High-emissivity ultrathin copper plate for heat preservation of pipeline and preparation method of high-emissivity ultrathin copper plate

Abstract

The invention discloses a high-emissivity ultra-thin copper plate for pipeline heat preservation and a preparation method of the high-emissivity ultra-thin copper plate. According to the method, the ultrathin copper substrate with the thickness of 0.1-0.5 mm is subjected to a three-step synergistic process of'constrained-state surface pretreatment, surface activation and constrained-state low-temperature in-situ oxidation ', and the method comprises the following steps: firstly, carrying out polishing pretreatment on the surface of the copper substrate under the tension constraint of 5-15 MPa; then preparing a nanoscale nickel-phosphorus-copper gradient diffusion layer as a catalytic transition layer through chemical plating to realize metallurgical bonding with a copper matrix and reduce oxidation activation energy; and finally, carrying out in-situ oxidation under the conditions of maintaining tension and being lower than 280 DEG C, and growing a radiation control layer with the thickness of 0.7-2 microns and a nano structure on the surface of the catalytic transition layer. The problems of deformation and poor binding force of an ultrathin copper plate in high-emissivity treatment, unstable performance caused by high-temperature treatment and the like are effectively solved, the emissivity of the prepared copper plate at the wave band of 100-650 DEG C is not lower than 0.90, and the prepared copper plate is good in shape stability, firm in interface bonding and suitable for an efficient pipeline heat preservation system.

Description

Technical Field

[0001] This invention relates to the field of metal surface treatment and pipe insulation materials, and particularly to a high emissivity ultrathin copper plate for pipe insulation and its preparation method. Background Technology

[0002] Industrial pipeline insulation technology typically relies solely on thickening the insulation layer (such as rock wool or aluminum silicate) to suppress heat conduction, often reaching thicknesses of 300-500 mm, which is cumbersome and has limited effectiveness. Alternatively, aluminum foil or stainless steel foil can be used as a reflective layer within the insulation layer, reflecting radiant heat through their low emissivity surfaces (ε≈0.05-0.1). However, this only reflects heat and cannot actively dissipate it, causing heat to accumulate within the insulation layer and leading to excessive external surface temperatures.

[0003] In recent years, using ultra-thin copper plates with a thickness of 0.1~0.5mm as the innermost layer (closely attached to the hot pipe) or intermediate radiant layer of the insulation system has unique advantages: extremely fast thermal conductivity, which can quickly and uniformly homogenize the surface temperature of the pipe and eliminate local hot spots; good ductility, which can closely fit complex pipe curves; and extremely thin thickness, which hardly increases the volume of the insulation system, making it particularly suitable for space-constrained applications. However, existing high emissivity treatments (such as high-temperature oxidation) can cause severe warping of the thin copper plate, making it impossible to maintain the pre-fabricated shape; moreover, the pipe is subject to thermal cycling (start-stop) and vibration, and the conventional coating / oxide film has weak adhesion to the copper substrate, making it prone to peeling off during thermal shock. Once peeled off, the emissivity drops sharply, and the peeling material may clog the insulation layer; vacuum coating and plasma spraying can prepare high emissivity layers at low temperatures, but the cost is extremely high (>500 yuan / m). 2 This is not suitable for large-scale pipeline projects.

[0004] In conclusion, there is currently no mature technology that can simultaneously achieve the morphological stability of ultra-thin copper plates, the durable reliability of high-emissivity coatings, and the low-cost feasibility for engineering applications. Therefore, developing a novel surface treatment technology that can resolve these contradictions is of decisive significance for realizing the large-scale application of ultra-thin copper plates in efficient industrial pipeline insulation systems. Summary of the Invention

[0005] This invention addresses the problem that existing high-emissivity surface treatment technologies (such as high-temperature oxidation) easily lead to substrate warping and deformation, and difficulty in maintaining the pre-formed shape when applied to ultrathin copper plates. It provides a high-emissivity surface treatment method specifically for ultrathin copper plates used in pipe insulation applications. This method utilizes a three-step synergistic process system of "constrained surface pretreatment → surface activation → constrained low-temperature in-situ oxidation" to prepare a composite radiation barrier copper plate that combines excellent shape stability, high radiation absorption capacity, and high interface reliability. The technical solution provided by this invention is as follows: On one hand, the present invention provides a high emissivity surface treatment method for ultra-thin copper plates used for pipe insulation, wherein the thickness of the copper substrate of the ultra-thin copper plate is 0.1~0.5mm, and the method includes the following steps: (1) Surface pretreatment under constraint: The surface of the copper substrate is polished under a constraint state of 5~15 MPa tension. (2) Surface activation: A catalytic transition layer is prepared on the surface of the polished copper substrate. The catalytic transition layer is a nanoscale nickel-phosphorus-copper gradient diffusion layer with a thickness of 30~80 nm, a nickel content of 5~8 at%, a phosphorus content of 2~4 at%, and forms a metallurgical bond with the copper substrate. (3) Confined low-temperature in-situ oxidation: Maintain a tension of 5~15 MPa and oxidize the surface-activated copper substrate in an oxidizing atmosphere of 180~280℃ to grow a radiation control layer with a thickness of 0.7~2 μm in situ on the surface of the catalytic transition layer.

[0006] In one specific implementation, in step (1), the grinding process uses silica sand with a particle size of 60~90 μm, grinding at a speed of 1000~2000 r / min, and cleaning the grinding tools every 3~10 minutes.

[0007] In one specific embodiment, the catalytic transition layer is prepared by a chemical nickel-phosphorus plating process, with the following specific process parameters: the catalytic solution is a nickel acetate-sodium citrate system, the pH value is 4.5~5.0, the temperature is 50~60℃, the nickel ion concentration is 1.5~2.5 g / L, the reducing agent sodium hypophosphite concentration is 10~20 g / L, and the immersion time is 1.5~3 min.

[0008] In one specific embodiment, the catalytic solution further contains tungsten salt or molybdenum salt, wherein the tungsten salt is sodium tungstate, and the addition amount is 0.5~3.0 g / L, or the molybdenum salt is sodium molybdate, and the addition amount is 0.3~2.0 g / L; the molar ratio of nickel ions to tungsten or molybdenum is (10:1)~(20:1) to form a nickel-tungsten-phosphorus ternary catalytic transition layer or a nickel-molybdenum-phosphorus ternary catalytic transition layer.

[0009] In one specific implementation, after step (2) and before step (3), a preheating step is also included: the copper substrate on which the nickel-tungsten-phosphorus ternary catalytic transition layer or the nickel-molybdenum-phosphorus ternary catalytic transition layer has been formed is preheated in an inert atmosphere at 200~220℃ for 3~5min.

[0010] In one specific implementation, the constrained low-temperature in-situ oxidation in step (3) is carried out in a horizontal continuous oxidation furnace. The copper substrate passes horizontally through the oxidation furnace while maintaining a tension of 5-15 MPa. The oxidation process includes the following stages in sequence: (3.1) Preheating zone: Treat in a pure nitrogen atmosphere at 150~180℃ for 1~2 min; (3.2) Catalytic oxidation zone: The copper oxide underlayer with a thickness of 0.2-0.5 μm is formed by treating the zone at 210-230℃, with an oxygen volume fraction of 2%-3% and a water vapor volume fraction of <0.4% for 6-8 min. (3.3) Structural growth region: copper oxide nanocones or copper oxide nanosheet array structures with a height of 0.5-1.5 μm are grown by treating the area at 250-270℃, with an oxygen volume fraction of 5%-7% and a water vapor volume fraction of 0.5%-1.0% for 10-15 min. (3.4) Stabilization zone: Treat in a dry nitrogen atmosphere at 270~280℃ with an oxygen volume fraction of 1%~2% for 2~3 min.

[0011] In one specific implementation, after step (3), step (4) is further included: spraying a transparent silicone resin protective layer with a thickness of 5~10 μm onto the surface of the formed radiation control layer.

[0012] In one specific implementation, prior to step (1), a pretreatment of the copper substrate is further included, the pretreatment comprising the following steps: (a) Degreasing: Immerse the copper substrate in a 3-10 wt% sodium hydroxide solution at room temperature for 3-20 minutes; (b) Deoxidation: Immerse the degreased copper substrate in 3-10 wt% dilute hydrochloric acid for 3-5 min; (c) Drying: After rinsing with deionized water, wipe with anhydrous ethanol and dry at 50~70℃ for 2~10 min.

[0013] On the other hand, the present invention also provides a high emissivity ultrathin copper plate, the copper plate comprising: A copper substrate with a thickness of 0.1~0.5mm; The catalytic transition layer attached to the surface of the copper substrate is a nickel-phosphorus-copper gradient diffusion layer with a thickness of 30~80 nm; The radiation control layer attached to the surface of the catalytic transition layer has a thickness of 0.7~2 μm and includes a copper oxide bottom layer and a copper oxide nanocone or copper oxide nanosheet array structure on the surface. The surface emissivity of the copper plate in the 100~650℃ band is not less than 0.90.

[0014] In one specific embodiment, the surface of the radiation control layer is further covered with a transparent silicone resin protective layer with a thickness of 5~10 μm.

[0015] By adopting the above technical solution, the high emissivity ultrathin copper plate for pipe insulation and its preparation method provided by the present invention have the following beneficial effects: 1. This invention performs oxidation treatment within a range below the copper recrystallization temperature (≤280℃) and combines it with elastic constraint tension control (5~15 MPa), effectively suppressing thermally induced warping and creep deformation easily caused by traditional high-temperature processes. After treatment, the surface flatness of the copper plate is ≤1.5 mm / m (equivalent to a height variation of no more than 1.5 mm within any 1-meter length range), and the diagonal difference is ≤15 mm (1 m × 1 m plate), meeting the requirements for high-precision assembly and long-term dimensional stability, and solving the problem of deformation control in the functionalization treatment of copper plate surfaces.

[0016] 2. The Ni constructed by surface activation in this invention P A Cu gradient diffusion layer reduces the activation energy of copper oxidation by more than 40%, enabling high-quality oxidation to occur at low temperatures. By precisely controlling the oxidation atmosphere (oxygen content, moisture) in specific zones, a dense CuO underlayer (0.2 g / L) is grown in situ on the copper substrate surface. 0.5μm) + CuO nanocone / sheet array (0.5 A composite micro / nano structure with a micrometer diameter of 1.5 μm was developed. Stable emissivity ε ≥ 0.9 was achieved in the pipeline operating temperature range of 100~650℃.

[0017] 3. Traditional spray coatings or high-temperature oxide layers are mostly mechanically bonded to the substrate or have brittle interfaces, making them prone to peeling off under pipeline thermal cycling and vibration conditions. This invention utilizes chemical plating to generate 30-80nm Ni in situ on a copper substrate. P The Cu gradient diffusion layer achieves atomic-level bonding and metallurgical integration between the functional layer and the substrate in terms of composition and structure. Adhesion testing using the cross-cut adhesion test (1mm × 1mm) shows a coating peeling area of ​​≤5%, far exceeding conventional coating standards. This ensures that the functional layer will not powder or peel off under thermal shock from pipeline start-up and shutdown, long-term vibration, or bending installation stress, eliminating the risk of a sudden drop in insulation performance and insulation layer blockage due to coating failure.

[0018] 4. The functional layer system prepared in this invention (from the gradient diffusion layer to the nano-oxidation structure) possesses high chemical stability and density. After 1000 hours of accelerated aging testing at 85°C and 85% relative humidity, the functional layer remained intact, without blistering, cracking, peeling, or significant performance degradation. This demonstrates its ability to withstand harsh environments with high temperature and humidity, meeting the reliability requirements for long-term service in industrial pipelines. The optional subsequent spraying of a transparent silicone resin thin layer can further extend the salt spray resistance time from 24 hours to 72 hours with minimal impact on emissivity (decrease ≤0.03). Detailed Implementation

[0019] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0020] The term "an embodiment" or "embodiment" as used herein refers to a specific feature, structure, or characteristic that may be included in at least one implementation of the invention. In the description of the invention, it should be understood that the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. Furthermore, the terms "first," "second," etc., are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such data can be interchanged where appropriate so that embodiments of the invention described herein can be implemented in orders other than those described herein.

[0021] When a numerical range is disclosed herein, the range is considered continuous and includes the minimum and maximum values ​​of the range, as well as every value between the minimum and maximum values. Furthermore, when the range refers to an integer, it includes every integer between the minimum and maximum values ​​of the range. Additionally, when multiple ranges are provided to describe a feature or characteristic, the ranges may be combined. In other words, unless otherwise specified, all ranges disclosed herein should be understood to include any and all subranges to which they are included. For example, a specified range from “1 to 10” should be considered to include any and all subranges between the minimum value 1 and the maximum value 10. Exemplary subranges of the range 1 to 10 include, but are not limited to, 1 to 6.1, 3.5 to 7.8, 5.5 to 10, etc.

[0022] This invention provides a high-emissivity surface treatment method for ultra-thin copper plates used for pipe insulation. The copper substrate thickness of the ultra-thin copper plate is 0.1~0.5mm. This method uses a three-step synergistic process of "constrained surface pretreatment → surface activation → constrained low-temperature in-situ oxidation" to obtain a radiation barrier copper plate with stable shape, high emissivity, and high reliability. Specifically, it includes the following steps: (1) Constrained Surface Pretreatment: Since the copper substrate is relatively soft and easily deformed during machining, this step applies a tension of 5~15 MPa to the copper substrate using a fixture, and performs surface grinding under this constrained state. This tension range is approximately 5%~10% of the yield strength of the copper material, aiming to induce controllable elastic deformation in the copper substrate, thereby effectively resisting warping or wavy deformation caused by localized stress during grinding, ensuring that the copper substrate maintains shape stability throughout the processing, and laying a smooth base for subsequent surface activation and oxidation steps. The lower limit of 5 MPa provides a clear deformation constraint, while the upper limit of 15 MPa avoids excessive stress approaching the material's yield point or increasing process complexity.

[0023] (2) Surface activation: To lower the subsequent oxidation temperature and improve the quality of the oxide layer, this step prepares a catalytic transition layer with catalytic function on the polished copper substrate surface. Specifically, a low-temperature chemical plating process is used in a nickel acetate-sodium citrate system (pH 4.5-5.0, temperature 50-60℃) to control the Ni²⁺ content. + With a concentration of 1.5-2.5 g / L and a reducing agent sodium hypophosphite concentration of 10-20 g / L, a nanoscale nickel-phosphorus-copper (Ni-P-Cu) gradient diffusion layer is formed after an impregnation reaction for 1.5-3 minutes. The layer has a thickness of 30-80 nm, a nickel content of 5-8 at%, and a phosphorus content of 2-4 at%. This layer forms a strong metallurgical bond with the copper substrate through atomic interdiffusion. This structure can reduce the activation energy of copper oxidation (Cu→CuO) by more than 40%, allowing the growth of high-quality copper oxide layers to be achieved at low temperatures below 300℃, fundamentally avoiding the risk of copper substrate deformation caused by high-temperature processing.

[0024] (3) Confined Low-Temperature In-Situ Oxidation: In this step, the surface-activated copper substrate is placed in an oxidizing atmosphere with a maximum temperature of 280℃ (below the recrystallization temperature of copper) under controlled oxidation while maintaining a tension of 5~15 MPa throughout the process. The preferred temperature is 180~280℃. By precisely controlling the atmosphere composition (oxygen and water vapor concentration), temperature, and time, oxygen atoms are induced to undergo a low-temperature in-situ reaction on the surface of the catalytic transition layer, resulting in the growth of a radiation control layer with a total thickness of 0.7~2 μm. This radiation control layer is a composite copper oxide layer, with a dense copper oxide bottom layer of 0.2~0.5 μm thickness at the bottom and an array of copper oxide nanocones or copper oxide nanosheets with a height of 0.5~1.5 μm on top. This nanostructure significantly improves the specific surface area and light trapping effect, which is the key to achieving an emissivity of not less than 0.90 in the 100~650℃ band; while the tension constraint and low-temperature process together ensure the shape stability and dimensional accuracy of the ultrathin copper substrate during the processing.

[0025] In one specific implementation, the grinding process in step (1) is carried out as follows: silica sand with a particle size range of 60~90 μm is used as the abrasive, and a rotary polishing wheel (i.e., "wool wheel") made of dense wool fibers is selected as the grinding tool and power carrier; the rotation speed of the wool wheel is controlled at 1000~2000 r / min, preferably 1500 r / min, which helps to reduce the melting and adhesion of copper shavings caused by frictional heat while effectively grinding; in order to prevent the copper shavings and abrasive mixture that fall off during the grinding process from clogging the gaps between the wool wheel fibers and affecting the grinding efficiency and uniformity, the wool wheel needs to be cleaned every 3~10 minutes, preferably every 5 minutes, to ensure that the grinding surface continuously obtains a stable grinding effect.

[0026] In one specific implementation, the catalytic transition layer is prepared by an electroless nickel-phosphorus plating process, with the following specific process parameters: a nickel acetate-sodium citrate system is used as the catalytic solution, wherein nickel acetate provides the nickel ion source, and sodium citrate acts as a complexing agent to stabilize the solution and control the deposition rate; the pH of the solution is precisely adjusted to a weakly acidic range of 4.5~5.0, the temperature is controlled between 50~60℃, the nickel ion concentration in the solution is 1.5~2.5 g / L, and the concentration of the reducing agent sodium hypophosphite is 10~20 g / L; a polished copper substrate is immersed in the catalytic solution for 1.5~3 min, and a nanoscale nickel-phosphorus-copper gradient diffusion layer is deposited on the surface of the copper substrate through an autocatalytic reduction reaction.

[0027] In one specific implementation, to further improve the overall performance of the catalytic transition layer, tungsten salt or molybdenum salt can be introduced into the nickel acetate-sodium citrate catalytic solution for modification; wherein the tungsten salt is sodium tungstate, and its addition amount is 0.5~3.0 g / L, or the molybdenum salt is sodium molybdate, and its addition amount is 0.3~2.0 g / L; by controlling the molar ratio of nickel ions to tungsten (W) or molybdenum (Mo) in the range of (10:1) to (20:1), nickel, phosphorus and tungsten or molybdenum are co-deposited to form a nickel-tungsten-phosphorus or nickel-molybdenum-phosphorus ternary catalytic transition layer; due to its solid solution strengthening effect and more stable amorphous / microcrystalline structure, this ternary catalytic transition layer is superior to conventional nickel-phosphorus binary coatings in terms of thermal stability, corrosion resistance and catalytic activity for subsequent copper oxidation; the addition amount of tungsten or molybdenum must be strictly controlled, because excessive content will inhibit the chemical plating reaction kinetics, leading to a decrease in deposition rate and possibly increasing the internal stress of the coating, causing brittleness.

[0028] In one specific implementation, after completing the surface activation step (2) and before performing the confined-state low-temperature in-situ oxidation step (3), a preheating treatment stage is included: the copper substrate with the formed nickel-tungsten-phosphorus or nickel-molybdenum-phosphorus ternary catalytic transition layer is placed in an inert nitrogen atmosphere and preheated at 200~220℃ for 3~5 minutes. This preheating process, on the one hand, further promotes the diffusion and migration of tungsten or molybdenum atoms to the surface of the copper substrate through a mild thermal activation effect, strengthening the metallurgical bonding interface between the catalytic transition layer and the copper substrate; on the other hand, it relaxes the metastable structure of the catalytic transition layer, releases internal stress and optimizes its atomic arrangement, thereby transforming it into a precatalytic structure with more thermodynamic stability and more uniform catalytic active sites, laying a better interfacial foundation for the rapid and orderly growth of a high-quality, uniform copper oxide layer in the subsequent low-temperature oxidation step.

[0029] In one specific implementation, the constrained low-temperature in-situ oxidation in step (3) is carried out in a horizontal continuous oxidation furnace. The copper substrate is held under tension of 5~15 MPa along its original rolling direction and passes through the furnace body at a horizontal and uniform speed under the continuous traction of the fixture. The oxidation process is precisely divided into four functionally coherent temperature zones: First, the material enters the preheating zone, where it is treated for 1-2 minutes in a high-purity nitrogen atmosphere (purity >99.99%) at 150-180℃ to ensure uniform heating and prevent thermal shock deformation caused by sudden heating. Next, it enters the catalytic oxidation zone, where it is treated for 6-8 minutes in a weakly oxidizing atmosphere at 210-230℃ with an oxygen volume fraction of 2%-3% and a water vapor volume fraction of <0.4%. Utilizing the catalytic transition layer, a continuous, dense copper oxide underlayer with a thickness of 0.2-0.5 μm is preferentially formed on the surface. Then, it enters the structural growth zone, where it is treated for 10-15 minutes in a strengthened oxidizing atmosphere at 250-270℃ with an oxygen volume fraction increased to 5%-7% and a water vapor volume fraction of 0.5%-1.0%. This promotes the directional epitaxial growth of copper oxide on the dense layer, forming a structure with a height of 0.5-1.5 μm. The nanocone or nanosheet array structure is formed at μm; finally, it enters the stabilization region and is treated for 2-3 minutes in a dry nitrogen atmosphere at 270-280℃ with oxygen volume fraction reduced to 1%-2% to complete the final crystal form stabilization of the nanostructure and further enhance its interfacial bonding force with the underlying layer, thereby obtaining a surface layer with complete structure, strong bonding and high radiation performance.

[0030] In one specific implementation, after the oxidation treatment and formation of the radiation control layer in step (3), a surface encapsulation protection step (4) is further included: a transparent silicone resin protective layer with a thickness of 5~10 μm is uniformly coated on the surface of the radiation control layer using a spraying process. This protective layer is preferably a high-temperature resistant transparent coating based on polydimethylsiloxane (PDMS) or modified methylphenyl silicone resin, which, after curing, forms a dense, continuous, and chemically stable film. This encapsulation layer, while maintaining the original high radiation performance, only reduces the surface emissivity in the 100~650℃ band by no more than 0.03; simultaneously, this protective layer provides excellent physical barrier and inert protection, significantly extending the corrosion resistance time of the product in the neutral salt spray test (according to GB / T 10125 standard) from approximately 24 hours before encapsulation to over 72 hours, thereby greatly enhancing the long-term durability and reliability of the product in harsh industrial environments such as humidity and salt spray.

[0031] In one specific implementation, before performing the constrained surface pretreatment in step (1), the copper substrate needs to undergo strict pre-cleaning and activation pretreatment. This process includes the following steps in sequence: First, chemical degreasing is performed by immersing the copper substrate in a sodium hydroxide aqueous solution with a concentration of 3-10 wt% (preferably 5 wt%) at room temperature for 3-20 minutes (preferably 10 minutes) to thoroughly remove grease, stains, and fingerprints adhering to the surface; then, acid pickling and activation are performed by immersing the degreased and thoroughly rinsed copper substrate in a sodium hydroxide aqueous solution with a concentration of 3-10 wt% (preferably 5 wt%). The copper substrate is treated in a dilute hydrochloric acid aqueous solution of wt% (preferably 5wt%) for 3-5 minutes to dissolve its natural oxide film and expose a clean, active, fresh copper surface. Finally, it is dehydrated and dried. First, the acid-washed copper substrate is thoroughly rinsed with deionized water (preferably repeated 3 times), then its surface is wiped with anhydrous ethanol to replace residual moisture and accelerate evaporation. After that, it is placed in an oven at 50-70°C for 2-10 minutes to completely remove moisture, preferably at 60°C for 5 minutes. This yields a clean, dry copper substrate with high surface activity for subsequent confined state treatment.

[0032] This invention also provides a high-emissivity ultrathin copper plate, the structure of which, from top to bottom, comprises: a copper substrate with a thickness of 0.1~0.5 mm, made of pure copper or low-alloy copper and retaining a rolled texture to provide excellent thermal conductivity, rapid thermal diffusion capability and mechanical support; a catalytic transition layer attached to the surface of the copper substrate, which is a nickel-phosphorus-copper gradient diffusion layer with a thickness of 30~80 nm. This catalytic transition layer achieves interface strengthening, stress buffering and catalytic effect on subsequent oxidation through metallurgical bonding; and a radiation control layer attached to the surface of the catalytic transition layer, with a total thickness of 0.7~2 μm. This radiation control layer is a copper oxide composite structure, consisting of a dense copper oxide layer with a bottom thickness of 0.2~0.5 μm and an array of copper oxide nanocones or copper oxide nanosheets with a surface height of 0.5~1.5 μm. This micro-nano composite structure endows it with a stable high surface emissivity in the 100~650℃ wavelength range, with an emissivity value of not less than 0.90.

[0033] In one specific implementation, to further enhance its environmental durability and protective performance, a protective encapsulation layer made of high-temperature resistant transparent silicone resin is also applied to the surface of the radiation control layer. This protective layer is formed by a spraying process, and its thickness is uniformly controlled within the range of 5~10 μm. After curing, the transparent silicone resin has excellent light transmittance, chemical inertness, and density. While maintaining the original high emissivity performance of the radiation control layer (ensuring that the emissivity decrease in the 100~650℃ band does not exceed 0.03), it provides an effective physical isolation and anti-permeation barrier for the underlying functional structure. This significantly extends the product's resistance to neutral salt spray corrosion from approximately 24 hours in the unprotected state to more than 72 hours, greatly improving its long-term service reliability in humid and corrosive industrial environments.

[0034] The following detailed description of examples of the present invention is exemplary and is used only to explain the present invention, and should not be construed as limiting the present invention.

[0035] Example 1 A method for high emissivity surface treatment of ultrathin copper plates for pipe insulation includes the following steps: 1. Material Preparation T2 pure copper strip with a thickness of 0.3 mm was selected as the copper substrate (dimensions: 200 mm wide and 500 mm long).

[0036] 2. Copper substrate pretreatment (a) Degreasing: Immerse the copper substrate in a 5 wt% sodium hydroxide aqueous solution for 10 min at room temperature.

[0037] (b) Deoxidation: Immerse the degreased copper substrate in a 5 wt% dilute hydrochloric acid solution for 4 min.

[0038] (c) Drying: Rinse repeatedly with deionized water 3 times, then wipe the surface with anhydrous ethanol to replace the moisture, and then dry in an oven at 60°C for 5 minutes to obtain a clean and dry copper substrate.

[0039] 3. Constrained Surface Pretreatment The pretreated copper substrate was placed in a horizontal continuous tension clamping device, and a constant tension of 10 MPa was applied along the rolling direction. Under this constraint, the substrate was polished on both sides using silica sandpaper with a grit of 75 μm at a speed of 1500 r / min. The wool wheel was cleaned with compressed air every 5 minutes, for a total polishing time of 15 minutes.

[0040] 4. Surface activation Using nickel acetate (providing Ni²) + A base plating solution was prepared using sodium citrate (15 g / L) as the main salt, sodium citrate (2.0 g / L) as the complexing agent, and sodium hypophosphite (15 g / L) as the reducing agent. Sodium tungstate (2.0 g / L) was added as a modifier to control the Ni² content. +The molar ratio of nickel to tungsten (Ni-WP) is approximately 15:1. The pH of the plating solution is adjusted to 4.8 using dilute ammonia and maintained at 55°C. The copper substrate is immersed in the plating solution for 2 minutes, and an initial nickel-tungsten-phosphorus (Ni-WP) ternary catalytic transition layer is formed through autocatalytic reduction. Subsequently, the copper substrate with the formed Ni-WP ternary catalytic transition layer is transferred to a nitrogen atmosphere and preheated at 210°C for 4 minutes. This results in a final Ni-WP gradient diffusion layer with a thickness of approximately 50 nm, uniform composition, and a strong metallurgical bond with the copper substrate, containing approximately 6.5 at% nickel and 3.0 at% phosphorus.

[0041] 5. Confined-state low-temperature in-situ oxidation Maintaining a tension of 10 MPa, the copper substrate is passed horizontally and uniformly through a horizontal four-zone continuous oxidation furnace. The oxidation process parameters are as follows: Preheating zone: Temperature 165℃, pure nitrogen atmosphere, treatment for 1.5 minutes to achieve uniform heating and avoid thermal shock.

[0042] Catalytic oxidation zone: Temperature 220℃, atmosphere is equilibrium gas with oxygen volume fraction of 2.5% and water vapor volume fraction of 0.3%, treatment for 7 min. Under the action of the catalytic transition layer, a continuous and dense copper oxide underlayer with a thickness of approximately 0.35 μm is formed.

[0043] Structure growth zone: Temperature 260℃, atmosphere 6.0% oxygen and 0.8% water vapor, treatment for 12 min. Under these conditions, copper oxide grows directionally, forming an array of copper oxide nanosheets with a height of approximately 0.8 μm.

[0044] Stabilization zone: temperature 275℃, atmosphere is dry nitrogen with oxygen volume fraction of 1.5%, treatment for 2.5 min, the final radiation control layer (i.e. composite copper oxide layer) has a total thickness of about 1.15 μm.

[0045] 6. Protective layer A transparent silicone resin protective layer is uniformly coated onto the surface of the radiation control layer using a spraying process. A high-temperature resistant silicone resin (such as Wacker Chemie's Elastosil® E50 series) is selected, and the dry film thickness is controlled to be 8 μm.

[0046] The high emissivity ultrathin copper plate prepared by the above method has the following layered composite structure: Copper substrate: 0.3 mm thick T2 pure copper; Catalytic transition layer: a nickel-tungsten-phosphorus-copper gradient diffusion layer with a thickness of approximately 50 nm; Radiation control layer: A composite copper oxide functional layer with a total thickness of approximately 1.15 μm. Its structure consists of a dense copper oxide layer of approximately 0.35 μm at the bottom and an array of copper oxide nanosheets of approximately 0.8 μm at the top; Transparent silicone protective layer: approximately 8 μm thick.

[0047] Example 2 The method is the same as in Example 1, except that the grinding speed is 800 r / min.

[0048] Example 3 The method is the same as in Example 1, except that the grinding speed is 3000 r / min.

[0049] Example 4 The method is the same as in Example 1, except that the pH value is 5.5 during electroless nickel-phosphorus plating.

[0050] Example 5 The method is the same as in Example 1, except that the amount of sodium tungstate added is 4.0 g / L.

[0051] Example 6 The method is the same as in Example 1, except that sodium tungstate is not added as a modifier to the base plating solution.

[0052] Example 7 The method is the same as in Example 1, except that no preheating treatment is performed after surface activation, and instead, a confined-state low-temperature in-situ oxidation treatment is performed directly.

[0053] Example 8 The method is the same as in Example 1, except that the temperature of the structure growth region under constrained low-temperature in-situ oxidation is 290°C.

[0054] Example 9 The method is the same as in Example 1, except that the thickness of the transparent silicone protective layer is 12 μm.

[0055] Example 10 The method is the same as in Example 1, except that a 12% sodium hydroxide solution is used for degreasing.

[0056] Comparative Example 1 Referring to the method of Example 1, the difference is that the surface of the copper substrate is polished in a free state without any external tension constraint.

[0057] Comparative Example 2 Referring to the method in Example 1, except that an electroplating nickel process (Watt nickel plating solution, current density 2 A / dm³) is used. 2 A pure nickel layer with a thickness of about 200 nm was prepared on the surface of a copper substrate (time 2 min).

[0058] Comparative Example 3 The method is the same as in Example 1, except that a tension of 10 MPa is maintained, but the oxidation process is carried out in an air atmosphere at 350°C for 15 min.

[0059] Comparative Example 4 Referring to the method of Example 1, the difference is that a constrained low-temperature in-situ oxidation process is performed in a free state without any external tension constraint.

[0060] Test case Performance tests were conducted on the copper plate samples prepared in Examples 1-10 and Comparative Examples 1-4. Specific items included: (1) Emissivity test: The normal spectral emissivity of the sample in the 100~650℃ band was measured using an integrating sphere reflectometer combined with a high-temperature heating stage according to ASTM E408 standard; (2) Shape stability test: The overall geometric deformation of the finished copper plate was quantitatively evaluated by comprehensively measuring the surface flatness and diagonal difference. First, a 1m×1m finished copper plate was placed horizontally on a reference platform. Using a laser profilometer or a high-precision dial indicator, the height deviation between the plate and the reference plane was measured at multiple points along the plate surface. The maximum height difference per unit length (mm / m) was used to characterize its micro-undulations and overall flatness. At the same time, the actual lengths of the two diagonals of the plate were measured using a high-precision distance measuring tool, and the absolute value of the difference between the two (unit: mm) was calculated. This diagonal difference directly reflects the degree of overall twisting and warping of the plate. (3) Bond strength test: The cross-cut test was conducted according to GB / T 9286 standard. The interfacial bond strength was evaluated by calculating the percentage of coating peeling area after the tape was torn. (4) Damp heat resistance test: According to GB / T 1740 standard, the sample was subjected to a 1000-hour damp heat aging test at 85℃ / 85% relative humidity. The coating was observed to show failure phenomena such as blistering, cracking, powdering or peeling. (5) Salt spray resistance test: A neutral salt spray test was conducted according to GB / T 10125 standard. The time when red rust or coating failure first appeared on the sample surface was recorded to evaluate its corrosion resistance. The characterization results are shown in Table 1.

[0061] Table 1

[0062] Based on the test results, this invention systematically solves the problems of deformation, poor adhesion, and unstable performance of ultrathin copper plates in high emissivity processing through a three-step synergistic process of "constrained surface pretreatment → surface activation → constrained low-temperature in-situ oxidation". Example 1, employing an optimized catalytic transition layer and a low-temperature oxidation process of ≤280℃, achieved optimal overall performance (emissivity 0.93, flatness 0.8 mm / m, adhesion grade 0, salt spray resistance >72 h). Examples 2-10 reveal the sensitivity and synergistic necessity of each process step through single parameter adjustments: In Examples 2 and 3, excessively low or high grinding speeds slightly reduce flatness; in Example 4, an increase in the pH value of chemical plating affects the quality of the catalytic layer, leading to a decrease in emissivity and adhesion; in Example 5, excessive tungsten addition increases the brittleness of the coating, weakening adhesion and corrosion resistance; in Example 6, although no tungsten modification maintains high emissivity, it significantly reduces salt spray resistance; in Example 7, the lack of preheating treatment weakens interfacial adhesion and protection; in Example 8, excessively high oxidation temperature directly leads to a sharp drop in emissivity, deterioration of flatness, and degradation of durability; while in Example 9, an excessively thick protective layer affects emissivity while improving salt spray resistance. The comparative results further verify the irreplaceability of the core features: In Comparative Examples 1 and 4, the lack of tension constraints leads to severe warping and adhesion failure of the substrate; Comparative Example 2, lacking a specific catalytic transition layer, suffers from extremely low emissivity and complete loss of adhesion due to the inability to effectively catalyze low-temperature oxidation; in Comparative Example 3, high-temperature oxidation, even with the maintenance of tension, still damages the substrate and degrades the quality of the oxide layer. The above data fully demonstrates that the three-step process and parameter system of the present invention constitute a complete and mutually supportive technical solution, verifying the creativity and practicality of the technical solution in balancing shape stability, high emissivity and high reliability.

Claims

1. A method for high emissivity surface treatment of ultrathin copper plates for pipe insulation, characterized in that, The ultrathin copper plate has a copper substrate thickness of 0.1~0.5mm, and the method includes the following steps: (1) Surface pretreatment under constraint: The surface of the copper substrate is polished under a constraint state of 5~15 MPa tension. (2) Surface activation: A catalytic transition layer is prepared on the polished copper substrate surface. The catalytic transition layer is a nanoscale nickel-phosphorus-copper gradient diffusion layer with a thickness of 30~80 nm, a nickel content of 5~8 at%, a phosphorus content of 2~4 at%, and forms a metallurgical bond with the copper substrate. (3) Confined low-temperature in-situ oxidation: Maintaining a tension of 5~15 MPa, the copper substrate after surface activation is oxidized in an oxidizing atmosphere of 180~280℃, thereby growing a radiation control layer with a thickness of 0.7~2 μm in situ on the surface of the catalytic transition layer.

2. The method according to claim 1, characterized in that, In step (1), the grinding process uses silica sand with a particle size of 60~90 μm, and the grinding is carried out at a speed of 1000~2000 r / min. The grinding tools are cleaned every 3~10 minutes.

3. The method according to claim 1, characterized in that, In step (2), the catalytic transition layer is prepared by electroless nickel-phosphorus plating process. The specific process parameters are as follows: the catalytic solution is a nickel acetate-sodium citrate system, the pH value is 4.5~5.0, the temperature is 50~60℃, the nickel ion concentration is 1.5~2.5 g / L, the reducing agent sodium hypophosphite concentration is 10~20 g / L, and the immersion time is 1.5~3 min.

4. The method according to claim 3, characterized in that, The catalytic solution also contains tungsten salt or molybdenum salt, wherein the tungsten salt is sodium tungstate, and the amount added is 0.5~3.0 g / L, or the molybdenum salt is sodium molybdate, and the amount added is 0.3~2.0 g / L; the molar ratio of nickel ions to tungsten or molybdenum is (10:1)~(20:1) to form a nickel-tungsten-phosphorus ternary catalytic transition layer or a nickel-molybdenum-phosphorus ternary catalytic transition layer.

5. The method according to claim 4, characterized in that, After step (2) and before step (3), a preheating step is also included: the copper substrate on which the nickel-tungsten-phosphorus ternary catalytic transition layer or the nickel-molybdenum-phosphorus ternary catalytic transition layer has been formed is preheated in an inert atmosphere at 200~220℃ for 3~5min.

6. The method according to claim 1, characterized in that, Step (3) involves confined low-temperature in-situ oxidation performed in a horizontal continuous oxidation furnace. The copper substrate passes horizontally through the furnace while maintaining a tension of 5-15 MPa. The oxidation process includes the following stages in sequence: (3.1) Preheating zone: Treat in a pure nitrogen atmosphere at 150~180℃ for 1~2 min; (3.2) Catalytic oxidation zone: The copper oxide underlayer with a thickness of 0.2-0.5 μm is formed by treating the zone at 210-230℃, with an oxygen volume fraction of 2%-3% and a water vapor volume fraction of <0.4% for 6-8 min. (3.3) Structural growth region: copper oxide nanocones or copper oxide nanosheet array structures with a height of 0.5-1.5 μm are grown by treating the area at 250-270℃, with an oxygen volume fraction of 5%-7% and a water vapor volume fraction of 0.5%-1.0% for 10-15 min. (3.4) Stabilization zone: Treat in a dry nitrogen atmosphere at 270~280℃ with an oxygen volume fraction of 1%~2% for 2~3 min.

7. The method according to any one of claims 1-6, characterized in that, After step (3), step (4) is also included: spraying a transparent silicone resin protective layer with a thickness of 5~10 μm onto the surface of the formed radiation control layer.

8. The method according to claim 1, characterized in that, Before step (1), a pretreatment of the copper substrate is included, which includes the following steps in sequence: (a) Degreasing: Immerse the copper substrate in a 3-10 wt% sodium hydroxide solution at room temperature for 3-20 minutes; (b) Deoxidation: Immerse the degreased copper substrate in 3-10 wt% dilute hydrochloric acid for 3-5 min; (c) Drying: After rinsing with deionized water, wipe with anhydrous ethanol and dry at 50~70℃ for 2~10 min.

9. A high-emissivity ultrathin copper plate prepared by the method according to any one of claims 1 to 8, characterized in that, The copper plate includes: A copper substrate with a thickness of 0.1~0.5mm; The catalytic transition layer attached to the surface of the copper substrate is a nickel-phosphorus-copper gradient diffusion layer with a thickness of 30~80 nm; The radiation control layer attached to the surface of the catalytic transition layer has a thickness of 0.7~2 μm and includes a copper oxide bottom layer and a copper oxide nanocone or copper oxide nanosheet array structure on the surface. The surface emissivity of the copper plate in the 100~650℃ band is not less than 0.

90.

10. The high emissivity ultrathin copper plate according to claim 9, characterized in that, The surface of the radiation control layer is also covered with a transparent silicone resin protective layer with a thickness of 5~10 μm.

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