A double-layer composite plating layer of nickel-cobalt / tungsten alloy on the inner wall of a gas cylinder and a preparation method and application thereof

Abstract

The application discloses a kind of gas cylinder inner wall's electroplating nickel cobalt / tungsten alloy double-layer composite coating and its preparation method and application, first electroplating nickel cobalt coating on gas cylinder inner wall, then continue to electroplating tungsten alloy coating on the surface of nickel cobalt coating, when the electroplating of nickel cobalt coating and tungsten alloy coating, all adopt pictograph anode, control electroplating nickel cobalt coating and electroplating tungsten alloy coating, the area ratio of cathode and anode is 1.5-2.0:1;The electroplating nickel cobalt / tungsten alloy double-layer composite coating provided by the application can reach 1500 hours without rusting in neutral salt spray test;100% can ensure that the base is protected by coating, can better play the role of tungsten alloy coating corrosion and wear resistance, and can resist sodium chloride, sulfide corrosion, meet the use requirements of gas cylinder under marine environment resistant to high pressure, erosion.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of electroplating, and particularly relates to an electroplated nickel-cobalt / tungsten alloy double-layer composite coating on the inner wall of a gas cylinder and a preparation method and application thereof. BACKGROUND

[0002] With the vigorous development of the market for the shipbuilding industry and the Chinese marine industry, various gas cylinders for storage use have become a hot industry. Various warships and submarines, offshore platforms, and marine ports all need to be equipped with gas cylinder products for breathing, medical treatment, engine oxygen supplementation, and metal cutting, and the large-scale, high-pressure, and high-end performance requirements of gas cylinders are the high-end demands of the industry chain. The production of gas cylinders in 2022 was more than 2000, and the production of gas cylinders in 2025 was more than 3000, especially the use of gas cylinders in the military industry has increased significantly. Among them, the production that needs surface treatment is more than 50%, and with the high-end performance requirements of gas cylinders, the wear resistance and corrosion resistance of the original chemical nickel surface treatment technology cannot meet the requirements of high-end products. The working environment of high-pressure air cylinders is relatively harsh (working pressure: ≤60 MPa, gas flow: >100 Nm 3 / h), and at the same time, compressed air contains a certain amount of condensed water (contains a certain amount of Cl - -), under the action of dry-wet alternating working conditions and stress, local corrosion will occur on the inner surface of the gas cylinder, and the stress corrosion sensitivity of the high-strength cylinder body will be aggravated. If local corrosion occurs on the gas cylinder base, the corrosion pit position will preferentially act as a crack source under the action of stress, which will cause accelerated corrosion, significantly increase the stress concentration coefficient, exceed the fatigue limit of the material, cause the fatigue failure of the gas cylinder, and adversely affect the safety and reliability of the gas cylinder. SUMMARY

[0003] In view of the deficiencies of the prior art, a first object of the present application is to provide a preparation method of an electroplated nickel-cobalt / tungsten alloy double-layer composite coating on the inner wall of a gas cylinder.

[0004] A second object of the present application is to provide an electroplated nickel-cobalt / tungsten alloy double-layer composite coating on the inner wall of a gas cylinder prepared by the above preparation method.

[0005] A third object of the present application is to provide an application of the electroplated nickel-cobalt / tungsten alloy double-layer composite coating on the inner wall of a gas cylinder prepared by the above preparation method.

[0006] To achieve the above objects, the present application adopts the following technical solutions:

[0007] The application provides a preparation method of a double-layer composite nickel-cobalt / tungsten alloy plating layer on the inner wall of a gas cylinder, which comprises the following steps: firstly, plating a nickel-cobalt plating layer on the inner wall of the gas cylinder, and then plating a tungsten alloy plating layer on the surface of the nickel-cobalt plating layer; during the plating of the nickel-cobalt plating layer and the tungsten alloy plating layer, a pictographic anode is used, which comprises a central conductive shaft, an expandable anode sheet arranged on the central conductive shaft, and a strutting device for driving the anode sheet to expand outward; before the anode sheet expands, the radial dimension of the pictographic anode is smaller than the diameter of the mouth of the gas cylinder; after the pictographic anode enters the gas cylinder through the mouth of the gas cylinder, the outward expansion of the anode sheet is controlled to ensure that the area ratio of the cathode to the anode is 1.5-2.0:1 during the plating of the nickel-cobalt plating layer and the tungsten alloy plating layer.

[0008] The nickel-cobalt plating layer comprises Ni and Co, and the mass fraction of Co in the nickel-cobalt plating layer is 8-12%, and the mass fraction of Ni is 88-91%; the tungsten alloy plating layer comprises W, Ni and P, and the mass fraction of W in the tungsten alloy plating layer is 12-30%, the mass fraction of Ni is 65-88%, and the mass fraction of P is 0.5-5%.

[0009] The application provides a preparation method of a double-layer composite nickel-cobalt / tungsten alloy plating layer on the inner wall of a gas cylinder, which comprises the following steps: firstly, plating a nickel-cobalt plating layer on the inner wall of the gas cylinder, and then plating a tungsten alloy plating layer on the surface of the nickel-cobalt plating layer; during the plating of the nickel-cobalt plating layer and the tungsten alloy plating layer, a pictographic anode is used, which comprises a central conductive shaft, an expandable anode sheet arranged on the central conductive shaft, and a strutting device for driving the anode sheet to expand outward; before the anode sheet expands, the radial dimension of the pictographic anode is smaller than the diameter of the mouth of the gas cylinder; after the pictographic anode enters the gas cylinder through the mouth of the gas cylinder, the outward expansion of the anode sheet is controlled to ensure that the area ratio of the cathode to the anode is 1.5-2.0:1 during the plating of the nickel-cobalt plating layer and the tungsten alloy plating layer.

[0010] The electroplated nickel-cobalt / tungsten alloy double-layer composite coating prepared by the preparation method has slightly larger crystal grains of the nickel-cobalt plating layer and smaller crystal grains of the tungsten alloy plating layer, so that a double-layer misalignment structure is generated between the outer tungsten alloy plating layer and the inner nickel-cobalt plating layer, and the misalignment arrangement can effectively eliminate the porosity of the plating layer. The nickel-cobalt plating layer combined with the substrate as a primer layer and the outer tungsten alloy plating layer form a double layer, the tungsten alloy plating layer has high hardness, good self-passivation, strong wear resistance and erosion resistance, the corrosion potential of the tungsten alloy plating layer is more negative than that of the nickel-cobalt plating layer, and the tungsten alloy plating layer acts as a sacrificial anode layer in the corrosion process, so it is not easy to corrode. If the surface layer is damaged, a large anode on the surface layer and a small cathode on the bottom layer are formed, and in the electrochemical corrosion process, the tungsten alloy plating layer as the anode is corroded first, and the nickel-cobalt plating layer as the cathode is well protected. In this way, the double-layer composite coating forms an effective electrochemical protection effect on the gas cylinder, reducing the risk of longitudinal pitting corrosion. Therefore, the double-layer composite coating has the performance characteristics of fatigue resistance, high toughness, high hardness, wear resistance, strong anti-corrosion ability and gas scouring resistance. By using the plating layer to isolate the contact between the marine atmospheric condensate corrosion medium and the substrate, the safety and service life of the gas cylinder can be greatly improved.

[0011] The preparation method of the present application uses a tungsten alloy plating layer alone or a tungsten alloy plating layer that cannot form the synergistic effect described above. For example, the plating layer has low current efficiency, the gas cylinder plating layer of the special-shaped part is not uniform, the plating solution depth capability is not strong, and after high-temperature treatment, the gas cylinder, especially the surface within 500mm of the two ports of the gas cylinder, cannot be electroplated to ensure 100% coverage, which may cause plating leakage and fail to protect the substrate. In addition, since the gas cylinder is a special-shaped part, the conventional anode cannot enter the gas cylinder or cannot effectively control the area ratio of the cathode (the inner wall of the gas cylinder) to the anode, thereby affecting the uniformity of the plating layer in different parts of the gas cylinder. Therefore, the present application provides an anode with expandable anode sheets, the radial dimension of the anode is smaller than the diameter of the gas cylinder before the anode sheets are expanded, and when the anode enters the gas cylinder through the gas cylinder opening, the anode sheets expand outward to approach the inner wall of the gas cylinder. When electroplating a layer of nickel-cobalt plating layer and a layer of tungsten alloy plating layer, the area ratio of the cathode to the anode is 1.5-2.0:1, thereby ensuring uniform electroplating.

[0012] Preferably, the pylon-shaped anode comprises a central conductive shaft, a plurality of anode sheet groups are arranged axially around the central conductive shaft, the anode sheet group at the top end of the pylon-shaped anode is provided with a fixed ring fixed on the central conductive shaft, the other ends of the remaining anode sheet groups and the bottom end of the anode sheet group at the top end of the pylon-shaped anode are welded on a movable ring, and a stretching device is arranged on the central conductive shaft away from the fixed ring. When the pylon-shaped anode enters the gas cylinder from the bottle mouth, the stretching device moves towards the fixed ring, so that the movable rings on the central shaft move towards each other, and drive the anode sheets to expand and bend outward, so as to make the anode sheet groups present a "lantern shape".

[0013] Experiments show that the anode sheet needs to be segmented to form a plurality of "lantern-shaped" structures in the gas cylinder, so as to control the area ratio of the cathode to the anode to be 1.5-2.0:1. If the anode sheet is not segmented and only one anode sheet is used, a long lantern-shaped anode will be formed after expansion, which not only causes the distance between the two ends of the anode and the cathode to be too far, but also causes the area ratio of the cathode to the anode to be unable to reach 1.5-2.0:1, ultimately resulting in uneven plating.

[0014] Further preferably, the number of the anode sheet groups is three. Experiments show that when the anode sheet is arranged in three groups to form three "lantern-shaped" structures in the gas cylinder, the plating thickness and performance are the most uniform.

[0015] Further preferably, the width of the anode sheet is 15-25mm. Experiments show that when the width of the anode sheet is controlled within the above range, the plating performance is optimal.

[0016] Preferably, the material of the pylon-shaped anode is selected from one of titanium-ruthenium coated metal oxide, titanium-iridium coated metal oxide and stainless steel.

[0017] Preferably, the inner wall of the gas cylinder is pretreated in sequence, washed with hot water, washed with cold water, activated, washed with tap water, washed with deionized water, and then plated with a layer of nickel-cobalt plating layer.

[0018] Further preferably, the pretreatment is to sequentially perform inner wall sand blasting, chemical degreasing and electrolytic degreasing on the inner wall of the gas cylinder.

[0019] Further preferably, the activation is to sequentially perform electric activation and chemical activation on the inner wall of the pretreated gas cylinder. The process of electric activation is to place the inner wall of the pretreated gas cylinder in a nitrate solution for electric activation for 10-20min, and the concentration of the nitrate solution is 380-420g / L. The process of chemical activation is to use a sulfuric acid solution with a mass fraction of 8-12% for activation for 5-10min.

[0020] Preferably, the electroplating solution A for the electroplating of the nickel-cobalt plating layer comprises nickel sulfate: 340-380 g / L, cobalt sulfate: 40-55 g / L, citric acid: 15-25 g / L, boric acid: 25-35 g / L; the electroplating of the nickel-cobalt plating layer is performed at a current density of 1-10 A / dm 2 , preferably 2-5 A / dm 2 , further preferably 2-4 A / dm 2 , at a temperature of 30-60℃, preferably 45-55℃, and at a pH of 2.0-5.0, preferably 3.0-4.5 (pH of the post-plating solution ≥ 3.0).

[0021] Preferably, the electroplating solution B for the electroplating of the tungsten alloy plating layer comprises nickel sulfate: 14-22 g / L, sodium tungstate: 25-35 g / L, phosphorous acid: 20-30 g / L, citric acid: 30-180 g / L, sodium citrate: 30-100 g / L; the electroplating of the tungsten alloy plating layer is performed at a current density of 3-15 A / dm 2 , preferably 4-12 A / dm 2 , further preferably 5-7 A / dm 2 , at a temperature of 50-80℃, preferably 55-75℃, and at a pH of 5.0-8.0, preferably pH 6.5-7.5.

[0022] The nickel-cobalt plating layer has a large current effect, resulting in slightly larger plating grains; while the tungsten alloy has a small current effect, resulting in a dense plating layer with small grains, so the dense performance of the outer tungsten alloy plating layer well compensates for the defects of the large grains of the nickel-cobalt plating layer, thereby the grains of the outer tungsten alloy and the inner nickel-cobalt plating layer form a double-layer misregistration structure, and the misregistration arrangement can effectively eliminate the porosity of the plating layer.

[0023] Preferably, the gas cylinder is vertically fixed on the support during the electroplating of the nickel-cobalt plating layer and the tungsten alloy plating layer.

[0024] Preferably, the upper end of the gas cylinder is provided with an upper box body, and the lower end is provided with a lower box body; during the electroplating of the nickel-cobalt plating layer and the tungsten alloy plating layer, a part of the electroplating solution A or the electroplating solution B enters from the lower box body inlet and flows out from the upper end box body overflow port, forming a solution flow closure inside.

[0025] Through the above arrangement, during the electroplating, the inner wall of the gas cylinder circulates and flows, which can further improve the uniformity of the thickness and the performance of the gas cylinder inner wall.

[0026] Further preferably, the flow rate of the solution flow is ≥ 185 L / min.

[0027] Preferably, the nickel-cobalt plating layer and the tungsten alloy plating layer are electroplated with air agitation at the bottom of the gas cylinder. It is found that air agitation is crucial during electroplating. Without air agitation, the compactness and uniformity of the plating layer are affected, and electroplated impurities fall to form dust nodules.

[0028] Further preferably, the air agitation intensity is 0.5-0.8 m 3 / (min·m 2 ). The performance is optimal when the air agitation intensity is controlled within the range. If the air agitation intensity is too high, a large number of agitation bubbles are generated in the solution, causing local underplating. If the air agitation intensity is too low, the solution is prone to stratification and impurities are precipitated on the surface of the plating layer to form nodules.

[0029] In actual operation, after the tungsten alloy plating layer is electroplated, the gas cylinder is washed with deionized water, dried, and treated for hydrogen removal.

[0030] The application also provides a gas cylinder inner wall electroplated with a nickel-cobalt / tungsten alloy double-layer composite plating layer prepared by the preparation method.

[0031] Further preferably, the thickness of the nickel-cobalt plating layer is 20-45 μm, preferably 40-45 μm, and the thickness of the tungsten alloy plating layer is 10-20 μm, preferably 14-20 μm.

[0032] In the application, the thickness of each plating layer is controlled within the above range for optimal performance. If the thickness of the plating layer is lower than the control value, the corrosion resistance of the plating layer is affected. If the thickness of the plating layer is too high, not only the cost is increased, but also the adhesion between the tungsten alloy surface plating layer and the base material is affected.

[0033] The application also provides the application of the gas cylinder inner wall electroplated with a nickel-cobalt / tungsten alloy double-layer composite plating layer prepared by the preparation method. The gas cylinder containing the nickel-cobalt / tungsten alloy double-layer composite plating layer is applied in a marine environment.

[0034] Principle and advantage

[0035] The electroplated nickel-cobalt / tungsten alloy double-layer composite coating has slightly larger crystal grains of the nickel-cobalt coating layer and smaller crystal grains of the tungsten alloy coating layer, so that the crystal grains of the outer tungsten alloy coating layer and the inner nickel-cobalt coating layer generate a double-layer dislocation structure, and the dislocation arrangement can effectively eliminate the porosity of the coating layer. The nickel-cobalt coating layer combined with the substrate as a primer layer and the outer tungsten alloy coating layer form a double layer, the tungsten alloy coating layer has high hardness, good self-passivation, strong wear resistance and erosion resistance, the corrosion potential of the tungsten alloy coating layer is more negative than that of the nickel-cobalt coating layer, and the tungsten alloy coating layer acts as a sacrificial anode layer in the corrosion process, so it is not easy to corrode. If the surface layer is damaged, a large anode structure and a small cathode structure are formed in the bottom layer, and in the electrochemical corrosion process, the tungsten alloy coating layer as the anode is corroded first, and the nickel-cobalt coating layer as the cathode is well protected. In this way, the double-layer composite coating forms an effective electrochemical protection effect on the gas cylinder, reducing the risk of longitudinal pitting corrosion. Therefore, the double-layer composite coating has the performance characteristics of fatigue resistance, high toughness, high hardness, wear resistance, strong anti-corrosion ability and gas erosion resistance. The coating layer can isolate the contact between the condensate corrosion medium of marine atmosphere and the substrate, which can greatly improve the safety and service life of the gas cylinder. In the optimal case, the neutral salt spray test of the electroplated nickel-cobalt / tungsten alloy double-layer composite coating can reach 1500 hours without rust. The electroplated nickel-cobalt / tungsten alloy double-layer composite coating can 100% ensure that the substrate is protected by the coating layer, and can better play the role of the tungsten alloy coating layer in corrosion resistance and wear resistance. Moreover, it can resist sodium chloride and sulfide corrosion, and meet the requirements of high pressure and erosion resistance of the gas cylinder in the marine environment.

[0036] The preparation method provided by the present application has the advantages that the gas cylinder is a special-shaped part, the conventional anode cannot enter the gas cylinder or cannot effectively control the suitable area ratio of the cathode to the anode, thereby affecting the uniformity of the coating in different parts of the gas cylinder. Therefore, the pictograph anode provided by the present application has an inflatable anode sheet. Before the anode sheet is inflated, the radial dimension of the pictograph anode is smaller than the diameter of the gas cylinder mouth. When the pictograph anode enters the gas cylinder from the gas cylinder mouth and the anode sheet inflates outward to approach the inner wall of the gas cylinder, the area ratio of the cathode to the anode is 1.5-2.0:1 during electroplating of the nickel-cobalt coating layer and the tungsten alloy coating layer. Therefore, the electroplating is uniform. BRIEF DESCRIPTION OF DRAWINGS

[0037] Figure 1 It is a schematic diagram of the device for electroplating the inner wall of the gas cylinder in the present application. In the figure, 1 is an exhaust pipe, 2 is an air inlet pipe, 3 is a liquid outlet pipe, 4 is an upper box body, 5 is an anode sheet, 6 is a central conductive shaft, 7 is a cathode conductive clamp, 8 is a gas cylinder, 9 is a lower box body, 10 is an anode conductive clamp, 11 is a rack, 12 is a liquid inlet pipe, and 13 is a gas pipe.

[0038] Figure 2 It is a schematic diagram of the process of the pictograph anode entering the gas cylinder to the expanded state in the present application.

[0039] Figure 3 Microstructure of the electroplated nickel-cobalt / tungsten alloy double-layer composite coating prepared in Example 1.

[0040] Figure 4 Microstructure of the electroplated nickel-cobalt / tungsten alloy double-layer composite coating prepared in Example 1. DETAILED DESCRIPTION

[0041] The following examples are all prepared by placing the gas cylinder on a support as shown in Figure 1 , the upper end of the gas cylinder is provided with an upper box, and the lower end is provided with a lower box. When the nickel-cobalt coating and the tungsten alloy coating are electroplated, the electroplating solution A and the electroplating solution B enter from the lower box inlet and flow out from the upper end box overflow port, forming a closed solution flow inside.

[0042] In addition, during electroplating, a pictographic anode is used, which comprises a central conductive shaft, a plurality of anode sheet groups are arranged around the central conductive shaft in the axial direction, preferably three groups, the width of the anode sheet is preferably 15-25mm, the anode sheet group at the top end of the pictographic anode is provided with a fixed ring fixed on the central conductive shaft, the two ends of the remaining anode sheet groups and the bottom end of the anode sheet group at the top end of the pictographic anode are all welded on a movable ring, and a strutting device is arranged on the central conductive shaft away from the fixed ring. When the pictographic anode enters the gas cylinder from the gas cylinder opening, the strutting device moves towards the fixed ring, so that the movable rings on the central shaft move towards each other and drive the anode sheets to expand and bend outward, so that the anode sheet groups form a "lantern shape", and the area ratio of the cathode to the anode is 1.5-2.0:1.

[0043] Example 1

[0044] Surface treatment of the inner wall of the gas cylinder: material: 9100QP.

[0045] 1. Preparation of the solution

[0046] Preparation of the nickel-cobalt solution:

[0047] Main raw materials: nickel sulfate, cobalt sulfate, citric acid, boric acid, and grooving additives. Preparation process: according to the amount of the prepared solution, add 70% pure water, heat to 55°C, add boric acid, citric acid, nickel sulfate, and cobalt sulfate in sequence, dissolve, and then add deionized water to the standard volume after dissolution, and stir uniformly; solution electrolysis: electrolyze for more than 12 hours at a current density of 1A / dm 2 2, the coating on the cathode plate is brownish yellow instead of black; adjust the pH with nickel carbonate, and add deionized water to the use range, and then test plating.

[0048] Preparation of the tungsten alloy solution:

[0049] Main raw materials: nickel sulfate, sodium tungstate, phosphorous acid, citric acid, sodium citrate, slotting additives. Preparation process: according to the preparation solution, add 70% pure water, heat to 55℃, add citric acid, sodium citrate, sodium tungstate, phosphorous acid, nickel sulfate in order, stir, adjust pH with ammonia, add deionized water to the use range, and then test plating.

[0050] 2. Pretreatment of plated parts

[0051] Sandblasting, chemical degreasing and electrolytic degreasing of inner wall.

[0052] 3. Workpiece activation

[0053] After the pretreated inner wall of the gas cylinder, hot water washing, cold water washing, then first electro-activation (nitrate) (sodium nitrate solution, concentration: 400g / L) for 15 minutes, then chemical activation (dilute sulfuric acid, mass fraction: 10%) for 10 minutes, after activation, tap water washing, deionized water washing.

[0054] 4. Plating

[0055] Nickel-cobalt plating and tungsten alloy plating are carried out in sequence. When nickel-cobalt plating is carried out, a titanium-iridium coated metal oxide material is used for the symbolic anode, three groups of anode pieces are arranged axially around the central conductive shaft, the symbolic anode is inserted into the gas cylinder through the cylinder opening, the anode pieces are controlled to expand outward by the opening device, the anode piece groups are in the shape of a "lantern", the area ratio of the cathode to the anode is 1.75:1, the width of the anode piece is 20mm, the nickel-cobalt plating solution is used for electroplating after being introduced, the composition of the nickel-cobalt plating solution is: nickel sulfate: 360g / L, cobalt sulfate: 50g / L, citric acid: 20g / L, boric acid: 30g / L, the current density is 3A / dm 2 , pH=4.0, the temperature is 55℃, and the electroplating time is 120 minutes.

[0056] When tungsten alloy plating is carried out, a stainless steel anode material is used for the symbolic anode, three groups of anode pieces are arranged axially around the central conductive shaft, the symbolic anode is inserted into the gas cylinder through the cylinder opening, the anode pieces are controlled to expand outward by the opening device, the anode piece groups are in the shape of a "lantern", the area ratio of the cathode to the anode is 1.75:1, the composition of the tungsten alloy plating solution is: nickel sulfate: 17g / L, sodium tungstate: 30g / L, phosphorous acid: 27g / L, citric acid: 40g / L, sodium citrate: 40g / L, the current density is 5A / dm 2 , pH=7.1, the temperature is 65℃, the electroplating time is 60 minutes, and deionized water is used for flushing for 10 minutes after electroplating, and then blow-drying.

[0057] During both electroplating processes, air agitation was performed at the bottom, and the intensity of the air agitation was controlled at 0.6 m. 3 / (min·m 2 );

[0058] In addition, the flow rate of electroplating solution A and electroplating solution B entering from the lower tank inlet and flowing out from the upper tank overflow outlet is controlled to be 185L / min.

[0059] 5. Hydrogen removal

[0060] After electroplating, hydrogen removal is carried out at 200℃ for 4.0 hours.

[0061] 6. Inspection

[0062] First, the coating was visually inspected; the surface was found to be uniform, fine, smooth, and continuous. Second, microstructural analysis was performed. Figure 3 , Figure 4 The coating is mainly composed of a nickel-cobalt coating and a tungsten alloy coating. The average thickness of the nickel-cobalt coating is 45 μm, and the average thickness of the tungsten alloy coating is 14 μm. The total coating thickness and the ratio of the thickness of each layer basically meet the experimental design requirements, and the overall distribution is relatively uniform, indicating that the coating process is relatively stable. The roughness test shows that it does not exceed Ra 0.8 μm. No rust was observed after 1500 hours of neutral salt spray testing. The surface hardness is 760 HV. The inner wall fatigue performance test passed more than 1100 cycles, indicating that the inner surface coating can meet the requirements of coating expansion and contraction during the filling and discharging of compressed air in the gas cylinder. The testing standard is GB / T 9252-2017 "Gas Cylinder Fatigue Test Method".

[0063] The composition of the coatings was analyzed using scanning electron microscopy and energy dispersive spectroscopy. The nickel-cobalt coating contained 88.45 wt% nickel and 10.44 wt% cobalt, with the remainder being unavoidable impurities such as zinc and copper. The tungsten alloy coating contained 19.67 wt% tungsten, 78.27 wt% nickel, and 1.5 wt% phosphorus, with the remainder being unavoidable impurities such as iron and copper. The analysis was conducted according to GB / T17359-2023.

[0064] Example 2

[0065] Surface treatment of the inner wall of the gas cylinder, material: 9100QP.

[0066] Preparation of nickel-cobalt solution:

[0067] Main raw materials: nickel sulfate, cobalt sulfate, citric acid, boric acid, slotting additives. Preparation process: according to the preparation solution quantity, add 70% pure water, heat to 55℃, add boric acid, citric acid, nickel sulfate, cobalt sulfate in order, dissolve, after dissolving, constant volume to standard volume, stir evenly; Solution electrolysis: electrolysis for more than 12 hours at a current density of 1A / dm 2 , until the plating layer on the cathode plate is brownish yellow instead of black; adjust the PH value with nickel carbonate and add deionized water to the use range, and then test plating.

[0068] Preparation of tungsten alloy solution:

[0069] Main raw materials: nickel sulfate, sodium tungstate, phosphorous acid, citric acid, sodium citrate, slotting additives. Preparation process: according to the preparation solution quantity, add 70% pure water, heat to 55℃, add citric acid, sodium citrate, sodium tungstate, phosphorous acid, nickel sulfate in order, dissolve, stir, adjust the pH value with ammonia water, add deionized water to the use range, and then test plating.

[0070] 2, Pretreatment of plated parts

[0071] Sandblasting, chemical degreasing and electrolytic degreasing of inner wall.

[0072] 3, Workpiece activation

[0073] After the inner wall of the gas cylinder is pretreated, hot water is washed, then cold water is washed, then electric activation (sodium nitrate solution, concentration: 400g / L) is carried out for 15 minutes, then chemical activation (dilute sulfuric acid solution, mass fraction: 10%) is carried out for 10 minutes, after activation, tap water is washed, and deionized water is washed.

[0074] 4, Plating

[0075] Nickel-cobalt plating and tungsten alloy plating are carried out in sequence. When nickel-cobalt plating is carried out, titanium-iridium coated metal oxide material is used for the shape anode, three groups of anode sheets are arranged around the central conductive shaft in the axial direction, the shape anode is inserted into the gas cylinder from the cylinder opening, the anode sheets are controlled to expand outward by the expansion device, so that the anode sheet group assumes a "lantern shape", the area ratio of the cathode to the anode is 1.75:1, after the nickel-cobalt plating solution is introduced, electroplating is carried out, the composition of the nickel-cobalt plating solution is: nickel sulfate: 360g / L, cobalt sulfate: 50g / L, citric acid: 20g / L, boric acid: 30g / L, the current density is 2A / dm 2 , the titanium-iridium coated metal oxide anode is used, the pH value is 4.0, the temperature is 55℃, and the electroplating time is 120 minutes. After electroplating is completed, the next process is directly entered.

[0076] When the tungsten alloy coating is electroplated, the pictograph anode of titanium-iridium coated metal oxide material is used, three groups of anode sheet groups are arranged along the axial direction around the central conductive shaft, the pictograph anode is introduced into the gas cylinder from the cylinder mouth, the anode sheet is controlled to expand outward by the opening device, the anode sheet groups are made to be in a “lantern shape”, the area ratio of the cathode to the anode is 1.75:1, the electroplating tungsten alloy solution composition is: nickel sulfate: 17g / L, sodium tungstate: 30g / L, phosphorous acid: 27g / L, citric acid: 40g / L, sodium citrate: 40g / L, the current density is 5A / dm 2 2, the pH is 7.1, the temperature is between 70℃, the electroplating time is 60 minutes, after the electroplating is completed, deionized water is used for flushing for 10 minutes, and then drying is performed.

[0077] During the two electroplating processes, air stirring is performed at the bottom, and the intensity parameter of the air stirring is controlled to be: 0.6m 3 / (min·m 2 );

[0078] In addition, the flow rate of electroplating liquid A and electroplating liquid B flowing out from the inlet of the lower tank body to the overflow port of the upper tank body is controlled to be 185L / min.

[0079] 5、Dehydrogenation

[0080] After the electroplating is completed, dehydrogenation is performed at 200℃ for 4.0 hours within 4.0 hours.

[0081] Example 3

[0082] The surface treatment of the inner wall of the gas cylinder is made of 9100QP.

[0083] Preparation of nickel-cobalt solution:

[0084] Main raw materials: nickel sulfate, cobalt sulfate, citric acid, boric acid, and grooving additives. Preparation process: according to the preparation solution amount, 70% pure water is added, heated to 55℃, boric acid, citric acid, nickel sulfate, and cobalt sulfate are sequentially added and dissolved, and after the dissolution is completed, the standard volume is determined, and the stirring is uniform; solution electrolysis: electrolysis is performed for more than 12 hours at a current density of 1A / dm 2 2, until the coating on the cathode plate is brownish yellow instead of black; the pH is adjusted by using nickel carbonate, and deionized water is added to the use range, and the test plating can be performed.

[0085] Preparation of tungsten alloy solution:

[0086] Main raw materials: nickel sulfate, sodium tungstate, phosphorous acid, citric acid, sodium citrate, slotting additives. Preparation process: according to the preparation solution, add 70% pure water, heat to 55℃, add citric acid, sodium citrate, sodium tungstate, phosphorous acid, nickel sulfate in order, stir, adjust pH with ammonia, add deionized water to the use range, and then test plating.

[0087] 2. Pretreatment of plated parts

[0088] Sandblasting, chemical degreasing and electrolytic degreasing of inner wall.

[0089] 3. Workpiece activation

[0090] After pretreatment, the inner wall of the gas cylinder is washed with hot water, then cold water, then electric activation (sodium nitrate solution, concentration: 400g / L) for 15 minutes, then chemical activation (dilute sulfuric acid solution, mass fraction: 10%) for 10 minutes. After activation, wash with tap water and deionized water.

[0091] 4. Plating

[0092] Electroplating of nickel-cobalt plating layer and tungsten alloy plating layer is carried out in sequence. During nickel-cobalt plating, titanium-iridium coated metal oxide anode is used, three groups of anode sheets are arranged axially around the central conductive shaft, the anode is inserted into the cylinder through the cylinder opening, the anode sheets are expanded outward by the expansion device, the anode sheet group forms a "lantern shape", the area ratio of cathode to anode is 1.75:1, after the nickel-cobalt plating solution is introduced, electroplating is carried out. The composition of the nickel-cobalt plating solution is: nickel sulfate 360g / L, cobalt sulfate 50g / L, citric acid 20g / L, boric acid 30g / L, the current density is 3A / dm 2 , titanium-iridium coated metal oxide anode is used, pH=4.0, temperature is 60℃, electroplating time is 120 minutes. After electroplating, the next process is directly entered.

[0093] During tungsten alloy plating, titanium-iridium coated metal oxide anode is used, three groups of anode sheets are arranged axially around the central conductive shaft, the anode is inserted into the cylinder through the cylinder opening, the anode sheets are expanded outward by the expansion device, the anode sheet group forms a "lantern shape", the area ratio of cathode to anode is 1.75:1, after the tungsten alloy plating solution is introduced, electroplating is carried out. The composition of the tungsten alloy plating solution is: nickel sulfate 17g / L, sodium tungstate 30g / L, phosphorous acid 27g / L, citric acid 40g / L, sodium citrate 40g / L, the current density is 7A / dm 2 , titanium-iridium coated metal oxide anode is used, pH=7.1, temperature is 75℃, electroplating time is 60 minutes. After electroplating, deionized water is used for rinsing for 10 minutes and then blow-drying.

[0094] In the two plating processes, air agitation is performed at the bottom, and the intensity parameter of the air agitation is controlled to be 0.6 m 3 / min·m 2 ;

[0095] In addition, the flow rate of the plating solution A and the plating solution B flowing out from the lower tank inlet to the upper tank overflow is controlled to be 185 L / min.

[0096] 5. Hydrogen removal

[0097] After the plating is completed, hydrogen removal is performed at 200°C for 4.0 hours within 4.0 hours.

[0098] Comparative Example 1

[0099] The comparative example 1 is a plating using a single plating tungsten alloy process.

[0100] ① The pretreatment before plating is the same as that of Example 1.

[0101] ② Plating of tungsten alloy.

[0102] Preparation of tungsten alloy solution:

[0103] Main raw materials: nickel sulfate, sodium tungstate, phosphorous acid, citric acid, sodium citrate, and slotting additives. Preparation process: according to the amount of solution to be prepared, 700% of pure water is added, heated to 55°C, citric acid, sodium citrate, sodium tungstate, phosphorous acid, and nickel sulfate are sequentially added and dissolved, stirred, and adjusted to PH with ammonia water, and deionized water is added to the use range, and the plating test can be performed.

[0104] The stainless steel anode is used for plating at a current density of 5 A / dm 2 , the plating temperature is 65°C, the time is 180 minutes, and after plating, deionized water is used for rinsing for 10 minutes, and then dried.

[0105] ③ Hydrogen removal

[0106] After the plating is completed, hydrogen removal is performed at 200°C for 4.0 hours within 4.0 hours.

[0107] Comparative Example 2

[0108] The other conditions are the same as those of Example 1, except that air agitation is not performed, and as a result, the compactness of the plating layer is greatly reduced, and the surface of the plating layer is not smooth and has a large number of nodules.

[0109] Comparative Example 3

[0110] Other conditions are the same as example 1, only the anode sheet in the pictograph anode is not grouped, the length of the single anode sheet is about three times of that in example 1, and a long lantern-shaped anode is formed after final expansion. The uniformity after electroplating is weaker than that in example 1, the middle is thick, the two ends are thin, and the thickness is shown in table 1. The coating thickness at the inlet and outlet of the gas cylinder is thinner, the middle is thicker, the corrosion resistance is also poorer at the two ends and better in the middle.

[0111]

[0112] The corrosion resistance of the coating of the gas cylinder in the example and the comparative example is tested, and the performance results are shown in table 2.

[0113]

[0114] The example is a preferred embodiment of the present application, but the present application is not limited to the above-mentioned embodiment. Any obvious improvement, replacement or modification made by those skilled in the art without departing from the essential content of the present application shall fall within the protection scope of the present application.

Claims

1. A method for preparing an electroplated nickel-cobalt / tungsten alloy double-layer composite coating on the inner wall of a gas cylinder, characterized in that: First, a nickel-cobalt plating layer is electroplated on the inner wall of the gas cylinder. Then, a tungsten alloy plating layer is electroplated on the surface of the nickel-cobalt plating layer. Both the nickel-cobalt plating layer and the tungsten alloy plating layer are electroplated using a shaped anode. The shaped anode includes a central conductive shaft, around which several anode plate groups are arranged axially. The anode plate group located at the top of the shaped anode has a fixing ring at its top, securing it to the central conductive shaft. The two ends of the remaining anode plate groups, as well as the bottom end of the anode plate group located at the top of the shaped anode, are welded to a movable ring on the central conductive shaft, away from the fixing ring. An expansion device is provided. When the shaped anode enters the gas cylinder through the cylinder opening, the expansion device moves towards the fixed ring, causing the movable rings on the central axis to move closer together and drive the anode plates to expand outward, causing the anode plate group to form a "lantern shape". Before the anode plates expand, the radial dimension of the shaped anode is smaller than the diameter of the gas cylinder opening. When the shaped anode enters the gas cylinder through the cylinder opening, the outward expansion of the anode plates controls the area ratio of the cathode to the anode to be 1.5-2.0:1 when electroplating nickel-cobalt coating and electroplating tungsten alloy coating. The number of anode plate groups is three; During the electroplating of the nickel-cobalt coating and the tungsten alloy coating, air is stirred at the bottom of the gas cylinder at an intensity of 0.5-0.8 m. 3 / (min·m 2 ); The nickel-cobalt coating comprises Ni and Co, wherein the mass fraction of Co is 8-12% and the mass fraction of Ni is 88-91%; the tungsten alloy coating comprises W, Ni, and P, wherein the mass fraction of W is 12-30%, the mass fraction of Ni is 65-88%, and the mass fraction of P is 0.5-5%.

2. The method for preparing an electroplated nickel-cobalt / tungsten alloy double-layer composite coating on the inner wall of a gas cylinder according to claim 1, characterized in that: The width of the anode plate is 15-25 mm; The material of the pictographic anode is selected from one of titanium-ruthenium coated metal oxide, titanium-iridium coated metal oxide, and stainless steel.

3. A method for preparing an electroplated nickel-cobalt / tungsten alloy double-layer composite coating on the inner wall of a gas cylinder according to any one of claims 1-2, characterized in that: First, the inner wall of the gas cylinder is pretreated in sequence: hot water washing, cold water washing, activation, tap water washing, deionized water washing, and then a nickel-cobalt plating layer is electroplated. The pretreatment involves sequentially performing sandblasting, chemical degreasing, and electrolytic degreasing on the inner wall of the gas cylinder. The activation process involves sequentially electroactivating and chemically activating the inner wall of the pretreated gas cylinder. The electroactivation process involves immersing the pretreated inner wall of the gas cylinder in a nitrate solution for 10-20 minutes. The concentration of the nitrate solution is 380-420 g / L. The chemical activation process involves activating the inner wall of the gas cylinder with a sulfuric acid solution of 8-12% by mass for 5-10 minutes.

4. A method for preparing an electroplated nickel-cobalt / tungsten alloy double-layer composite coating on the inner wall of a gas cylinder according to any one of claims 1-2, characterized in that: The electroplating solution A for the nickel-cobalt plating layer comprises nickel sulfate: 340-380 g / L, cobalt sulfate: 40-55 g / L, citric acid: 15-25 g / L, and boric acid: 25-35 g / L; the current density during the nickel-cobalt plating process is 1-10 A / dm³. 2 The temperature is 30-60℃, and the pH is 2.0-5.0; The electroplating solution B for the tungsten alloy coating comprises nickel sulfate: 14-22 g / L, sodium tungstate: 25-35 g / L, phosphorous acid: 20-30 g / L, citric acid: 30-180 g / L, and sodium citrate: 30-100 g / L; the current density during the tungsten alloy coating electroplating is 3-15 A / dm³. 2 The temperature is 50-80℃ and the pH is 5.0-8.

0.

5. A method for preparing an electroplated nickel-cobalt / tungsten alloy double-layer composite coating on the inner wall of a gas cylinder according to any one of claims 1-2, characterized in that: During the electroplating of the nickel-cobalt coating and the tungsten alloy coating, the gas cylinder is vertically fixed on the support.

6. The method for preparing an electroplated nickel-cobalt / tungsten alloy double-layer composite coating on the inner wall of a gas cylinder according to claim 5, characterized in that: The gas cylinder is provided with an upper box at the top and a lower box at the bottom. During the electroplating of the nickel-cobalt coating and the tungsten alloy coating, electroplating solution A and electroplating solution B enter from the inlet of the lower box and flow out from the overflow port of the upper box, forming a closed solution flow inside; the flow rate of the solution flow is ≥185L / min.

7. The electroplated nickel-cobalt / tungsten alloy double-layer composite coating on the inner wall of a gas cylinder prepared by the preparation method according to any one of claims 1-2, characterized in that: The electroplated nickel-cobalt / tungsten alloy double-layer composite coating consists of a nickel-cobalt coating and a tungsten alloy coating from the inside out; the thickness of the nickel-cobalt coating is 20-45μm, and the thickness of the tungsten alloy coating is 10-20μm.

8. The application of the electroplated nickel-cobalt / tungsten alloy double-layer composite coating on the inner wall of a gas cylinder prepared by the preparation method according to any one of claims 1-2, characterized in that: Gas cylinders with electroplated nickel-cobalt / tungsten alloy double-layer composite coatings are used in marine environments.

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