LT5481B - Sarminis cinko-kobalto lydinio dangu nusodinimo elektrolitas - Google Patents

Abstract

The present invention relates to chemical industry. The invention discloses the bath composition for depositing zinc-cobalt alloys onto conductive support the content of Co in the coating being up to 3-80 % by weight depending on the electrolyte composition and cuurent density. With the content of Co in the coating varied it is possible to obtain coatings with high resistance to corrosion which are not to be chromated. The elctrolyte composition claimed is as follows, in g/l: Zinc oxide (ZnO) 8-10 Cobalt sulphate (CoSO4 .7 H2O) 1-20@Sodium hydroxide (NaOH) 100-120 Aminoethylethanolamine (H2N(CH2)2NH(CH2)2OH 10-40 Water up to 1 l. Electrolyte's pH 13

Description

The invention relates to the chemical industry, namely, electrolytic deposition of metal coatings, more particularly to electrolytes for the preparation of zinc-cobalt alloy coatings.

Zinc-cobalt electrolytic alloys exhibit better corrosion resistance compared to zinc 10 coatings. Due to the good combination of physicochemical properties, these coatings are mainly used:

(a) the automotive industry;

(b) in the aviation industry, where the main task is to replace the prohibition on the use of toxic cadmium coatings.

Both alkaline and acidic electrolytes are used to produce zinc-cobalt coatings. Both of these processes have their own advantages and disadvantages, for example, in acidic solutions, the cathodic process has high throughput but not enough spreading force. Alkaline electrolytes have a lower cathodic yield, but these processes have a very good spreading power. Therefore, the development of new electrolytes for zinc-cobalt coatings is relevant.

It is reported in the literature that small amounts (up to 1%) of cobalt in the cobalt-zinc alloy increase the corrosion resistance of the coating several times, but this effect is achieved only after the coating has been chromatographed. Known uncoated zinc-cobalt (<1% Co) coatings have the same corrosion resistance as zinc coatings.

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There is very little data on the deposition of zinc-cobalt coatings with higher cobalt content. This may be due not only to the economic aspects of the process but also to the difficulty of precipitating higher amounts of cobalt. However, there is a recent interest in coatings with higher cobalt content, as the resulting coatings exhibit better physico-chemical properties compared to zinc coatings, such as higher hardness, better soldering properties, and the like. In addition, an alloy containing 9-11% cobalt is comparable to cadmium coatings in sea conditions due to its anti-corrosive properties.

Alkaline electrolytes for the preparation of cyanide-free zinc-cobalt coatings usually contain zinc compound, cobalt compound, alkali metal hydroxide and may contain appropriate additives. In the absence of a stabilizing agent, cobalt oxide / hydroxide precipitates in alkaline solutions, so a complexing agent is required to stabilize Co ²⁺ under alkaline conditions.

U.S. Pat. No. 4,299,671 describes a weakly alkaline (pH 6.0-9.0) electrolyte for cobalt-zinc alloy deposition, from which coatings look similar to conventional chromium coatings. The electrolyte contains 1-12 g / l cobalt ions, 0.75-9 g / l zinc ions and the complexing agent is selected from the group consisting of citric acid, gluconic acid, alpha-glucoheptonic acid, tartaric acid or their salts mixtures.

A number of Japanese patents are known in which complexing agents used in alkaline (pH> 13) zinc-cobalt electrolytes often refer to composite compositions such as urea or thiourea and dialkylaminoalkylamine in combination with dichloroalkyl ether and epihalohydrin [JP 2001214293]; urea or thiourea, dialkylaminoethylamine and / or dialkylaminopropylamine together with soluble reactive dichloroalkyl ether [JP 2001226793] and others. Alkaline electrolytes of zinc alloys, including zinc-cobalt alloys, sometimes contain polymers of special structure [JP 11193487, JP 11193488, US 5435898, EP 1114206].

The use of N- (2-aminoethyl) -ethanolamine (aminoethylethanolamine) as a bleaching agent in small amounts in the electrolyte compared to significant amounts of other complexing agents (e.g., gluconates or glucoheptonate ions) is mentioned in U.S. Patent No. 4,428,803 for cobalt-tin coatings. obtained from a weakly alkaline electrolyte (pH 6.0-9.0). This source mentions that a similar electrolyte may be used to obtain zinc-cobalt coatings, but subsequent passivation is desirable to protect the coating from fading at elevated temperatures and to provide fingerprint resistance. small current densities and process efficiencies are very low.

An alkaline zinc-cobalt alloy deposition electrolyte is described.

October 1997, p. 53-56], characterized by low concentrations of cobalt, optimally in a solution of 0.5-1 g / L Co. It is stated that in the said electrolyte diethylamine was used, among others, as a complexing agent, but additional chromimetry had to be used. In addition, cobalt content greater than 5% in the resulting coatings is reported as undesirable.

European Patent EP 0677598 discloses an alkaline zinc-cobalt coating electrolyte comprising a zinc compound, a cobalt compound, a reaction product of an alkali metal hydroxide and an alkylene amine, which acts as a complexing agent. Based on the examples presented in the description, the ratio of zinc to cobalt compounds in this electrolyte was 8-10 g / l of Zn compound with 0.05-10 g / l of Co compound [ie about 1: 0.005-1], various products of alkylenamine reaction with alkylene oxide. in the range of 0.2-100 g / l. The cobalt content of the coatings obtained in the alloy was in the range of 0.1-10 A / dm ² and 15-35 ° C in the current density range 0.05-20%. However, to ensure good corrosion resistance and suitable other physicochemical properties, the resulting coatings of Zn-Co alloy were further chromated in all cases.

The object of the present invention is to produce an electrolyte which can be easily deposited on a conductive substrate with high quality zinc-cobalt alloy coatings which, depending on the electrolyte composition and current density, have a Co content in the coating of from 3 to 80% by weight.

By changing the amount of cobalt in the coating, coatings of extremely good corrosion resistance and no need for chromation can be obtained.

SUMMARY OF THE INVENTION It is an object of the present invention that aminoethyl ethanolamine is used as a complexing agent for electrolyte deposition of zinc-cobalt alloy coatings in the following composition of the electrolyte, g / l:

Zinc Ion Source 6-8

Cobalt ion source 0.2-4.2

Sodium (or potassium) hydroxide 80-120

Aminoethyl ethanolamine (H2N (CH2) 2NH (CH2) 2OH) 10-40; Water up to 1 liter.

The preferred electrolyte for the deposition of zinc-cobalt alloy coatings according to the present invention is the following composition (g / l):

Zinc Oxide (ZnO) 8-10;

Cobalt Sulfate (COSO4'7H2O) 1 -20;

Sodium hydroxide (NaOH) 100-120;

Aminoethyl ethanolamine (H2N (CH2) 2NH (CH2) 2OH) 10-40; Water up to 1 liter.

The optimum ratio of zinc compound to cobalt compound to aminoethyl ethanolamine in the proposed electrolyte is about 1: 1-2: 2-4, respectively.

The invention is illustrated by the following non-limiting examples.

1 Example. Preparation of Zn-Co Alloy Coating Deposition Electrolyte.

To make a stock solution of sodium zinc, dissolve 100 g of NaOH in 200 ml of distilled water and heat. Dissolve 10 g of ZnO (zinc oxide) in hot NaOH (sodium hydroxide) solution. Dissolve 20 g of aminoethyl ethanolamine (AEEA) in 400 ml of distilled water.

100 ml of distilled water was dissolved 10 g of cobalt sulfate CoSO4 '7H ₂ O and the resulting solution is mixed with Aminoethylethanolamine solution.

The solution of the cobalt complex thus obtained is slowly added to a previously prepared solution of sodium zincate, diluted to 1 l with distilled water. The electrolyte is strongly alkaline (pH> 13). The electrolyte is stable during storage and does not lose properties for up to 2 years.

As the amount of cobalt in the solution increases, the electrolyte changes color from light cherry to dark cherry.

Examples 2-10. Zn-Co coatings electrolytes and cobalt levels in the coatings.

According to the description of Example 1, several electrolytes having the compositions shown in Tables 1-2 are prepared.

Table 1. Compositions of electrolytes suitable for the deposition of Zn-Co coatings (using aminoethyl ethanolamine as complexing agent)

Electrolyte composition Sample (electrolyte) no. 2 3 4 5 6th Zinc compound, g / i ZnO, 10th ZnSO4, 20th ZnSO ₄ , 18 ZnCl ₂ , 15 ZnO, 10th Cobalt compound, g / i CoCl ₂ , 1 CoSO ₄ '7H ₂ O, 10 CoCl ₂ , 8 CoSO ₄ 7H ₂ O, 4 CoSO ₄ 7H ₂ O, 1 Alkaline metal hydroxide, g / i NaOH, 100 KOH, 120 NaOH, 120 NaOH, 100 NaOH, 80 AEEA, g / l 5 20th 20th 10th 10th

Table 1 shows the cobalt content of the coating as determined by X - ray photoelectron spectroscopy.

table. Electrolytes, further used for deposition of Zn-Co coatings and Co content in coatings

Electrolyte composition Sample (electrolyte) no. 7th 8th 9th 10th Zinc oxide, & 8th 10th 10th 10th Sodium hydroxide, g / l 100 100 100 120 Cobalt sulphate, g / l 1 4 10th 20th AEEA, g / 1 10th 10th 20th 40 Co,% by weight of coating 5-30 15-89 31-85 20-80

The Zn-Co electrolyte according to the invention enables high quality coatings to be obtained using both galvanostatic and pulsed methods. Electrolysis was carried out using 7-10 electrolytes by galvanostatic and pulsed methods. The constant current density was varied in the range of 1-60 mA / cm ² . The pulse current parameters were changed as follows: pulse duration 1-10 ms; pause duration 1-200 ms; current pulse size 10-1000 mA / cm ² .

Impulse-deposited coatings have a smoother, more glossy finish.

Depending on the electrolyte composition and electrolysis parameters, various compositions of zinc-cobalt coatings are deposited from the electrolytes of the invention, the properties of which are given in Tables 3 and 4.

table. The dependence of the composition and appearance of Zn-Co alloy coatings on DC parameters

Elek troll No. Ban- dymo No. Constant current Current density, mA / cm ² Co., masses % Zn, masses % Exterior view of the pavement 7th 1 1 30th 70 Light gray, shiny 7th 2 2 30th 70 Light gray, shiny 7th 3 5 7th 93 Dark gray, non-glossy 7th 4 10th 5 95 Dark gray, non-glossy 8th 5 1 89 11th Shiny 8th 6th 2 84 16th Bright, shiny 8th 7th 5 24th 76 v * Sun gray, semi-glossy 8th 8th 10th 18th 82 St. gray, matte

Continuation of Table 3 8th 9th 15th 21st 79 Sun gray, matte 8th 10th 20th 10th 90 Gray, matte 8th 11th 30th 15th 85 Gray, matte 9th 12th 1 85 15th Shiny 9th 13th 2 77 23rd Shiny 9th 14th 5 30th 70 Light gray, shiny 9th 15th 10th 33 67 Light gray, shiny 9th 16th 15th 32 68 Light gray, shiny 9th 17th 20th 32 68 Light gray, shiny 9th 18th 30th 31st 69 Light gray, shiny 10th 19th 10th 80 20th Light gray, shiny 10th 20th 20th 20th 80 Light gray, shiny 10th 21st 40 20th 80 Light gray, shiny 10th 22nd 60 20th 80 Light gray, shiny

table. Dependence of composition and appearance of Zn-Co alloy coatings on pulse current parameters

Elek troll No. Ban- dymo No. Pulse current, mA / cm ² (Current impulse so duration 1 ms) Pauses duration ms Current impulse size, mA / cm ² Co., masses % Zn, masses % Exterior view of the pavement 7th 1 10th 10th 25th 75 Shiny 7th 2 10th 20th 16th 84 Shiny 7th 3 10th 55 3 97 Gray, matte 7th 4 100 100 18th 82 Shiny 8th 5 1 10th 81 19th shiny 8th 6th 10th 10th 85 15th shiny 8th 7th 10th 20th 70 30th shiny 8th 8th 10th 100 17th 83 St. gray, shiny 8th 9th 100 100 83 17th Gray, matte 8th 10th 100 200 34 66 shiny 8th 11th 100 500 28th 72 Gray, shiny 8th 12th 200 500 80 20th Metallic luster

Continuation of Table 4 9th 13th 10th 11th 87 13th Metallic luster 9th 14th 10th 55 39 61 St. gray, shiny 9th 15th 10th 110 36 64 St. gray, shiny 9th 16th 10th 220 32 68 St. gray, shiny 9th 17th 100 200 85 15th Metallic luster 9th 18th 100 500 43 57 Shiny 9th 19th 100 1000 37 63 Sun gray, semi-glossy

The results in the tables show that the coating of solutions of good quality is deposited from solutions 9 and 10, the optimum electrolyte composition is g / 1: zinc oxide (ZnO) - 10; cobalt sulfate (COSO47H2O) - 10-20; sodium hydroxide (NaOH) - 100-120;

Aminoethylethanolamine (H 2 N (CH ₂₎ 2 NH (CH 2) 2 OH) - 20-40.

Depending on the current density, the process yields 40-80%. The coating composition is independent of current density over a wide range of current densities.

example. Anticorrosive properties of Zn-Co coatings.

The corrosion resistance of the resulting Zn-Co coatings was investigated in a salt fog chamber. Salt fog chamber tests were performed according to LST ISO 9227: 1997.

The coatings were evaluated according to ISO 10289: 1999.

The results are shown in Table 5; final results are presented after 2102 hours. maintenance.

table. Corrosion resistance of Zn-Co (20%) coatings in salt fog chamber

Zn-Co (20%) coating deposition current density Steel plates No. The onset of Zn corrosion, baby. Zn corrosion 5% of the area, or. Fe corrosion onset, ch. Ic = 10 mA cm- ² 1 696 (9 points) (0 <% <0, l) 826 2030 2 360 (9 points) (0 <% <0.1) 768 1982 Ik = 20 mA cm ' ² 3 168 (9 points) (0 <% <0, l) 720 1982 4 696 (9 points) (0 <% <0, l) 950 2102 5 672 (9 points) (0 <% <0, l) 854 2030 6th 168 (9 points) (0 <% <0, l) 720 1958

The results of the corrosion tests (Table 5) showed that the corrosion resistance of the zinc-cobalt (20% Co) alloy coatings to the iron corrosion in the salt fog chamber is about 2000 hours. This equates to the corrosion resistance of chromium-plated zinc coatings.

The deposited zinc-cobalt alloy coatings are of high quality, even, well adhering to the substrate. The composition of coatings is constant over a wide range of current densities.

The results presented above show that the proposed electrolyte allows the deposition of coatings which do not require additional chromation. Cr (VI) is known to be highly toxic, its use is constantly being reduced, and it will be banned in the future, so elimination of the chromation operation is highly desirable from an ecological point of view. In addition, the deposited zinc-cobalt coatings are harder compared to zinc coatings and have better soldering properties.

The electrolyte is stable and is made from a small number of ingredients; the coatings are deposited at room temperature without mixing.

v

Electrolyte preparation is not difficult; The use of relatively low concentrations of salts and complexing agents provides additional ecological effects by facilitating the purification of process waste.

Claims (3)

1. An alkaline zinc-cobalt alloy deposition electrolyte containing a zinc ion source, a cobalt ion source, an alkali metal hydroxide complexing agent, and, optionally, 5 additional substances, wherein the complexing agent is an aminoethyl ethanolamine having the following composition ( g / 1): Zinc Ion Source 6-8 Cobalt ion source 0.2-4.2 Sodium (or potassium) hydroxide 80-120 10 Aminoethyl ethanolamine (H2N (CH2) 2NH (CH2) 2OH) 10-40; Water up to 1 liter. 2. The electrolyte according to claim 1, characterized in that the electrolyte components have a composition (g / l): 15 Zinc oxide (ZnO) 8-10; Cobalt sulfate (CoSO4 '7H2O) 1 -20; Sodium hydroxide (NaOH) 100-120; Aminoethyl ethanolamine (H2N (CH2) 2NH (CH2) 2OH) 10-40; Water up to 1 liter. 3. The electrolyte according to claim 1 and / or 2, wherein the optimum ratio of zinc compound, cobalt compound and aminoethyl ethanolamine is about 1: 1-2: 2-4, respectively.