Method for directly converting surface corrosion of steel structure into carbonate protective coating

Abstract

The invention discloses a method for directly converting surface corrosion of a steel structure into a carbonate protective coating, which comprises the following steps: sequentially carrying out electron beam irradiation and plasma activated gas treatment on a corroded steel material, anchoring reaction active sites in a corrosion area on the surface of the steel structure through electron beam irradiation, reaction active sites on the surface of the steel material react with an active intermediate excited by plasma jet through plasma activation gas treatment, and formed corrosion is converted into a carbonate protective coating on the surface of the steel structure; the electron beam irradiation is carried out under a vacuum condition; the gas adopted in the plasma activation gas treatment is CO2 gas. According to the method, electron beam irradiation is combined with plasma activation gas treatment, the formed corrosion film can be directly converted into a protection layer on the surface of the steel structure, and therefore the tedious operation that a surface corrosion part needs to be completely removed in a traditional corrosion prevention method is avoided in the maintenance process of the steel structure.

Description

Technical Field

[0001] The invention relates to a method for anticorrosion of steel structure surface, in particular to a method for directly converting corrosion on the steel structure surface into a carbonate protective coating. Background Art

[0002] Steel structures are widely used in construction, bridges, marine engineering, energy facilities and other fields due to their high strength, good ductility and machinability. However, the corrosion of steel has always been an important challenge affecting its long-term service performance and safety. Corrosion not only leads to a decrease in the strength of steel structures and shortens their service life, but may also cause serious economic losses and safety hazards. According to statistics, the direct economic losses caused by corrosion in the world account for 3% to 4% of GDP, of which the corrosion of steel materials accounts for a large proportion.

[0003] The corrosion layer on the surface of steel exposed to humid air for a long time is usually composed of oxides such as Fe3O4 and Fe2O3 and hydroxides such as Fe(OH)3, and they usually have a porous structure, which is easy to absorb moisture and pollutants and accelerate corrosion, resulting in rapid decline in material thickness and strength. In order to effectively extend the service life of steel structures, surface coatings are usually generated on their surfaces as a barrier to isolate the steel structures from external environmental attacks. Specific methods include chemical conversion coatings, electrochemical plating, organic coatings, anodizing, thermal spray coatings, etc.

[0004] However, the above treatments inevitably produce significant chemical waste. In addition, for steel structures that have already corroded, the surface must be carefully pre-treated to remove pre-existing corrosion products to ensure uniform coating coverage and sufficient adhesion between the substrate and the coating. Therefore, the development of a new method that can clean the surface corrosion of steel structures while converting them into a protective coating is crucial for the development of fields such as construction, bridges, and marine engineering.

[0005] It should be noted that the information disclosed in the above background technology section is only used to enhance the understanding of the background of the present disclosure, and therefore may include information that does not constitute the prior art known to ordinary technicians in the field. Summary of the invention

[0006] The purpose of the present invention is to provide a method for directly converting the surface corrosion of steel structures into a carbonate protective coating, which solves the problem that the existing methods inevitably produce significant chemical waste or are cumbersome to handle, and can directly convert the corrosion layer into a new protective layer without mechanically removing the previous corrosion products.

[0007] In order to achieve the above-mentioned purpose, the present invention provides a method for directly converting the surface corrosion of a steel structure into a carbonate protective coating, the method comprising: sequentially performing electron beam irradiation and plasma activated gas treatment on the corroded steel material, anchoring the reaction active sites in the corrosion area on the surface of the steel structure by electron beam irradiation, reacting the reaction active sites on the surface of the steel material with active intermediates excited by a plasma jet by plasma activated gas treatment, and converting the formed corrosion into a carbonate protective coating on the surface of the steel structure; the electron beam irradiation is performed under vacuum conditions; the plasma activated gas treatment uses CO2 gas.

[0008] Preferably, the method comprises the following steps: (1) Clean the corroded steel surface; (2) transferring the steel material obtained in step (1) into a high vacuum chamber after vacuum drying to ensure uniform electron beam irradiation, and then evacuating the chamber; (3) starting the electron beam irradiation equipment to perform electron beam irradiation treatment on the surface of the steel material, inducing the formation of defects in the oxide structure of the corrosion zone on the surface of the steel structure and activating chemical reaction sites; (4) Turn off the electron beam irradiation equipment and gradually introduce CO2 gas into the chamber; (5) Activating a plasma gas treatment device to treat the CO2 gas in the chamber, exciting the CO2 to form plasma, and generating active intermediates; (6) maintaining the equipment parameters of step (5) to allow the active sites on the surface of the steel material to react with the active intermediates; (7) Turn off the electron beam and plasma equipment, gradually reduce the chamber temperature to room temperature, take out the treated steel material, and obtain a corrosion-resistant steel sheet with a protective coating attached to the surface.

[0009] Preferably, the vacuum condition is controlled to a vacuum degree of less than 10 -4 Pa.

[0010] Preferably, the electron beam irradiation has a beam intensity of 0.1 A / cm 2 .

[0011] Preferably, the electron beam irradiation treatment time is 15 min.

[0012] Preferably, in the plasma activated gas treatment, the pressure of the CO2 gas introduced is 2 Pa, the flow rate is 50 sccm, and the plasma treatment power is 600 W.

[0013] Preferably, the purity of the CO2 gas is >99.99%.

[0014] Preferably, the activation process of the CO2 gas is stimulated by a plasma jet, and the resulting active intermediate CO* comprises: CO2 + 、CO3 - , O + and C + Any one or more of the above.

[0015] Preferably, the plasma activated gas treats the corroded steel material.

[0016] Preferably, the time for the reactive sites on the surface of the steel material to react with the reactive intermediates excited by the plasma jet is not less than 30 minutes.

[0017] Preferably, before the electron beam irradiation, the surface of the corroded steel material is ultrasonically cleaned in a deionized water bath.

[0018] Preferably, the steel material is selected from 304 stainless steel or Q235 steel.

[0019] The method of directly converting the surface corrosion of steel structure into carbonate protective coating solves the problem that the existing method inevitably generates significant chemical waste or has cumbersome treatment, and has the following advantages: (1) The method of the present invention can directly transform the formed corrosion film into a protective layer on the surface of the steel structure by electron beam irradiation combined with plasma activated gas treatment, thereby avoiding the cumbersome operation of completely removing the surface corrosion part in the traditional anti-corrosion method during the maintenance of the steel structure; (2) The method of the present invention carbonizes the oxide / hydroxide film or hydrate corrosion product formed on the surface of the steel material into a smooth and dense FeCO3 protective surface layer by reacting with CO2 material activated by a high-energy electron beam at room temperature; iron carbonate is an insoluble corrosion product that can deposit on the metal surface and form a dense solid thin layer, thereby isolating the metal from direct contact with the corrosive medium (such as water, oxygen, carbon dioxide) and slowing down the corrosion reaction; in addition, iron carbonate also slows down the electrochemical reaction rate and reduces the corrosion current, thereby playing a role similar to that of a passivation film; (3) The method of the present invention does not require additional heating or pretreatment, making it possible to protect ferroalloy workpieces of small size or complex shape and to repair parts that have been corroded but are still in service by directly converting the corrosion layer into a new protective layer without mechanically removing the previous corrosion products; (4) The method of the present invention uses high-purity carbon dioxide (CO2) as the gas, which is more environmentally friendly than traditional anti-corrosion methods such as chemical conversion coating, electrochemical plating, organic coating, anodizing, thermal spray coating, etc.; (5) The protective coating converted by the method of the present invention has good interface interaction and adhesion with the base steel, which can effectively maintain the excellent intrinsic mechanical properties of the steel structure. At the same time, the protective layer obtained by the method also has excellent corrosion resistance. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 It is a schematic diagram of the method of the present invention for directly converting the surface corrosion of steel structure into carbonate protective coating.

[0021] Figure 2 Schematic diagram of the chemical reaction between the active sites on the surface of the steel sheet and the activated CO* according to the present invention.

[0022] Figure 3 The XRD patterns of the FeCO3 protective coating attached to the surface of the 304 stainless steel in Example 1 and the Q235 steel sheet in Example 3 obtained after treatment.

[0023] Figure 4 It is a comparison chart of the mechanical properties of Example 1 of the present invention and Comparative Example 1.

[0024] Figure 5 It is a comparison chart of the mechanical properties of Example 3 of the present invention and Comparative Example 3.

[0025] Figure 6 It is a comparison chart of the mechanical properties of Example 1 and Example 2 of the present invention.

[0026] Figure 7 It is a comparison chart of the mechanical properties of Example 3 and Example 4 of the present invention.

[0027] Figure 8 It is a comparison chart of the mechanical properties of Example 1 of the present invention and Comparative Example 2.

[0028] Fig. 9 It is a comparison chart of the mechanical properties of Example 3 of the present invention and Comparative Example 4. DETAILED DESCRIPTION

[0029] The technical solutions in the embodiments of the present invention are described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0030] It should be noted that if the specific conditions are not specified in the examples, the experiments were carried out according to conventional conditions or the conditions recommended by the manufacturer. If the manufacturers of the reagents or instruments are not specified, they are all conventional products that can be purchased from the market.

[0031] In the present invention, all features defined in the form of numerical ranges or percentage ranges, such as values, quantities, contents and concentrations, are only for brevity and convenience. Accordingly, the description of numerical ranges or percentage ranges should be deemed to have included and specifically disclosed all possible secondary ranges and individual values ​​within the range (including integers and fractions).

[0032] The features mentioned in the present invention can be combined arbitrarily, as long as there is no contradiction in the combination of these features, all possible combinations should be considered as the scope of this specification. Each feature disclosed in the specification can be replaced by any alternative feature that can provide the same, equal or similar purpose. Therefore, unless otherwise specified, the disclosed features are only general examples of equal or similar features.

[0033] Iron carbonate is an insoluble corrosion product that can deposit on the metal surface and form a dense solid thin layer, thereby isolating the metal from direct contact with the corrosive medium (such as water, oxygen, carbon dioxide) and slowing down the corrosion reaction; in addition, iron carbonate also slows down the electrochemical reaction rate and reduces the corrosion current, thus playing a role similar to a passivation film.

[0034] However, for corrosion products on the surface of steel structures, iron oxides and hydroxides usually cannot directly react with carbon dioxide (CO2) to form iron carbonate (FeCO3), and CO2 has low chemical activity at room temperature. Chemical reactions will only occur under specific conditions (such as high temperature and the presence of a catalyst). However, high temperature environments usually also have an impact on uncorroded steel.

[0035] Based on this, the present invention provides a method for directly converting the surface corrosion of steel structure into carbonate protective coating, see Figure 1 The method comprises: sequentially performing electron beam irradiation and plasma activated gas treatment on the corroded steel material, anchoring the reaction active sites in the corrosion area on the surface of the steel structure by electron beam irradiation, reacting the reaction active sites on the surface of the steel material with the active intermediates excited by the plasma jet by plasma activated gas treatment, and converting the formed corrosion into a carbonate protective coating on the surface of the steel structure; wherein, the electron beam irradiation is carried out under vacuum conditions; and the gas used in the plasma activated gas treatment is CO2 gas.

[0036] The present invention can anchor the reaction active sites in the corrosion area on the surface of the steel structure through electron beam irradiation treatment, and significantly increase the reaction rate of gas molecules and solids by exciting the gas or electron-induced electrostatic field effect with memory effect adsorbed on the surface of the solid reactant, and adsorb CO2 on the surface of the natural oxide. Secondly, the CO2 used in the present invention is activated to CO* through plasma, and the reaction activity is greatly improved. It can also react with iron oxides and iron hydroxides on the surface of the steel structure under electron beam irradiation to gradually generate a FeCO3 protective layer. As the reaction continues, when the surface FeCO3 protective layer is dense enough to completely cover the entire steel structure, the reaction stops. The specific reaction principle diagram is shown in the figure. Figure 2 shown.

[0037] The following is a detailed description of a method provided by the present invention for directly converting surface corrosion of a steel structure into a carbonate protective coating through embodiments and experimental examples.

[0038] Example 1 A method for directly converting steel structure surface corrosion into a carbonate protective coating, the method comprising the following steps: (1) 4000-grit sandpaper was used to clean the surface of 304 stainless steel sheets that had been exposed to humid air for 3 months to remove some corrosion products. These corrosion products usually cover the surface of the steel, forming an uneven and fragile corrosion layer. The shape parameters of 304 stainless steel are 5 mm*2 mm*50 mm (length*width*height). The cleaned steel sheets were then transferred to a water bath ultrasonic cleaner and ultrasonically cleaned for 10 min at a power of 100 W and a frequency of 40 kHz in a deionized water bath to remove surface rust. (2) After vacuum drying, the steel sheet from step (1) is transferred to a high vacuum chamber and placed on a pre-installed sample holder to ensure that it can evenly receive electron beam irradiation. The chamber is then evacuated to a vacuum degree of less than 10 -4 Pa; (3) Start the electron beam irradiation equipment at 0.1 A / cm 2 The surface of the stainless steel sheet was irradiated with an electron beam at a beam intensity of 1000 nm for 15 min to induce defect formation in the oxide structure and activate chemical reaction sites. (4) Turn off the electron beam irradiation equipment and gradually introduce high-purity CO2 gas (purity>99.99%) into the chamber, where the pressure of the introduced CO2 gas is 2 Pa and the flow rate is 50 sccm; (5) Activate a plasma gas treatment device to treat the CO2 gas in the chamber at a power of 600 W to excite the CO2 to form plasma and generate active intermediates CO*, wherein the active intermediates CO* include but are not limited to CO2+ 、CO3 - , O + , C + wait; (6) maintaining the equipment parameters of step (5) to allow the active sites on the surface of the steel sheet to react with the activated CO* for 30 min; (7) Turn off the electron beam and plasma equipment, gradually lower the chamber temperature to room temperature, take out the treated steel sheet, and obtain a corrosion-resistant steel sheet with a FeCO3 protective coating attached to the surface.

[0039] Example 3 A method for directly converting the surface corrosion of a steel structure into a carbonate protective coating, wherein the Q235 steel sheet that has been exposed to humid air for 3 months is treated by the same method as in Example 1 above.

[0040] Experimental Example 1 Characterization Experiment Process X-ray diffraction experiments were performed on the samples of Example 1 and Example 3, as follows: Use deionized water and anhydrous ethanol to wipe the sample surface to remove other contaminants. Select the corrosion layer or contaminated area on the steel sheet for XRD testing. Place the cleaned steel sheet on the sample stage of the XRD instrument. Select the commonly used copper (Cu) Kα ray, set the XRD scanning rate to 0.1° / s, adjust the incident angle (θ) to 1°, activate the X-ray source, and start scanning.

[0041] On the surface of the steel sheet or in the corrosion layer, FeCO3 will produce specific diffraction peaks, and the characteristic positions of these peaks can be compared with the standard database to identify the presence of FeCO3. After completing the scan, the instrument will output a diffraction pattern.

[0042] like Figure 3 As shown, the spectrum will show several characteristic peaks corresponding to different crystal plane spacings. The diffraction peak characteristics of FeCO3 will appear at certain specific positions at an angle of 2θ.

[0043] Experimental Example 2 Mechanical Properties Evaluation 1. Set up each experimental group The details are as follows: Example 1: The corrosion-resistant steel sheet with the FeCO3 protective coating on the surface obtained in Example 1 was directly evaluated for mechanical properties; Example 2: The corrosion-resistant steel sheet with the FeCO3 protective coating on the surface obtained in Example 1 was exposed to a humid environment for 30 days, and then the mechanical properties were evaluated; Example 3: Mechanical properties of the corrosion-resistant steel sheet with FeCO3 protective coating attached to the surface obtained from Q235 steel sheet were directly evaluated; Example 4: The corrosion-resistant steel sheet with FeCO3 protective coating attached to the surface of Q235 steel sheet was exposed in a humid environment for 30 days, and then the mechanical properties were evaluated; Comparative Example 1: Mechanical properties of an uncorroded steel sheet having the same shape parameters and material (304 stainless steel) as those in Example 1 were evaluated; Comparative Example 2: The mechanical properties of 304 stainless steel that has been corroded but not surface-modified were evaluated, that is, a steel sheet with the same shape parameters and material (304 stainless steel) as in Example 1 was exposed to humid air for 3 months, and then the mechanical properties were evaluated.

[0044] Comparative Example 3: Mechanical properties of an uncorroded Q235 steel sheet having the same shape parameters and material as those of Example 3 were evaluated; Comparative Example 4: The mechanical properties of corroded but surface-unmodified Q235 steel were evaluated, that is, a Q235 steel sheet having the same shape parameters and material as those in Example 3 was exposed to humid air for 3 months, and then the mechanical properties were evaluated.

[0045] 2. Mechanical properties evaluation experimental process The mechanical properties of the samples of Examples 1 to 4 and Comparative Examples 1 to 4 were evaluated, and the specific steps were as follows: Use the fixture of the universal testing machine to fix the steel sheet to ensure that the stress acts evenly on the center of the steel sheet during the test. Zero the displacement and load, fill in the sample size data, and during the test, set the loading rate to 2 mm / min to ensure that the stress and strain changes in the experiment are stable and measurable. During the stretching process of the steel sheet, the force and displacement data are recorded in real time, and the strain value is calculated by the ratio of displacement to original length.

[0046] The stress value of the steel sheet is calculated by dividing the load applied by the universal testing machine by the original cross-sectional area of ​​the steel sheet (width × thickness). The stress and strain values ​​of each experimental group of samples at different stretching stages are measured and recorded. The stress-strain curve of each sample can be automatically generated to evaluate the mechanical properties of the steel sheet.

[0047] 3. Experimental results The steel sheets of Examples 1 to 4 and Comparative Examples 1 to 4 were subjected to mechanical property tests, and the stress-strain curves of each sample during the test were recorded. By comparison, it was found that the stress-strain curves of the steel sheets after surface treatment basically overlapped with those of the stainless steel sheets with intact structures. It can be considered that the treated protective layer has good interface interaction and adhesion with the internal intact steel structure during the plastic deformation process (see Figure 4 and Figure 5 ).

[0048] Moreover, the performance of the steel sheet exposed to a humid environment for 30 days after surface modification was almost the same as that of the steel sheet tested for mechanical properties immediately after treatment, which fully proves that the FeCO3 protective layer has good corrosion resistance (see Figure 6 and Figure 7 ).

[0049] In comparison, the stress and strain of the corroded steel sheet without surface treatment were significantly lower than those of the other three samples, which fully demonstrated that the coating prepared by this method has a good protective effect and will not affect the excellent intrinsic performance of the steel structure (see 8 and Fig. 9 ).

[0050] Although the content of the present invention has been described in detail through the above preferred embodiments, it should be appreciated that the above description should not be considered as a limitation of the present invention. After reading the above content, it will be apparent to those skilled in the art that various modifications and substitutions of the present invention will occur. Therefore, the protection scope of the present invention should be limited by the appended claims.

Claims

1. A method for directly converting steel structure surface corrosion into a carbonate protective coating, characterized in that: The method includes: The corroded steel material is subjected to electron beam irradiation and plasma activated gas treatment in sequence, the electron beam irradiation is used to anchor the reaction active sites in the corrosion area on the surface of the steel structure, and the reaction active sites on the surface of the steel material are reacted with the active intermediates stimulated by the plasma jet through the plasma activated gas treatment, so that the formed corrosion is converted into a carbonate protective coating on the surface of the steel structure; The electron beam irradiation is carried out under vacuum conditions; The gas used in the plasma activated gas treatment is CO2 gas.

2. The method according to claim 1, characterized in that The vacuum condition is controlled to be less than 10 -4 Pa.

3. The method according to claim 1, characterized in that: The electron beam irradiation has a beam intensity of 0.1 A / cm 2 .

4. The method according to claim 1, characterized in that The electron beam irradiation treatment time is 15 min.

5. The method according to claim 1, characterized in that In the plasma activated gas treatment, the pressure of the CO2 gas introduced is 2 Pa, the flow rate is 50 sccm, and the plasma treatment power is 600 W.

6. The method according to claim 1, characterized in that The purity of the CO2 gas is >99.99%.

7. The method according to claim 1, characterized in that The activation process of the CO2 gas is stimulated by a plasma jet, and the resulting active intermediate CO* includes: CO2 + 、CO3 - , O + and C + Any one or more of the above.

8. The method according to claim 1, characterized in that: The plasma activated gas treatment will corrode the steel material.

9. The method according to claim 1, characterized in that: The time for the reaction of the reactive sites on the surface of the steel material with the reactive intermediates excited by the plasma jet is not less than 30 minutes.

10. The method according to claim 1, characterized in that Before the electron beam irradiation, the surface of the corroded steel material is ultrasonically cleaned in a deionized water bath.

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