DE3316678A1 - METHOD AND DEVICE FOR CONTINUOUSLY ELECTROLYTICALLY APPLYING A ZINC ALLOY LAYER UNDER HIGH CURRENT DENSITY - Google Patents

Description

HOEGER, LEGAL LAW «STPARTNETR

PATENT LAWYERS UHLANDSTRASSE 1Λ C D 7OOO STUTTGART 1

A 45 617 m applicant: "Cockerill-Sambre"

Λ - 176 1, Quai Greiner

April 29, 1983 B-Seraing

description

Method and device for continuous electrolytic Application of a zinc alloy layer under high current density

The invention relates to a method for the continuous electrolytic application of a zinc alloy layer under high current density on an object in the form of a tape, wire, rod, pipe or The like, in which the object is in at least one electrolytic cell against an anode advances an electrolyte containing zinc sulfate.

In known methods of this type, a distinction is essentially made between two techniques.

A first technique is, in a simple manner, that the object is passed through one or more baths can pass through which the to be applied

-9-

A 45 617 m

ια - 176 - 9 -

April 29, 1983

Contains metal in a molten state, see, for example, US Pat. No. 3,858,333. According to a second technique, the object is coated by successively carrying out electrolytic metal depositions on the object, see, for example, DE-OS
21 o6 226 or JP patent application 81 oo 297.

These procedures are generally very complicated and costly, partly because they Requiring going through a relatively large number of procedural steps, each of which is very rigorous Must be subject to control of the respective operating conditions.

In particular in the case of the known methods for coating objects in the form of tapes, namely of sheet steel, one uses an electrolyte of relatively complex composition, which is a very strict control of operating conditions makes it necessary to produce alloys of sufficient purity to obtain a commercially required degree of efficiency.

Thus, large-scale or industrial-scale application of these processes is quite substantial Problems facing.

For example, DE-PS 30 05 159, which relates to a method for producing a zinc-nickel alloy, is a Sulphate bath mentioned, which is a relatively large amount

-lo-

A 45 617 m

m - 176 - Io -

April 29, 1983

contains Na ₃ SO ₄ as a carrier electrolyte. The use of such a carrier electrolyte is essential in order to ensure that the electrolysis bath of the electrolysis cell is sufficiently electrically conductive at a pH of at least 2. In practice, the electrolysis bath must therefore be kept at this pH, as mentioned in the examples of the aforementioned publication.

DE-OS 3o 11 911, which relates in the same way to a method for producing a coating with zinc-nickel alloy, describes the use of SrSO ₄ as a carrier electrolyte in an electrolytic bath, the pH of which is always above 2, as can also be seen from the examples of this prior publication.

In the known methods of the type in question here, the current density in the industrial scale generally do not exceed 20 A / dm, as can also be seen from the previously published examples.

It is the object of the invention to remedy the aforementioned disadvantages and to provide an extremely simple and reliable one To propose method of the type in question, which is suitable for an application in large-scale Scale is suitable and can be carried out continuously under high current density without doing so toxic substances are produced.

-11-

A 45 617 τη

m - 176 -U-

April 29, 1983

The object is achieved according to the invention in that the electrolyte of the electrolysis cell has a pH of less than 2 , a temperature of 40 to 70 ° C. and a concentration of 0.2 to 2 mol / 1 of zinc sulfate and of 0.3 to 2 mol / 1 of an iron, nickel and / or cobalt sulfate, depending on the type of layer to be applied.

A pH of less than 1.2, in particular less than 0.4, is preferably maintained in the electrolyte.

In a preferred embodiment of the invention
one maintains a molar ^{ratio M + VZn +} " ¹ " in the electrolyte, which is less than 1.5, namely at
a pH less than or at most equal to 1.2, where M
means: Ni, Fe or Co. Preferably this is
Ratio in the production of a Zn-Fe alloy between 2 and 3.

The invention also relates to a method for
continuous regeneration of the electrolyte of an electrolytic cell during the continuous electrolytic application of a zinc alloy layer under high
Current density on an object in the form of a tape, wire, rod, tube or the like, with in particular one of the aforementioned electrolytes being regenerated.

According to the invention, the pH value in the electrolyte is kept below 2 and at least part of this is drawn

-12-

A 45 617 m

m - 176 - 12 -

April 29, 1983

Electrolyte continuously from the electrolytic cell from, xiiQ to regenerate it by subtracting int Part in the proportions corresponding to the desired alloy on the one hand zinc and on the other hand Nickel, iron and / or cobalt dissolves, depending on the type of alloy to be applied. That way regenerated electrolyte is then also continuously fed back into the electrolysis cell.

In a particularly preferred embodiment. the According to the invention, the zinc is introduced into the electrolyte to be regenerated in metallic form.

In a further particularly advantageous embodiment of the invention, the zinc and the other metal are used the alloy to be produced, this zinc and this metal regenerating the electrolyte serve, introduced in separate amounts of the electrolyte. These quantities are then combined, before they are fed back into the electrolytic cell. The ratio of these amounts is dependent on the desired ratio of metals in the alloy to be produced in the electrolytic cell regulated.

Finally, the invention also relates to a device for carrying out what is described and claimed here Electrolysis process.

-13-

A 45 617 ro

m - 176 - 13 -

April 29, 1983

This device is characterized in that it for the continuous regeneration of the electrolyte comprises a device with a buffer tank which directly to the Electrolytic cell is connected.

Further details and special features of the invention emerge from the following description, based on which various embodiments according to the invention in conjunction with the accompanying drawing explained. Show it:

Fig. 1 is a block diagram of a first embodiment of a device for Carrying out an electrolysis process and

Fig. 2 is a block diagram of another embodiment.

In the drawing, the same reference symbols denote the same or analogous parts.

The invention relates in particular to a method for continuous electrolyte deposition at high current density, preferably between 2o

2 2

and 3oo A / dm, preferably between 3o and 2oo A / dm. Z a is thereby deposited inklegierungsschicht with a thickness pn preferably 1-12

-14-

A 45 617 m

in - 176 - 14 -

April 29, 1983

varies. The layer is applied to an object in the form of a tape, wire, rod, Tube or the like, for example made of steel or soft iron.

It is a process according to which the object is placed in one or more electrolysis cells across from an anode through an electrolyte, which has a content of zinc sulfate having. The cell can be of conventional construction, for example as described in GB-PS Io 38 671 is described. According to the invention, such a cell is improved by an electrolyte circulation system. This is especially true when it comes to objects in the form of wires, pipes or rods.

In addition, you can, especially with the coating of strips, namely sheet steel, use an electrolytic cell, as is the subject of US Pat. No. 4,343,653

According to the method according to the invention, a pH of less than 2 is kept in the electrolyte of the electrolytic cell, a temperature between 40 and 70 ° C and a concentration of 0.2 to 2 mol / 1 of zinc sulfate and of 0.3 up to 2 mol / 1 of an iron, nickel and / or cobalt sulfate, upright depending on the type of alloy layer to be applied .

-15-

a «ο

A 45 617 m

m - 176 - 15 -

April 29, 1983

The resulting alloy can be a zinc-nickel, zinc-iron, zinc-cobalt alloy or else an alloy of zinc-nickel-iron, zinc-nickel-cobalt, Zinc-iron-cobalt or an alloy of zinc-iron-cobalt-nickel.

It is particularly advantageous to keep it in the electrolyte the electrolytic cell has a pH less than 1.2, preferably less than 0.8, in particular between 0 and 0.5 upright.

For example, if the current density is high, an electrolyte with an acidity that is greater can be used than 1 iaol / 1 and in particular of the order of magnitude of 1.5 mol / 1.

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

The relative concentrations of the metal ions in the electrolyte are advantageously regulated in such a way that a zinc-nickel alloy is obtained with a nickel content of 2 to 14%, a zinc-iron alloy with a content of 2 to 15% of iron or a zinc-cobalt alloy with a content of 2 to 12% Cobalt.

In contrast to certain previously known methods, an electrolysis bath is used according to the invention; which is free of metal chlorides and also does not contain any carrier electrolytes. That way it gets a bath that is as pure as possible, which consequently results in the electrolytic deposition of a zinc

-16-

A 45 617 m

ro - 176 - 16 -

April 29, 1983

alloy on the object in question, which is of excellent homogeneity and purity, without the need to take any special precautions in this regard.

If the electrolyte is free of chlorides and an insoluble anode is used, one can use one Make use of anode which is made of a lead-silver alloy and has a silver content, which in turn is preferably between 0.6 and 1.2%.

In contrast, if a soluble anode is used, it is based on zinc or consists of an alloy which corresponds to that alloy of the electrolytically applied layer.

If the anode is made of pure zinc, the electrolyte will have ions of the other metal or the other Metals added to the alloy to be formed.

Furthermore, when the soluble anode is made of an alloy, the composition of this alloy can be as follows the same as or different from the composition of the applied layer.

If the anode consists of an alloy, its composition is special that of the electrolytic applied alloy layer is different, the composition of the electrolysis bath can be

-17-

A 45 617 m

m - 176 - 17 -

April 29, 1983

be adapted that one ions of the metal in question or of the metals in question.

A soluble anode is particularly suitable for forming a zinc-iron alloy coating.

Thanks to the fact that the electrolyte used according to the invention has a very low pH value, an M ⁺⁺ / Zn ⁺⁺ molar ratio of less than 1.5 can be maintained in the electrolyte. M means nickel or cobalt. The ratio is between 2 and 3 when M is iron. This therefore makes it possible to reduce the relative amount of the metal M used in the manufacture of the zinc alloy.

This can be an essential characteristic of the electrolyte.

To enable working with relatively high current densities, especially with current densities up to 300

A / dm, the relative speed of the electrolyte with respect to the object to be coated is advantageously kept at a value above 1 m / sec or even above 2 m / sec, although this speed can also be above 4 m / sec in certain applications, especially with current densities in the order of magnitude of 2oo to 3oo K / dm, depending on the type and shape of the object to be coated.

-18-

A 45 617 m

m - 176 - 18 -

April 29, 1983

To perform electrolysis in a very acidic bath to be able to, i.e. at a pH value up to 0 or even deeper, one assigns the electrolysis to a continuous regeneration of the electrolyte, which results in the pH value in the electrolytic cell or cells can be stabilized. This regeneration becomes that high acidity produced, which is responsible for the dissolution of metals deposited on the cathode have, is cheap in the electrolyte to be regenerated.

In order to ensure such a regeneration of the electrolyte, the pH value in it is kept below 2, preferably less than 1.2 and continuously extracts part of the electrolyte from the electrolytic cell, to in the extracted part in .relationships that correspond to the desired alloys, on the one hand zinc and on the other hand nickel, iron and / or cobalt dissolve. The electrolyte regenerated in this way is then also continuously returned to the electrolytic cell returned.

About the entrainment of undissolved particles, which may come from this regeneration, into the electrolysis bath of the cell itself and thus contamination of the electrodeposition on the object to be coated, as well as to ensure a smooth setting in the same way the regeneration process depending on

-19-

A 45 617 m

in - 176 - 19 -

April 29, 1983

to enable the operating conditions of the cell the addition of these metals to separate amounts of the electrolyte to be regenerated outside the electrolytic cell instead, these quantities are then mixed again before they are put into the electrolysis cell be returned, namely when all metals are completely dissolved and, if necessary, after implementation a decantation of insoluble impurities resulting from this regeneration.

The measure of isolating adjustable amounts of electrolyte, which one then has to dissolve separately Adding metals for the purpose of regeneration allows the dissolution conditions of these metals to be independent to regulate the circulation of the electrolyte in the electrolytic cell itself, during the Electrolysis process itself and in the course of a likewise continuous regeneration, which is connected to that electrolysis is fully adapted.

The 'zinc is advantageously introduced into the electrolyte to be regenerated in metallic form, as a result of which contamination of the electrolysis bath is excluded or at least reduced to a minimum.

Nickel and cobalt are advantageously introduced into the electrolyte in the form of carbonates, while the Iron is preferably introduced in metallic form or in the form of Fe «-hydroxides. The two The last ways of introducing the iron can also be combined with one another.

-2o-

A 45 617 m

m - 176 - 2o -

April 29, 1983

It is useful for the formation of Zn-Fe alloys depending on the operating conditions and It is often necessary to take certain precautions in order to significantly reduce the overall electrolytic yield to be avoided due to the formation of Fe ions from Fe ions on the anode.

Therefore, according to the invention, ammonium sulfate is added to the electrolyte in order to add the Fe ions in the form of complexes stabilize.

Furthermore, it is advantageous to subject at least part of the electrolyte to a reduction process in such a way that

j I ₁ I ι ι

that Fe ions transform into Fe ions.

In this regard, it has been found that SO- is particularly suitable as a reducing agent. This substance allows the formation of Fe and SO ^. The reducing agent SO ₂ can then be regenerated with the aid of an ion exchange resin.

1 shows a block diagram of a first embodiment an apparatus for performing continuous electrolytic deposition of a Zinc alloy layer under high current density on an object in the form of a tape, wire, rod, Pipe or the like.

The device comprises an electrolytic cell 1, in which one or more objects are attached at the same time

-21-

A 45 617 m

m - 176 - 21 -

April 29, 1983

pass an insoluble anode and through an electrolyte containing zinc sulfate. Of the The object or objects, as well as the anode and the cathode, are not shown in the drawing, since these can be electrolysis cells known per se.

The article therefore depends in fact on the cathode while using an insoluble anode this preferably consists of an alloy of lead and silver, the silver content of which is between 0.6 and 1.2%.

The device is characterized in that it is equipped with a device for continuous regeneration of the Electrolyte is provided. This device is branched off from the electrolytic cell 1.

The regeneration device comprises a buffer tank 2, which via an input line 3 and a Output line 4 is connected directly to the electrolytic cell 1. There are also two dissolving reaction vessels 5 and 6 are provided, which are connected to the container 2 in a parallel circuit. Furthermore are Means are provided to the relative amounts of electrolyte which flow through the reaction vessels 5, 6, in To be able to adjust depending on the ratio of metals in the alloy to be produced in cell 1.

-22-

A 45 617 m

m - 176 - 22 -

April 29, 1983

These means are formed, for example, by valves 7 and 8 which are arranged in front of the reaction vessels 5 and 6, respectively. An input line leads to the valves 7, 8 9 out. An output or return line Io leads from the vessels 5, 6 to the buffer tank 2 back.

The container 2 can, if necessary, also take on the function of a decanting device, and in the case in which insoluble materials, which from the metal solution in the reaction vessels 5 and 6 come into the container 2 via the line Io.

The electrolyte circulation between cell 1 and container 2 is ensured by a pump 12, for example is arranged in the line 4. The circulation between the container 2 and the reaction vessels 5 and 6 are maintained by a pump 13 which is located in the line 9, for example.

The device can be used to produce a Zn-Fe alloy furthermore comprise a reduction reaction vessel 18 which, with the interposition of λτοπ lines 19 and 2o branched off from the container 2. One that can be regulated, for example, with regard to its delivery rate Pump 21 ensures the circulation between container 2 and vessel 18.

-23-

A 45 617 m

in - 176 - 23 -

April 29, 1983

A reducing agent, for example SO ₉ , is added to the

s a trap in the reaction s ge barrel 18 introduced to Fe To convert ions into Fe ions.

An ion exchange resin, which is present in the reaction vessel 18 in the form of a grid, for example, is permitted it to regenerate the reducing agent.

The device described works in the following way:.

In the course of the electrolysis reaction taking place in cell 1 Zinc and one or more other metals separate and form an alloy with zinc should, on the object or objects that are pushed forward in the cell. This leads to exhaustion of the electrolyte of metal ions and an increase in the acidity of the electrolytic bath. Operational endeavors are made to maintain a pH value below 2 and preferably below 1.2 in the bath .

The electrolyte generally circulates in the cell 1 with relative speeds of 1 to 4 m / sec or even higher with reference to the mentioned object, depending on the desired current density. The electrolyte is drawn off via the input line 3 and introduced into the buffer tank 2, in which a relatively stable pH value, which is essentially that in the cell 1 corresponds to the desired pH value, maintained.

-24-

A 45 617 m

m - 176 - 24 -

April 29, 1983

Some of the electrolyte from container 2 is over the supply line 9 to the two dissolution reaction vessels 5 and 6, which can also be called regenerators. Ih one of these reaction vessels, for example in vessel 5, the necessary zinc is introduced, about the depletion of the Γ zinc in the electrolysis bath of «cell 1 to compensate. In the other reaction vessel, the other metal is added, which is associated with the Zinc is supposed to form an alloy in cell 1.

The relative amounts of electrolyte which flow through the reaction vessels 5 and 6 are regulated via the valves 7 and 8 in such a way that the proportion of the dissolved metals that return to the container 2 via the return line Io corresponds to the concentration ratio of these metals., which is necessary to achieve the desired alloy. The arrow 11 indicates an addition of water into the container 2, by means of which the water consumption is compensated for in the course of the electrolysis reaction.

As already stated above, the zinc can be in metallic form, for example in the form of rods or Ingot, are introduced into the reaction vessel 5.

When a Zn-Fe alloy is formed, a part becomes of the electrolyte that arrives in the buffer container 2, directed to the reaction vessel 18, in a

-25-

A 45 617 m

in - 176 - 25 -

April 29, 1983

XJ, .A ₄

Amount that depends on the concentration of Fe ions in the electrolyte.

In the following the electro-chemical reactions at the electrodes are described in detail. on which the electrolysis and regeneration of the electrolyte are based. In addition, the preferred operating conditions specified, namely for the electrolytic deposition of a zinc-nickel—, Zinc-iron and zinc-cobalt alloy.

1. Zinc-Nickel

a) Composition of the electrolysis bath in cell 1:

ZnSO ₄ ϊ 0.5 to 2 mol / 1
NiSO ₄ : 0.2 to 2 mol / 1
pH: 0 to 1.2 (by adding R-SOJ

b) Operating parameters of the electrolytic cell 1:

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) Regenerating agents introduced into reaction vessels 5 and 6:
Zn and NiCO ₃ .2Ni (OH) ₂

-26-

3'S 1 6 6 7

A 45 617 m

m - 176 - 26 -

April 29, 1983

d) Composition of the alloy obtained: 2 to 14% nickel

e) Electro-chemical reactions:

at the cathode: Zn ⁺ "*" + 2e => Zn

2H ⁺ + 2e> H ₂

at the anode: 2H ₂ O > O ₂ + 4H ⁺ + 4e.

2. zinc-iron

a) Composition of the electrolysis bath in cell 1:

ZnSO ₄ : 0.3 to 2 mol / 1 FeSO ₄ : 0.6 to 2 mol / 1 pH: 0 to _{1.2 (by adding H 2} SO ₄ ),

if necessary

(NH ₄ ) ₂ SO ₄ : 0.5 to 1 mol / l.

b) Operating parameters of the electrolytic cell:

Temperature: 40 to 70 ° C Current density: 20 to 300 A / dm ²

relative circulation speed of the Electrolytes: 1 to 8 m / sec.

-27-

• «ft

A 45 617 m

m - 176 - 27 -

April 29, 1983

c) Composition of the alloy obtained: 2 to 15% of Fe?

A. If the anode is insoluble (e.g. Pb-Ag 0.6%)

1) Regenerants introduced into reaction vessels 5 and 6:

Zn and Pe (possibly Fe + Fe (QH) -)

2) Electro-chemical reactions:

- at the cathode: Zn ⁺⁺ + 2e > Zn

Fe ⁺⁺ + 2e r "Fe

2H ⁺ + 2e ^ H ₂

₂ - at the anode: 2 H ₃ O > 0- + 4H ⁺ + 4e

⁴ > Fe ⁺⁺⁺ + e

ι ι ι! j ι

3) Reduction of Fe ions to Fe ions: The Fe ions generated at the anode are converted into Fe ions The output of the electrolysis cell 1 is reduced to Fe ions due to three mechanisms:

a. - In the zinc reaction vessel 5:

Zn + 2 feet + 2 Fe or
Zn +
H ₂ -K 2 H ⁺ +
+ *
2 Zn + 2 Fe ⁺ ^ i- + 2 ² Fe ⁺⁺ Fe ⁺⁺ - > - > ■ 7, n ⁺⁺ Zn ⁺⁺
2 H ⁺ Zn ⁺⁺

-28-

A 45 617 χα

m - 176 - 28 -

April 29, 1983

b. - In the iron reaction vessel 6: Fe + 2 H ⁺ ^ Fe ⁺⁴ "+ H ₂

₂ + 2 Fe "^ Ü> 2 H ⁺ + 2 Fe ⁺⁺

Fe + 2 Fe ⁺ Ü> 3 Fe ⁺⁺

c. - In the reduction reaction vessel 17: 2 Fe ⁺ " ¹ " ¹ "+ SO ₂ + 2H ₂ O—> 2 Fe ⁺⁺ + H ₃ SO ₄ + 2H ⁺

Depending on the operating conditions, the dimensions of the three reaction vessels are determined in such a way that a constant composition of Fe, Zn ⁺ and a low content of Fe ^{+ +} ions are maintained.

B. With soluble anode

1) Anode: Zn-Fe alloy of the same composition like the coating to be applied; or pure zinc with iron regeneration in one attached Reaction vessel.

2) Electro-chemical reactions:

- at the cathode: Fe + 2e ^ Fe

Zn ⁺⁺ + 2e> Zn

2 H ⁺ + 2e> H ₂

- at the anode: Fe> Fe + 2e

Zn> Zn ⁺⁺ + 2e

-29-

A 45 617 m

m - 176 - 29 -

April 29, 1983

3) Reduction of Fe ions to Fe ions:

Thanks to the use of a soluble anode, there is no formation of Fe on it and as a result basically only causes an oxydation of the Fe ⁺⁺ ions through the air.

This has the consequence that the amount of

, j. χ χ

lytes formed Fe ions is relatively small and generally does not require _{the addition of a reducing agent such as SO 2.}

3. Zinc-Cobalt

a) Composition of the electrolysis bath in the cell

ZnSO ₄ : 0, 3 to 2 mol / 1 CoSO ₄ : 0, 6 to 2 mol / 1 pH : 0 up to 2 (by adding

b) Operating parameters of the electrolytic cell:

.2

Temperature: 40 to 70 ° C

Current density: 20 to 300 A / dm '
relative circulation speed of the electrolyte: 1 to 8 m / sec.

c) Regenerating agents introduced into reaction vessels 5 and 6:
Zn and CoCO ₃ .2Co (OH) ₂

-3o-

Ü * β 0

■ a * ■

A 45 617 m

ro - 176 - 3o -

April 29, 1983

d) Composition of the alloy obtained: 2 to 12t and Co

e) Electro-chemical reaction:

J ₁ -1

- on the cathode: Zn + 2e

Co ⁺⁺ + 2e

2H ⁺ + 2e- ^ ₄ *.

- at the anode: 2H ₂ O> O ₂ + · 4H + 4e,

In summary, it can be said that for these three types of alloys in the course of the electrolysis except for a consumption of metal ions for the to producing alloy a consumption of H., 0, a production of H and a release of oxygen results.

Furthermore, especially in the case of a zinc-nickel alloy, the molar ratio Ni ⁺⁺ / Zn ⁺⁺ = (X is below 1.5 and generally between 0.5 and 1.2. These data apply to the electrolysis bath.

The above-mentioned generation of H ions leads to acidification of the electrolysis bath in the cell

As already stated above, an essential feature of the invention is to use these H ions to to generate the electrolyte.

You can therefore keep the pH in the electrolysis bath of cell 1 above a minimum value and at the same time

-31-

• 0 a

"JS16678

A 45 617 m

in - 176 - 31 -

April 29, 1983

replace the metal ions in the electrolysis bath, which as a result Electrolytic deposition were withdrawn from the bath without the need for special aids to resort to the formation of these ions.

The metals or metal compounds that are used for regeneration in reaction vessels 5 and 6, must preferably be easily soluble in the acidic baths without leaving any insoluble traces, which could contaminate the electrolysis bath. Hence, metallic additives like zinc and Iron and carbonates or hydroxides of nickel, cobalt and iron particularly cheap. Are particularly preferred

for example, basic nickel and cobalt carbonates and ferric hydroxides, optionally mixed with metallic iron particles.

When using carbonates, the solution is, as it were, stirred by the released CO. This will the homogeneity of the electrolyte in the vessels 5 and increases.

The method according to the invention is further explained below with the aid of some practical exemplary embodiments.

example 1

In the production of an electrolytic deposition of a zinc-nickel alloy on a steel sheet leads

-32-

A 45 617 m

ro - 176 - 32 -

April 29, 1983

electrolysis is carried out in an electrolysis bath containing 1.2 »ol / l of NiSO ₄ and 1 mol / l of ZnSO. contains. The bath is maintained at a pH of the order of 1 and a temperature of the order of 50 ° C. The extractions current density

is 100 A / dm, while the relative circulation speed of the electrolyte with reference to the Sheet is 1 m / sec.

The anodes used are made of iron-silver with a silver content of 1.2%.

The thickness of the deposited layer is 5 p? .. The pH of the electrolyte at the outlet of the cell and in the line 3 leading to the buffer tank 2 is of the order of 0.8, while the pH of the Electrolyte, which has been subjected to dissolution and flows back through the line Io, has a pH value is on the order of 1.5. The alloy obtained contains about 8% nickel.

Example 2

A bath of 0.5 mol / l of ZnSO is used in the electrolysis cell. and 0.6 mol / l of NiSO ₄ . The bath is at a temperature of 50 ⁰ C and at a. Maintained pH of 1.2 (by adding H-SO.). In the bath, a steel sheet is coated by an electrolytic deposit of a Ni-Zn alloy.

-33-

A 45 617 m

m - 176 - 33 -

April 29, 1983

The density of the cathodic output current is in the order of 30 A / dm , while the circulation speed of the electrolyte is in the order of 1 m / sec. amounts to.

For the regeneration in the reaction vessels 5 and 6, metallic zinc and basic nickel carbonate are required.

The electrolytic deposit is made of a nickel-zinc alloy with a nickel content of 11% and has a thickness of about 5 µm.

The electrolytic precipitate was uniformly clear and gray in appearance.

Example 3

The electrolysis bath contains 2 mol / 1 of ZnSO. and 2 mol / 1 of NiSO ₄ and is kept at a temperature of about 50 ° C (by adding H ₂ SO ₄ ) at a pH of 0. In the bath, a steel sheet is covered with an electrolytic deposit of a Ni-Zn alloy. The density of the cathodic current is 300 A / dir. , while the relative speed of the electrolyte with respect to the sheet to be coated with the alloy is 4 m / sec.

The regeneration takes place by adding metallic zinc and basic nickel carbonate to the electrolyte instead of. The alloy contains 8% nickel and has a uniform, brilliant gray appearance.

-34-

A 45 617 m

m - 176 - 34 -

April 29, 1983

Example 4

The electrolysis bath contains 0.5 mol / l of NiSO ₄ , 0.5 mol / l of ZnSO ₄ and 1.5 mol / _{l of H-SO 4} . The bath is kept at a temperature of 50 ° C. and is used to coat a nickel sheet with an electrolytic deposit of a Zn-Ni alloy.

The cathodic current density is 200 A / dm, while the relative speed of the electrolyte with respect to the sheet to be coated is 4 m / sec.

The regeneration takes place through the addition of metallic substances Zinc and from basic nickel carbonate to the electrolyte instead. The alloy contains 8% nickel and shows a metallic gray appearance.

Example 5

To produce an electrolytic deposition of a zinc-nickel alloy on a steel wire with a diameter of 1 mm, the electrolysis is carried out in an electrolysis bath which contains 0.5 mol / l of NiSO ₄ and 0.7 mol / l of ZnSO ₄ . The bath is kept at a pH of about 0.3 and at a temperature of about 50 ^° C. by adding sulfuric acid. The density of the extraction current is 30 A / dm. The voltage at the terminals of the cell is 4 volts. The cathodic yield is 74%. The circulation speed of the electrolyte is 3 m / sec,

-35-

A 45 617 m

m - 176 - 35 -

April 29, 1983

while the speed of the thread in the opposite direction to this circulation is 1 m / sec.

The anodes used are made of lead-silver with a silver content of 0.6%. For regeneration in the In reaction vessels 5 and 6, metallic zinc and basic nickel carbonate are used.

The thickness of the deposit is 4 pn.

The alloy obtained contains approximately 13% nickel.

The precipitate has a clear, gray, uniform and shiny appearance.

Example 6

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

For this purpose, a bath of 1 mol / 1 of ZnSO is used in the electrolysis cell. and 0.8 mol / l of NiSO ₄ . The bath is kept at a pH of 0.5 and at a temperature of 50 ° C. _{by adding H 3} SO _4.

The density of the cathodic extraction stream is

2 on the order of 50 A / dm. The tension on the Clamping the electrolytic cell is 5.3 volts. The cathodic current efficiency is 74%. The circulation speed of the electrolyte is about 3 m / sec, while the speed at which the thread is displaced in the opposite direction is about 6 m / sec amounts to.

-36-

A 45 617 m

m - 176 - 36 -

April 29, 1983

Metallic zinc and basic nickel carbonate are used for regeneration in vessels 5 and 6.

The electrodeposition consists of a nickel-zinc alloy with a nickel content of 11% and a thickness of about 1 µm.

The deposit showed a clear, even gray.

Example 7

A steel wire; with a diameter of 3.5 mm is coated with a zinc-nickel alloy. The electrolysis bath used contains 2 mol / 1 of ZnSO, and 2 mol / 1 of NiSO-. The bath is made by adding H-SO. at a pH value of 0.2 and at a temperature about 50 ⁰ C -from maintained.

The cathodic current density is 150 A / dm. The voltage at the terminals of the cell is 12 volts. The cathode current yield is 74%. The speed of the electrolyte is A m / sec, while that of the wire in the opposite direction is 3.3 m / sec.

The electrodes used are made of lead-silver with a silver content of 0.6%.

The regeneration takes place by adding metallic zinc and basic nickel carbonate to the electrolyte instead of.

The alloy obtained contains 13% nickel and has a shiny, gray appearance.

-37-

A 45 617 m

m - 176 - 37 -

April 29, 1983

Example 8

A steel pipe with an outside diameter of about 16 microns. and an inside diameter of 14.5 mm is coated inside and outside with a - zinc-nickel alloy.

The electrolysis bath used contains 1 mol / l of NiSO ₄ , 1 mol / l of ZnSO ₄ and is kept at a pH of 0.8 and at a temperature of about 50.degree. The cathode current density is 50 A / dm. The voltage at the terminals of the cell is 5.3 volts, the cathode current yield is 76%. The circulation speed of the electrolyte is 2 m / sec, while the feed speed of the pipe in the opposite direction is 1.2 m.

The anodes used are made of lead-silver with a silver content of 0.6%.

The regeneration takes place by adding metallic Zinc and basic nickel carbonate to the electrolyte instead.

The alloy contains 10% nickel and has a clear, evenly gray appearance. The thickness of the deposited Layer is on the order of 5 µm.

Example 9

A steel sheet is coated with a Zn-Fe alloy in an electrolytic bath. The electrolytic bath had the following composition:

-38-

A 45 617 m

m - 176 - 38 -

April 29, 1983

Ζτι : 25 g / l

Fe ⁺ *: 65.3 g / l

Fe ⁺⁺⁺ : 3 g / l

H ₂ SO ₄ : 46 g / l

Y-SO. : 80 g / l

The anode is made of lead-silver with a silver content of 0.6%.

The current density is 60 A / dm ² .

The relative speed of the electrolyte in the cell is 1 m / sec, while the speed is with at which the steel sheet passes the anode, is 8 m / min.

The current yield is 88% and the anode voltage is 9.7 volts.

The electrolytic deposit formed in this way consists of a zinc-iron alloy with a 92% zinc and 8% iron content. The deposit is clear, ductile, uniform, it yields a complete coverage of the substrate and shows a fine crystallization.

Example 10

A steel sheet is coated with a layer of a Zn-Fe alloy in an electrolytic bath. The electrolysis bath has the following composition:

-39-

A 45 617 m

m - 176 - 39 -

April 29, 1983

-H- 23 g / l

Zn
Fe
Fe
H ₂ SO ₄

68 g / i 0.2 g / i 50 g / i

120 g / l

The anode is designed as a soluble anode made of pure zinc.

The current density is 70 A / dm.

The relative speed of the electrolyte in the cell is 1 m / sec, while the displacement speed of the sheet is 8 m / min.

The cathodic current yield is 90%, the anode-cathode voltage 8.2 volts.

The electrodeposition consists of a zinc-iron alloy with 91% zinc and 9% iron.

The deposit is clear, ductile, provides good coverage of the substrate and shows fine crystal formation.

Examples 1 to 8 are repeated, only the NiSO _{4 being} replaced by FeSO ₄ or CoSO ₄ in order to produce zinc-iron or zinc-cobalt alloys. Example 10 is repeated, the Fe ions being replaced by Ni ions or Co ions

111

and the (NH ₄ ) ₂ ^SO 4 and the Fe ions omit. In this way, Zn-Ni or Zn-Co alloys are created.

In the case of the production of a zinc-iron alloy, metallic zinc and zinc are used for regeneration

-4o-

33115678

A 45 617 m

m - 176 - 4o -

April 29, 1983

a mixture of iron and goethite and, in the same way, iron alone.

In the case of the production of a zinc-cobalt alloy regeneration takes place with the help of metallic zinc and basic cobalt carbonate.

The other parameters and operating conditions are kept roughly the same as those of the eight examples the production of a zinc-nickel alloy.

Fig. 2 shows a .Blockschema a second embodiment of a device for continuous electrolytic Deposition at high current density. A zinc alloy layer is also obtained with the device according to FIG deposited on an object in the form of a tape, wire, rod, pipe or the like.

In this embodiment one leaves continuously all of the electrolyte flow through a closed circuit 15 in which a circulation pump 18 is arranged, with the help of which the required circulation speed in the electrolytic cell 1 is maintained. The pump also allows a sufficiently high current density to be maintained obtain.

Only part of the electrolyte is the aforementioned th regeneration, namely in a device which comprises a buffer tank 2. This

-41-

"'331d678

A 45 617 m

m - 176 - 41 -

April 29, 1983

The container also serves as a dissolving reaction vessel in the same way as the reaction vessels 5 and 6 in the embodiment according to FIG. Furthermore, a circulation pump 12 and a valve 17 for regulating the amount flowing in the line 4 are provided.

This enables the circulation in the flow circuit kept separate and independent of the circulation through the electrolytic cell itself. This will make the The advantage achieved is that, for example, in container 2, which takes on the function of the dissolving reaction vessel, the conditions necessary for the dissolution of the ones intended for regeneration of the electrolytic bath Metals can create.

From the above description and in particular the practical examples it follows that the inventive Method has the advantage that a coating on an object in the form of a tape, Wire, rod, pipe or the like receives in a single operation. This is in contrast to the known processes which require a series of successive metal plating baths to go through, which are separated from each other by washing baths and to which a thermal Final treatment follows.

-42-

A 45 617 m

m - 176 - 42 -

April 29, 1983

With this known technique, a coating is obtained which is formed from at least two superimposed ^ layers, between which a potential difference can develop.

As a result, this can cause material migration and, in this way, the formation of corrosion centers in the coating.

The invention is based on the embodiments of the methods and devices described and illustrated here not restricted.

In certain cases, for example, when regenerating the electrolyte, you can rely on the addition the required metals in the buffer tank 2 to limit the depletion of the electrolytic bath in to compensate the cell 1 without making use of the closed circuit 15 of FIG. 2, in such a way that that all the electrolyte of the cell passes through the container 2.

Nevertheless, there is the possibility of taking special precautions in this embodiment to ensure that it is taken along to prevent solid particles originating from the regeneration and via line 4 in the electrolytic cell.

Incidentally, depending on the type of alloy desired or the operating conditions, either one can be used

-43-

A 45 617 m

m - 176 - 43 -

April 29, 1983

Provide a single reaction vessel or two or even more than two reaction vessels that are connected in parallel to the buffer container 2. In a further embodiment, these reaction vessels can, if desired, also be combined with a closed circuit corresponding to the circuit 15 according to FIG. 2
to ensure the circulation in the cell. Furthermore, a reduction vessel 18 can also be attached if necessary.

The invention can be applied to coatings of any object in the form of tapes, wires, rods, Use pipes or the like, insofar as these objects are made of an electrically conductive material, in particular Steel.

Blank page

Claims (28)

Claims 1. A method of continuous electrolytic deposition of a zinc alloy layer under high Current density on an object in the form of a tape, wire, rod, tube or the like, in which the object in at least one electrolysis cell against an anode by a Zinc sulphate-containing electrolytes, characterized in that that the electrolyte of the electrolytic cell has a pH of less than 2, a temperature of 4o to 7o ° C and a concentration of 0.2 to 2 mol / l of zinc sulfate and from 0.3 to 2 mol / l of an iron, nickel and / or cobalt sulfate, depending on the type of sulfate to be applied Layer maintains. 2. The method according to claim 1, characterized in that one has a pH less than 1.2 in the electrolyte, preferably less than 0.4. 3. The method according to claim 1 or 2, characterized in that the pH value in the electrolyte is adjusted by adding sulfuric acid. -2- A 45 617 τη in - 176 - 2 - April 29, 1983 4. The method according to claim 3, characterized in that there is a sulfuric acid concentration in the electrolyte above 1 mol / 1 is maintained. 5. The method according to any one of claims 1 to 4, characterized characterized in that the metal ion concentration in the electrolyte is set in such a way that a zinc-nickel alloy is used with a content of 2 to 14% of nickel, a zinc-iron alloy with a content from 2 to 15% of iron or a zinc-cobalt alloy with a content of 2 to 12% of cobalt. 6. The method according to any one of the preceding claims, characterized in that a substantially chloride-free electrolytic bath is used. 7. The method according to any one of the preceding claims, characterized in that a molar ratio M / Zn of less than 1.5 is maintained in the electrolyte obtained, where M means Ni or Co. 8. The method according to any one of claims 1 to 6, characterized characterized in that when applying a Zn-Pe alloy in the electrolyte, a molar ratio Fe / Zn maintains between 2 and 3. 9. The method according to any one of the preceding claims, characterized in that an insoluble anode is used in the electrolytic cell, which consists of a • OO I DD / A 45 617 m ro - 176 - 3 - April 29, 1983 Lead-silver alloy is formed, the silver content of which is preferably between 0.6 and 1.2%. 10. The method according to any one of claims 1 to 8, characterized characterized in that one uses a soluble zinc-based anode and the electrolyte if necessary Ions of the other metal or metals added to the alloy to be produced. 11. The method according to claim Io, characterized in that that one uses a soluble anode made of an alloy having essentially the same composition how the zinc alloy layer to be applied has. 12. The method according to claim 11, characterized in that the anode is formed from a Zn-Fe alloy is. 13. The method according to any one of claims 1 to 6 and 8 to 12, characterized in that at least part of the electrolyte is subjected to a reduction when a layer is formed from a Zn-Fe alloy
Ions transformed. It ₁ I I 1 In doing so, Fe ions in Fe are subjected to production 14. The method according to claim 13, characterized in that a _{reducing agent containing SO 2} is used in such a way that Fe ⁺⁺ ions and SO ₄ ions -4- A 45 617 m m - 176 - 4 - April 29, 1983 form, and that the reducing agent, preferably by means of an ion exchange resin, regenerated. 15. The method according to any one of claims 1 to 6 and 8 to 14, characterized in that in the case of Forming a layer of a Zn-Fe alloy to the electrolyte adds ammonium sulfate to the Fe Stabilize ions. 16. The method according to claim 14, characterized in that there is a concentration of ammonium sulfate in the electrolyte between 0.5 and 1 mol / 1 is maintained. 17. The method, in particular according to one of the preceding claims, characterized in that one is im Electrolyte maintains a pH less than 2. and electrolyte continuously from the electrolytic cell subtracts in order to regenerate it by putting in it in proportions according to the desired Alloy zinc on the one hand and nickel, iron and / or cobalt on the other hand, depending on the type of application Layer, dissolves, and that the electrolyte regenerated in this way is then also continuously again returns to the electrolytic cell. 18. The method according to claim 17, characterized in that the zinc is in the electrolyte to be regenerated brings in metallic form. -5- A 45 617 m m - 176 - 5 - April 29, 1983 19. The method according to claim 17 or 18, characterized in, that.! Nickel and cobalt introduced into the electrolyte to be regenerated in the form of carbonates while the iron in metallic and / or in the form of Fe -hydroxyd in the to be regenerated Electrolyte is introduced. 20. The method according to any one of claims 17 to 19, characterized characterized in that the zinc and the other metal of the alloy to be applied for the purpose of Regeneration of the electrolyte in separate amounts of the electrolyte are introduced that this Quantities are then combined before they are returned to the electrolytic cell, and that the ratio of these amounts depending on the desired ratio of metals in the in the Electrolytic cell to be produced alloy is set. 21. An apparatus for performing the method according to claims 1 to 2o with an electrolytic cell through which is continuously guidable article to be coated, characterized in that t that it is provided for the continuous regeneration of the electrolyte contained in the electrolytic cell with a buffer vessel (2), which is connected directly to the electrolysis cell by input and output lines. -6- A 45 617 m m - 176 - 6 - April 29, 1983 22. The device according to claim 21, characterized in that it comprises at least one dissolving reaction vessel (5, 6) which from the buffer vessel (2) oe- tttit
separates, and _x that is connected by branch lines (9, lo) and through which circulate the originating from the buffer vessel electrolyte. 23. The device according to claim 22, characterized in that it has at least two dissolving reaction vessels (5, 6) which are connected in parallel to one another with respect to the buffer vessel (2) and through which electrolyte from the buffer vessel can circulate, and that means (7, 8) are provided, with the help of which the relative quantities flowing through the reaction vessels (5, 6) of the electrolyte as a function of the proportions of the metals in the in the electrolytic cell to be produced alloy are adjustable. 24. Device according to one of claims 21 to 23, characterized in that it has a Electrolytic cell includes closed circulation flow path for the electrolyte, which is from the said regeneration means (5, 6) is independent. 25. Device according to one of claims 21 to 24, characterized in that it is used for training a Zn-Fe Leaieruno a reducing reaction vessel -7- A 45 617 m m - 176 - 7 - April 29, 1983 , 1 .1 1 -f + (18) for converting Pe ions into Fe electrolytes. 26. Object in the form of a tape, wire, rod, tube or the like, characterized in that that it is coated with a zinc alloy layer using the methods described herein and illustrated methods and devices is coated. 27. Process for the continuous electrolytic deposition of a zinc alloy layer under high current density on an object in the form of a band, wire, rod, pipe or the like, as described and shown on the drawing. 28. Performing continuous electrolytic Coating under high current density as described and shown in the drawing.