A method for preparing an anti-corrosion coating for the flow channel of a microchannel heat exchanger for a marine engineering platform.

Abstract

This invention discloses a method for preparing an anti-corrosion coating for the flow channels of a microchannel heat exchanger on a marine engineering platform. The method involves sequentially degreasing, pickling, washing and drying the microchannel heat exchanger, and activating it. Then, the microchannel heat exchanger is thermally decomposed and coated using high-purity nickel tetracarbonyl vapor and an inert gas. After thermal decomposition coating, the coating is purged with exhaust gas, cooled, and treated to obtain the final product. This invention achieves efficient and uniform preparation of the anti-corrosion nickel coating for the flow channels of marine engineering microchannel heat exchangers by optimizing the pretreatment process, precisely controlling the nickel tetracarbonyl vapor preparation and thermal decomposition parameters, and combining this with the structural characteristics of the microchannel heat exchanger. This ensures that the coating meets the requirements of the extreme corrosive environment in marine engineering, significantly improving the corrosion resistance and service life of the microchannel heat exchanger, while also ensuring the safety and environmental protection of the production process. This method can be widely applied to the thermal management systems of marine engineering platforms, ships, and offshore oil and gas development equipment.

Description

Technical Field

[0001] This invention relates to the field of heat exchanger technology, specifically to a method for preparing an anti-corrosion coating for the flow channel of a microchannel heat exchanger for marine engineering platforms. Specifically, it relates to a method for preparing an anti-corrosion coating for the surface of the flow channel of a microchannel heat exchanger suitable for extreme corrosive environments (high salt spray, high humidity, strong chloride ion corrosion) on marine engineering platforms. It is particularly suitable for marine engineering microchannel heat exchangers with small channel sizes (0.1~2mm) and complex structures, and can be widely used in the thermal management systems of marine engineering platforms, ships, and marine oil and gas development equipment. Background Technology

[0002] The marine engineering environment is characterized by extreme conditions such as high salt spray (NaCl concentration 3.5%~5%), high humidity (relative humidity ≥85%), strong chloride ion corrosion, and large diurnal temperature range (-20℃~60℃), which imposes stringent requirements on the corrosion resistance of core components of marine engineering equipment. Microchannel heat exchangers, as a core component of the thermal management system of marine engineering equipment, have been widely used in heat exchange scenarios such as cooling of marine engineering platforms, ship air conditioning, and offshore oil and gas extraction due to their advantages of high heat exchange efficiency, small size, and light weight.

[0003] The core challenge of microchannel heat exchangers lies in the difficulty of corrosion protection of their microchannel surfaces. On the one hand, their channels are tiny (0.1~2mm) and complex (serpentine, Z-shaped, L-shaped, etc.) with large heat exchange surface areas. Traditional liquid-phase plating processes (electroplating, electroless plating) have significant drawbacks—the plating solution cannot penetrate into the microchannels, easily forming "plating dead zones" and resulting in local coating loss. At the same time, liquid-phase plating coatings have poor uniformity (thickness deviation is usually > ±10μm) and high porosity (3%~5%), allowing chloride ions to easily penetrate to the substrate surface, causing pitting and crevice corrosion, leading to coating peeling and failure. Traditional electroplated nickel coatings have a short corrosion resistance time in marine engineering environments with 3.5% NaCl salt spray, which cannot meet the service requirements of marine equipment for more than 10 years.

[0004] In view of the above shortcomings, there is an urgent need in this field for a method to manufacture an anti-corrosion coating for microchannel heat exchangers of marine engineering platforms that has excellent coating uniformity and density, outstanding corrosion resistance, can effectively adapt to extreme marine engineering conditions, and has high nickel plating efficiency and good coating quality. Summary of the Invention

[0005] Based on the above analysis, this invention aims to solve the technical bottlenecks in the production of anti-corrosion coatings for microchannel heat exchangers in marine engineering, such as uneven plating, low coating purity, insufficient corrosion resistance, and poor adhesion, which are inherent in traditional plating processes. It provides a method for producing a nickel-plated anti-corrosion coating using tetracarbonyl nickel, achieving the preparation of a uniform, dense, and high-purity anti-corrosion nickel coating on the inner wall of the microchannel heat exchanger. This ensures the coating meets the requirements of extreme corrosive environments in marine engineering, significantly improving the corrosion resistance and service life of the microchannel heat exchanger, while also ensuring the safety and environmental protection of the production process.

[0006] To achieve the above-mentioned technical effects, the present invention employs the following technical means:

[0007] This invention first discloses a method for preparing an anti-corrosion coating for the flow channel of a microchannel heat exchanger on a marine engineering platform, comprising the following steps:

[0008] (1) Pretreatment of substrate for microchannel heat exchanger (core: surface activation to improve coating adhesion)

[0009] The core objective of pretreatment is to remove oil, oxide layers, marine organism deposits, and impurities from the substrate surface, activate the substrate surface, provide stable nucleation sites for the thermal decomposition deposition of nickel tetracarbonyl, improve the adhesion between the nickel coating and the substrate, and adapt to the mechanical requirements of marine engineering conditions. The specific operations are as follows:

[0010] (1.1) Degreasing treatment: The microchannel heat exchanger is placed in an alkaline degreasing solution and soaked at a constant temperature of 60-80℃ for 10-30 minutes. At the same time, 200-400W ultrasonic-assisted degreasing is used to ensure that the oil stains in the microchannels are completely removed. The alkaline degreasing solution is composed of sodium hydroxide, sodium carbonate and sodium dodecylbenzene sulfonate, which can effectively remove oil stains and marine organism residues attached to the marine environment.

[0011] (1.2) Pickling treatment: After degreasing, the heat exchanger is rinsed with deionized water 3 to 5 times to remove residual degreasing liquid on the surface. Then, it is placed in the dilute acid solution of the corresponding substrate and pickled at room temperature for 5 to 15 minutes to remove the surface oxide film and passivation layer. The dilute acid solution is adapted according to the type of substrate: 5% to 8% dilute hydrochloric acid is used for aluminum alloy substrates, 3% to 5% hydrofluoric acid-nitric acid mixture (volume ratio 1:3) is used for titanium alloy substrates, and 8% to 10% dilute sulfuric acid is used for stainless steel substrates to avoid excessive corrosion of the substrate.

[0012] (1.3) Washing and drying: After pickling, rinse repeatedly with deionized water until the surface pH is 6.5~7.5 (neutral), then put it in a hot air circulating drying oven at 100~120℃ and dry for 1~2 hours to completely remove the moisture from the surface of the substrate and the inside of the flow channel, so as to avoid the moisture affecting the thermal decomposition reaction of nickel tetracarbonyl and the density of the coating.

[0013] (1.4) Activation treatment: Argon plasma activation or dilute acid activation can be used, either one is acceptable; Argon plasma activation parameters: power 80~200W, time 10~30 minutes, which can form active sites on the substrate surface and destroy the passivation film; Dilute acid activation parameters: 1%~3% by mass dilute hydrochloric acid, soak at room temperature for 5~15 minutes to further remove the residual oxide layer and improve surface activity; After activation, immediately transfer to the next process to avoid secondary oxidation of the surface.

[0014] (2) Preparation of nickel tetracarbonyl vapor (core: stable purity, suitable for microchannel transport)

[0015] The purity and stability of nickel tetracarbonyl vapor directly determine the purity and uniformity of the coating. This step involves precise temperature control and purification to prepare vapor that meets the requirements. The specific operation is as follows:

[0016] (2.1) Raw material preparation: Use tetracarbonyl nickel with a purity of ≥99.99% to avoid impurities (such as metal impurities and moisture) from entering, so as to prevent coating defects and affect corrosion resistance.

[0017] (2.2) Steam generation: High-purity nickel tetracarbonyl is loaded into a 316L stainless steel sealed steam generator and heated to 40~80℃ by water bath or oil bath. The pressure inside the steam generator is controlled at 0.1~0.3MPa. Stable tetracarbonyl carbon vapor is formed by utilizing the volatility of nickel tetracarbonyl. During the heating process, the temperature and pressure are monitored in real time. The temperature control accuracy is ±1℃ and the pressure control accuracy is ±0.01MPa to avoid the decomposition of nickel tetracarbonyl due to excessive temperature.

[0018] (2.3) Steam purification: The generated tetracarbonyl carbon vapor is passed through a 5A molecular sieve filter (pore size 0.1nm) to remove trace amounts of moisture and impurity gases in the vapor, ensuring that the vapor purity is ≥99.99% and avoiding impurities from affecting the coating density and corrosion resistance.

[0019] (3) Thermal decomposition coating (core: uniform heating and uniform deposition on both sides of the heat exchanger to form an anti-corrosion coating)

[0020] This step is crucial for the formation of the anti-corrosion coating. By combining the characteristics of the microchannel heat exchanger and precisely controlling the reaction parameters and optimizing the steam transport method, uniform coating of the inner wall of the microchannel heat exchanger channel is achieved. The specific operation is as follows:

[0021] (3.1) The microchannel heat exchanger is divided into cold side and hot side channels. Based on the characteristics of the microchannel heat exchanger, when the inner wall of the cold side channel is plated with nickel, nitrogen or other inert gas with a temperature of >180℃ (to meet the decomposition requirements of nickel tetracarbonyl) is circulated into the hot side channel to ensure that the inner wall temperature of the cold side channel is uniform and ≥180℃. Conversely, when the hot side channel is plated with nickel, nitrogen or other inert gas with a temperature of >180℃ is circulated into the cold side channel to ensure that the inner wall temperature of the hot side channel is uniform and ≥180℃.

[0022] (3.2) Steam transport and proportioning: Purified nickel tetracarbonyl vapor and inert gas (argon or nitrogen) are introduced into the flow channel through a mass flow controller. The volume ratio of the two is controlled at 1:5-1:20. The inert gas is used to dilute the concentration of nickel tetracarbonyl vapor, reduce the thermal decomposition reaction rate, avoid coarse coating grains, and promote the uniform penetration of steam into the micro-flow channel. The flow control accuracy is ±1%FS.

[0023] (3.3) Control of thermal decomposition reaction parameters: Adjust the reaction time according to the target coating thickness (5-50μm). During the reaction, the tetracarbonyl nickel vapor undergoes thermal decomposition reaction on the activated substrate surface, depositing a uniform and dense high-purity nickel anti-corrosion coating. At the same time, the tetracarbonyl nickel and carbon monoxide and other tail gases enter the subsequent treatment system.

[0024] (4) Post-treatment (core: remove residues to ensure coating performance and safety)

[0025] The purpose of post-treatment is to remove residual nickel tetracarbonyl and carbon monoxide from the reaction, prevent coating oxidation, ensure coating performance stability, and guarantee production safety. The specific procedures are as follows:

[0026] (4.1) Exhaust gas purging: After the plating is completed, stop heating and continue to purge the microchannel with inert gas for 10 minutes to thoroughly purge the residual tetracarbonyl carbon vapor and carbon monoxide in the flow channel to the exhaust gas treatment system to avoid residual gas pollution or safety accidents.

[0027] (4.2) Cooling: Stop the supply of high-temperature nitrogen or inert gas to the heat source side and allow the heat exchanger to cool naturally to room temperature (≤40℃) to avoid internal stress, cracking or oxidation of the coating caused by high temperature cooling, and to ensure the stability of the coating structure.

[0028] (4.3) Finished product processing: Rinse the surface of the flow channel with anhydrous ethanol to remove any remaining trace impurities, and then place it in an oven at 80-100℃ and dry for 0.5-1 hour to obtain a smooth, uniform and dense nickel-based anti-corrosion coating on the surface of the flow channel; the waste liquid after cleaning is collected and treated in a centralized manner to avoid environmental pollution.

[0029] The present invention also discloses the application of the above-described preparation method in the anti-corrosion coating treatment of thermal management systems for marine engineering platforms, ships and marine oil and gas development equipment.

[0030] The beneficial effects of this invention are as follows:

[0031] To address the corrosion protection requirements of marine microchannel heat exchangers, this coating method offers the following significant advantages, and all performance characteristics are superior to existing technologies:

[0032] 1. Excellent coating uniformity and density: Utilizing gas-phase transport, nickel tetracarbonyl can fully penetrate into the microchannels of 0.1-2mm, eliminating plating dead zones. The coating thickness uniformity deviation is ≤±2μm, far superior to the ±10μm of traditional electroplating; the coating porosity is ≤0.2 cells / cm². 2 It can effectively block the penetration of corrosive media such as chloride ions in the marine engineering environment, forming a complete anti-corrosion barrier, which meets the density requirements of marine anti-corrosion coatings.

[0033] 2. Outstanding corrosion resistance: The nickel coating has a purity of ≥99.9%, which is higher than that of traditional electroplated nickel (below 99.5%). It forms a metallurgical bond with the substrate, and the adhesion level reaches 0 (cross-cut test), with no peeling or flaking. The corrosion resistance time is much better than that of traditional electroplated nickel, which can extend the service life of microchannel heat exchangers in marine environments to 8-10 years, meeting the design requirements of marine engineering equipment.

[0034] 3. Adaptable to extreme marine engineering conditions: By optimizing reaction parameters and pretreatment processes, the coating combines high corrosion resistance and mechanical strength, and can withstand the diurnal temperature difference (-20℃~60℃), high humidity and strong chloride ion corrosion in marine environments. It is also compatible with mainstream marine microchannel heat exchanger substrates such as aluminum alloy, titanium alloy and stainless steel, covering a full range of channels from 0.1-2mm, with a wide range of applications.

[0035] 4. High nickel plating efficiency and excellent coating quality: Utilizing the inherent structural characteristics of the microchannel heat exchanger, a heat source is provided by circulating high-temperature nitrogen or inert gas within the flow channel. The heat exchanger flow channel can quickly reach the set temperature for the decomposition reaction of nickel tetracarbonyl. Compared with traditional whole-workpiece heating methods, it has a faster heating rate and better temperature uniformity, shortening the nickel plating time while ensuring coating quality. Attached Figure Description

[0036] Figure 1 This is a schematic diagram showing the nickel plating on both sides of the heat exchanger's flow channels. Detailed Implementation

[0037] The present invention will be described in more detail below with reference to the embodiments. It should be understood that the implementation of the present invention is not limited to the embodiments below, and any modifications and / or alterations made to the present invention will fall within the protection scope of the present invention.

[0038] The core of this invention is to achieve efficient and uniform preparation of anti-corrosion nickel coatings for marine microchannel heat exchangers by optimizing the pretreatment process, precisely controlling the parameters for nickel tetracarbonyl vapor preparation and thermal decomposition, and combining these with the structural characteristics of the microchannel heat exchanger itself. The specific steps are as follows:

[0039] Example 1

[0040] The fabrication of an anti-corrosion coating for an aluminum alloy microchannel heat exchanger (channel size 0.5mm, overall dimensions 100×50×20mm) includes:

[0041] (1) Pretreatment of substrate for microchannel heat exchanger

[0042] (1.1) Degreasing treatment: The aluminum alloy microchannel heat exchanger is placed in an alkaline degreasing solution and immersed at a constant temperature of 70°C for 20 minutes. At the same time, 300W ultrasonic-assisted degreasing is used to ensure that the oil stains in the microchannels are completely removed. The alkaline degreasing solution is composed of sodium hydroxide (50g / L), sodium carbonate (30g / L), and sodium dodecylbenzenesulfonate (3g / L).

[0043] (1.2) Pickling treatment: The heat exchanger after degreasing was rinsed with deionized water 4 times, and the aluminum alloy substrate was placed in dilute hydrochloric acid with a mass fraction of 6.5% and pickled for 10 minutes at room temperature.

[0044] (1.3) Washing and drying: After pickling, rinse repeatedly with deionized water until the surface pH=7, and then put into a hot air circulating drying oven at 110℃ for 1.5 hours;

[0045] (1.4) Activation treatment: Argon plasma activation is used. The activation parameters are: power 120W, time 15 minutes. After activation, the process is immediately transferred to the next step to avoid secondary oxidation of the surface.

[0046] (2) Preparation of nickel tetracarbonyl vapor

[0047] (2.1) Steam generation: Nickel tetracarbonyl with a purity ≥99.99% is loaded into a 316L stainless steel sealed steam generator and heated to 60°C by water bath or oil bath. The pressure inside the steam generator is controlled at 0.2MPa. During the heating process, the temperature and pressure are monitored in real time. The temperature control accuracy is ±1°C and the pressure control accuracy is ±0.01MPa to avoid the decomposition of nickel tetracarbonyl due to excessive temperature.

[0048] (2.2) Steam purification: The generated tetracarbonyl carbon vapor is passed through a 5A molecular sieve filter (pore size 0.1nm) to remove trace amounts of moisture and impurity gases in the vapor, ensuring that the vapor purity is ≥99.99% and avoiding impurities from affecting the coating density and corrosion resistance.

[0049] (3) Thermal decomposition coating

[0050] (3.1) The microchannel heat exchanger is divided into cold side and hot side channels. Based on the characteristics of the microchannel heat exchanger, when the inner wall of the cold side channel is nickel plated, nitrogen gas at 215°C is circulated into the hot side channel to ensure that the temperature of the inner wall of the cold side channel is uniform and greater than 180°C. When the hot side channel is nickel plated, nitrogen gas at 215°C or other inert gas is circulated into the cold side channel to ensure that the temperature of the inner wall of the hot side channel is uniform and greater than 180°C.

[0051] (3.2) Steam transport and proportioning: Purified nickel tetracarbonyl vapor and inert gas are introduced into the flow channel through a mass flow controller, and the volume ratio of the two is controlled at 1:15. The inert gas is used to dilute the concentration of nickel tetracarbonyl vapor, reduce the thermal decomposition reaction rate, avoid coarse coating grains, and at the same time promote the uniform penetration of steam into the micro-flow channel. The flow control accuracy is ±1%FS.

[0052] (3.3) Thermal decomposition reaction parameter control: The reaction time is adjusted according to the target coating thickness (25μm). During the reaction, the tetracarbonyl nickel vapor undergoes thermal decomposition reaction on the activated substrate surface, depositing a uniform and dense high-purity nickel anti-corrosion coating. At the same time, the tetracarbonyl nickel and carbon monoxide and other tail gases enter the subsequent treatment system.

[0053] (4) Post-processing

[0054] (4.1) Exhaust gas purging: After the plating is completed, stop heating and continue to purge the microchannel with inert gas for 10 minutes to thoroughly purge the residual tetracarbonyl carbon vapor and carbon monoxide in the flow channel to the exhaust gas treatment system to avoid residual gas pollution or safety accidents.

[0055] (4.2) Cooling: Stop the supply of high-temperature nitrogen or inert gas to the heat source side and allow the heat exchanger to cool naturally to room temperature (≤40℃) to avoid internal stress, cracking or oxidation of the coating caused by high-temperature cooling, and to ensure the stability of the coating structure.

[0056] (4.3) Finished product processing: Rinse the surface of the flow channel with anhydrous ethanol to remove any remaining trace impurities, and then place it in an oven at 90°C for 45 minutes to obtain a smooth, uniform and dense nickel-based anti-corrosion coating finished product on the surface of the flow channel; the waste liquid after cleaning is collected and treated in a centralized manner to avoid environmental pollution.

[0057] Example 2

[0058] The fabrication of an anti-corrosion coating for a titanium alloy microchannel heat exchanger (channel size 1.0mm, overall dimensions 150×80×30mm) includes:

[0059] (1) Pretreatment of substrate for microchannel heat exchanger

[0060] (1.1) Degreasing treatment: The microchannel heat exchanger is placed in an alkaline degreasing solution and soaked at a constant temperature of 60°C for 30 minutes, while 400W ultrasonic-assisted degreasing is used at the same time; the alkaline degreasing solution is composed of sodium hydroxide (60g / L), sodium carbonate (40g / L) and sodium dodecylbenzenesulfonate (5g / L).

[0061] (1.2) Pickling treatment: The heat exchanger after degreasing was rinsed with deionized water 3 times, and the titanium alloy substrate was placed in a 4% hydrofluoric acid-nitric acid mixture (volume ratio 1:3) and pickled for 5 minutes at room temperature.

[0062] (1.3) Washing and drying: After pickling, rinse repeatedly with deionized water until the surface pH=7 (neutral), and then put it into a hot air circulating drying oven at 120℃ for 1 hour;

[0063] (1.4) Activation treatment: Dilute acid activation is used. The dilute acid activation parameters are: 1% by mass dilute hydrochloric acid, soaking at room temperature for 10 minutes to further remove the residual oxide layer and improve surface activity; after activation, the process is immediately transferred to the next step to avoid secondary oxidation of the surface.

[0064] (2) Preparation of nickel tetracarbonyl vapor

[0065] (2.1) Steam generation: High-purity nickel tetracarbonyl is loaded into a 316L stainless steel sealed steam generator and heated to 70°C by water bath or oil bath. The pressure inside the steam generator is controlled at 0.25MPa. During the heating process, the temperature and pressure are monitored in real time. The temperature control accuracy is ±1°C and the pressure control accuracy is ±0.01MPa to avoid the decomposition of nickel tetracarbonyl due to excessive temperature.

[0066] (2.2) Steam purification: The generated tetracarbonyl carbon vapor is passed through a 5A molecular sieve filter (pore size 0.1nm) to remove trace amounts of moisture and impurity gases from the vapor, ensuring that the vapor purity is ≥99.99%;

[0067] (3) Thermal decomposition coating

[0068] (3.1) The microchannel heat exchanger is divided into cold side and hot side channels. Nitrogen gas at 250°C is circulated into the hot side to ensure that the temperature of the inner wall of the cold side channel is uniform and maintained at 220°C. Similarly, when the hot side channel is nickel plated, nitrogen gas at 250°C is circulated into the cold side to ensure that the temperature of the inner wall of the hot side channel is uniform and maintained at 220°C.

[0069] (3.2) Steam transport and proportioning: Purified nickel tetracarbonyl vapor and inert gas are introduced into the flow channel through a mass flow controller, with the volume ratio of the two controlled at 1:15. The inert gas is used to dilute the concentration of nickel tetracarbonyl vapor, reduce the thermal decomposition reaction rate, avoid coarse coating grains, and at the same time promote the uniform penetration of steam into the micro-flow channel. The flow control accuracy is ±1%FS.

[0070] (3.3) Thermal decomposition reaction parameter control: The reaction time is adjusted according to the target coating thickness (18μm). During the reaction, the tetracarbonyl nickel vapor undergoes thermal decomposition reaction on the activated substrate surface, depositing a uniform and dense high-purity nickel anti-corrosion coating. At the same time, the tetracarbonyl nickel and carbon monoxide and other tail gases enter the subsequent treatment system.

[0071] (4) Post-processing

[0072] (4.1) Exhaust gas purging: After the plating is completed, stop heating and continue to purge the microchannel with inert gas for 10 minutes to thoroughly purge the residual tetracarbonyl carbon vapor and carbon monoxide in the flow channel to the exhaust gas treatment system to avoid residual gas pollution or safety accidents.

[0073] (4.2) Cooling: Stop the supply of high-temperature nitrogen or inert gas to the heat source side and allow the heat exchanger to cool naturally to room temperature (≤40℃) to avoid internal stress, cracking or oxidation of the coating caused by high temperature cooling, and to ensure the stability of the coating structure.

[0074] (4.3) Finished product processing: Rinse the surface of the flow channel with anhydrous ethanol to remove any remaining trace impurities, and then place it in an oven at 80°C and dry for 1 hour to obtain a smooth, uniform and dense nickel-based anti-corrosion coating on the surface of the flow channel; the waste liquid after cleaning is collected and treated in a centralized manner to avoid environmental pollution.

[0075] Example 3

[0076] The anti-corrosion coating fabrication for stainless steel microchannel heat exchangers (channel size 2.0mm, overall dimensions 200×100×40mm) includes:

[0077] (1) Pretreatment of substrate for microchannel heat exchanger

[0078] (1.1) Degreasing treatment: The microchannel heat exchanger is placed in an alkaline degreasing solution and immersed at a constant temperature of 80°C for 10 minutes, while 200W ultrasonic-assisted degreasing is used; the alkaline degreasing solution is composed of sodium hydroxide (40g / L), sodium carbonate (20g / L), and sodium dodecylbenzenesulfonate (2g / L);

[0079] (1.2) Pickling treatment: The heat exchanger after degreasing is rinsed with deionized water 5 times, and the stainless steel substrate is placed in 10% dilute sulfuric acid and pickled for 15 minutes at room temperature.

[0080] (1.3) Washing and drying: After pickling, rinse repeatedly with deionized water until the surface pH=6.8 (neutral), and then put it into a hot air circulating drying oven at 120℃ for 1 hour;

[0081] (1.4) Activation treatment: Argon plasma activation is used. Argon plasma activation parameters: power 200W, time 10 minutes; after activation, the process is immediately transferred to the next step to avoid secondary oxidation of the surface.

[0082] (2) Preparation of nickel tetracarbonyl vapor

[0083] (2.1) Steam generation: High-purity nickel tetracarbonyl is loaded into a 316L stainless steel sealed steam generator and heated to 80°C by water bath or oil bath. The pressure inside the steam generator is controlled at 0.15MPa. During the heating process, the temperature and pressure are monitored in real time. The temperature control accuracy is ±1°C and the pressure control accuracy is ±0.01MPa to avoid the decomposition of nickel tetracarbonyl due to excessive temperature.

[0084] (2.2) Steam purification: The generated tetracarbonyl carbon vapor is passed through a 5A molecular sieve filter (pore size 0.1nm) to remove trace amounts of moisture and impurity gases in the vapor, ensuring that the vapor purity is ≥99.99% and avoiding impurities from affecting the coating density and corrosion resistance;

[0085] (3) Thermal decomposition coating

[0086] (3.1) The microchannel heat exchanger is divided into cold side and hot side channels. Nitrogen gas at 250°C is circulated into the hot side to ensure that the temperature of the inner wall of the cold side channel is uniform and maintained at 230°C. When the hot side channel is nickel plated, nitrogen gas at 250°C is circulated into the cold side to ensure that the temperature of the inner wall of the hot side channel is uniform and maintained at 230°C.

[0087] (3.2) Steam transport and proportioning: Purified nickel tetracarbonyl vapor and argon are introduced into the flow channel through a mass flow controller, and the volume ratio of the two is controlled at 1:8. Argon is used to dilute the concentration of nickel tetracarbonyl vapor, reduce the thermal decomposition reaction rate, avoid coarse coating grains, and at the same time promote the uniform penetration of steam into the micro-flow channel. The flow control accuracy is ±1%FS.

[0088] (3.3) Control of thermal decomposition reaction parameters: The reaction time is adjusted according to the target coating thickness (35μm). During the reaction, the tetracarbonyl nickel vapor undergoes thermal decomposition reaction on the activated substrate surface, depositing a uniform and dense high-purity nickel anti-corrosion coating. At the same time, the tetracarbonyl nickel and carbon monoxide and other tail gases enter the subsequent treatment system.

[0089] (4) Post-processing

[0090] (4.1) Exhaust gas purging: After the coating is completed, stop heating and continue to purge the microchannel with argon gas for 10 minutes to thoroughly purge the residual tetracarbonyl carbon vapor and carbon monoxide in the flow channel to the exhaust gas treatment system to avoid residual gas pollution or safety accidents.

[0091] (4.2) Cooling: Stop the supply of high-temperature nitrogen on the heat source side and allow the heat exchanger to cool naturally to room temperature (≤40℃) to avoid internal stress, cracking or oxidation of the coating caused by high-temperature cooling, and to ensure the stability of the coating structure.

[0092] (4.3) Finished product processing: Rinse the surface of the flow channel with anhydrous ethanol to remove trace impurities, and then place it in an oven at 100°C and dry for 0.5 hours to obtain a smooth, uniform and dense nickel-based anti-corrosion coating on the surface of the flow channel; the waste liquid after cleaning is collected and treated in a centralized manner to avoid environmental pollution.

[0093] Experimental Example 1

[0094] To objectively verify the advantages of the anti-corrosion coating prepared by the tetracarbonyl carbon Mond process for nickel plating in this invention compared with traditional plating processes, a comparative experiment was set up. A microchannel heat exchanger with the same substrate and size as the embodiment of this invention was selected, and the traditional electroplating nickel process was used as a comparative example. The experiment was conducted simultaneously with the embodiments of this invention 1 to 3. The test items, test standards and test results are as follows.

[0095] Comparative process parameters (traditional process):

[0096] Traditional nickel electroplating: Pretreatment (consistent with the embodiments of the present invention) → Nickel electroplating (plating solution is nickel sulfate plating solution, temperature 50℃, current density 2A / dm², electroplating time 2~4 hours, target coating thickness consistent with the corresponding embodiment) → washing and drying.

[0097] Test items and standards:

[0098] 1. Coating thickness and uniformity: The coating thickness is measured at 10 different points (including 5 points inside the flow channel) on each workpiece using a coating thickness gauge. The average value and deviation are calculated. A deviation of ≤±2μm is considered qualified (marine grade requirement).

[0099] 2. Coating purity: The purity of nickel in the coating is detected by scanning electron microscopy (SEM) combined with energy dispersive spectroscopy (EDS). A purity of ≥99.9% is considered excellent.

[0100] 3. Adhesion: The cross-cut test (GB / T 9286-1998) is used. After the cross-cut test is completed, the coating is adhered with tape and the peeling is observed. Grade 0 is the best (no peeling), and grades 1 to 5 are progressively worse.

[0101] 4. Salt spray resistance: The coating is subjected to a 3.5% NaCl salt spray test (GB / T 10125-2021) with continuous spraying. The time it takes for the coating to pit and peel off is recorded. A coating with a resistance of ≥1000 hours is considered qualified for marine engineering.

[0102] 5. Immersion resistance: Immerse the workpiece in artificial seawater at 40±2℃ (compliant with GB / T 12763.1-2007) and record the time when the coating blisters and rusts. ≥4000 hours is considered qualified.

[0103] 6. High pressure holding performance: The high pressure holding cycle test is adopted (0.5MPa pressure holding for 30min, pressure released to normal pressure, repeated for 10 cycles) to observe whether the coating cracks or peels off. No defects are qualified.

[0104] The results of the experimental data comparison are shown in Table 1:

[0105] Table 1

[0106]

[0107] As shown in Table 1, the method of this invention, regardless of whether it is used for electroplating aluminum alloys, titanium alloys, or stainless steel, results in significantly lower coating thickness and uniformity deviations compared to traditional nickel electroplating processes. The coating purity is higher than that of traditional nickel electroplating processes, and the adhesion grade is 0 for all materials. Salt spray tests revealed that its corrosion resistance time is more than 10 times longer than that of traditional nickel electroplating processes; immersion time in artificial seawater also showed a significantly longer time. No cracking, peeling, or fissures were observed after high-pressure holding tests. This demonstrates that the coating obtained by this invention exhibits excellent uniformity and density, outstanding corrosion resistance, suitability for extreme marine engineering conditions, high nickel plating efficiency, and superior coating quality.

[0108] The concepts described in this invention can be implemented in other forms without departing from their spirit and characteristics. The specific embodiments disclosed should be considered illustrative rather than restrictive. Therefore, the scope of the invention is determined by the appended claims, and not by the foregoing description. Any modifications within the literal meaning and equivalent scope of the claims should fall within the scope of those claims.

Claims

1. A method for preparing an anti-corrosion coating for the flow channel of a microchannel heat exchanger on a marine engineering platform, comprising: (1) Pretreatment of microchannel heat exchanger substrate: The microchannel heat exchanger is subjected to degreasing, pickling, water washing and drying and activation treatment in sequence to obtain pretreated microchannel heat exchanger substrate; (2) Preparation of nickel tetracarbonyl vapor: High-purity nickel tetracarbonyl is loaded into a 316L stainless steel closed steam generator, heated under high pressure to generate tetracarbonyl carbon vapor, and then filtered through a 5A molecular sieve filter to remove impurities, yielding nickel tetracarbonyl vapor for later use. (3) Thermal decomposition coating: (3.1) The microchannel heat exchanger is divided into cold side and hot side channels. When the inner wall of the cold side channel is nickel plated, an inert gas with a temperature of >180℃ is circulated into the hot side channel to ensure that the temperature of the inner wall of the cold side channel is uniform and ≥180℃. When the hot side channel is nickel plated, an inert gas with a temperature of >180℃ is circulated into the cold side channel to ensure that the temperature of the inner wall of the hot side channel is uniform and ≥180℃. (3.2) Steam transport and proportioning: Purified nickel tetracarbonyl vapor and inert gas are introduced into the flow channel through a mass flow controller, with a flow control accuracy of ±1% FS; (3.3) Thermal decomposition reaction parameter control: The reaction time is adjusted according to the target coating thickness. During the reaction, the tetracarbonyl nickel vapor undergoes thermal decomposition reaction on the activated substrate surface, depositing a uniform and dense high-purity nickel anti-corrosion coating. At the same time, the tetracarbonyl nickel and carbon monoxide and other tail gases enter the subsequent treatment system. (4) Post-treatment: After the thermal decomposition coating is completed, stop heating, continue to purge the microchannel with inert gas for 10 minutes, allow the heat exchanger to cool naturally to room temperature, rinse the surface of the channel with anhydrous ethanol to remove residual impurities, and dry to obtain the final product.

2. The preparation method according to claim 1, wherein: The degreasing process in step (1) includes: immersing the microchannel heat exchanger in an alkaline degreasing solution and soaking it at a constant temperature of 60-80℃ for 10-30 minutes, while simultaneously using 200-400W ultrasonic-assisted degreasing. The pickling process includes: rinsing with deionized water 3 to 5 times, then immersing in a dilute acid solution corresponding to the substrate and pickling at room temperature for 5 to 15 minutes; The washing and drying process includes: repeatedly rinsing with deionized water until the surface pH is 6.5-7.5, and then placing it in a hot air circulating drying oven at 100-120°C for 1-2 hours; The activation treatment includes: argon plasma activation or dilute acid activation.

3. The preparation method according to claim 2, wherein: The alkaline degreasing solution is composed of 40-60 g / L sodium hydroxide, 20-40 g / L sodium carbonate, and 2-5 g / L sodium dodecylbenzenesulfonate.

4. The preparation method according to claim 2, wherein: The dilute acid solution corresponding to the substrate includes: Aluminum alloy substrates use 5%~8% dilute hydrochloric acid by mass, titanium alloy substrates use 3%~5% hydrofluoric acid-nitric acid mixture by mass, and stainless steel substrates use 8%~10% dilute sulfuric acid by mass. In the hydrofluoric acid-nitric acid mixture, the volume ratio of hydrofluoric acid to nitric acid is 1:

3.

5. The preparation method according to claim 2, wherein: The argon plasma activation parameters are: power 80~200W, time 10~30 minutes; The dilute acid activation parameters are: 1%~3% by mass dilute hydrochloric acid, soaking at room temperature for 5~15 minutes.

6. The preparation method according to claim 1, wherein: The high-purity tetracarbonyl nickel mentioned in step (2) is tetracarbonyl nickel with a purity ≥ 99.99%; The high-pressure heating conditions are as follows: heating to 40~80℃ via water bath or oil bath, controlling the pressure inside the steam generator to 0.1~0.3MPa, monitoring temperature and pressure in real time during the heating process, with temperature control accuracy ±1℃ and pressure control accuracy ±0.01MPa; The 5A molecular sieve filter has a pore size of 0.1 nm.

7. The preparation method according to claim 1, wherein: The volume ratio of the tetracarbonyl nickel vapor to the inert gas in step (3.2) is 1:5 to 1:

20.

8. The preparation method according to claim 1, wherein: The drying conditions described in step (4) are: drying in an oven at 80-100℃ for 0.5-1 hour.

9. The application of a preparation method according to any one of claims 1 to 8 in the anti-corrosion coating treatment of thermal management systems for marine engineering platforms, ships and marine oil and gas development equipment.

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