Hydrophobic / chromium-rich corrosion-resistant composite coating, preparation method therefor, and use thereof

Abstract

A hydrophobic / chromium-rich corrosion-resistant composite coating, a preparation method therefor, and the use thereof, relating to the technical field of material surface coatings. The preparation method comprises: preheating a workpiece; applying a coating slurry to the surface of the preheated workpiece, and performing drying and curing and sintering treatment to obtain a chromium-rich corrosion-resistant coating on the surface of the workpiece, the coating slurry comprising a solid-phase component and a liquid-phase component, wherein the solid-phase component comprises chromium powder, nickel powder, iron powder and a rare earth compound, and the liquid-phase component comprises Al(H2PO4)3, water glass, an ammonium halide, polyvinyl alcohol and Cr2O3; and spray-coating a layer of a superhydrophobic material on the surface of the chromium-rich corrosion-resistant coating, and then performing curing treatment to obtain the hydrophobic / chromium-rich corrosion-resistant composite coating. A workpiece undergoes chromizing treatment and superhydrophobic treatment and thus possesses corrosion resistance, wear resistance and hydrophobic properties, so that water vapor in tubes cannot stay on the inner walls of the tubes, thereby preventing corrosion of the inner walls of the tubes, improving the comprehensive performance of the tubes, and prolonging the service life.

Description

A hydrophobic / chromium-rich corrosion-resistant composite coating, its preparation method, and its application.

[0001] Cross-references to related applications

[0002] This application claims priority to Chinese Patent Application No. 202410975831.4, filed on July 19, 2024, entitled "Hydrophobic / Chromium-Rich Corrosion-Resistant Composite Coating and its Preparation Method and Application", the entire contents of which are incorporated herein by reference. Technical Field

[0003] This disclosure belongs to the field of material surface coating technology, specifically relating to a hydrophobic / chromium-rich corrosion-resistant composite coating and its preparation method and application. Background Technology

[0004] Hot corrosion of the inner surface of boiler pipes has always been one of the factors restricting thermal power generation. Especially at present, thermal power generation is developing towards higher steam temperatures and pressures, so it is imperative to improve the thermal corrosion resistance of the inner surface of pipes.

[0005] Pipeline corrosion problems mainly consist of two parts: corrosion caused by gas and metal oxidation corrosion caused by water vapor. Applying a corrosion-resistant coating to the pipe surface can solve problems such as short pipe lifespan, the need for regular oxide removal, and prevent dangerous incidents like pipe bursts.

[0006] The most common anti-corrosion technology currently is the infiltration of corrosion-resistant metals onto alloy surfaces, such as Al, Si, and Cr. This involves forming a corrosion-resistant coating on the alloy surface through Cr infiltration. There are many methods for preparing Cr-rich coatings, typically including powder embedding, vapor deposition, and liquid phase methods. The liquid phase method usually involves placing Cr powder in molten salt and holding it at high temperature to form a Cr-infiltrated layer. However, the molten salt is prone to volatilization at high temperatures, causing damage to the workpiece and the environment. The slurry method involves directly applying or spraying a slurry onto the workpiece surface and then sintering it at high temperatures to obtain a coating. This method produces coatings with excellent corrosion resistance and good adhesion. Compared to other Cr infiltration methods, this method is simple to operate and suitable for large-scale industrial production.

[0007] However, based on the saturated vapor pressure of water, it has been found that liquid water can still exist inside pipelines under high temperature and high pressure conditions. Therefore, the aforementioned corrosion prevention methods can only delay pipeline corrosion to a certain extent and cannot fundamentally solve the problem of pipeline oxidation and corrosion.

[0008] Summary of the Invention

[0009] This disclosure aims to at least solve one of the technical problems existing in the prior art, and to provide a hydrophobic / chromium-rich corrosion-resistant composite coating, its preparation method, and its application.

[0010] One aspect of this disclosure provides a method for preparing a hydrophobic / chromium-rich corrosion-resistant composite coating, the method comprising:

[0011] Preheating treatment of the workpiece;

[0012] A coating slurry is applied to the surface of a preheated workpiece, followed by drying, curing, and sintering to obtain a chromium-rich corrosion-resistant coating. The coating slurry comprises a solid phase component and a liquid phase component. The solid phase component includes chromium powder, nickel powder, iron powder, and rare earth compounds. The liquid phase component includes Al(H2PO4)3, water glass, ammonium halide, polyvinyl alcohol, and Cr2O3.

[0013] A layer of superhydrophobic material is sprayed onto the surface of the chromium-rich corrosion-resistant coating, and then cured to obtain a hydrophobic / chromium-rich corrosion-resistant composite coating.

[0014] Optionally, the solid-liquid ratio of the solid phase component to the liquid phase component is 10:(1-5).

[0015] Optionally, the chromium powder content is 40-80%;

[0016] The content of the nickel powder is 5-30%;

[0017] The content of the iron powder is 2-20%;

[0018] The content of the rare earth compound is 5-45%.

[0019] Optionally, the content of Al(H2PO4)3 is 10-30%;

[0020] The water glass content is 15-25%;

[0021] The content of the ammonium halide is 5-10%;

[0022] The polyvinyl alcohol content is 10-35%;

[0023] The Cr2O3 content is 10-30%.

[0024] Optionally, the rare earth compound is a rare earth oxide or a rare earth chloride; and / or,

[0025] The ammonium halide is ammonium bromide or ammonium iodide.

[0026] Optionally, a layer of superhydrophobic material is sprayed onto the surface of the chromium-rich corrosion-resistant coating, and then cured to obtain a hydrophobic / chromium-rich corrosion-resistant composite coating, comprising:

[0027] Anhydrous ethanol, HDTMS and nano-alumina particles were mixed to form a suspension, which was then stirred, centrifuged and dried to obtain superhydrophobic Al2O3 nanoparticles modified with HDTMS.

[0028] An epoxy resin, polydimethylsiloxane, epoxy resin curing agent, and Al2O3 nanoparticles treated with HDTMS hydrophobicity were dissolved in xylene to prepare a suspension. This suspension was then sprayed onto the surface of a chromium-rich corrosion-resistant coating, and after curing, a superhydrophobic / chromium-rich corrosion-resistant composite coating was obtained.

[0029] Optionally, the workpiece preheating treatment is performed at a temperature of 150–220°C for a time of 30–60 min; and / or,

[0030] Under inert gas protection, the sintering temperature is 980-1150℃ and the time is 8-30 min.

[0031] Optionally, the thickness of the chromium-rich corrosion-resistant coating is 5-50 μm; and / or,

[0032] The thickness of the hydrophobic / chromium-rich corrosion-resistant composite coating is 13-64 μm.

[0033] In another aspect of this disclosure, a hydrophobic / chromium-rich corrosion-resistant composite coating is provided, prepared according to the preparation method described above.

[0034] In another aspect of this disclosure, an application of a hydrophobic / chromium-rich corrosion-resistant composite coating is proposed, wherein the hydrophobic / chromium-rich corrosion-resistant composite coating described above is applied to the inner surface of boiler pipes.

[0035] This disclosure proposes a hydrophobic / chromium-rich corrosion-resistant composite coating, its preparation method, and its application. The preparation method includes: preheating the workpiece; applying a coating slurry to the surface of the preheated workpiece, followed by drying, curing, and sintering to obtain a chromium-rich corrosion-resistant coating on the workpiece surface; the coating slurry includes a solid phase component and a liquid phase component; wherein the solid phase component includes chromium powder, nickel powder, iron powder, and rare earth compounds; the liquid phase component includes Al(H2PO4)3, water glass, ammonium halide, polyvinyl alcohol, and Cr2O3; spraying a layer of superhydrophobic material onto the surface of the chromium-rich corrosion-resistant coating, followed by curing to obtain the hydrophobic / chromium-rich corrosion-resistant composite coating. This method, through chromium infiltration and superhydrophobic treatment of the workpiece, endows the workpiece with corrosion resistance, wear resistance, and hydrophobic properties, preventing water vapor from remaining on the inner wall of the pipe, thus avoiding corrosion of the inner wall and improving the overall performance and service life of the pipe. Attached Figure Description

[0036] Figure 1 is a flowchart of a method for preparing a hydrophobic / chromium-rich corrosion-resistant composite coating according to an embodiment of the present disclosure. Detailed Implementation

[0037] To enable those skilled in the art to better understand the technical solutions of this disclosure, the disclosure will be further described in detail below with reference to the accompanying drawings and specific embodiments. Obviously, the described embodiments are only some, not all, of the embodiments of this disclosure. All other embodiments obtained by those skilled in the art based on the described embodiments of this disclosure without creative effort are within the protection scope of this disclosure.

[0038] As shown in Figure 1, one aspect of this disclosure provides a method S100 for preparing a hydrophobic / chromium-rich corrosion-resistant composite coating, specifically including the following steps S110-S130:

[0039] S110. Preheating treatment of the workpiece.

[0040] Specifically, the workpiece is preheated at a temperature of 150–220°C for 30–60 minutes.

[0041] In this embodiment, preheating treatment can optimize the microstructure of the metal workpiece, eliminate residual stress, reduce workpiece deformation, improve surface quality, and increase the workpiece temperature, which is beneficial for subsequent chromium diffusion paste coating on its surface.

[0042] It should be understood that the workpiece can also be cleaned before preheating treatment. For example, alcohol or acetone can be used to clean oil stains and dust from the pipe surface, while steel brushes can be used to remove surface oxide scale, thereby increasing the specific surface area of ​​the workpiece, enhancing the subsequent penetration effect of metal powder, and increasing the adhesion of the coating.

[0043] S120. The coating slurry is applied to the surface of the preheated workpiece, and after drying, curing and sintering, a chromium-rich corrosion-resistant coating is obtained on the surface of the workpiece.

[0044] In this embodiment, the coating slurry includes a solid phase component and a liquid phase component; wherein, the solid phase component includes chromium powder, nickel powder, iron powder, and rare earth compounds; and the liquid phase component includes Al(H2PO4)3, water glass, ammonium halide, polyvinyl alcohol, and Cr2O3. By mixing the solid phase component and the liquid phase component in a certain proportion to form a slurry, it is helpful for the metal powders to be coated on the surface of the workpiece, forming a corrosion-resistant coating.

[0045] In some alternative embodiments, the solid-liquid ratio (g:mL) of the solid phase component to the liquid phase component is 10:(1-5), for example, the two components are mixed in proportions of 10:1, 10:2, 10:3, 10:4, 10:5, etc.

[0046] It should be noted that this embodiment does not specifically limit the mixing method of the solid and liquid components. The solid component can be directly added to the liquid component, or the liquid component can be injected into the solid component for mixing. Of course, the powders in the solid component can also be premixed. For example, the solid components can be ball-milled in a star mill at a speed of 350-400 r / min for 6-24 h to premix the solid components, and then the mixed solid components can be mixed with the liquid components.

[0047] In some optional embodiments, the chromium powder content is 40-80%, for example, 40%, 50%, 60%, 70%, 80%; the nickel powder content is 5-30%, for example, 5%, 10%, 15%, 20%, 25%, 30%; the iron powder content is 2-20%, for example, 2%, 7%, 10%, 15%, 17%, 20%; and the rare earth compound content is 5-45%, for example, 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%.

[0048] As an alternative, the rare earth compound can be a rare earth oxide, such as samarium oxide, europium oxide, yttrium oxide, etc. Of course, the rare earth compound can also be a rare earth chloride, such as lanthanum chloride, etc.

[0049] In the solid phase composition of this embodiment, rare earth atoms are provided by adding rare earth element oxides and chlorides. During sintering, the rare earth element oxides or chlorides segregate at the grain boundaries, acting as grain boundary pinning agents and refining the coating grains. Simultaneously, they prevent Cr atoms from diffusing deeper into the substrate, allowing the coating to grow outwards, increasing the coating thickness and the Cr element concentration within the coating. During service, they segregate at the oxide film grain boundaries, thereby suppressing Cr... 3+ Rapid "short-circuit diffusion" along grain boundaries causes the coating's oxidation mechanism to change from Cr... 3+ The main direction is outward diffusion, which transforms into O. 2－ The internally grown oxide film diffuses inward and bonds tightly to the substrate, improving its resistance to peeling and thus enhancing the coating's corrosion resistance.

[0050] Furthermore, in the solid phase component of this embodiment, a small amount of iron and nickel are added mainly to increase the chromium diffusion rate and reduce the chromium diffusion temperature; chromium forms solid solutions with iron and nickel elements respectively, and compared with a single chromium diffusion coating, chromium-iron-nickel co-diffusion can significantly improve the wear resistance and corrosion resistance of the diffusion layer.

[0051] In other alternative embodiments, the content of Al(H2PO4)3 is 10-30%, for example, 10%, 15%, 20%, 25%, or 30%; the content of water glass is 15-25%, for example, 15%, 20%, or 25%; the content of ammonium halide is 5-10%, for example, 5%, 7%, or 10%; the content of polyvinyl alcohol is 10-35%, for example, 10%, 20%, 25%, 30%, or 35%; and the content of Cr2O3 is 10-30%, for example, 10%, 15%, 20%, 25%, or 30%.

[0052] As an alternative, the ammonium halide is either ammonium bromide or ammonium iodide.

[0053] In the liquid phase component of this embodiment, the synergistic effect of the liquid phase component and the solid phase component can achieve a coating of the required thickness in a single coating process, and the coating surface is smooth, the interior is uniform and dense, and it has good corrosion resistance.

[0054] Furthermore, in the liquid phase component of this embodiment, Al(H2PO4)3 serves as a binder, exhibiting high bonding strength with the metal substrate, allowing the required coating thickness to be achieved in a single coating process; simultaneously, this component possesses good high-temperature toughness, making it less prone to cracking during curing and drying.

[0055] Furthermore, in the liquid phase component of this embodiment, the binder is modified by adding water glass and polyvinyl alcohol, which further increases the high-temperature toughness of Al(H2PO4)3 and its adhesion to the metal substrate. As an inorganic binder, Al(H2PO4)3 can directly volatilize during the drying process of the slurry, preventing the formation of pores inside the coating due to gas generation during sintering. In other words, polyvinyl alcohol in this embodiment serves as a substance that can improve the high-temperature toughness and bonding strength of Al(H2PO4)3.

[0056] Furthermore, in the liquid phase component of this embodiment, NH4I or NH4Br acts as a permeation enhancer to promote the generation of active chromium atoms and nickel atoms.

[0057] Furthermore, in the liquid phase component of this embodiment, Cr2O3 acts as a curing agent, causing the acidic phosphate ions in the binder to dehydrate and condense, which can effectively reduce the curing film temperature of the slurry. In addition, adding an appropriate amount of Cr2O3 can also improve the curing film performance of Al(H2PO4)3, making the surface of the coating layer smooth and flat and the interior uniform and dense after drying and curing.

[0058] It should be further noted that this embodiment does not specifically limit the method of applying the coating slurry to the surface of the workpiece. For example, the chromium-impregnating slurry can be applied to the surface of the workpiece by spraying or brushing.

[0059] It should be noted that this embodiment does not specifically limit the temperature of drying and curing and sintering. For example, the temperature of drying and curing is 60-300℃ and the time is 5 min-150 min, and the temperature of sintering is 980-1150℃ and the time is 8-30 min.

[0060] In some alternative embodiments, the drying and curing adopts a segmented gradient curing process. For example, pre-drying at 60-85°C for 5-30 minutes, then drying at 100-160°C for 30-60 minutes, and finally curing at 250-300°C for 20-60 minutes. The segmented curing process ensures that the coating slurry will not have surface quality problems due to local stress during the curing process, and at the same time, it is beneficial to increase the adhesion of the coating.

[0061] In some alternative embodiments, to prevent oxidation of the components in the slurry in air at high temperatures, an inert gas protection system is used throughout the sintering process. The workpiece is subjected to chromium diffusion treatment via rapid heating, followed by furnace cooling. The sintering temperatures are 980℃, 1000℃, 1050℃, 1100℃, and 1150℃, with durations of 8 min, 15 min, 20 min, and 30 min, respectively. Under this process, the required slurry thickness is 0.5-1.0 mm, and the resulting chromium-rich corrosion-resistant coating on the workpiece surface is approximately 5-50 μm thick.

[0062] S130. A layer of superhydrophobic material is sprayed or coated onto the surface of the chromium-rich corrosion-resistant coating and cured to obtain the chromium-rich corrosion-resistant coating. The thickness of the composite coating is 13-64μm.

[0063] Specifically, a layer of superhydrophobic material is sprayed or coated onto the surface of the chromium-rich corrosion-resistant coating, including:

[0064] Anhydrous ethanol, HDTMS and nano-alumina particles were mixed to form a suspension, which was then stirred, centrifuged and dried to obtain superhydrophobic Al2O3 nanoparticles modified with HDTMS.

[0065] An epoxy resin, polydimethylsiloxane, epoxy resin curing agent, and Al2O3 nanoparticles treated with HDTMS hydrophobicity were dissolved in xylene to prepare a suspension. This suspension was then sprayed onto the surface of a chromium-rich corrosion-resistant coating, and after curing, a superhydrophobic / chromium-rich corrosion-resistant composite coating was obtained.

[0066] In some alternative embodiments, the volume of anhydrous ethanol is preferably 45-55 mL, for example, 45 mL, 50 mL, 55 mL, etc., the volume of hexadecyltrimethoxysilane (HDTMS) is preferably 0.5 mL, 1 mL, 1.5 mL, etc., and the content of nano-alumina particles is preferably 1 g, 2 g, 3 g, etc.

[0067] It should be noted that this embodiment does not specifically limit the mixing method of anhydrous ethanol, HDTMS and nano-alumina particles. For example, each component can be placed in a constant temperature magnetic stirrer and stirred for 12 hours to make the alumina particles uniformly distributed in the suspension. Then, superhydrophobic Al2O3 nanoparticles modified with HDTMS can be obtained by centrifugation. After that, the formed nanoparticles are washed with anhydrous ethanol and dried at 120°C for 3 hours to obtain superhydrophobic Al2O3 nanoparticles modified with HDTMS.

[0068] In some alternative embodiments, the content of epoxy resin (EP) is preferably 0.5-1.5g, for example, 0.5g, 1g, 1.5g, etc.; the content of polydimethylsiloxane (PDMS) is preferably 0.5-0.7g, for example, 0.5g, 0.6g, 0.67g, 0.7g, etc.; the content of HDTMS hydrophobically treated Al2O3 nanoparticles is preferably 1-2g, for example, 1g, 1.5g, 2g, etc.; and the volume of xylene is preferably 10-30mL, for example, 10mL, 15mL, 20mL, 25mL, 30mL, etc.

[0069] In some alternative embodiments, the ratios of EP and PDMS to the curing agent are 3:1 and 10:1, respectively. That is, the content ratio of EP to epoxy resin curing agent is 3:1, and the ratio of PDMS to curing agent is 10:1.

[0070] It should be further noted that this embodiment does not specifically limit the method of preparing a suspension by dissolving epoxy resin, polydimethylsiloxane, epoxy resin curing agent, and HDTMS hydrophobic Al2O3 nanoparticles in xylene. For example, each component can be dissolved in xylene, and then HDTMS hydrophobic Al2O3 nanoparticles can be added. The suspension can be uniformly dispersed by heating in a constant temperature water bath at 50°C for 1 hour to obtain a suspension.

[0071] In some alternative embodiments, the process parameters for spraying the suspension onto the surface of the chromium-rich corrosion-resistant coating are as follows: the distance between the spray gun and the substrate is 15-20 cm, for example, 15 cm, 18 cm, or 20 cm, and the spray pressure is 0.8 MPa.

[0072] In some alternative embodiments, the curing temperature is preferably 90-110°C, for example, 90°C, 95°C, 100°C, 110°C, and the curing time is 1-3 hours, for example, 1 hour, 2 hours, 3 hours.

[0073] In this embodiment, superhydrophobic treatment forms a hydrophobic film on the workpiece surface, preventing water vapor from remaining on the surface and ensuring the inner surface of the pipe remains dry, thereby improving its overall performance, such as corrosion resistance and wear resistance. Furthermore, this process can eliminate surface micro-defects and improve its gloss and smoothness.

[0074] The preparation method of this embodiment is simple and does not require vacuum conditions. At the same time, the preparation efficiency of the chromium infiltration coating is high, the pollution is small, the thickness is adjustable, and the wear resistance is good. In particular, it has excellent resistance to high and low temperature corrosion and steam oxidation. It also has superhydrophobic properties, which can prevent metal oxidation corrosion caused by water vapor, thereby solving the problem of pipeline oxidation corrosion from the root.

[0075] In another aspect of this disclosure, a hydrophobic / chromium-rich corrosion-resistant composite coating is provided, prepared according to the preparation method described above.

[0076] In another aspect of this disclosure, an application of a hydrophobic / chromium-rich corrosion-resistant composite coating is proposed, wherein the hydrophobic / chromium-rich corrosion-resistant composite coating described above is applied to the inner surface of boiler pipes.

[0077] The coating of this embodiment has good surface quality, strong hydrophobic effect, excellent corrosion resistance and oxidation resistance, and can be applied to various carbon steel, austenitic steel and high temperature alloy metal parts that need to be strengthened.

[0078] The preparation method of the hydrophobic / chromium-rich corrosion-resistant composite coating will be further illustrated below with reference to several specific embodiments:

[0079] Example 1

[0080] This example uses a large boiler pipe made of carbon steel as an example to prepare a hydrophobic / chromium-rich corrosion-resistant composite coating. The pipe specifications are all 55mm outer diameter, 8mm wall thickness, and 4000mm length. The steps include:

[0081] S1. Pipe surface cleaning

[0082] Use alcohol or acetone to remove oil stains and dust from the pipe surface, and use a steel brush to remove the oxide scale.

[0083] S2, Pipeline preheating treatment

[0084] Preheat the pipe at 220℃ for 30 minutes.

[0085] S3, Slurry coating on pipe surface

[0086] The coating slurry should be applied to a suitable thickness in one go using spraying (or brushing, etc.), and multiple layers should not be applied; the thickness of the coating slurry layer should be 0.5 mm.

[0087] The preparation method of the coating slurry is as follows: Based on the mass percentage of the solid phase components, weigh 60% chromium powder, 15% nickel powder, 5% iron powder, 5% aluminum powder, and 15% yttrium oxide, respectively. The mixed metal powders are then ball-milled at 350 r / min for 8 hours to obtain the final solid phase component. Based on the mass percentage of the liquid phase components, weigh 25% Al(H2PO4)3, 18% water glass, 7% ammonium iodide, 15% polyvinyl alcohol, and 35% Cr2O3, and mix them to obtain the liquid phase component. The solid and liquid phase components are then mixed at a solid-liquid (g:ml) ratio of 10:2 to obtain the final coating slurry.

[0088] S4, Drying and Curing

[0089] The metal pipe coated with chromium-impregnated material was pre-dried at 60°C for 5 minutes, then dried at 100°C for 55 minutes, and finally cured at 250°C for 30 minutes.

[0090] S5, Rapid Sintering

[0091] The pipeline was subjected to rapid sintering and diffusion chromizing using a rapid heating method, followed by air cooling to room temperature; the heating rate was set at 1000℃ / min, the holding temperature at 980℃, and the holding time at 8min.

[0092] S6, Superhydrophobic treatment

[0093] A suspension was prepared by mixing 50 mL of anhydrous ethanol, 1 mL of hexadecyltrimethoxysilane (HDTMS), and 2 g of nano-alumina particles. The suspension was stirred for 12 h using a constant-temperature magnetic stirrer to ensure uniform distribution of the alumina particles. HDTMS-modified superhydrophobic Al₂O₃ nanoparticles were obtained by centrifugation. The nanoparticles were then washed with anhydrous ethanol and dried at 120 °C for 3 h. 1 g of epoxy resin (EP) and 0.67 g of polydimethylsiloxane (PDMS) were completely dissolved in 20 mL of xylene, with an EP to PDMS curing agent ratio of 3:1 and 10:1, respectively. Then, 1.5 g of HDTMS-treated hydrophobic Al₂O₃ nanoparticles were added, and the mixture was heated in a constant-temperature water bath at 50 °C for 1 h to ensure uniform dispersion, resulting in a suspension. Finally, the suspension was sprayed onto a chromium-rich corrosion-resistant coating surface at a spray gun / substrate distance of 15 cm and a spray pressure of 0.8 MPa. After curing at 100℃ for 2 hours, a composite corrosion-resistant coating with a thickness of approximately 13 μm was obtained.

[0094] The hydrophobic / chromium-rich corrosion-resistant composite coating prepared in Example 1 has a static water contact angle of 154.1° and a roll-off angle of 2.3°. Water droplets can roll freely on the surface of the coating prepared in Example 1, and the coating still maintains good superhydrophobic properties after undergoing 80 sandpaper abrasion tests (one test cycle is defined as the coating sample is placed face down on a piece of sandpaper (2000 grit) under a 100g load and moved 20cm along a ruler with the help of a horizontal external force).

[0095] Furthermore, the hydrophobic / chromium-rich corrosion-resistant composite coating prepared in Example 1 showed a significantly improved charge transfer resistance (RCT) value of more than 7 orders of magnitude in a 3.5 wt.% sodium chloride solution, with a corrosion inhibition rate of 99.99%.

[0096] Example 2

[0097] This example uses a large boiler pipe made of austenitic steel as an example to prepare a hydrophobic / chromium-rich corrosion-resistant composite coating. The pipe specifications are all 55mm outer diameter, 8mm wall thickness, and 4000mm length. The steps include:

[0098] S1. Pipe surface cleaning

[0099] Use alcohol or acetone to remove oil stains and dust from the pipe surface, and use a steel brush to remove the oxide scale.

[0100] S2, Pipeline preheating treatment

[0101] Preheat the pipe at 220℃ for 20 minutes.

[0102] S3, Slurry coating on pipe surface

[0103] The coating slurry should be applied to a suitable thickness in one go using spraying (or brushing, etc.), and multiple layers should not be applied; the thickness of the coating slurry layer should be 0.5 mm.

[0104] The preparation method of the coating slurry is as follows: Based on the mass percentage of the solid phase component, weigh 70% chromium powder, 15% nickel powder, 5% iron powder, 5% aluminum powder, and 5% yttrium oxide, respectively. Ball mill the mixed metal powder at 350 r / min for 10 h to obtain the final solid phase component. Based on the mass percentage of the liquid phase component, weigh 30% Al(H2PO4)3, 25% water glass, 10% ammonium iodide, 15% polyvinyl alcohol, and 20% curing agent, and mix them to obtain the liquid phase component. Mix the solid and liquid phase components at a solid-liquid (g:ml) ratio of 10:3 to obtain the final coating slurry.

[0105] S4, Drying and Curing

[0106] The metal pipe coated with chromium-impregnated material was pre-dried at 70°C for 5 minutes, then dried at 120°C for 55 minutes, and finally cured at 300°C for 30 minutes.

[0107] S5, Rapid Sintering

[0108] The pipeline was subjected to rapid sintering and diffusion chromizing using a rapid heating method, followed by air cooling to room temperature; the heating rate was set at 1000℃ / min, the holding temperature at 1080℃, and the holding time at 20min.

[0109] S6, Superhydrophobic treatment

[0110] A superhydrophobic material was directly sprayed or coated onto the surface of the prepared chromium-rich corrosion-resistant coating. The spraying process was the same as in Example 1. After curing, a composite corrosion-resistant coating with a thickness of approximately 43 μm was obtained.

[0111] The hydrophobic / chromium-rich corrosion-resistant composite coating prepared in Example 2 has a static water contact angle of 155.6° and a roll-off angle of 1.8°. Water droplets can roll freely on the surface of the coating prepared in Example 2, and the coating still maintains good superhydrophobic properties after undergoing 80 sandpaper abrasion tests (one test cycle is defined as the coating sample is placed face down on a piece of sandpaper (2000 grit) under a 100g load and moved 20cm along a ruler with the help of a horizontal external force).

[0112] Furthermore, the hydrophobic / chromium-rich corrosion-resistant composite coating prepared in Example 2 also showed a charge transfer resistance (RCT) value that was increased by more than 7 orders of magnitude in a 3.5 wt.% sodium chloride solution, and the corrosion inhibition rate also reached 99.99%.

[0113] Example 3

[0114] This example uses a large boiler pipe made of high-temperature alloy as an example to prepare a hydrophobic / chromium-rich corrosion-resistant composite coating. The pipe specifications are all 55mm outer diameter, 8mm wall thickness, and 4000mm length. The process includes the following steps:

[0115] S1. Pipe surface cleaning

[0116] Use alcohol or acetone to remove oil stains and dust from the pipe surface, and use a steel brush to remove the oxide scale.

[0117] S2, Pipeline preheating treatment

[0118] Preheat the pipe at 220℃ for 50 minutes.

[0119] S3, Slurry coating on pipe surface

[0120] The coating slurry should be applied to a suitable thickness in one go using spraying (or brushing, etc.), and multiple layers should not be applied; the thickness of the coating slurry layer should be 1.0 mm.

[0121] The preparation method of the coating slurry is as follows: Based on the solid phase components by mass percentage, weigh 70% chromium powder, 5% nickel powder, 5% iron powder, 5% aluminum powder, and 15% yttrium oxide. Ball mill the mixed metal powders at 350 r / min for 12 h to obtain the final solid phase component. Based on the liquid phase components by mass percentage, weigh 30% Al(H2PO4)3, 20% water glass, 5% ammonium iodide, 15% polyvinyl alcohol, and 30% curing agent, and mix them to obtain the liquid phase component. Mix the solid and liquid phase components at a solid-liquid (g:ml) ratio of 10:5 to obtain the final coating slurry.

[0122] S4, Drying and Curing

[0123] The metal pipe coated with chromium-impregnated material was pre-dried at 80°C for 10 minutes, then dried at 150°C for 30 minutes, and finally cured at 300°C for 20 minutes.

[0124] S5, Rapid Sintering

[0125] The pipeline was subjected to rapid sintering diffusion chromizing by rapid heating, followed by air cooling to room temperature; the heating rate was set at 1000℃ / min, the holding temperature was 1150℃, and the holding time was 30min.

[0126] S6, Superhydrophobic treatment

[0127] A superhydrophobic material was directly sprayed or coated onto the prepared chromium-rich corrosion-resistant coating surface. The spraying process was the same as in Example 1. After curing, a composite corrosion-resistant coating was obtained with a thickness of approximately 64 μm.

[0128] The hydrophobic / chromium-rich corrosion-resistant composite coating prepared in Example 3 has a static water contact angle of 154.5° and a roll-off angle of 2.7°. Water droplets can roll freely on the surface of the coating prepared in Example 3, and the coating still maintains good superhydrophobic properties after undergoing 80 sandpaper abrasion tests (one test cycle is defined as the coating sample is placed face down on a piece of sandpaper (2000 grit) under a 100g load and moved 20cm along a ruler with the help of a horizontal external force).

[0129] Furthermore, the charge transfer resistance (RCT) value of the hydrophobic / chromium-rich corrosion-resistant composite coating prepared in Example 3 in 3.5 wt.% sodium chloride solution is also increased by more than 7 orders of magnitude, and the corrosion inhibition rate reaches 99.99%.

[0130] This disclosure presents a hydrophobic / chromium-rich corrosion-resistant composite coating, its preparation method, and its application, which have the following advantages compared to the prior art:

[0131] First, this disclosure combines chromium diffusion treatment with surface hydrophobic treatment, so that the surface of the workpiece not only has wear-resistant and corrosion-resistant properties, but also hydrophobic properties, which can prevent metal oxidation and corrosion caused by water vapor, thereby solving the problem of pipeline oxidation and corrosion from the root.

[0132] Secondly, the chromium infiltration treatment disclosed herein is highly efficient, produces little pollution, and the coating thickness is adjustable.

[0133] It is understood that the above embodiments are merely exemplary embodiments used to illustrate the principles of this disclosure, and this disclosure is not limited thereto. For those skilled in the art, various modifications and improvements can be made without departing from the spirit and substance of this disclosure, and these modifications and improvements are also considered to be within the scope of protection of this disclosure.

Claims

A method for producing a hydrophobic / chromium-rich corrosion-resistant composite coating, characterized by The preparation method comprises: preheating the workpiece; applying a coating slurry on the surface of the preheated workpiece, drying and curing, and sintering to obtain a chromium-rich corrosion-resistant coating on the surface of the workpiece; the coating slurry comprises solid components and liquid components; the solid components comprise chromium powder, nickel powder, iron powder and rare earth compounds; the liquid components comprise Al(H2PO4)3, water glass, ammonium halide, polyvinyl alcohol and Cr2O3; spraying a layer of super-hydrophobic material on the surface of the chromium-rich corrosion-resistant coating, and curing to obtain a hydrophobic / chromium-rich corrosion-resistant composite coating. The production method according to claim 1, wherein The solid-liquid ratio of the solid components to the liquid components is 10:(1-5). The production method according to claim 1, wherein The content of the chromium powder is 40-80%; The content of the nickel powder is 5-30%; The content of the iron powder is 2-20%; The content of the rare earth compound is 5-45%. The production method according to claim 1, wherein The content of the Al(H2PO4)3 is 10-30%; The content of the water glass is 15-25%; The content of the ammonium halide is 5-10%; The content of the polyvinyl alcohol is 10-35%; The content of the Cr2O3 is 10-30%. The production method according to claim 1, wherein The rare earth compound is a rare earth oxide or a rare earth chloride; and / or, The ammonium halide is ammonium bromide or ammonium iodide. The production method according to any one of claims 1 to 5, characterized in that Spraying a layer of super-hydrophobic material on the surface of the chromium-rich corrosion-resistant coating, and curing to obtain a hydrophobic / chromium-rich corrosion-resistant composite coating, comprising: mixing anhydrous ethanol, HDTMS and nano-aluminum oxide particles to prepare a suspension, and obtaining HDTMS-modified super-hydrophobic Al2O3 nanoparticles through stirring, centrifugation and drying; dissolving epoxy resin, polydimethylsiloxane, an epoxy resin curing agent and HDTMS-hydrophobic-treated Al2O3 nanoparticles in dimethylbenzene to prepare a suspension, and spraying the suspension on the surface of the chromium-rich corrosion-resistant coating to obtain a super-hydrophobic / chromium-rich corrosion-resistant composite coating after curing. The production method according to any one of claims 1 to 5, characterized in that The preheating temperature of the workpiece is 150-220℃, and the preheating time is 30-60min; and / or, The sintering temperature under inert gas protection is 980-1150℃, and the sintering time is 8-30min. The production method according to any one of claims 1 to 5, characterized in that The thickness of the chromium-rich corrosion-resistant coating is 5-50μm; and / or, The thickness of the hydrophobic / chromium-rich corrosion-resistant composite coating is 13-64μm. A hydrophobic / chromium-rich corrosion-resistant composite coating characterized in that, The preparation method according to any one of claims 1 to 8. Use of a hydrophobic / chromium-rich corrosion-resistant composite coating, characterized in that The hydrophobic / chromium-rich corrosion-resistant composite coating according to claim 9 is applied to the inner surface of a boiler pipeline.

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