RU1786189C - Method to determine the rate of current-free reduction of nickel - Google Patents

Abstract

Usage: continuous monitoring of the process. Currentless deposition of nickel coatings, increasing accuracy and simplifying the process of measuring nickel plating, maintaining a high deposition rate and improving the quality of the coating. The essence of the method lies in the fact that they carry out the polarization of the witness anode with pulses of duration 5 with an anode current density that determines the tangent of the slope of the tangent to the dependence curve (t) of at least 5 V / s and determines the speed using the formula Ј A1 T9 No. V P 1d 2 tg p where v is the current rate of the currentless reduction of nickel, µm / h; q is the electrochemical equivalent of nickel, g / A x; p is the density of the reduced nickel coating, g / cm3; IA- and) D2 - anode current densities, A / dm2; tg p and tg (pi are the tangents of the angles of inclination of the tangents to the dependence curve (t), V / s. 8 il. eat С х | 00 о 00 о

Description

The invention relates to the deposition of chemical coatings on various products, especially complex ones, and powder materials with the aim of hardening the bearing surfaces of parts, restoring worn parts, the use of abrasive metals: ifas; free-flowing powders and a diamond-abrasive tool.

Chemical coatings and composites based on chemical nickel

allows to increase the service life of parts subject to accelerated wear from 2-5 to 10-20 times, thereby reducing material and labor costs for the manufacture of new products and their processing.

The use of diamond, cubonite or other refractory powder materials with coatings in the tool and free state allows to increase the productivity of processing various

hard materials 2-5 times.

In addition, the process of chemical reduction of nickel in its chemistry and kinetics is very complex and unstable in 5 times. In this regard, the automation of the process and its control are very relevant. The invention allows directly and precisely during the chemical reduction process 10 to determine and control the rate of nickel evolution by applying short-term anode current pulses to the witness anode and fixing them simultaneously by applying pulses of the functional dependence E f (t) followed by mathematical processing of the curves to estimate the numerical values of the nickel deposition rate, coating thickness, and production the main components of the solution. 20

The proposed method allows continuous and accurate control of the process, timely correction of the solution and maintain a practically constant deposition rate, to improve the quality of the coating.

A gravimetric method for determining the rate of chemical reduction is known. The mass of precipitated nickel was determined using an apparatus for automatically controlling the weight gain of the sample during the experiment. The sensitive element of the installation - a diode mechanotron with a hanging anode of 6MX2B grade is switched on according to a symmetrical bridge circuit. The mechanical circuit 35 of this apparatus is designed based on a hydrostatic weighing apparatus.

Given the weight gain of the deposited metal in a fixed time and surface area of 40, the rate of reduction reaction is calculated.

Significant disadvantages of the method are as follows: the gravimetric method for controlling the speed is only suitable for 45 laboratory tests and completely unsuitable for serial production; the method does not allow measuring the reaction rate without reaching a certain coating mass exceeding the 50 measurement limits of the weights used.

A known method for determining the rate of chemical nickel plating is based on the use of an apparatus for assessing the rate of vacuum deposition of metals. 55

The method is based on irradiating the deposited coating of electron beams and calculating the thickness by broadening the x-ray lines. Significant disadvantages of this method are the complexity of the hardware design; the need for additional protection against ionized radiation.

The closest analogue (prototype) of the proposed method is the coulostatic method for evaluating the currentless deposition process 4. The essence of the method is as follows.

A test sample is immersed in a chemical reduction bath. At the same time, it is polarized through an auxiliary electrode to a polarization potential tj () of several millivolts. At the end of the polarization, the dependence is measured) and the polarization resistance of the reaction is calculated from the CRI. After the potential (f (t)) returns to the potential of the EELP reaction, the test sample is again polarized to a polarization voltage of 50 mV or more. From this curve, the anode coefficient Tuffel of the reaction () is calculated. After the potential returns to the reaction potential, the sample is again polarized until a voltage of 50 Mv or more is reached, and the A-f} dependence is again obtained. From this curve, the cathode coefficient of the Tuffel reaction (bs) is calculated. Given the magnitude of the polarization resistance of the reaction (RELP) and the Tuffel coefficients (NaaI // s), the magnitude of the reaction current density is calculated: -, D, &

lELP 2,3) RELP where / For - Tuffel coefficient (anode);

 - Tuffel coefficient (cathode);

RELP - polarization resistance.

Hence, the rate of the chemical reduction reaction is determined by the formula M

Where

VELP M

P

IELP

- electrochemical equivalent

n F nickel;

IELP is the current density of the reaction.

A disadvantage of the known method is that it is necessary to simultaneously obtain at least three electrochemical characteristics using several modes of polarization from the calculation of polarization resistance and Tuffel coefficients.

In addition, the nature (type of complexation) of a chemical metallization solution has a significant influence on the accuracy of determining the deposition rate.

The measurement accuracy is therefore reduced by 15-20%. Thus, the method is not universal and is more of a private nature of determining the rate for a given composition of a solution (a given process), i.e. in each case, using several polarization modes, it is necessary to calculate the partial values of the polarization resistance.

The purpose of the invention is to improve the accuracy of continuous monitoring of the recovery process, simplify mathematical processing, maintain a constant high deposition rate and improve the quality of the coating.

The goal is achieved in that in the method for determining the current rate of nickel recovery, including polarization of the witness anode with short pulses, recording the curves (t), their mathematical processing, according to the invention, the polarization of the witness anode is carried out with pulses of duration - with an anode density AI current, 1d2. determining the tangents of the slope angles tg (p and tg p2 of the tangents to the curves of dependence (t) of at least 5 V / s, and the mathematical processing is carried out according to

g i-Ai tq (- JA2 tg p .Ptg (pi tg p where v is the current rate of the currentless nickel reduction;

q is the electrochemical equivalent of nickel;

p is the density of the Nickel-phosphorus alloy;

| D2, AI - anode current density;

tg pr, tg (pi are the tangents of the slope of the tangents to the curve of the dependence E f (t).

As the patent studies have shown, the proposed features are not known, the invention hardly meets the criterion of significant differences.

As will be shown below (see examples), when going beyond the proposed limits, the object of the invention is not achieved.

In FIG. 1 shows a diagram of a device that implements the proposed method; in FIG. 2.4-8 are given the dependence curves (t); in FIG. Figure 3 shows histograms of the rate of recovery over time.

A device that implements the method comprises an electrochemical cell 1 (see Fig. 1), an auxiliary electrode 2, a reference electrode 3 and a working electrode 4 acting as a witness anode (witness sample). The device also cov Ј

holds a switching power supply 5 and a recording device 6.

Sample 4 must have a pre-polished surface, so that the active surface being coated is as close as possible to the true one, with a thin layer of deposited chemical nickel.

The method is carried out as follows.

From a switching power supply through an auxiliary electrode 2, a series of short-duration pulses of a duration of 5

5 10 -5 10 by its anode current density, which determines the tangent of the slope of the tangent to the dependence (t) of at least 5 V / s. For this, two or three test pulses are applied with an increasing density of the anode current, fixing on the recording device 6 for each pulse tg of the angle of inclination of the tangent to the dependence (t). The anode current density at which tg ip is reached - 5 V / s and somewhat more is basic

5 to determine the rate of chemical nickel plating of this solution. It should also be taken into account that the reaction potential has a stable value of Ep (Fig. 2) and is determined only by the composition of the solution. Therefore, pulsed polarization of the anode should begin at its steady state value.

Thus, having reached the base value igtp angle; 5 V / s (tg p) and fixing the corresponding anodic current density (IAI), the next pulsed polarization of the witness sample is carried out with the same pulse duration of -5-10 s and the corresponding fixation tg (p2 and 1d2. tg p tg yes, but

.

In FIG. 2 shows typical curves of dependence (t),

where to is the start time of pulsed polarization 5;

And - the time to establish the required current density on the witness sample;

t2 the end time of the pulse,

T.e.t2-to 5-10 4-5-10 3c,

Knowing the values of tg p and tg pi (tg).

we determine the cathode current density 1k i.e. such a current density at which the same amount of metal is released during equal time during electrolysis, with a current output of 100%, according to the formula

 Ai tQ (pi - JA2; tg if tg pi - tg $

(3)

The current rate of the currentless nickel reduction will then be determined by A

v

AND

z-f-

(4)

where p q is the electrochemical equivalent of nickel;

p is the density of nickel, or

8 1k (μm / h).

As the analysis of the errors found as the ratio of the theoretical values of speed to the practical one determined by the gravimetric method shows, only the measurement limits given in the proposed method allow us to obtain reliable values with the least error.

Thus, knowing the value of the reaction current of nickel-free reduction of nickel, the composition of the solution used / the operating parameters of the bath, it is easy to calculate the decrease in the main components, timely and accurately adjust the solution and obtain the required coating quality.

For example, it is known that the volume of a chemical nickel plating bath is 50 l (v). We cover the surface of the parts - dm2 (cm2). The composition of the solution includes NiSCM 7H20 30 g / l, NaH2PO H20 20 g / l and a certain amount of complexing agents, ligands and stabilizer, phosphorus content in the coating is 8%;

According to the speed measurement data, the amount of nickel salt and reducing agent required to make up for the decrease in reaction rate should be calculated with a hypophosphite utilization factor of 0.4. The speed measurement time is every 10 minutes for 1 hour.

As a result of measurements and calculation of the reaction speed of the currentless nickel release, it was found that the average speed over time t was 25 µm / h (see Fig. 3).

During this time, the VnoKp SnoB coating volume precipitated. ; 5covers The thickness Inonp is determined by the velocity data

 25 -10 4 17, 17. cm.

cover 60

VnoKp 1 10 4 .Yu. M.P. Coating weight: (g / cm3) V, v tpocr 4.17 ",, 3Ј g, .. Hence pure nickel: (100-8) 92% or 33.36" 0, 69 (NI) 30.69

or

59

- 0.52 mmol.

At 0.52 mmol of nickel, taking into account the utilization rate of hypophosphite consumed 52

or 1.3., 84 (g) of hypophosphite was used. Nickel salts 0.52-280, 07 (g).

Thus, for correction after 10 minutes, it is necessary to add a solution containing in its composition NaH2P02 H20 137.84 g NIS04-7H20; 146.07 g

- The whole process of measuring speed, calculating data, correcting the solution can be fully automated with the appropriate hardware design using computer equipment associated with devices responsible for correcting the solution, supplying anode pulses, recording the electrode potential,

In addition, it is known that without adjustment or continuous drip adjustment, the nickel rate decreases rapidly and most often due to inaccurate vision of the process, the solution completely decomposes spontaneously. Invention

It allows you to clearly control the process over time, maintain a high deposition rate and obtain good coating quality for a long time with repeated use of the solution.

Examples of specific performance. Example 1. Measurements are carried out according to the scheme shown in FIG. 1. In the bathtub where the chemical metallization process is carried out, an anode witness 2 is placed with an area of 0.02-0.05 dm. Using the base complex of the potentiostat of the brand PI 50-1.1 or another similar to him, providing feed

pulse signal, fed to the witness anode, the first pulse lasting 5-10 s and a current density (IA) of 2 A / dm2. Fix the dependence E-f (t) on the screen of the storage oscilloscope (RP),

for example, grades C9-8 (Fig. 4). In this case, when using the lower limit of the pulse duration and low current density, the dependence (t) will have the form (see Fig; 4), where

Ep is the potential of the currentless nickel reduction reaction (const for a given solution);

to - pulse start time (reference point):, ....

ti-time of installation on the witness specimen asked and:

ts is the pulse stop time.

I1

After determining tg p -t-, a second pulse is supplied with a density of lechek, 37

A / dm2 and tg {% -tg 8.7 V / s,

32 b

The obtained numerical data are substituted into the formula (3) and the nickel current density is determined

i IAI tg (pi - 2 tg tg pi - tg p

2 -8.7 -2.37-5

 1.5 (A / dm2).

8.7 - 5

Then the reaction speed of the currentless nickel reduction will be equal to A

10

fifteen

v

of a pot, the volume of electrolyte, the total surface area to be coated and the process speed at any time, the production of components, the utilization rate of the nickel salt and reducing agent are calculated. According to the results obtained, the solution is adjusted. The above control of the currentless nickel reduction process allows one to obtain high-quality ones with good adhesion to the coating surface.

Example 3. Measurements are carried out according to the scheme shown in FIG. 1. The area of the witness anode is 0.02-0.05 dm2. First served on the anode witness first

twenty

IK 13.8-1.5-20.7 (μm / g). Po- pulse of 2 s and /

current density, 18 A / dm2. The dependence (t) is recorded on the oscilloscope screen

(Fig. 6) .0 limit tg rh 5 (V / s). We feed a second pulse with a current density of 1, 55A / dm2

32

and determine 7.4 (V / s). Received.

numerical data are used to calculate 25 current density and nickel plating rate

Z-F-p determination error is 1%,

The error was determined in comparison with the gravimetric method for determining the rate of reduction of chemical nickel.

Knowing the loading of the working bath, the total surface area to be coated and the speed of the process at any time, the production of components, the utilization rate of the basic salt and reducing agent are calculated. The results obtained make it possible to carry out strict adjustment of the solution, thereby maintaining a high (close to the initial) process speed and the required coating quality,

The tangent to the dependence curve (t) in this case practically coincides with the curve itself,

Example 2. Measurements are carried out according to the circuit shown in FIG. 1, An anode witness with an area of 0.02-0.05 dm2 is placed in the working bath. As in Example 1, the anode-witness is polarized with the first pulse signal with a duration of c and a current density of OAI) equal to 2.18 A / dm2. The dependence (t), which will have the form (see Fig. 5), is fixed on the screen of the storage device,

After determining tg tp tr. supply a second pulse with a current density of 9

NWF

A / dm and determine tg # 2, 1 V / s.

The obtained numerical data are substituted into formulas (3) and (4) to determine the nickel current density and reduction rate

2.18 -7.4 -2.55

thirty

35

40

45

fifty

2.18

to - ---

10.1 -2.9 -5

 1,471 (A / dm2)

55

10.1 -5, 8.1,, 3 (μm / h). In this experiment, the measurement error (A) is 1.0%. Know the loading. RA-7 G5 --- 1-406 (A / dm2),

, 8 1,, 4 (μm / h) ./

The measurement error in this experiment is D 5.4%. Having specific values for the speed of the currentless nickel reduction process and bath loading data, the solution is adjusted in a timely manner, maintaining a high deposition rate and the required coating quality. The utilization rate of nickel salt is 8.6%, and the reducing agent is 56%.

Example 4. All measurements were carried out according to the procedure described in examples 1-3.

Using the base complex of the potentiostat, a first pulse of 2.510 s duration with an anode current density of 18 A / dm 2 is applied to the witness anode. The dependence (t) is fixed (see Fig. 7), tg (p- 64 (V / c) A second pulse is supplied with a current density of 9 A / dm2 and determined

(B / c).

The current density and the speed of the currentless nickel plating are calculated 2.18 -89 -2.9 89 -64

1 to

§1 o, 34 (A / dm2)

.8 0,, 6 (μm / h). The experimental error is D 77%. Thus, with a decrease in pro0

5

of a pot, the volume of electrolyte, the total surface area to be coated and the process speed at any time, the production of components, the utilization rate of the nickel salt and reducing agent are calculated. According to the results obtained, the solution is adjusted. The above control of the currentless nickel reduction process allows one to obtain high-quality ones with good adhesion to the coating surface.

Example 3. Measurements are carried out according to the scheme shown in FIG. 1. The area of the witness anode is 0.02-0.05 dm2. First served on the anode witness first

pulse duration 2 s and

2.18 -7.4 -2.55

0

5

0

5

0

5

-7 G5 --- 1-406 (A / dm2),

, 8 1,, 4 (μm / h) ./

The measurement error in this experiment is D 5.4%. Having specific values for the speed of the currentless nickel reduction process and bath loading data, the solution is adjusted in a timely manner, maintaining a high deposition rate and the required coating quality. The utilization rate of nickel salt is 8.6%, and the reducing agent is 56%.

Example 4. All measurements were carried out according to the procedure described in examples 1-3.

Using the base complex of the potentiostat, a first pulse of 2.510 s duration with an anode current density of 18 A / dm 2 is applied to the witness anode. The dependence (t) is fixed (see Fig. 7), tg (p- 64 (V / c) A second pulse is supplied with a current density of 9 A / dm2 and determined

(B / c).

The current density and the speed of the currentless nickel plating are calculated 2.18 -89 -2.9 89 -64

1 to

§1 o, 34 (A / dm2)

.8 0,, 6 (μm / h). The experimental error is D 77%. Thus, when the pulse duration is shorter than the suggested one, the calculated values of current density and recovery rate are not reliable. This is due to the fact that with such a small value of the pulse time, the constant current density cannot be established on the witness sample (Fig. 7). Therefore, the tangent to the curve of dependence (t) reflects only the growth rate of the current density at the electrode. :

Example 5. All measurements were carried out according to the procedure described in examples 1-3.

A pulse with a duration of 5-10 is supplied to its anode-witness with its anode current density, 18 A / dm. The dependence E f (t) is fixed, and tg is calculated (p 31 V / s. A second pulse is supplied with a current density of 5 A / dm2 and tg 952 17 is calculated

w / c ..; .. - .-. . ,:

Nickel plating current density and current recovery process are determined

, 297 A / dm2.

8 0, 97 (μm / g).

The error (experimental measurement is 3.2%).

This example shows the results of an experiment conducted from a similar chemical nickel plating solution, but at a lower reduction temperature.

Knowing the volume of the bath, the composition of the solution, the deposition rate and time, the surface area to be coated, the flow rate of the main components is calculated and the initial solution is adjusted.

The process speed is maintained almost at the initial level. The quality of the coating is stable. Thus, in comparison with the prototype, the proposed method allows to increase the accuracy of measuring the rate of chemical nickel plating with a minimum error, since the measurement process is universal for any solution composition and the output parameters do not depend on the nature of the components entering the solution / Mathematical processing of the obtained data and instrumentation is much simpler and easier to process.

Application of the proposed method for coating only parts of textile machines will provide an economic effect of 150 thousand rubles per machine TK-630.

Claims (1)

SUMMARY OF THE INVENTION A method for determining the speed of currentless nickel recovery, including polarization of the witness anode with short pulses, recording the curves (t), their metal processing, characterized in that, in order to increase the reaction rate, polarization of the witness anode is carried out with pulses lasting 5 s with anode current density AI m 1d2, which determines the tangent of the slope angles tg pi with respect to the dependence E f (t) of at least 5 V / s, and the mathematical processing is carried out according to  5. A1 9 F2 A2 tg 1 P tg pz where v is the reaction rate of the currentless reduction of nickel, µm / h; q is the electrochemical equivalent of nickel, g / A.h; p is the density of reduced nickel, g / em; JAJ and 1d2 - anode current densities, A / dm2; tg f and tg pz are the tangents of the slope of the tangents to the dependence (t), V / s. FIG. I Re / g 2 z z z, z4 zf zsz Fig. E