A method for judging the corrosion resistance of low-tin tin-plated plates

Abstract

The present invention particularly relates to a method for quickly judging the corrosion resistance of a tinplate with a low tin content, which belongs to the field of quality inspection technology. The method includes: pre-treating the tinplate by degreasing and removing surface impurities to obtain a sample of a certain area; performing electrochemical testing on the sample to obtain a time-voltage curve; drawing a time-voltage differential curve according to the voltage change of the time-voltage curve, and judging the corrosion resistance of the tinplate by the value of the voltage differential. Through the voltage differential test, a test method for evaluating the corrosion resistance of the coating of a tinplate with a low tin content is established, which solves the problem of the current blank of the corrosion resistance evaluation technology of the tinplate.

Description

Technical Field

[0001] The invention belongs to the technical field of quality detection, and particularly relates to a method for judging the corrosion resistance of a low-tin tin-plated plate. Background Art

[0002] The corrosion resistance of tinplate comes from the cathodic protection of the tin layer on the iron substrate. Once the coating cannot completely cover the substrate surface, the substrate iron will be corroded first under the conditions of electrochemical corrosion. Therefore, whether the coating is uniform and continuous plays a vital role in the corrosion resistance of tinplate. In order to reduce the production cost of tinplate, tinplate with low tin coating is the development direction of tinplate. With the decrease of tin coating, the continuity of the coating gradually decreases due to the influence of the surface morphology of the substrate, which increases the probability of iron leakage and produces pitting rust. However, current research is mostly focused on the corrosion resistance test of high tin content tinplate, and there is little research on the test method of corrosion resistance of low tin content tinplate, and there is a lack of quantifiable corrosion resistance indicators.

[0003] In the prior art, Chinese invention patent application CN109557016B discloses a method for detecting corrosion active points on the surface of cold-rolled tin-plated steel sheets with low tin content, and introduces a reagent for testing corrosion active points on the surface of cold-rolled tin-plated steel sheets with low tin content, including a coloring solution and a color fixing solution. The size, quantity, and color development time of the colored points are observed with the naked eye by direct spraying or combining rubbing, so as to judge the corrosion resistance of the tin-plated sheet. This method lacks statistical tools in practical applications, and can only semi-quantitatively judge the corrosion resistance of the tin-plated sheet, and cannot form a quantitative index. Chinese invention patent application CN102998470A discloses a fully automatic multifunctional measurement system for the surface coating quality of tin-plated sheets, and introduces a test device including a PC and a constant current power supply, which can test the tin coating amount and alloy tin amount, passivation film amount, oxide film amount, and lead content in the coating on the surface of the tin-plated sheet. The coating surface is corroded by using a constant current by preparing different corrosive solutions, and the relationship between the test time and voltage is used to calculate the amount of each coating. It is only used to monitor the amount of coating on the production line, and does not study the distribution and coverage of each coating, as well as the impact of this condition on the corrosion resistance of the tinplate. Chinese invention patent application CN105021516B is a test liquid and test film for detecting the corrosion resistance of tinplate, and its detection method. It introduces a test liquid prepared with ascorbic acid, cupric chloride, hydrochloric acid, and Triton (0P-10), which is applied to the surface of the tinplate through a sticker made of cellulose paper and plastic film. The corrosion resistance of the tinplate is judged by the number and density of red spots. The test method is semi-quantitative, the spot size and number are fuzzy, and the experimental results are affected by subjective factors. Although the exposed iron on the surface of the tinplate can be identified, the continuity of the passivation layer, the elemental tin layer, and the alloy tin layer cannot be identified one by one.

[0004] At present, in the quality inspection of tinplate production, the test method for the corrosion resistance of low-tin tinplate has not been established. There is a lack of strict evaluation method for the coverage of the coating on the substrate surface with different surface morphologies, so that the pitting and corrosion resistance problems of tinplate can only be verified through usage, and there is a lack of experimental methods to test and prevent them. Summary of the invention

[0005] The purpose of this application is to provide a method for judging the corrosion resistance of tinplate with low tin content, so as to solve the problem of the current blank technology for evaluating the corrosion resistance of tinplate.

[0006] An embodiment of the present invention provides a method for judging the corrosion resistance of a low-tin tin-plated plate, the method comprising:

[0007] The tinplate is pretreated by degreasing and removing surface impurities to obtain a sample of a certain area;

[0008] Conducting electrochemical testing on the sample to obtain a time-voltage curve;

[0009] According to the voltage change of the time-voltage curve, a time-voltage differential curve is drawn;

[0010] According to the time-voltage differential curve, a value of the voltage differential is obtained;

[0011] The corrosion resistance of the tinplate is determined based on the value of the voltage differential.

[0012] Optionally, judging the corrosion resistance of the tinplate according to the voltage change of the time-voltage curve specifically includes:

[0013] Deriving the time-voltage curve to obtain a time-voltage differential curve;

[0014] According to the time-voltage differential curve, a voltage differential peak value from the corrosion of the tin layer to the alloy layer is obtained;

[0015] The corrosion resistance of the tin-plated sheet is determined based on the voltage differential peak value.

[0016] It should be noted that the voltage differential refers to the rate of change of corrosion voltage dE / dt when the inorganic acid corrodes the tin layer and then the inorganic acid corrodes the alloy layer. When the instrument scanning frequency is constant (△t is a constant), the value of dE represents the relationship between the continuity of the tin layer and the corrosion resistance of the tinplate.

[0017] Optionally, the voltage differential peak is a voltage differential peak when the tin layer is corroded to the alloy layer.

[0018] Optionally, when the scanning frequency is 1 MHz-10 MHz, if the voltage differential peak value from the corrosion of the tin layer to the alloy layer is greater than 0.015, the corrosion resistance of the tin-plated sheet is good.

[0019] Optionally, the higher the voltage differential peak value, the better the corrosion resistance of the tinplate.

[0020] Optionally, the pretreatment of degreasing the tinplate and removing surface impurities specifically includes: wiping the surface of the tinplate with a dust-free cloth dipped in alcohol and blowing it dry with cold air.

[0021] Optionally, the electrolyte for the electrochemical test is 0.5 mol / L-2 mol / L of inorganic acid.

[0022] Optionally, the current density of the electrochemical test is 4 mA / cm 2 -6mA / cm 2 .

[0023] Optionally, the scanning frequency is 1 MHz-10 MHz.

[0024] Optionally, the quick judgment is that the test time is ≤ 2 minutes.

[0025] Optionally, the tin content of the tin plate is ≤2.8g / m 2 .

[0026] One or more technical solutions in the embodiments of the present invention have at least the following technical effects or advantages:

[0027] The method for judging the corrosion resistance of a tin-plated plate with a low tin content provided in an embodiment of the present invention establishes a test method for evaluating the corrosion resistance of a tin-plated plate with a low tin content through the test of a voltage differential curve, thereby solving the problem of the current lack of technology for evaluating the corrosion resistance of tin-plated plates.

[0028] The above description is only an overview of the technical solution of the present invention. In order to more clearly understand the technical means of the present invention, it can be implemented according to the contents of the specification. In order to make the above and other purposes, features and advantages of the present invention more obvious and easy to understand, the specific implementation methods of the present invention are listed below. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0030] Figure 1 is a flow chart of a method provided by an embodiment of the present invention;

[0031] Figure 2 It is a schematic diagram of the implementation principle provided by an embodiment of the present invention;

[0032] Figure 3 is a voltage differential curve diagram provided by Example 1 of the present invention;

[0033] Figure 4 is a voltage differential curve diagram provided by Example 2 of the present invention;

[0034] Figure 5 is a voltage differential curve diagram provided by Example 3 of the present invention;

[0035] Figure 6 This is a voltage differential curve diagram provided by Example 4 of the present invention. DETAILED DESCRIPTION

[0036] The present invention will be described in detail below in conjunction with specific implementations and examples, and the advantages and various effects of the present invention will be more clearly presented. It should be understood by those skilled in the art that these specific implementations and examples are used to illustrate the present invention, rather than to limit the present invention.

[0037] Throughout the specification, unless otherwise specifically stated, the terms used herein should be understood as meanings commonly used in the art. Therefore, unless otherwise defined, all technical and scientific terms used herein have the same meanings as those generally understood by those skilled in the art to which the present invention belongs. In the event of a conflict, the present specification takes precedence.

[0038] Unless otherwise specified, various raw materials, reagents, instruments and equipment used in the present invention can be purchased from the market or prepared by existing methods.

[0039] The technical solution of the embodiment of the present application is to solve the above technical problems, and the overall idea is as follows:

[0040] During the invention process, the applicant discovered that: at present, there is still no accurate and convenient test method to evaluate the corrosion resistance of tinplate in the factory inspection, nor is there a relevant standard to evaluate the risk of pitting rust. 2) can only rely on customer application feedback, causing huge economic losses. The purpose of this technical solution is to provide a quantifiable corrosion resistance index to accurately evaluate the corrosion resistance of low-tin tinplate, and to identify the continuity of the coating formed by substrates with different surface morphologies under different electroplating processes, thereby providing an accurate testing method for the prediction and prevention of tinplate pitting. Through the test of voltage differential curves, the relationship between the surface morphology of the substrate, the continuity of the coating and the corrosion resistance of the tinplate is comprehensively considered, and a test method for evaluating the corrosion resistance of the coating of low-tin tinplate is established.

[0041] The present technical solution uses electrochemical analysis to test the tinplate coating. The electrochemical analysis is a type of instrumental analysis method based on the electrochemical properties of substances in solution. The test solution is used as a component of a chemical battery and is measured based on a certain relationship between certain electrical parameters of the battery, such as resistance, conductivity, potential, current, charge or current-voltage curve, and the concentration of the substance being measured.

[0042] Since the coating of the tinplate is structurally divided into an alloy tin layer, a single tin layer and a passivation layer from the inside to the outside, the prepared solution corrodes the coating from the outside to the inside, and different corrosion potentials appear according to different corrosive substances. It can be known that the positions of different corrosion interfaces corresponding to different corrosion times. The instrument uses the chronopotentiometry to test the change of potential in the battery over time. The corrosion interface is stable at different potentials in the passivation layer, the single tin layer, the alloy tin layer and the iron layer. The change in potential represents the switching of the corrosion interface between the layers, and the speed of the potential change (voltage differential) represents the flatness of the layer interface when the corrosion interface switches. If the substrate is flat, the thickness of the alloy layer and the tin layer is uniform, the interface of the hydrochloric acid corroding the tin layer directly switches to the alloy layer, the voltage rises rapidly, and the voltage differential is high; if the surface of the substrate is uneven, the thickness of the alloy layer and the tin layer is uneven, or the tin layer is discontinuous, while the hydrochloric acid corrodes the tin layer, there is also a phenomenon of corrosion of the alloy layer on its interface, the voltage rises slowly, and the voltage differential is low.

[0043] Schematic diagram Figure 2 As shown in the figure, when the surface morphology of the substrate is uneven, the distribution of the coating after tin plating will also be affected, and under the soft melting condition, the alloy tin layer grows close to the substrate, while the single tin layer has a tendency to flatten, resulting in the single tin layer showing uneven thickness on the substrate surface. When the corrosion interface of hydrochloric acid gradually corrodes from the single tin layer to the alloy tin layer over time, the single tin and the alloy tin will be corroded at the same time, resulting in the corrosion potential of tin not being able to quickly change to the corrosion potential of the alloy tin, that is, the voltage differential is small. When the corrosion interface gradually corrodes from the alloy tin layer to the substrate iron, the same situation will occur.

[0044] Therefore, the voltage differential curve can be obtained by using the method of differentiating the voltage with respect to time. The higher the peak value, the smoother the layer interface, and the lower the peak value, the rougher the layer interface. The high or low voltage differential value is used to evaluate the continuous distribution of the coating on the substrate surface.

[0045] According to a typical embodiment of the present invention, a method for judging the corrosion resistance of a low-tin tin-plated plate is provided, the method comprising:

[0046] S1. Pre-treating the tinplate to obtain a sample;

[0047] Specifically, alkaline cleaning solution or organic solvent is used to remove grease and impurities from the surface of tinplate.

[0048] S2. subjecting the sample to electrochemical testing to obtain a time-voltage curve;

[0049] Specifically, the electrochemical test includes: preparing an electrolyte, using 0.5-2 mol / L inorganic acid to corrode the tin layer and alloy layer of the tin-plated plate; then using an electrochemical test system to set a constant current density of 4 mA / cm 2 ~6mA / cm 2 , scanning frequency 1MHz-10MHz, time 60~120s, test time-voltage curve;

[0050] S3. Determine the corrosion resistance of the tinplate according to the voltage change of the time-voltage curve.

[0051] Specifically, the time-voltage curve is derived to obtain a time-voltage differential curve, and the height of the voltage differential peak value when the inorganic acid corrodes the tin layer to the alloy layer is calculated.

[0052] Generally speaking, the higher the voltage differential, the better the corrosion resistance; in this embodiment, when the voltage differential is lower than 0.015, the corrosion resistance is poor.

[0053] This technical solution can establish a set of factory inspection standards for the corrosion resistance of tinplate. Each test only takes 1 minute to obtain accurate experimental data, achieving the purpose of quantitative testing. Especially for low-tin tinplate (tin content 2.8 g / m 2 , 2.0g / m 2 , 1.4 g / m 2 , 1.1 g / m 2 , 0.5 g / m 2 ) has a very effective control function and can predict the possibility of pitting rust on tinplate during transportation and use.

[0054] The method for determining the corrosion resistance of the low-tin tin-plated sheet of the present application will be described in detail below in combination with the embodiments, control examples and experimental data.

[0055] Example 1

[0056] This example uses a tin-plated plate produced by a certain company, with a tin coating amount of 1.1 g / m 2 , select tinplate with excellent corrosion resistance for testing. The test method is as follows:

[0057] (1) For 10 cm 2 Degrease the sample and wipe it dry with a dust-free cloth.

[0058] (2) Prepare 1.8 mol / L hydrochloric acid as the electrolyte to corrode the tin-plated plate to be tested.

[0059] (3) Use an electrochemical workstation to test the time-voltage curves of the four samples with a constant current of 50 mA, a scanning frequency of 1 MHz, and a time of 70 s to measure the time-voltage curves.

[0060] (4) Derivative the time-voltage curve to obtain the time-voltage differential curve, and calculate the peak height of the voltage differential when the inorganic acid corrodes the tin layer to the alloy layer.

[0061] Example 2

[0062] This example uses a tin-plated plate produced by a certain company, with a tin coating amount of 1.1 g / m 2 , select tinplate with good corrosion resistance for testing. The test method is as follows:

[0063] (1) For 10 cm 2 Degrease the sample and wipe it dry with a dust-free cloth.

[0064] (2) Prepare 1.8 mol / L hydrochloric acid as the electrolyte to corrode the tin-plated plate to be tested.

[0065] (3) Use an electrochemical workstation to test the time-voltage curves of the four samples with a constant current of 50 mA, a scanning frequency of 1 MHz, and a time of 70 s to measure the time-voltage curves.

[0066] (4) Derivative the time-voltage curve to obtain the time-voltage differential curve, and calculate the peak height of the voltage differential when the inorganic acid corrodes the tin layer to the alloy layer.

[0067] Example 3

[0068] This example uses a tin-plated plate produced by a certain company, with a tin coating amount of 1.1 g / m 2 , select a tin plate with slight rust for testing. The test method is as follows:

[0069] (1) For 10 cm 2 Degrease the sample and wipe it dry with a dust-free cloth.

[0070] (2) Prepare 1.8 mol / L hydrochloric acid as the electrolyte to corrode the tin-plated plate to be tested.

[0071] (3) Use an electrochemical workstation to test the time-voltage curves of the four samples with a constant current of 50 mA, a scanning frequency of 1 MHz, and a time of 70 s to measure the time-voltage curves.

[0072] (4) Derivative the time-voltage curve to obtain the time-voltage differential curve, and calculate the peak height of the voltage differential when the inorganic acid corrodes the tin layer to the alloy layer.

[0073] Example 4

[0074] This example uses a tin-plated plate produced by a certain company, with a tin coating amount of 1.1 g / m 2 , select the severely corroded tinplate for testing. The test method is as follows:

[0075] (1) For 10 cm 2 Degrease the sample and wipe it dry with a dust-free cloth.

[0076] (2) Prepare 1.8 mol / L hydrochloric acid as the electrolyte to corrode the tin-plated plate to be tested.

[0077] (3) Use an electrochemical workstation to test the time-voltage curves of the four samples with a constant current of 50 mA, a scanning frequency of 1 MHz, and a time of 70 s to measure the time-voltage curves.

[0078] (4) Derivative the time-voltage curve to obtain the time-voltage differential curve, and calculate the peak height of the voltage differential when the inorganic acid corrodes the tin layer to the alloy layer.

[0079] The voltage differential data of Examples 1 to 4 are shown in the following table:

[0080]

[0081] Based on this, an evaluation standard for the corrosion resistance of low-tin tinplate coatings in a large steel plant was established: a voltage differential higher than 0.015 indicates good corrosion resistance, and a voltage differential lower than 0.015 indicates poor corrosion resistance. This standard is used for factory inspection and rust prediction.

[0082] The voltage differential curve results of Examples 1 to 4 are as follows: Figures 3 to 6As shown, it should be noted that the horizontal axis is time / s, the left vertical axis is corrosion voltage / V, and the right vertical axis is voltage differential; the first peak of the blue curve is the peak of the voltage differential from the tin layer to the alloy layer corroded by inorganic acid; the right vertical axis corresponding to the first blue peak is the required voltage differential; it can be seen from the figure that the height of the voltage differential peak value (i.e., the first peak) from the corrosion tin layer to the alloy layer of the tin-plated plate with excellent corrosion resistance, the tin-plated plate with good corrosion resistance, the tin-plated plate with slight rust and the tin-plated plate with severe rust gradually decreases, showing a certain regularity, which shows that this method can effectively evaluate the corrosion resistance of the tin-plated plate.

[0083] One or more technical solutions in the embodiments of the present invention have at least the following technical effects or advantages:

[0084] The method provided by the embodiment of the present invention can establish a set of factory inspection standards for the corrosion resistance of tinplate. Each test only takes 1 minute to obtain accurate experimental data, achieving the purpose of quantitative testing. Especially for low-tin tinplate (tin content 2.8g / m 2 , 2.0g / m 2 , 1.4 g / m 2 , 1.1 g / m 2 , 0.5 g / m 2 ) has a very effective control function and can predict the possibility of pitting rust on tinplate during transportation and use.

[0085] Finally, it should be noted that the terms "comprises," "includes," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that includes a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements that are inherent to such process, method, article, or apparatus.

[0086] Although the preferred embodiments of the present invention have been described, those skilled in the art may make other changes and modifications to these embodiments once they have learned the basic creative concept. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments and all changes and modifications that fall within the scope of the present invention.

[0087] Obviously, those skilled in the art can make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalents, the present invention is also intended to include these modifications and variations.

Claims

1. A method for quickly judging the corrosion resistance of low-tin tin-plated plates, characterized in that: The method comprises: The tinplate is pretreated by degreasing and removing surface impurities to obtain a sample; Conducting electrochemical testing on the sample to obtain a time-voltage curve; According to the voltage change of the time-voltage curve, a time-voltage differential curve is drawn; According to the time-voltage differential curve, a value of the voltage differential is obtained; According to the value of the voltage differential, the corrosion resistance of the tin-plated sheet is judged; The step of judging the corrosion resistance of the tinplate according to the voltage change of the time-voltage curve specifically includes: Deriving the time-voltage curve to obtain a time-voltage differential curve; According to the time-voltage differential curve, a voltage differential peak value from the corrosion of the tin layer to the alloy layer is obtained; According to the voltage differential peak value, the corrosion resistance of the tin-plated plate is judged; The tin coating amount of the tin plate is ≤2.8g / m 2 ; The electrochemical test includes: preparing 0.5-2 mol / L inorganic acid as an electrolyte, using an electrochemical test system to set a constant current density of 4 mA / cm 2 ~6mA / cm 2 , scanning frequency 1MHz-10MHz, time 60~120s, test time-voltage curve; The voltage differential peak value is the first peak peak value of the voltage differential curve.

2. The method for quickly judging the corrosion resistance of low-tin tin-plated sheet according to claim 1, characterized in that: When the scanning frequency is 1MHz-10 MHz, if the voltage differential peak value from the corrosion of the tin layer to the alloy layer is greater than 0.015, the corrosion resistance of the tin-plated sheet is good.

3. The method for quickly judging the corrosion resistance of low-tin tin-plated sheet according to claim 1, characterized in that: The higher the voltage differential peak value is, the better the corrosion resistance of the tin-plated sheet is.

4. The method for quickly judging the corrosion resistance of low-tin tin-plated sheet according to claim 1, characterized in that: The pretreatment of degreasing the tinplate and removing surface impurities specifically includes: wiping the surface of the tinplate with a dust-free cloth dipped in alcohol and blowing it dry with cold air.

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