High-stability self-repairing normal-temperature blackening agent, and preparation method and application thereof

Abstract

The application belongs to the technical field of metal surface treatment, and discloses a high-stability self-repairing normal-temperature blackening agent and a preparation method and application thereof. The blackening agent is formed by mixing A liquid and B liquid during use, and thickening anti-settling agents and interfacial compatibilizers are added. The A liquid contains copper sulfate pentahydrate, ammonium tungstate, nickel sulfate, ammonium thiosulfate, copper ion transient complexing agent and antioxidant. The B liquid contains trisodium nitrilotriacetate, lignosulfonate-doped polyaniline reaction liquid, dispersion stabilizer and buffer solution. Hydroxyethyl cellulose and polyethylene glycol are added during mixing. The application solves the problems of poor storage stability and insufficient controllability of synthesis of the existing self-repairing normal-temperature blackening agent by means of two-component split design, copper ion transient complexing protection, double oxygen removal system, synergistic effect of dispersion stabilizer and buffer solution, and introduction of thickening anti-settling agents and interfacial compatibilizers.

Description

Technical Field

[0001] This invention relates to the field of metal surface treatment technology, specifically to a highly stable self-healing room temperature blackening agent, its preparation method, and its application. Background Technology

[0002] Blackening treatment of steel parts is an important process for metal surface protection. Traditional alkaline chemical oxidation requires treatment at 135-150℃ for 30-90 minutes. Although the film is fine, uniform, strong, and corrosion-resistant, it suffers from problems such as long production cycle, high energy consumption, poor working conditions, and serious environmental pollution. Among room temperature blackening methods, acidic chemical oxidation can be operated at room temperature, but most blackening agents contain pollutants such as phosphorus, selenium, and nitrites. The process is complex and costly, and for cast iron parts, a separate immersion in an anti-rust solvent is required after blackening, making it impossible to achieve blackening and rust prevention simultaneously.

[0003] In the military industry, rust prevention of artillery barrels has long been a technical challenge. The outer wall of an artillery barrel is constantly exposed to the atmosphere, subjected to multiple corrosive factors such as wind, rain, sun, and salt spray. It also needs to withstand the temperature rise caused by heat conduction during firing, typically reaching 100-200°C. Traditional barrel protection methods often involve phosphating followed by coating or directly applying anti-rust paint. However, phosphating films lack sufficient toughness and are prone to cracking during repeated thermal expansion and contraction of the barrel. Anti-rust paint, on the other hand, suffers from reduced adhesion, aging, and peeling, resulting in short maintenance cycles and high costs. Furthermore, scratches and dents are inevitable on the outer wall of artillery barrels during transportation, loading, and maintenance. Once traditional anti-rust coatings are damaged, the damaged area becomes the starting point for corrosion, lacking self-repairing capabilities.

[0004] The prior art (Chinese invention patent with publication number CN110923683A and publication date of 2020-03-27) discloses a self-healing room temperature blackening agent for cold-drawn steel pipes. Its main film-forming materials include copper sulfate pentahydrate, ammonium tungstate, and sodium lignosulfonate-doped polyaniline reaction solution. Through the reversible oxidation-reduction reaction between sodium lignosulfonate-doped polyaniline and oxygen, the self-healing function is achieved when scratches appear on the blackened film. At the same time, blackening and rust prevention are achieved. It is also selenium-free and phosphorus-free, and has good environmental protection properties.

[0005] However, through long-term practice, the inventors discovered that the above technical solution still has the following technical problems: First, the blackening agent has insufficient storage stability. This blackening agent is a multi-component mixture; copper sulfate pentahydrate (CuSO4·5H2O) in solution A can undergo a redox reaction with ammonium thiosulfate in the liquid phase, causing Cu... 2+ Reduced to Cu +This process leads to the formation of Cu2S precipitate, causing the blackening agent to become ineffective during storage. Simultaneously, the sodium lignosulfonate-doped polyaniline reaction solution in solution B is an acidic system; the pH change after mixing with solution A may cause dedoping or aggregation and sedimentation of the polyaniline. Furthermore, its optimal storage temperature is only 20-35℃, a very narrow range, making it prone to deterioration under high summer temperatures or low winter temperatures.

[0006] Second, the self-healing function of the blackening film relies solely on the single passivation mechanism of sodium lignosulfonate doped with polyaniline. For larger scratches, this mechanism may not be able to completely cover the exposed metal surface, and there is a lack of verification on its self-healing ability after repeated scratches.

[0007] Therefore, how to improve the storage stability and self-healing efficiency of self-healing room temperature blackening agents, and expand their application in military fields such as the outer wall of artillery barrels, has become a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0008] The purpose of this invention is to overcome the shortcomings of the prior art and provide a highly stable self-healing room temperature blackening agent and its preparation method, so as to solve the problems of poor storage stability and limited self-healing efficiency of existing self-healing room temperature blackening agents, and apply it to the surface blackening and rust prevention treatment of cold-drawn steel pipes, artillery barrel outer walls and other steel parts.

[0009] To achieve the above objectives, the present invention adopts the following technical solution: A highly stable, self-healing, room-temperature blackening agent, wherein the blackening agent is prepared by mixing liquid A and liquid B during use, and thickening and anti-settling agents and interface compatibilizers are added; wherein: The A solution comprises the following components by weight: 10-200 parts copper sulfate pentahydrate, 20-300 parts ammonium tungstate, 5-100 parts nickel sulfate, 10-150 parts ammonium thiosulfate, 5-45 parts copper ion transient complexing agent, 4-23 parts antioxidant, and 500-1200 parts deionized water. The B solution comprises the following components by weight: 5-100 parts of trisodium triacetate, 50-1000 parts of sodium lignosulfonate-doped polyaniline reaction solution, 7-37 parts of dispersant stabilizer, 6-31 parts of buffer solution, and 400-1000 parts of deionized water. The thickening and anti-settling agent is 3-20 parts by weight of hydroxyethyl cellulose; the interface compatibilizer is 10-40 parts by weight of polyethylene glycol; the weight parts of liquid A, liquid B, thickening and anti-settling agent, and interface compatibilizer are based on the same standard; liquid A and liquid B are mixed at a mass ratio of liquid A:liquid B = 1:1.5-3 when used.

[0010] Among them, copper ion transient complexing agent is used to inhibit the redox reaction between copper sulfate pentahydrate and ammonium thiosulfate; antioxidant is used to remove dissolved oxygen in the system; dispersing stabilizer is used to prevent the aggregation and sedimentation of sodium lignosulfonate-doped polyaniline particles. Specifically, the dispersing stabilizer is used to prevent the aggregation and sedimentation of sodium lignosulfonate-doped polyaniline particles. Its mechanism of action is to form an adsorption layer on the surface of polyaniline particles through steric hindrance effect and electrostatic repulsion effect, which prevents the particles from getting close to each other and aggregating. It belongs to the particle-scale dispersion stabilization mechanism; buffer solution is used to maintain the system in the pH range where the polyaniline conduction state is stable; thickening and anti-settling agent is used to increase the viscosity of the system and reduce the particle sedimentation rate; interface compatibilizer is used to enhance the compatibility between the components and improve low-temperature storage performance.

[0011] The role of trisodium nitrile triacetate (NTA-3Na) in solution B is as follows: After mixing solutions A and B, NTA-3Na forms a double chelate system with EDTA-2Na in solution A. EDTA-2Na is mainly responsible for stabilizing copper ions during storage in solution A, preventing premature precipitation; while NTA-3Na preferentially chelates Fe dissolved from the surface of the steel matrix in the mixed working solution. 2+ / Fe 3+ The presence of NTA-3Na helps prevent non-film-forming side reactions between iron ions and tungstate ions, thus ensuring the orderly progress of the film-forming reaction. Furthermore, NTA-3Na's chelating ability is stronger than EDTA-2Na in the pH range of 3-5, better matching the operating pH range of the working solution (3.5-5.0), compensating for the decreased chelating efficiency of EDTA-2Na in this pH range. When the amount of NTA-3Na is less than 5 parts, its chelating capacity for iron ions is insufficient to effectively suppress side reactions; when it is more than 100 parts, the excess chelating agent will competitively chelate copper ions in the working solution, reducing the film-forming reaction rate. The preferred amount of NTA-3Na is 10-50 parts.

[0012] It should be noted that hydroxyethyl cellulose (HEC) and polyethylene glycol (PEG) are components added during mixing and are not stored with solution A or solution B. Instead, they are packaged and stored separately as solid powders and added during the mixing step before use. The long shelf life of the blackening agent of this invention refers to the long shelf life when solutions A and B are stored separately in sealed containers. Hydroxyethyl cellulose and polyethylene glycol, as solid powders, are stable for a long time under normal sealed storage conditions and are not within the scope of storage stability testing.

[0013] The self-healing mechanism of the blackening film of this invention is as follows: Sodium lignosulfonate doped polyaniline (LGS-PANI) is uniformly dispersed in the blackening film in the form of emerald green imine salt. When the blackening film is scratched, exposing the steel substrate, under the action of corrosion micro-cells, anodic dissolution of iron (Fe→Fe) occurs at the scratch site. 2+ +2e- The emerald green imine salt in LGS-PANI has a higher redox potential than iron, enabling it to gain electrons from the iron matrix and be reduced to colorless emerald green imine, while simultaneously reducing Fe... 2+ Oxidized to Fe 3+ Fe 3 + Subsequently, it reacts with the tungstate ions in the blackened film to form an insoluble iron tungstate passivation film in situ at the scratch site, achieving chemical self-healing of the scratch. The reduced colorless emerald green imine is then reoxidized by oxygen in the air to an active emerald green imine salt. From the reaction mechanism, this redox cycle is reversible, providing a chemical basis for the cyclical nature of the self-healing function. Furthermore, the sulfonic acid groups in the lignin sulfonate ion have a chelating effect on iron ions, enabling the accumulation of Fe at the scratch site. 2+ / Fe 3+ This invention accelerates the in-situ formation of the passivation film. Through the synergistic effect of sodium lignosulfonate doping with polyaniline and tungstate, it achieves effective self-repair of micron-sized scratches (scratch width ≤ 50 μm). It should be noted that sodium lignosulfonate, as a macromolecular sulfonic acid dopant, maintains the polyaniline backbone in a conductive state (in the form of emerald green imine salt) through a proton acid doping mechanism. Within the pH range of the buffer solution (pH 3.8-4.5) of solution B and the working solution after mixing solutions A and B (3.5-5.0), this pH condition is within the stable range of polyaniline emerald green imine salt (pH < 5.5). The doping balance between lignosulfonate and the polyaniline backbone is maintained, allowing polyaniline to stably exist in the blackening film in the form of emerald green imine salt, thus ensuring its self-repair activity.

[0014] Furthermore, the copper ion transient complexing agent is a compound of triethanolamine and disodium ethylenediaminetetraacetate, wherein triethanolamine is 3-30 parts and disodium ethylenediaminetetraacetate is 2-15 parts; the antioxidant is a compound of ascorbic acid and sodium sulfite, wherein ascorbic acid is 1-8 parts and sodium sulfite is 3-15 parts.

[0015] Furthermore, the dispersant stabilizer is a compound of polyvinylpyrrolidone and polyoxyethylene octylphenol ether, wherein 5-25 parts of polyvinylpyrrolidone and 2-12 parts of polyoxyethylene octylphenol ether are present; the buffer solution is a compound of citric acid, sodium citrate and potassium hydrogen phthalate, wherein 1-8 parts of citric acid, 3-15 parts of sodium citrate and 2-8 parts of potassium hydrogen phthalate are present.

[0016] Furthermore, the sodium lignosulfonate-doped polyaniline reaction solution is synthesized by emulsion polymerization. The weight ratio of sodium lignosulfonate to aniline in the synthesis components is 1:1. The synthesis steps include: taking 13-24 parts by weight of sodium lignosulfonate and pouring it into 70-130 parts by weight of 0.8-1.2 mol / L sulfuric acid solution, and stirring evenly; then taking 13-24 parts by weight of aniline, slowly adding it and stirring evenly to prepare solution D; taking 32-59 parts by weight of ammonium persulfate and dissolving it in 70-130 parts by weight of 0.8-1.2 mol / L citric acid solution to obtain ammonium persulfate-citric acid solution, adding it dropwise to solution D, and carrying out the reaction at 0-5℃ with thorough stirring; continuing to stir the reaction at 20-30℃ for 6-12 hours until the color of the reaction solution is stable as dark green and the pH value is stable in the range of 4.5-5.5, thus obtaining the sodium lignosulfonate-doped polyaniline reaction solution.

[0017] In the sodium lignosulfonate-doped polyaniline reaction solution, the solid content of sodium lignosulfonate-doped polyaniline (LGS-PANI) is 8-15 wt%, preferably 10-12 wt%; the solid content is defined as the percentage of LGS-PANI solid mass in the reaction solution relative to the total mass of the reaction solution. In this invention, the "parts by weight" of the sodium lignosulfonate-doped polyaniline reaction solution refers to the total weight of the synthesized reaction solution, and not just the LGS-PANI solid mass. The above-mentioned solid content range (8-15 wt%) is determined based on the following material balance: Taking the synthesis formulation of Example 1 as an example, in the polymerization reaction of 18.6 parts by weight of sodium lignosulfonate and 18.6 parts by weight of aniline, the polymerization yield of aniline monomer to polyaniline is 85%-95%, and 60%-80% of sodium lignosulfonate, as a dopant, is embedded in the polyaniline backbone. The total amount of LGS-PANI solid formed by the two is 28-35 parts by weight; the total amount of materials in the reaction system (including sulfuric acid solution, citric acid solution, etc.) is 280-290 parts by weight. After deducting the water consumed and volatilized in the reaction, the total mass of the reaction liquid is 260-280 parts by weight. Therefore, the solid content is calculated to be 10-13 wt%, which falls within the range of 8-15 wt%. The solid content can be determined by the following method: Take 5g of the reaction liquid (accurate to 0.001g), dry it in an oven at 105℃ to constant weight, and divide the mass of the solid after drying by the mass of the reaction liquid before drying to obtain the solid content. It should be further clarified that the "parts by weight" used in the synthesis steps of the sodium lignosulfonate-doped polyaniline reaction solution described above uses the same standard as the "parts by weight" of each component in the formulations of blackening agent A and B, meaning that they represent the same actual mass. For example, in Example 1, 400 parts by weight of the synthesized reaction solution (i.e., 400 parts used in the formulation of solution B) corresponds to the amount of raw materials fed into the synthesis formulation, such as 18.6 parts by weight of sodium lignosulfonate, 18.6 parts by weight of aniline, and 45.6 parts by weight of ammonium persulfate. When scaling up or down the synthesis of the reaction solution, those skilled in the art should maintain the proportional relationship between each raw material in the synthesis formulation and the final obtained reaction solution to ensure that the solid content (8-15 wt%) of the reaction solution and the doping state of LGS-PANI are consistent.

[0018] Furthermore, the weight ratio of copper sulfate pentahydrate to ammonium tungstate is 4:5; the polyvinylpyrrolidone is PVPK30 with a molecular weight of 35,000-45,000; and the polyethylene glycol is PEG 4000 with a molecular weight of 3,500-4,500.

[0019] This invention also discloses a method for preparing the above-mentioned highly stable self-healing room temperature blackening agent, comprising the following steps: Take 60%-80% of the total amount of deionized water in the formula, and add sodium sulfite, disodium ethylenediaminetetraacetate, ammonium tungstate, nickel sulfate, and triethanolamine in sequence, stirring until dissolved after each addition; then slowly add copper sulfate pentahydrate, stirring until dissolved; then add ascorbic acid, stirring until dissolved; finally add ammonium thiosulfate, stirring until dissolved; add the remaining deionized water, stir well, and obtain solution A; Take 50%-70% of the total amount of deionized water in the formula, and add citric acid, sodium citrate, potassium hydrogen phthalate, and trisodium triacetate in sequence, stirring until dissolved after each addition; then add polyvinylpyrrolidone and stir until dissolved; then add polyoxyethylene octylphenol ether and stir evenly; then slowly add sodium lignosulfonate-doped polyaniline reaction solution at a dropping rate of 5-10 mL / min, stirring at 500-600 rpm for 30-60 min; add the remaining deionized water and stir evenly to obtain solution B. Slowly add solution B to solution A at a dropping rate of 10-15 mL / min and a stirring speed of 400-500 rpm for 20-30 min. Add hydroxyethyl cellulose and stir until dissolved. Add polyethylene glycol and stir until homogeneous. Let stand for 2-4 hours to obtain the finished blackening agent.

[0020] Furthermore, the operation is carried out at a temperature of 20-30℃, wherein the temperature does not exceed 30℃ when ammonium thiosulfate is added; all operations in step (2) are carried out at a temperature of 20-30℃, wherein the temperature is controlled at 20-25℃ when sodium lignosulfonate-doped polyaniline reaction solution is added dropwise; all operations in step (3) are carried out at a temperature of 20-30℃.

[0021] Furthermore, the base cellulose is pre-dissolved in warm water at 40-50℃ into a gel-like solution before being added to the mixing system.

[0022] The present invention also includes the application of a highly stable self-healing room temperature blackening agent in the blackening and rust prevention treatment of the outer wall surface of artillery barrels.

[0023] Furthermore, the blackening and rust prevention treatment of the outer wall surface of the artillery barrel includes pretreatment, blackening treatment, post-treatment, and sealing treatment; wherein, the blackening treatment is carried out by brushing or dipping, and the blackening agent is evenly coated on the outer wall surface of the barrel, with a reaction time of 8-15 minutes; the sealing treatment uses a high-temperature resistant sealant, which is dried and cured at 120-150℃ for 30-60 minutes; the high-temperature resistant sealant is an organosilicon-modified acrylic resin with a solid content of 30-50%, an organosilicon content of 20-40% of the resin solids, and a heat resistance temperature ≥250℃.

[0024] Compared with the prior art, the beneficial effects of the present invention are as follows: First, storage stability is significantly improved. By introducing triethanolamine and EDTA-2Na as transient complexing agents for copper ions, the redox reaction between copper sulfate pentahydrate and ammonium thiosulfate is effectively inhibited, preventing the formation of Cu2S precipitate; among them, EDTA-2Na has a significant effect on Cu ion stability. 2+ It possesses a high complexation stability constant, logK≈18.8, and primarily functions to stabilize copper ions during storage in solution A. Its complexation effect is more pronounced under weakly acidic to neutral conditions. Triethanolamine, in the initial stages of solution A preparation, i.e., when the pH is relatively high, can assist in the complexation of Cu. 2+ Meanwhile, triethanolamine, as an organic base, can moderately adjust the pH of solution A, slowing down the decomposition of ammonium thiosulfate caused by excessive local acidity. Furthermore, triethanolamine also has surface wetting properties, facilitating the uniform spreading of the blackening agent on the steel surface during subsequent blackening treatment. The combined use of the two complexing agents forms a synergistic protective mechanism during the storage of solution A, with EDTA-2Na as the primary complexing agent and triethanolamine as the auxiliary complexing agent, along with pH adjustment. The dual oxygen removal system of ascorbic acid and sodium sulfite inhibits the oxidative decomposition of ammonium thiosulfate; the dispersion protection of PVP K30 and Triton X-100, and the thickening and interfacial compatibility effects of HEC and PEG 4000 effectively prevent the aggregation and sedimentation of polyaniline particles. The combined effect extends the storage temperature range of the blackening agent from 20-35℃ to 5-45℃, and the sealed storage period at room temperature is extended to more than 6 months. This invention employs a separate packaging design for solutions A and B. Solution A contains copper ions and tungstate ions. Under acidic conditions, long-term coexistence of these two components may lead to a slow redox side reaction catalyzed by copper ions, resulting in the gradual consumption of the active ingredient and precipitation. Solution B contains sodium lignosulfonate-doped polyaniline reaction solution. This component has redox activity; if mixed with solution A for a long period, it will react slowly with the oxidizing components in solution A, causing a change in the doping state of the polyaniline and loss of its self-healing activity. Therefore, storing solutions A and B separately and mixing them only when needed is a key technical means to ensure a shelf life of more than 6 months for the blackening agent.

[0025] Secondly, the controllability of the synthesis is ensured. By introducing a triple buffer solution of citric acid-sodium citrate-potassium hydrogen phthalate, the pH of solution B is stabilized within the optimal range (3.8-4.5) for the conductive state of polyaniline (emerald green imine salt), avoiding dedoping problems caused by pH fluctuations. At the same time, sodium lignin sulfonate, as a macromolecular sulfonic acid dopant, can stably dope the polyaniline backbone within this pH range, ensuring that LGS-PANI remains in the emerald green imine salt form in the blackening film and ensuring self-healing activity. Through strict control of the dropping rate (5-10 mL / min) and stirring speed, the particle size and dispersion state of each batch of polyaniline dispersion are ensured to be consistent.

[0026] Third, improved low-temperature storage performance. By introducing PEG 4000 and utilizing its excellent antifreeze properties, the freezing point of the system is lowered to below -5°C, avoiding problems with component analysis during low-temperature storage.

[0027] Fourth, improved process reliability. The two-component (liquid A + liquid B) packaging design fundamentally avoids premature reactions between active components during storage; strict control of the addition sequence and process parameters ensures the consistency and reliability of each batch of product.

[0028] Fifth, this blackening agent is not only suitable for surface blackening and rust prevention treatment of military products such as the outer wall of artillery barrels, projectile bodies, firearm parts, structural components of military vehicles, and metal parts of ammunition packaging boxes, but also particularly effective for the outer wall of artillery barrels. Its self-healing function can effectively repair scratches generated during transportation, loading, and maintenance. Combined with subsequent sealing treatment, it can significantly extend the rust prevention and maintenance cycle of the barrel's outer wall. Simultaneously, the blackening film is a uniform glossy black with excellent matting properties, reducing the detectability of the barrel's outer wall under sunlight and providing a certain degree of camouflage assistance. Attached Figure Description

[0029] The invention will be further described below with reference to the accompanying drawings: Figure 1 This is a schematic diagram of the preparation process of the blackening agent of the present invention.

[0030] Figure 2 A schematic diagram of the preparation process for liquid A.

[0031] Figure 3 A schematic diagram of the process flow for preparing solution B.

[0032] Figure 4 This is a schematic diagram of the mixing process of liquid A and liquid B. Detailed Implementation

[0033] The technical solution of the present invention will be further described in detail below with reference to specific embodiments, but the scope of protection of the present invention is not limited thereto.

[0034] Example 1: Blackening treatment of cold-drawn steel pipe surface: refer to Figure 1 A highly stable, self-healing, room-temperature blackening agent, which is made by mixing liquid A and liquid B during use, and adding hydroxyethyl cellulose and polyethylene glycol.

[0035] Solution A comprises the following components by weight: 80 parts copper sulfate pentahydrate, 100 parts ammonium tungstate, 20 parts nickel sulfate, 60 parts ammonium thiosulfate, 15 parts triethanolamine, 5 parts disodium ethylenediaminetetraacetate, 4 parts ascorbic acid, 6 parts sodium sulfite, and 1000 parts deionized water. The mechanism of action of nickel sulfate in Solution A of this invention is as follows: During the blackening and film-forming process, Ni…2+ Ni ions, along with copper ions and tungstate ions, participate in the chemical transformation reactions on the surface of steel. 2+ It can partially replace iron atoms on the surface of the iron substrate, forming Ni-Fe alloy microregions. These microregions serve as nucleation centers for subsequent copper-tungsten composite conversion films, promoting uniform film deposition. Simultaneously, Ni... 2+ During film formation, nickel sulfate is partially reduced to metallic nickel and embedded in the conversion film, enhancing the film's density and corrosion resistance. When the amount of nickel sulfate is less than 5 parts, the nucleation-promoting effect is not significant, and the film uniformity decreases; when it is more than 100 parts, excessive nickel deposition occurs, causing the film color to deviate from deep black and appear grayish-black, and increasing costs. The preferred amount of nickel sulfate is 10-50 parts.

[0036] Solution B comprises the following components by weight: 40 parts of trisodium triacetate, 400 parts of sodium lignosulfonate-doped polyaniline reaction solution, 12 parts of polyvinylpyrrolidone (PVP K30), 6 parts of polyoxyethylene octylphenol ether (Triton X-100), 3 parts of citric acid, 7 parts of sodium citrate, 4 parts of potassium hydrogen phthalate, and 800 parts of deionized water.

[0037] When mixing solution A and solution B, 10 parts by weight of hydroxyethyl cellulose (HEC) and 20 parts by weight of polyethylene glycol (PEG 4000) are also added. The "parts by weight" of hydroxyethyl cellulose and polyethylene glycol mentioned above are based on the same "parts by weight" of each component in the solution A formulation.

[0038] Synthesis of the sodium lignosulfonate-doped polyaniline reaction solution: Take 18.6 parts by weight of sodium lignosulfonate and pour it into 100 parts by weight of 1 mol / L sulfuric acid solution, and stir evenly; then take 18.6 parts by weight of aniline, slowly add it and stir evenly to prepare solution D; take 45.6 parts by weight of ammonium persulfate and dissolve it in 100 parts by weight of 1 mol / L citric acid solution to obtain ammonium persulfate-citric acid solution, add it dropwise to solution D, and carry out the reaction at 0-5℃ with thorough stirring; continue stirring the reaction at 20-30℃ for 8-10 hours until the color of the reaction solution is stable to dark green and the pH value is stable in the range of 4.5-5.5, thus obtaining the sodium lignosulfonate-doped polyaniline reaction solution.

[0039] refer to Figure 2 , 3 4. The specific preparation method is as follows: (1) Preparation of solution A: Take 70% of the total amount of deionized water in the formula, and add 6 parts of sodium sulfite, 5 parts of EDTA-2Na, 100 parts of ammonium tungstate, and 20 parts of nickel sulfate in sequence under stirring at 25℃ and 300 rpm, stirring for 5-15 minutes after each addition until dissolved; add 15 parts of triethanolamine and stir for 5 minutes; slowly add 80 parts of copper sulfate pentahydrate and stir for 15 minutes until completely dissolved; add 4 parts of ascorbic acid and stir for 10 minutes; add 60 parts of ammonium thiosulfate and stir for 10 minutes; add deionized water to make up the difference, stir evenly, and obtain solution A.

[0040] (2) Preparation of solution B: Take 60% of the total amount of deionized water in the formula, and add 3 parts of citric acid, 7 parts of sodium citrate, 4 parts of potassium hydrogen phthalate, and 40 parts of trisodium triacetate in sequence under stirring at 25℃ and 300 rpm. Stir for 5-15 min after each addition until dissolved. Add 12 parts of PVP K30 and stir for 15-20 min until completely dissolved. Add 6 parts of Triton X-100 and stir for 5-10 min. Slowly add 400 parts of sodium lignosulfonate-doped polyaniline reaction solution at 20-25℃ and 550 rpm using a peristaltic pump with a dropping rate of 8 mL / min and stir for 40 min. Add deionized water to make up the difference and stir evenly to obtain solution B.

[0041] (3) Mixing: Add solution B slowly to solution A at a rate of 12 mL / min, and stir at 25°C and 450 rpm for 25 min; pre-dissolve 10 parts of HEC in 50 parts of deionized water at 45°C to form a gel, add it to the mixture, and stir for 25 min; add 20 parts of PEG 4000, and stir for 15 min; let stand and mature for 3 hours to obtain a dark green uniform blackening agent product.

[0042] Blackening process for cold-drawn steel pipes: After degreasing, washing with water, pickling (10% hydrochloric acid, 1-3 min at room temperature), and washing with water, immerse the 20# cold-drawn steel pipe in the above-mentioned blackening agent for 5 min at room temperature, take it out and wash it with water, scald it with hot water, immerse it in the sealing agent, i.e., water-based acrylic resin sealing liquid, for 2 min, and dry it at a low temperature of 60℃ for 15 min to obtain a uniform bright black film.

[0043] Example 2: Blackening and rust prevention treatment on the outer wall surface of the artillery barrel.

[0044] The same blackening agent formulation and preparation method as in Example 1 were used.

[0045] Blackening process for the outer wall of artillery barrel: (1) Pretreatment: After degreasing the outer wall of the gun barrel with a diameter ≥100mm and made of PCrNi3MoV gun steel with organic solvent, it is immersed in an alkaline cleaning agent composed of sodium silicate 20g / L + sodium hydroxide 10g / L + surfactant 5g / L at 60℃ for 10min. Then, it is acid-washed with 10% hydrochloric acid containing 0.5% hexamethylenetetramine corrosion inhibitor at room temperature for 1-3min to remove the surface oxide scale, and then washed with water until neutral.

[0046] (2) Blackening treatment: Apply the blackening agent evenly to the outer wall surface of the tube using a brush or immersion method. For brush application, use a wool brush to apply the blackening agent evenly along the tube axis three times, with a 3-minute interval between each application to allow the blackening agent to fully react. The total reaction time is controlled within 15 minutes. During the reaction, the color of the outer wall of the tube gradually changes from a silvery-white metallic luster to a bluish-black, eventually forming a uniform dark black film.

[0047] (3) Post-treatment: After blackening is completed, rinse the surface with clean water to remove any remaining blackening agent, and then scald with 80℃ hot water for 2 minutes to further densify the film. Allow it to air dry or blow it dry with compressed air.

[0048] (4) Sealing treatment: Immerse the outer wall of the gun barrel, which has formed a black film, in a high-temperature resistant sealant for 5 minutes. After removal, allow it to dry at room temperature for 15 minutes, and then cure it at 150°C for 40 minutes. The high-temperature resistant sealant is an organosilicon-modified acrylic resin (Hubei Longsheng Sihai New Material Co., Ltd., model SH-9606).

[0049] Example 3: Blackening and rust prevention treatment on the surface of the shell body.

[0050] The same blackening agent formulation and preparation method as in Example 1 were used.

[0051] After the shell body made of 45# steel is degreased, washed with water, and pickled, it is immersed in a blackening agent and soaked at room temperature for 4-8 minutes. It is then taken out, washed with water, scalded with hot water, and immersed in the sealing agent described in Example 2 for 2 minutes. After being taken out and dried, a uniform glossy black film is obtained.

[0052] Example 4: Blackening and rust prevention treatment of firearm parts.

[0053] The same blackening agent formulation and preparation method as in Example 1 were used.

[0054] Gun parts made of 30CrMnSiA alloy steel were degreased, washed with water, and pickled. They were then immersed in a blackening agent at room temperature for 6 minutes, removed, washed with water, scalded with hot water, and immersed in the sealing agent described in Example 2 for 2 minutes. After being removed and dried, a uniform glossy black film was obtained.

[0055] Example 5: The difference from Example 1 is as follows: Solution A contains 10 parts triethanolamine, 3 parts EDTA-2Na, 2 parts ascorbic acid, and 5 parts sodium sulfite; Solution B contains 8 parts PVP K30, 4 parts Triton X-100, 2 parts citric acid, 5 parts sodium citrate, and 3 parts potassium hydrogen phthalate; when mixed, HEC contains 5 parts and PEG 4000 contains 15 parts. The rest is the same as in Example 1.

[0056] Example 6: The difference from Example 1 is as follows: Solution A contains 20 parts triethanolamine, 10 parts EDTA-2Na, 6 parts ascorbic acid, and 10 parts sodium sulfite; Solution B contains 18 parts PVP K30, 8 parts Triton X-100, 5 parts citric acid, 10 parts sodium citrate, and 6 parts potassium hydrogen phthalate; when mixed, HEC contains 15 parts and PEG 4000 contains 30 parts. The rest is the same as in Example 1.

[0057] Example 7: The difference from Example 1 is that: in solution A, there are 40 parts of copper sulfate pentahydrate, 50 parts of ammonium tungstate, 10 parts of nickel sulfate, and 40 parts of ammonium thiosulfate; in solution B, there are 200 parts of sodium lignosulfonate-doped polyaniline reaction solution and 20 parts of trisodium triacetate; the rest is the same as in Example 1.

[0058] Example 8: The difference from Example 1 is that: in solution A, there are 100 parts of copper sulfate pentahydrate, 150 parts of ammonium tungstate, 50 parts of nickel sulfate, and 100 parts of ammonium thiosulfate; in solution B, there are 600 parts of sodium lignosulfonate-doped polyaniline reaction solution and 80 parts of trisodium triacetate; the rest is the same as in Example 1.

[0059] Comparative Example 1: In this comparative example, a room temperature blackening agent is disclosed, comprising the following components: 80 parts by weight of copper sulfate pentahydrate, 100 parts by weight of ammonium tungstate, 400 parts by weight of sodium lignosulfonate-doped polyaniline reaction solution, 20 parts by weight of nickel sulfate, 60 parts by weight of ammonium thiosulfate, and 40 parts by weight of trisodium triacetate.

[0060] The sodium lignosulfonate-doped polyaniline reaction solution can be synthesized by the following method: Weigh 18.6 parts by weight of sodium lignosulfonate and pour it into 100 parts by weight of 1 mol / L sulfuric acid solution. Stir and mix thoroughly. Then take 18.6 parts by weight of aniline and slowly add it to the mixed solution while stirring. Stir and mix thoroughly to prepare solution D.

[0061] Weigh 45.6 parts by weight of ammonium persulfate and dissolve it in 100 parts of 1 mol / L citric acid solution to obtain ammonium persulfate-citric acid solution. Add the ammonium persulfate-citric acid solution dropwise to solution D. The reaction system is carried out at a temperature of 0-5℃ and stirred thoroughly. Allow it to react further at room temperature to obtain the target reaction solution.

[0062] Without adding any stabilizing additives, it is used for blackening the outer wall of the artillery barrel, and the processing technology is the same as in Examples 1 and 2.

[0063] Performance testing: The following performance tests were performed on the blackening agents and blackening films obtained in Examples 1-8 and Comparative Example 1: (1) Storage stability test: After sealing liquid A and liquid B respectively, they were stored at 5℃, 25℃ and 45℃ respectively. On the 30th, 60th, 90th, 120th, 150th and 180th days of storage, liquid A and liquid B under each temperature condition were taken and mixed according to the mixing ratio of Example 1, that is, liquid A: liquid B = 1:2 mass ratio. The blackening film was prepared according to the above blackening film performance test method and the performance was tested. If the film performance meets all of the following conditions compared with the initial state, the storage stability is deemed to be qualified: (a) The film appearance is still uniformly bright black, with no visible color difference or mottled spots; (b) The adhesion grade has not decreased (i.e., it remains at grade 0); (c) The 3% copper sulfate dripping time is not less than 80% of the initial value (i.e. ≥60 seconds); (d) The 3% NaCl immersion corrosion resistance time is not less than 80% of the initial value (i.e. ≥64 hours). Meanwhile, observe the appearance of solutions A and B at each time point. Solution A should remain clear and transparent, without precipitation, turbidity, or discoloration; solution B should remain a uniform dark green, without precipitation, stratification, or discoloration. If the appearance of solutions A and B meets the above requirements, and the resulting black film after mixing meets the above four performance criteria, then the storage stability is deemed qualified. Hydroxyethyl cellulose and polyethylene glycol are packaged and stored separately in solid powder form. At each time point test, newly opened hydroxyethyl cellulose and polyethylene glycol are added to the mixing system according to the formula amount.

[0064] (2) Basic performance test of blackening film: Film appearance inspection: Under natural diffused light (illuminance not less than 300 lx), observe the blackened film surface at a visual distance of 300 mm. The film layer should be uniform, continuous, without flow marks, pinholes, peeling, or flaking. The color should be uniformly bright black or dark black, without obvious color difference or mottled phenomena.

[0065] 3% Copper Sulfate Droplet Density Test: Using a dropper, drop a 3% (mass fraction) copper sulfate solution (CuSO4·5H2O, analytical grade, prepared with deionized water) onto the surface of the blackened film. Test at least three different locations for each sample. The droplet diameter should be approximately 5–8 mm. Allow the film to stand at room temperature (20–25℃) and record the time (s) required for the droplet to change from blue to dark red (copper precipitation). Take the arithmetic mean. A droplet time ≥ 60 s is considered acceptable for density.

[0066] Abrasion resistance test of the film layer: The drop test method was used. 200-mesh No. 00 corundum was dropped freely from a height of 500 mm through a guide tube with an inner diameter of φ5-6 mm to impact the film layer surface at an impact velocity of approximately 30-40 g per minute. The amount of abrasive (g) consumed when the film layer was worn through and the base metal was exposed was recorded. The amount of abrasive dropped characterizes the abrasion resistance of the film layer. The greater the amount of abrasive dropped, the better the abrasion resistance.

[0067] Corrosion resistance test by immersion in 3% sodium chloride solution: Prepare a 3% (mass fraction) sodium chloride (NaCl, analytical grade) solution, completely immerse the blackened sample in the solution, and allow it to stand at room temperature (20-25℃). Observe the surface changes of the film every 12 hours. Record the changes from the start of immersion until the first appearance of rust spots or discoloration (area ≥1 mm) on the film surface. 2 The corrosion resistance time (h) is specified. A corrosion resistance time of ≥24h is considered acceptable.

[0068] (3) Low temperature storage test: Store the blackening agent at -5℃ for 7 days and observe whether ice crystals precipitate or components separate.

[0069] (4) Self-healing performance test: Cross-cutting marks with a width of about 30-50 μm and a length of about 20 mm were made on the surface of the blackened film with a cross-cutting knife to ensure that the marks penetrated the film layer and reached the substrate. The scratched sample was placed in a 3.5% NaCl solution and immersed at 25°C. It was taken out after 24h, 48h, 72h and 120h respectively, rinsed with deionized water and dried with cold air: (1) the color change and corrosion of the scratched area were observed under an optical microscope; (2) the charge transfer resistance Rct of the film layer at the scratched area was tested by electrochemical impedance spectroscopy (EIS). The electrochemical criterion for the completion of self-healing was that Rct recovered to more than 80% of the initial value of Rct of the intact film layer before the scratch. It should be noted that the full immersion condition of 3.5% NaCl solution was used as an accelerated test method in this test. This condition simulates the harsh corrosion conditions of the blackened film in a marine atmospheric environment, such as naval artillery or salt spray. Compared to atmospheric exposure, full immersion accelerates the corrosion micro-cell reaction, allowing the self-healing effect to appear in a shorter time. Those skilled in the art will understand that under actual atmospheric exposure conditions, the self-healing rate may vary due to lower corrosive medium concentrations and different oxygen diffusion rates, but the self-healing mechanism, namely the redox cycle of the emerald green imine salt, remains consistent.

[0070] (4-2) Cyclic Self-Healing Performance Test: To further verify the cyclical nature of the self-healing function, a repeated scratch-repair test was conducted on the blackened film sample of Example 1. Cross-cuts approximately 30-50 μm wide and 20 mm long were made on the surface of the blackened film using a cross-cutting knife. The sample was then immersed in a 3.5% NaCl solution at 25°C for 120 h. After the first repair, the sample was removed, rinsed with deionized water, and dried with cold air. Under an optical microscope, it was confirmed that the color at the scratched area had recovered and there was no rust. Then, scratches of the same specifications were made again at the same location, and the above repair process was repeated for a total of 3 cycles. After each cycle of repair, the color recovery and rust at the scratched area were observed, and the Rct was tested using EIS. The test results showed that after 3 cycles of scratch-repair, the color at the scratched area of ​​the blackened film of Example 1 recovered after 120 h of each repair, with no rust, and the Rct recovered to more than 80% of its initial value, verifying that the self-healing function has good cyclical nature.

[0071] (5) Suitability test of the outer wall of the artillery barrel: Thermal shock test: The blackened film sample on the outer wall of the tube prepared in Example 2 was placed in an oven and heated to 200°C at a rate of 10°C / min. After holding at this temperature for 30 minutes, the sample was removed and allowed to cool naturally to room temperature. The thermal cycle was repeated 10 times, and the film was observed to see if it cracked, peeled, or fell off.

[0072] Salt spray resistance test: A neutral salt spray test (NSS) was used. The test solution was a 5% (mass fraction) sodium chloride solution (prepared with analytical grade sodium chloride and deionized water, with the pH value controlled within the range of 6.5 to 7.2). The temperature inside the test chamber was controlled at (35±1)℃, and the salt spray deposition rate was controlled at 1.0 to 2.0 mL / (80cm²). 2 • h), the sample is placed at an angle of 15° to 30° to the vertical direction and sprayed continuously for 240 hours. After the test, the sample is removed, the surface salt deposits are rinsed with flowing deionized water, and dried with cold air. The corrosion of the film is visually observed under natural light, and the number and area percentage of rust spots are recorded. Acceptance criteria: After 240 hours, the area of ​​rust spots on the film surface does not exceed 5% of the total area, and there is no blistering, peeling, or flaking.

[0073] Humidity and heat resistance test: An alternating damp heat test method was adopted. Test conditions: the temperature cyclically changed between 25℃ and 55℃ and back to 25℃, and the relative humidity was maintained at (95±3)%. Each cycle was 24 hours, consisting of a 3-hour heating phase (25℃ to 55℃), a 9-hour constant temperature phase at 55℃ (humidity ≥95%), a 3-hour cooling phase (55℃ to 25℃), and a 9-hour constant temperature phase at 25℃ (humidity ≥95%); a total of 10 cycles (240 hours). After the test, the samples were removed and allowed to recover to room temperature for 2 hours. The film was then visually inspected for blistering, peeling, cracking, chalking, or discoloration. Pass / Fail criteria: No blistering, peeling, or cracking of the film after 10 cycles.

[0074] Outdoor exposure test: The blackened film sample on the outer wall of the tube prepared in Example 2 was placed in an outdoor exposure field (subtropical climate), facing south at a 45° angle, and exposed for 6 months to observe the corrosion, chalking and discoloration of the film.

[0075] The test results are shown in the table below: ; ; Table 1 Storage stability of blackening agents and basic properties of blackening films in each embodiment Note 1: ">180 days without precipitation" means that under their respective storage conditions, neither solution A nor solution B showed any precipitation by the 180-day observation period, and the black film performance after mixing met the judgment criteria. The storage stability test cutoff time was 180 days. Storage periods exceeding 180 days were not verified in this test, but based on the fact that there was no obvious decline trend in various performance indicators at 180 days, those skilled in the art can reasonably expect that the actual storage period can be further extended.

[0076] ; Table 2. Results of the test on the suitability of the blackening film on the outer wall of the artillery barrel. It can be seen from the above table: (1) The blackening agents of the various embodiments of the present invention are significantly better than those of Comparative Example 1 in terms of storage stability. The storage period at room temperature of 25°C is extended from about 30 days to more than 180 days. The storage stability at extreme temperatures of 5°C and 45°C is also greatly improved. No ice crystals are precipitated when stored at low temperature of -5°C.

[0077] (2) The basic performance indicators of the blackened film were not reduced by the addition of stabilizing agents, but were slightly improved in terms of wear resistance and corrosion resistance. This is due to the enhancing effect of HEC and PEG 4000 on the film density and cohesion.

[0078] (3) In the application to the outer wall of artillery barrels, Example 2, after sealing treatment, exhibited excellent thermal shock resistance (no cracking or peeling after 10 cycles at 200℃), good resistance to damp heat, and no powdering or pitting after 6 months of outdoor exposure, significantly better than Comparative Example 1. This indicates that the blackening agent, combined with the high-temperature resistant sealant, can effectively meet the rust prevention requirements of the outer wall of artillery barrels.

[0079] (4) The self-healing function performed well in various application scenarios. The color of the scratch was restored within 72 hours and there was no rust, which verified that the self-healing mechanism of sodium lignosulfonate doped polyaniline is effective under normal temperature and medium temperature conditions.

[0080] The above description is merely a preferred embodiment of the present invention and is not intended to limit the scope of the invention. Any equivalent transformations or modifications made to the technical solutions of the present invention without departing from the inventive concept should be included within the protection scope of the present invention.

Claims

1. A highly stable, self-healing, room-temperature blackening agent, characterized in that, The blackening agent is prepared by mixing liquid A and liquid B during use, and thickening and anti-settling agents and interface compatibilizers are added; wherein: The A solution comprises the following components by weight: 10-200 parts copper sulfate pentahydrate, 20-300 parts ammonium tungstate, 5-100 parts nickel sulfate, 10-150 parts ammonium thiosulfate, 5-45 parts copper ion transient complexing agent, 4-23 parts antioxidant, and 500-1200 parts deionized water. The B solution comprises the following components by weight: 5-100 parts of trisodium triacetate, 50-1000 parts of sodium lignosulfonate-doped polyaniline reaction solution, 7-37 parts of dispersant stabilizer, 6-31 parts of buffer solution, and 400-1000 parts of deionized water. The thickening and anti-settling agent is 3-20 parts by weight of hydroxyethyl cellulose; the interface compatibilizer is 10-40 parts by weight of polyethylene glycol; the weight parts of liquid A, liquid B, thickening and anti-settling agent, and interface compatibilizer are based on the same standard; liquid A and liquid B are mixed at a mass ratio of liquid A:liquid B = 1:1.5-3 when used.

2. The high-stability self-healing room-temperature blackening agent according to claim 1, characterized in that: The copper ion transient complexing agent is a compound of triethanolamine and disodium ethylenediaminetetraacetate, wherein triethanolamine is 3-30 parts and disodium ethylenediaminetetraacetate is 2-15 parts; the antioxidant is a compound of ascorbic acid and sodium sulfite, wherein ascorbic acid is 1-8 parts and sodium sulfite is 3-15 parts.

3. The high-stability self-healing room-temperature blackening agent according to claim 1, characterized in that: The dispersant stabilizer is a compound of polyvinylpyrrolidone and polyoxyethylene octylphenol ether, wherein 5-25 parts of polyvinylpyrrolidone and 2-12 parts of polyoxyethylene octylphenol ether are present; the buffer solution is a compound of citric acid, sodium citrate and potassium hydrogen phthalate, wherein 1-8 parts of citric acid, 3-15 parts of sodium citrate and 2-8 parts of potassium hydrogen phthalate are present.

4. The high-stability self-healing room-temperature blackening agent according to claim 1, characterized in that: The sodium lignosulfonate-doped polyaniline reaction solution is synthesized by emulsion polymerization. The weight ratio of sodium lignosulfonate to aniline in the synthesis components is 1:

1. The synthesis steps include: taking 13-24 parts by weight of sodium lignosulfonate and pouring it into 70-130 parts by weight of 0.8-1.2 mol / L sulfuric acid solution, and stirring evenly; then taking 13-24 parts by weight of aniline, slowly adding it and stirring evenly to prepare solution D; taking 32-59 parts by weight of ammonium persulfate and dissolving it in 70-130 parts by weight of 0.8-1.2 mol / L citric acid solution to obtain ammonium persulfate-citric acid solution, adding it dropwise to solution D, and carrying out the reaction at 0-5℃ with thorough stirring; continuing to stir the reaction at 20-30℃ for 6-12 hours until the color of the reaction solution is stable at a dark green and the pH value is stable in the range of 4.5-5.5, thus obtaining the sodium lignosulfonate-doped polyaniline reaction solution.

5. The high-stability self-healing room-temperature blackening agent according to claim 1, characterized in that: The weight ratio of copper sulfate pentahydrate to ammonium tungstate is 4:5; the polyvinylpyrrolidone is PVP K30 with a molecular weight of 35,000-45,000; and the polyethylene glycol is PEG 4000 with a molecular weight of 3,500-4,500.

6. The method for preparing the highly stable self-healing room temperature blackening agent according to any one of claims 1 to 5, characterized in that, Includes the following steps: Take 60%-80% of the total amount of deionized water in the formula, and add sodium sulfite, disodium ethylenediaminetetraacetate, ammonium tungstate, nickel sulfate, and triethanolamine in sequence, stirring until dissolved after each addition; then slowly add copper sulfate pentahydrate, stirring until dissolved; then add ascorbic acid, stirring until dissolved; finally add ammonium thiosulfate, stirring until dissolved; add the remaining deionized water, stir well, and obtain solution A; Take 50%-70% of the total amount of deionized water in the formula, and add citric acid, sodium citrate, potassium hydrogen phthalate, and trisodium triacetate in sequence, stirring until dissolved after each addition; then add polyvinylpyrrolidone and stir until dissolved; then add polyoxyethylene octylphenol ether and stir evenly; then slowly add sodium lignosulfonate-doped polyaniline reaction solution at a dropping rate of 5-10 mL / min, stirring at 500-600 rpm for 30-60 min; add the remaining deionized water and stir evenly to obtain solution B. Slowly add solution B to solution A at a dropping rate of 10-15 mL / min and a stirring speed of 400-500 rpm for 20-30 min. Add hydroxyethyl cellulose and stir until dissolved. Add polyethylene glycol and stir until homogeneous. Let stand for 2-4 hours to obtain the finished blackening agent.

7. The preparation method according to claim 6, characterized in that: In step (1), all operations are carried out at a temperature of 20-30℃, and the temperature does not exceed 30℃ when adding ammonium thiosulfate; in step (2), all operations are carried out at a temperature of 20-30℃, and the temperature is controlled at 20-25℃ when adding sodium lignosulfonate-doped polyaniline reaction solution; in step (3), all operations are carried out at a temperature of 20-30℃.

8. The preparation method according to claim 6, characterized in that: The hydroxyethyl cellulose mentioned in step (3) is pre-dissolved in warm water at 40-50℃ into a gel before being added to the mixing system.

9. The application of the high-stability self-healing room-temperature blackening agent according to any one of claims 1 to 5 in the blackening and rust prevention treatment of the outer wall surface of artillery barrels.

10. The application according to claim 9, characterized in that, The blackening and rust prevention treatment of the outer wall surface of the artillery barrel includes pretreatment, blackening treatment, post-treatment, and sealing treatment. The blackening treatment involves brushing or dipping to evenly coat the blackening agent onto the outer wall surface of the barrel, with a reaction time of 8-15 minutes. The sealing treatment uses a high-temperature resistant sealant, which is dried and cured at 120-150℃ for 30-60 minutes. The high-temperature resistant sealant is an organosilicon-modified acrylic resin with a solid content of 30-50%, an organosilicon content of 20-40% of the resin solids, and a heat resistance temperature ≥250℃.

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