CN114609028A - Portable device and method for in-situ detection of corrosion resistance of organic coating - Google Patents
Portable device and method for in-situ detection of corrosion resistance of organic coating Download PDFInfo
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Abstract
The invention discloses a portable device for in-situ detection of corrosion resistance of an organic coating, which comprises a portable electrochemical probe, a test system and software, and can be used for in-situ nondestructive detection of the corrosion resistance of the organic coating on the metal surface, and the corrosion resistance of the coating can be simply detected without damaging the coating. The device disclosed by the invention is based on the principle that the corrosion resistance of the coating is represented by using the impedance modulus value obtained under the characteristic frequency of a low frequency region, and can be used for rapidly, in-situ and nondestructively detecting the corrosion resistance of the organic coating in an industrial field or a laboratory by combining a novel movable double electrochemical probe, a precise electrochemical test module and a microprocessor technology.
Description
Technical Field
The invention belongs to the technical field of physical and chemical detection, and particularly relates to a portable device and a method for in-situ detection of corrosion resistance of an organic coating.
Background
The corrosion of metal materials not only causes huge economic loss, but also can bring serious potential safety hazard far exceeding the loss caused by natural disasters. The means for protecting the metal material from corrosion mainly comprises organic coating protection, electrochemical protection, corrosion inhibitor protection and the like, wherein the organic coating protection is widely applied due to the advantages of low cost, easy operation and the like.
The coating protection is realized by providing a barrier effect, slowing down the contact of a corrosive medium and metal and reducing the corrosion speed. However, the surface of the coating inevitably has some microscopic defects, so that the coating cannot completely isolate the invasion of corrosive media, and meanwhile, the coating per se is degraded and aged in the service process, so that the protection performance is reduced, and the protection period is shortened. Therefore, the development of the detection and evaluation technology of the protective performance of the organic coating system has important significance for evaluating the protective performance of the coating and developing a novel protective coating system.
The detection technology of the protective performance of the coating is divided into a laboratory test technology and an industrial field detection technology. Laboratory testing techniques include electrochemical impedance spectroscopy, polarization curve testing, electrochemical noise and infrared spectroscopy, salt spray testing, ultraviolet aging, cathodic disbanding, and the like. However, the laboratory testing technology has strict requirements on testing environment and equipment, and is difficult to apply to industrial fields. The industrial field detection technology mainly comprises coating thickness detection, electric spark detection, color difference detection and the like. It is worth noting that metal corrosion under an organic coating is an electrochemical process in nature, and most of the existing field test technologies are based on a non-electrochemical principle, so that the existing field test technologies can only be used as a reference value and cannot accurately evaluate the protective performance of the coating. There is a need for a testing technique based on electrochemical principles that can be used to test the protective properties of coatings in both laboratory studies and industrial fields.
Disclosure of Invention
In order to overcome the defects of the prior art, the invention provides a portable device and a method for detecting the corrosion resistance of an organic coating in situ.
Wherein, portable electrochemical probe is used for the normal position detection coating impedance data, its characterized in that:
1) the probe is a two-electrode system of a double electrolytic cell, a Pt working electrode and an Ag/AgCl reference electrode are arranged in the electrolytic cell on the left side, and a Pt counter electrode which is the same as the Pt counter electrode in the electrolytic cell on the left side is arranged in the electrolytic cell on the right side;
2) the electrolytic cells on the left and right sides are filled with solid ion conducting materials as electrolyte solutions.
The testing system comprises a low-pass filter, a potentiostat, an amplifier, an analog-to-digital converter (A/D or D/A converter), an I/V converter, a microprocessor and the like, and the functional characteristics of each part are as follows:
1) an analog switch: controlling the electrochemical reaction process of simulating the complete metal;
2) potentiostat unit: outputting a direct current dynamic potential scanning excitation signal and a constant frequency alternating current impedance excitation signal;
3) galvanometer with low internal resistance: collecting a sample current signal according to an instruction;
4) analog-to-digital conversion: converting the continuous analog signal into a discrete digital signal by sampling;
5) the microprocessor: the control module switch and the very constant potentiometer unit are used for controlling, and the galvanometer and the analog-to-digital conversion are controlled for data acquisition and processing.
The test system works according to the following procedures: signals obtained by a working electrode of the electrochemical probe (1) are transmitted to a low-pass filter (3) through an I/V converter (2), then are amplified by an amplifier (4), then enter a microprocessor (6) through an A/D converter (5) for processing, and the processed signals enter a potentiostat (8) through a D/A converter (7); and finally, feeding back the data to a counter electrode of the electrochemical probe to form a complete test system, and displaying the required test data on a microprocessor.
The software is developed by adopting java language based on an android platform, and is provided with two measurement modules of direct current impedance and alternating current impedance: the direct current impedance testing module has the characteristics of adjustable direct current voltage scanning range and speed, can reflect the change condition of real-time current along with scanning voltage after entering a scanning page, and calculates to obtain the direct current impedance of the coating. The alternating current impedance testing module has the characteristic of adjustable alternating current frequency and can calculate to obtain the alternating current impedance value of the coating under the selected frequency. The software has an interactive software interface system, and the whole system has the technical indexes of high measurement precision, strong anti-interference performance, high automation degree and the like.
The portable device for detecting the corrosion resistance of the organic coating in situ is characterized in that:
1) the device can provide circulating direct current potential scanning, and the scanning speed, the scanning interval and the scanning range are adjustable;
2) the current signal in the potential scanning process can be collected in real time, and the resistance value is calculated;
3) capable of providing an AC excitation at a selected frequency and measuring the impedance at that frequency
The device measures the corrosion resistance of the coating by combining a multi-potentiodynamic scanning polarization technology (MCPPDP) with a specific frequency alternating current impedance method. And evaluating the protective performance of the organic coating by comparing the polarization current in a set time or the time for reaching a preset polarization current. Under the same conditions, the smaller the polarization current in a set time or the longer the time to reach the set polarization current, the more excellent the corrosion resistance of the coating.
The invention is characterized in that the cathode and anode symmetrical potential multi-polarization measurement is adopted, which can not only accelerate the measurement process, but also avoid the damage of the coating caused by the accumulation of the acceleration process. Meanwhile, in order to meet the requirement of nondestructive testing on an industrial field, the rapid coating corrosion resistance detector adopts a movable double-electrolytic-cell probe, can effectively avoid the requirement that the conventional electrochemical testing needs to scrape a coating to expose a metal substrate so as to carry out related testing, and is suitable for field-portable nondestructive coating corrosion resistance advanced evaluation.
Drawings
FIG. 1 is a schematic view of a nondestructive testing probe for coating.
FIG. 2 is a schematic diagram of the operation of the coating nondestructive testing system.
FIG. 3 metallographic microscope images of different degrees of metal substrate contamination (20X), (a) untreated, (b)0.18M H2SO4 solution treated, (c)1.8M H2SO4 solution treated.
FIG. 4 multiple potentiodynamic test results for samples of Q235 carbon steel treated with dilute sulfuric acid and coated with a modified polyurethane coating, which were (a) untreated, (b)0.18M H2SO4Solution treatment, (c)1.8M H2SO4And (4) solution treatment.
FIG. 5 metallographic microscope images (5x) of the surface of the modified polyurethane coating with defects, (a) untreated, (b) artificially scratched, and (c) spiked with NaCl particles.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is described in further detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.
Examples
The portable device and the method for detecting the corrosion resistance of the organic coating in situ are characterized by comprising a portable electrochemical probe, a test system and software.
Wherein, portable electrochemical probe is used for the normal position detection coating impedance data, its characterized in that:
1) the probe is a two-electrode system of a double electrolytic cell, a Pt working electrode and an Ag/AgCl reference electrode are arranged in the electrolytic cell on the left side, and a Pt counter electrode which is the same as the Pt counter electrode in the electrolytic cell on the left side is arranged in the electrolytic cell on the right side;
2) the electrolytic cells on the left and right sides are filled with solid ion conducting materials as electrolyte solutions.
The testing system comprises an analog switch, a potentiostat unit, a low internal resistance galvanometer, analog-to-digital conversion (A/D or D/A conversion), an I/V control, a microprocessor and the like.
The test system works according to the following procedures: signals obtained by a working electrode of the electrochemical probe (1) are transmitted to a low-pass filter (3) through an I/V converter (2), then are amplified by an amplifier (4), then enter a microprocessor (6) through an A/D converter (5) for processing, and the processed signals enter a potentiostat (8) through a D/A converter (7); and finally, feeding back the data to a counter electrode of the electrochemical probe to form a complete test system, and displaying the required test data on a microprocessor.
The software is developed by adopting java language based on an android platform, and is provided with two measurement modules of direct current impedance and alternating current impedance: the direct current impedance testing module has the characteristics of direct current voltage scanning range and adjustable speed, can reflect the condition that real-time current changes along with scanning voltage after entering a scanning page, and calculates to obtain the direct current impedance of the coating. The alternating current impedance testing module has the characteristic of adjustable alternating current frequency and can calculate to obtain the alternating current impedance value of the coating under the selected frequency. The software has an interactive software interface system, and the whole system has the technical indexes of high measurement precision, strong anti-interference performance, high automation degree and the like.
The device measures the corrosion resistance of the coating by combining a multi-potentiodynamic scanning polarization technology (MCPPDP) with a specific frequency alternating current impedance method. And evaluating the protective performance of the organic coating by comparing the polarization current within a set time or the time for reaching a preset polarization current. Under the same conditions, the smaller the polarization current in a set time or the longer the time to reach the set polarization current, the more excellent the corrosion resistance of the coating.
The following are experimental data for the use of the device of the present invention for in situ testing of samples:
respectively dripping 0.18mol/L and 1.8mol/LH on the surface of the Q235 carbon steel of an experimental sample2SO4Acidifying the solution for 30min, drying at room temperature for 1d, and coating the modified polyurethane coating. FIG. 3 is a metallographic microscope image (20X) of the surface of Q235 carbon steel treated with dilute sulfuric acid. As can be seen from the figure, the surface of the untreated carbon steel sample only left a trace when sanded; 0.18M H2SO4After the solution is acidized, pitting pits appear on the surface of the carbon steel; 1.8MH2SO4After the acidification treatment of the solution, the surface of the carbon steel has extensive corrosion, and a large amount of corrosion products attached to the surface are generated.
Fig. 4 is the results of multiple potentiodynamic testing of samples of Q235 carbon steel treated with dilute sulfuric acid and coated with a modified polyurethane coating. It can be seen that: the maximum polarization current of the carbon steel sample which is not polluted is 7.12 muA, and the surface of the carbon steel is dripped with 0.18M and 1.8M H2SO4The maximum polarization currents after solution were 92.33. mu.A and 810.03. mu.A, respectively. Comparing the polarization current shows that the more serious the Q235 carbon steel substrate is polluted, the more obvious the organic coating has the function of breaking the protective performance of the Q235 carbon steel system, which is mainly because the protective performance is reduced because the adhesion of the coating is reduced when the Q235 carbon steel substrate is polluted. In addition, it is also stated that contamination of the metal substrate under the coating can occurAnd detecting the magnitude of the polarization current of the sample by a coating rapid detector to perform primary reflection.
In order to simulate the influence of coating defects on the protective performance, modified polyurethane coatings were prepared, experimental groups were conducted to artificially scratch the surface of the coating with a utility knife without exposing the carbon steel substrate, and 1% wt. NaCl particles were added during the coating preparation, and the thickness of the three groups of coatings was 100 + -10 μm.
FIG. 5 is a metallographic microscopic image (5x) of the surface of the modified polyurethane coating with defects, from which it can be seen that the surface structure of the untreated coating is relatively complete; after artificial scratch damage, the surface of the coating has concave marks, but part of the surface of the coating is complete; after the particles are added into the coating, a pit-shaped structure appears on the surface of the coating in a large range.
TABLE 1Z of modified polyurethane coatings with defects0.01HzResistance value of polarization scanning with multiple dynamic potentials
Table 1 is Z of the modified polyurethane coating with defects0.01HzAnd the DC resistance value of multiple potentiodynamic scans. The comparison shows that Z of the control group0.01HzAnd the direct current impedance is obviously higher than that of the experimental group, the difference between the test results of the control group and the NaCl particle-doped coating is about 7 orders of magnitude, which shows that the structural defects greatly affect the protective performance of the coating, and the impedance data obtained by the two test methods have good consistency.
The applicability of the coating corrosion resistance rapid detector to different types of coatings is inspected, three types of coatings of alkyd varnish coating, chlorinated rubber and modified polyurethane are prepared on the surface of Q235 carbon steel, and the thickness of the coating is 50 +/-5 mu m.
TABLE 2Z for the three types of coatings0.01HzCompared with the direct current resistance value of multiple dynamic potential scanning, the protective performance of different types of coatings is greatly different, the modified polyurethane coating is excellent, and the impedance data obtained by the two testing methods have good consistencyThe results also show that the coating corrosion resistance rapid detector can be used as a test method for rapidly distinguishing the corrosion resistance of different types of organic coatings.
TABLE 2Z of the three types of coating0.01HzResistance value with multiple potentiodynamic scans
The failure of the organic coating on the metal surface is closely related to the service environment, and the detection accuracy of the coating corrosion resistance rapid detector under different environments is examined. Selecting modified polyurethane coating/Q235 carbon steel as objects, and respectively performing acidic treatment (0.2M H)2SO4) And 3.5% wt. NaCl solution of neutral and alkaline (0.2M NaOH) for 72h, and then tested by electrochemical specific impedance spectroscopy and multiple potentiodynamic scanning.
Table 3 shows the Z values of the modified polyurethane coating after being soaked in 3.5 wt% NaCl solution for 72h under different environments0.01HzAnd the DC resistance value of multiple potentiodynamic scans. The comparison shows that two groups of impedance values are in the same order of magnitude under three environments, which shows that the two test results have good consistency, and the rapid detector for the corrosion resistance of the coating can rapidly compare the protection performance of the organic coating under different environments.
Table 3Z of the coating at different pH values in a 3.5% wt. nacl environment0.01HzComparison with DC impedance data
Claims (6)
1. A portable device for detecting the corrosion resistance of an organic coating in situ is characterized in that: comprises a portable electrochemical probe, a test system and software;
the portable electrochemical probe structure is as follows:
1) the probe is a two-electrode system of a double electrolytic cell, a Pt working electrode and an Ag/AgCl reference electrode are arranged in the electrolytic cell on the left side, and a Pt counter electrode which is the same as the Pt counter electrode in the electrolytic cell on the left side is arranged in the electrolytic cell on the right side;
2) the electrolytic cells on the left and right sides are filled with solid ion conducting materials as electrolyte solutions.
2. The portable apparatus for in situ testing of the corrosion resistance of organic coatings according to claim 1, wherein said testing system is comprised of a low pass filter, potentiostat, amplifier, analog to digital converter (a/D or D/a conversion), I/V converter and microprocessor.
3. The portable apparatus for in situ detection of corrosion resistance of organic coatings according to claim 1, wherein said testing system operates according to the following procedure: signals obtained by a working electrode of the electrochemical probe (1) are transmitted to a low-pass filter (3) through an I/V converter (2), then are amplified by an amplifier (4), then enter a microprocessor (6) through an A/D converter (5) for processing, and the processed signals enter a potentiostat (8) through a D/A converter (7); and finally, feeding back the data to a counter electrode of the electrochemical probe to form a complete test system, and displaying the required test data on a microprocessor.
4. The portable device for in-situ detection of corrosion resistance of organic coatings according to claim 1, wherein said software is developed in java language based on android platform, having two measurement modules of dc impedance and ac impedance: the direct current impedance testing module has the characteristics of direct current voltage scanning range and adjustable speed, can reflect the condition that real-time current changes along with scanning voltage after entering a scanning page, and calculates to obtain the direct current impedance of the coating; the alternating current impedance testing module has the characteristic of adjustable alternating current frequency and can calculate to obtain a coating alternating current impedance value under the selected frequency; the software has an interactive software interface system, and the whole system has the technical indexes of high measurement precision, strong anti-interference performance, high automation degree and the like.
5. The portable apparatus for in-situ testing of corrosion resistance of organic coatings according to claim 1,
1) the device can provide circulating direct current potential scanning, and the scanning speed, the scanning interval and the scanning range are adjustable;
2) the current signal in the potential scanning process can be collected in real time, and the resistance value is calculated;
3) an ac excitation at a selected frequency can be provided and the impedance value at that frequency measured.
6. The method for testing the portable device for in-situ detection of the corrosion resistance of the organic coating is characterized in that the corrosion resistance of the coating is measured by combining a multi-potentiodynamic scanning polarization technology (MCPDP) with a specific frequency alternating current impedance method.
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| US20230143519A1 (en) * | 2021-11-11 | 2023-05-11 | Beihang University | Field monitoring electrochemical method for anticorrosion performance of organic coatings in seawater environment |
| US11892391B2 (en) * | 2021-11-11 | 2024-02-06 | Beihang University | Field monitoring electrochemical method for anticorrosion performance of organic coatings in seawater environment |
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