Desulfurizing tower coated with coating and construction process thereof

Abstract

The invention belongs to the technical field of flue gas desulfurization treatment equipment, and discloses a desulfurization tower coated with a coating and a construction process thereof, the desulfurization tower comprises a desulfurization tower body and an anticorrosive coating coated on the lining surface of the desulfurization tower body; graphene coating is adopted as the anti-corrosion coating; specifically, the graphene coating is prepared from raw materials in parts by weight as follows: 80-100 parts of epoxy resin, 15-20 parts of deionized water, 1-18 parts of graphene sheets, 1-25 parts of a graphene dispersant, 25-55 parts of an RS preservative, 10-18 parts of isooctyl ester, 3-10 parts of a thickener, 5-20 parts of dimethyl fumarate, 5-20 parts of a demolding preservative and 10-25 parts of a silane coupling agent. The surface of the lining of the desulfurization tower body is coated with the graphene coating, so that corrosion of acid, alkali and other chemical media can be effectively resisted, the coating can stably run for a long time, the inner wall of the desulfurization tower is protected against corrosion and corrosion, and the service life of the desulfurization tower is prolonged.

Description

Technical Field

[0001] This invention belongs to the technical field of flue gas desulfurization equipment, and specifically relates to a desulfurization tower coated with paint and its construction process. Background Technology

[0002] A desulfurization tower is a device used for flue gas desulfurization treatment. Its main function is to remove sulfur-containing gases from flue gas to purify it. During the desulfurization process, the inner wall of the tower is corroded by acidic media formed by the combination of acidic gases such as SO2, SO3, and HF with water vapor in the flue gas. It is also affected by electrochemical corrosion, scouring corrosion, and temperature changes. These corrosive factors can cause wear, aging, and even detachment of the inner wall material, thus shortening the equipment's lifespan and increasing maintenance costs. Therefore, taking effective anti-corrosion measures for the inner lining is crucial for ensuring the stable operation of the desulfurization tower.

[0003] Currently, the main method for preventing corrosion on the inner wall of desulfurization towers is to apply anti-corrosion coatings. These coatings isolate the tower from corrosive substances such as air and moisture, thus achieving the effect of corrosion prevention. However, existing anti-corrosion coatings have poor thermal stability and are prone to aging and peeling off under the high-temperature operating environment of desulfurization towers, resulting in a short service life and seriously affecting the stable operation of desulfurization towers. Summary of the Invention

[0004] In view of the technical problems existing in the prior art, the present invention provides a desulfurization tower coated with paint and its construction process, so as to solve the technical problem that the existing anti-corrosion paint has poor thermal stability, is prone to aging and peeling under the high temperature operating environment of the desulfurization tower, has a short service life, and seriously affects the stable operation of the desulfurization tower.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows: The present invention provides a desulfurization tower coated with a paint, comprising a desulfurization tower body and an anti-corrosion paint coated on the inner lining surface of the desulfurization tower body; wherein the anti-corrosion paint is a graphene paint. Specifically, the graphene coating, by weight, comprises the following raw materials: 80-100 parts epoxy resin, 15-20 parts deionized water, 1-18 parts graphene sheets, 1-25 parts graphene dispersant, 25-55 parts RS preservative, 10-18 parts isooctyl ester, 3-10 parts thickener, 5-20 parts dimethyl fumarate, 5-20 parts release preservative, and 10-25 parts silane coupling agent.

[0006] Furthermore, the graphene coating, by weight, also includes the following raw materials: 15-30 parts of anionic acrylic emulsion, 3-5 parts of leveling agent, 5-7 parts of wetting and dispersing agent, 3-5 parts of pigment, 30-45 parts of ethanol solvent, 15-20 parts of defoamer, 5-20 parts of curing agent, 10-40 parts of polyaniline, 5-35 parts of film-forming aid, and 3-15 parts of toughening agent.

[0007] Furthermore, the graphene coating, by weight, comprises the following raw materials: 90 parts epoxy resin, 17 parts deionized water, 15 parts graphene sheets, 16 parts graphene dispersant, 40 parts RS preservative, 13 parts isooctyl ester, 8 parts thickener, 12 parts dimethyl fumarate, 12 parts release preservative, and 17 parts silane coupling agent.

[0008] Furthermore, the graphene coating, by weight, also includes the following raw materials: 28 parts of anionic acrylic emulsion, 5 parts of leveling agent, 5 parts of wetting and dispersing agent, 5 parts of pigment, 36 parts of ethanol solvent, 18 parts of defoamer, 10 parts of curing agent, 25 parts of polyaniline, 20 parts of film-forming aid, and 10 parts of toughening agent.

[0009] Furthermore, the isooctyl ester is one of isooctyl acetate, isooctyl stearate, and diisooctyl maleate.

[0010] Furthermore, the thickener is a cellulose-based thickener.

[0011] Furthermore, the curing agent is an alkyd resin, and the leveling agent is an organosilicon leveling agent.

[0012] Furthermore, the thickness of the anti-corrosion coating is 2-7 mm.

[0013] Furthermore, the preparation process of the anti-corrosion coating is as follows: Epoxy resin, deionized water, graphene dispersant, isooctyl ester, and dimethyl fumarate are mixed and stirred under vacuum until uniformly dissolved to obtain a mixture. RS preservative, release preservative, thickener, and silane coupling agent are added to the mixture, and the mixture is stirred and differentiated to form a homogeneous slurry. The homogeneous slurry is then subjected to micro-milling to a fineness of less than 90 μm to obtain a micro-milled homogeneous slurry. The micro-milled homogeneous slurry is then subjected to secondary stirring and differentiation to obtain the graphene coating.

[0014] The present invention also provides a construction process for a desulfurization tower coated with a paint, comprising: Construct the desulfurization tower body according to design requirements; Determine the anti-corrosion treatment area on the inner lining surface of the desulfurization tower body, and apply a graphene coating of a predetermined thickness to the surface of the area requiring anti-corrosion treatment.

[0015] Compared with the prior art, the beneficial effects of the present invention are as follows: The desulfurization tower coated with a graphene coating provided by this invention utilizes graphene flakes in the graphene coating to effectively resist the erosion of chemical media such as acids and alkalis. This allows the coating to operate stably for a long time, protecting the inner wall of the desulfurization tower from corrosion and extending its service life. Secondly, the graphene coating exhibits good thermal and chemical stability, enabling it to withstand the passage of high-temperature exhaust gas during tower operation and ensuring long-term stability. Furthermore, the addition of graphene flakes enhances the coating's adhesion, allowing it to firmly adhere to the inner wall of the desulfurization tower. Simultaneously, the layered structure of the graphene flakes effectively inhibits the wetting, penetration, and diffusion of corrosive media, improving the coating's wear resistance and extending its service life. Attached Figure Description

[0016] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0017] Figure 1 This is a process flow diagram of the construction of the desulfurization tower coated with paint in Example 1. Detailed Implementation

[0018] To make the technical problems, technical solutions, and beneficial effects solved by this application clearer, the technical solutions in the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this application without creative effort are within the scope of protection of this application.

[0019] This invention provides a desulfurization tower coated with a paint, comprising a desulfurization tower body and an anti-corrosion paint coated on the inner lining surface of the desulfurization tower body; wherein, the anti-corrosion paint is a graphene paint; specifically, the graphene paint, by weight, comprises the following raw materials: 80-100 parts epoxy resin, 15-20 parts deionized water, 1-18 parts graphene sheets, 1-25 parts graphene dispersant, 25-55 parts RS preservative, 10-18 parts isooctyl ester, 3-10 parts thickener, 5-20 parts dimethyl fumarate, 5-20 parts release preservative, and 10-25 parts silane coupling agent; wherein, the thickener is a cellulose-based thickener.

[0020] Preferably, the graphene coating, by weight, further comprises the following raw materials: 28 parts of anionic acrylic emulsion, 5 parts of leveling agent, 5 parts of wetting and dispersing agent, 5 parts of pigment, 36 parts of ethanol solvent, 18 parts of defoamer, 10 parts of curing agent, 25 parts of polyaniline, 20 parts of film-forming aid, and 10 parts of toughening agent; wherein the curing agent is alkyd resin, and the leveling agent is silicone leveling agent.

[0021] The preparation process of the anti-corrosion coating in this invention is as follows: Epoxy resin, deionized water, graphene dispersant, isooctyl ester, and dimethyl fumarate are mixed and stirred under vacuum until uniformly dissolved to obtain a mixture. RS preservative, release preservative, thickener, and silane coupling agent are added to the mixture, and the mixture is stirred and differentiated to form a homogeneous slurry. The homogeneous slurry is then subjected to micro-milling to a fineness of less than 90 μm to obtain a micro-milled homogeneous slurry. The micro-milled homogeneous slurry is then subjected to secondary stirring and differentiation to obtain the graphene coating.

[0022] In this invention, the construction process of the desulfurization tower coated with paint includes: Construct the desulfurization tower body according to the design requirements; determine the anti-corrosion treatment area on the inner lining surface of the desulfurization tower body, and apply a graphene coating of a preset thickness to the surface of the area requiring anti-corrosion treatment; wherein the coating thickness of the graphene coating is 2-7mm.

[0023] Corrosion prevention principle: In this invention, by coating the inner lining surface of the desulfurization tower body with graphene coating, its anti-corrosion principle is mainly based on the combined effect of the excellent physical and chemical properties of graphene, forming a highly efficient anti-corrosion barrier.

[0024] Specifically, the two-dimensional sheet structure of graphene is stacked and interwoven in the coating, forming a dense physical barrier that effectively prevents the wetting, penetration, and diffusion of corrosive media (such as water, oxygen, and chloride ions), extending the penetration path of corrosive media and thus improving the coating's impermeability and service life. The sheet structure of graphene forms a "maze-like" shielding structure in the coating, making the diffusion of corrosive media in the coating more complex and difficult, further enhancing the physical barrier properties of the coating. The small size effect of graphene allows it to fill the tiny pores and defects in the coating, reducing the porosity of the coating, enhancing the density and integrity of the coating, and helping to further prevent the intrusion of corrosive agents.

[0025] Secondly, graphene has extremely high chemical stability and can resist the erosion of chemical media such as acids and alkalis, so that graphene anti-corrosion coatings can still maintain good anti-corrosion performance in harsh chemical environments. Graphene can also effectively adsorb and catalyze harmful substances (such as oxygen, moisture and acids and alkalis) on the metal surface and convert them into harmless substances, thereby eliminating the corrosive factors on the metal surface and slowing down the metal corrosion process.

[0026] Furthermore, graphene possesses excellent electrical conductivity, enabling it to form a conductive network within the anti-corrosion coating. When localized damage occurs in the coating, graphene's conductivity allows it to transfer electrons from the anodic reaction to the coating surface, facilitating the cathodic reaction. The OH- ions generated in the cathodic reaction then react with the Fe- ions generated in the anodic reaction. 3+ The inability to react with the anionic acrylic emulsion inhibits further corrosion; secondly, the positive and negative attraction between the anions in the anionic acrylic emulsion and the ions in the atmosphere causes the ions to lose their conductivity.

[0027] It should also be noted that the high strength of graphene in graphene coatings significantly improves the mechanical properties of the coating film, such as hardness, impact strength, and flexibility, helping the coating maintain its integrity and corrosion resistance when subjected to external impacts or abrasion. Graphene's UV resistance gives the anti-corrosion coating better weather resistance, allowing it to maintain its color and gloss for a long time in the harsh environment of desulfurization towers, thus extending its service life. Compared with traditional anti-corrosion coatings, graphene coatings can reduce or even eliminate the addition of environmentally harmful substances, causing no pollution, saving energy and reducing emissions. No irritating or toxic gases are emitted during the application process, making them safe to use.

[0028] Example 1 This embodiment 1 provides a desulfurization tower coated with a coating, including a desulfurization tower body and an anti-corrosion coating applied to the inner lining surface of the desulfurization tower body; wherein the anti-corrosion coating is a graphene coating.

[0029] The graphene coating, by weight, comprises the following raw materials: 90 parts epoxy resin, 17 parts deionized water, 15 parts graphene sheets, 16 parts graphene dispersant, 40 parts RS preservative, 13 parts isooctyl ester, 8 parts thickener, 12 parts dimethyl fumarate, 12 parts release preservative, and 17 parts silane coupling agent; wherein the isooctyl ester is isooctyl acetate; and the thickener is a cellulose-based thickener.

[0030] The preparation process of the graphene coating is as follows: Epoxy resin, deionized water, graphene dispersant, isooctyl ester, and dimethyl fumarate are mixed and stirred under vacuum until uniformly dissolved to obtain a mixture. RS preservative, release preservative, thickener, and silane coupling agent are added to the mixture, and the mixture is stirred and differentiated to form a homogeneous slurry. The homogeneous slurry is then subjected to micro-milling to a fineness of less than 90 μm to obtain a micro-milled homogeneous slurry. The micro-milled homogeneous slurry is then subjected to secondary stirring and differentiation to obtain the graphene coating.

[0031] It should be noted that the vacuum stirring process is carried out in a vacuum stirring dissolving machine, the stirring differentiation and secondary stirring differentiation are carried out in a vacuum spiral stirring differentiation machine, and the micro-sand milling treatment is carried out in a micro-sand mill.

[0032] As attached Figure 1 As shown, this embodiment 1 also provides a construction process for a desulfurization tower coated with paint, including the following steps: The desulfurization tower body was constructed according to the design requirements.

[0033] Identify the anti-corrosion treatment areas on the inner lining surface of the desulfurization tower body, and apply a graphene coating of a predetermined thickness to the areas requiring anti-corrosion treatment. The graphene coating is applied manually or by machine spraying; the predetermined thickness is 2-7 mm.

[0034] Example 2 The desulfurization tower coated with a paint provided in this embodiment 2 has a basically the same structure as the desulfurization tower coated with a paint provided in embodiment 1 above. The difference is that the raw material ratio of the graphene paint is different.

[0035] In this embodiment 2, the graphene coating, by weight, includes the following raw materials: 100 parts epoxy resin, 15 parts deionized water, 18 parts graphene sheets, 25 parts graphene dispersant, 25 parts RS preservative, 10 parts isooctyl ester, 6 parts thickener, 20 parts dimethyl fumarate, 5 parts release preservative, and 25 parts silane coupling agent; wherein, the isooctyl ester is isooctyl stearate.

[0036] In this Example 2, the preparation method of the graphene coating and the construction process of the desulfurization tower coated with the coating are basically the same as those in Example 1 above, and will not be repeated here.

[0037] Example 3 The desulfurization tower coated with a coating provided in this embodiment 3 has a basically the same structure as the desulfurization tower coated with a coating provided in embodiment 1 above. The difference is that the raw material ratio of the graphene coating is different.

[0038] In this embodiment 3, the graphene coating, by weight, includes the following raw materials: 80 parts epoxy resin, 20 parts deionized water, 7 parts graphene sheets, 10 parts graphene dispersant, 35 parts RS preservative, 15 parts isooctyl ester, 10 parts thickener, 8 parts dimethyl maleate, 16 parts release preservative, and 10 parts silane coupling agent; wherein, the isooctyl ester is diisooctyl maleate.

[0039] In this embodiment 3, the preparation method of the graphene coating and the construction process of the desulfurization tower coated with the coating are basically the same as those in embodiment 1 above, and will not be repeated here.

[0040] Example 4 The desulfurization tower coated with a paint provided in this embodiment 4 has a basically the same structure as the desulfurization tower coated with a paint provided in embodiment 1 above. The difference is that the raw material ratio of the graphene paint is different.

[0041] In this embodiment 4, the graphene coating, by weight, includes the following raw materials: 85 parts epoxy resin, 16 parts deionized water, 1 part graphene sheet, 1 part graphene dispersant, 55 parts RS preservative, 18 parts isooctyl ester, 3 parts thickener, 5 parts dimethyl maleate, 20 parts release preservative, and 13 parts silane coupling agent; wherein, the isooctyl ester is diisooctyl maleate.

[0042] In this embodiment 4, the preparation method of the graphene coating and the construction process of the desulfurization tower coated with the coating are basically the same as those in embodiment 1 above, and will not be repeated here.

[0043] Example 5 The desulfurization tower coated with a paint provided in this embodiment 5 has a basically the same structure as the desulfurization tower coated with a paint provided in embodiment 1 above. The difference is that the raw material ratio of the graphene paint is different.

[0044] In this Example 5, the graphene coating, in addition to including the same raw materials and proportions as in Example 1 above, also includes the following raw materials by weight: 28 parts of anionic acrylic emulsion, 5 parts of leveling agent, 5 parts of wetting and dispersing agent, 5 parts of pigment, 36 parts of ethanol solvent, 18 parts of defoamer, 10 parts of curing agent, 25 parts of polyaniline, 20 parts of film-forming aid, and 10 parts of toughening agent.

[0045] In this Example 5, the preparation method of the graphene coating is basically the same as that in Example 1 above, except that: before the first stirring and differentiation, anionic acrylic emulsion, leveling agent, wetting and dispersing agent, pigment, ethanol solvent, defoamer, curing agent, polyaniline, film-forming aid and toughening agent are added to the mixture.

[0046] In this embodiment 5, the construction process of the desulfurization tower coated with paint is basically the same as that in embodiment 1 above, and will not be repeated here.

[0047] Example 6 The desulfurization tower coated with a paint provided in this embodiment 6 has a basically the same structure as the desulfurization tower coated with a paint provided in embodiment 1 above. The difference is that the raw material ratio of the graphene paint is different.

[0048] In this Example 6, the graphene coating, in addition to including the same raw materials and proportions as in Example 1 above, also includes the following raw materials by weight: 15 parts of anionic acrylic emulsion, 4 parts of leveling agent, 7 parts of wetting and dispersing agent, 4 parts of pigment, 45 parts of ethanol solvent, 20 parts of defoamer, 5 parts of curing agent, 40 parts of polyaniline, 5 parts of film-forming aid, and 3 parts of toughening agent.

[0049] In this embodiment 6, the preparation method of the graphene coating and the construction process of the desulfurization tower coated with the coating are basically the same as those in embodiment 5 above, and will not be repeated here.

[0050] Example 7 The desulfurization tower coated with a paint provided in this embodiment 7 has a basically the same structure as the desulfurization tower coated with a paint provided in embodiment 1 above. The difference is that the raw material ratio of the graphene paint is different.

[0051] In this Example 7, the graphene coating, in addition to including the same raw materials and proportions as in Example 1 above, also includes the following raw materials by weight: 30 parts of anionic acrylic emulsion, 3 parts of leveling agent, 6 parts of wetting and dispersing agent, 3 parts of pigment, 30 parts of ethanol solvent, 15 parts of defoamer, 20 parts of curing agent, 10 parts of polyaniline, 35 parts of film-forming aid, and 15 parts of toughening agent.

[0052] In this embodiment 7, the preparation method of the graphene coating and the construction process of the desulfurization tower coated with the coating are basically the same as those in embodiment 5 above, and will not be repeated here.

[0053] In this invention, graphene sheets are added to the graphene coating. Graphene is a honeycomb-shaped planar film formed by carbon atoms in an sp² hybridization manner. This allows it to form an isolation layer between the inner wall of the desulfurization tower and the external water vapor, preventing diffusion and penetration. It has a good physical shielding effect on the diffusion of water, oxygen and ions, thereby achieving the anti-corrosion function. Secondly, by adding leveling agents, wetting and dispersing agents, pigments and ethanol solvents, the fluidity, wetting and dispersibility of the coating are improved, making the coating more uniform and smooth during the construction process.

[0054] In this invention, the addition of pigments can provide the desired color for the coating; the addition of ethanol solvent helps with the dilution and spraying of the coating; defoamers can eliminate bubbles generated during the mixing and application of the coating, preventing defects such as pinholes in the coating; curing agents can accelerate the curing speed of the coating and improve its hardness and wear resistance; since polyaniline is a conductive polymer material, its addition can further improve the conductivity and corrosion resistance of the coating; film-forming aids help the film-forming process of the coating, making the coating denser and more uniform; and toughening agents can enhance the flexibility and impact resistance of the coating.

[0055] The desulfurization tower coated with a graphene coating provided by this invention utilizes the extremely high chemical stability of the graphene sheets in the coating. Furthermore, the ultra-large specific surface area and excellent shielding properties of graphene further enhance the anti-corrosion effect of the coating, delaying and preventing corrosive agents from entering the substrate surface. This allows the coating to operate stably for a long time, protecting the inner wall of the desulfurization tower from corrosion and extending its service life. In addition, the layered structure of graphene can effectively fill the gaps in the coating, reduce the porosity of the coating, enhance the density of the coating, and thus improve the wear resistance of the coating.

[0056] The above embodiments are merely one of the implementation methods for achieving the technical solution of the present invention. The scope of protection claimed by the present invention is not limited to this embodiment, but also includes any variations, substitutions and other implementation methods that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention.

Claims

1. A desulfurization tower coated with a paint, characterized in that, The system includes a desulfurization tower body and an anti-corrosion coating applied to the inner lining surface of the desulfurization tower body; wherein the anti-corrosion coating is a graphene coating. Specifically, the graphene coating, by weight, comprises the following raw materials: 80-100 parts epoxy resin, 15-20 parts deionized water, 1-18 parts graphene sheets, 1-25 parts graphene dispersant, 25-55 parts RS preservative, 10-18 parts isooctyl ester, 3-10 parts thickener, 5-20 parts dimethyl fumarate, 5-20 parts release preservative, and 10-25 parts silane coupling agent.

2. A desulfurization tower coated with paint according to claim 1, characterized in that, The graphene coating, by weight, further includes the following raw materials: 15-30 parts of anionic acrylic emulsion, 3-5 parts of leveling agent, 5-7 parts of wetting and dispersing agent, 3-5 parts of pigment, 30-45 parts of ethanol solvent, 15-20 parts of defoamer, 5-20 parts of curing agent, 10-40 parts of polyaniline, 5-35 parts of film-forming aid, and 3-15 parts of toughening agent.

3. A desulfurization tower coated with paint according to claim 1, characterized in that, The graphene coating, by weight, comprises the following raw materials: 90 parts epoxy resin, 17 parts deionized water, 15 parts graphene sheets, 16 parts graphene dispersant, 40 parts RS preservative, 13 parts isooctyl ester, 8 parts thickener, 12 parts dimethyl fumarate, 12 parts release preservative, and 17 parts silane coupling agent.

4. A desulfurization tower coated with paint according to claim 3, characterized in that, The graphene coating, by weight, also includes the following raw materials: 28 parts of anionic acrylic emulsion, 5 parts of leveling agent, 5 parts of wetting and dispersing agent, 5 parts of pigment, 36 parts of ethanol solvent, 18 parts of defoamer, 10 parts of curing agent, 25 parts of polyaniline, 20 parts of film-forming aid, and 10 parts of toughening agent.

5. A desulfurization tower coated with paint according to claim 1, characterized in that, The isooctyl ester is one of isooctyl acetate, isooctyl stearate, and diisooctyl maleate.

6. A desulfurization tower coated with paint according to claim 1, characterized in that, The thickener is a cellulose-based thickener.

7. A desulfurization tower coated with paint according to claim 2, characterized in that, The curing agent is an alkyd resin, and the leveling agent is an organosilicon leveling agent.

8. A desulfurization tower coated with paint according to claim 1, characterized in that, The thickness of the anti-corrosion coating is 2-7 mm.

9. A desulfurization tower coated with paint according to claim 1, characterized in that, The preparation process of the anti-corrosion coating is as follows: Epoxy resin, deionized water, graphene dispersant, isooctyl ester, and dimethyl fumarate are mixed and vacuum stirred until uniformly dissolved to obtain a mixture. RS preservative, release preservative, thickener, and silane coupling agent are added to the mixture, and the mixture is stirred and differentiated to form a homogeneous slurry. The homogeneous slurry is then subjected to micro-milling to a fineness of less than 90 μm to obtain a micro-milled homogeneous slurry. The uniformly mixed slurry after micro-sand milling is subjected to secondary stirring and differentiation to obtain the graphene coating.

10. A construction process for a desulfurization tower coated with paint as described in any one of claims 1-9, characterized in that, include: Construct the desulfurization tower body according to design requirements; Determine the anti-corrosion treatment area on the inner lining surface of the desulfurization tower body, and apply a graphene coating of a predetermined thickness to the surface of the area requiring anti-corrosion treatment.

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