DE1250712B - Galvanic nickel sulfamate bath and process for depositing nickel coatings - Google Patents

Description

FEDERAL REPUBLIC OF GERMANY

GERMAN

PATENT OFFICE

EDITORIAL

Int. CL:

C23b

German class: 48 a - 5/08

Number: 1250 712

File number: J 25865 VI b / 48 a

Filing date: May 20, 1964

Opened on: September 21, 1967

For some time now, mainly sulphamate baths have been used in the production of galvanic deposits from nickel used both in electrolytic molding and in creating decorative ones Coatings. This generally creates an internal tension in the precipitates in the form of tensile stress. The deposits become glossy if the bath contains a gloss-producing agent, otherwise dull.

Although the bath can be made by directly dissolving pure nickel sulfamate, it stands practically mostly nickel sulfamate is available in the form of a concentrated solution, and the bath will then prepared in such a way that the concentrated solution is diluted and then purified. the Cleansing is essential to keep scarring and precipitation to a minimum to give the best quality. It is generally produced by electrolysis at low current densities and subsequent electrolysis carried out at the usual current densities. Contains the concentrated solution organic substances, treatment with activated charcoal may be necessary.

In general, an additive with a polishing effect, almost always boric acid, and a substance for promoting it are also used the anode corrosion, and in almost all cases nickel chloride, added to the diluted solution. Often one also adds substances to counter the formation of hydrogen scars or the to convert internal tensile stress into compressive stress.

The concentration of nickel sulfamate in the solution used as the electrolyte has fluctuated in practice from 250 to 370 g / l. However, a solution with 450 g / l content of nickel sulfamate has also been used occasionally. It is known that during electroplating the rate of deposition increases with the current density, but that under the given electroplating conditions the current density is practically drawn to a maximum above which so-called burning occurs. The amount of this practical maximum of the current density depends not only on the operating temperature, but also on the speed of bath movement and the arrangement of the anode and cathode in the tub. In SuIfamatbädern in which the operating temperature is between 25 and 6O ⁰ C, and the at 6O ⁰ C and a solution of 300 g / l Nickelsulfamatgehalt be operated, a typical value of the maximum current density is 22 A / dm *. In connection with solutions whose content / l of nickel sulfamate is 450 g, are current densities of 32 A / dm ² at 60 ° C and ² have been described at 38 ⁰ C 16 A / dm. However, the inventors have ge-galvanic nickel sulfamate bath and method
for the deposition of nickel coatings

Applicant:

International Nickel Limited, London

Representative:

Dr.-Ing. G. Eichenberg

and Dipl.-Ing. H. Sauerland, patent attorneys,

Düsseldorf, Cecilienallee 76

Named as inventor:

Richard John Kendrick,

Shirley, Solihull, Warwickshire;

Sidney Alec Watson,

Pedmore, Stourbridge, Worcestershire

(Great Britain)

Claimed priority:

Great Britain of May 22, 1963 (20 443),

dated September 25, 1963 (37748)

found that under certain conditions, the movement of the bath and electrode assembly in which satisfactory results are achieved during electroplating in a Nickelsulfämatlösung, the maximum current density at 6O ⁰ C in a solution containing g / l content of nickel sulfamate only 27 A / dm. ²

The invention is based on the knowledge that by working with higher than usual concentrations it is possible to obtain various advantageous results in connection with the particular one used To obtain current density.

The invention consists generally in the teaching, in the production of galvanic nickel deposits with to work in a nickel sulfamate bath containing 500 to g / l nickel sulfamate. In the preferred Execution of the invention a bath is used, the content of nickel sulfamate 550 to 650 g / l is, and it has also been found that particularly favorable results are obtained when the concentration is approximately 600 g / l.

It was found that when the concentration of nickel sulfamate was changed both the maximum permissible current density and the internal stress state in

709 648/296

the precipitation change in a remarkable way. This is in iri-g. 1 and 2 shown. In Fig. 1, the practical maximum value of the current density in A / dm ^{2 is} plotted against the nickel sulfate concentration in g / l. Curve A in FIG. 1 was obtained by varying the nickel sulfamate concentration at 60 ° C. As shown in Fig. 1, Kurvet has a pronounced maximum in the range of 300 to 900 g / l, a maximum which is an unexpected phenomenon. The maximum itself extends over a range from about 500 to 700 g / l. The curve rises rapidly to 43 A / dm ² at 600 g / l and then drops off steeply.

In Fig. 2, the internal stresses in the precipitate in kg / mm ^{2 are} plotted against the nickel sulfamate concentration in g / l. The drawn curve B was carried out at 6O ⁰ C and a current density of 5.5 A / dm ^{2 is} obtained. Curve B has a reciprocal similarity to curve A, that is to say shows a pronounced drop in the tensile stress in the concentration range within which the invention teaches to work.

The operating temperature has a marked influence on the result. The solution is heated to 7O ⁰ C, curve A so moves upwards, and the practical maximum of the current density to the remarkable amount of 86 A / dm ² is raised. Increasing the bath temperature shifts the curve .Β in the direction of increased compressive stress. Accordingly, for a given current density and at a higher bath temperature, the compressive stress is greater or the tensile stress is smaller. Reduction in temperature causes at 5O ⁰ C, that the internal stress sharply shifts in the direction of increasing tension.

The internal voltage also changes with the current density. This dependency is shown in FIG. 3, where the voltage in kg / mm ^{2 is} plotted against the current density in A / dm ^2. Fig. 3 shows two curves C and D, which were taken at a Nickelsulfamatkonzentration l of '600 g /, and indeed curve C at 60 ⁰ G and curve D at 70 ° C. The graph shows that at this concentration, the internal stress is carried out at 60 ⁰ C decreases to zero, if the current density is ² / dm about 18 a, while the same is done at 7O ⁰ C when a Stron> density of 33 a / dm ^2.

The pH of the solution is expediently 4.0, but may vary between 2.0 and 5.5. The bathroom can be moved through air in the usual way during electroplating. Preferably it contains a polishing component, in particular boric acid, which can be present in the usual amount, for example from 10 g / l to the saturation value.

It is known that hydrolysis of nickel sulfamate should be avoided. Increasing the bath temperature increases the rate of hydrolysis, and so does a decrease in the pH of the bath and a decrease in the concentration below the value of 600 g / l nickel sulfamate within the range which the invention teaches to be used. In contrast, an increase in the rate of hydrolysis at a bath temperature of 70 ^° C. (in contrast to ^{a bath temperature of 60 °} C.) is practically entirely permissible. If, for example, a bath with a content of 600 g / l nickel sulfamate and a pH value of 4 is kept at a temperature of 65 ° C, the rate of accumulation of ammonium ions is of the order of 1 g / l per year.

If a similar solution is kept at 70 ^° C., the rate of accumulation only increases to 5 to 6 g / l per year. This accumulation results from the cleavage of only about one hundredth of the original nickel sulfamate. It is possible to galvanize using a solution whose temperature has the considerably high value of 8O ⁰ C. The improvement in the obtained properties of the product, however, becomes a great part

ίο lifted by the difficulties that arise when one wants to keep such a bath thermally under control. The preferred embodiment of the invention therefore provides no more than 70 ^° C. as the operating temperature.

The invention can be used with particular advantage in precision electrolytic molding. In this case, ⁰ C is preferably at a temperature between 55 and 7O worked and in any case a produced in the electrolytic precision molds precipitate is not intended to have low internal stress at less than 5O ⁰ C. As is well known, if it is to receive the dimensional stability required for many purposes will. For example, in the production of metal disks, which are used to punch records, an internal tensile stress of up to 5.75 kg / mm ^{2 is} permitted. But it would be very desirable if the internal tension were zero. For some other purposes, an internal compressive stress, for example up to 1.5 kg / mm ² , would be quite desirable.

It can be seen from Fig. 3 that the voltage changes with both current density and temperature. In precision electrolytic molding, it is useful to measure the current density and the temperature in the range shown in FIG. 4 obvious ways to relate them to each other. There the temperature is plotted against the current density. In the preferred embodiment of the invention, the current density is chosen so that it is between the lines EF and GH at the temperature used in each case

, is between 10.8 and 19.0 A / dm ² at 55 ° C, between 16.0 and 25.0 A / dm ² at 60 ° C, between 21.5 and 35.5 A / dm ² at 65 ⁰ C and between 27.0 and 48.5 A / dm ² at 7O ⁰ C. At a concentration of 600 g / l, the stress is then normally between 1.5 kg / mm ² compressive stress and 5.75 kg / mm ² tensile stress. At the same concentration, the stress is normally between 0.75 kg / mm ² compressive stress and 3.0 kg / mm ² tensile stress when the current density at the respective temperature is between the lines IJ and KL , i.e. between 11.8 and 16.0 A / dm ² at 55 ° C, between 17.3 and 21.5 A / dm ² at 6O ⁰ C, between 22.5 and 26.5 A / dm ² at 65 ° C and between 28.0 and 36, 5 A / dm ² at 70 ⁰ C. If the current density at the respective temperature between lines IJ and MN, so it does not exceed 13.5 A / dm ² at 55 ° C, 18.5 A / dm ² at 60 ° C, 26.0 A / dm ² at 65 ⁰ C and 31.0 A / dm ² at 70 ⁰ C, then normally the tension does not exceed the value of 0.75 kg / mm ² as tensile stress, so that when working between these two lines IJ and MN an approximation of the zero value of the voltage will in general be obtained.
If it is not important to keep the internal stress low, the invention can be used to generate nickel deposits at high speed. The current density increases with temperature, and the same applies from the area

which the current density can be selected with the greatest advantage for the temperature used, as can be seen from FIG. 5 results, in the same way as in FIG. 4 the temperature is plotted against the current density. The current density should lie between the lines OP and QR at the selected operating temperature. Accordingly, at 55 ° C. the current density becomes between 19.0 and 27.0 A / dm ² , at 60 ° C. between 27.0 and 43.0 A / dm ² , at 65 ° C. between 38.0 and 65.0 A / dm ² and between 48.5 and 86.0 A / dm ^{2 at 70 ° C.} At a concentration of 600 g / l and an operating point lying between the lines OP and QR , an internal tensile stress will generally be obtained which is between 5.75 and 12.5 kg / mm ² . The generation of precipitates at such a high speed is useful, for example, in cases where it is a question of reconditioning worn surfaces by electroplating, because there is a tensile stress in the precipitate of between 5.75 and 10.0 kg / mm ² , is portable.

With precipitation produced under the various conditions of current density and temperature as indicated above, the internal tensions depend on the concentration. However, within the range from 550 to 650 g / l they are in the same order of magnitude as the tensions in the precipitates obtained at a concentration of 600 g / l.

The hardness of the precipitates obtained changes with the current density. If nickel sulfamate solutions are used which contain 600 g / l nickel sulfamate, ^{a Vickers hardness of about 220 results at 21.5 A / dm 2.} At 5.5 to 7.5 A / dm ² and a temperature in the range from 55 to 70 ° C a Vickers hardness of 300 is obtained. If, on the other hand, the current density is reduced to 3.25 A / dm ² , a Vickers hardness of 400 is obtained. In this way, it is possible to simply change the hardness of successive layers of nickel plating within the same plating bath to vary so that the current density changes as the electroplating proceeds. For example, a thin, very hard nickel layer can first be deposited, followed by a somewhat thicker layer of lower hardness, so that a body with a hard outer surface is obtained which is manufactured by precision electrolytic molding. At such low current densities, a considerable compressive stress also arises in the precipitate, which has the advantage that the creep strength of parts which are provided with a coating of such a precipitate is increased.

The precipitates obtained by proceeding in the manner described in electrolytic forming are dull. If, on the other hand, one works with a customary current density, i.e. a density that ^{does not exceed 7.5 A / dm 2} , a glossy precipitate can be obtained at temperatures of 55 to 70 ° C. without adding a gloss-producing agent. This in turn represents a surprising phenomenon. Such a glossy deposit also has the advantage of good ductility. It was found that the specific elongation which was necessary to produce cracks in a deposit applied to a highly ductile base metal body was 12%.

If you work with a high current density, for example between 16.0 and 38.0 A / dm ² , then at a temperature of 55 to 75 ° C using a "; gloss-producing agent, glossy deposits can be obtained extremely quickly. Such low-; Strikes are under moderate internal tension, which: however, is generally meaningless if it is only a decorative layer: If a gloss-producing agent is used, one can use any such agent that is otherwise used in conventional bright nickel baths which are based on the Watt bath, such as p-toluenesulphonamide, saccharine, arylsulphonic acids or acetylene alcohols.

When working with nickel sulphamate solutions containing 500 to 700 g / l nickel sulphamate, it is desirable to use reactive nickel anodes, for example those containing a small amount of sulfur, in order to cause uniform corrosion. _;

It may be advantageous to add nickel chloride to the solution in order to bring about a uniform and gradual dissolution of the anode. If the anode is not reactive, then the current density at the anode cannot be increased above about 22 A / dm ² ,? without gas formation, even in the presence of the preferred amount of nickel chloride, namely about 5 g / l. If an object is to be electroplated with a sulfur-free anode at a current density of about 43 A / dm ² , the surface of the anode must be about two to three times larger than that of the object to be electroplated. If the current density is to be 86 A / dm ² , then the ratio between the surfaces must be made about 5: 1. It will be evident that it is difficult to provide an anode whose surface is twice or possibly even larger than the cathode surface if one works with adapted anodes, that is to say with anodes which have the shape of the cathode. .:

If a sulfur-containing anode made of electrolyte nickel or another suitable reactive anode is used, the current density can go up to 58.0 A / dm ² , provided that the concentration of the nickel chloride in; of the solution is at least 30 g / l. _;

Although the nickel chloride has the effect of increasing the tension in the precipitates formed and for this reason the concentration should be kept as low as possible, so stand but, on the other hand, the precipitations obtained at the highest current densities are already less than considerable Tension, so that any further increase in tension is meaningless.

Galvanic baths, which contain 500 to 700 g / l nickel sulfamate, have compared to conventional baths galvanic baths have further advantages. In particular, their throwing power is that of a common one Superior to sulfamate solution and a Watts-type electrolyte. This determines the scattering power according to the well-known Field formula:

T = -

100 (P - M)
(P + M - 2)

where T is the scattering power in%, P is the primary current ratio and M is the metal distribution.

The scattering power generally decreases when the current density is in a galvanic nickel bath is increased. An electrolyte according to the invention with

600 g / l nickel sulphamate and approximately 5 g / l nickel chloride were compared at 60 ° C. with a conventional nickel sulphamate solution containing 300 g / l nickel sulphamate and 5 g / l nickel chloride. Another comparison was made with a standard Watts solution consisting of nickel sulfamate, nickel chloride and boric acid. A Hull cell was used and the measurements were carried out at a primary current ratio of 5: 1 and average current densities of 5.5 and 16.0 A / dm ² . In the lower average current density of the scattering power was Watts solution at 8 ° / _0, that of the conventional sulfamate 10 ° / ₀ and the solution of the invention that 13%. At the higher average current density, the corresponding results of the three comparative solutions 4, 7 and 8 ° / ₀ were.

Finally, the conductivity of nickel sulfamate solutions is also which contain 500 to 700 g / l nickel sulfamate, quite satisfactory. The conductivity a solution consisting only of chlorides is better than the conductivity of the invention designed solutions. The latter, however, have higher conductivities than both the usual Watts solution as well as the usual nickel sulfamate solution.

When using the electrolyte, for example, in precision electrolytic molding, it is recommended conduct electrolysis in an auxiliary tank with a low current density, through which the Main electrolyte circulates continuously. This ensures that metallic impurities such as copper, iron and zinc, which poison the electrolyte and counteract the formation of precipitation, be removed continuously.

The invention also extends to an electrolyte made from a purified solution of nickel sulfate in Water containing 500 to 700 g / l nickel sulfamate and also a gloss-forming component, preferably Boric acid, and possibly also nickel chloride.

40

Claims (6)

Patent claims: 1. Galvanic nickel sulfamate bath if necessary with a content of nickel chloride and boric acid, characterized in that that it is 500 to 700 g / l, preferably 550 to 650 g / l. in particular contains 600 g / l nickel sulfamate. 2. A method for the electrodeposition of nickel coatings using a bath according to claim 1, characterized in that the current density and bath temperature within the by the coordinates 10.8 to 19.0 A / dm ² at 55 ° C, 16.0 to 25, 0 A / dm ² at 6O ⁰ C, 21.5 to 35.5 A / dm ² at 65 ° C and 27.0 to 48.5 A / dm ² at 70 ⁰ C in the temperature-current density diagram be matched. 3. The method according to claim 2, characterized in that the current density and bath temperature within the by the coordinates 11.8 to 16.0 A / dm ² at 55 ° C, 17.3 to 21.5 A / dm ² at 6O ⁰ C. , 22.5 to 26.5 A / dm ² at 65 ° C and 28.0 to 36.5 A / dm ² at 70 ⁰ C determined field in the temperature - current density - diagram are matched to one another. 4. The method according to claim 2, characterized in that the current density and bath temperature within the by the coordinates 11.8 to 13.5 A / dm ² at 55 ° C, 17.3 to 18.5 A / dm ² at 6O ⁰ C. , 22.5 to 26.0 A / dm ² at 65 ° C and 28.0 to 31.0 A / dm ² at 70 ⁰ C specific field in the temperature-current density diagram are matched to one another. 5. A method for the electrodeposition of nickel coatings using a bath according to claim 1, characterized in that the current density and bath temperature within the by the coordinates 19.0 to 27.0 A / dm ² at 55 ⁰ C, 27.0 to 43, 0 A / dm ² at 6O ⁰ C, 38.0 to 65.0 A / dm ² at 65 ° C and 48.5 to 86.0 A / dm ² at 70 ° C in the temperature-current density diagram be matched. 6. A method for electrodeposition of nickel coatings using a bath according to claim 1, characterized in that the deposition in the absence of a gloss-producing agent at a current density of 3.25 to 7.5 A / dm ² or in the presence of a gloss-producing agent with a Current density of 16.0 to 38.0 A / dm ^{2 in} each case at a temperature of 55 to 70 ⁰ C is carried out. 1 sheet of drawings 709 648/296 9. 67 © Bundesdruckerei Berlin