CN100570348C - Comprehensive Analysis Method of Electrochemical Impedance Spectroscopy for Surface Properties of Metallic Materials - Google Patents

Abstract

The invention relates to a method for comprehensive analysis of electrochemical impedance spectroscopy on the surface properties of metal materials. First, the mCRR transmission line model is used to fit the electrochemical impedance spectroscopy measured under the conditions of causality, stability and linearity, wherein m is a positive integer, C and R represent pure capacitance and pure resistance respectively; then according to the formula f ^* ＝1/(2πC _i R _i ), the characteristic frequency f ^* of each branch of parallel connection of C _i and R _i is obtained respectively, and the results are obtained under different series of research conditions The logarithmic plot of the distribution of the discrete parameters C _i and R _i as a function of the characteristic frequency and the plot of R _o as a function of the research conditions; finally, the differences in the surface properties of metallic materials are determined according to the characteristics of the plots. The invention utilizes the sensitivity and richness of information of the electrochemical impedance spectrum, and the objectivity and universality of the mCRR transmission line model, thereby objectively and sensitively identifying the difference between the surface properties of metal materials under different conditions.

Description

Comprehensive Analysis Method of Electrochemical Impedance Spectroscopy for Surface Properties of Metallic Materials

【Technical field】

The present invention relates to an electrochemical impedance spectroscopy comprehensive analysis method for analyzing the surface properties of metal materials under the influence of different factors, so as to identify the differences in the surface states of metal samples. These different influencing factors include pretreatment conditions, corrosion potential, dielectric concentration and composition , system temperature and sample immersion time, and the differences in sample performance include cleanliness, wettability, corrosion activity, dielectric properties of surface oxide film or pretreatment film, film integrity and compactness.

【Background technique】

In many cases, a convenient and fast method is needed to comprehensively evaluate the surface properties of metal materials, such as various links in the production process of formed foil, the monitoring and control of the effect and quality of metal material surface pretreatment in the coating, welding or electroplating industry, and the battery industry. The surface properties of medium-conducting electrode plates and their bonding force with active materials, the screening and evaluation of optimal process conditions for silane pretreatment of metals, and other research and development areas related to metal materials.

There is no shortage of methods for evaluating the surface properties of metallic materials. The relevant macroscopic methods include wetting angle for evaluating surface wettability, and polarization curve and surface observation for evaluating corrosion activity. Relevant microscopic methods include: microelectrode dynamic scanning to measure the distribution of surface potential, ellipsometry (Ellipsometry) to measure surface film thickness, scanning electron microscopy, Auger electron spectroscopy (AES) and atomic force microscopy to characterize the microscopic morphology. And its changes, using X-ray photoelectron spectroscopy (XPS), Fourier transform infrared transform and reflection absorption-infrared spectroscopy to characterize the chemical structure of the film and its changes, etc.

Although the above-mentioned methods can provide information on the surface properties of metal materials from different angles, there are still some irreparable defects. First, some large-scale instruments are expensive and difficult to popularize; It is destructive, and it is not convenient to continuously monitor the change of surface properties over time on site; third, a method can usually only characterize one performance, and cannot perform comprehensive evaluation of multiple properties; fourth, the most important surface performance of metal materials is electrochemical Therefore, the electrochemical characterization method is the most basic characterization method and cannot be replaced by other methods; fifth, in the electrochemical method, the polarization curve is destructive to the sample, and the form of the disturbance signal is single, and it is difficult to separate the influence of diffusion. Therefore, it can provide limited information and is not suitable for evaluating metal surface film, wettability, etc.

Electrochemical impedance spectroscopy can continuously monitor the change of the surface state of metal materials in the corrosion system. The measurement conditions are simple, easy to obtain, and non-destructive, and can simultaneously evaluate the basic properties of the macroscopic surface such as wettability (through interface capacitance) and corrosion resistance. , gives rich information about the change mechanism, and has important potential advantages in characterizing the surface properties of metal materials. It is a promising and important means of characterizing the surface properties of materials, and has attracted a lot of attention from researchers at home and abroad. At present, the most commonly used spectrogram analysis method is to use an equivalent circuit model with a fixed structure, and it is recognized that equivalent resistance elements can be used to characterize the electrochemical reaction resistance on the surface of metal materials, and equivalent capacitance elements can be used to characterize its surface electric double layer or surface film. Thickness, porosity, dielectric constant and other related properties, and this equivalent capacitance can be described by the definition of a plate capacitor: $C={\mathrm{\ϵ}}_0{\mathrm{\ϵ}}_r\frac{A}{d}$ , where ε ₀ is the vacuum permittivity, ε _r is the relative permittivity, A is the electrode area, and d is the distance between the plates of the plate capacitance model.

Although equivalent elements can be used to characterize the surface properties of metal materials, the method of determining these equivalent elements is not obvious, and one spectral line can correspond to multiple equivalent circuit models. Obviously, different analysis results can be obtained by using different equivalent circuit models. In addition, various factors such as surface wettability, electrochemical activity, and corrosion products have different effects on the impedance component, resulting in variable impedance spectrum morphology, and one of the basis for establishing an equivalent circuit model with a fixed structure is the impedance spectrum morphology. , that is, according to the characteristics of the specific impedance spectrum, combined with the physical meaning of the system to determine the appropriate equivalent circuit structure and the number of parameters, in order to have a satisfactory fitting result while the physical meaning is relatively clear. In this method, a certain physical meaning is given to each equivalent component, and the performance of the system and its variation law are evaluated according to the change of component parameters. Since the impedance spectra of different features need to be fitted with equivalent circuit models of different structures, the intermediate process of the system change corresponding to the sudden change of the circuit structure cannot be well explained. In addition, even if the equivalent circuit structure is changed according to the characteristics of the impedance spectrum, a considerable part of the impedance spectrum is difficult to fit. In particular, it should be pointed out that the CPE component widely used in the equivalent circuit model can obviously improve the fitting accuracy, but it is a superficial component after all, and it is a mathematical formula established to fit the test curve. The meanings of the two parameters Y ₀ and n are rather ambiguous, and they are still being discussed. They are neither purely capacitive nor purely resistive, and their changes directly affect the values of other resistance and capacitance elements in the equivalent circuit model. To a certain extent, it confuses and conceals the root cause and regularity of their changes, resulting in the obtained parameters being the result of the joint action of various influencing factors, which cannot objectively and accurately reflect the actual situation of the studied system as the analyst hopes. Since the influence of various factors on the morphology of the impedance spectrum cannot be found and separated fundamentally, various models have been established, which directly affect the objectivity, regularity and comparability of the analysis results, so that in quite a few cases The relationship between analytical parameters and system performance is not clear, resulting in the cross-change of analytical parameters of different systems at different times, often requiring a 10-fold difference for comparison. The results obtained are mostly qualitative, and even contradict the system performance. The disadvantages of the above fixed-structure equivalent circuit model to a considerable extent conceal the advantages of rich and sensitive electrochemical impedance spectroscopy, which seriously hinders the application of electrochemical impedance spectroscopy as an independent analysis technique in scientific research and industrial production. actual.

In view of the above reasons, in the industrial production related to metal materials such as forming foil, battery, electroplating, metal pretreatment, etc., there is a lack of technology for on-site tracking and detection of surface performance changes of metal materials in each process link, usually only according to a certain process. The quality of the finished product or semi-finished product speculates whether the process conditions are appropriate or not, and there is a lack of appropriate adjustment basis for some key production links, which is quite blind. In the research and development process of related products, the lack of suitable, objective and sensitive evaluation methods to provide reliable detailed information on the changes in metal surface wettability and electrochemical properties also hinders the efficiency and clarity of research and development work.

【Content of invention】

In order to solve the above problems, the present invention establishes a comprehensive analysis method of electrochemical impedance spectroscopy for characterizing the surface properties of gold metal materials. The present invention utilizes the sensitivity and richness of information of electrochemical impedance spectroscopy, and the fitting of mCRR transmission line models, Analyzing the objectivity and versatility of the impedance spectrum, so that the difference between the surface properties of metal materials can be comprehensively characterized objectively, consistently and sensitively, and used to guide the actual production; the electrochemical impedance spectrum of different samples can also be amplified by changing the measurement conditions The difference between them improves the sensitivity of the analysis results.

The technical solution adopted by the present invention to solve the technical problem is: a comprehensive analysis method of electrochemical impedance spectroscopy for the surface properties of metal materials, first adopting the mCRR transmission line model to fit the electrochemical impedance measured under the conditions of causality, stability and linearity spectrum, wherein m is a positive integer, C and R represent pure capacitance and pure resistance respectively; then according to the formula f ^* =1/(2πC _i R _i ), the characteristic frequency f ^* of each C _i and R _i parallel branch is calculated respectively, And draw the logarithmic graph of the discrete parameters C _i and R _i changing with the characteristic frequency under different series of research conditions and the graph of R _o changing with the research conditions; finally, according to the characteristics of the graph, determine the difference of the surface properties of the metal material.

For the impedance spectra of metal material samples under different conditions, the optimal m value of the transmission line model can be determined respectively according to the fitting variance and the relative error of the components.

For impedance spectra measured in different samples and at different times, the optimal m value can be different under the condition that the fitting variance is satisfied and the relative error of the components is small.

The value of element R _o in the mCRR model to determine the optimal m value is consistent with the size of the surface corrosion resistance of each metal material sample.

As the discrete parameters C _i and R _i of the mCRR transmission line model under the condition of optimal m value vary with the characteristic frequency $f_i^{*}(f^{*}=1/\left(2\mathrm{\π}{C}_i{R}_i\right))$ The logarithmic curve of the change, according to the logarithmic curve and its change characteristics, characterizes the characteristics of the metal surface state.

For some specific systems, when the optimal m value is determined, compare the logarithm of the discrete parameters C _i and R _i of the transmission line models of different lengths corresponding to m, m+1, and m-1 with the characteristic frequency f _i ^* From the curve, it can be found that the corrosion system has several characteristic discrete values that do not vary with the length of the transmission line model.

In the battery system, the number of such characteristic discrete values is very small, or even none, reflecting the differences in the intrinsic characteristics of the system.

The change characteristics of the logarithmic curve include: (1) the distribution value of the discrete element value varies with the time of the characteristic frequency, (2) the rate at which the discrete element value changes with the characteristic frequency, (3) the distribution of the discrete element with the characteristic frequency (4) The variation law of the characteristic frequency corresponding to the extreme value of discrete components.

Through the matching computer software, the optimal m value of the mCRR transmission line model corresponding to the impedance spectrum of different samples can be automatically determined according to the mCRR transmission line model, and the impedance spectrum data can be automatically processed, fitted, and analyzed, and finally the surface properties of the metal material can be given Difference analysis results.

The first theoretical basis of the present invention is: the transmission line model is suitable for describing the transport process of substances, and the mass transfer process generally exists in all electrochemical systems, so this model has universal applicability to different electrochemical systems, and can separate The impact of the diffusion process, and at the same time reveal the differences in factors that affect the diffusion process in the system, such as the barrier properties of the surface film and the relative size of the electrochemical reaction resistance.

The second theoretical basis of the present invention is: the extreme value of the discrete element is the result of the opposite effect of the two series process influencing factors of charge transfer resistance and diffusion resistance, that is, the smaller the charge transfer resistance (the larger the electrochemical reaction rate), the greater the diffusion resistance. The more obvious the importance, the higher the eigenfrequency of discrete component extrema, and vice versa. Therefore, the extremum of the discrete element and the corresponding eigenfrequency can reflect the important properties of the system related to this feature

The third theoretical basis of the present invention is: since the model only includes resistance and capacitance elements with clear physical meanings, the relationship between the variation of discrete parameter values and the difference in metal surface properties is clear.

The fourth theoretical basis of the present invention is: due to the influence of roughness, the actual surface area of metal is a quantity that is difficult to accurately measure and control. The difference in roughness between series samples will directly affect the values of capacitance and resistance components, but will not affect the resistance. and the product of capacitance, thus does not affect the characteristic frequency. Therefore, when the characteristic frequency is used to characterize the system, it can not be disturbed by the roughness, which improves the clarity and regularity of the analysis results.

The positive effects of the present invention are: use the sensitivity and richness of information of electrochemical impedance spectroscopy, and the objectivity and versatility of mCRR transmission line model fitting and analysis impedance spectroscopy, thereby objectively, consistently and sensitively comprehensively characterize the surface of metal materials The difference between the properties is used to guide the production practice, and it also has important theoretical significance in terms of the analysis method of impedance spectroscopy.

Measure the change of electrochemical impedance spectrum under different conditions before and after the important process in the metal material processing process, and analyze the impedance spectrum data according to the mCRR transmission line model fitting analysis, according to the fitting error (including the total error and the relative error of the equivalent element ) change to determine the best m value, and determine the values of all equivalent components in the mCRR transmission line model, and make the logarithmic curves of the discrete parameters C _i and R _i changing with the characteristic frequency f ^* , and R ₀ changing with the test conditions curve. Evaluate the change characteristics of the surface properties of metal materials according to the curve change characteristics, such as the wetting condition of the metal material surface, the degree of cleanliness and the relevant characteristics of the surface film, etc.; evaluate the corrosion activity of the metal material surface according to R ₀ . Computer programs can also be used to automatically analyze and analyze the changing laws of parameters, and provide reliable information on the surface state of the metal material to be measured, thereby playing the role of predicting, monitoring and evaluating the process, in order to reasonably adjust process conditions and control product quality. Provide reliable evidence.

The present invention is applied at the beginning of the forming foil process, first immersing the aluminum foil sample after suitable surface pretreatment in a suitable electrolyte solution, measuring the change of its impedance spectrum under different conditions, and then comprehensively analyzing the differences between the surface states of different batches of metal materials The difference can provide reliable information for determining the subsequent process conditions.

Since impedance spectroscopy is not destructive to the tested sample, it can be used in production lines related to metal raw materials to monitor changes in the surface state of metal materials.

The invention is used in the electroplating production process, and can monitor and analyze the causes of quality problems such as foaming of the electroplating parts.

The invention is used in the production and development process of the secondary battery, and can comprehensively evaluate the electrochemical activity of the battery grid, the binding state with the surface active substance, the reaction activity and the like.

The invention can also be used for detecting product quality, evaluating and screening the optimal conditions of the metal material pretreatment process.

[Drawings and Description of Drawings]

Fig. 1 is a schematic diagram of the mCRR transmission line model of the present invention;

Fig. 2 is the impedance spectrum fitting result figure of A ₃ steel sample soaked in 3% NaCl solution for 3 hours;

Fig. 3 and 4 are the example figure that the comprehensive evaluation of electrochemical impedance spectrum of the present invention acetone and water cleaning affect the surface performance of _A3 steel;

Fig. 5 and 6 are the example diagrams of the influence of electrochemical impedance spectroscopy comprehensive evaluation silane aging temperature and time on _A3 steel surface properties of the present invention;

Fig. 7 is an example diagram of the characteristic frequency corresponding to the discrete parameter extremum of the silane hydrolysis time affecting the pretreatment _A3 steel according to the present invention;

Fig. 8 is an example diagram of the eigenfrequency corresponding to the extreme value of discrete parameters affected by the silane pretreatment of _A3 steel according to the present invention changing with the soaking time;

Fig. 9 is the example figure that the silane pretreatment _A3 steel of the present invention affects the minimum value of the discrete resistance as the soaking time of the sample changes;

Fig. 10 is an example diagram of the minimum value of the discrete resistance component of the mCRR transmission line model and its corresponding characteristic frequency affected by the concentration of the corrosion inhibitor according to the present invention;

11 is an example diagram of the influence of the concentration of the electrolyte solution of the present invention on the distribution of the resistance component of the mCRR transmission line model (the value in the legend is the concentration of the electrolyte, and the unit is mole/liter);

Fig. 12 is an example diagram of the influence of the overpotential of the present invention on the resistance component of the mCRR transmission line model (the physical quantities in the legend represent different overpotentials);

Fig. 13-Fig. 16 are in different potential intervals described in the present invention, with the difference of the electrode process that takes place on the surface of the sample, the variation of the discrete capacitance of the CR transmission line model with the characteristic frequency has completely different characteristics (simultaneously located in different characteristics An example plot of the frequency interval). The characteristics of the potential intervals corresponding to the four figures are: Figure 13 corresponds to the electric double layer potential interval, Figure 14 corresponds to the potential interval of oxide film formation, Figure 15 corresponds to the potential interval of oxide film growth, and Figure 16 corresponds to the potential interval of oxygen precipitation.

Figures 17-20 show that in different potential intervals according to the present invention, the discrete resistance of the CR transmission line model varies with the characteristic frequency according to the different electrode processes that occur on the sample surface. frequency range. The characteristics of the potential intervals corresponding to the four figures are: Figure 17 corresponds to the electric double layer potential interval, Figure 18 corresponds to the potential interval of oxide film formation, Figure 19 corresponds to the potential interval of oxide film growth, and Figure 20 corresponds to the potential interval of oxygen precipitation.

【Detailed ways】

The present invention will be further described below in conjunction with example and accompanying drawing.

Fig. 1 is the equivalent circuit model of the fitting metal material electrochemical impedance spectrum adopted in the present invention, wherein C and R represent pure capacitance and pure resistance respectively. Use the subscript i to distinguish the discrete equivalent components in different circuit branches in the figure, and there are m series branches of C and R in total.

Example 1, the present invention can be used to evaluate the impact of the medium and process conditions used to clean the metal surface on the wettability and electrochemical activity of the metal surface. For example, A ₃ steel after scrubbing the rust-removed sandpaper with cotton wool dipped in acetone, heated in an oven at different temperatures for a certain period of time, and then cooled to room temperature in a desiccator. After soaking in 3% NaCl aqueous solution, the impedance spectra of different soaking times were measured immediately at the open circuit potential. The specific measurement conditions are: use Solartron 1280Z electrochemical instrument, the disturbance amplitude is 5mV, the frequency range is 0.1Hz-10kHz, the stainless steel sheet is used as the auxiliary electrode, the saturated calomel electrode is used as the reference electrode, and the apparent measurement area is about 12cm ^2. Fit the data with the mCRR transmission line model. Figure 2 is a legend of the discrete parameter C _i changing with the characteristic frequency f ^* . It can be seen that near the optimal m value, the length of the transmission line does not affect the distribution of C _i , and in the low frequency range of f ^* , C _i is stable value (expressed as C ^* ) and is related to the wettability of the metal surface. The changes of C ^* and R ₀ with the square root of immersion time (t ^0.5 ) at different heating temperatures and times are shown in Figure 3 and Figure 4. For comparison, the figure also shows the direct use of tap water and deionized water after sandpaper rust removal. Results of A ₃ steel samples measured immediately after rinsing.

As shown in Fig. 3, C ^* of all samples increased with immersion time, and the difference among different samples was large. The capacitance value C ^* of the sample after direct washing with water is the largest, ranging from 1.5×10 ^-4 to 3×10 ^-4 F.cm ^-2 (pentagram). The minimum value of C ^* of the sample after washing with acetone is about 5×10 ^-5 F.cm ^-2 , and it increases with the heating temperature and time (square). If the acetone cleaning is performed for a longer time and at a higher temperature (such as 160°C, 1h), the C ^* value is still smaller than that of the water-rinsed sample (lower triangle), indicating that the influence of acetone on surface wettability is difficult to eliminate. In addition, the C ^* of all samples increased significantly with the immersion time, especially at the initial stage of immersion, because corrosion and other effects reduced the acetone attached to the surface and increased the hydrophilicity or roughness of the metal surface, resulting in an increase in C ^* . It can also be seen from surface observation that the color of corrosion products appears on the surface of some substrates, and the lower the open circuit potential, the larger the area showing corrosion color.

Figure 4 shows that the method of acetone cleaning has little effect on the corrosion resistance (R ₀ ) of A ₃ steel. The value and trend of change of R ₀ of all samples are relatively concentrated, and they all increase with the immersion time. This is the metal substrate without any protective effect. characteristic of corrosion.

Although the present invention is relatively close to the sample analysis results under different conditions (the difference is less than 5 times), the difference and the regularity of the reflected surface state are very clear, which reflects the impact of different cleaning methods on the surface wettability of metal materials. and corrosion resistance. The sensitivity of this method is better than that of other fixed structure equivalent circuit models, and its simplicity is better than the microscopic analysis method of large instruments.

Example 2, the effect of silane pretreatment on the metal surface is greatly affected by the process conditions. Among them, it is of great significance to accurately determine the appropriate aging temperature and time. Now an example is given to illustrate the application of this method in this respect. Soak the _A3 steel cleaned with acetone in ethanol solution containing 1% KH-550 for 30-60 seconds, take it out, dry it at room temperature, and then put it in an oven for aging under different conditions (140°C, 0.5h, five-pointed star; 140°C, 1h, upper triangle; 160°C, 1h, solid circle), and finally cooled to room temperature in a desiccator. The measurement conditions and data analysis method of the impedance spectrum are the same as Example 1, and 4 parallel samples are measured for each condition, and the analysis results are shown in Fig. 5 and Fig. 6 . It can be seen that the distribution of C ^* and R ₀ parameter values of the parallel samples is relatively concentrated, and the difference between different samples is obvious, which shows that the influence of aging conditions on the wettability and corrosion resistance of the metal surface is obviously different. This example shows that this method can identify the influence of small process conditions on the metal surface state, and the result has high sensitivity and reproducibility, so it has important application value in related product development and industrial production.

Example 3, the hydrolysis conditions of silane have a great influence on the pretreatment effect of metal materials. This example illustrates that this method can be used to evaluate and screen the optimal conditions for silane hydrolysis. Take the aqueous solution containing 0.6% KH-550 and hydrolyze it for different time, act on the surface of _A3 steel under the same pretreatment condition, measure the change of its impedance spectrum with the immersion time (2.5% _{Na2SO4 aqueous} solution is the corrosion medium, At room temperature, the impedance spectrum measurement conditions are the same as example 2), and then analyzed with this method. The influence of different hydrolysis times on the characteristic frequency (f ^* _min ) corresponding to the extremum value of discrete components is shown in Figure 7 (measured after soaking in corrosive medium for 4 minutes), and the dotted line in the figure indicates the sample without silane treatment. It can be seen that the silane film formed by the pretreatment process obviously affects the value of f ^* _min , and it shows that the silane aqueous solution can be stable for nearly 8 days. The change of f ^* _min with immersion time is shown in Figure 8. As the immersion time prolongs, the silane film is gradually destroyed, so the f ^* _min value gradually decreases and is close to the result of the blank sample (solid square). The minimum value R _i,min of the discrete resistance decreases with the prolongation of immersion time (see Fig. 9), which is an important sign of film damage, while the R _i,min of the blank sample without pretreatment (solid square) decreases with the immersion time The elongation shows an increasing trend, which is an important feature of corrosion of metallic material substrates. When the silane film obtained by pretreatment (such as film formation in dilute solution) is thin (the principle of silane pretreatment to increase the metal/coating interface adhesion requires thin film), the impedance spectrum morphology on the complex plane is similar to that of the blank sample , and the change trend is consistent with the increase of immersion time, that is, the single arc on the complex plane and the modulus value on the Bode diagram both increase with immersion time, indicating that the corrosion of the substrate conceals the change of film properties. However, the analysis by this method can separate the influence of corrosion and reveal the characteristic changes of the silane film on the surface of the metal material.

Example 4, this method can also study the mechanism that the corrosion inhibitor in the corrosive medium increases the corrosion resistance of the material surface. For the low-carbon steel sample in 5% HCl corrosion medium, the influence of the change of tannic acid concentration on f ^* _min and R _{i, min} is shown in Figure 10. It can be seen from the figure that f ^* _min increases with (corrosion agent) concentration increases linearly, indicating that the mechanism of action of the corrosion inhibitor is to reduce the corrosion active area and increase the resistance of diffusion, so the influence of diffusion resistance appears in the higher characteristic frequency range. Figure 10 also shows that the value of R _i,min fluctuates with the increase of the concentration of tannic acid, indicating that the mechanism of action of the corrosion inhibitor is mainly to increase the corrosion resistance by the adsorption of tannic acid on the surface of the material, while the stability of the adsorption film is obviously not as good as that of The reaction produces a film (such as the silane film pretreated in Example 3).

Example 5, this method can also be used to study the effect of electrolyte concentration. Partial results of impedance spectroscopy analysis of Cu-65Ni alloy system in aqueous solutions with different Na ₂ SO ₄ concentrations at room temperature are shown in Figure 11 (the numbers in the legend represent the concentration of Na ₂ SO ₄ in mol/L), where The variation of the discrete resistance R _i with the characteristic frequency is shown. It can be seen from the figure that as the electrolyte concentration increases, the characteristic frequency corresponding to R _i,min moves to the high frequency direction, and mainly affects the R _i of the high frequency part, but has no effect on the R _i of the low frequency part.

Example 6, this method can also be used to study the influence of bias potential on the metal material system. The impedance spectrum analysis results of the Co electrode system under different bias potentials in 6mol/L KOH solution are shown in Figure 12 (the corresponding bias potential values are given in the legend, relative to Hg/HgO, OH ^-1 reference electrode) , which gives the discrete resistance R _i as a function of characteristic frequency. It can be seen from the figure that the bias potential mainly affects the R _i of the low frequency part, but has no effect on the R _i of the high frequency part. And as the bias potential increases, R _i,min gradually increases, and its corresponding characteristic frequency moves to the high frequency direction at the same time, indicating that with the increase of the bias potential, the reactivity of the Co electrode increases, the resistance of the electrochemical reaction decreases, and the transmission The resistance to qualitative processes gradually increases, and its effects appear at higher and higher frequency ranges.

Example 7, this method can also be used to study different processes that occur on the surface of metal materials in different bias potential intervals. Figures 13 to 20 show the impedance spectroscopy analysis results of the In electrode system in the H ₃ BO ₃ +NaOH solution containing 0.1 mol/L at pH 10 under different bias potentials. The distribution of the electric double layer potential interval C _i and R _i with the characteristic frequency between -1.25 ~ -1.20V is shown in Figure 13 and 17 respectively; the oxide film formation potential interval between -1.15 ~ -0.90V, C _i The distributions of C i and R _i with the characteristic frequency are shown in Figures 14 and 18, respectively; in the oxide film growth potential range between -0.85 and 1.10V, the distributions of C _i and R _i with the characteristic frequency are shown in Figures 15 and 19, respectively; For the range of oxygen evolution potential between 1.60V, the distributions of C _i and R _i with characteristic frequency are shown in Figures 16 and 20, respectively. It can be seen that when the process of the electrode surface is different, the distribution of the discrete components C _i and R _i with the characteristic frequency has completely different characteristics, so the process of the metal material can be inferred according to these characteristics, and then its surface characteristics can be inferred.

The above examples illustrate that the present invention has multiple uses, and can be widely used in various production fields related to metal materials. For example, it can fill the gap in the lack of suitable and sensitive methods to characterize the surface characteristics of metal materials in the production fields of chemical forming foil, electroplating, batteries, etc.; it can determine more suitable process options for different batches of metals and their alloys with the same composition but different surface electrochemical activities On-line monitoring of standards, technological process combinations and production process quality reduces the blindness of the production process, and minimizes production costs and improves production efficiency under the condition of meeting certain specifications of product indicators. In addition, this method can also be used to evaluate the effect of metal material surface pretreatment, screen and optimize pretreatment formula and process.

In the process of implementing the specific technical solution, there are the following problems worth noting.

1. For the impedance spectra of different samples and measured at different times, the optimal m values are allowed to be different from each other under the condition that the total error and the relative error of the components are small.

2. Although different optimal m values will lead to different numbers of discrete parameters in the circuit, and it is currently impossible to determine the one-to-one correspondence between all discrete parameters and specific electrochemical processes, the law of discrete parameters changing with f ^* is simple and clear, and is consistent with There is a clear correlation between the surface properties of the system.

3. The present invention avoids the difficulty of determining equivalent circuit models of different structures for impedance spectra of different characteristics and the subjective interference of analysts when building models due to the adoption of the mCRR transmission line model with consistent structure to fit and analyze relevant impedance spectrum data. The objectivity of the analysis results has been greatly improved.

4. By changing the corrosion medium composition and measurement conditions, the difference between the surface properties of metal materials can be amplified to improve the sensitivity of the analysis results.

5. Through the supporting computer software, it can automatically process, fit and analyze the impedance spectrum data, and give the analysis results of the difference in the surface properties of metal materials.

Claims (7)

1, a kind of comprehensive analysis method of electrochemical impedance spectrum of metal material surface characteristics is characterized in that:

Analysis is under the influence of the factor that comprises pretreatment condition, corrosion potential, dielectric concentration and composition, system temperature and sample soak time, the comprehensive analysis method of electrochemical impedance spectrum of metal material surface characteristics, thereby differentiate the difference of metal sample surface state, and the difference of properties of sample comprises the dielectric properties of cleanliness, wetting state, corrosion activity, surface film oxide or pre-service film, the complete and compactness of film;

At first adopt the mCRR transmission line model to fit within and satisfy the electrochemical impedance spectroscopy of measuring under causality, stability and the linear conditions, wherein m is a positive integer, and C and R represent pure electric capacity and pure resistance respectively; Then according to formula f*=1/ (2 π C _iR _i) obtain each C respectively _iAnd R _iThe characteristic frequency f* of parallel branch, and be made in discrete parameter C under the different series of studies conditions _iAnd R _iThe figure that changes with study condition with the logarithmic graph of characteristic frequency change profile and Ro; Make the discrete parameter C of mCRR transmission line model under the best m value condition _iAnd R _iWith characteristic frequency f _i* (f _i*=1/ (2 π C _iR _i)) logarithmic curve that changes, come the feature of characterizing metal surface state according to logarithmic curve and variation characteristics thereof; The variation characteristic of described logarithmic curve comprises: (1) discrete elements value with the distribution value of characteristic frequency over time, (2) the discrete elements value is with the speed of characteristic frequency variation, (3) discrete elements is with the Changing Pattern of characteristic frequency distribution value, the Changing Pattern of (4) discrete elements extreme value characteristic of correspondence frequency size; At last, determine the difference of metal material surface characteristics according to the feature of figure; Utilize the rich of the sensitivity of electrochemical impedance spectroscopy and information, and the match of mCRR transmission line model, analyze objectivity, the versatility of impedance spectrum, thereby difference objective, consistent, that exist between the comprehensive characterization metal material surface character delicately, and be applied to comprise and change into paper tinsel, battery, plating and the metal pretreatment production technology relevant with metal material.

2, the comprehensive analysis method of electrochemical impedance spectrum of metal material surface characteristics as claimed in claim 1, it is characterized in that:, determine the best m value of its transmission line model respectively according to the relative error of match variance and element for the impedance spectrum of the metal material sample under the different condition.

3, the comprehensive analysis method of electrochemical impedance spectrum of metal material surface characteristics as claimed in claim 1 or 2, it is characterized in that: for different samples, different time measured impedance spectrum, satisfying under the little situation of match variance and element relative error, best m value can be different.

4, the comprehensive analysis method of electrochemical impedance spectrum of metal material surface characteristics as claimed in claim 1 or 2 is characterized in that: the numerical value of the element Ro in the mCRR model of determining best m value is big or small consistent with each metal material sample surfaces corrosion resistance.

5, the comprehensive analysis method of electrochemical impedance spectrum of metal material surface characteristics as claimed in claim 1 or 2, it is characterized in that: for some specific system, after having determined best m value, compare the discrete parameter C of the transmission line model of m, m+1, the pairing different length of m-1 _iAnd R _iWith characteristic frequency f _i ^*The logarithmic curve that changes can find that corrosion system has not the certain characteristics discrete value that the length with transmission line model changes.

6, the comprehensive analysis method of electrochemical impedance spectrum of metal material surface characteristics as claimed in claim 1 is characterized in that: the number of this feature discrete value seldom even does not have in battery system, has reflected the difference of system internal characteristics.

7, the comprehensive analysis method of electrochemical impedance spectrum of metal material surface characteristics as claimed in claim 1 or 2, it is characterized in that: by the computer software that matches, according to the mCRR transmission line model is definite automatically and the m value of the mCRR transmission line model that the impedance spectrum of different samples is corresponding, and automatically processing, match, analysis impedance spectrum data, provide the analysis result of metal material surface characteristics difference at last.

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