CN101748449A - Method for plating chromium by using trivalent chromium - Google Patents

Abstract

The invention discloses a method for chrome plating with trivalent chromium, which comprises dissolving rare earth oxides in acid to prepare a rare earth salt solution; dissolving chromium sulfate, aluminum sulfate, sodium fluoride, urea and a complexing agent in water, adding For the rare earth salt solution obtained above, adjust the pH value of the solution with sodium bicarbonate solution to make chromium sulfate-aluminum sulfate-sodium fluoride-urea-complexing agent-rare earth salt electroplating solution; put the plated parts to be plated Electroplating in solution, the process conditions of controlled electroplating are: current density is 28-90A/dm ² , pH value of electroplating solution is 1-4, temperature is 25-60°C, stirring speed is 100-600rpm, plating time is 30- 90min; After the electroplating is completed, the plated parts are rinsed with water and air-dried, and the plated parts to be plated are chrome-plated with trivalent chromium. The hardness and wear resistance of the obtained chromium coating are obviously improved, the hardness is ≥815HV, and the wear quality is ≤0.08mg.

Description

A method of chrome plating with trivalent chromium

technical field

The invention belongs to the technical field of electrochemistry, that is, the invention relates to a method for plating chromium with trivalent chromium.

Background technique

Chrome plating has good hardness, wear resistance, corrosion resistance and decorative appearance. It is not only used for decorative coatings, but also widely used for functional coatings, so it is listed as one of the three major plating types. The chromic acid in the traditional hexavalent chromium solution is highly toxic, is a strong carcinogen, and causes great environmental pollution. In order to replace the hexavalent chromium plating process, a lot of research has been done on trivalent chromium plating. The current trivalent chromium plating systems mainly include sulfate solution system, chloride solution system and sulfate-chloride mixed solution system. Chromium plating with chloride solution system and sulfate-chloride mixed solution system will affect the environment due to the generation of chlorine gas at the anode, which is not conducive to the clean production of the electroplating industry. In the trivalent chromium electroplating process of the sulfate system, there is no chlorine gas generated at the anode, which is clean and pollution-free, and does not corrode the equipment. Adding rare earth elements to the plating solution of trivalent chromium plating in sulfate system can improve the wear resistance, corrosion resistance and hardness of the coating.

Contents of the invention

The purpose of the invention is to propose a method for chrome-plating with trivalent chromium in order to improve properties such as wear resistance and hardness of the chromium coating.

Technical solutions

A method for chrome plating with trivalent chromium, comprising the steps of:

(1), dissolving rare earth oxides in acid to prepare a rare earth salt solution;

The rare earth oxides are one or more mixtures of rare earth oxides of lanthanum, cerium, praseodymium, neodymium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium, lutetium, yttrium, and scandium;

The acid in which is concentrated nitric acid;

The prepared rare earth salt is rare earth nitrate, and the concentration of the rare earth in the rare earth salt solution is 10-50 g/L.

(2), dissolve chromium sulfate salt, aluminum sulfate, sodium fluoride, urea, complexing agent with water, add the rare earth salt solution of above-mentioned step (1) gained, adjust solution pH value with sodium bicarbonate solution, make chromium sulfate salt - aluminum sulfate - sodium fluoride - urea - complexing agent - rare earth salt electroplating solution;

Wherein the chromium sulfate is one or a mixture of potassium chromium sulfate and chromium sulfate;

The complexing agent is one or more mixtures of formic acid, acetic acid, malic acid, citric acid, oxalic acid, tartaric acid, lactic acid, aminoacetic acid, glycolic acid, and succinic acid;

Among them, the concentrations of chromium sulfate, aluminum sulfate, sodium fluoride, urea, complexing agent, and rare earth salt are: 200~400g/L, 150~300g/L, 30~50g/L, 30~300g/L, 30 ～100g/L, 0.05～6g/L;

The concentration of the sodium bicarbonate solution used is 20g/L;

The pH value of the chromium sulfate-aluminum sulfate-sodium fluoride-urea-complexing agent-rare earth salt electroplating solution is 1-4.

(3), put the plated parts to be plated into the electroplating solution for electroplating;

Put the plated parts to be plated into the chromium sulfate-aluminum sulfate-sodium fluoride-urea-complexing agent-rare earth salt electroplating solution obtained in step (2), and control the process conditions of electroplating: the current density is 28～90A /dm ² , the pH value of the electroplating solution is 1~4, the temperature is 25~60°C, the stirring speed is 100~600rpm, and the plating time is 30~90min;

(4), with the plated piece after step (3) electroplating, rinse with water, air-dry, promptly complete the plated piece to be plated with trivalent chromium plating.

Beneficial effects of the present invention

After the method for chrome plating with trivalent chromium of the present invention chrome-plates the plated piece to be plated, the hardness and wear resistance of the obtained chromium coating are obviously improved, the hardness is ≥815HV, and the wear quality is ≤0.08mg. Compared with the general trivalent chromium plating, the hardness of the chromium plating is increased by 15%, and the wear resistance is increased by 2 times.

Detailed ways

The present invention is further described below by embodiment, but does not limit the present invention.

A pin-on-disk friction and wear tester (TRB 01-02539 type) was used to measure the wear performance of the coating of the plated parts.

Test conditions: dry friction at room temperature, the friction pair is a small ball with a diameter of 6mm, the material is 100Cr6, the load is 5N, the speed is 0.12m/s, the radius of the wear scar is 5mm, and the number of revolutions is 5000.

Example 1

Weigh 2.9320g of lanthanum oxide in a 100mL small beaker, add 15mL of concentrated nitric acid under stirring, heat to dissolve it, and after it cools down, transfer it to a 50mL volumetric flask and dilute to the mark with water. The concentration of lanthanum in the solution is 50g/L.

Add 200g of chromium sulfate, 150g of aluminum sulfate, 30g of sodium fluoride, 30g of urea, 15g of formic acid, and 15g of citric acid into a 1L beaker, add 985mL of water to dissolve, add 1mL of the above solution with a concentration of lanthanum of 50g/L, stir well, and use Adjust the pH value of the solution to 1 with sodium bicarbonate solution, transfer it into a 1L volumetric flask, and dilute to the mark with water to prepare the electroplating solution.

Transfer the above electroplating solution into a 1L beaker, put the 80mm×80mm×0.5mm steel plate to be plated into the electroplating solution as the cathode, and the anode as the 150mm×100mm×2mm Ir-Ta oxide-coated Ti plate, magnetically stir , the stirring speed is 100rpm, the current density is 28A/dm ² , the pH value of the electroplating solution is 1, the temperature is 25°C, and the plating time is 90min.

Remove the plated parts, rinse with water, and air dry. The hardness of the chrome plating is 860.3HV.

A pin-on-disk friction and wear tester was used to measure the wear performance of the coating. The test conditions were dry friction at room temperature, the friction pair was a small ball with a diameter of 6mm, the material was 100Cr6, the load was 5N, the speed was 0.12m/s, the radius of the wear scar was 5mm, and the number of revolutions 5000, wear mass 0.07mg.

Example 2

Weigh 1.1664g of neodymium oxide in a 100mL small beaker, add 6mL of concentrated nitric acid under stirring, heat to dissolve it, and after it cools down, transfer it to a 50mL volumetric flask and dilute to the mark with water. The concentration of neodymium in the solution is 20g/L.

Add 400g potassium chromium sulfate, 300g aluminum sulfate, 50g sodium fluoride, 300g urea, 100g tartaric acid into a 1L beaker, add 935mL water to dissolve, add 50mL of the above-mentioned solution with a concentration of neodymium of 20g/L, stir well, and use sodium bicarbonate Adjust the pH value of the solution to 2, transfer it into a 1L volumetric flask, and dilute to the mark with water to prepare an electroplating solution.

Transfer the above electroplating solution into a 1L beaker, put the 80mm×80mm×0.5mm steel plate to be plated into the electroplating solution as the cathode, and the anode as the 150mm×100mm×2mm Ir-Ta oxide-coated Ti plate, magnetically stir , the stirring speed is 200rpm, the current density is 90A/dm ² , the pH value of the electroplating solution is 2, the temperature is 40°C, and the plating time is 30min.

Remove the plated parts, rinse with water, and air dry. The hardness of the chrome plating is 815.6HV.

A pin-on-disc friction and wear tester was used to measure the wear performance of the coating, the test condition was dry friction at room temperature, and the wear mass was 0.08mg.

Example 3

Weigh 2.8948g of europium oxide in a 100mL small beaker, add 15mL of concentrated nitric acid under stirring, heat to dissolve it, and after it cools down, move it to a 50mL volumetric flask and dilute to the mark with water. The concentration of europium in the solution is 50g/L.

Add 300g potassium chromium sulfate, 250g aluminum sulfate, 35g sodium fluoride, 200g urea, 50g aminoacetic acid into a 1L beaker, add 935mL water to dissolve, add 50mL of the above-mentioned solution with a concentration of europium of 50g/L, stir well, and use bicarbonate Adjust the pH value of the solution to 3 with sodium solution, transfer it into a 1L volumetric flask, and dilute to the mark with water to prepare the electroplating solution.

Transfer the above electroplating solution into a 1L beaker, put the 80mm×80mm×0.5mm steel plate to be plated into the electroplating solution as the cathode, and the anode as the 150mm×100mm×2mm Ir-Ta oxide-coated Ti plate, magnetically stir , the stirring speed is 300rpm, the current density is 50A/dm ² , the pH value of the electroplating solution is 3, the temperature is 60°C, and the plating time is 70min.

Remove the plated parts, rinse with water, and air dry. The hardness of the chrome plating is 870.2HV.

A pin-on-disc friction and wear tester was used to measure the wear performance of the coating, the test condition was dry friction at room temperature, and the wear mass was 0.07 mg.

Example 4

Weigh 5.7981g of samarium oxide in a 100mL small beaker, add 30mL of concentrated nitric acid under stirring, heat to dissolve it, and after it cools down, transfer it to a 100mL volumetric flask and dilute to the mark with water. The concentration of samarium in the solution is 50g/L.

Weigh 5.7631g of gadolinium oxide in a 100mL small beaker, add 30mL of concentrated nitric acid under stirring, heat to dissolve it, and after it cools down, move it to a 100mL volumetric flask and dilute to the mark with water. The concentration of gadolinium in the solution is 50g/L. Add 300g potassium chromium sulfate, 200g aluminum sulfate, 40g sodium fluoride, 100g urea, 20g lactic acid, 20g tartaric acid in a 1L beaker, add 865mL water to dissolve, add 60mL of the above samarium concentration of 50g/L solution and the above gadolinium concentration of 60mL of 50g/L solution, stir evenly, adjust the pH value of the solution to 4 with sodium bicarbonate solution, transfer it into a 1L volumetric flask, dilute with water to the mark, and prepare the electroplating solution.

Transfer the above electroplating solution into a 1L beaker, put the 80mm×80mm×0.5mm steel plate to be plated into the electroplating solution as the cathode, and the anode as the 150mm×100mm×2mm Ir-Ta oxide-coated Ti plate, magnetically stir , the stirring speed is 400rpm, the current density is 60A/dm ² , the pH value of the electroplating solution is 4, the temperature is 50°C, and the plating time is 60min. Remove the plated parts, rinse with water, and air dry. The hardness of the chrome plating is 871.8HV.

A pin-on-disc friction and wear tester was used to measure the wear performance of the coating, the test condition was dry friction at room temperature, and the wear mass was 0.06 mg.

Embodiment 5 (comparative embodiment of embodiment 4)

Add 300g chromium potassium sulfate, 200g aluminum sulfate, 40g sodium fluoride, 100g urea, 20g lactic acid, 20g tartaric acid into a 1L beaker, add 965mL water to dissolve, stir evenly, adjust the pH value of the solution to 4 with sodium bicarbonate solution, and transfer to In a 1L volumetric flask, dilute to the mark with water to prepare the electroplating solution.

Transfer the above electroplating solution into a 1L beaker, put the 80mm×80mm×0.5mm steel plate to be plated into the electroplating solution as the cathode, and the anode as the 150mm×100mm×2mm Ir-Ta oxide-coated Ti plate, magnetically stir , the stirring speed is 400rpm, the current density is 60A/dm ² , the pH value of the electroplating solution is 4, the temperature is 50°C, and the plating time is 60min.

Remove the plated parts, rinse with water, and air dry. The hardness of the chrome plating is 710.6HV.

A pin-on-disc friction and wear tester was used to measure the wear performance of the coating, the test condition was dry friction at room temperature, and the wear mass was 0.25 mg.

The effect of embodiment 5 is worse than that of embodiment 4. It can be seen that after the present invention adds rare earth elements to the plating solution, the hardness and wear resistance of the chromium coating obtained by electroplating have been significantly improved.

Example 6

Weigh 0.5686g of lutetium oxide into a 50mL small beaker, add 3mL of concentrated nitric acid under stirring, heat to dissolve it, and after it cools down, transfer it to a 50mL volumetric flask and dilute to the mark with water. The concentration of lutetium in the solution is 10g/L.

Weigh 2.9282g of cerium oxide in a 50mL small beaker, add 15mL of concentrated nitric acid under stirring, heat to dissolve it, and after it cools down, move it to a 50mL volumetric flask and dilute to the mark with water. The concentration of cerium in the solution is 50g/L.

Add 350g potassium chromium sulfate, 250g aluminum sulfate, 35g sodium fluoride, 80g urea, 80g glycolic acid into a 1L beaker, add 865mL water to dissolve, add 50mL of the above-mentioned lutetium solution with a concentration of 10g/L and the above-mentioned cerium concentration of 50g/L 50 mL of the solution in L, stir well, adjust the pH of the solution to 2.5 with sodium bicarbonate solution, transfer it into a 1L volumetric flask, and dilute to the mark with water to prepare the electroplating solution.

Transfer the above electroplating solution into a 1L beaker, put the 80mm×80mm×0.5mm steel plate to be plated into the electroplating solution as the cathode, and the anode as the 150mm×100mm×2mm Ir-Ta oxide-coated Ti plate, magnetically stir , the stirring speed is 600rpm, the current density is 40A/dm ² , the pH value of the electroplating solution is 2.5, the temperature is 50°C, and the plating time is 40min.

Remove the plated parts, rinse with water, and air dry. The hardness of the chrome plating is 882.6HV.

A pin-on-disc friction and wear tester was used to measure the wear performance of the coating, the test condition was dry friction at room temperature, and the wear mass was 0.06 mg.

The above content is only a basic description of the concept of the present invention, and any equivalent transformation made according to the technical solution of the present invention shall fall within the scope of protection of the present invention.

Claims (4)

1. a method for chrome plating with trivalent chromium, is characterized in that comprising the steps: (1), dissolving rare earth oxides in acid to prepare a rare earth salt solution; The rare earth oxides are one or more mixtures of rare earth oxides of lanthanum, cerium, praseodymium, neodymium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium, lutetium, yttrium, and scandium; The acid in which is concentrated nitric acid; The prepared rare earth salt is rare earth nitrate, and the concentration of the rare earth in the rare earth salt solution is: 10-50g/L; (2), dissolve chromium sulfate salt, aluminum sulfate, sodium fluoride, urea, complexing agent with water, add the rare earth salt solution of above-mentioned step (1) gained, adjust solution pH value with sodium bicarbonate solution, make chromium sulfate salt - aluminum sulfate - sodium fluoride - urea - complexing agent - rare earth salt electroplating solution; Wherein the chromium sulfate is one or a mixture of potassium chromium sulfate and chromium sulfate; The complexing agent is one or more mixtures of formic acid, acetic acid, malic acid, citric acid, oxalic acid, tartaric acid, lactic acid, aminoacetic acid, glycolic acid, and succinic acid; Among them, the concentrations of chromium sulfate, aluminum sulfate, sodium fluoride, urea, complexing agent, and rare earth salt are: 200~400g/L, 150~300g/L, 30~50g/L, 30~300g/L, 30 ～100g/L, 0.05～6g/L; The concentration of the sodium bicarbonate solution used is 20g/L; The pH value of the chromium sulfate-aluminum sulfate-sodium fluoride-urea-complexing agent-rare earth salt electroplating solution is 1-4; (3), put the plated parts to be plated into the electroplating solution for electroplating; Put the plated parts to be plated into the chromium sulfate-aluminum sulfate-sodium fluoride-urea-complexing agent-rare earth salt electroplating solution obtained in step (2), and control the process conditions of electroplating: the current density is 28～90A /dm ² , the pH value of the electroplating solution is 1~4, the temperature is 25~60°C, the stirring speed is 100~600rpm, and the plating time is 30~90min; (4), after the electroplating of step (3), the plated piece is rinsed with water and air-dried, and the plated piece to be plated is chrome-plated with trivalent chromium. 2. A method for chrome-plating with trivalent chromium as claimed in claim 1, characterized in that the preferred rare earth oxide in step (1) is lanthanum oxide, samarium oxide or gadolinium oxide. 3. a kind of method as claimed in claim 1, is characterized in that preferred complexing agent is citric acid, oxalic acid or tartaric acid in the step (2). 4. A method for chrome plating with trivalent chromium as claimed in claim 1, characterized in that the preferred control electroplating process conditions in step (3) are: current density is 45～70A/dm ² , the temperature is 35～55℃.