, for these three types of alloys, there is, at the level of electrolysis,

  in addition to a consumption of metal ions for the

  age to produce, consumption of H 20, production of H + ions and release of oxygen. In addition, especially in the case of an alloy

  zinc-nickel, the Ni / Zn + = a molar ratio is lower

  less than 1.5 and generally between 0.5 and 1.2

in the electrolytic bath.

  The production of H + ions, of which question below

  above, therefore leads to an acidification of the electro- bath

lytic in the cell.

  As already mentioned above, a characteristic

  essential tick of the invention is to use

  these H ions produced to regenerate the electrolyte.

  Thus, one can maintain the p H in the electrolytic bath of the cell above a minimum value and, at the same time, replace in this one, the metal ions, which have been extracted from this bath by

  following electrolytic dep Ot, without it being necessary

  be able to use special means to

form these ions.

  The metals or metal compounds used for regeneration in reactors 5 and 6 should preferably be easily soluble in acid baths without leaving insoluble traces, which risk polluting 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 2 O is for example given to basic carbonates of nickel

  and cobalt and possibly mixed ferric hydroxide

  actually with metallic iron particles.

  In the case of the use of carbonates, the release of C 02, stirs 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.

  after by some practical examples of implementation.

Example 1.

  In order to produce an electrolytic depot

  tick of a zinc-nickel alloy on a steel sheet, an electrolysis of an electrolytic bath containing 1.2 moles / liter of Ni SO 4 and 1 mole / liter was carried out

  of Zn 504, maintained at a p H of the order of 1 and at a time

  temperature of the order of 50 C. The extraction current density was 100 A / dm 2, while the relative circulation speed of the electrolyte, relative

at sheet metal, was 1 m / sec.

  The anodes used were made of lead-silver, with a

1.2% silver content.

  The thickness of the dep Ot obtained was 5 Le p H of the electrolyte at the outlet of the cell and passing through the conduit 3 towards the buffer tank 2

  was around 0.8, while the p H of the elect

  trolyte having served for dissolution: passing through the

  return line 10 had a p H of the order of 1.5.

  The alloy obtained contained about 8% nickel.

Example 2.

  a bath of 0.5 moles / liter of Zn SO 4 and 0.6 moles / liter of Ni So 4 was used in the electrolysis cell, maintained at a temperature of 500 C and a p H of 1 , 2 by the addition of H 2504, to cover a steel sheet

  by electrolytic deposition of a Ni-Zn alloy.

  The density of the cathodic extraction current was around 30 A / dm, while the circulation speed

  of the electrolyte was of the order of 1 m / sec.

  For regeneration in reactors 5 and 6, we used

  metallic zinc and basic nickel carbonate.

  The electrolytic deposit obtained was formed by a nickel-zinc alloy containing 11% nickel and having a thickness of the order of 5

  The appearance of the deposit was a uniform light gray.

Example 3.

  The electrolytic bath used contained 2 moles / liter of Zn 504 and 2 moles / liter of Ni SO 4 and was maintained at a temperature of the order of 500 C and a p H of 0, by the addition of H 2504, to cover a sheet

  of steel by electrolytic deposition of a Ni-Zn alloy.

  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 the addition to the electrolyte,

  of metallic zinc and basic nickel carbonate.

  The alloy contained 8% nickel and exhibited a

uniform shiny gray appearance.

Example 4.

  The electrolytic bath used contained 0.5 moles / liter of Ni SO 4, 0.5 moles / liter of Zn SO 4 and 1.5 moles / liter of H 2 SO 4 and was kept at a temperature of 50 C to cover a steel sheet by an electrical deposit

trolytic of a Zn-Ni alloy.

  The density of the cathodic current was 200 A / dm 2, while the relative speed of the electrolyte relative to the t Ole to be covered by the alloy was

4 m / sec.

  The regeneration took place by the addition to the electro-

  lyte of metallic zinc and basic nickel carbonate.

  The alloy contained 8% nickel and exhibited as-

metallic gray pect.

Example 5.

  In order to produce an electrolytic depot

  tick 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 Ni SO 4 and 0.7 mole / liter was carried out of Zn SO 4, maintained at a p H of the order

  0.3 by addition of sulfuric acid, and at a temperature

  ture of the order of 50 C The density of the extraction current

  tion was 30 A / dm The voltage across the cell

  the lule was 4 Volts and the cathodic yield was 74% The speed of circulation of the electrolyte was 3 m / sec, while the speed of the wire, in opposite direction

  at that of this circulation, was lm / sec.

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

basic nickel carbonate.

  The thickness of the deposit obtained was 4 d

  The alloy obtained contained about 13% nickel.

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

Example 6.

  A steel wire with a diameter of 3 mm was

coated with a zinc-nickel alloy.

  For this purpose, a bath of 1 mole / liter of Zn 504 and 0.8 mole / liter of Ni SO 4 was used in the electrolysis cell, maintained at a p H of 0.5, per l addition of H 2 SO 4 and at a temperature of 500 C. The cathode current density of extraction was of the order of 50 A / dm 2 The voltage across the terminals of the cell was 5.3 Volts and the efficiency cathode current was 74% The electrolyte circulation speed was around 3 m / sec, while the speed of

  displacement of the wire in opposite direction to that of the elect

  trolyte was around 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 an al-

  nickel-zinc bonding containing 11% nickel and having a thickness of the order of 1) J%

  The appearance of the deposit was a uniform light gray.

Example 7.

  A steel wire with a diameter of 3.5 mm has

  was coated with a zinc-nickel alloy.

  The electrolytic bath used contained 2 moles / liter of Zn SO 4 and 2 moles / liter of Ni SO and

4 4

  was maintained at a p H of 0.2 by the addition of H 2504 r and at a temperature of the order of 500 C. The density of the cathode current was 150 A / dm 2 The voltage across the terminals of the cell was of 12 Volts

  and the efficiency of the cathode current was 74%.

  The electrolyte speed was 4 m / sec, while

  than that of the wire, in the opposite direction to that of the elect

trolyte, was 3.3 m / sec.

  The anodes used were made of lead-silver, with a

silver content of 0.6%.

  The regeneration took place by the addition, to the electro-

  lyte, metallic zinc and basic nickel carbonate. The alloy contained 13% nickel and exhibited a

shiny gray appearance.

Example 8.

  A steel tube with an outside diameter of

  5/8 inch and an internal diameter of 14.5 mm was -

  coated internally and externally with a zinc-nickel alloy. The electrolytic bath used contained lmcie / liter of Ni SO 4, 1 mole / liter of Zn SO 4 and was maintained at a p H of 0.8 and at a temperature of the order of 500 C. The density of the cathode current was 50 A / dm 2 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 made of lead-silver, with a

silver content of 0.6%.

  Regeneration took place by 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 around 55 L,

Example 9.

  A steel sheet was covered with a deposit of a Zn-Fe alloy in an electrolytic bath whose composition was as follows Zn: 25 g / l Fe ++ 65.3 g / l Fe 3 g / l H 2 SO 4: 46 g / l (NH 4) 2504 80 g / l The anode used was lead-silver, with a content

in silver of 0.6%.

  The current density was 60 A / dm The relative speed of the electrolyte in the electrolysis cell was 1 m / sec, while the speed of

  sheet steel scrolling was 8 m / min.

  The current efficiency was 88% and the anode voltage

cathode was 9.7 Volts.

  The electrolytic deposit obtained was formed from an alloy

  zinc-iron, containing 92% zinc and 8% iron.

  This deposit was clear, ductile, uniform and very covering

  and having a fine crystallization.

Example 10.

  A steel sheet was covered with a deposit of a Zn-Fe alloy in an electrolytic bath, the composition of which was maintained as follows Zn 23 g / l Fe 68 g / l Fe 0.2 g / l H 2 SO 4 50 g / i (NH 4) 2504 120 g / i

  The anode used was a pure zinc soluble anode.

  The current density was 70 A / dm The relative speed of the electrolyte in the cell was 1 m / sec, while the speed of movement

sheet metal was 8 m / min.

  The cathodic current efficiency was 90% and the

  anode-cathode voltage was 8.2 Volts.

  The electrolytic deposit was formed from a zinc-

  iron containing 91% zinc and 9% iron.

  This deposit was clear, ductile, very covering and of

fine crystallization.

  Examples 1 to 8 were reproduced in replacement

  simply placing Ni SO 4 respectively with Fe SO 4

  and Co 004 to produce zinc-iron and zinc- alloys

  cobalt Example 10 was reproduced by replacing the ions

  Fe ++ respectively not Ni ++ and Co ++ ions and suppressing

  mant the (NH 4) 2504 and the Fe + ions, to produce

Zn-Ni and Zn-Co alloys.

  For regeneration, in the case of pro-

  duction of a zinc-iron alloy, we used zinc

  metallic and a mixture of iron and goethite and also

iron only.

  In the case of the production of a zinc-cobalt alloy, the regeneration took place by means of

  metallic zinc and basic cobalt carbonate.

  The other operating parameters and conditions

  roofs were kept similar to those of these eight

  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 on an element in the form of strip, wire, bar,

of tube or the like.

  In this embodiment, all of the electrolyte is continuously circulated through a closed circuit 15, in which a circulation pump 16 is provided, to achieve the speed

  necessary circulation in the electro- cell

  lysis 1 and thus make it possible to obtain a density of

  cathode current sufficiently high.

  Only a fraction of the electrolyte is subjected to the abovementioned regeneration in a device which comprises a buffer tank 2, the latter also acting as dissolution reactor, to the same degree as reactors 5 and 6 of the first embodiment

  shown in figure 1 This tank 2 is connected directly

  Tement on 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 being provided on this

hose 4.

  This makes it possible to make the circulation in this separate circuit independent of the circulation through the electrolysis cell itself, which would have the advantage of being able to create, for example, in the tank 2, therefore acting as a dissolution reactor, the conditions dissolution kits

  metals intended for the regeneration of the electro- bath

lytic.

  Description, including examples

  practices given above, it follows that the process according to the invention has the advantage that a coating of an element in the form of a strip, wire, bar, tube or the like is obtained by an alloy in a single operation. , contrary to what is for example the case in the known processes according to which it is necessary for example to pass through a series of successive baths of covering metals, which are separated by baths

  washing, and followed by a final heat treatment.

  According to this known technique, a coating formed from at least two successive layers is obtained.

  between which a difference in po may form

essential.

  This can therefore give rise to a migration of ma-

  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 invention.

  Thus, for example, in certain cases, for the regeneration of the electrolyte, it could be limited to the addition to the buffer tank 2 of the metals necessary to compensate for the exhaustion of the bath in the cell d electrolysis 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 solid particles, originating from regeneration, in

  the electrolysis cell through line 4.

  Furthermore, depending on the nature of the alloy

  desired or the operating conditions, we could pre-

  see either a single reactor or two or more of two reactors in parallel with the buffer tank 2, whether or not combined with a closed circuit of the same type as

  the circuit 15 of FIG. 2 to ensure the circulation

  tion in the cell and, if necessary, a

reduction 18.

  Finally, the following method and installation> the invention applies to the coating of any type of strip, wire, tube, bar or the like made of an electrically conductive material, in particular steel.

Claims (24)

  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 strip, wire, bar, tube or the like, according to which this element is moved in an electrolysis cell, opposite an anode, through an electrolyte containing zinc sulphate, characterized in that the p H lower than the electrolyte of the electrolysis cell is maintained 2, a temperature of 40 to 700 ° C. and a concentration of 0.2 to 2 moles / liter of zinc sulfate and of 0.3 to 2 moles / liter of an iron, nickel and / or cobalt sulfate according to the   nature of the covering layer to be produced.   2 Method according to claim 1, ca-   characterized in that one maintains in the electrolyte a   p H less than 1.2 and preferably less than 0.4.   3 Process according to one or other of the   claims 1 or 2, characterized in that one adjusts   p H in the electrolyte by addition of sulfuric acid.   4 Method according to claim 3, charac-   which is maintained in the electrolyte of the   electrolysis cell a concentration of sulfuric acid risk greater than 1 mole / liter.   Process 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, a zinc alloy -fer containing 2 to% iron or a zinc-cobalt alloy containing 2 to 12% cobalt.   6 Method according to any one of   previous claims, characterized in that   uses a substantially free electrolytic bath chlorides.   7 Method according to any one of   previous claims, characterized in that   keeps in the electrolyte of the elect cell   trolysis an M / Zn molar ratio of less than 1.5, M being Ni or Co. 8 Process according to any one of   Claims 1 to 6, characterized in that, for the   preparation of a Zn-Fe alloy, an Fe / Zn molar ratio is maintained in the electrolyte between 2 and 3.   9 Method according to any one of   previous claims, characterized in that   uses, in the electrolysis cell, an insoluble anode formed of a lead-silver alloy, the   silver content is preferably 0.6 to 1.2%.   10 Method according to any one of   claims 1 to 8, characterized in that one uses   a soluble anode based on zinc and in that, if necessary, added to the electrolyte ions of the other metal   or other metals of the alloy to be produced.   1 L Method according to claim 10, characterized in that a soluble anode is used   formed of an alloy having substantially the same   position than that of the covering layer to be produced. 12 Method according to claim 11, characterized in that the anode is formed of a Zn-Fe alloy. 32 2526447   13 Method according to any one of   Claims 1 to 6 and 8 to 12 characterized in that,   in the case of the formation of a cover layer   In a Zn-Fe alloy, at least part of the electrolyte is subjected to a reduction, so as to trans- to form Fe ions into Fe + ions.   14 Method according to claim 13, characterized in that a reducing agent comprising 502 is used, so as to form Fe and SQ 4 ions, and in that this reducing agent is regenerated,   in particular by means of an ion exchange resin.   Method according to any one of   claims 1 to 6 and 8 to 14, characterized in that,   in the case of the formation of a cover layer   made of a Zn-Fe alloy, add ammonium sulphate   to the electrolyte to stabilize the Fe + ions.   16 Method according to claim 14, characterized in that a concentration of ammonium sulfate in the electrolyte of between 0.5 and i mole / liter.   17 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 strip, wire, bar, tube or the like, according to which displaces this element in at least one electrolysis cell opposite an anode and through a   electrolyte bath containing zinc sulfate, including   method according to any one of the claims   above, characterized in that a p H less than 2 is maintained in the electrolyte and that the electrolyte is continuously extracted from the cell (1) in order to regenerate it by dissolving therein, in the ratios corresponding to the desired alloy, zinc, on the one hand, and nickel, iron and / or cobalt, on the other hand, according to   the nature of the covering layer, of the electro-   lyte thus regenerated then being reintroduced, also   continuously, in the electrolysis cell.   18 The method of claim 17,   characterized in that zinc is introduced into the elect   trolyte to be regenerated in metallic form.   19 Method according to either of the   claims 17 and 18, characterized in that the nickel   and cobalt are introduced into the electrolyte at reg-   born in the form of carbonates, while iron is introduced into the electrolyte to be regenerated in the form   metallic and / or ferric hydroxide.   2 Q Method according to any one of   claims 17 to 19, characterized in that the   zinc and the other metal of the alloy to be produced and used for the regeneration of the electrolyte are introduced into separate quantities of electrolyte, these quantities being   then reunited before being reintroduced into the cell   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.   21 Installation for electrolytic deposition   tick, continuously and at high current density, of a layer of a zinc-based alloy on an element in the form of a strip, wire, bar, tube or the like, comprising a cell in which can move at least one aforementioned element, continuously, opposite an anode and through an electrolyte containing zinc sulfate, this installation being characterized   in that it is equipped, for regeneration in con-   of the electrolyte, of a device comprising a buffer tank (2) connected directly, by inlet (9) and outlet (10) pipes on the electrolysis cell (1). 22 Installation according to claim 21, characterized in that it comprises at least one separate dissolution reactor (5, 6) connected to the tank   buffer (2) and through which electricity can flow   trolyte from the buffer tank (2).   23 Installation according to claim 22,   characterized in that it comprises at least two reactions   dissolving agents (5 and 6) mounted in parallel on this reservoir and through each of which electrolyte can flow from the buffer reservoir (2), means (7, 8 and 13) being provided for regulating the relative flow rate electrolyte through these reactors depending on the ratio of metals in the alloy to produce in the cell (1).   24 Installation according to any of   claims 21 to 23, characterized in that it comprises   takes a circulation circuit (15) for the electrolyte   closed on the cell (1) which is independent of the device   aforementioned regeneration positive.   25 Installation according to any of   Claims 21 to 24, characterized in that, for the   formation of a Zn-Fe alloy, it includes a reactor   reduction (18) for transformation, in electricity trolyte, from Fe +++ ions to Fe ++ ions.   26 Element in the form of a strip, wire, bar, tube or the like coated with a zinc-based alloy according to the process or by means of the installation   as described above or shown in the accompanying drawings.   27 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 strip, wire, bar, tube or the like, as described   above or shown in the accompanying drawings.   28 Installation for electrolytic deposition   that, continuously and at high current density, as described above or shown schematically in the attached drawings.