RU2175690C2 - Electrolyte of bright nickel plating - Google Patents

Abstract

FIELD: electroplating, more particularly applying nickel coatings from pyrophosphate electrodes in machine building and instrument making. SUBSTANCE: electrolyte comprises, g; nickel sulfate, 40-60; potassium pyrophosphate, 160-200; ammonium chloride, 3-5; borax, 3,5;2,4- dinitrophenyl hydrazine, 1.3 mmol/l; red methyl, 1.5 mmole/l; and water, up to 1 l. EFFECT: pore-free nickel coatings within wide range of current densities at maximum hydrogen absorption of steel substrate. 2 cl, 2 ex, 3 tbl

Description

 The invention relates to electroplating, in particular to the deposition of nickel coatings from pyrophosphate electrolytes and will find application in mechanical engineering and instrumentation, where it is important to obtain high-quality galvanic precipitation with minimal hydrogenation of the steel base.

Known electrolyte for Nickel plating, containing Nickel sulfate, potassium phosphate, ammonium chloride, borax [1], from which are obtained crystalline non-porous coatings. The disadvantage of this electrolyte is a low current efficiency (65-75%), a small scattering power (28-30%), a narrow range of current density (1-1.5 A / dm ² ).

 Nickel plating electrolytes [2-5] based on pyrophosphate salts with organic additives are known. The disadvantages of these electrolytes is the inability to obtain high-quality galvanic precipitation without hydrogenation of the steel base.

The closest in technical solution and composition of the components is nickel electrolyte [2], from which high-quality precipitates with a fine-crystalline structure, a shiny and mirror surface, and high ductility of steel samples are obtained. The disadvantage of this electrolyte is the high porosity of nickel coatings (4-13 pores per 1 cm ² at δ = 10 μm). The objective of the invention is to obtain high-quality non-porous nickel coatings in a wide range of current densities with minimal hydrogenation of the steel base.

и метиловый красный (n'-диметиламиноазобензол - 2 - карбоновая кислота, М.М. 269)

при следующем соотношении компонентов:
Никель сернокислый, г - 40-60
Калий пирофосфорнокислый, г - 60-200
Аммoний хлористый, г - 3-5
Бура, г - 3-5
2,4-динитрофенилгидразин, ммоль/л - 1-3
Метиловый красный, ммоль/л - 1-5
Вода, л - До 1
Метиловый красный - фиолетовые кристаллы, плохо растворимы в воде, хорошо растворимы в спирте [7].It is achieved by the fact that the brilliant nickel electrolyte contains nickel sulfate, potassium pyrophosphate, ammonium chloride, brighteners, water and additionally borax, while it contains 2,4-dinitrophenylhydrazine (MM198) as brighteners

and methyl red (n'-dimethylaminoazobenzene - 2 - carboxylic acid, M.M. 269)

in the following ratio of components:
Nickel sulfate, g - 40-60
Potassium pyrophosphate, g - 60-200
Ammonium chloride, g - 3-5
Borax, g - 3-5
2,4-dinitrophenylhydrazine, mmol / l - 1-3
Methyl red, mmol / l - 1-5
Water, l - Up to 1
Methyl red - violet crystals, poorly soluble in water, well soluble in alcohol [7].

 To obtain the pyrophosphate electrolyte of brilliant nickel plating, three mixtures of components were prepared (see Table 1).

The electrolyte is prepared as follows: separately dissolved at a temperature of 40-50 ^o C Nickel sulfate, potassium pyrophosphate, ammonium chloride and borax. A solution of potassium pyrophosphate is added to the nickel sulfate solution. The precipitate of nickel pyrophosphate formed at the beginning dissolves with stirring. Then, ammonium chloride and borax solutions are added to the mixture. The electrolyte is worked out for 4-6 hours at DK = 1 A / dm ² in order to remove impurities, filtered and brightening additives are added. For the preparation of solutions, reagent grade grade reagents were used.

где Ккор.I - скорость коррозии без покрытия,
Ккор.II - скорость коррозии с покрытием

где Δm - изменение массы покрытий пластины;
S - площадь пластины;
τ - время опыта.Electrodeposition of nickel was carried out on 44 x 40 x 2 mm plates of steel 20. The appearance of the coatings was described using a microscope. The cathode potential was measured on a R-375 potentiometer relative to a silver chloride electrode, calculated on a standard hydrogen scale. The gloss of the coatings was measured on an FB-2 gloss meter (with photocell) in relation to uviole glass, the gloss of which is 65 rel. The range of values 10-50 corresponds to a semi-brilliant, 50-90 to a brilliant and 90-100 mirror surface. The current efficiency was determined using a copper coulometer. Steel hydrogenation was determined by measuring the ductility of U8A carbon steel spring wire ⌀ 1 mm (sample length 100 mm, tensile load 1.5 kg), measured by the number of revolutions before failure when twisting on a K-5 machine. The ductility (N) of steel samples was determined by the formula
N = (a / a ₀ ) • 100,
where a and a ₀ - the number of revolutions of the wire sample to the destruction of the coated and uncoated with Nickel. The porosity of nickel coatings was determined according to GOST 9.302-79. Corrosion resistance was carried out in a salt spray chamber [8]. The protective effect was determined by the formula

where Kcor.I - corrosion rate without coating,
Cor. II - Coated corrosion rate

where Δm is the change in the mass of the coating of the plate;
S is the area of the plate;
τ is the time of the experiment.

 Otherwise, the technique did not differ from the previously described [9].

 The results of the experimental analysis are given in table. 2 and 3.

The high efficiency of the bright-forming and inhibitory effect of organic additives is associated with the structure of their molecules. Thus, the adsorption capacity of the 2,4-dinitrophenylhydrazine additive seems to be determined by four adsorption centers — nitrogen atoms, which can interact with the surface of the steel cathode. The hydrogen-inhibiting effect is 86-97% at DK = 1-4 A / dm ² , which is consistent with the quality of the coating and its porosity (Tables 2 and 3, N 1-3).

 The presence in the molecule of the methyl red azo group, N = N, of a nitrogen heteroatom containing two electron-homogeneous methyl groups, causes a very strong chemisorption bond between the molecules of this inhibitor and the cathode surface. In addition, the nitrogen atoms contain two unpaired electrons, which can go over to the unfilled d - orbitals of the iron atom, as a result of which the additive molecules can linger on the surface of the cathode. The molecule of this dye has a linear structure, benzene rings fit well on the surface of the cathode. The ductility of steel samples is 91-100%, the precipitates are fine crystalline, well adhered to the base, shiny surface, practically non-porous (Tables 2 and 3, N 4-7).

 The addition of 2,4-dinitrophenylhydrazine to the pyrophosphate electrolyte together with methyl red enhances the effectiveness of the brightening and inhibitory effects, i.e. synergism is shown (tab. 2 and 3, N 8).

Example 1. For the deposition of Nickel from pyrophosphate electrolyte was used composition III (table. 1) at a concentration of additives N 1 = 3 and N 2 = 5 mmol / l at DK = 4 A / DM ² (tables 2 and 3, N 8) . Strongly lowering the cathode potential (E = - 1.101 V), organic additives significantly affect the structure of the deposited metal. Precipitates are fine crystalline, well adhered to the base, dense, smooth, uniform, non-porous (at δ = 7–10 μm, the number of pores is 1–0 per 1 cm ² ), their increased texturing enhances gloss (γ = 90 rel. Units). Diffusion of hydrogen through such dense coatings is difficult and the ductility of steel samples is 95-97%. The current efficiency is 85%. The microhardness of nickel precipitation reaches 483 kgf / mm ² . The electrolyte has a high dissipative ability (PC = 80%), which allows you to evenly cover products over the entire surface of the sample. Electroplating is very resistant to corrosion, the degree of corrosion damage is 1, i.e. only slight darkening is observed on the surface, the protective effect reaches 94%.

Example 2. Nickel plating was carried out from composition III (table. 1) at the same concentrations Dk = 1 A / dm ² .

High cathodic potential (E = 1.043 V) contributes to the production of high-quality galvanic deposits with a fine-grained structure, a mirror surface (100 rel. Units), good adhesion, and non-porous (at δ = 7-10 mm pores). Almost no hydrogenation (99-100%). The current efficiency is quite high - 93%. The electrolyte has a high dissipation ability (92%). The microhardness of nickel precipitation is 450 kgf / mm ² , and the precipitation is corrosion resistant, the degree of corrosion damage is I and the protective effect is 87%.

As can be seen from the above examples, the introduction of 2,4-dinitrophenylhydrazine in combination with methyl red into the nickel-plating electrolysis of brighteners strongly reduces the cathode potential (E = - 1.043 - 1.101 V), allows us to extend the range of working current densities to 4 A / dm ² , to obtain high-quality galvanic deposits with a fine crystalline structure, dense, smooth, well adhered to the substrate, a mirror surface (γ = 90-100 rel. units), practically non-porous (at δ = 7-10 μm, the number of pores is 1-0). Hydrogenation of the steel base is practically excluded (95-100%). The current efficiency is 85-93%. The microhardness of nickel samples is 450-582 kgf / mm ² . Nickel coatings are resistant to corrosion, the protective effect is quite high 87-94%, and the degree of corrosion damage is 1. The electrolyte has a high PC - 80-92, which allows you to evenly cover parts with complex configurations.

Sources of information
1. A.S. 234810, USSR B.I. 1969, N 4.

 2. A.S. 430189, USSR B.I. 1974, N 20.

 3. A.S. 198875, USSR B.I. 1967, N 14.

 4. A.S. 210599, USSR B.I. 1968, N 6.

 5. A.S. 1629355, USSR B.I. 1991, N 7.

 6. Milushkin A.S., Urbonas A.A. Quinazolino arylidenehydrazine derivatives as brighteners and electrocrystallization inhibitors in nickel plating. Metal Protection, 1997, v. 33, No. 1, p. 65 to 69.

 7. Chemical encyclopedia. Dictionary, M.: Sov. encyclical. 1983, p. 334.

 8. Loshkarev Yu.M. Dis. for the degree of Dr. Chem. sciences. Dnepropetrovsk, state University, 1973.

 9. Milushkin A.S., Beloglazov S.M. Hydrogenation and electrocrystallization inhibitors during copper plating and nickel plating. L .: Leningrad State University, 1986, 168 p.

Claims (1)

Brilliant nickel electrolyte containing nickel sulfate, potassium pyrophosphate, ammonium chloride, brightening agents and water, characterized in that it additionally contains borax, and 2,4-dinitrophenylhydrazine, M.M.198 as brighteners

and methyl red, M.M. 269

in the following ratio of components:
Nickel sulfate, g - 40 - 60
Potassium pyrophosphate, g - 160 - 200
Ammonium chloride, g - 3 - 5
Bura, g - 3 - 5
2,4-dinitrophenylhydrazine, mmol / l - 1 - 3
Methyl red, mmol / l - 1 - 5
Water, l - Up to 1

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