RU2292409C1 - Nickel-chrome alloy coating electrodeposition process - Google Patents

Abstract

FIELD: electrochemical production processes, possibly deposition of bright coatings of nickel-chrome alloy.

SUBSTANCE: process comprises steps of electrolysis of aqueous solution containing nickel sulfate, amino-acetic acid, chrome-potassium alum, 1,4-butynediol, saccharin, boric acid, ammonium sulfate; sustaining pH value of electrolyte in range 2,0 - 5,0; placing non-soluble lead anode in additional anode cell with sulfuric solution having anion-exchange membrane. Method provides increased pH value at generation of chrome (III) hydrate.

EFFECT: stabilized composition of electrolyte, possibility for depositing bright coatings, enhanced buffer properties of electrolyte.

1 ex, 2 dwg, 2 tbl

Description

The proposed method relates to the technology of electrochemical production and can be used for electrodeposition of corrosion-resistant, hard and wear-resistant electroplated nickel-chromium alloys in mechanical engineering and instrumentation.

A known method of electrodeposition of coatings by an alloy of hydrofluoric acid electrolyte [1-3], according to which galvanic coatings with a nickel-chromium alloy containing up to 20% chromium can be obtained at a current density of 40-90 A / dm ² and a temperature of 70-80 ° C.

The disadvantage of this method is that it does not allow to obtain shiny coatings, the electrolyte is aggressive and environmentally hazardous.

Of the known closest in technological essence is an amino acetic electrolyte [4], according to which brilliant galvanic coatings with an alloy with different chromium contents can be obtained at a temperature of 16-30 ° C, pH 1.8-3.0 and a current density of 10-50 A / dm ² .

However, this method does not allow to obtain time-stable galvanic coatings with an alloy of constant composition due to the oxidation of chromium (III) to chromium (VI) at the anode during electrolysis. The oxidation of chromium not only leads to a change in the composition of the electrolyte, but also affects the quality of the plating and the deposition rate.

The technical result of the proposed method is to stabilize the composition of the electrolyte by eliminating the process of oxidation of chromium (III) to chromium (VI), obtaining shiny coatings by introducing bright-forming additives into the electrolyte, increasing the buffer properties of the electrolyte and increasing the pH of hydration of chromium (III) by introducing sulfate ammonium

The essence of the proposed method lies in the fact that the electrodeposition of a nickel-chromium alloy is carried out from an electrolyte containing chromium potassium alum, nickel sulfate, aminoacetic acid, according to the invention, the electrolyte further comprises ammonium sulfate, 1,4-butynediol, saccharin. In this case, the pH of the electrolyte is maintained in the range 2.0-5.0.

In addition, to prevent the oxidation of chromium (III), an insoluble anode, for example, a lead anode, is placed in an additional anode cell with an MA-40 separation anion-exchange membrane.

This combination of new features with the known ones makes it possible to stabilize the composition of the electrolyte and the composition of the alloy, to obtain brilliant alloy coatings and to expand the pH range of the electrolyte.

The proposed method of electrochemical deposition of plating with a nickel-chromium alloy in a plating bath with an additional anode cell for an insoluble anode is illustrated by drawings.

The figure 1 shows a diagram of its implementation: 1 - galvanic bath, 2 - cathode, 3 - soluble nickel anode, 4 - additional anode cell, 5 - anionite membrane MA-40, 6 - insoluble, for example, lead anode.

The figure 2 shows an additional anode cell for an insoluble anode with a dividing wall. An additional anode cell for an insoluble anode with an MA-40 anion-exchange membrane contains: 7, 8 - perforated vinyl-plastic partitions; 9, 10, 11 - rubber gaskets; 12 - vinyl plastic rivets; 13 - anion exchange membrane MA-40.

The cell is welded from sheet vinyl plastic. The front wall is perforated, and is 10 mm larger on each side for attaching an ion-exchange membrane. On both sides of the ion-exchange membrane there are perforated partitions for the passage of ions from the plating bath to the additional cell and vice versa. Rubber gaskets are used to create the tightness of the anode cell and for a uniform transition of ions over the entire surface of the ion exchange membrane. The cell is inserted into the plating bath to the opposite wall from the cathode, perforated to the cathode. A nickel anode is hung next to the anode cell. A current is supplied to the nickel anode and to the insoluble (lead) anode located in the additional anode cell from the anode terminal of the current source through a divider.

и не пропускает катионы Ni²⁺ и Cr³⁺.The method is as follows. At the beginning of the process, a glycol-ammonia electrolyte is poured into the process bath to precipitate the nickel-chromium alloy, and a dilute sulfuric acid solution is added to the additional anode cell. During electrolysis, the anion-exchange membrane passes anions into the additional anode cell from the electrolyte under the influence of electric current

and does not pass cations Ni ²⁺ and Cr ³⁺ .

In the process of electrolysis at the cathode, the following reactions proceed:

As can be seen from the equations, a nickel-chromium alloy can be deposited on the cathode according to reactions 1, 2, 5. Due to the high polarization of the discharge of nickel, its potential easily reaches the chromium evolution potential in reaction 5.

On a nickel anode located in a glycol-ammonia electrolyte, the reaction will occur:

On an insoluble (lead) anode located in an additional anode cell, the reaction will occur:

раствор в дополнительной анодной ячейке будет подкисляться. Поэтому периодически часть раствора серной кислоты будет отбираться из дополнительной анодной ячейки и направляться на приготовление раствора декапирования. Взамен отобранной кислоты в дополнительную анодную ячейку вводится дистиллированная вода.As a result of reaction 8 and the transition from the volume of the electrolyte to an additional anode cell of anions

the solution in the additional anode cell will be acidified. Therefore, periodically, part of the sulfuric acid solution will be taken from the additional anode cell and sent to the preparation of the decapitation solution. Instead of the selected acid, distilled water is introduced into the additional anode cell.

To maintain the concentration of nickel in the electrolyte in the given parameters, it is necessary to maintain certain ratios of currents going to the nickel and insoluble (lead) anodes taking into account electrochemical equivalents, the current yield of the alloy and the chromium content in the alloy.

The total current in the bath is equal to:

where I _spl - current going to the deposition of the alloy. The current yield of the alloy is 20%, therefore, the current flowing to the selection of the alloy is 20% of the total current, that is, I _sp = 0.20 · I _vol .

I _n2 - current _flowing to the evolution of hydrogen, I _H2 = 0.80 · I _rev ;

- current flowing to the nickel anode, in relative units:

where m _Ni - the mass of nickel in the alloy in fractions is 0.85, that is, the nickel content in the alloy is 85%;

- current flowing to the insoluble (lead) anode for the deposition of chromium at the cathode, in relative units:

where m _Cr is the mass of chromium in the alloy in fractions of 0.15, that is, the chromium content in the alloy is 15%;

K _Ni and K _Cr are the electrochemical equivalents of nickel and chromium (III).

The total current spent on the release of Nickel, chromium and hydrogen is:

The total current at the anodes is divided in proportion to the release of nickel, chromium and hydrogen.

An insoluble (lead) anode is supplied

The nickel anode is fed

Thus, in order to maintain the nickel concentration in the electrolyte in the specified parameters, it is necessary from the current source through the divider to apply 0.15 · I _rev , A to the nickel anode, to the insoluble (lead) anode, which is in the additional cell - 0.85 I _rev , A. To maintain the concentration of chromium (III) in the electrolyte in the given parameters, it must be periodically adjusted for chromium (III) ions.

The electrolysis process is carried out at a temperature of 40-50 ° C. The choice of temperature 40-50 ° C due to the need for shiny coatings. If the temperature is below 30 ° C and above 60 ° C, matte or semi-shiny coatings are deposited on the cathode.

Example.

The method of electrochemical coating with a nickel-chromium alloy is carried out in an electrolyte of the composition (g / l): nickel sulfate - 200-250, nickel chloride - 40-50, potassium alum - 250, aminoacetic acid - 220-230, ammonium sulfate - 190-200, boric acid - 25-30, 1,4-butynediol, saccharin - 0.7-1.0, at pH 2.0-5.0.

Before starting electrolysis, a solution of sulfuric acid with a concentration of 30-50 g / l is poured into an additional anode cell. The electrolyte and sulfuric acid solution are heated to a temperature of 40-50 ° C. Nickel anodes are hung in the process bath, and insoluble (lead) anodes are added to the additional anode cells. Parts for coating are hung on the cathode rod and include current. The cathode density is set to 5-6 A / dm ² and, using a divider, the ratio of currents on nickel and insoluble (lead) anodes is 0.15: 0.85. Electrolysis is carried out to obtain a given coating thickness.

The proposed method provides a technical effect and can be carried out using means known in the art.

The composition of the electrolyte and the deposition mode affect the composition of the alloy, the current efficiency and appearance of the coating. With an increase in the concentration of chromium (III) in the electrolyte from 10 to 45 g / l and a current density of 4 and 6 A / dm ^2, its content in the alloy increases from 2 and 3%, respectively, to 13.5 and 14.7%.

The dependence of the chromium content in the alloy on the concentration of chromium (III) in the electrolyte with a high correlation coefficient obeys the polynomial equation:

the correlation coefficient is R ² = 0.9993.

Over the entire range of concentrations of chromium (III) in the electrolyte at a temperature of 40-60 ° C and a current density of 4 and 6 A / dm ^2, shiny coatings with nickel-chromium alloy densely coupled to the base are deposited on the cathode.

The current yield of the alloy with an increase in the concentration of chromium (III) in the electrolyte from 10 to 45 g / l at a current density of 4 and 6 A / dm ² decreases from 22.6 to 10.5% and from 26.1 to 14%, respectively. With increasing current density, the current output of the alloy increases.

The dependence of the alloy current output (W) on the concentration of chromium (III) obeys a polynomial dependence with a high value of the correlation coefficient

The correlation coefficient is R ² = 0.9969.

With increasing temperature from 20 to 60 ° C at a current density of 4 and 6 A / dm ^2, the chromium content in the alloy increases from 9.5 and 10.2 to 13 and 15%, respectively. The dependence of the chromium content in the alloy (%) on temperature obeys a polynomial dependence with high values of the correlation coefficients.

the correlation coefficient is R ² = 0.9997.

The current efficiency of the alloy with increasing temperature from 20 to 60 ° C at a current density of 4 and 6 A / dm ² increases linearly from 10.5% and 14% to 16.5% and 20%, respectively, that is, with increasing temperature and density current output alloy current increases.

Shiny coatings with nickel-chromium alloy are obtained at a temperature of 40 and 60 ° C and a current density of 4 and 6 A / dm ² . At temperatures below 35 ° C, matte coatings precipitate. Thus, it is possible to recommend an electrolyte temperature of 40-60 ° C and a current density of 4 and 6 A / dm ² .

With an increase in the pH of the electrolyte from 4.0 to 5.0, the chromium content in the alloy decreases, which is associated with an increase in the strength of the ammonia-glycolic complex. The dependence of the chromium content in the alloy on the pH of the electrolyte obeys a polynomial equation of the following form:

the correlation coefficient is R ² = 0.9983.

The current yield of the alloy increases almost linearly with increasing pH of the electrolyte, which is associated with a decrease in the chromium content in the alloy. In the pH range from 4.0 to 5.0 at a temperature of 60 ° C, a current density of 4.0-6.0 A / dm ² and a chromium (III) concentration of 35-45 g / l, shiny coatings are deposited with the alloy. At pH below 3.5 and above 5.5, less shiny coatings are deposited, which is associated with a deterioration in the quality of the shiny nickel coating.

To optimize the technological process of electrodeposition of the alloy, a multivariate equation was obtained that establishes the dependence of the optimization criterion with input parameters that affect the process.

For a nickel-chromium alloy, the optimization criterion is the composition of the alloy, and the input parameters are the concentration of chromium (III) in the electrolyte, current density, temperature and pH of the electrolyte. The mathematical model of the process is the regression equation that relates the optimization criterion - the composition of the alloy (y) with the input parameters (factors): concentration of chromium (III) in the electrolyte (x ₁ ), current density (x ₂ ), temperature (x ₃ ) and pH of the electrolyte (x ₄ ).

To optimize the electrolyte composition and deposition mode in order to obtain a nickel-chromium alloy with a content of 12-13% chromium, a four-factor experimental design method was used. Table 1 shows the factors affecting the change in the composition of the alloy, and their ranges of variation: x ₁ - concentration of chromium (III) in the electrolyte; x ₂ - current density, A / dm ² ; x ₃ - temperature, ° C; x ₄ is the pH of the electrolyte.

Table 1 Planning Conditions Factors x ₁ x ₂ x ₃ x ₄ Main level 35 5,0 thirty 4,5 Range of variation 5 1,0 10 0.5 Upper level 40 6.0 40 5,0 Lower level thirty 4.0 twenty 4.0

The optimization parameter is the percentage of chromium in the alloy (y), which should be 12-13%. Table 2 shows the data on the percentage of chromium in the alloy, calculated on the basis of a chemical analysis of the obtained alloys and the regression coefficients calculated on their basis.

table 2 The chromium content in the alloy,% Regression Equation Coefficients y ₁ = 6.5 Y ₉ = 8.6 b ₀ = 10.86 b ₂₃ = 0.04 Y ₂ = 8.3 y ₁₀ = 11.6 b ₁ = 1.46 b ₂₄ = 0.04 Y ₃ = 7.0 y ₁₁ = 10.3 b ₂ = 0.81 b ₃₄ = 0.11 y ₄ = 10.5 y ₁₂ = 13.3 b ₃ = 1.34 b ₁₂₃ = -0.11 ₅ = 8.2 Y ₁₃ = 11.5 b ₄ = l, 54 b ₁₂₄ = -0.11 ₆ = 11.2 y ₁₄ = 14.5 b _l2 = 0.11 b ₁₃₄ = -0.04 Y ₇ = 9.9 y ₁₅ = 13.2 b ₁₃ = 0.04 b ₂₃₄ = -0.04 ₈ = 12.9 y ₁₆ = 16.2 b ₁₄ = 0.04 b ₁₂₃₄ = 0.11

After finding the coefficients of the regression equation, their significance was checked by Student's criterion. For this, three parallel experiments were set in the center of the plan at the basic level for all factors. The results of a chemical analysis of the obtained nickel-chromium alloys showed that the alloy contains chromium at ₁ = 11.4, at ₂ = 11.9, and at ₃ = 12.4.

As a result of the verification, insignificant coefficients of the regression equation were discarded, and the obtained model was checked for adequacy by the Fisher criterion.

The regression equation, adequately describing the influence of technological factors on the composition of the nickel-chromium alloy, has the form:

As can be seen from the equation, the composition of the alloy is largely influenced by single factors: the concentration of chromium (III) in the electrolyte, current density, temperature and pH of the electrolyte. To a lesser extent, interaction factors influence: the concentration of chromium (III) in the electrolyte is the current density, the temperature is the pH of the electrolyte, the concentration of chromium in the electrolyte is the current density is the temperature, the concentration of chromium (III) in the electrolyte is the current density is the pH of the electrolyte. This influence of factors on the composition of the coating allows the alloy composition to be maintained within the specified limits during the electrodeposition process by changing the deposition mode without resorting to correction of the electrolyte with chromium (III) salts.

The derived one-factor polynomial equations of the dependence of the composition of the alloy on the concentration of chromium (III) in the electrolyte, current density, temperature and pH of the electrolyte, as well as the four-factor regression equation, are used to automatically maintain and control the composition of the alloy, and therefore, the properties of the nickel-chromium plating during their deposition on automated lines.

Thus, the optimal electrolysis conditions for obtaining brilliant coatings with a nickel-chromium alloy are: current density 4.0-6.0 A / dm ² , temperature 40-60 ° C, pH 4.0-5.0.

Information sources

1. Kudryavtsev N.T. Electrolytic deposition of chromium and its alloys // Itogi Nauki. Chemistry, electrochemistry, electrodeposition of metals and alloys. - M .: AN USSR. - 1966. - S.209-229.

2. AC 136992 USSR / Stepanov S.G., Malkova S.A. (R.F.) // Bull. Fig. - 1961.

3. Soboleva LI, Tsupak TE, Kudryavtsev N. T. // Transactions of Moscow Institute of Chemical Technology D.I. Mendeleev. - 1969. - Issue 62. - S. 191-192.

4. The USSR AS No. 144442 / Kudryavtsev N.T., Pshilussky A.B. (R.F.) // Bull. Fig. - 1962.

Claims (1)

The method of electrodeposition of coatings with a nickel-chromium alloy, including the electrolysis of an aqueous solution of nickel sulfate, aminoacetic acid, characterized in that the electrolyte additionally contains chromium potassium alum, 1.4 butynediol, saccharin, boric acid, ammonium sulfate, the pH of the electrolyte is maintained within 2.0- 5.0, and the insoluble lead anode is placed in an additional anode cell with a solution of sulfuric acid and an anion-exchange separation membrane MA-40.

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