DE102012216011A1 - Boric acid-free zinc-nickel electrolyte - Google Patents

Abstract

The invention relates to a process for the acidic, boric acid-free galvanic zinc-nickel deposition using an electrolyte containing wetting agents, base glossers, brighteners, complexing agents and buffers, in particular organic acids.

Description

The invention relates to a process for galvanic zinc-nickel deposition using an acidic, boric acid-free electrolyte containing wetting agents, ground glazes, brighteners, complexing agents and buffers, in particular organic acids, and optionally further auxiliaries.

DE 2 251 103 A1 describes an acidic zinc electrolyte. The main features are the pH of 3.5-4.5, the use of ammonium chloride and the zinc plating concentration of 105-360 g / L, which can not be used for alloy baths. The specified high current density of 10 to 100 A / dm ^{2 is} not repeated in the claim. The sodium succinate concentration is in the range of 5 to 30 g / L. The task of succinate is to stabilize the pH of the zinc electrolyte.

U.S. Patent 4,877,497 also describes an acidic zinc electrolyte. Essential is the pH of 4.0, which is extended to pH 2 to 5 in claim 10, and the high zinc concentration ≥ 50 g / L. In the examples, high current densities of 10 to 80 A / dm ^{2 are} described. The succinate concentration is here in a wide range (2 to 40 g / L of the potassium rate). Table 1 describes the use of 2 g / L adipic acid. Many of the alternative acids described in Table 1 are not suitable for a zinc-nickel alloy process.

U.S. Patent 5,779,873 describes a strongly acidic nickel electrolyte. In the case of 10 g / L succinic acid as a buffer is worked here at a pH = 2.22, generally pH ≤ 3. As in US 4,877,497 Here, too, a range of alternative, for a zinc-nickel electrolyte partially inappropriate buffers is described.

JP 2001-107284 A2 According to an English-language abstract, Watts nickel bath is used in which succinic acid, glutaric acid and adipic acid are used as buffer substances at pH = 4.8.

DE 1 953 707 A1 describes plating baths for nickel from baths without chloride and bromide. All experiments described were carried out at current densities> 53.8 A / dm ² ; the electrolytes work in the pH range 2.0 to 4.0. The alternative buffer substances indicated in the table on page 11 can not be used in a zinc-nickel electrolyte according to the present invention.

U.S. Patent 3,986,843 describes an acidic zinc bath with pH = 4.0 with small amounts of chromium, tin and indium. The claims include only the use of these metals. In the description itself high current densities (45 A / dm ² ) and a low exposure time (4 s) are given. The deposits are thus in no way comparable to those from a zinc-nickel bath.

All processes in the aforementioned prior art for zinc electrolytes on the one hand and nickel electrolytes on the other hand operate at pH values ≦ 5, i. d. R. but still much lower.

The aforementioned prior art thus includes zinc electrolytes or nickel electrolytes, but not zinc-nickel alloy electrolytes (ZnNi electrolytes). The production of a galvanic deposition of a defined alloy, in particular clearly different noble metals such as zinc (E ⁰ = -0.7618 V for Zn ⇆ Zn ²⁺ + 2e ^- ) and nickel (E ⁰ = -0.257 V for Ni ⇆ Ni ²⁺ + 2e ^- , both values from: CRC Handbook of Chemistry and Physics, 73rd Edition) is for this very reason much more difficult than the deposition of layers of only one metal. The behavior of acidic ZnNi baths is not comparable to that of acidic nickel baths and hardly to that of acidic zinc baths.

Electroplating 2011 109 (10) pp. 2199-2205 describes the electrochemical deposition of ZnNi coatings and their usual framework conditions. In that regard, reference is made in full to the content of this publication.

The object of the present invention is to provide an acidic, boric acid-free process for the galvanic deposition of ZnNi.

The above object is achieved in a first embodiment by a process for acidic, boric acid-free, galvanic zinc-nickel deposition at a pH in the range of 4.5 to 6.5 using an electrolyte containing nickel ions (for example, nickel chloride, Nickel acetate, nickel sulfate), zinc ions (e.g., zinc chloride, zinc oxide, zinc sulfate, zinc acetate), conductive salt (e.g. Potassium chloride, sodium chloride), wetting agents (for example composed of one or more building blocks such as [1] optionally substituted or otherwise substituted aliphatic or aromatic bases having, for example, oxygen, nitrogen or sulfur functionalities, [ii] chains of different lengths from, for example, ethylene oxide, propylene oxide, ethyleneamine or Mixtures thereof and [iii] hydrophilic end groups, for example as produced by sulfopropylation or synthesis of a sulfosuccinic acid ester or half ester), base glaziers (for example arylcarboxylic acids and their salts), brighteners (for example benzylideneacetone, o-chlorobenzaldehyde or derivatives thereof), complexing agents (for example mono- or polyvalent amines or carboxylic acids, polyamines, amino acids) and buffer substances, in particular organic acids, and optionally other excipients, which is characterized in that the buffer substances are selected from the group b consisting of adipic acid, succinic acid, glutaric acid and sulfosuccinic acid and propionic acid, including their alkali metal salts, and mixtures thereof.

Zinc salts and nickel salts serve to provide ions of the metals to be deposited. Conducting salts serve to increase the conductivity of the electrolyte. Wetting agents serve to lower the surface tension of the electrolyte and ensure good wetting of the surface to be coated. Basic glazes and brighteners serve in combination with the control of gloss level and brilliance of the deposition. Chelating agents serve to complex the nickel ions to reduce the preferential deposition of nickel, which is nobler in comparison to zinc, to the level dictated by the desired alloy composition. The buffer substances serve to balance the electrolyte, which is becoming increasingly alkaline as it approaches the surface of the cathode, toward a neutral or weakly acidic pH. A too basic electrolyte can no longer be ordered; In addition, it can lead to precipitation of metal hydroxides. The effect of the electrolyte becoming more alkaline in the vicinity of the cathode surface increases with the current density. Individual substances can also fulfill multiple functions.

In the method used according to the invention with a pH in the range of 4.5 to 6.5 are the first acid functions of polybasic carboxylic acids, eg. B. with pK _a1 <4.5, already largely deprotonated before. The buffer effect used is therefore based essentially on the second acid functionality with a higher pk _a2 value> 5. The acid groups of monohydric carboxylic acids are also deprotonated to a large extent at pH 4.5 to 6.5. Here, the buffer effect is due to the not yet deprotonated portion of the carboxylic acid in the electrolyte (Table 1). Table 1: pK _a values of relevant carboxylic acids [CRC Handbook of Chemistry and Physics, 73rd Edition] acid pk _a 1 pk _a 2 T [° C] acetic acid 4.75 - 25 propionic 4.87 - 25 adipic acid 4.43 5.41 25 Succinic acid 4.16 5.61 25 glutaric 4.31 5.41 25 sulfosuccinic - No data available -

• (a) Verträglichkeit mit hohen Salzkonzentrationen (beispielsweise Ionen von Nickel, Zink, Kalium, Chlor),
• (b) Gewährleistung der Verfahrensmerkmale (Eisenfällbarkeit, Optik der Abscheidung, Elektrolytstabilität, Legierungskomposition).

The choice of carboxylic acids was limited by three factors:

• (a) compatibility with high salt concentrations (for example ions of nickel, zinc, potassium, chlorine),
• (b) ensuring the process characteristics (iron precipitability, optics of deposition, electrolyte stability, alloy composition).

The inventive selection of the carboxylic acids is limited to adipic acid, succinic acid, glutaric acid, sulfosuccinic acid and propionic acid, including their salts and mixtures.

In a further preferred embodiment of the present invention, not the individual acids, but mixtures of the acids are used in any proportions with each other.

In addition to the abovementioned five acids, acetic acid may also be present in the electrolyte for the purposes of the present invention. Like propionic acid, acetic acid itself acts as a pH buffer, increasing the maximum applicable current density. In addition, the use of acetic acid and propionic acid significantly improves the solubility of the dicarboxylic acids. However, if the proportion of acetic acid and / or propionic acid is chosen too high, the appearance of the surface obtained can be massively impaired become. Accordingly, the amount of acetic acid should not exceed 60 g / L and that of propionic acid should not exceed 100 g / L.

The concentration of the acids present is critical to the desired effect of the present invention and is limited upwardly by the solubility in the electrolyte. Accordingly, the total content of organic acid should preferably be 1 to 100 g / L based on the electrolyte, in particular 10 to 60 g / L. If the total content of the acids is chosen too low, this results in too low a maximum applicable current density. If, on the other hand, the total content of the organic acids is chosen too high, precipitations result due to insufficient solubilities.

Particularly preferred according to the present invention, the pH of the electrolyte is adjusted to a value in the range of 4.5 to 6.5, in particular 5.0 to 6.0. If, on the other hand, the pH is chosen too low, the current efficiency drops. However, if the pH value is set too high, precipitations of metal salts occur.

The current density for performing the desired ZnNi deposition can be varied within wide limits. It is particularly preferable to carry out the deposition at a theoretically applicable current density of> 10 A / dm ² , in particular 0.2 to 5.0 A / dm ² , particularly preferably 0.5 to 3.5 A / dm ² . Too low a current density often leads to dark deposition with a high nickel deposition rate. Too high current density leads to dendritic, ie disordered deposition.

As a substitute for boric acid and ammonium with pK _a = 9,25, which are both due to registration problems (REACH) or for practical reasons not to be used in the electrolyte, other carboxylic acids with pK _a > 5 in addition to the invention mentioned inappropriate.

On the other hand, acids with pK _a <5, which could buffer the electrolytes described in the patents, are widely known, such as acetic acid as a cost effective compound.

With regard to the aforementioned properties, the following Hull cell experiments were carried out with otherwise identical parameters.

EXAMPLES

All electrolytes containing 200 g / L of potassium chloride, 100 g / L Nickel chloride hexahydrate 50 g / L of zinc chloride, 10 g / L RALUFON ^® NAPE 14-90, 600 mg / L of sodium benzoate, 500 mg / L of diethylene triamine, 100 mg / L benzylideneacetone and the amounts of acid mentioned in the individual experiments and were adjusted to pH = 5.3.

The approach of the electrolytes was carried out at room temperature. The dissolution of the solids was significantly accelerated by heating the batch to 40 to 60 ° C. The cloud point of the electrolytes was partly below 40 ° C. At temperatures below the cloud point, electrolytes are clear and homogeneous, cloudy at temperatures above the cloud point, and the results may be lower. U. not reproducible.

Depending on the concentration of buffer substances, the electrolytes were prepared according to two variants. The examples indicate which variant was used.

Due to the neutralization of the acids, they were no longer in their free form in the electrolyte at pH = 5.3, but partly deprotonated and partly as free acid. In the experimental descriptions, for simplicity, the concentrations were further given in terms of the free acids used in the batch.

Adipic acid, succinic acid, glutaric acid and propionic acid were used as pure compounds, acetic acid in technical grade as a solution with 80 percent by weight and sulfosuccinic acid in technical grade as a solution with about 70 percent by weight. The measures in this patent refer to the pure compounds.

Due to the small amounts of acid, a solution of 12.50 g / L adipic acid, succinic acid, glutaric acid was added to the electrolytes of Examples 25 to 27 with potassium hydroxide solution 50% (500.00 g / kg potassium hydroxide in water) to pH = 5.5 and sulfosuccinic acid used in water. The volumes of this solution used can be found in the respective examples.

Potassium chloride, zinc chloride, nickel chloride hexahydrate, potassium hydroxide, hydrochloric acid 32%, diethylenetriamine, sodium benzoate and benzylideneacetone were used in industrial grade. The water used was completely deionized tap water. RALUFON ^® NAPE 14-90 was used in original quality.

Variant 1 for electrolytes with low concentrations of buffer substances:

Potassium chloride (50.00 g), zinc chloride solution (12.50 mL of a solution of 1000.0 g / L zinc chloride in water), basic additive (1.000 mL of a solution of 150.00 g / L sodium benzoate and 125.00 g / L diethylenetriamine in water) and organic acids (indicated in the respective experiments) were stirred in water (total volume about 200 ml). With potassium hydroxide solution 50% (500.00 g / kg potassium hydroxide in water) the pH was adjusted to pH = 6.00-6.25 so that at this pH a clear solution was present. Subsequently, nickel chloride solution (25.00 mL of a solution of 1000.0 g / L of nickel chloride hexahydrate in water), and Brightener were (5.00 mL of a solution of 500.00 g / L RALUFON ^® NAPE 14-90 and 5, 00 g / L benzylideneacetone in water) and made up to about 240 mL total volume. The pH of the electrolyte was adjusted to pH = 5.3 with hydrochloric acid 1: 1 and it was made up to 250 ml total volume.

Variant 2 for electrolytes with high concentrations of buffer substances:

Potassium chloride (50.00 g), nickel chloride solution (25.00 mL of a solution of 1000.0 g / L nickel chloride hexahydrate in water), basic addition (1.000 mL of a solution of 150.00 g / L sodium benzoate and 125.00 g / L diethylenetriamine in water) and organic acids (indicated in the respective experiments) were stirred in water (total volume about 175 ml). With potassium hydroxide solution 50% (500.00 g / kg potassium hydroxide in water) the pH was adjusted to pH = 5.75-6.00 so that at this pH there was a clear solution. Then zinc chloride solution (12.50 mL of a solution of 1000.0 g / L of zinc chloride in water), and Brightener (5.00 mL of a solution of 500.00 g / L RALUFON ^® NAPE 14-90 and 5.00 g of / L benzylideneacetone in water) and made up to about 240 mL total volume. The pH of the electrolyte was adjusted to pH = 5.3 with hydrochloric acid 1: 1 and it was made up to 250 ml total volume.

Execution and evaluation of the Hullzell experiments:

The Hullzell experiments were carried out according to DIN 50957 carried out in a tempered 250 mL Hull cell with a nickel anode, which deviates from DIN 50957 the dimensions were 5.0 cm × 7.5 cm × 1.0 cm. One sheet of 10.0 cm x 7.5 cm x 0.03 cm was coated on a 10 cm x 5 cm area as a cathode at 2.00 A DC and 35 ° C electrolyte temperature for 600 seconds. The electrolyte was mixed with a paddle of 1 cm width, which was about 1 cm away from the cathode with about 5 cm / s was moved.

(1)

Ungeordnete, in der Regel schwarze, teils silberfarbene, raue Abscheidung; im Übergang zu (2) häufig amorph.

(2)

Ungeordnete, raue, schwarze und silberfarbene Abscheidung in der Orientierung vertikaler Streifen von 1 bis 5 mm Breite; insbesondere im Übergang zu (3) auch Streifen mit geordneter Abscheidung.

(3)

Ungeordnete, raue, silberfarbene Abscheidung in der Orientierung vertikaler Streifen von 1 bis 5 mm Breite; insbesondere im Übergang zu (4) auch zunehmend breitere Streifen mit geordneter Abscheidung.

(4)

Glatte, geordnete Abscheidung; bei den gegebenen Parametern wurde in der Regel eine brillante, hochglänzende Optik erzielt.

(5)

Nicht beschichteter Teil des Hullzellbleches, der aus dem Elektrolyten herausragte.

Domains with different deposits were visible on the Hullzell plates. 1 shows a sketch of a coated Hullzellbleches (for Example 4, below). For the sake of clarity, the boundaries between the domains have been simplified. In fact, the boundaries were not exactly vertical, but often slightly curved, sometimes even diffuse. The following domains could be distinguished:

(1)

Disordered, usually black, partly silver-colored, rough deposit; in the transition to (2) often amorphous.

(2)

Disordered, rough, black and silver-colored deposit in the orientation of vertical strips of 1 to 5 mm width; especially in the transition to (3) also strips with ordered deposition.

(3)

Disordered, rough, silver-colored deposit in the orientation of vertical strips of 1 to 5 mm in width; especially in the transition to (4) increasingly broader stripes with ordered deposition.

(4)

Smooth, ordered deposition; with the given parameters, a brilliant, high-gloss appearance was generally achieved.

(5)

Uncoated part of the Hullzell sheet, which protruded from the electrolyte.

Not all types of deposits were observed in all experiments. In particular, at very low concentrations of the buffer substances, sometimes no large area of ordered deposition (4) could be obtained.

Due to the standardized structure of the Hull cell, the Hull cell plate connected as a cathode is oriented diagonally to the anode. At the left edge of the Hullzellbleches the distance to the anode is less than at the right edge, so that due to the intrinsic resistance of the electrolyte, the current density at the left edge of Hullzellbleches is greater than the right edge.

For the summary of examples ( 2 and 3 ), the uncoated areas of the hull cell plates were not taken into account and the sketches of the coated areas were compressed vertically. The maximum applicable current density, that is, the current density at which the deposition is no longer uniformly ordered, was determined using the in DIN 50957 given table on the distance to the left edge of Hullzellbleches determined.

Comparative Example 1;

without buffer substances (variant 1)

The Hullzell sheet exhibited randomly disordered deposits in the entire current density range, the proportion decreasing with the current density.

Comparative Example 2;

20.00 g / L acetic acid (variant 1):

Hullzellblech 2 showed from about 3 cm to an orderly deposition. The maximum applicable current density of this electrolyte was 5.2 A / dm ² .

Example 1;

1.00 g / L adipic acid (variant 1):

Similar to Comparative Example 1, Example 1 also exhibited randomly disordered deposits in the entire current density range. However, the proportion of ordered deposition in the low current density range was higher than that of Hullzell sheet 1.

Example 2;

2.50 g / L adipic acid (variant 1):

Example 2 showed significant improvements over Example 1. An ordered deposition occurred to 1.0 A / dm ² .

Example 3;

10.00 g / L adipic acid (variant 1):

Example 3 represented a further improvement of the maximum applicable current density to 5.2 A / dm ² .

Example 4;

12.50 g / L adipic acid (variant 2):

The maximum soluble concentration of adipic acid under the conditions mentioned caused a maximum applicable current density of 6.2 A / dm ² . 12.50 g / L adipic acid thus already had a stronger effect than 20.00 g / L acetic acid.

Example 5;

20.00 g / L adipic acid + 20.00 g / L acetic acid (variant 2):

By additional use of 20.0 g / L acetic acid significantly more adipic acid could be brought into solution. The maximum applicable current density was further increased to 8.4 A / dm ² , also compared to Comparative Example 2 (20.00 g / L acetic acid), a significant improvement had occurred.

Example 6;

40.00 g / L adipic acid + 20.00 g / L acetic acid (variant 2):

At the maximum soluble concentration of adipic acid in the presence of 20.00 g / L acetic acid, the maximum applicable current density was 4.9 A / dm ² back.

Example 7;

1.00 g / L succinic acid (variant 1):

Similar to Example 1, an improvement over Comparative Example 1 was visible.

Example 8;

2.50 g / L succinic acid (variant 1):

Analogous to Example 2, a further improvement was observed. In the low current density range, a good deposition was obtained, but with a maximum applicable current density <0.5 A / dm ² .

Example 9;

10.00 g / L succinic acid (variant 2):

Compared with Example 8, the maximum applicable current density had risen to 4.5 A / dm ² . 10.00 g / L of succinic acid were about the maximum soluble amount under the specified conditions.

Example 10;

20.00 g / L succinic acid + 20.00 g / L acetic acid (variant 2):

By additional use of 20.00 g / L acetic acid significantly more succinic acid could be brought into solution. The maximum applicable current density further increased to 8.4 A / dm ² , also compared to Comparative Example 2 (20.00 g / L acetic acid), a significant improvement had occurred.

Example 11;

75.00 g / L succinic acid + 20.00 g / L acetic acid (variant 2):

At the maximum soluble concentration of succinic acid in the presence of 20.00 g / L acetic acid, the maximum applicable current density fell to 7.0 A / dm ² .

Example 12;

1.00 g / L glutaric acid (variant 1):

Here, a clear improvement compared to Comparative Example 1 was visible, the maximum applicable current density was already 0.6 A / dm ² .

Example 13;

2.50 g / L glutaric acid (variant 1):

Analogous to Example 2, a further improvement was observed. In the low current density range, good deposition was obtained up to a maximum applicable current density of 1.6 A / dm ² .

Example 14;

10.00 g / L glutaric acid (variant 1):

Compared with Example 13, a further increase in the maximum applicable current density to 4.5 A / dm ^{2 could be} achieved.

Example 15;

12.50 g / L glutaric acid (variant 2):

Compared to Example 14, a further increase in the maximum applicable current density to 6.4 A / dm ^{2 was} achieved. Similar to adipic acid in Example 4, 12.50 g / L glutaric acid also represented approximately the maximum amount soluble under these conditions; the maximum applicable current density was also increased more by 12.50 g / L glutaric acid than by 20.00 g / L acetic acid in Comparative Example 2.

Example 16;

20.00 g / L glutaric acid + 20.00 g / L acetic acid (variant 2):

In the presence of 20.00 g / L acetic acid, significantly more than 12.50 g / L glutaric acid dissolved. An electrolyte with 20.00 g / L glutaric acid and 20.00 g / L acetic acid had a maximum applicable current density of 3.9 A / dm ² .

Example 17;

50.00 g / L glutaric acid + 20.00 g / L acetic acid (variant 2):

In the presence of 20.00 g / L acetic acid, a maximum of about 50.00 g / L glutaric acid dissolved. As a result, a maximum applicable current density of 3.2 A / dm ^{2 was} achieved.

Example 18;

1.00 g / L sulfosuccinic acid (variant 1):

Analogously to Example 1, the appearance of Hullzellbleches was compared to Comparative example significantly improved, without a perfect coating would have been recognized.

Example 19;

2.50 g / L sulfosuccinic acid (variant 1):

By using 2.50 g / L sulfosuccinic acid, the appearance was further improved compared to Example 18.

Example 20;

10.00 g / L sulfosuccinic acid (variant 1):

By using 10.00 g / L sulfosuccinic acid, the appearance was further improved compared to Example 19.

Example 21;

20.00 g / L sulfosuccinic acid (variant 2):

When using 20.00 g / L sulfosuccinic acid, a maximum applicable current density of 1.9 A / dm ^{2 was} achieved. However, the area of perfect deposition showed less brilliance and gloss than comparable hull cell plates with other buffer substances.

Example 22;

75.00 g / L sulfosuccinic acid (variant 2):

Even without admixture of acetic acid, sulfosuccinic acid had a good solubility in the electrolyte. An electrolyte with 75.00 g / L sulfosuccinic acid had a maximum applicable current density of 5.1 A / dm ² . Again, the separation lacked compared to some brilliance and shine.

Example 23;

20.00 g / L sulfosuccinic acid + 20.00 g / L acetic acid (variant 2):

For direct comparison with Comparative Example 2 and Examples 5, 10 and 16, a Hull cell experiment was also carried out with an electrolyte containing 20.00 g / L acetic acid and 20.00 g / L sulfosuccinic acid. The good deposition to a maximum applicable current density of 5.1 A / dm ² lacked compared to the other examples, some brilliance and gloss.

Example 24;

75.00 g / L sulfosuccinic acid + 20.00 g / L acetic acid (variant 2):

In direct comparison with experiments with less sulfosuccinic acid in Example 23 or less total acid in Example 22, the maximum applicable current density decreased slightly in this example.

Example 25;

0.25 g / L adipic acid + 0.25 g / L succinic acid + 0.25 g / L glutaric acid + 0.25 g / L sulfosuccinic acid (variant 1):

The electrolyte was made up with 20.00 mL / L of the above-described solution of the carboxylic acids in water. Similar to Examples 1, 7, 12 and 18, each with 1.00 g / L of a single acid, the image of the deposit was also improved in this example compared to Comparative Example 1.

Example 26;

0.625 g / L adipic acid + 0.625 g / L succinic acid + 0.625 g / L glutaric acid + 0.625 g / L sulfosuccinic acid (variant 1):

The electrolyte was prepared with 50.00 ml / L of the above-described solution of the carboxylic acids in water. Compared to Example 25, a further improvement of the deposition image was evident.

Example 27;

2.50 g / L adipic acid + 2.50 g / L succinic acid + 2.50 g / L glutaric acid + 2.50 g / L sulfosuccinic acid (variant 1):

The electrolyte was prepared with 200.00 mL / L of the above-described solution of the carboxylic acids in water. The zero cell had a maximum applicable current density of 5.4 A / dm ² .

Example 28;

5.00 g / L adipic acid + 5.00 g / L succinic acid + 5.00 g / L glutaric acid + 5.00 g / L sulfosuccinic acid + 20.00 g / L acetic acid (variant 2):

With this electrolyte composition, a maximum applicable current density of 8.1 A / dm ^{2 was} achieved.

Example 29;

10,00 g / L adipic acid + 18,75 g / L succinic acid + 12,50 g / L glutaric acid + 18,75 g / L sulfosuccinic acid + 20,00 g / L acetic acid (variant 2):

In this example, in each case 25% of the maximum soluble amount of the individual acids were dissolved in the presence of 20.00 g / L of acetic acid. A maximum applicable current density of 5.1 A / dm ^{2 was} achieved.

Example 30;

1.00 g / L of propionic acid (variant 1):

Similar to Comparative Example 1, this also had locally disordered deposits in the entire current density range. However, the proportion of ordered deposition in the low current density range was higher than in Comparative Example 1.

Example 31;

2.50 g / L of propionic acid (variant 1):

Compared to Example 30, the disordered deposits are present in finer, vertical stripes. The applicable current density range is still <0.5 A / dm ² .

Example 32;

20.00 g / L propionic acid (variant 1):

Here, the current density range up to 4.0 A / dm ² is already applicable.

Example 33;

60.00 g / L propionic acid (variant 2):

The applicable current density is further increased to 7.0 A / dm ² .

Example 34;

100.00 g / L of propionic acid (variant 2):

In this example, the applicable current density has decreased to 6.0 A / dm ² compared to Example 33.

Example 35;

20.00 g / L of propionic acid + 20.00 g / L of acetic acid (variant 2):

Acetic acid has no influence on the good solubility of propionic acid. Compared to Example 32 with 20.00 g / L propionic acid, the applicable current density increases to 5.2 A / dm ² .

Example 36;

20.00 g / L propionic acid + 20.00 g / L adipic acid (variant 2):

The maximum applicable current density is 6 A / dm ² .

The maximum applicable current density up to which no disordered dendritic deposits occur is dependent not only on the concentration of organic acids but also on a host of other parameters. The parameters of the embodiments have been chosen so that they clearly reflect the effect of the present invention. If the parameters are chosen differently, considerably higher current densities can be used.

Due to the concentration of brightener, the deposition up to the maximum applicable current density in all experiments had a brilliantly shiny appearance. Only in the experiments with sulfosuccinic acid (18-24) was a slightly matt appearance obtained in the low current density range, which could be obtained by other experimental parameters, such as more acetic acid, but also brilliant brilliant.

Among other things, the nickel incorporation rate is based on the concentrations of the complexing agents, the zinc ions and the nickel ions and in the exemplary embodiments is generally in the range from 4 to 24%, in particular in the range from 7 to 16%.

In addition to a direct dependence on the applied current strength, for example, temperature, pH, electrolyte movement, the concentrations of inorganic (here nickel chloride, zinc chloride, potassium chloride) and organic (here wetting agents, brighteners, ground glitter, complexing agent) ingredients as well as their selection are crucial.

Evaluation:

2 shows a tabular summary of the Hullzellexperimente Comparative Examples 1 and 2 and Examples 1 to 29th 3 shows a tabular overview of Examples 30 to 36.

The Hullzell sheets showed the deposition from the electrolyte over a wide current density range. All Hullzell sheets 1 to 29 illustrate that compared to Comparative Example 1 without buffer substances in all experiments only at a much higher current density sometimes disordered, dendritic deposits occurred ("higher firing strength"). Electrolytes with the described polybasic carboxylic acids or mixtures thereof, optionally in each case additionally with acetic acid, could thus be operated at higher current densities than electrolytes without these acids.

In particular, it is clear that an increase in the concentration of the individual buffer substances or mixtures was always accompanied by an improvement in the deposition pattern or an increase in the maximum applicable current density (Examples 1 to 4, 7 to 9, 12 to 15, 18 to 22, 25 -27, all compared to Comparative Example 1). Adipic acid, succinic acid and glutaric acid behaved very similarly in terms of buffering action and solubility (for example Examples 3, 9 and 14). In contrast, sulfosuccinic acid had a poorer buffering effect (example 20 compared to figures 3, 9 and 14). However, sulfosuccinic acid was significantly more soluble than the dicarboxylic acids described (Example 22 compared to 4, 9 and 15). The use of the acids as a mixture was very possible, but brought no particular advantage (for example Example 27 compared to 3, 9, 14 and 20).

When acetic acid, for example 20.00 g / L, was added to the electrolyte, the solubility of the dicarboxylic acids increased significantly (for example Example 6 vs. 4, 11 vs. 9, 17 vs. 15). Except in the case of glutaric acid, the maximum applicable current density increased in comparison to the examples with only one polybasic carboxylic acid, even compared with Comparative Example 2 exclusively with acetic acid (Example 5 compared to 4 and Comparative Example 2, Example 10 compared to 9 and Comparative Example 2, Example 23 versus 21 and Comparative Example 2). This also applied to the mixture of all four polybasic carboxylic acids with acetic acid (Example 28 versus 27 and Comparative Example 2).

In the case of glutaric acid, the maximum applicable current density in the case of analogous experiments with acetic acid already decreased again (Example 16 versus 15 and Comparative Example 2).

In all series with acetic acid it became clear that at very high concentrations of polybasic carboxylic acids the maximum applicable current density decreases again (Examples 5 to 6, 10 to 11, 16 to 17, 28 to 29).

Examples 30 to 34 illustrate that propionic acid is also suitable alone as a buffer substance. Compared to acetic acid, higher concentrations can be used without loss of optics.

Examples 35 and 36 show that all of the corresponding examples of acetic acid can be completely or partially replaced by propionic acid.

All described polybasic carboxylic acids are suitable alone, alone in combination with acetic acid and / or propionic acid, as a mixture and as a mixture in combination with acetic acid and / or propionic acid as buffer substances for acid ZnNi baths. In this case, the mixture with acetic acid and / or propionic acid can serve to achieve an even better result with respect to the maximum applicable current density or to replace part of the polybasic carboxylic acids with comparable results.

Propionic acid is also suitable as the sole buffer substance for acidic ZnNi baths.

All acids can be used as free acids or as their alkali metal salts or mixtures thereof.

QUOTES INCLUDE IN THE DESCRIPTION

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Cited patent literature

• DE 2251103 A1 [0002]
• US 4877497 [0003, 0004]
• US 5779873 [0004]
• JP 2001-107284 A2 [0005]
• DE 1953707 A1 [0006]
• US 3986843 [0007]

Cited non-patent literature

• Electroplating 2011 109 (10) p. 2199-2205 [0010]
• DIN 50957 [0034]
• DIN 50957 [0034]
• DIN 50957 [0038]

Claims (9)

Process for the acidic boric acid-free galvanic zinc-nickel deposition at a pH in the range of 4.5 to 6.5 using an electrolyte containing wetting agents, base glazes, brighteners, complexing agents and buffers, in particular organic acids, and auxiliaries, characterized in that the organic acids are selected from the group consisting of adipic acid, succinic acid, glutaric acid, sulfosuccinic acid and propionic acid, including their alkali metal salts, and mixtures thereof. A method according to claim 1, characterized in that a mixture of the organic acids adipic acid, succinic acid, glutaric acid, sulfosuccinic acid and propionic acid each in an amount of 20 to 30 wt.%, Based on the acids. A method according to claim 1 or 2, characterized in that the electrolyte may further comprise acetic acid. Method according to one of claims 1 to 4, characterized in that the total content of organic acid is 1 to 100 g / L. A method according to claim 4, characterized in that the total content of organic acid is 10 to 60 g / L. Method according to one of claims 1 to 5, characterized in that the pH of the electrolyte has a value in the range of 5.0 to 6.0. Method according to one of claims 1 to 6, characterized in that the deposition at a maximum current density to> 10 A / dm ² , in particular 0.2 to 5.0 A / dm ² , more preferably 0.5 to 3.5 A. / dm ^{2 is} performed. A method according to claim 7, characterized in that the deposition is carried out at a maximum current density of 0.2 to 5 A / dm ² . A method according to claim 8, characterized in that the deposition is carried out at a maximum current density of 0.5 to 3.5 A / dm ² .

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