RU2349686C1 - Method of electro-deposition of alloy coatings of cobalt-nickel - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: method involves electrolysis of an aqueous solution of cobalt sulphate, nickel sulphate, boric acid and potassium chloride. Electrolysis is carried out after magneto-hydrodynamic activation of the whole volume of the electrolyte with a permanent or alternating electromagnetic field outside the plating bath with electromagnetic field strength of 80-200 kA/m and the value of magnetic induction 0.10-0.25 T with the electrolyte circulating at a speed of 0.5-2.5 m/s.

EFFECT: increase in the operating current density, coulomb efficiency, micro-hardness and wear resistance of the alloy coating of cobalt-nickel on different objects.

4 tbl, 1 ex, 4 dwg

Description

The proposed method relates to the technology of electrochemical production and can be used to intensify the process of electrodeposition, increase microhardness and wear resistance of cobalt-nickel alloy coatings.

A known method of conducting electrolysis [1], in which a constant electric current is supplied to the electrodes immersed in the electrolyte, which creates a constant electric field in the interelectrode space, and at the same time a constant magnetic field is created in the interelectrode space with magnetic lines intersecting the lines of force of the electric field .

There are also known methods of magnetizing liquids in technological processes [2-3], which can be used in the purification of additional water from steam-powered plants, reverse cooling systems and water to feed heating networks.

However, these methods are not intended to obtain electroplated coatings, since, if there are steel parts for the coating in the electrolyte, the magnetic lines of force will not go through the electrolyte, but directly through the steel part and there will be no effect of magneto-hydrodynamic activation of the electrolyte.

A disadvantage of the known methods is that electromagnetic processing is performed to purify water. The use of magnetized water in the preparation of electrolytes for the deposition of metals and alloys does not give positive results. So, the working current density of the deposition of cobalt-nickel alloy from an electrolyte prepared on water magnetized by an electromagnetic device has not changed.

Of the known closest in technological essence is the method of electrodeposition of coatings with a cobalt-nickel alloy from an electrolyte of the following composition [4] in g / l: cobalt sulfate 130-140; nickel sulfate 110-120; boric acid 20-30; potassium chloride 10-15; the pH of the electrolyte is 4.0-5.0; the temperature of the electrolyte is 50-60 ° C, according to which the coatings are deposited at a working current density of 1-1.5 A / dm ² .

The disadvantage of this method is that the electrodeposition is carried out at elevated temperature and low current densities, i.e. the deposition rate of the coating with a cobalt-nickel alloy is small.

The technical result of the proposed method is to increase the working current density, current efficiency, microhardness and wear resistance of cobalt-nickel alloy coatings during plating of various parts, including steel.

The essence of the proposed method is to conduct electrodeposition of cobalt-nickel alloys, in which a constant electric current is applied to the electrodes immersed in the electrolyte, creating a constant electric field in the interelectrode space, the method differs in that magnetohydrodynamic activation of the electrolyte is carried out outside the galvanic bath.

A magnetic device creates a constant or alternating magnetic field with a strength of 80-200 kA / m and a magnitude of magnetic induction of 0.10-0.25 T, the lines of force of which cross an electrolyte circulating at a speed of 0.5-2.5 m / s from galvanic bathtubs in polymer pipes with a diameter of 20 mm, located between the poles of the electromagnetic device.

This combination of new features with the known ones makes it possible to increase the working current density of the electrodeposition of a cobalt-nickel alloy, current efficiency, microhardness, wear resistance and gloss of coatings.

The proposed method of electrochemical deposition of plating alloys is illustrated by drawings.

Figure 1 shows a diagram of its implementation: 1 - anodes; 2 - cathode; 3 - galvanic bath; 4 - adjustable pump; 5 - case; 6 - coils; 7 - core; 8 - pipeline of polymer pipes.

Figure 2 shows a device for magnetohydrodynamic activation of an electrolyte.

A device for magnetohydrodynamic activation of an electrolyte consists of a housing (5) in which an electromagnet is placed. Polymer pipes (8) are located in the gap between the poles of the electromagnet, through which the electrolyte circulates at a speed of 0.5-2.5 m / s. The electrolyte is affected by a magnetic field with a strength of 80-200 kA / m with a magnetic induction of 0.1-0.25 T.

The method is as follows. At the beginning of the process, an electrolyte is poured into a galvanic bath to precipitate a cobalt-nickel alloy, the composition of which is shown in Table 1. Next, a device for magnetohydrodynamic activation of the electrolyte is included. After magnetohydrodynamic activation of the entire electrolyte volume, the electrolysis process begins.

Table 1 - Electrolyte composition for electrodeposition of a cobalt-nickel alloy. Electrolyte components Concentration, g / l Cobalt sulfate (for metal) thirty Nickel sulfate (for metal) 17-25 Boric acid 25 Potassium chloride 5

Magnetohydrodynamic activation of the electrolyte leads to an increase in the current density of the electrodeposition of shiny coatings. So, when coating from an electrolyte after magnetohydrodynamic activation, shiny coatings are deposited to a current density of 4-4.5 A / dm ² , which is 2 times higher than when deposited from an inactive electrolyte. When electrodeposited from an electrolyte after magnetohydrodynamic activation, precipitates are formed with a finer-grained and uniform structure (Fig. 3), which contributes to the production of brilliant coatings.

Magnetohydrodynamic activation of the electrolyte increases the nickel content in the alloy and significantly increases the current efficiency of the alloy, compared with electrodeposition from an inactive electrolyte. So, the nickel content in the alloy at a nickel concentration of 25 g / l in the electrolyte, an electrolyte temperature of 20 ° C, an electrodeposition current density of 3 A / dm ² and an electrolyte pH of 4.5, respectively, are: 25% from the electrolyte after magnetohydrodynamic activation and not activated electrolyte - 22%. An increase in the nickel content in the alloy as compared to precipitation from an inactive electrolyte is due to a decrease in the polarization of the discharge stage, to which nickel is more susceptible. A decrease in the polarization of the discharge stage is associated with an increase in the mobility of ions. An increase in the mobility of ions leads to an increase in the electrical conductivity of the solution after magnetohydrodynamic activation. So, after magnetohydrodynamic processing of the electrolyte, the electrical conductivity increased from 0.495 S / m to 0.525 S / m. Spectrophotometric studies showed that the composition of cobalt and nickel ions did not change (Fig. 4). The increase in current efficiency can be explained by an increase in the overvoltage of hydrogen evolution at the cathode due to an increase in the nickel content in the alloy. The current efficiency for the above electrodeposition conditions is: 98% from electrolyte after magnetohydrodynamic activation and 92% from non-activated electrolyte.

During electrodeposition of a cobalt-nickel alloy from an electrolyte after magnetohydrodynamic activation, an increase in the microhardness and wear resistance of coatings is observed.

The microhardness of galvanic coatings with a cobalt-nickel alloy obtained at an electrodeposition current density of 3 A / dm ² , an electrolyte pH of 4.5 and an electrolyte temperature of 20 ° C from an electrolyte after magnetohydrodynamic activation and from an inactive electrolyte, respectively, is equal to 5.4 GPa and 4.6 GPa The increase in microhardness of precipitates obtained from the electrolyte after magnetohydrodynamic activation is explained by the production of finer-grained coatings (figure 3).

The wear resistance of cobalt-nickel alloy coatings obtained from an electrolyte after magnetohydrodynamic activation and from an inactive electrolyte under a 2H contact load is 115,000 and 90,000 cycles, respectively. All precipitates were obtained at an electrodeposition current density of 3 A / dm ² , an electrolyte temperature of 20 ° C and an electrolyte pH of 4.5. An increase in the wear resistance of an alloy obtained from an electrolyte after magnetohydrodynamic activation relative to a coating of an alloy obtained from an inactive electrolyte is associated with a finer-grained structure of the coatings.

The magnetic properties of cobalt-nickel alloy coatings from electrolyte after magnetohydrodynamic activation and from non-activated electrolyte with a thickness of 1 μm and electrodeposition mode: current density 3 A / dm ² , electrolyte temperature 20 ° C, pH 4.5 are presented in table 2.

Table 2 - Magnetic properties of the alloy cobalt-Nickel The properties Stationary mode A magnetic field Coercive force, kA / m 14.5 16 Residual magnetization, T 0.8 one Hysteresis loop squareness coefficient 0.67 0.71

The improvement of the magnetic properties of the coating with a cobalt-nickel alloy obtained from an electrolyte after magnetohydrodynamic activation relative to a coating obtained in a stationary mode can be explained by a more uniform microstructure of the coating obtained from an activated electrolyte.

Thus, the magnetohydrodynamic activation of the electrolyte makes it possible to increase the process productivity, current efficiency, microhardness, wear resistance and gloss of cobalt-nickel alloy coatings, as well as improve its magnetic properties.

Example.

The method of electrodeposition of a cobalt-nickel alloy is carried out in an electrolyte of the following composition (g / l): cobalt sulfate (for metal) 30; nickel sulfate (for metal) 25; boric acid 25; potassium chloride 5; electrolyte pH 4.5; electrolyte temperature 20 ° C; at a working current density of 3 A / dm ² activated by an electromagnetic device with a magnetic field of 80 kA / m, a magnetic induction of 0.1 T and an electrolyte circulation rate of 0.5 m / s through polymer pipes with a diameter of 20 mm.

Under such conditions, electrodeposition coatings contain 25% nickel. The current efficiency of the alloy is 98%. The microhardness of the coating is 5.4 GPa, the wear resistance is 115,000 cycles with a contact load of 2 N. Magnetic properties of the coating: coercive force 16 kA / m; residual magnetization of 1 T; the coefficient of rectangularity of the hysteresis loop is 0.71.

The technical result of the proposed method is to increase the working current density by 2 times, current efficiency by 6%, microhardness by 15%, wear resistance by 22%, and also improve the magnetic properties of coatings with cobalt-nickel alloy.

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.

When conducting electrodeposition from an electrolyte after magnetohydrodynamic activation, an increase in the nickel concentration in the electrolyte is from 17 to 25 g / l, at a constant cobalt concentration of 30 g / l, electrodeposition current density is 3 A / dm ² , the electrolyte temperature is 20 ° C and the electrolyte pH is 4.5 leads to an increase in the nickel content in the alloy from 21% to 25%. An increase in the nickel content in the alloy leads to an increase in current efficiency, which for the same nickel concentrations in the electrolyte is 95% and 98%.

An increase in the electrodeposition current density from 1 to 4 A / dm ² (at a nickel concentration in the electrolyte of 25 g / l, an electrolyte temperature of 20 ° C and an electrolyte pH of 4.5) leads to an increase in the nickel content in the alloy from 22% to 26%. The current efficiency of the alloy also increases due to an increase in the overvoltage of hydrogen evolution due to an increase in the nickel content in the alloy.

An increase in the electrolyte temperature (electrodeposition current density of 3 A / dm ² , nickel concentration in the electrolyte is 25 g / l, electrolyte pH 4.5) from 20 ° C to 40 ° C leads to an increase in the nickel content in the alloy from 25% to 27%. The current yield of the alloy increases accordingly from 98% to 99%.

When changing the pH of the electrolyte from 4 to 5, the composition of the alloy and the current efficiency change slightly. The nickel content in the alloy is 25%, the current efficiency is 98%, at an electrodeposition current density of 3 A / dm ² , an electrolyte temperature of 20 ° C and an electrolyte pH of 4.5.

During electrodeposition of an alloy from an electrolyte after magnetohydrodynamic activation, shiny coatings well adhered to the base are deposited to an electrodeposition current density of 4-4.5 A / dm ² .

To automate the process, mathematical dependences were obtained with a high correlation coefficient, linking the nickel content in the alloy with the concentration of nickel in the electrolyte (table 3) and the temperature of the electrolyte (table 4).

Table 3 - Mathematical dependences of the nickel content in the alloy on the concentration of nickel in the electrolyte and current density during electrolysis from the electrolyte after magnetohydrodynamic activation. The current density, A / DM ² Mathematical dependence Correlation coefficient one [Ni] _spl = 18.05Ln ([Ni ²⁺ ]) - 36.49 0.98 2 [Ni] _spg = 15.53Ln ([Ni ²⁺ ]) - 26.15 0.99 3 [Ni] _spl = 10.35Ln ([Ni ²⁺ ]) - 8.43 0.99 four [Ni] _spl = 7.84Ln ([Ni ²⁺ ]) + 0.89 0.99

Table 4 - Mathematical dependences of the nickel content in the alloy on the electrolyte temperature and current density during electrolysis from the electrolyte after magnetohydrodynamic activation. The current density, A / DM ² Mathematical dependence Correlation coefficient one [Ni] _sp = 2.87Ln ([t °]) + 13.31 0.99 2 [Ni] _sp = 2.87Ln ([t °]) + 15.32 0.99 3 [Ni] _sp = 2.87Ln ([t °]) + 16.32 0.99 four [Ni] _sp = 2.87Ln ([t °]) + 17.31 0.99

The derived one-factor equations for the dependence of the alloy composition on the concentration of nickel in the electrolyte, current density, and temperature of the electrolyte obey the logarithmic law and serve to automatically maintain and control the composition of the alloy and, therefore, the properties of the electroplated coating with cobalt-nickel alloy when they are deposited on automated lines.

Thus, when conducting electrolysis from an electrolyte after magnetohydrodynamic activation, the working range of the current density of obtaining shiny coatings is doubled, the current efficiency of the alloy, microhardness, wear resistance are increased, the magnetic characteristics and appearance of the coatings by the cobalt-nickel alloy are improved.

Information sources

1. Application for invention 2005102507/15 Russia, IPC С02F 1/48. Method and device for electrolysis / Nedkov I.V.

2. Application for invention 2002126517/15 Russia, IPC ⁷ C02F 1/48. A method of treating an electrolyte with an electric and magnetic field and a device for its implementation / Bulgakov BB, Bulgakov AB, Gurvich GA

3. Application for invention 2003112893/15 Russia, IPC ⁷ C02F 1/48. Device for magnetic processing of liquids / Kibirev D.I., Kitanov S.E., Kunevich A.V., Kuprikov N.P., Nikiforov G.I., Podolsky A.V.

4. Melnikov P.S. Handbook of Electroplating in Mechanical Engineering. - M.: Mechanical Engineering, 1979. - 296 p.

Claims (1)

Method of electrodeposition of cobalt-nickel alloy coatings, including electrolysis of an aqueous solution of cobalt sulfate, nickel sulfate, boric acid and potassium chloride, characterized in that the electrolysis is carried out after magnetohydrodynamic activation of the entire electrolyte volume by a constant or alternating electromagnetic field outside a galvanic bath with an electromagnetic field of 80- 200 kA / m and a magnitude of magnetic induction of 0.10-0.25 T during the circulation of the electrolyte at a speed of 0.5-2.5 m / s.

Images