JB/T 7704.6-1995 Test methods for electroplating solutions - Determination of polarization curves
Some standard content:
Mechanical Industry Standard of the People's Republic of China
Test Methods for Electroplating Solutions
Determination of Polarization Curves
Subject Content and Scope of Application
This standard specifies the method for measuring the polarization curve of electroplating solutions. This standard is applicable to the measurement of cathode and anode polarization curves of electroplating solutions. 2 Terminology
2.1 Polarization
JB/T 7704.6—95
The change of electrode potential during electrolysis. In this change, the anode potential is always more positive than its static potential (the potential when there is no current), and the cathode potential is more negative than its static potential. The polarization value is equal to the difference between the static potential and the dynamic potential, usually expressed in mV. 2.2 Polarization Curve
The curve of the relationship between the electrode potential and the current density passing through the electrode. 2.3 Liquid Interface Potential
The potential difference at the interface of two different electrolyte solutions in contact. 3 Overview
When measuring the polarization curve of the plating solution, if the current density is controlled at different constant values ??in turn and the electrode potential at the corresponding current density value is measured at the same time, the measured polarization curve is a constant current polarization curve. If the electrode potential is constant and the current density corresponding to its constant value is measured, the measured polarization curve is a constant potential polarization curve. Usually, both the constant current method and the constant potential method can be used to measure the polarization curve of a monotonic function (i.e., one current density corresponds to only one potential or one potential corresponds to only one current density) (e.g., Figure 1). However, when the electrode polarization in some electrode processes reaches a certain degree, the current density will reach a maximum value as the electrode polarization increases, and the constant current method cannot be used. Because in this electrode process, one current value may correspond to several electrode potential values, at this time, the constant potential method must be used to measure the true polarization curve (e.g., Figure 2). In actual measurement, the steady-state electrostatic potential method can be used, that is, the readings are measured point by point at a certain current (or potential) time interval. Steady-state dynamic potentiometry can also be used, that is, the current density or electrode potential is automatically and continuously changed in a slow scanning manner, and the relationship curve between the corresponding electrode potential and current density is automatically recorded. This standard mainly specifies the steady-state method for measuring polarization curves. I+
Figure 1 A cathode polarization curve
Approved by the Ministry of Machinery Industry on June 20, 1995
Figure 2 Anode polarization curve
Implementation on January 1, 1996
4 Factors affecting measurement results
4.1 Plating solution
JB/T 7704.6--95
Impurities (metallic impurities or organic impurities) in the plating solution will adsorb on the electrode surface and affect its electrochemical behavior, causing great interference to the measurement. Therefore, in addition to using analytical pure chemical reagents and distilled water to prepare the plating solution, the plating solution should also be purified, such as pre-electrolysis, to eliminate various impurities in the plating solution. The oxygen dissolved in the bonding liquid has a serious impact on the measurement results. If necessary, pure nitrogen or hydrogen should be passed through the plating solution before measurement to remove it.
4.2 Electrolytic Cell
The geometric structure of the electrolytic cell has different degrees of influence on the current distribution on the electrode and the measurement accuracy. Therefore, when designing, making or selecting, the volume of the electrolytic cell, the placement of each electrode in the electrolytic cell, and the rationality of the convenience of adding or discharging the plating liquid and gas should be considered. 4.3 Electrode Area and Electrode Placement
The size of the electrode area, the ratio of the electrode area to the solution volume, and the distance between the electrodes have an impact on the measurement accuracy. The size of the electrode area should be considered comprehensively based on the measurement purpose, equipment conditions (such as the output power of the instrument), and calculation convenience. The ratio of the electrode area to the solution volume should be considered based on the changes in the solution composition during the measurement process. The distance between the electrodes should be determined based on the conductivity of the solution and the power of the instrument. The placement and direction of the electrode in the electrolytic cell are very important. Due to the different paths of the solution electric lines between the surface of the electrode to be tested and the auxiliary electrode, the current distribution is different, which causes different ohmic voltage drops in the solution, so that the controlled or measured potential is different. In order to make the current and potential evenly distributed on the electrode surface, the working surface of the electrode to be tested and the auxiliary electrode should be placed symmetrically and parallel. In order to eliminate the ohmic voltage drop caused by the electrolyte, the Luggin capillary tube at one end of the salt bridge connected to the reference electrode should be as close as possible to the middle position of the working surface of the electrode to be tested. 4.4 Reference electrode
The reference electrode should have a stable, reproducible reversible electrode potential under specified conditions and should have the characteristics of a small temperature coefficient. When it is used for a long time or due to improper use, the electrode potential may change, even greatly, causing a large error in the measurement result, so the reference electrode should be calibrated regularly. 4.5 Salt bridge
When the plating solution to be tested is different from the reference electrode solution, in order to eliminate the mutual contamination between the solutions and reduce the influence of the liquid boundary potential, a salt bridge should be used to connect them. The concentration of the salt bridge solution should be saturated. The smaller the difference in diffusion rate of anions and cations in the solution, the better. 5 Measurement method
5.1 Constant current method
5.1.1 Basic principle
When a certain current output by the constant current power supply passes through the electrode to be tested, the auxiliary electrode and the plating solution to be tested, the electrode is polarized, and the potentiometer on the constant current meter is adjusted. The current value passing through the electrode to be tested can be changed to obtain a series of different current density values. At the same time, the electrode potential under the corresponding current density is measured by the potential measuring instrument, thereby obtaining the corresponding polarization curve. 5.1.2 Measurement circuit
The circuit for measuring the polarization curve by the constant current method is shown in Figure 3. 22
JB/T 7704. 6-95
Figure 3 Schematic diagram of the circuit for measuring polarization curves by constant current method G-constant current instrument: P-potential measuring instrument: A-DC ammeter: WE-electrode to be measured: AE-auxiliary electrode; RE-reference electrode: 1-electrolytic cell: 2-salt bridge t3-intermediate container 5.1.3 Measuring device, instrument and equipment
5.1.3.1 Constant current instrument
The DC constant current instrument used as polarization power supply should have a stable and wide current range, and its accuracy should meet the measurement requirements of the measured plating solution system. When using, it should be operated according to the instrument manual. 5.1.3.2 Potential measuring instrument
The potential measuring instrument should have an input resistance of not less than 105, so that the current passing through the measuring circuit is small enough during measurement, and should have sufficient range (-0.5-~2V), accuracy (<1.0mV) and sensitivity (i.e. measurement speed and response speed). A DC digital voltmeter can meet the measurement needs.
5.1.3.3 Current measuring instrument
The current measuring instrument should be able to make the relative error of the measured current less than 1% in the range of 105~1A. In order to make the reading accurate during measurement, a DC milliammeter or micro-ammeter can be connected to the circuit. 5.1.3.4 Electrolytic cell
The electrolytic cell must be made of materials that are corrosion-resistant, non-deteriorating, and non-polluting to the plating solution. Its structure should meet the relevant requirements of 4.2. The electrolytic cell can have various structural forms. The example shown in Figure 4 is only a simple and convenient "H\-shaped electrolytic cell.WE
5.1.3.5 Electrode to be tested
Figure 4 Example of H-shaped electrolytic cell
JB/T 7704.6—95
According to the system of the plating solution to be tested, select the corresponding metal sheet, stainless steel sheet or platinum sheet as the electrode to be tested. Accurately measure the surface area of ??the electrode working surface (usually 1cm\), and the non-working surface of the electrode and the wire must take effective packaging insulation measures. 5.1.3.6 Auxiliary electrode
The auxiliary electrode is only used to pass current to achieve polarization of the electrode to be tested. High-purity anode materials used in actual electroplating can be selected, and platinum sheets can also be used as auxiliary electrodes. The surface area of ??the auxiliary electrode should be larger than that of the electrode to be tested, and effective packaging insulation measures must be taken for the non-working parts of the electrode.
5.1.3.7 Reference electrode
According to the system of the plating solution to be tested, the reference electrode should be reasonably selected, for example: sulfuric acid or hydrochloric acid calomel electrode can be used for acidic solution, mercuric oxide electrode can be used for alkaline solution, saturated calomel electrode can be used for neutral solution, saturated calomel or silver chloride electrode can be used for chloride solution, and mercurous sulfate electrode can be used for sulfate solution. |tt||5.1.3.8 Salt bridge
The salt bridge is made of glass and is filled with a suitable saturated solution according to the plating solution system to be tested. No air bubbles should be left in the salt bridge. 5.1.3.9 Intermediate container
When the anion composition of the plating solution to be tested is similar to that of the reference electrode solution, the intermediate container is generally filled with the solution to be tested. When the anion composition of the plating solution to be tested and the reference electrode solution is significantly different, the intermediate container should be filled with the same solution as the reference electrode. 5.1.4 Measurement steps
5.1.4.1 Prepare the plating solution to be tested with analytically pure chemical reagents and distilled water. Inject it into the electrolytic cell. Inject the appropriate solution into the intermediate container. 5.1.4.2 Place the auxiliary electrode and reference electrode in the electrolytic cell and the intermediate container respectively, and connect them with a salt bridge. 5.1.4.3 If temperature is required, the electrolytic cell can be placed in a constant temperature water bath to control the temperature. 5.1.4.4 If necessary, pure nitrogen or hydrogen can be passed through the plating solution to remove all oxygen from the plating solution. 5.1.4.5. Grind the working surface (single side) of the electrode to be tested with 280, 320, 400, and 600 silicon carbide water-grinding sandpapers in turn, and then polish it with metallographic sandpapers until it is mirror-bright. After washing and drying, accurately measure its surface area. 5.1.4.6 After degreasing, activating, and washing with distilled water, the electrode to be tested is placed in the electrolytic cell after being dried with filter paper, so that its working surface is opposite to the auxiliary electrode. Adjust the Luggin capillary so that the capillary opening is about 2 mm or twice the diameter of the capillary opening from the middle of the surface of the electrode to be tested.
5.1.4.7 Connect the circuit according to Figure 3 (you can also connect the circuit according to the manual of the instrument used). When measuring the cathode polarization curve, the electrode to be tested is used as the cathode and should be connected to the negative pole of the power supply output. When measuring the anodic polarization curve, the electrode to be tested is used as the anode and should be connected to the positive pole of the power supply output. After the circuit is checked and found to be correct, it can be prepared for measurement. 5.1.4.8 When the electrode to be tested is left in the solution for a certain period of time (30~60min) to reach a steady state, measure the electrode potential when the circuit is open (no current flows).
5.1.4.9 Turn on the power switch, adjust the potentiometer, and gradually change the current value from small to large according to the predetermined current interval and time interval (depending on the different systems to be tested. The current is generally selected between 0.5~1mA, and the time is selected between 0.5~10min). Measure the corresponding electrode potential and record the electrode potential corresponding to different current densities. The specific instrument operation method should be carried out according to the instrument instruction manual. 5.1.5 Measurement results
Convert a series of polarization current values ??into current density values, and draw a curve of the relationship between current density and electrode potential on the coordinate paper, that is: E=f0
Note: In polarization curve measurement, the potential of the reference electrode is often taken as zero, and the measured potential value is equal to the potential of the electrode to be measured relative to the reference electrode. Therefore, the reference electrode used should be described in words on the coordinate graph. In addition, the composition, concentration, temperature and other related conditions of the measured system should also be noted. 5.2 Constant potential method
5.2.1 Basic principle
The potentiostat keeps the voltage constant when the current flowing through the electrolytic cell changes, that is, the potential of the electrode to be measured is constant at a given value. By adjusting the potentiometer on the potentiostat, a series of different electrode potential values ??can be obtained, and the current value under the corresponding electrode potential can be measured at the same time. 5.2.2 Measurement circuit
JB/T 7704. 6- 95
The circuit for measuring polarization curve by constant potential method is shown in Figure 5. G
Figure 5 Circuit diagram for measuring polarization curve by constant potential methodG- Constant potential instrument: WE-electrode to be measured AE-auxiliary electrode: RE-reference electrode: 1-electrolytic cell + 2-salt bridge: 3 intermediate container
5.2.3 Measuring device, instrument and equipment
5.2.3.1 Constant potential instrument
The constant potential instrument used as polarization power supply shall have a stable wide potential range and a wide current output, and its accuracy shall meet the measurement requirements of the measured plating solution system. When using, it shall be operated according to the instrument manual. 5.2.3.2 Potential measuring instrument
The potential measuring instrument shall comply with the provisions of 5.1.3.2. Many constant potential instruments already have the circuit required by 5.1.3.2. 5.2.3.3 AmpereometerbzxZ.net
Same as specified in 5.1.3.3.
5.2.3.4 Electrolytic cell
Same as specified in 5.1.3.4.
5.2.3.5 Electrode to be measured
Same as specified in 5.1.3.5.
5.2.3.6 Auxiliary electrode
Same as specified in 5.1.3.6.
5.2.3.7 Reference electrode
Same as specified in 5.1.3.7.
5.2.3.8 Salt bridge
Same as specified in 5.1.3.8.
5.2.3.9 Intermediate container
Same as specified in 5.1.3.9.
5.2.4 Measurement steps
5.2.4.1 Follow steps 5.1.4.1 to 5.1.4.6. 5.2.4.2 Connect the circuits according to Figure 5 and follow the relevant provisions of 5.1.4.7. 5.2.4.3 Same as 5.1.4.8.
5.2.4.4 Turn on the power switch, adjust the potentiometer, and gradually change the potential value from low to high according to the predetermined potential interval and time interval (depending on the different measured systems, the potential is selected between 5~~100mV and the time is selected between 0.5~10min), and record the current density values ??corresponding to different potentials. The specific instrument operation method should be carried out according to the instrument instruction manual. 5.2.5 Measurement results
The measurement results are the same as 5.1.5.
5.3 Automatic polarization curve recording method
JB/T 7704.6-95
Based on the above two measurement methods, a device (such as a plating parameter measuring instrument) that automatically and continuously changes the polarization circuit current (or potential) is used with a sufficiently slow scanning speed. Equipped with an x-y function recorder, the polarization current and electrode potential are directly input into the function recorder: directly record the polarization curve. The measurement should be carried out according to the instrument manual. 6 Test report
The test report should generally include the following: 8. Name of the plating solution system to be tested:
b. The number of this standard and the test method;
Testing instruments and equipment;
Testing conditions, including solution concentration, temperature, electrode material, electrode area, reference electrode and potential value, scanning speed, etc.: d.
Measurement results and analysis:
Test date and tester.
Additional Notes:
This standard was proposed by the National Metal and Non-metal Covering Standardization Committee. This standard was drafted by the Wuhan Materials Protection Research Institute of the Ministry of Machinery Industry. The main drafter of this standard is Zhong Lichang.2. Many potentiostats already have the circuits required by 5.1.3.2. 5.2.3.3 Amperetrometer
Same as in 5.1.3.3.
5.2.3.4 Electrolytic cell
Same as in 5.1.3.4.
5.2.3.5 Electrode to be measured
Same as in 5.1.3.5.
5.2.3.6 Auxiliary electrode
Same as in 5.1.3.6.
5.2.3.7 Reference electrode
Same as in 5.1.3.7.
5.2.3.8 Salt bridge
Same as in 5.1.3.8.
5.2.3.9 Intermediate container
Same as in 5.1.3.9.
5.2.4 Measurement steps
5.2.4.1 Follow the steps 5.1.4.1 to 5.1.4.6. 5.2.4.2 Connect the circuits according to Figure 5 and follow the relevant provisions of 5.1.4.7. 5.2.4.3 Same as 5.1.4.8.
5.2.4.4 Turn on the power switch, adjust the potentiometer, and gradually change the potential value from low to high according to the predetermined potential interval and time interval (depending on the different measured systems, the potential is selected between 5~~100mV and the time is selected between 0.5~10min), and record the current density values ??corresponding to different potentials. The specific instrument operation method should be carried out according to the instrument instruction manual. 5.2.5 Measurement results
The measurement results are the same as 5.1.5.
5.3 Automatic polarization curve recording method
JB/T 7704.6-95
Based on the above two measurement methods, a device (such as a plating parameter measuring instrument) that automatically and continuously changes the polarization circuit current (or potential) is used with a sufficiently slow scanning speed. Equipped with an x-y function recorder, the polarization current and electrode potential are directly input into the function recorder: directly record the polarization curve. The measurement should be carried out according to the instrument manual. 6 Test report
The test report should generally include the following: 8. Name of the plating solution system to be tested:
b. This standard number and test method;
Testing instruments and equipment;
Testing conditions, including solution concentration, temperature, electrode material, electrode area, reference electrode and potential value, scanning speed, etc.: d.
Measurement results and analysis:
Test date and tester.
Additional Notes:
This standard was proposed by the National Metal and Non-metal Covering Standardization Committee. This standard was drafted by the Wuhan Materials Protection Research Institute of the Ministry of Machinery Industry. The main drafter of this standard is Zhong Lichang.2. Many potentiostats already have the circuits required by 5.1.3.2. 5.2.3.3 Amperetrometer
Same as in 5.1.3.3.
5.2.3.4 Electrolytic cell
Same as in 5.1.3.4.
5.2.3.5 Electrode to be measured
Same as in 5.1.3.5.
5.2.3.6 Auxiliary electrode
Same as in 5.1.3.6.
5.2.3.7 Reference electrode
Same as in 5.1.3.7.
5.2.3.8 Salt bridge
Same as in 5.1.3.8.
5.2.3.9 Intermediate container
Same as in 5.1.3.9.
5.2.4 Measurement steps
5.2.4.1 Follow steps 5.1.4.1 to 5.1.4.6. 5.2.4.2 Connect the circuits according to Figure 5 and follow the relevant provisions of 5.1.4.7. 5.2.4.3 Same as 5.1.4.8.
5.2.4.4 Turn on the power switch, adjust the potentiometer, and gradually change the potential value from low to high according to the predetermined potential interval and time interval (depending on the different measured systems, the potential is selected between 5~~100mV and the time is selected between 0.5~10min), and record the current density values ??corresponding to different potentials. The specific instrument operation method should be carried out according to the instrument instruction manual. 5.2.5 Measurement results
The measurement results are the same as 5.1.5.
5.3 Automatic polarization curve recording method
JB/T 7704.6-95
Based on the above two measurement methods, a device (such as a plating parameter measuring instrument) that automatically and continuously changes the polarization circuit current (or potential) is used with a sufficiently slow scanning speed. Equipped with an x-y function recorder, the polarization current and electrode potential are directly input into the function recorder: directly record the polarization curve. The measurement should be carried out according to the instrument manual. 6 Test report
The test report should generally include the following: 8. Name of the plating solution system to be tested:
b. The number of this standard and the test method;
Testing instruments and equipment;
Testing conditions, including solution concentration, temperature, electrode material, electrode area, reference electrode and potential value, scanning speed, etc.: d.
Measurement results and analysis:
Test date and tester.
Additional Notes:
This standard was proposed by the National Metal and Non-metal Covering Standardization Committee. This standard was drafted by the Wuhan Materials Protection Research Institute of the Ministry of Machinery Industry. The main drafter of this standard is Zhong Lichang.
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