Trivalent chromium plating solution of sulfate and chloride mixed system, and preparation and application thereof

Abstract

This invention discloses a method for preparing and electroplating a trivalent chromium rapid chromium plating solution using a sulfate and chloride mixed system. The plating solution comprises chromium salt, complexing agent, conductive salt, buffer, stabilizer, and wetting agent. The preparation method is as follows: first, heat 50% of the volumetric volume of water to 50-60°C, add the conductive salt and buffer, stir until completely dissolved, then add the chromium salt, complexing agent, and stabilizer sequentially, and finally add the wetting agent. Adjust the pH to between 2.0 and 3.0 with sulfuric acid or sodium hydroxide, and maintain the temperature between 50-60°C for 4 hours to obtain the electroplating solution of this invention. The plating solution of this invention is simple to prepare, with an average chromium deposition rate of 0.48 μm / min, a coating thickness of 29 micrometers, and a hardness ≥1000 HV.

Description

Technical Field

[0001] This invention belongs to the field of metal surface treatment technology, specifically relating to a trivalent chromium rapid chromium plating solution of sulfate and chloride mixed system and its preparation and application. Background Technology

[0002] Chromium plating boasts advantages such as a bright white appearance, high hardness, corrosion resistance, and a low coefficient of friction, making it a widely used coating in fields including automotive, aerospace, electronics, medical devices, furniture, bathroom fixtures, and decoration. Traditional chromium plating processes use hexavalent chromium, a known human carcinogen. Chromium plating wastewater is difficult and costly to treat, and traditional treatment methods struggle to completely remove it, easily causing secondary pollution. Against this backdrop, environmentally friendly trivalent chromium electroplating processes have been extensively researched. Trivalent chromium has only 1% the toxicity of hexavalent chromium, making it relatively environmentally friendly. Furthermore, it does not produce chromium mist during the electroplating process, reducing harm to the operating environment, and wastewater treatment is relatively easier, lowering treatment costs.

[0003] For example, in the patent CN 108456898 A, which discloses a "low-concentration sulfate trivalent chromium rapid chromium plating solution and its preparation method", the main salt is 15-35 g / L, the main complexing agent and auxiliary complexing agent are 7.5-18 g / L, the molar ratio of main salt to total complexing agent is 1:0.95-2.6, the conductivity is 80-120 g / L, the buffer is 60-100 g / L, the surfactant is 10-500 mg / L, and the brightener is 60-750 mg / L. The hardness of the plating layer obtained by this solution is 780-830 HV, the chromium deposition rate is 0.25 μm / min, and the deposition rate is difficult to increase.

[0004] For example, CN 103014784A discloses a room-temperature environmentally friendly trivalent chromium electroplating solution and its electroplating method, which consists of 150-200 g / L chromium trichloride, 80-90 g / L potassium thiosulfate, 65-75 g / L potassium chloride, 30-50 g / L boric acid, 10-15 g / L ammonium oxalate, 5-10 g / L ammonium bromide, 0.2-0.5 g / L coumarin, 0.02-0.04 g / L sodium dodecyl sulfate, and 0.02-0.2 g / L sodium dioctyl sulfosuccinate. This plating solution can produce a 10-15 μm plating depth and a hardness of 600-800 HV after 20-30 minutes of electroplating. However, the plating solution contains a large amount of chloride, and a large amount of chlorine gas will be generated during electroplating, which poses a certain environmental hazard.

[0005] It is evident that trivalent chromium electroplating has not completely replaced hexavalent chromium. It still suffers from color issues, slow deposition rate, difficulty in thickening, and low hardness. It is mainly used in decorative trivalent chromium electroplating where film thickness requirements are relatively low. Summary of the Invention

[0006] The purpose of this invention is to provide a method for preparing and electroplating a trivalent chromium rapid chromium plating solution using a sulfate and chloride mixture. The chromium layer deposition rate is 0.5–1 μm / min, and the plating thickness can reach 29 micrometers in 1 hour, producing a bright coating with a hardness ≥1000 HV. This solves the problems of slow deposition rate and difficulty in achieving thicker trivalent chromium plating, and the invention also contains a low chloride content.

[0007] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0008] A rapid chromium plating solution for trivalent chromium using a mixture of sulfate and chloride, comprising: trivalent chromium salt, complexing agent, conductive salt, stabilizer, buffer, wetting agent, and water.

[0009] Preferably, the composition includes the following components: 50-75 g / L of the trivalent chromium salt, 15-30 g / L of the complexing agent, 150-200 g / L of the conductive salt, 3-5 ml / L of the stabilizer, 60-80 g / L of the buffer, 1-3 ml / L of the wetting agent, and diluted to volume with water.

[0010] Preferably, it also includes a pH adjuster; the pH of the trivalent chromium rapid chromium plating solution in the sulfate and chloride mixture system is 2.0 to 3.0.

[0011] Preferably, the trivalent chromium salt includes one or more of chromium sulfate and chromium chloride; the complexing agent includes one or more of formic acid, acetic acid, glycine, tartaric acid, malic acid, citric acid and their salts; the conductive salt includes one or more of potassium sulfate and sodium sulfate; the buffer includes one or more of aluminum sulfate and boric acid; the stabilizer includes one or more of methanol and sodium sulfite; the wetting agent includes one or more of sodium dodecyl sulfate, sodium sulfosuccinate, and polyethylene glycol 200; and the pH adjuster includes one or more of sulfuric acid and sodium hydroxide.

[0012] A method for preparing a rapid chromium plating solution of trivalent chromium using the above-mentioned sulfate and chloride mixed system includes the following steps:

[0013] A. Heat a portion of the water, add the conductive salt and the stabilizer, stir, and obtain a second premixed solution;

[0014] B. Add the trivalent chromium salt, the complexing agent, the stabilizer, and the wetting agent to the premixed solution in sequence, adjust the pH to acidic, and add the remaining water to obtain the second premixed solution;

[0015] C. Keep the second premixed solution at a constant temperature, and then cool it down to obtain the trivalent chromium rapid chromium plating solution of the sulfate and chloride mixed system.

[0016] Preferably, in step A, the heating temperature includes 50-60°C; in step B, the pH adjustment includes adjusting the pH to 2.0-3.0; in step C, the heat preservation temperature includes 50-60°C, the heat preservation time includes 4 hours, and the cooling temperature includes 30-40°C; the volume ratio of water added in step A to step B is 1:1.

[0017] An application of a trivalent chromium rapid chromium plating solution of the above-mentioned sulfate and chloride mixed system, characterized in that it is used for electroplating.

[0018] Preferably, the steps include:

[0019] S1, Degreasing;

[0020] S2, Water washing;

[0021] S3, Activation;

[0022] S4, Water washing;

[0023] S5, Chrome plating:

[0024] S5-1. Fill the plating bath with the trivalent chromium rapid chromium plating solution of the sulfate and chloride mixture system;

[0025] S5-2, Set the operating temperature;

[0026] S5-3. Adjust the circulation flow rate of the plating solution;

[0027] S5-4. Immerse the workpiece in the plating bath;

[0028] S5-5, Set the distance between the cathode and anode;

[0029] S5-6. Set the current density and start the chrome plating process;

[0030] S6. Wash with water to obtain the electroplated workpiece.

[0031] Preferably, in step S5-2, the operating temperature includes 30–40°C; in step S5-3, the plating solution circulation flow rate includes circulating the plating solution in the tank twice per hour; in step S5-5, the distance between the cathode and the anode includes 4–6 cm, and the area ratio of the cathode to the anode includes 1:1.2; in step S5-6, the current density includes 8–13 A / dm³. 2 This allows for chromium layer deposition rates ranging from 0.5 to 1 μm / min.

[0032] The plating solution circulation rate is twice per hour. If the circulation rate is too fast, the chromium layer will be difficult to deposit successfully on the cathode. If it is too slow, the chromium hydroxyl bridge compound formed during electroplating will accumulate near the cathode, preventing further thickening of the plating layer.

[0033] The distance between the cathode and anode is 4-6 cm, and the cathode-anode area ratio is 1:1.2. The anode uses a DSA anode, which can reduce the oxygen evolution potential, prevent trivalent chromium from being oxidized to hexavalent chromium at the anode, and improve the stability of the plating solution.

[0034] Current density 8–13 A / dm 2 Generally, during trivalent chromium electroplating, severe hydrogen evolution at the cathode leads to an increase in the nearby pH. When the pH exceeds 4, the generated hydroxide ions and trivalent chromium ions in the plating bath readily undergo hydroxyl-bridged polymerization. This polymer is very stable, making it difficult for chromium ions to deposit. It also accumulates near the cathode, hindering chromium deposition. This is the main reason why the deposition rate of traditional trivalent chromium electroplating is difficult to improve. However, through long-term research, this invention has successfully increased the chromium layer deposition rate to 0.5–1 μm / min, achieving a thickness of 29 micrometers in one hour of electroplating, with a bright coating and a hardness ≥1000 HV.

[0035] The working temperature range of the plating solution is 30-40℃. If the temperature is too high, the deposition rate of the coating will be reduced, and if the temperature is too low, precipitates will be formed, and the conductivity of the plating solution will decrease.

[0036] An electroplated workpiece obtained by the above application.

[0037] Compared with the prior art, implementing the present invention has the following beneficial effects:

[0038] First, the addition of a complexing agent in this invention can inhibit the hydroxyl bridging reaction of chromium and improve the stability of the plating solution. By selecting different complexing agents and ratios, the optimal solution can be achieved.

[0039] Second, the present invention incorporates a high concentration of buffer to stabilize the pH, enabling electroplating to be maintained for a longer period of time.

[0040] Third, the present invention reduces the amount of hydroxyl-bridged compounds in the plating solution by appropriately circulating and renewing the plating solution in the tank, thereby reducing the obstacles to chromium deposition.

[0041] Fourth, the plating solution of the present invention can be used for electroplating at a lower current density, thereby reducing the occurrence of hydroxyl bridging reactions.

[0042] Fifth, the chromium chloride in the trivalent chromium salt of the present invention can both increase the deposition rate and prevent the generation of hexavalent chromium at the anode during electroplating. Attached Figure Description

[0043] Figure 1 SEM image of the chromium plating layer in Example 1;

[0044] Figure 2 This is a metallographic image of the chromium plating layer in Example 1. Detailed Implementation

[0045] To make the technical solution of the present invention easier to understand, the present invention will be further described in detail below with reference to specific embodiments, so that those skilled in the art can better understand and implement the present invention. However, the embodiments are not intended to limit the present invention. Modifications or substitutions made to the methods, steps, or conditions of the present invention without departing from the spirit and substance of the present invention are all within the scope of the present invention. Unless otherwise specified, the technical means used in the embodiments are conventional means well known to those skilled in the art.

[0046] Example 1

[0047] Preparation of chrome plating solution:

[0048] First, heat 50% of the volume of water to 50-60℃. Add 120g / L of conductive salt sodium sulfate, 50g / L of potassium sulfate, and 70g / L of buffer boric acid. Stir until completely dissolved. Then, add 50g / L of chromium salt chromium sulfate, 5g / L of chromium chloride, 10g / L of complexing agent formic acid, 5g / L of sodium acetate, and 4ml / l of stabilizer methanol. Finally, add 2ml / l of a 10% by weight sodium dodecyl sulfate solution as a wetting agent. Adjust the pH to between 2.0 and 3.0 with sulfuric acid or sodium hydroxide. Add the remaining water and maintain the temperature between 50-60℃ for 4 hours. Then, cool the temperature to 30-40℃ to obtain the plating solution.

[0049] Electroplating process flow: Degreasing → Water washing → Activation → Water washing → Chrome plating → Water washing

[0050] Chrome plating method:

[0051] The plating solution circulation rate is twice per hour, the distance between the cathode and anode is 4-6 cm, the cathode-to-anode area ratio is 1:1.2, and the current density is 10 A / dm³. 2 Electroplating thickness of 29 micrometers after 1 hour, chromium deposition rate of 0.48 μm / min, bright coating, hardness of 1040 HV.

[0052] Example 2

[0053] Preparation of chrome plating solution:

[0054] First, heat 50% of the volume of water to 50-60℃. Add 120g / L of conductive salt sodium sulfate, 50g / L of potassium sulfate, and 70g / L of buffer boric acid. Stir until completely dissolved. Then, add 50g / L of chromium salt chromium sulfate, 5g / L of chromium chloride, 10g / L of complexing agent formic acid, 5g / L of sodium acetate, and 4ml / l of stabilizer methanol. Finally, add 2ml / l of a 10% by weight sodium dodecyl sulfate solution as a wetting agent. Adjust the pH to between 2.0 and 3.0 with sulfuric acid or sodium hydroxide. Add the remaining water and maintain the temperature between 50-60℃ for 4 hours. Then, cool the temperature to 30-40℃ to obtain the plating solution.

[0055] Electroplating process flow: Degreasing → Water washing → Activation → Water washing → Chrome plating → Water washing

[0056] Chrome plating method:

[0057] The plating solution circulation rate is twice per hour, the distance between the cathode and anode is 4-6 cm, the cathode-to-anode area ratio is 1:1.2, and the current density is 10 A / dm³. 2 Electroplating for 5 minutes resulted in a thickness of 5 micrometers, with a chromium deposition rate of 1 μm / min. The plating was bright and had a hardness of 286 HV.

[0058] Example 3

[0059] Preparation of chrome plating solution:

[0060] First, heat 50% of the volume of water to 50-60℃. Add 120g / L of conductive salt sodium sulfate, 50g / L of potassium sulfate, and 70g / L of buffer boric acid. Stir until completely dissolved. Then, add 70g / L of chromium salt chromium sulfate, 5g / L of chromium chloride, 10g / L of complexing agent formic acid, 5g / L of sodium acetate, and 4ml / l of stabilizer methanol. Finally, add 2ml / l of a 10% by weight sodium dodecyl sulfate solution as a wetting agent. Adjust the pH to between 2.0 and 3.0 with sulfuric acid or sodium hydroxide. Add the remaining water and maintain the temperature between 50-60℃ for 4 hours. Then, cool the temperature to 30-40℃ to obtain the plating solution.

[0061] Electroplating process flow: Degreasing → Water washing → Activation → Water washing → Chrome plating → Water washing

[0062] Chrome plating method:

[0063] The plating solution circulation rate is twice per hour, the distance between the cathode and anode is 4-6 cm, the cathode-to-anode area ratio is 1:1.2, and the current density is 10 A / dm³. 2 Electroplating thickness of 27 micrometers after 1 hour, chromium deposition rate of 0.45 μm / min, bright coating, hardness of 887 HV.

[0064] Example 4

[0065] Preparation of chrome plating solution:

[0066] First, heat 50% of the volume of water to 50-60℃. Add 120g / L of conductive salt sodium sulfate, 50g / L of potassium sulfate, and 70g / L of buffer boric acid. Stir until completely dissolved. Then, add 50g / L of chromium salt chromium sulfate, 5g / L of chromium chloride, 10g / L of complexing agent formic acid, 5g / L of glycine, and 4ml / l of stabilizer methanol. Finally, add 2ml / l of a 10% by weight sodium dodecyl sulfate solution as a wetting agent. Adjust the pH to between 2.0 and 3.0 with sulfuric acid or sodium hydroxide. Add the remaining water and maintain the temperature between 50-60℃ for 4 hours. Then, cool the temperature to 30-40℃ to obtain the plating solution.

[0067] Electroplating process flow: Degreasing → Water washing → Activation → Water washing → Chrome plating → Water washing

[0068] Chrome plating method:

[0069] The plating solution circulation rate is twice per hour, the distance between the cathode and anode is 4-6 cm, the cathode-to-anode area ratio is 1:1.2, and the current density is 10 A / dm³. 2 Electroplating thickness of 25 micrometers in 1 hour, chromium deposition rate of 0.42 μm / min, bright coating, hardness of 856 HV.

[0070] Example 5

[0071] Preparation of chrome plating solution:

[0072] First, heat 50% of the volume of water to 50-60℃. Add 120g / L of conductive salt sodium sulfate, 50g / L of potassium sulfate, and 70g / L of buffer boric acid. Stir until completely dissolved. Then, add 50g / L of chromium salt chromium sulfate, 5g / L of chromium chloride, 10g / L of complexing agent formic acid, 9g / L of tartaric acid, and 4ml / l of stabilizer methanol. Finally, add 2ml / l of 10% by weight sodium dodecyl sulfate solution as a wetting agent. Adjust the pH to between 2.0 and 3.0 with sulfuric acid or sodium hydroxide. Add the remaining water and maintain the temperature between 50-60℃ for 4 hours. Then, cool the temperature to 30-40℃ to obtain the plating solution.

[0073] Electroplating process flow: Degreasing → Water washing → Activation → Water washing → Chrome plating → Water washing

[0074] Chrome plating method:

[0075] The plating solution circulation rate is twice per hour, the distance between the cathode and anode is 4-6 cm, the cathode-to-anode area ratio is 1:1.2, and the current density is 10 A / dm³. 2 Electroplating thickness of 22 micrometers after 1 hour, chromium deposition rate of 0.37 μm / min, bright coating, hardness of 841 HV.

[0076] Example 6

[0077] Preparation of chrome plating solution:

[0078] First, heat 50% of the volume of water to 50-60℃. Add 120g / L of conductive salt sodium sulfate, 50g / L of potassium sulfate, and 70g / L of buffer boric acid. Stir until completely dissolved. Then, add 50g / L of chromium salt chromium sulfate, 5g / L of chromium chloride, 10g / L of complexing agent formic acid, 8g / L of malic acid, and 4ml / l of stabilizer methanol. Finally, add 2ml / l of 10% by weight sodium dodecyl sulfate solution as a wetting agent. Adjust the pH to between 2.0 and 3.0 with sulfuric acid or sodium hydroxide. Add the remaining water and maintain the temperature between 50-60℃ for 4 hours. Then, cool the temperature to 30-40℃ to obtain the plating solution.

[0079] Electroplating process flow: Degreasing → Water washing → Activation → Water washing → Chrome plating → Water washing

[0080] Chrome plating method:

[0081] The plating solution circulation rate is twice per hour, the distance between the cathode and anode is 4-6 cm, the cathode-to-anode area ratio is 1:1.2, and the current density is 10 A / dm³. 2 Electroplating thickness of 23 micrometers after 1 hour, chromium deposition rate of 0.38 μm / min, bright coating, hardness of 845 HV.

[0082] Example 7

[0083] Preparation of chrome plating solution:

[0084] First, heat 50% of the volume of water to 50-60℃. Add 120g / L of conductive salt sodium sulfate, 50g / L of potassium sulfate, and 70g / L of buffer boric acid. Stir until completely dissolved. Then, add 50g / L of chromium salt chromium sulfate, 5g / L of chromium chloride, 10g / L of complexing agent formic acid, 12g / L of citric acid, and 4ml / l of stabilizer methanol. Finally, add 2ml / l of a 10% by weight sodium dodecyl sulfate solution as a wetting agent. Adjust the pH to between 2.0 and 3.0 with sulfuric acid or sodium hydroxide. Add the remaining water and maintain the temperature between 50-60℃ for 4 hours. Then, cool the temperature to 30-40℃ to obtain the plating solution.

[0085] Electroplating process flow: Degreasing → Water washing → Activation → Water washing → Chrome plating → Water washing

[0086] Chrome plating method:

[0087] The plating solution circulation rate is twice per hour, the distance between the cathode and anode is 4-6 cm, the cathode-to-anode area ratio is 1:1.2, and the current density is 10 A / dm³. 2 Electroplating thickness of 20 micrometers in 1 hour, chromium deposition rate of 0.33 μm / min, bright coating, hardness of 809 HV.

[0088] Example 1

[0089] Taking Example 1 as an example, SEM images and metallographic images of the electroplated workpiece were analyzed, and the results are as follows: Figure 1 , Figure 2 As shown. From Figure 1 , Figure 2 As can be seen, the chromium plating layer is free of cracks and particles, and the coating thickness can reach up to 29 micrometers, achieving excellent chromium plating results.

[0090] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A rapid chromium plating solution for trivalent chromium using a mixture of sulfate and chloride, characterized in that, It consists of 50 g / L chromium sulfate, 5 g / L chromium chloride, 10 g / L formic acid, 5 g / L sodium acetate, 120 g / L sodium sulfate, 50 g / L potassium sulfate, 4 ml / L methanol, 70 g / L boric acid, 2 ml / L of a 10% (by weight) sodium dodecyl sulfate solution, a pH adjuster, and water; the pH adjuster adjusts the pH to 2.0-3.0, and the solution is brought to a final volume with water; the pH adjuster is one or both of sulfuric acid and sodium hydroxide.

2. A method for preparing a rapid chromium plating solution of trivalent chromium using a sulfate and chloride mixture as described in claim 1, characterized in that, Includes the following steps: A. Heat a portion of the water, add sodium sulfate, potassium sulfate, and boric acid, stir, and obtain the first premixed solution; B. Add chromium sulfate, chromium chloride, formic acid, sodium acetate, methanol, and sodium dodecyl sulfate solution to the first premix solution in sequence, adjust the pH to acidic, and add the remaining water to obtain the second premix solution. C. Keep the second premixed solution at a constant temperature, and then cool it down to obtain the trivalent chromium rapid chromium plating solution of the sulfate and chloride mixed system.

3. The preparation method according to claim 2, characterized in that, In step A, the heating temperature is 50~60℃; in step B, the pH adjustment includes adjusting the pH to 2.0~3.0; in step C, the heat preservation temperature is 50~60℃, the heat preservation time is 4 hours, and the cooling temperature is 30~40℃; the volume ratio of water added in step A to step B is 1:

1.

4. An application of a trivalent chromium rapid chromium plating solution using a sulfate and chloride mixture as described in claim 1, characterized in that, Used for electroplating.

5. The application as described in claim 4, characterized in that, Includes the following steps: S1, Degreasing; S2, Water washing; S3, Activation; S4, Water washing; S5, Chrome plating: S5-1. Fill the plating bath with the trivalent chromium rapid chromium plating solution of the sulfate and chloride mixture system; S5-2, Set the operating temperature; S5-3. Adjust the circulation flow rate of the plating solution; S5-4. Immerse the workpiece in the plating bath; S5-5, Set the distance between the cathode and anode; S5-6. Set the current density and start the chrome plating process; S6. Wash with water to obtain the electroplated workpiece.

6. The application as described in claim 5, characterized in that, In step S5-2, the operating temperature is 30~40℃; in step S5-3, the plating solution circulation flow rate includes circulating the plating solution in the tank twice per hour; in step S5-5, the distance between the cathode and the anode is 4~6cm, and the area ratio of the cathode to the anode is 1:1.2; in step S5-6, the current density is 8~13A / dm².

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