RU2293144C2 - Zinc plating electrolyte - Google Patents

Abstract

FIELD: electroplating processes and equipment, possibly zinc plating of different-designation parts for protecting them against corrosion.

SUBSTANCE: electrolyte contains zinc (II), 1-hydroxyethane-1,1-diphosphonic acid or soluble compound of such acid and water and in addition it contains matter selected from group including dicarboxylic acid, hydroxycarboxylic acid, polyhydric alcohol, amine, amino alcohol and their salts used separately or in any combination at next relation of ingredients: zinc (II), 0.05 - 0.5 mol/l; 1-hydroxyethane-1,1-diphosphonic acid or its soluble compound, 0.1 - 2.0 mol/l; dicarboxylic or hydroxycarboxylic acid or polyhydric alcohol or amine or amino alcohol or their salts, 0.001 - 1.0 mol/l; water, up to 1.0 l; at pH in range 6.0 - 13.5. Invention offers zinc plating electrolyte on base of complex of zinc (II) with 1-hydroxyethan-1,1-diphosphonic acid.

EFFECT: possibility for plating uniform fine-crystal coatings with increased cathode electric current yield of metal at wide temperature range and pH values, enlarged assortment of complex phosphonate electrolytes for zinc plating.

12 cl, 9 ex

Description

The invention relates to electroplating, in particular to electrolytes for producing zinc coatings on parts for various purposes in order to protect them from corrosion.

To cover parts with complex configurations, it is preferable to use complex galvanizing electrolytes containing water-soluble zinc salt, which is the source of zinc cation, and a ligand for binding zinc to the complex.

Of the complex electrolytes, galvanizing cyanide electrolytes are the most famous and have long been used (Kudryavtsev N.T. Electrolytic coatings with metals. - M .: Chemistry, 1979, S.147-153).

However, the disadvantages of cyanide electrolytes (instability and high toxicity) stimulate the search for cyanide-free galvanizing electrolytes, which provide high-quality zinc coatings, but are safe and convenient to use.

Known are cyanide complex galvanizing electrolytes containing ammonia, caustic soda, potassium and sodium pyrophosphates, ethylenediamine and other compounds as ligands, but none of them fully meets the requirements (Belenky M.A., Ivanov A. F. Electrodeposition of metal coatings. Handbook. - M.: Metallurgy, 1985, S. 59-64. Kudryavtsev NT. Electrolytic coatings with metals. - Moscow: Chemistry, 1979, S. 153-172).

Cyanide-free galvanizing electrolytes based on zinc (II) complexes with organophosphoric ligands, in particular 1-hydroxyethane-1,1-diphosphonic acid (Haynes RT, Irani RR, Langguth RP US Patent 3475293, US Cl. 204-48, Int .Cl. C 23 b 5/30, 5/46, publ. 1969. Kowalski X. US Patent 3706635, US Cl. 204-46, Int. Cl. C 23 b 5/02, 5/46, publ. 1972 Kowalski X. US Patent 3914162, US Cl. C 25 D 3/04, 3/12, 3/38, 3/56, publ. 1975).

The closest in technical essence to the claimed invention is a zinc plating electrolyte based on a complex consisting of zinc (II) ion and 1-hydroxyethane-1,1-diphosphonic acid anion (Haynes RT, Irani RR, Langguth RP US Patent 3475293, US Cl. 204-48, Int. Cl. C 23 b 5/30, 5/46, publ. 1969). The specified electrolyte contains a salt of zinc (II) in an amount of from 1 to 5 wt.% (Metal), tetrakali salt of 1-hydroxyethane-1,1-diphosphonic acid, potassium carbonate and water at a pH of from 7.0 to 11.5, It is environmentally friendly and allows to obtain zinc coatings of satisfactory quality on a steel base at a temperature of 50 to 70 ° C and a current density of 0.5 to 15 A / dm ² .

An experimental verification of this electrolyte showed that its drawback is the low cathodic metal current output, which not only reduces the deposition rate of the coating and increases the pH of the electrolyte due to intensive hydrogen evolution, but also leads to the accumulation of excess zinc ions in the electrolyte during prolonged electrolysis and violation of the initial composition of the complex, that is, the quantitative ratio between the metal and the ligand, and the associated deterioration in the quality of the coating and dissolution of the anodes. This is especially noticeable at temperatures below 50 ° C, at which the drop in metal current output is most significant. So, at a temperature of 20-30 ° C, the cathode current output is only 8-9%.

The aim of the invention is to develop a galvanizing electrolyte based on a complex of zinc (II) with 1-hydroxyethane-1,1-diphosphonic acid, which provides uniform and fine-grained coatings with a high cathodic metal current output over a wide range of temperatures and pH values, as well as expanding the range complex phosphonate galvanizing electrolytes.

This goal is achieved by the fact that in the galvanizing electrolyte containing zinc (II), 1-hydroxyethane-1,1-diphosphonic acid or its soluble compound and water, a substance selected from the group consisting of dicarboxylic acid, hydroxycarboxylic acid, polyhydric is additionally introduced alcohol, amine, aminoalcohol or their salts, taken separately or in any combination, in the following ratio of components:

Zinc (II), mol / L 0.05-0.5

1-hydroxyethane-1,1-diphosphonic

acid or its soluble compound, mol / l 0.1-2.0

Dicarboxylic acid, or hydroxycarboxylic

acid, or carboxyl-containing complexon,

or polyhydric alcohol, or amine, or amino

alcohol or their salts, mol / l 0.001-1.0

pH 6.0-13.5.

As a dicarboxylic acid, it is desirable to use a substance selected from the group consisting of oxalic, malonic, succinic, maleic, glutaric, adipic acids. As the hydroxycarboxylic acid, it is desirable to use a substance selected from the group consisting of glycolic, lactic, malic, tartaric, citric, gluconic, salicylic acids. As salts of the above acids, it is desirable to use sodium and potassium salts of acids. As a polyhydric alcohol, it is desirable to use a substance selected from the group consisting of ethylene glycol, propylene glycol, tetramethylene glycol, glycerol, mannitol, xylitol, sorbitol. As an amine, it is desirable to use a substance selected from the group consisting of methylamine, ethylamine, dimethylamine, diethylamine, ethylenediamine, dimethylethylenediamine, tetramethylethylenediamine, cyclohexanediamine, propylenediamine, hexamethylenediamine, hexamethylenetetramine, diethylene diethylene. As an amino alcohol, it is desirable to use a substance selected from the group consisting of ethanolamine, N, N-dimethylethanolamine, N, N-diethylethanolamine, diethanolamine, triethanolamine, ephedrine. As salts of amines and amino alcohols, it is desirable to use chlorides, sulfates, nitrates, carbonates. As a source of zinc (II), it is desirable to use zinc oxide (II) or zinc (II) sulfate heptahydrate. As the soluble compound of 1-hydroxyethane-1,1-diphosphonic acid, it is desirable to use the sodium or potassium salts of this acid. As the sodium salt of 1-hydroxyethane-1,1-diphosphonic acid, it is desirable to use the monosodium, disodium, trisodium salt, and as the potassium salt of 1-hydroxyethane-1,1-diphosphonic acid, it is desirable to use the monopotassium salt. The pH of the electrolyte is preferably maintained in the range of 7.5 to 11.5.

The implementation of the claimed invention is carried out in a galvanic bath, which is filled with a galvanizing electrolyte containing zinc (II), 1-hydroxyethane-1,1-diphosphonic acid and water as the main components, when using a product on which it is necessary to apply a zinc coating as a cathode , and as an anode - plates of pure zinc.

As a result of the introduction of galvanizing, containing zinc (II) and 1-hydroxyethane-1,1-diphosphonic acid into the aqueous electrolyte, individually or in any combination of the above substances, the current yield of zinc is increased, uniform fine-crystalline coatings are deposited on the cathode, and zinc anodes dissolve uniformly, without the formation of hydroxide or zinc (II) salts insoluble in the electrolyte on their surface.

The lower limit of the concentration of zinc (II) in the electrolyte is selected in accordance with the desired rate of electrodeposition of zinc. The upper limit of zinc concentration is limited by the solubility of the complex zinc salt in the electrolyte.

The lower limit of the concentration of 1-hydroxyethane-1,1-diphosphonic acid is due to the need to form a strong complex with zinc (II), the upper limit of the concentration of 1-hydroxyethane-1,1-diphosphonic acid is limited by its solubility in the electrolyte.

The lower concentration limit of the substance additionally introduced into the electrolyte corresponds to the concentration at which the beneficial effect of its introduction is achieved, that is, the uniformity and quality of the coating is improved, and the current efficiency increases. The upper limit of the concentration of the substance additionally introduced into the electrolyte corresponds to the concentration at which the effect of its introduction into the electrolyte begins to decrease significantly, that is, the quality of the coating deteriorates, and the current efficiency decreases.

The pH of the electrolyte may be in the range from 6.0 to 13.5. The lower value of this range is due to the possibility of the formation of complexes of zinc (II) with 1-hydroxyethane-1,1-diphosphonic acid. The upper value of this range is due to the need to avoid the formation of extraneous zinc (II) complexes.

Recommended conditions for the electrodeposition of zinc from the proposed electrolyte:

The electrolyte temperature is from 20 to 70 ° C.

The cathodic current density is from 0.5 to 5 A / dm ² .

The pH of the electrolyte is preferably maintained in the range of 7.5 to 11.5.

As anodes, zinc grade Ts0 or C1 is used.

The anodes dissolve without the formation of anode sludge at an anode current density not exceeding 1-1.5 A / DM ² .

The preparation of the electrolyte can be carried out in various ways, for example:

Method 1

To a solution of 140 g of monopotassium salt of 1-hydroxyethane-1,1-diphosphonic acid C ₂ H ₇ O ₇ P ₂ K · 2 H ₂ O in 500 ml of water heated to 60-80 ° C, 16.3 g of oxide are added with stirring zinc ZnO and stirred until complete dissolution of the precipitate. The solution was allowed to cool to room temperature and a 30% potassium hydroxide solution was added with stirring until a pH of 8.3 was reached. In the resulting solution, 0.001 to 1.0 mol of an additional substance (dicarboxylic acid, hydroxycarboxylic acid, polyhydric alcohol, amine, amino alcohol) is dissolved with stirring, or an additional substance is introduced in the form of an aqueous solution. If necessary, set the desired pH by adding a 3-30% solution of potassium hydroxide or sulfuric acid. Water is added to a total volume of 1.0 L and the electrolyte is mixed.

Method 2

To a solution of 70.0 g of monopotassium salt of 1-hydroxyethane-1,1-diphosphonic acid dihydrate C ₂ H ₇ O ₇ P ₂ K · 2 H ₂ O and 42.0 g of potassium hydroxide in 400 ml, a solution of 28.8 g is added with stirring ZnSO ₄ · 7H ₂ O zinc sulfate heptahydrate in 200 ml of water. In the resulting solution, 0.001 to 1.0 mol of an additional substance (dicarboxylic acid, hydroxycarboxylic acid, polyhydric alcohol, amine, amino alcohol) is dissolved with stirring, or an additional substance is introduced in the form of an aqueous solution. If necessary, set the desired pH by adding a 3-30% solution of potassium hydroxide or sulfuric acid. Water is added to a total volume of 1.0 L and the electrolyte is mixed.

Electrolytes prepared in this way are stable in operation and do not require preliminary study.

With prolonged operation of the electrolyte, due to the mismatch of the anode and cathode current outputs, the pH of the electrolyte can increase, especially in neutral and slightly alkaline environments. To stabilize the pH values, it is advisable to introduce buffering substances into the electrolyte, which are recommended to use ammonium acetate and other ammonium salts.

To eliminate the possibility of hydrogen pitting in the electrolyte, it is advisable to add nonionic surfactants such as polyoxyethylene alkyl ethers (preparation OS-20, syntanol DS-10) or polyoxyethylene alkyl phenyl ethers (OP-7, OP-10).

To increase the gloss of the coating and improve its appearance in the electrolyte, it is advisable to add brighteners, for example, nitrogen-containing polymers such as polyalkylene polyamines or their derivatives.

The above examples of buffering, surfactants, and brightening agents do not exhaust the range of additives that can be introduced into the galvanizing electrolyte according to the claimed invention in addition to the basic composition given above, in order to improve the quality of the zinc coating and expand the range of electrodeposition conditions.

Examples of the implementation of the claimed invention are given below.

In all examples, zinc was precipitated in a bath placed in a water thermostat onto samples of steel 0.4 mm thick at a cathodic current density of 2 A / dm ² , anodes — zinc of grade C1. The temperature was measured and maintained with an accuracy of ± 1 ° C. The pH value was measured using an ionomer, the cathode current yield of zinc - using a copper coulometer. The quality of the coating was evaluated visually.

Example 1

A galvanizing electrolyte is prepared containing 0.2 mol / L zinc (II), 0.5 mol / L 1-hydroxyethane-1,1-diphosphonic acid and 0.5 mol / L maleic acid, having a pH of 8.2. The electrolysis is carried out at a temperature of 46 ° C for 20 minutes. As a result of electrolysis at the cathode, a uniform fine crystalline frosted zinc coating with a thickness of 4.8 μm is obtained. The cathodic current efficiency is 38.4%; the zinc deposition rate is 14.4 μm / h.

Example 2

A galvanizing electrolyte is prepared containing 0.2 mol / L zinc (II), 0.5 mol / L 1-hydroxyethane-1,1-diphosphonic acid and 0.5 mol / L and potassium sodium tartrate tetrahydrate having a pH of 8, 0. The electrolysis is carried out at a temperature of 20 ° C for 20 minutes. As a result of electrolysis at the cathode, a uniform finely crystalline semi-brilliant zinc coating with a thickness of 5.0 μm is obtained. The cathodic current efficiency is 35.6%, the zinc deposition rate is 14.9 μm / h.

Example 3

A galvanizing electrolyte is prepared containing 0.2 mol / L zinc (II), 0.5 mol / L 1-hydroxyethane-1,1-diphosphonic acid and 0.3 mol / L mannitol having a pH of 7.8. The electrolysis is carried out at a temperature of 32 ° C for 20 minutes. As a result of electrolysis at the cathode, a uniform finely crystalline semi-brilliant zinc coating with a thickness of 1.7 μm is obtained. The cathodic current efficiency is 9.4%; the zinc deposition rate is 5.1 μm / h.

Example 4

A galvanizing electrolyte is prepared containing 0.2 mol / L zinc (II), 0.5 mol / L 1-hydroxyethane-1,1-diphosphonic acid and 0.05 mol / L diethylenetriamine having a pH of 7.7. The electrolysis is carried out at a temperature of 70 ° C for 20 minutes. As a result of electrolysis at the cathode, a uniform fine crystalline frosted zinc coating with a thickness of 14.7 μm is obtained. The cathodic current efficiency is 96.1%, the zinc deposition rate is 44.1 μm / h.

Example 5

A galvanizing electrolyte is prepared containing 0.2 mol / L zinc (II), 0.5 mol / L 1-hydroxyethane-1,1-diphosphonic acid and 0.005 mol / L diethylenetriamine having a pH of 7.7. The electrolysis is carried out at a temperature of 30 ° C for 20 minutes. As a result of electrolysis at the cathode, a uniform finely crystalline matte zinc coating with a thickness of 7.9 μm is obtained. The cathodic current efficiency is 51.6%; the zinc deposition rate is 23.6 μm / h.

Example 6

A galvanizing electrolyte is prepared containing 0.2 mol / L zinc (II), 0.5 mol / L 1-hydroxyethane-1,1-diphosphonic acid and 0.3 mol / L ethanolamine having a pH of 8.3. The electrolysis is carried out at a temperature of 30 ° C for 20 minutes. As a result of electrolysis at the cathode, a uniform fine crystalline semi-brilliant zinc coating with a thickness of 3.4 μm is obtained. The cathodic current efficiency is 23.7%; the zinc deposition rate is 10.5 μm / h.

Example 7

A galvanizing electrolyte is prepared containing 0.2 mol / L zinc (II), 0.5 mol / L 1-hydroxyethane-1,1-diphosphonic acid and 0.5 mol / L potassium sodium tartrate tetrahydrate having a pH of 12.5 . The electrolysis is carried out at a temperature of 38 ° C for 20 minutes. As a result of electrolysis at the cathode, a uniform finely crystalline semi-brilliant zinc coating with a thickness of 11.3 μm is obtained. The cathodic current efficiency is 91.7%; the zinc deposition rate is 33.9 μm / h.

Example 8

A galvanizing electrolyte is prepared containing 0.2 mol / L zinc (II), 0.5 mol / L 1-hydroxyethane-1,1-diphosphonic acid, 0.1 mol / L mannitol, 0.1 mol / L triethanolamine, having pH 8.2. The electrolysis is carried out at a temperature of 40 ° C for 20 minutes. As a result of electrolysis at the cathode, a uniform fine crystalline zinc coating with a thickness of 4.4 μm is obtained. The cathode current efficiency is 31.6%, the zinc deposition rate is 13.2 μm / h.

Example 9 (prototype).

A galvanizing electrolyte is prepared containing 0.2 mol / L zinc (II) and 0.5 mol / L 1-hydroxyethane-1,1-diphosphonic acid having a pH of 8.2. The electrolysis is carried out at a temperature of 30 ° C for 20 minutes. As a result of electrolysis at the cathode, an uneven spotty zinc coating with an average thickness of 1.1 μm is obtained. The cathodic current efficiency is 8.5%; the zinc deposition rate is 3.3 μm / h.

As can be seen from the above examples, the galvanizing electrolyte according to the claimed invention allows to obtain zinc coatings of good quality with a high current output, in a wide range of temperatures and pH values. Coatings have a fine crystalline structure, are highly uniform and can be applied to parts of complex profile.

Claims (12)

1. Galvanizing electrolyte containing zinc (II), 1-hydroxyethane-1,1-diphosphonic acid or its soluble compound and water, characterized in that it further comprises a substance selected from the group consisting of dicarboxylic acid, hydroxycarboxylic acid, polyhydric alcohol, amine, aminoalcohol or their salts, taken individually or in any combination, with the following components, mol / l: Zinc (II) 0.05-0.5 1-hydroxyethane-1,1-diphosphonic acid or soluble compound thereof 0.1-2.0 Dicarboxylic acid, or hydroxycarboxylic acid, or polyhydric alcohol or amine, or aminoalcohol, or their salts 0.001-1.0 Water, l Up to 1.0 pH 6.0-13.5 2. The electrolyte according to claim 1, characterized in that as the dicarboxylic acid use a substance selected from the group consisting of oxalic, malonic, succinic, maleic, glutaric, adipic acids. 3. The electrolyte according to claim 1, characterized in that as a hydroxycarboxylic acid use a substance selected from the group consisting of glycolic, lactic, malic, tartaric, citric, gluconic, salicylic acids. 4. The electrolyte according to any one of claims 1 to 3, characterized in that their sodium or potassium salts are used as acid salts. 5. The electrolyte according to claim 1, characterized in that as a polyhydric alcohol, a substance selected from the group consisting of ethylene glycol, propylene glycol, tetramethylene glycol, glycerol, mannitol, xylitol, sorbitol is used. 6. The electrolyte according to claim 1, characterized in that the substance used is an amine selected from the group consisting of methylamine, ethylamine, dimethylamine, diethylamine, ethylenediamine, dimethylethylenediamine, tetramethylethylenediamine, cyclohexanediamine, propylene diamine, hexamethylenediamine diethylene triethane, diethylene triethane, diethamethienetriamine, diethamethylene diethylene triethane, diethamethienetriamine, diethamethienetiethylene diethamine, hexamethiamine diethylamine diethylamine diethylamine diethylamine diethylamine diethylamine diethylene triethane 7. The electrolyte according to claim 1, characterized in that as an amino alcohol use a substance selected from the group consisting of ethanolamine, N, N-dimethylethanolamine, N, N-diethylethanolamine, diethanolamine, triethanolamine, ephedrine. 8. The electrolyte according to any one of claims 1, 6 and 7, characterized in that their chlorides, sulfates, nitrates, carbonates are used as salts of amines or aminoalcohols. 9. The electrolyte according to claim 1, characterized in that the zinc (II) oxide or heptahydrate of zinc (II) sulfate is used as the source of zinc (II). 10. The electrolyte according to claim 1, characterized in that the sodium or potassium salt of this acid is used as a water-soluble compound of 1-hydroxyethane-1,1-diphosphonic acid. 11. The electrolyte of claim 10, characterized in that the sodium salt of 1-hydroxyethane-1,1-diphosphonic acid is used monosodium, disodium, trisodium salt of this acid, and as the potassium salt of 1-hydroxyethane-1,1-diphosphonic acids use the monopotassium salt of this acid. 12. The electrolyte according to claim 1, characterized in that it has a pH from 7.5 to 11.5.