CN116642822A - Electrochemical method for judging desalting endpoint of iron cultural relics - Google Patents
Electrochemical method for judging desalting endpoint of iron cultural relics Download PDFInfo
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- CN116642822A CN116642822A CN202310670121.6A CN202310670121A CN116642822A CN 116642822 A CN116642822 A CN 116642822A CN 202310670121 A CN202310670121 A CN 202310670121A CN 116642822 A CN116642822 A CN 116642822A
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- XEEYBQQBJWHFJM-UHFFFAOYSA-N Iron Chemical compound [Fe] XEEYBQQBJWHFJM-UHFFFAOYSA-N 0.000 title claims abstract description 92
- 229910052742 iron Inorganic materials 0.000 title claims abstract description 46
- 238000011033 desalting Methods 0.000 title claims abstract description 40
- 238000002848 electrochemical method Methods 0.000 title claims abstract description 24
- 238000005260 corrosion Methods 0.000 claims abstract description 101
- 230000007797 corrosion Effects 0.000 claims abstract description 101
- 238000010612 desalination reaction Methods 0.000 claims abstract description 54
- 238000004458 analytical method Methods 0.000 claims abstract description 21
- 238000012545 processing Methods 0.000 claims abstract description 11
- 238000000840 electrochemical analysis Methods 0.000 claims abstract description 5
- 238000000034 method Methods 0.000 claims description 23
- 238000002161 passivation Methods 0.000 claims description 13
- 230000001052 transient effect Effects 0.000 claims description 13
- 238000001228 spectrum Methods 0.000 claims description 12
- 229910052751 metal Inorganic materials 0.000 claims description 11
- 239000002184 metal Substances 0.000 claims description 11
- 238000012360 testing method Methods 0.000 claims description 10
- 238000006243 chemical reaction Methods 0.000 claims description 9
- 238000001514 detection method Methods 0.000 claims description 9
- 230000008859 change Effects 0.000 claims description 6
- BASFCYQUMIYNBI-UHFFFAOYSA-N platinum Chemical compound [Pt] BASFCYQUMIYNBI-UHFFFAOYSA-N 0.000 claims description 6
- 230000002035 prolonged effect Effects 0.000 claims description 4
- 230000009466 transformation Effects 0.000 claims description 4
- 241000270722 Crocodylidae Species 0.000 claims description 3
- LNNWVNGFPYWNQE-GMIGKAJZSA-N desomorphine Chemical compound C1C2=CC=C(O)C3=C2[C@]24CCN(C)[C@H]1[C@@H]2CCC[C@@H]4O3 LNNWVNGFPYWNQE-GMIGKAJZSA-N 0.000 claims description 3
- ZOMNIUBKTOKEHS-UHFFFAOYSA-L dimercury dichloride Chemical class Cl[Hg][Hg]Cl ZOMNIUBKTOKEHS-UHFFFAOYSA-L 0.000 claims description 3
- 229910052697 platinum Inorganic materials 0.000 claims description 3
- 238000005070 sampling Methods 0.000 claims description 3
- 230000003595 spectral effect Effects 0.000 claims description 3
- 238000002474 experimental method Methods 0.000 claims description 2
- 239000000243 solution Substances 0.000 description 26
- VEXZGXHMUGYJMC-UHFFFAOYSA-M Chloride anion Chemical compound [Cl-] VEXZGXHMUGYJMC-UHFFFAOYSA-M 0.000 description 25
- JEIPFZHSYJVQDO-UHFFFAOYSA-N iron(III) oxide Inorganic materials O=[Fe]O[Fe]=O JEIPFZHSYJVQDO-UHFFFAOYSA-N 0.000 description 11
- 229910001018 Cast iron Inorganic materials 0.000 description 8
- 239000012670 alkaline solution Substances 0.000 description 6
- 238000010586 diagram Methods 0.000 description 6
- 230000010287 polarization Effects 0.000 description 6
- 239000000460 chlorine Substances 0.000 description 5
- 238000005516 engineering process Methods 0.000 description 5
- 238000011161 development Methods 0.000 description 4
- 238000011065 in-situ storage Methods 0.000 description 4
- 238000013508 migration Methods 0.000 description 4
- 230000005012 migration Effects 0.000 description 4
- 230000008569 process Effects 0.000 description 4
- 238000002791 soaking Methods 0.000 description 4
- ZAMOUSCENKQFHK-UHFFFAOYSA-N Chlorine atom Chemical compound [Cl] ZAMOUSCENKQFHK-UHFFFAOYSA-N 0.000 description 3
- HEMHJVSKTPXQMS-UHFFFAOYSA-M Sodium hydroxide Chemical compound [OH-].[Na+] HEMHJVSKTPXQMS-UHFFFAOYSA-M 0.000 description 3
- 230000006399 behavior Effects 0.000 description 3
- 229910052801 chlorine Inorganic materials 0.000 description 3
- 238000004090 dissolution Methods 0.000 description 3
- 230000000694 effects Effects 0.000 description 3
- 239000011159 matrix material Substances 0.000 description 3
- 230000035945 sensitivity Effects 0.000 description 3
- 229910001060 Gray iron Inorganic materials 0.000 description 2
- 229910001037 White iron Inorganic materials 0.000 description 2
- 230000004913 activation Effects 0.000 description 2
- 239000003513 alkali Substances 0.000 description 2
- 239000002585 base Substances 0.000 description 2
- 230000001066 destructive effect Effects 0.000 description 2
- 238000011156 evaluation Methods 0.000 description 2
- 239000000463 material Substances 0.000 description 2
- 238000004321 preservation Methods 0.000 description 2
- 239000000126 substance Substances 0.000 description 2
- 238000012546 transfer Methods 0.000 description 2
- UGFAIRIUMAVXCW-UHFFFAOYSA-N Carbon monoxide Chemical compound [O+]#[C-] UGFAIRIUMAVXCW-UHFFFAOYSA-N 0.000 description 1
- CWYNVVGOOAEACU-UHFFFAOYSA-N Fe2+ Chemical compound [Fe+2] CWYNVVGOOAEACU-UHFFFAOYSA-N 0.000 description 1
- 239000002253 acid Substances 0.000 description 1
- 230000003213 activating effect Effects 0.000 description 1
- 229910045601 alloy Inorganic materials 0.000 description 1
- 239000000956 alloy Substances 0.000 description 1
- 230000009286 beneficial effect Effects 0.000 description 1
- 238000004140 cleaning Methods 0.000 description 1
- 239000011248 coating agent Substances 0.000 description 1
- 238000000576 coating method Methods 0.000 description 1
- 238000006298 dechlorination reaction Methods 0.000 description 1
- 230000007423 decrease Effects 0.000 description 1
- 238000000835 electrochemical detection Methods 0.000 description 1
- 238000005530 etching Methods 0.000 description 1
- 239000003546 flue gas Substances 0.000 description 1
- 238000010438 heat treatment Methods 0.000 description 1
- 238000001453 impedance spectrum Methods 0.000 description 1
- 239000003112 inhibitor Substances 0.000 description 1
- 230000005764 inhibitory process Effects 0.000 description 1
- 239000007788 liquid Substances 0.000 description 1
- 230000007774 longterm Effects 0.000 description 1
- 239000007769 metal material Substances 0.000 description 1
- 150000002739 metals Chemical class 0.000 description 1
- 239000000203 mixture Substances 0.000 description 1
- 238000012986 modification Methods 0.000 description 1
- 230000004048 modification Effects 0.000 description 1
- 238000012806 monitoring device Methods 0.000 description 1
- 238000012544 monitoring process Methods 0.000 description 1
- 238000007254 oxidation reaction Methods 0.000 description 1
- 239000012466 permeate Substances 0.000 description 1
- 239000011148 porous material Substances 0.000 description 1
- 230000008439 repair process Effects 0.000 description 1
- 150000003839 salts Chemical class 0.000 description 1
- 238000012216 screening Methods 0.000 description 1
- 238000007789 sealing Methods 0.000 description 1
- 238000004901 spalling Methods 0.000 description 1
- 239000000758 substrate Substances 0.000 description 1
Classifications
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N17/00—Investigating resistance of materials to the weather, to corrosion, or to light
- G01N17/006—Investigating resistance of materials to the weather, to corrosion, or to light of metals
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N17/00—Investigating resistance of materials to the weather, to corrosion, or to light
- G01N17/02—Electrochemical measuring systems for weathering, corrosion or corrosion-protection measurement
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N27/00—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means
- G01N27/26—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating electrochemical variables; by using electrolysis or electrophoresis
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
Technical Field
The invention relates to the technical field of cultural relic desalination judgment, in particular to an electrochemical method for judging the desalination endpoint of an iron cultural relic.
Background
The iron relics are witnessed for the development of ancient social productivity, and have important historic and scientific values. Because of the active nature of iron, the iron is easy to corrode, and many of the excavated ironware are rusty spots, if the ironware is not protected, the service life of cultural relics is greatly shortened. The general steps of iron cultural relic protection include: cleaning, rust removal, desalination, corrosion inhibition and sealing. Desalination is an important link for protecting iron cultural relics, wherein salt refers to chloride in the cultural relics, and serious pitting reaction can be caused by existence of chloride ions, so that corrosion of the iron cultural relics is aggravated. Therefore, for the iron cultural relics, particularly for the ocean effluent iron cultural relics, the removal of chloride ions in the cultural relics is beneficial to slowing down the corrosion of the iron cultural relics, so that the long-term stable preservation of the cultural relics is realized.
In cultural relic protection work, the most commonly used desalination method is an alkali liquor soaking method, namely, the cultural relic to be desalted is soaked in a sodium hydroxide solution with a certain concentration (0.1 or 0.5 mol/L), and desalination and chlorine removal of the cultural relic are realized based on free migration of chloride ions. And the efficiency of the chlorine ion migration is improved by periodically replacing the soaking liquid. The determination of the desalination degree is often based on the content of chloride ions in the desalination solution, and when the concentration of chloride ions in the solution is below 50ppm (mg/L) and the concentration is not changed significantly after a plurality of changes of the solution, the desalination process can be considered to be finished (museum iron cultural relics protection technical manual, 2011). The concentration of 20ppm chloride ion was also considered by the learner as an indication of the end of the desalination process. In an ideal state, the concentration value of chloride ions in the desalting solution is equal to the concentration of chloride ions in the treated cultural relics. However, factors such as soaking time, volume ratio of soaking solution to cultural relics, existence of rust layers on the surfaces of the cultural relics and the like can influence the migration efficiency of chloride ions. The chloride ion concentration in the solution is not representative of the chloride ion content of the cultural relics.
The scholars dissolve the desalted cultural relics by using strong acid and then measure the concentration of chloride ions. Still other scholars store the cultural relics subjected to desalination treatment 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 method has irrecoverable loss for the cultural relics with poor desalting degree and low efficiency after detection, and does not accord with the 'reversibility principle' and the 'minimum intervention principle' in the protection of the cultural relics. Therefore, a method capable of instantly/timely judging whether the desalination process of the cultural relics is finished is needed.
The traditional electrochemical method mainly comprises the following steps: polarization curve method and electrochemical impedance spectrum, however, both methods can apply polarization to the system to be measured, which is likely to change the phase composition of the rust layer, and can not accurately measure the local electrochemical parameters of metal corrosion under the rust layer. Electrochemical noise is an in-situ, non-destructive electrochemical method, and external disturbance for changing the surface corrosion process of the electrode is not required to be applied to the electrode in the test. Information on corrosion systems is explored by detecting random unbalanced fluctuations in noise potential and noise current in the system over time (Zhang Jianqing, 2002; bertocci U, 1995). At present, the electrochemical noise technology is widely applied to the corrosion and protection fields of industrial metals, and is an important means for researching metal local corrosion, coating performance evaluation, corrosion inhibitor screening and the like.
The first prior art is: shang Sugong, he Jiquan; simulating the electrochemical behavior of ancient cast iron in alkali liquor, chemical technology and development, 2014,43 (01), 16-19.
Summary: the electrochemical behavior of the simulated ancient gray cast iron, white cast iron was studied in several typical aqueous alkaline solutions containing different chloride concentrations by the potentiodynamic polarization curve method. The results show that the passivation/activation sensitivity of the same cast iron sample to chloride ion concentration in different alkaline solutions is different; cast iron samples of different materials also have different sensitivity to chloride ions in the same solution. In addition, for alkaline solutions of the same solute, the sensitivity of cast iron to chloride ions decreases as the pH of the solution increases. The result provides an important basis for judging the endpoint of desalting and chlorine removal of iron cultural relics.
Conclusion: (1) High pH alkaline solutions can promote passivation of the simulated ancient cast iron. The existence of chloride ions exceeding the critical concentration can play a destructive role in activating corrosion of the pseudo-classic cast iron.
(2) Different alkaline solutions have a certain influence on the electrochemical performance of the simulated ancient cast iron.
(3) Under the condition of the same solute, the performance of simulating the chloride ion resistance of the ancient gray cast iron and the white cast iron is enhanced along with the increase of the alkalinity of the solution.
(4) In alkaline solutions of different pH values, the critical chloride ion concentration of the 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 an end point for judging whether the sample dechlorination treatment can be stopped or not; the method can be used for evaluating whether the electrochemical polarization curve of the iron device in the medium is passivated or not to be used as an evaluation method for detecting the chlorine removal effect of the iron cultural relics.
The polarization curve method used by the technology is an electrochemical test method of external reinforced polarization, which can influence the rust layer on the surface of the cultural relics to be tested, so that the surface of the cultural relics is subjected to phase change, and the principle of cultural relic protection is not met.
And the second prior art is as follows: publication No.: the invention discloses a method for detecting side corrosion of boiler flue gas based on electrochemical noise, which realizes real-time monitoring of high-temperature corrosion conditions in an electrochemical noise mode by adopting a corrosion monitoring device in a high-temperature corrosion environment. According to the method, electrochemical noise data are processed to obtain the pitting corrosion index and the noise impedance, whether local corrosion occurs is judged according to the pitting corrosion index, and the corrosion occurrence speed is judged according to the noise impedance, so that the purpose of truly reflecting corrosion and spalling of the high-temperature alloy on the heating surface of the boiler is achieved.
The aim of the technology is to ensure the safe operation of the boiler by nondestructively detecting the corrosion state of the metal material of the boiler; the above technique uses pitting corrosion indicators (pitting corrosion coefficient and noise resistance) to determine the extent of corrosion of the sample.
We have therefore proposed an electrochemical method for endpoint determination in desalination of ferrous cultural relics to solve the above-mentioned problems.
Disclosure of Invention
In order to overcome the above-mentioned drawbacks of the prior art, an embodiment of the present invention provides an electrochemical method for determining the endpoint of desalination of iron cultural relics, so as to solve the above-mentioned problems in the prior art.
In order to achieve the above purpose, the present invention provides the following technical solutions: an electrochemical method for determining the desalting endpoint of an iron cultural relic, comprising 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.
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.
In a preferred embodiment, in step S1, the working electrode is the sample to be tested, and the sample is connected to the testing system 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.
In a preferred embodiment, in step S1, a zero resistance ammeter mode is used in the connection of the three electrode system to the electrochemical workstation, the auxiliary electrode is connected to the ground, 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 relics in the desalination solution is determined according to the transient peaks and the current noise in the time domain analysis chart, and the desalination degree is further determined according to the corrosion state of the cultural relics.
In a preferred embodiment, the fluctuation frequency of potential and current noise is faster, and the current noise has a strong current noise peak with a service life of >30s and a magnitude of >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.
In a preferred embodiment, in step S2, EN data processing software is self-written in MATLAB software, data processing is performed, and the direct current component is removed by using a polynomial fitting method (generally, a polynomial of 5 th degree is at most);
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.
In a preferred embodiment, the low frequency region white noise level, the high frequency linear region linear segment slope is used to determine the type of corrosion and the magnitude of the corrosion rate.
In a preferred embodiment, the lower the white noise level in the low frequency region, the less the localized corrosion tendency of the cultural relics, the lower frequency region tends to be associated with anodic reactions of the metal in the localized region, the greater the white noise level value, the greater the tendency to be indicative of localized corrosion reactions;
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.
In a preferred embodiment, it can be seen by comparing the white noise level values that when desalting once and desalting again, the white noise level value of the cultural relics is higher, indicating that the corrosion rate is higher, and the corrosion rate of the cultural relics is lower after desalting 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.
The invention has the technical effects and advantages that:
1. 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.
2. According to the invention, in a desalting solution, EN detection data of cultural relics are obtained by utilizing a three-electrode system, a data processing program is written based on MATLAB software, and the problem of EN in the process of judging the desalting endpoint in the process of protecting the iron cultural relics is solved by comparing EN data of the cultural relics in solutions with different desalting degrees.
3. The invention provides an in-situ and lossless electrochemical method, which judges the stability of cultural relics by detecting the corrosion state of the cultural relics so as to infer whether the desalination treatment of the cultural relics can be terminated or not, wherein the invention utilizes the transient peak and the current noise in a time domain diagram and the W, K in a PSD diagram; to judge the corrosion state of the iron cultural relics.
Drawings
FIG. 1 is a schematic diagram of an electrochemical noise test system according to the present invention;
FIG. 2 is a graph showing the change of potential noise with time in the present invention;
FIG. 3 is a graph showing the current noise over time in the present invention;
FIG. 4 is an enlarged schematic view of a portion of FIG. 3;
FIG. 5 is a chart of the fast Fourier transform analysis of the potential noise in the present invention;
fig. 6 is a diagram of a fast fourier transform analysis of current noise in the present invention.
Detailed Description
The following description of the embodiments of the present invention will be made clearly and completely with reference to the accompanying drawings, in which it is apparent that the embodiments described are only some embodiments of the present invention, but not all embodiments. All other embodiments, which can be made by those skilled in the art based on the embodiments of the invention without making any inventive effort, are intended to be within the scope of the invention.
Referring to fig. 1-6, an electrochemical method for determining the desalination endpoint of an iron relic is an in-situ, nondestructive electrochemical detection method, and can be detected at any time in the desalination process of the iron relic, so that the detected environment is in the desalination solution of the iron relic.
Data acquisition, firstly constructing a three-electrode system for electrochemical test, wherein the three-electrode system comprises a working electrode, a reference electrode and an auxiliary electrode.
The working electrode is a sample to be tested, and the sample is connected with the testing system by using crocodile clips or other clamps;
the reference electrode is the most commonly used saturated calomel electrode, and the iron cultural relics are cast and formed thousands of years ago, so that the identical materials cannot be found, and the test in the invention adopts an asymmetric electrode system to collect EN data;
the auxiliary electrode is a platinum electrode.
The three electrodes are connected with an electrochemical workstation to realize data acquisition of electric signals, a Zero Resistance Ammeter (ZRA) mode is adopted, an auxiliary electrode is grounded to GND, the sampling frequency is 2Hz, and the testing time is 1024s.
And transmitting the noise potential and the noise current acquired by the electrochemical workstation to a computer for data processing, as shown in figure 1 of the specification.
And (3) data processing, namely programming based on MATLAB software, performing polynomial fitting and fast Fourier transform analysis on the noise signals to obtain a time domain and power spectral density distribution diagram of the detection sample.
Time domain analysis:
first, the experimentally measured potential noise changes over time E-t and current noise changes over time I-t are plotted as FIG. 2 of the specification and FIG. 3 of the specification.
Judging the local corrosion rate of the cultural relics in the desalting solution according to the transient peaks and the current noise, and judging the degree of desalting according to the corrosion state of the cultural relics;
in the change curves of potential noise and current noise along with time, transient peaks with high amplitude appear;
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;
when desalting is carried out once, the chloride ion content in the rust layer of the cultural relic is high, and the potential noise and the current noise have typical local corrosion characteristics, namely transient peaks with high amplitude.
The observed rapid rise of the transient peak of the current noise is caused by the rapid dissolution of the metal matrix at the pitting point, while the fall of the transient peak of the current noise is caused by the fact that the mass transfer rate of Cl < - > can not meet the requirement of the pitting development after the migration rate of the Cl < - > into the etching hole reaches the limit, and the repair rate of the passivation film at the pitting point is larger than the dissolution rate of the metal matrix.
When the pitting corrosion is not developed any more, the transient peak of the current noise completely disappears, and the fluctuation of the potential noise is caused by the charge and discharge of the passivation film by the anode current generated by dissolution of the metal matrix at the pitting corrosion.
It should be noted that although chloride ions in the rust layer of the cultural relics are more in one desalting process, the cultural relics are preserved in the atmospheric environment and are soaked in the desalting solution, and a plurality of bubbles are adhered to the surface of the cultural relics, and the solution is not completely filled in the pores of the porous rust layer, so that potential noise is higher, the amplitude of current noise is smaller, the service life is 3-5 seconds shorter, and the amplitude of current noise peaks is 0.01-1uA lower, and metastable state pitting events occur.
When desalting is carried out again, the desalting solution fully permeates the porous rust layer, the fluctuation frequency of potential and current noise is faster, the current noise has strong current noise peaks with the service life of more than 30s and the amplitude of more than 1uA, the current noise is increased and is larger than that of one-time desalting, 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 to become a corrosion anode, and the larger passivation area and the smaller activation area form a corrosion battery with a large cathode and a small anode, so that the corrosion on the surface of the cultural relics is aggravated.
After multiple desalination, the fluctuation amplitude of potential noise and current noise is obviously reduced, the fluctuation period is gradually prolonged, and the method shows that chloride ions in the rust layer can be less contacted with a metal substrate and can not trigger pitting reaction, and in alkaline desalination solution, the covering effect of the rust layer on the surface of the cultural relic can slow down the substance transfer rate and the corrosion development rate of the cultural relic.
Frequency domain analysis:
firstly, EN data processing software is self-written in MATLAB software to perform data processing, and a polynomial fitting method (generally, a 5 th-degree polynomial) is utilized to remove direct current components.
And carrying out frequency domain analysis of the fast Fourier transform, obtaining the relation between potential noise and current noise and frequency through the fast Fourier transform, and obtaining a power density spectrum curve.
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.
The power density spectrum curve shows 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 shows a declining section, the power density spectrum curve of the noise signal shows a linear relation with the logarithm of the frequency, and the slope is K;
as the frequency continues to increase, the power density spectrum curve eventually drops to the base noise level (horizontal segment curve after 0.1), and some tests do not appear base noise, which is related to instrument background noise at the time of detection.
The lower the white noise level in the low frequency region, the less the local corrosion tendency of the cultural relics. The low frequency region tends to be associated with anodic reactions of metal in localized areas, with greater white noise levels indicating greater propensity for localized corrosion reactions.
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.
Reference is made to figures 4, 5 and 6 of the description;
as can be seen by comparing the white noise level values, when desalting is carried out once and desalting is carried out 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 desalting for a plurality of times. 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.
The slope of a high-frequency linear region of the potential and current PSD can be seen by calculating, wherein the PSD is a power density spectrum curve, and the K value in one desalting is smaller than-20 dB/decade, so that the corrosion form is mainly local corrosion; the curves of the re-desalination and the repeated desalination are steeper, and the uniform corrosion with a larger corrosion range is generated in the whole cultural relics in the re-desalination by combining with the judgment of other characteristic parameters, and the cultural relics after the repeated desalination are in a more stable passivation state.
The electrochemical method is used for judging the desalting end point of the iron cultural relics for the first time, EN detection is carried out on the iron-out devices with different desalting degrees in alkaline desalting solution, polynomial fitting and fast Fourier transform data processing are carried out on noise signals based on MATLAB software, and a time domain and power spectrum density map (PSD map) of a detection sample is obtained.
The result shows that: along with the progress of desalination treatment, relevant characteristic parameters used for representing corrosion behaviors of cultural relics in a time domain spectrogram and a PSD (phase-sensitive detector) spectrogram of the cultural relics are correspondingly changed. In the time domain distribution diagram of the noise data, the corrosion rate of the cultural relics in the desalted solution can be judged according to the transient peak and the current noise. Transient peaks are typical local corrosion characteristics, and the magnitude of the current noise is also related to the corrosion rate. The more the transient peak number is, the larger the fluctuation amplitude of the current noise is, and the greater the tendency of corrosion of cultural relics is. Similarly, the white noise level (W) in the low frequency region, the slope (K) and the amplitude of the linear section in the high frequency region in the PSD map are also related to the type of corrosion that occurs in the cultural relics and the corrosion state of the cultural relics.
The higher the white noise level, the greater the anodic oxidation reaction of the metal in the local area, and the greater the local corrosion reaction. K is related to the corrosion type, and the steeper the curve, namely the more negative the K value, the more uniform corrosion or passivation state of the system is predicted; the flatter the curve, i.e., the closer the K value is to 0, the more indicative of localized corrosion of the system. The higher the level of the linear part of the high-frequency region, the higher the corrosion rate occurring on the surface of the whole cultural relic to be detected, and the cultural relic tends to be uniformly corroded.
To sum up, the fewer the transient peak number in the time domain spectrogram of the cultural relics in the desalted solution, the smaller the current noise fluctuation amplitude; the lower the W in the PSD graph, the lower the level of the linear part and the steeper the slope, which shows that the passivation state of the cultural relics in the alkaline desalting solution is smaller in the tendency of pitting corrosion of the cultural relics, and the surface state of the cultural relics tends to be stable. Therefore, the EN technology can be used for in-situ and nondestructive detection of the pitting tendency of the iron cultural relics in the desalting solution, and the end point of the desalting treatment is judged according to the corrosion state of the cultural relics, so that the stable preservation of the iron cultural relics is realized.
The above abbreviations and meanings: electrochemical noise EN; a power density spectrum curve PSD; white noise level W; high frequency linear segment slope K; fast fourier transform, FFT.
Finally: the foregoing description of the preferred embodiments of the invention is not intended to limit the invention to the precise form disclosed, and any such modifications, equivalents, and alternatives falling within the spirit and principles of the invention are intended to be included within the scope of the invention.
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.
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