CN116642822A - An electrochemical method for determining the end point of desalination of iron cultural relics - Google Patents

Abstract

The invention discloses an electrochemical method for judging the desalting endpoint of an iron cultural relic, which comprises the following steps of: step S1: data acquisition, namely constructing a three-electrode system for electrochemical test, and connecting the three-electrode system with an electrochemical workstation to realize data acquisition of electric signals; transmitting the noise potential and the noise current acquired by the electrochemical workstation to a computer for data processing; the three-electrode system comprises a working electrode, a reference electrode and an auxiliary electrode; step S2: data processing; time domain analysis; and (5) frequency domain analysis. The invention discloses an electrochemical method for judging the desalination degree of an iron cultural relic, which can be used for nondestructively detecting the corrosion state of the iron cultural relic in the desalination process and solving the problem of judging the desalination degree of the iron cultural relic.

Description

An electrochemical method for determining the end point of desalination of iron cultural relics

technical field

The invention relates to the technical field of cultural relics desalination judgment, and more specifically, the invention relates to an electrochemical method for judging the desalination end point of iron cultural relics.

Background technique

Iron cultural relics are witnesses to the development of productive forces in ancient society and have important historical and scientific value. Due to the lively nature of iron, it is easily corroded. Many iron objects unearthed are rusty. If they are not protected, the life of the cultural relics will be greatly shortened. The general steps for the protection of iron cultural relics include: cleaning and rust removal, desalination, corrosion inhibition and sealing. Among them, desalination is an important part of the protection of iron cultural relics. The salt here refers to the chloride in the cultural relics. The existence of chloride ions will cause severe pitting reactions and aggravate the corrosion of iron cultural relics. Therefore, for iron cultural relics, especially iron cultural relics from ocean water, the removal of chloride ions in cultural relics is beneficial to slow down the corrosion of iron cultural relics, so as to achieve long-term stable preservation of cultural relics.

In the protection of cultural relics, the most commonly used desalination method is the lye soaking method, which is to soak the cultural relics to be desalted in a sodium hydroxide solution of a certain concentration (0.1 or 0.5mol/L), based on the free migration of chloride ions, to achieve Desalination and chlorine removal of cultural relics. And by regularly replacing the soaking solution, the removal efficiency of chloride ions is improved. The determination of the degree of desalination treatment is often based on the content of chloride ions in the desalination solution. When the concentration of chloride ions in the solution is below 50ppm (mg/L), and the concentration has not changed significantly after changing the solution many times, it can be considered The desalination process is over (Technical Manual for Museum Iron Relics Conservation, 2011). Some scholars also regard the chloride ion concentration of 20ppm as a sign of the end of the desalination process. Ideally, the concentration of chloride ions in the desalination solution should be equal to the concentration of chloride ions in the cultural relics being treated. However, factors such as soaking time, the volume ratio of soaking solution to cultural relics, and the presence of rust on the surface of cultural relics will all affect the migration efficiency of chloride ions. The concentration of chloride ions in the solution does not represent the chloride ion content of cultural relics.

Some scholars use strong acid to dissolve the desalted cultural relics, and then measure the concentration of chloride ions. There are also scholars who store the desalted cultural relics in an environment with high relative humidity for 9 months, and observe the state of the cultural relics to judge the degree of desalination treatment. However, the above method has already caused irreparable losses to cultural relics with poor desalination degree and low efficiency after passing the test, which does not conform to the "principle of reversibility" and "principle of minimum intervention" in the protection of cultural relics. Therefore, there is a need for a method capable of instantly/in time judging whether the desalination treatment of cultural relics is finished.

Traditional electrochemical methods mainly include: polarization curve method and electrochemical impedance spectroscopy. However, both methods will apply polarization to the measured system, which may change the phase composition of the rust layer, and cannot accurately measure Local electrochemical parameters of metal corrosion under rust layers. Electrochemical noise is an in-situ, non-destructive electrochemical method that does not require external disturbances to the electrode that alter its surface corrosion process during testing. By detecting the random non-equilibrium fluctuations of noise potential and noise current in the system over time, the information of the corrosion system can be explored (Zhang Jianqing, 2002; BertocciU, 1995). At present, electrochemical noise technology has been widely used in the field of corrosion and protection of industrial metals, and it is an important means to study metal localized corrosion, coating performance evaluation and corrosion inhibitor screening.

Existing technology 1: Shang Suhong, He Jiquan; Simulating the electrochemical behavior of ancient cast iron in typical lye [J]. Chemical Technology and Development, 2014,43(01):16-19.

Abstract: By means of potentiodynamic polarization curve method, the electrochemical behavior of simulated ancient gray cast iron and white cast iron was studied in several typical alkaline aqueous solutions containing different concentrations of chloride ions. The results show that the passivation/activation sensitivities of the same cast iron samples to chloride ion concentration are different in different alkaline solutions; the sensitivity of cast iron samples of different materials to chloride ions is also different in the same solution. Moreover, for the alkaline solution of the same solute, the sensitivity of cast iron to chloride ions decreases as the pH value of the solution increases. This result will provide an important basis for the determination of the end point of desalination and chlorine removal of iron cultural relics.

Conclusion: (1) Alkaline solution with high pH value can promote the passivation of simulated ancient cast iron. The presence of chloride ions exceeding the critical concentration will have a destructive effect on the activation and corrosion of simulated ancient cast iron.

(2) Different alkaline solutes have a certain influence on the electrochemical performance of simulated ancient cast iron.

(3) In the case of the same solute, the chloride ion resistance of the simulated ancient gray cast iron and white cast iron increases with the increase of the alkalinity of the solution.

(4) In alkaline solutions with different pH values, the critical concentration of chloride ions for the conversion of cast iron from stable passivation to unstable passivation is different. Therefore, the extremely low critical chloride ion content in the alkaline medium at a lower pH value can be used as the end point for judging whether the sample dechlorination treatment can be stopped; Chemical as an evaluation method to test the dechlorination effect of iron cultural relics.

The polarization curve method used in the above technology is an electrochemical test method with externally enhanced polarization, which will affect the rust layer on the surface of the cultural relics to be tested, resulting in a biophase change on the surface of the cultural relics, which does not conform to the principles of cultural relics protection.

Prior Art 2: Publication No.: CN113984637A The present invention discloses a method for detecting side corrosion of boiler flue gas based on electrochemical noise. By adopting a corrosion monitoring device in a high-temperature corrosion environment and using electrochemical noise, real-time monitoring of high-temperature corrosion conditions is realized. monitor. The invention processes the electrochemical noise data to obtain the pitting corrosion index and noise impedance, judges whether local corrosion occurs through the pitting corrosion index, and judges the speed of corrosion occurrence through the noise impedance, so as to achieve the purpose of truly reacting the corrosion and exfoliation of the superalloy on the heating surface of the boiler.

The purpose of the above technology is to ensure the safe operation of the boiler by nondestructively testing the corrosion state of the metal material of the boiler; the above technology uses the pitting corrosion index (pitting corrosion coefficient and noise resistance) to judge the degree of sample corrosion.

Therefore, we propose an electrochemical method for determining the end point of desalination of iron artifacts to solve the above problems.

Contents of the invention

In order to overcome the above-mentioned defects of the prior art, an embodiment of the present invention provides an electrochemical method for determining the end point of desalination of iron cultural relics, so as to solve the problems raised in the above-mentioned background technology.

In order to achieve the above object, the present invention provides the following technical solution: an electrochemical method for determining the end point of desalination of iron cultural relics, including the following methods:

Step S1: Data collection, build a three-electrode system for electrochemical testing, connect the three-electrode system with an electrochemical workstation, and realize data collection of electrical signals;

Transmit the noise potential and noise current collected by the electrochemical workstation to the computer for data processing;

The three-electrode system includes working electrode, reference electrode and auxiliary electrode;

Step S2: data processing, write a program based on MATLAB software, perform polynomial fitting and fast Fourier transform analysis on the noise signal, and obtain the time domain analysis diagram and power spectral density distribution diagram of the detected sample;

Time-domain analysis, plotting the experimentally measured potential noise and current noise over time;

Frequency domain analysis, the relationship between potential noise and current noise and frequency is obtained through fast Fourier transform, and the power density spectrum curve is obtained.

The invention discloses an electrochemical method for judging the desalination degree of iron cultural relics, which can non-destructively detect the corrosion state of iron cultural relics in the desalination process, and solves the problem of judging the desalination degree of iron cultural relics. The judgment of the corrosion state of iron cultural relics in other solutions provides a quantitative and reliable method for the protection of iron cultural relics.

In a preferred embodiment, in step S1, the working electrode is the sample to be tested, and the sample is connected to the test system using alligator clips or other fixtures;

The reference electrode is the most commonly used saturated calomel electrode;

The auxiliary electrode is a platinum electrode.

In a preferred embodiment, in step S1, the zero-resistance ammeter mode is used in the connection between the three-electrode system and the electrochemical workstation, the auxiliary electrode is connected to the ground terminal of the wire, the sampling frequency is 2Hz, and the test time is 1024s.

In a preferred embodiment, in step S2, the local corrosion rate of the cultural relic in the desalination solution is judged by the magnitude of the transient peak and the current noise in the time-domain analysis diagram, and the degree of desalination is judged according to the corrosion state of the cultural relic.

In a preferred embodiment, the fluctuation frequency of the potential and current noise is relatively fast, and the current noise has a strong current noise peak with a long life > 30s and a high amplitude > 1uA, so the local corrosion rate of the cultural relic is high;

If the current noise is a current noise peak with a short lifetime of 3-5s and a low amplitude of 0.01-1uA, it is a metastable pitting event;

If the fluctuation amplitudes of potential noise and current noise are significantly reduced, and the fluctuation period gradually becomes longer, the corrosion rate of cultural relics will be smaller.

In a preferred embodiment, in step S2, write EN data processing software in MATLAB software by oneself, carry out data processing, utilize polynomial fitting method (generally up to 5 polynomials), remove DC component;

Frequency domain analysis using fast Fourier transform;

The relationship between potential noise and current noise and frequency is obtained by fast Fourier transform, and the power density spectrum curve is obtained.

In a preferred embodiment, the corrosion type and the corrosion rate are judged by using the white noise level in the low frequency region and the slope of the linear segment in the high frequency linear region.

In a preferred embodiment, the lower the white noise level in the low-frequency region, the smaller the local corrosion tendency of cultural relics, and the low-frequency region is often related to the anodic reaction of metals in a local area, and the larger the white noise level value, it indicates the local corrosion reaction the greater the tendency

The higher the level of the high-frequency linear section, the more active the corrosion system. The high-frequency section is related to the entire surface of the cultural relics. The flatter the linear section and the closer the slope is to 0, the pitting corrosion may occur on the surface of the cultural relics; the steeper the linear section indicates that the corrosion system occurs evenly. Corroded or in a passivated state.

In a preferred embodiment, by comparing the white noise level value, it can be seen that the white noise level value of the cultural relic is higher during the first desalination and the second desalination, indicating that its corrosion rate is larger, and after multiple desalination, the corrosion of the cultural relic The rate is small;

Judging the corrosion type according to the slope of the linear segment, local corrosion occurs during the first desalination, and after the second desalination or multiple desalinations, the cultural relics are in a state of uniform corrosion or passivation;

According to the level of the high-frequency linear segment, the corrosion rate in the first desalination is greater than that in the second desalination, and the corrosion rate is the smallest after multiple desalinations.

Technical effect and advantage of the present invention:

1. The present invention discloses an electrochemical method for judging the degree of desalination of iron cultural relics, which can non-destructively detect the corrosion state of iron cultural relics during the desalination process, and solves the problem of judging the degree of desalination of iron cultural relics. This method can be applied to The judgment of the corrosion state of iron cultural relics immersed in other solutions provides a quantitative and reliable method for the protection of iron cultural relics.

2. In the desalination solution, the present invention uses a three-electrode system to obtain the EN detection data of cultural relics, writes a data processing program based on MATLAB software, and realizes EN in iron by comparing EN data of cultural relics in solutions with different desalination degrees. Solve the problem of determining the end point of desalination in the protection of quality cultural relics.

3. The present invention proposes an in-situ, non-destructive electrochemical method. By detecting the corrosion state of cultural relics, the stability of cultural relics is judged, thereby inferring whether the desalination treatment of cultural relics can be terminated. The present invention utilizes the transient peak in the time domain diagram and the size of current noise, the size of W and K in the PSD diagram; to judge the corrosion state of iron cultural relics.

Description of drawings

Fig. 1 is the schematic diagram of electrochemical noise test system in the present invention;

Fig. 2 is the variation diagram of potential noise with time in the present invention;

Fig. 3 is the variation diagram of current noise with time among the present invention;

Fig. 4 is a partially enlarged schematic diagram in Fig. 3;

Fig. 5 is the fast Fourier transform analysis figure of electric potential noise among the present invention;

Fig. 6 is a fast Fourier transform analysis diagram of current noise in the present invention.

Detailed ways

The following will clearly and completely describe the technical solutions in the embodiments of the present invention with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only some, not all, embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by persons of ordinary skill in the art without making creative efforts belong to the protection scope of the present invention.

Referring to Figures 1-6, an electrochemical method for determining the end point of desalination of iron cultural relics, the present invention is an in-situ, nondestructive electrochemical detection method, which can be detected at any time during the desalination process of iron cultural relics, so , the detection environment is a desalination solution for iron artifacts.

For data acquisition, a three-electrode system for electrochemical testing was first built, including a working electrode, a reference electrode and an auxiliary electrode.

Wherein, the working electrode is the sample to be tested, and the sample is connected to the test system by using crocodile clips or other fixtures;

The reference electrode is the most commonly used saturated calomel electrode. Since the shape of cultural relics is irregular, and the iron cultural relics were smelted and formed thousands of years ago, it is impossible to find the exact same material. Therefore, the test in the present invention uses Asymmetrical electrode system collects EN data;

The auxiliary electrode is a platinum electrode.

Connect the three electrodes with the electrochemical workstation to realize the data acquisition of electrical signals, adopt the zero resistance ammeter (ZRA, Zero resistance ammeter) mode, the auxiliary electrode is grounded to GND, the sampling frequency is 2Hz, and the test time is 1024s.

The noise potential and noise current collected by the electrochemical workstation are transmitted to the computer for data processing, as shown in Figure 1 of the specification.

For data processing, the program is written based on MATLAB software, polynomial fitting and fast Fourier transform analysis are performed on the noise signal, and the time domain and power spectral density distribution diagrams of the detected samples are obtained.

Time domain analysis:

First, the experimentally measured changes in potential noise with time E-t and current noise with time I-t are plotted in Figure 2 and Figure 3 of the specification.

Judging the local corrosion rate of cultural relics in desalination solution by the size of transient peak and current noise, and then judging the degree of desalination according to the corrosion state of cultural relics;

In the time-varying curves of potential noise and current noise, there are transient peaks with high amplitude;

The fluctuation frequency of the potential and current noise is fast, and the current noise has a strong current noise peak with a long life > 30s and a high amplitude > 1uA, so the local corrosion rate of cultural relics is high;

If the current noise is a current noise peak with a short lifetime of 3-5s and a low amplitude of 0.01-1uA, it is a metastable pitting event;

If the fluctuation amplitudes of potential noise and current noise are significantly reduced, and the fluctuation period gradually becomes longer, the corrosion rate of cultural relics is smaller;

During primary desalination, the content of chloride ions in the rust layer of cultural relics is very large, and both potential noise and current noise have typical local corrosion characteristics, that is, there are transient peaks with high amplitude.

The observed rapid rise of the current noise transient peak is due to the rapid dissolution of the metal matrix at the pitting site, while the decrease of the current noise transient peak is due to the migration rate of Cl- into the corrosion pit reaching the limit, the Cl- The mass transfer rate cannot meet the needs of pitting corrosion development. At this time, the repair rate of the passivation film at the pitting site is greater than the dissolution rate of the metal matrix.

When the pitting no longer develops, the transient peak of the current noise disappears completely, and the fluctuation of the potential noise is due to the charging and discharging of the passivation film by the anode current generated by the dissolution of the metal matrix at the pitting corrosion.

It should be noted that although there are many chloride ions in the rust layer of the cultural relics during the first desalination, since the cultural relics are stored in the atmospheric environment and then soaked in the desalination solution, it can also be observed that there are many bubbles attached to the surface of the cultural relics, and the solution has not yet fully recovered. It is filled into the pores of the porous rust layer. Therefore, the potential noise at this time is still relatively high, and the amplitude of the current noise is relatively small. is a metastable pitting event.

When desalting again, the desalting solution completely soaks the porous rust layer, and at this time the fluctuation frequency of the potential and current noise is relatively fast, and the current noise has a strong current noise peak with a long life > 30s and a high amplitude > 1uA, and the current noise increases And when the desalination is more than one time, it means that a large amount of Cl- in the solution is adsorbed on the surface of the cultural relics, the passivation area on the surface of the cultural relics is destroyed and becomes a corrosion anode, and the larger passivation area and the smaller activation area form a large cathode and a small anode. Corrosion of the battery aggravates the corrosion of the surface of cultural relics.

After repeated desalination, the fluctuation amplitudes of potential noise and current noise were significantly reduced, and the fluctuation period gradually became longer, which indicated that the chloride ions in the rust layer were less able to contact the metal matrix and failed to trigger pitting reactions. In the alkaline desalination solution, the covering effect of the rust layer on the surface of cultural relics slows down the material transfer rate and the corrosion development rate of cultural relics.

Frequency domain analysis:

First, write the EN data processing software in the MATLAB software for data processing, and use the polynomial fitting method (generally the highest polynomial is 5th degree) to remove the DC component.

The frequency domain analysis of fast Fourier transform is carried out, and the relationship between potential noise and current noise and frequency is obtained through fast Fourier transform, and the power density spectrum curve is obtained.

Use the white noise level in the low-frequency region and the slope of the linear segment in the high-frequency linear region to judge the corrosion type and corrosion rate.

The power density spectrum curve has a frequency-independent white noise level in a very low frequency range (0.001-0.01); as the frequency increases (0.01-0.1), the power density spectrum curve appears to decline, and the power density spectrum curve of the noise signal It has a linear relationship with the logarithm of the frequency, and the slope is K;

As the frequency continues to increase, the power density spectrum curve finally drops to the base noise level (the horizontal section curve after 0.1), and some tests do not show base noise, which is related to the background noise of the instrument during detection.

The lower the white noise level in the low frequency area, the smaller the local corrosion tendency of cultural relics. The low-frequency region is often related to the anodic reaction of the metal in a local area, and the larger the value of the white noise level, the greater the tendency of the local corrosion reaction.

The higher the level of the high-frequency linear section, the more active the corrosion system. The high-frequency section is related to the entire surface of the cultural relic. The flatter the linear section and the closer the slope is to 0, the pitting corrosion may occur on the surface of the cultural relic; the steeper the linear section, it indicates the occurrence of corrosion system. Corroded uniformly or in a passivated state.

Referring to accompanying drawings 4, 5 and 6 of the description;

By comparing the white noise level values, it can be seen that the white noise level value of cultural relics is higher in the first desalination and second desalination, indicating that the corrosion rate is larger, while after multiple desalination, the corrosion rate of cultural relics is lower. According to the level of the high-frequency linear segment, the corrosion rate in the first desalination is greater than that in the second desalination, and the corrosion rate is the smallest after multiple desalinations.

It can be seen by calculating the slope of the high-frequency linear region of the potential and current PSD, where PSD is a power density spectrum curve, and the K value during the first desalination is less than -20dB/decade, indicating that the corrosion form is mainly localized corrosion; while desalination and multiple The curve for the second desalination is steeper, combined with other characteristic parameters, the overall corrosion of the relics during the second desalination is uniformly corroded with a large corrosion range, while the relics after multiple desalination are in a relatively stable passivation state.

In the present invention, for the first time, the electrochemical method is used to determine the end point of desalination of iron cultural relics. In the alkaline desalination solution, the EN detection is performed on the ironware with different desalination degrees, and the polynomial fitting and fast Fourier transform are performed on the noise signal based on MATLAB software. Data processing to obtain the time domain and power spectral density map (PSD map) of the detected sample.

The results found that: with the desalination treatment, in the time domain spectrum and PSD spectrum of the cultural relics, the relevant characteristic parameters used to characterize the corrosion behavior of the cultural relics are also changing accordingly. In the time domain distribution diagram of noise data, the corrosion rate of cultural relics in desalination solution can be judged by the size of transient peak and current noise. The transient peak is a typical characteristic of localized corrosion, and the magnitude of the current noise is also related to the corrosion rate. The greater the number of transient peaks and the greater the fluctuation amplitude of current noise, the greater the tendency of cultural relics to be corroded. Similarly, the white noise level (W) in the low-frequency area of the PSD diagram, the slope (K) and amplitude of the linear segment in the high-frequency area are also related to the type of corrosion and the corrosion state of the cultural relics.

The higher the level of white noise, it indicates that a large number of anodic oxidation reactions occur in the local area, and the degree of local corrosion reactions increases. K is related to the corrosion type. The steeper the curve, that is, the more negative the K value, indicates that the system is in a uniform corrosion or in a passivation state; the flatter the curve, that is, the closer the K value is to 0, it indicates that the system is in localized corrosion. The higher the level of the linear part in the high-frequency region, the greater the corrosion rate that occurs on the entire surface of the cultural relic to be tested, and the cultural relic tends to undergo uniform corrosion.

In summary, the fewer the number of transient peaks in the time-domain spectrum of cultural relics in desalination solution, the smaller the amplitude of current noise fluctuations; the lower the W in the PSD diagram, the lower the level of the linear part, and the steeper the slope, indicating that alkaline desalination The more passivated the cultural relics are in the solution, the smaller the tendency of the cultural relics to be pitted, and the surface state of the cultural relics tends to be stable. Therefore, EN technology can be used to in-situ and non-destructively detect the pitting tendency of iron cultural relics in desalination solution, and determine the end point of desalination treatment according to the corrosion state of cultural relics, so as to realize the stable preservation of iron cultural relics.

Abbreviations and meanings of the above contents: electrochemical noise EN; power density spectrum curve PSD; white noise level W; high-frequency linear segment slope K; fast Fourier transform FFT.

Finally: the above is only a preferred embodiment of the present invention, and is not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention shall be included in the present invention within the scope of protection.

Claims (9)

1. An electrochemical method for judging the desalting endpoint of an iron cultural relic is characterized by comprising the following steps of; the method comprises the following steps:

step S1: data acquisition, namely constructing a three-electrode system for electrochemical test, and connecting the three-electrode system with an electrochemical workstation to realize data acquisition of electric signals;

transmitting the noise potential and the noise current acquired by the electrochemical workstation to a computer for data processing;

the three-electrode system comprises a working electrode, a reference electrode and an auxiliary electrode;

step S2: performing data processing, namely performing polynomial fitting and fast Fourier transform analysis on noise signals based on MATLAB software programming to obtain a time domain analysis chart and a power spectral density distribution chart of a detection sample;

time domain analysis, namely drawing the change of potential noise and current noise which are measured through experiments along with time into a graph;

and (3) carrying out frequency domain analysis, and obtaining the relation between potential noise and current noise and frequency through fast Fourier transformation to obtain a power density spectrum curve.

2. The electrochemical method for determining the desalination endpoint of an iron relic of claim 1, wherein:

in step S1, the working electrode is a sample to be tested, and the sample is connected with a testing system by using crocodile clips or other clamps;

the reference electrode is selected from the most commonly used saturated calomel electrode;

the auxiliary electrode is a platinum electrode.

3. The electrochemical method for determining the desalination endpoint of an iron relic of claim 1, wherein:

in the step S1, a zero resistance ammeter mode is adopted in the connection of the three-electrode system and the electrochemical workstation, the auxiliary electrode is connected with the wire grounding end, the sampling frequency is 2Hz, and the testing time is 1024S.

4. The electrochemical method for determining the desalination endpoint of an iron relic of claim 1, wherein:

in step S2, the local corrosion rate of the cultural relics in the desalting solution is judged according to the transient peaks and the current noise in the time domain analysis chart, and the degree of desalting is further judged according to the corrosion state of the cultural relics.

5. The electrochemical method for determining the desalination endpoint of an iron relic of claim 4, wherein:

the fluctuation frequency of potential and current noise is faster, and the current noise has strong current noise peaks with the service life of more than 30s and the amplitude of more than 1uA, so that the local corrosion rate of cultural relics is high;

if the current noise is a current noise peak with a service life of 3-5s and a amplitude of 0.01-1uA, a metastable state pitting event occurs;

if the fluctuation amplitude of the potential noise and the current noise is obviously reduced, the fluctuation period is gradually prolonged, and the corrosion rate of the cultural relics is smaller.

6. The electrochemical method for determining the desalination endpoint of an iron relic of claim 1, wherein:

in step S2, self-programming EN data processing software in MATLAB software by frequency domain analysis, and removing a direct current component by using a polynomial fitting method;

performing frequency domain analysis by using fast Fourier transform;

and obtaining the relation between potential noise and current noise and frequency through fast Fourier transformation, and obtaining a power density spectrum curve.

7. The electrochemical method for determining the desalination endpoint of an iron relic of claim 6, wherein:

and judging the corrosion type and the corrosion rate by using the white noise level of the low-frequency region and the linear section slope of the high-frequency linear region.

8. The electrochemical method for determining the desalination endpoint of an iron relic of claim 7, wherein:

the lower the white noise level of the low-frequency area is, the smaller the local corrosion tendency of the cultural relics is, the low-frequency area is often related to anodic reaction of metal in the local area, and the larger the white noise level value is, the larger the tendency of the local corrosion reaction is predicted;

the higher the level of the high-frequency linear section is, the more active the corrosion system is, the high-frequency section is related to the surface of the whole cultural relic, the linear Duan Yue is flat, and the slope is close to 0, so that the surface of the cultural relic can be pitted; the steeper the linear segment, the more likely the corrosion system will be uniformly corroded or in a passivated state.

9. The electrochemical method for iron relic desalination endpoint determination of claim 8, wherein:

as can be seen by comparing the white noise level values, when the cultural relics are desalted once and desalted again, the white noise level value of the cultural relics is higher, which indicates that the corrosion rate is higher, and the corrosion rate of the cultural relics is lower after the cultural relics are desalted for a plurality of times;

judging the corrosion type according to the slope of the linear section, wherein the corrosion type is locally corroded when desalting is performed once, and the cultural relics are in a uniform corrosion or passivation state after desalting is performed again and repeated desalting is performed;

and according to the level of the high-frequency linear section, the corrosion rate in the first desalination is larger than that in the second desalination, and the corrosion rate after multiple desalination is minimum.