A Chemical Blackening Process for Stainless Steel and Its Application

Abstract

This application relates to the field of material surface treatment, and specifically discloses a chemical blackening process and application of stainless steel. The chemical blackening process of stainless steel is as follows: degrease the stainless steel workpiece, and then perform activation treatment and sensitization treatment in sequence; the plating solution components include nickel sulfate, sodium hypophosphite, sodium citrate, and carbon nanotubes. Control the pH value of the plating solution at 4.8 - 5.2 and the temperature at 90 - 92 °C. Place the workpiece in the plating solution, and after plating for 1 - 2 hours, obtain the blackened stainless steel workpiece. The chemical blackening process of stainless steel in this application can be used for components such as shielding parts of camera modules and reflection parts of millimeter-wave radars, and has the advantages of high stray light suppression rate, high millimeter-wave reflectivity, and high coating durability.

Description

Technical Field

[0001] The present application relates to the field of material surface treatment, and more specifically, to a chemical blackening process and application of stainless steel. Background Art

[0002] In the field of camera modules, light control has a great impact on the imaging effect. Once stray light invades, halos will appear in the image, just like covering the picture with a hazy veil, blurring the details; the contrast is reduced, the distinction between the bright and dark parts is no longer clear, and the sense of layering of the picture is missing. The currently used traditional shielding materials perform poorly in light absorption performance and cannot effectively block stray light. In complex environments such as high temperature, high humidity, and strong ultraviolet rays, problems such as aging and deformation are likely to occur, greatly reducing the durability and making it difficult to meet the increasing market demand for imaging quality.

[0003] Millimeter-wave radars are widely used in fields such as intelligent transportation, autonomous driving, and security monitoring. Its detection accuracy and distance depend on the reflection and directional ability of the reflecting component to millimeter-wave signals. However, the reflection characteristics of existing materials have shortcomings. Facing the increasing requirements for high-precision detection, the reflection characteristics of existing materials will be weakened and affected to varying degrees in harsh environments such as extreme cold, extreme heat, and dust, severely restricting the application expansion of millimeter-wave radars.

[0004] Due to its advantages such as high strength, corrosion resistance, and stable performance, stainless steel has become an excellent base material for manufacturing these two types of components. However, the optical and electromagnetic characteristics of the original stainless steel surface are difficult to meet the strict light control requirements of camera modules and the high requirements for signal reflection of millimeter-wave radars. It is urgent to optimize its surface characteristics through a special blackening process to promote the further development and breakthrough of related technologies. Summary of the Invention

[0005] In order to provide a stainless steel surface blackening process applicable to shielding components of camera modules and reflecting components of millimeter-wave radars, the present application provides a chemical blackening process and application of stainless steel.

[0006] The chemical blackening process of stainless steel provided by the present application adopts the following technical solutions:

[0007] A chemical blackening process of stainless steel includes the following steps:

[0008] Put the stainless steel workpiece into a solution containing a surfactant and an alkaline auxiliary agent for degreasing, and process it for 15 - 30 minutes under the conditions of 40 - 50 kHz ultrasonic wave and 55 - 65 °C;

[0009] Immerse the degreased workpiece in the activation solution and soak it at room temperature for 40 - 50 minutes, then put the workpiece into the sensitizing solution and soak it at 60 - 80 °C for 40 - 60 minutes;

[0010] The plating solution components include nickel sulfate, sodium hypophosphite, sodium citrate, and carbon nanotubes. The pH value of the plating solution is controlled at 4.8 - 5.2, and the temperature is 90 - 92 °C. The workpiece is placed in the plating solution, and after plating for 1 - 2 hours, a blackened stainless steel workpiece is obtained.

[0011] By adopting the above technical solution, ultrasonic-assisted alkaline degreasing is used and processed for 15 - 30 minutes under the conditions of 40 - 50 kHz ultrasonic waves and 55 - 65 °C. The cavitation effect generated by the ultrasonic waves can effectively peel off the oil stains tightly attached to the surface of the stainless steel. The alkaline auxiliary agent undergoes a saponification reaction with the oil stains, converting the grease into substances soluble in water. The surfactant further reduces the interfacial tension between the oil stains and the stainless steel surface, making it easier for the oil stains to detach. Thorough degreasing provides a clean and pollution-free surface for subsequent activation, sensitization, and electroless plating. Immersing in the activation solution at room temperature for 40 - 50 minutes can form micro-etching pits on the surface of the stainless steel, increasing the active sites. These micro-etching pits greatly increase the specific surface area of the stainless steel surface, enabling the reactants to come into contact and react more fully during the subsequent sensitization and electroless plating processes. Immersing in the sensitizing solution at 60 - 80 °C for 40 - 60 minutes can adsorb catalytically active tin ions on the surface, providing a catalytic center for electroless plating. The pH value of the plating solution is controlled at 4.8 - 5.2, and the temperature is 90 - 92 °C, and plating is carried out for 1 - 2 hours. Under these conditions, components such as nickel sulfate, sodium hypophosphite, and sodium citrate in the plating solution can undergo stable chemical reactions. Sodium hypophosphite reduces nickel ions to form a coating, and sodium citrate stabilizes the nickel ions in the plating solution to prevent their premature precipitation. The appropriate pH value and temperature ensure the stability of the plating solution and the high efficiency of the reaction, thereby obtaining a blackened coating that is uniform, dense, and has good optical and electromagnetic properties.

[0012] Optionally, the plating solution components by weight include 25 - 35 parts of nickel sulfate, 20 - 30 parts of sodium hypophosphite, 10 - 15 parts of sodium citrate, 2 - 6 parts of carbon nanotubes, and 400 - 600 parts of deionized water.

[0013] By adopting the above technical solution, nickel sulfate provides sufficient nickel ions to ensure the thickness and quality of the coating; sodium hypophosphite, as a reducing agent, its proportion ensures sufficient reducing ability to reduce nickel ions to metallic nickel; sodium citrate, as a complexing agent, can effectively stabilize the nickel ions in the plating solution to prevent their premature precipitation; carbon nanotubes can optimize the light absorption and reflection characteristics of the coating and, in synergy with other components, enhance the comprehensive performance of the coating.

[0014] Optionally, the plating solution components further include 2 - 4 parts of nano-titanium dioxide.

[0015] By adopting the above technical solution, 2-4 parts of nano-titanium dioxide are added to the plating solution. Nano-titanium dioxide has excellent optical properties and chemical stability. It acts synergistically with carbon nanotubes, which can further enhance the ultraviolet absorption capacity of the composite coating, improve the optical stability of the coating in ultraviolet environments such as outdoors, and broaden the application scenarios of blackened stainless steel workpieces. For example, in outdoor camera module shielding components, it can effectively resist the damage of ultraviolet rays to the coating and extend the service life of the components.

[0016] Optionally, the carbon nanotubes are surface-modified. The specific method for surface-modifying the carbon nanotubes is as follows:

[0017] Add the carbon nanotubes to absolute ethanol and disperse them by ultrasonic treatment to obtain a carbon nanotube suspension;

[0018] Add nitric acid to the carbon nanotube suspension to make the concentration of nitric acid reach 3-5 mol / L, and stir and react at 50-60 °C for 2-3 hours. After the reaction, centrifuge and wash until neutral;

[0019] Prepare a solution of polydiallyldimethylammonium chloride with a concentration of 0.1-0.3 g / L, and prepare a solution of an organic dye with sulfonic acid groups with a concentration of 0.05-0.1 g / L;

[0020] Add the carbon nanotubes to the polydiallyldimethylammonium chloride solution, stir and react at 20-25 °C for 1-2 hours, and the stirring speed is 200-300 r / min. After the reaction, centrifuge and wash. Then add the carbon nanotubes to the organic dye solution with sulfonic acid groups, stir and react for 1-2 hours, and centrifuge and wash again to obtain the modified carbon nanotubes;

[0021] Vacuum-dry the modified carbon nanotubes at 60-80 °C for 6-8 hours.

[0022] By adopting the above technical solution, adding absolute ethanol for ultrasonic dispersion can effectively break the agglomeration of carbon nanotubes and make them evenly dispersed; adding nitric acid for oxidation treatment introduces oxygen-containing functional groups on the surface of carbon nanotubes, increases its surface activity, and is beneficial to subsequent modification. By alternately adsorbing polydiallyldimethylammonium chloride and an organic dye with sulfonic acid groups, a double-layer structure is formed. Polydiallyldimethylammonium chloride is positively charged and is adsorbed to the negatively charged carbon nanotubes and organic dye through electrostatic interaction. This self-assembled structure improves the dispersion of carbon nanotubes in the plating solution by more than 30%, enhances its binding force with the black nickel coating, so that the carbon nanotubes can be more evenly embedded in the coating and fully play its role in optimizing the coating performance. Vacuum-drying at 60-80 °C for 6-8 hours can remove the moisture and impurities on the surface of carbon nanotubes and ensure its stability in the plating solution and compatibility with other components.

[0023] Optionally, the workpiece is placed in the plating solution and assisted by a pulsed current. The pulse period of the pulsed current is 0.1 - 0.5 s, and the pulse duty cycle is 30 - 50%.

[0024] By adopting the above technical solution, during electroless plating, under a conventional direct current, the deposition of ions in the plating solution on the electrode surface is relatively continuous and stable, and it is easy to form grains with larger sizes. When assisted by a pulsed current with a pulse period of 0.1 - 0.5 s and a pulse duty cycle of 30 - 50%, the periodic change of the current makes the ion deposition process also show periodicity. During the pulse conduction period, ions are rapidly deposited; during the pulse off period, ions diffuse and adjust, inhibiting the continuous growth of grains. This periodic deposition process makes the grains in the coating refined, and the size of the refined grains is significantly smaller than that of conventional direct current electroplating. The refinement of the coating grains brings a significant improvement in hardness and wear resistance. From the perspective of the microstructure, the fine grains increase the number of grain boundaries. As defects in the crystal structure, grain boundaries hinder the movement of dislocations. When an external force acts on the coating, the dislocations are blocked at the grain boundaries, and a greater external force is required to cause plastic deformation of the material, thereby increasing the hardness of the coating. In terms of wear resistance, the refined grains make the coating structure more compact, reducing the phenomenon of abrasive particle shedding and increased wear caused by pores and defects during the wear process.

[0025] Optionally, the blackened stainless steel workpiece is further subjected to ion implantation treatment. The ion implantation treatment uses nitrogen ions, and the energy of the ion implantation treatment is 50 - 100 keV, and the dose is (1 - 5)×10 16 ions / cm 2 ².

[0026] By adopting the above technical solution, nitrogen ions are implanted into the surface of the blackened stainless steel workpiece, with an energy of 50 - 100 keV and a dose of (1 - 5)×10¹ 6 ions / cm². Under the action of high energy, the nitrogen ions hit the atoms on the surface of the stainless steel at high speed, overcome the binding force between atoms, and enter the matrix. The nitrogen ions react chemically with elements such as iron and chromium in the stainless steel to form nitrides with higher hardness, such as Fe 4 N, CrN, etc. These nitrides are evenly distributed in the surface layer of the stainless steel, changing the surface tissue structure and chemical composition. In terms of corrosion resistance, the formed nitrides have good chemical stability, which can prevent the direct contact between corrosive media and the stainless steel matrix, playing an isolation and protection role. In terms of surface hardness, the high hardness characteristics of the nitrides significantly increase the surface hardness of the stainless steel, enhancing its ability to resist external force scratching and wear, improving the surface mechanical properties, and making the blackened stainless steel workpiece show better durability and reliability in various application scenarios.

[0027] Optionally, the components of the acidic activation solution include 5-10% hydrofluoric acid, 10-15% nitric acid, 0.5-2% thiourea, 0.05-0.1% sodium dodecyl sulfate by mass percentage, and the rest is water. The components of the sensitizing solution include 3-5% stannous chloride, 10-15% hydrochloric acid, 0.05-0.1% polyethylene glycol, and the rest is water.

[0028] By adopting the above technical solution, in the acidic activation solution, 5-10% hydrofluoric acid reacts with the stainless steel surface to form micro-etching pits, increasing the active sites; 10-15% nitric acid assists in oxidative etching, making the micro-etching pits more uniform and removing impurities and oxide films; 0.5-2% thiourea acts as a corrosion inhibitor to inhibit excessive corrosion and maintain the mechanical properties of the substrate; 0.05-0.1% sodium dodecyl sulfate enhances the wettability, enabling the activation solution to act uniformly on the stainless steel surface and improving the consistency of the activation effect, laying a good foundation for subsequent sensitization and electroless plating.

[0029] In the sensitizing solution, 3-5% stannous chloride provides sufficient tin ions to adsorb on the stainless steel surface to form a catalytic active layer; 10-15% hydrochloric acid provides an acidic environment to prevent the hydrolysis of tin ions and promote their adsorption and activation on the stainless steel surface; 0.05-0.1% polyethylene glycol has a dispersing effect, making the tin ions more evenly dispersed in the solution and thus more evenly adsorbed on the stainless steel surface, enhancing the sensitization effect and ensuring the smooth progress of electroless plating and the quality of the coating.

[0030] In the second aspect, the present application provides an application of a chemical blackening process for stainless steel, adopting the following technical solution:

[0031] An application of a chemical blackening process for stainless steel, wherein the chemical blackening process is applied to the surface blackening treatment of components for shielding in camera modules and components for reflecting in millimeter-wave radars.

[0032] By adopting the above technical solution, after applying this blackening process to the shielding components of the camera module, the stray light suppression rate reaches more than 98%, the imaging clarity is improved by 30%, and the color reduction error is reduced to within 5%, effectively improving the image quality. After the millimeter-wave radar reflection components are blackened, the reflection efficiency is increased by 25%, the detection accuracy is improved by 15%, and the maximum detection distance is increased by 20%, significantly enhancing the overall performance of the millimeter-wave radar system. The treated stainless steel components have no peeling or discoloration of the surface blackening layer after 1000 hours of durability testing under harsh environments such as high and low temperatures (-40°C - 80°C) and high humidity (95% RH), and the performance remains stable.

[0033] In summary, the present application has the following beneficial effects:

[0034] 1. The process of this application thoroughly removes the oil stains on the stainless - steel surface through the synergistic effects of the impact force generated by ultrasonic cavitation, the saponification reaction between the alkaline auxiliary agent and the oil stains, and the reduction of the interfacial tension by the surfactant, providing a clean surface for the subsequent process. Then, it is soaked in the activation solution to form micro - etching pits to increase the surface active sites, and soaked in the sensitizing solution to adsorb catalytically active tin ions, providing a catalytic center for electroless plating. Finally, the pH value of the plating solution is controlled at 4.8 - 5.2, the temperature is maintained at 90 - 92 °C, and plating is carried out for 1 - 2 hours, enabling the stable reaction of components such as nickel sulfate, sodium hypophosphite, and sodium citrate. Sodium hypophosphite reduces nickel ions into the coating, and sodium citrate stabilizes nickel ions, thereby obtaining a blackened coating that is uniform, dense, and has good optical and electromagnetic properties.

[0035] 2. In this application, preferably in the surface modification process of carbon nanotubes, nitric acid is added for oxidation treatment to introduce oxygen - containing functional groups on the surface of carbon nanotubes, enhancing the surface activity and creating conditions for subsequent modification. Subsequently, a solution of poly(diallyldimethylammonium chloride) and a solution of an organic dye with sulfonic acid groups are prepared. The carbon nanotube suspension is successively stirred and reacted with both of them, and a self - assembled structure is formed by alternating adsorption through electrostatic interaction, increasing the dispersibility of carbon nanotubes in the plating solution by more than 30%, enhancing the bonding force with the black nickel coating, and ensuring its uniform embedding in the coating to optimize the coating performance.

[0036] 3. The method of this application, by using pulsed current assistance during electroless plating, makes the ion deposition periodic. During the conduction period, rapid deposition occurs, and during the off - period, diffusion adjustment takes place, inhibiting the continuous growth of grains. The grain size of the refined coating decreases, and the increase in grain boundaries hinders dislocation movement, improving hardness and wear resistance. After blackening, the workpiece is further treated by nitrogen ion implantation. Nitrogen ions react with stainless - steel elements to form high - hardness nitrides, which are uniformly distributed in the surface layer, changing the organizational structure and composition, enhancing corrosion resistance and surface hardness, and improving durability and reliability. Specific Embodiments

[0037] The following further elaborates on this application with reference to embodiments. It should be specifically noted that: for those not specifying specific conditions in the following embodiments, they are carried out according to conventional conditions or the conditions recommended by the manufacturer. Except for special instructions, the raw materials used in the following embodiments can all be obtained from ordinary commercial sources.

[0038] Preparation Example 1

[0039] A method for surface modification of carbon nanotubes:

[0040] Weigh 1 kg of multi - walled carbon nanotubes with a purity ≥ 98%, add them to 5 kg of absolute ethanol. Place the container containing the mixture of carbon nanotubes and absolute ethanol into an ultrasonic cleaner, set the ultrasonic power to 250 W, and perform ultrasonic dispersion for 45 minutes to form a carbon nanotube suspension.

[0041] Transfer the carbon nanotube suspension into a reaction kettle, start the stirring device, set the stirring speed to 300 r / min, add concentrated nitric acid into the reaction kettle, and stop adding when the nitric acid concentration reaches 4 mol / L. Adjust the temperature of the reaction kettle to 55 °C, maintain this temperature and continuously stir and react for 2.5 hours. After the reaction, transfer the suspension in the reaction kettle to a centrifuge, centrifuge at a speed of 10000 r / min for 10 minutes, pour out the supernatant, and wash the carbon nanotubes with clear water until the pH value of the washing liquid is neutral.

[0042] Add deionized water to polydiallyldimethylammonium chloride to prepare a solution with a concentration of 0.2 g / L. Weigh accurately an organic dye with sulfonic acid groups, add deionized water, and prepare a solution with a concentration of 0.08 g / L.

[0043] Add the washed carbon nanotubes into the polydiallyldimethylammonium chloride solution, place the reaction vessel on a magnetic stirrer, set the temperature to 25 °C, and the stirring speed to 250 r / min, stir and react for 1.5 hours to form the first adsorption layer. After the reaction, centrifuge the solution to separate the carbon nanotubes modified with polydiallyldimethylammonium chloride, wash with deionized water, then add the carbon nanotubes modified with polydiallyldimethylammonium chloride into the organic dye solution with sulfonic acid groups, react under the same conditions for 1.5 hours to form the second adsorption layer, and perform centrifugation and washing operations again to obtain the surface-modified carbon nanotubes.

[0044] Put the surface-modified carbon nanotubes into a vacuum drying oven, set the temperature to 70 °C, and the drying time to 7 hours.

[0045] Preparation Example 2

[0046] A method for surface modification of carbon nanotubes: The difference from Preparation Example 1 is that deionized water is added to polydiallyldimethylammonium chloride to prepare a solution with a concentration of 0.1 g / L. Weigh accurately an organic dye with sulfonic acid groups, add deionized water, and prepare a solution with a concentration of 0.1 g / L.

[0047] Preparation Example 3

[0048] A method for surface modification of carbon nanotubes: The difference from Preparation Example 1 is that deionized water is added to polydiallyldimethylammonium chloride to prepare a solution with a concentration of 0.3 g / L. Weigh accurately an organic dye with sulfonic acid groups, add deionized water, and prepare a solution with a concentration of 0.05 g / L.

[0049] Preparation Example 4

[0050] A method for surface modification of carbon nanotubes:

[0051] Weigh 1 kg of multi-walled carbon nanotubes with a purity of ≥98% and add them to 5 kg of absolute ethanol. Place the container with the mixture of carbon nanotubes and absolute ethanol into an ultrasonic cleaner, set the ultrasonic power to 250 W, and ultrasonically disperse for 45 minutes to form a carbon nanotube suspension.

[0052] Add deionized water to polydiallyldimethylammonium chloride to prepare a solution with a concentration of 0.2 g / L. Accurately weigh an organic dye with sulfonic acid groups, add deionized water, and prepare a solution with a concentration of 0.08 g / L.

[0053] Add the washed carbon nanotubes to the polydiallyldimethylammonium chloride solution. Place the reaction container on a magnetic stirrer, set the temperature to 25°C, the stirring speed to 250 r / min, and stir and react for 1.5 hours to form the first adsorption layer. After the reaction, centrifuge the solution to separate the carbon nanotubes modified with polydiallyldimethylammonium chloride, add deionized water for washing, and then add the carbon nanotubes modified with polydiallyldimethylammonium chloride to the organic dye solution with sulfonic acid groups and react under the same conditions for 1.5 hours to form the second adsorption layer. Centrifuge and wash again to obtain the surface-modified carbon nanotubes.

[0054] Place the surface-modified carbon nanotubes in a vacuum drying oven, set the temperature to 70°C, and the drying time to 7 hours.

[0055] Example 1, a chemical blackening process for stainless steel:

[0056] Dissolve sodium dodecylbenzenesulfonate and sodium hydroxide in deionized water, with the content of sodium dodecylbenzenesulfonate being 10 g / L and the content of sodium hydroxide solution being 25 g / L to obtain a degreasing agent. Place the stainless steel workpiece in the degreasing agent, set the ultrasonic frequency to 45 kHz, control the temperature at 60°C, and the treatment time to 20 minutes. After the degreasing treatment is completed, take out the workpiece from the degreasing solution and rinse it thoroughly with deionized water.

[0057] Immerse the degreased workpiece in an acidic activation solution. The components of the acidic activation solution include 8% hydrofluoric acid, 12% nitric acid, 1.4% thiourea, 0.08% sodium dodecyl sulfate by mass percentage, and the rest is water. Immerse it at room temperature for 45 minutes. After the activation treatment is completed, take out the workpiece from the activation solution and rinse it thoroughly with deionized water to remove the residual activation solution on the surface.

[0058] Place the activated workpiece in a sensitizing solution. The components of the sensitizing solution include 4% stannous chloride, 12% hydrochloric acid, 0.08% polyethylene glycol, and the rest is water. Control the temperature of the sensitizing solution at 70°C and soak for 50 minutes. After the sensitizing treatment is completed, take out the workpiece from the sensitizing solution and rinse it thoroughly with deionized water to remove the residual sensitizing solution on the surface.

[0059] Add 3 kg of nickel sulfate, 2.5 kg of sodium hypophosphite, 1.2 kg of sodium citrate, and 0.4 kg of carbon nanotubes into 50 kg of deionized water, stir for 15 min at a stirring speed of 400 r / min to obtain a plating solution. Measure the pH value of the plating solution using a pH meter, and control the pH value of the plating solution at 4.8 - 5.2 by adding dilute sulfuric acid or sodium hydroxide solution. Place the plating solution into a heating device, control the temperature at 91 ± 1 °C, and turn on the stirring device to make the plating solution evenly heated.

[0060] Put the workpiece that has undergone sensitization treatment into the plating solution, perform plating while maintaining a stirring speed of 200 r / min, and the plating time is 1.5 hours. After the plating is completed, take out the workpiece from the plating solution, rinse it thoroughly with deionized water to remove the residual plating solution on the surface. Dry the workpiece in a vacuum drying oven at 60 °C to obtain a blackened stainless steel workpiece.

[0061] Example 2, a chemical blackening process for stainless steel: The difference from Example 1 is that 2.5 kg of nickel sulfate, 2 kg of sodium hypophosphite, 1 kg of sodium citrate, and 0.2 kg of carbon nanotubes are added into 40 kg of deionized water, and stirred for 15 min at a stirring speed of 400 r / min to obtain a plating solution.

[0062] Example 3, a chemical blackening process for stainless steel: The difference from Example 1 is that 3.5 kg of nickel sulfate, 3 kg of sodium hypophosphite, 1.5 kg of sodium citrate, and 0.6 kg of carbon nanotubes are added into 60 kg of deionized water, and stirred for 15 min at a stirring speed of 400 r / min to obtain a plating solution.

[0063] Example 4, a chemical blackening process for stainless steel: The difference from Example 1 is that 3 kg of nickel sulfate, 2.5 kg of sodium hypophosphite, 1.2 kg of sodium citrate, 0.4 kg of carbon nanotubes, and 0.3 kg of nano-titanium dioxide are added into 50 kg of deionized water, and stirred for 15 min at a stirring speed of 400 r / min to obtain a plating solution.

[0064] Example 5, a chemical blackening process for stainless steel: The difference from Example 1 is that the carbon nanotubes in the plating solution are surface-modified and are prepared from Preparation Example 1.

[0065] Example 6, a chemical blackening process for stainless steel: The difference from Example 5 is that the carbon nanotubes in the plating solution are surface-modified and are prepared from Preparation Example 2.

[0066] Example 7, a chemical blackening process for stainless steel: The difference from Example 5 is that the carbon nanotubes in the plating solution are surface-modified and are prepared from Preparation Example 3.

[0067] Example 8, a chemical blackening process for stainless steel: The difference from Example 1 is that the sensitized workpiece is placed in the plating solution, and plating is carried out while maintaining a stirring speed of 200 r / min.

[0068] Set the pulse period of the pulse power supply to 0.3 s, the pulse duty cycle to 40%, and the initial current density to 1.5 A / dm². Fix the anode graphite electrode on one side of the plating solution tank to ensure full contact between the anode electrode and the plating solution. The stainless steel workpiece serves as the cathode and is fixed in the plating solution tank with a fixture. Turn on the pulse power supply switch to apply a pulsed current.

[0069] The plating time is 1.5 hours. After the plating is completed, turn off the pulse power supply simultaneously, take the workpiece out of the plating solution, rinse it thoroughly with deionized water to remove the residual plating solution on the surface. Dry the workpiece in a vacuum drying oven at 60 °C to obtain the blackened stainless steel workpiece.

[0070] Example 9, a chemical blackening process for stainless steel: The difference from Example 8 is that the pulse period of the pulse power supply is set to 0.1 s and the pulse duty cycle is set to 30%.

[0071] Example 10, a chemical blackening process for stainless steel: The difference from Example 8 is that the pulse period of the pulse power supply is set to 0.5 s and the pulse duty cycle is set to 50%.

[0072] Example 11, a chemical blackening process for stainless steel: The difference from Example 8 is that:

[0073] Place the blackened stainless steel workpiece on the sample stage of the ion implanter, close the door of the implantation chamber, and conduct a sealing inspection. Start the vacuum system and pre-pump the chamber to the order of 10 -5 -10 -6 Pa;

[0074] Pass nitrogen with a purity of ≥98% through the extraction system of the ion source, extract and accelerate the nitrogen ion beam to 80 keV, start the rotation of the sample stage to make the surface of the workpiece uniformly receive ion implantation, and record the ion implantation dose in real time to ensure that the implantation dose reaches 3×10 16 ions / cm².

[0075] Example 12, a chemical blackening process for stainless steel: The difference from Example 11 is that the nitrogen ion beam is extracted and accelerated to 50 keV, and the implantation dose reaches 1×10 16 ions / cm².

[0076] Example 13, a chemical blackening process for stainless steel: The difference from Example 11 is that the nitrogen ion beam is extracted and accelerated to 100 keV, and the implantation dose reaches 5×1016 ions / cm².

[0077] Comparative Example 1

[0078] A chemical blackening process for stainless steel: The difference from Example 1 is that the activation treatment and sensitization treatment are not carried out.

[0079] Comparative Example 2

[0080] A chemical blackening process for stainless steel: The difference from Example 1 is that the pH value of the plating solution is controlled at 4.3 - 4.7.

[0081] Comparative Example 3

[0082] A chemical blackening process for stainless steel: The difference from Example 1 is that the pH value of the plating solution is controlled at 5.3 - 5.7.

[0083] Comparative Example 4

[0084] A chemical blackening process for stainless steel: The difference from Example 5 is that the carbon nanotubes in the plating solution are prepared from Preparation Example 4.

[0085] Comparative Example 5

[0086] A treatment process for stainless steel:

[0087] Dissolve sodium dodecylbenzenesulfonate and sodium hydroxide in deionized water, with the content of sodium dodecylbenzenesulfonate being 10 g / L and the content of sodium hydroxide being 25 g / L to obtain a degreasing agent. Put the stainless steel workpiece into the degreasing agent, set the ultrasonic frequency to 45 kHz, control the temperature at 60 °C, and the treatment time to 20 minutes. After the degreasing treatment is completed, take out the workpiece from the degreasing solution and rinse it thoroughly with deionized water to obtain the degreased stainless steel workpiece.

[0088] Performance detection test detection method

[0089] (I) Stray light suppression rate test

[0090] Test equipment: integrating sphere (with a xenon lamp standard light source inside), spectrometer (wavelength range 200 - 1100 nm), high-precision optical power meter.

[0091] Cut the blackened stainless steel part into a size of 10 mm × 10 mm, with the surface clean and free of contaminants.

[0092] Place a standard reflection white board (reflectivity ≥ 99%) inside the integrating sphere and record the reference light intensity value. Remove the white board, put in the sample to be tested, and adjust the angle between the sample and the light source to 45°. The light source emits a full spectrum, and measure the light intensity output by the integrating sphere.

[0093] Calculate the stray light suppression rate: Suppression rate = (1 - Isample / I ref ) * 100%.

[0094] Repeat the test 3 times and take the average value.

[0095] (2) Millimeter-wave reflection efficiency test

[0096] Test equipment: Vector network analyzer (Keysight N5245A), millimeter-wave horn antenna (frequency coverage 24 - 77 GHz), anechoic chamber (background noise ≤ -60 dB), three-dimensional positioning platform (accuracy ±0.1 mm).

[0097] Process the blackened component into a standard reflector (size ≥ 10λ, where λ is the wavelength) and fix it on a bracket. Calibrate the VNA using a standard gain horn antenna to eliminate cable loss. Record the reflection coefficient of the anechoic chamber.

[0098] Place the sample 1 m in front of the antenna at an incident angle of 0°. Scan the frequency range 24 - 77 GHz and record the reflection coefficient.

[0099] Calculate the reflection efficiency: Reflection efficiency = [(S 11 sample - S 11 bg ) / (1 - S 11 bg )] 2 * 100%.

[0100] (3) Corrosion resistance test

[0101] Standard: ASTM D6869;

[0102] Condition: 10 * 10 cm sample;

[0103] Phase 1: Salt spray (5% NaCl) for 2 hours;

[0104] Phase 2: Drying (40 °C, 0% RH) for 4 hours;

[0105] Phase 3: Damp heat (50 °C, 95% RH) for 18 hours;

[0106] Cycle period: 24 hours;

[0107] Total time: 1000 hours.

[0108] After the test, check the surface coating morphology of the sample.

[0109] Table 1 Experimental data

[0110] Combined with Example 1 and Comparative Example 1 and Table 1, it can be seen that in Comparative Example 1, without activation treatment and sensitization treatment, the stray light suppression rate is 94.6%, the millimeter-wave reflection efficiency is 91.7%, and there are damages and peelings in the coating during the salt spray test; while in Example 1, the stray light suppression rate is 97.9%, the millimeter-wave reflection efficiency is 94.8%, and there are no damages and no peelings in the salt spray test coating. This indicates that the activation treatment and sensitization treatment can increase the active sites on the stainless steel surface, adsorb catalytically active tin ions, provide a good foundation for electroless plating, make the coating more uniform and dense, thereby improving the stray light suppression rate and millimeter-wave reflection efficiency, and at the same time enhancing the corrosion resistance of the coating.

[0111] Combined with Example 1 and Comparative Examples 2-3 and Table 1, it can be seen that in Comparative Example 2, the pH value of the plating solution is controlled at 4.3-4.7, and in Comparative Example 3, the pH value of the plating solution is controlled at 5.3-5.7. Their stray light suppression rates and millimeter-wave reflection efficiencies are both lower than those of Example 1 (the pH value of the plating solution is controlled at 4.8-5.2), and there are damages and peelings in the coating during the salt spray test. This shows that an appropriate pH value of the plating solution (4.8-5.2) is crucial for ensuring the stability of the plating solution and the high efficiency of the reaction. Within this pH value range, the components in the plating solution can undergo stable chemical reactions to form a uniform and dense coating, thereby improving the optical properties and corrosion resistance of the product. When the pH value deviates from this range, the stability of the plating solution is affected and the coating quality deteriorates.

[0112] Combined with Example 5 and Comparative Example 4 and Table 1, it can be seen that in Example 5, the carbon nanotubes in the plating solution are surface-modified by Preparation Example 1, and in Comparative Example 4, the carbon nanotubes in the plating solution are prepared by Preparation Example 4 (the difference from Preparation Example 1 is that the nitric acid oxidation treatment step is missing). The stray light suppression rate of Example 5 is 98.9%, the millimeter-wave reflection efficiency is 95.9%, and there are no damages and no peelings in the salt spray test coating; the stray light suppression rate of Comparative Example 4 is 98.1%, the millimeter-wave reflection efficiency is 95.2%, and there are damages and peelings in the salt spray test coating. This indicates that the nitric acid oxidation treatment step of carbon nanotubes can introduce oxygen-containing functional groups on its surface, increase the surface activity, and through subsequent layer-by-layer self-assembly modification, make the carbon nanotubes have better dispersion in the plating solution and stronger binding force with the black nickel coating, thereby improving the optical properties and corrosion resistance of the product. The lack of this step will lead to an unsatisfactory combination of carbon nanotubes and the coating, resulting in a decline in performance.

[0113] Combined with Example 1 and Comparative Example 5 and Table 1, it can be seen that in Comparative Example 5, only degreasing treatment is carried out, and its stray light suppression rate is 63.5%, and the millimeter-wave reflection efficiency is 76.9%, which is much lower than that of Example 1. This fully shows that steps such as activation, sensitization, and electroless plating in the chemical blackening process play a key role in improving the stray light suppression rate and millimeter-wave reflection efficiency of stainless steel components. Only degreasing treatment cannot form a blackening coating with good performance.

[0114] Combined with Examples 1-4 and Table 1, it can be seen that in Examples 1-3, by adjusting the contents of components such as nickel sulfate, sodium hypophosphite, sodium citrate, and carbon nanotubes in the plating solution, compared with Example 1, the stray light suppression rate and millimeter-wave reflection efficiency have certain fluctuations, but the overall performance is good, and the coatings in the salt spray test have no damage or peeling. This indicates that the proportions of the components in the plating solution of the present application can act synergistically to ensure the quality and performance of the coating. Nano-titanium dioxide has excellent optical properties and chemical stability. Its synergistic effect with carbon nanotubes can further enhance the ultraviolet absorption ability of the composite coating and improve the optical stability of the coating in ultraviolet environments such as outdoors.

[0115] Combined with Example 1 and Examples 5-7 and Table 1, it can be seen that in Examples 5-7, the carbon nanotubes in the plating solution are surface-modified by different preparation examples (Preparation Examples 1-3). Compared with Example 1 (without using surface-modified carbon nanotubes), both the stray light suppression rate and the millimeter-wave reflection efficiency are improved, and the coatings in the salt spray test have no damage or peeling. This shows that surface-modifying carbon nanotubes to form a multi-layer structure through layer-by-layer self-assembly can significantly improve the dispersibility of carbon nanotubes in the plating solution, enhance their bonding force with the black nickel coating, thereby optimizing the performance of the coating, further improving the stray light suppression rate and millimeter-wave reflection efficiency of the product, and at the same time not affecting the corrosion resistance of the coating.

[0116] Combined with Example 1 and Examples 8-10 and Table 1, it can be seen that in Examples 8-10, pulse current assistance is adopted during the plating process, and the pulse periods and pulse duty ratios are different. Compared with Example 1 (without pulse current assistance), both the stray light suppression rate and the millimeter-wave reflection efficiency are improved, and the coatings in the salt spray test have no damage or peeling. This indicates that adopting pulse current assistance during electroless plating and controlling the pulse period and pulse duty ratio can optimize the ion deposition process, refine the coating grains, thereby improving the hardness and wear resistance of the coating, and at the same time enhancing the optical performance of the product, increasing the stray light suppression rate and millimeter-wave reflection efficiency, and not affecting the corrosion resistance of the coating.

[0117] Combined with Example 1 and Examples 11-13 and Table 1, it can be seen that in Examples 11-13, the blackened stainless steel workpieces are subjected to nitrogen ion implantation treatment with different energies and doses. Compared with Example 1, the stray light suppression rate and the millimeter-wave reflection efficiency are further improved, and the coatings in the salt spray test have no damage or peeling. This shows that nitrogen ion implantation treatment can form nitrides with relatively high hardness on the surface of stainless steel, change the surface microstructure and chemical composition, thereby improving the corrosion resistance and surface hardness of the coating, and at the same time having a positive impact on the optical performance of the product, further increasing the stray light suppression rate and millimeter-wave reflection efficiency.

[0118] This specific embodiment is only an interpretation of the present application and does not limit the present application. After reading this specification, those skilled in the art can make modifications to this embodiment without creative contributions as needed, but as long as it is within the scope of the claims of the present application, it is protected by the patent law.

Claims

1. A chemical blackening process for stainless steel, characterized in that: The following steps are involved: Place the stainless steel workpiece in a solution containing a surfactant and an alkaline additive for degreasing, and treat it at 40-50kHz ultrasonic waves and 55-65℃ for 15-30 minutes; Immerse the degreased workpiece in the activation solution for 40-50 minutes at room temperature, then put the workpiece into the sensitizing solution for 40-60 minutes at 60-80℃; Plating the workpiece in a plating solution, controlling the pH value of the plating solution at 4.8-5.2 and the temperature at 90-92° C., wherein the plating solution components include, by weight, 25-35 parts of nickel sulfate, 20-30 parts of sodium hypophosphite, 10-15 parts of sodium citrate, 2-6 parts of carbon nanotubes, 400-600 parts of deionized water, and 2-4 parts of nano-titanium dioxide, and plating for 1-2 hours to obtain a blackened stainless steel workpiece; The carbon nanotubes are surface modified, and the specific method of surface modification of the carbon nanotubes is: Adding carbon nanotubes into anhydrous ethanol and ultrasonically dispersing them to obtain a carbon nanotube suspension; Add nitric acid to the carbon nanotube suspension to make the concentration of nitric acid reach 3-5 mol / L, stir and react at 50-60° C. for 2-3 hours, and centrifuge and wash to neutral after the reaction. The polydiallyldimethylammonium chloride is prepared into a solution with a concentration of 0.1-0.3 g / L, and the organic dye with a sulfonic acid group is prepared into a solution with a concentration of 0.05-0.1 g / L; Adding carbon nanotubes to a polydiallyldimethylammonium chloride solution, stirring and reacting at 20-25°C for 1-2 hours at a stirring speed of 200-300 r / min, centrifuging and washing after the reaction, then adding the carbon nanotubes to an organic dye solution with a sulfonic acid group, stirring and reacting for 1-2 hours, centrifuging and washing again, to obtain modified carbon nanotubes; The modified carbon nanotubes were vacuum dried at 60-80°C for 6-8 hours.

2. The chemical blackening process of stainless steel according to claim 1, characterized in that: The workpiece is placed in the plating solution and pulse current is used as an aid, wherein the pulse period of the pulse current is 0.1-0.5s and the pulse duty ratio is 30-50%.

3. The chemical blackening process of stainless steel according to claim 1, characterized in that: The blackened stainless steel workpiece is also subjected to ion implantation, wherein nitrogen ions are used in the ion implantation, and the energy of the ion implantation is 50-100 keV and the dose is (1-5)×10 16 ions / cm 2 .

4. The chemical blackening process of stainless steel according to claim 1, characterized in that: The activation solution components include 5-10% hydrofluoric acid, 10-15% nitric acid, 0.5-2% thiourea, 0.05-0.1% sodium dodecyl sulfate, and the rest is water in terms of mass percentage. The sensitizing solution components include 3-5% stannous chloride, 10-15% hydrochloric acid, 0.05-0.1% polyethylene glycol, and the rest is water.

5. An application of the chemical blackening process of stainless steel as claimed in any one of claims 1 to 4, characterized in that: The chemical blackening process is applied to camera module shielding components and millimeter wave radar reflection components for surface blackening treatment.

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