CN102719864B - Method for preparing cerium-containing zinc coating - Google Patents

Abstract

The invention discloses a method for preparing a cerium-containing zinc coating. The main steps are: (1) preparing a sulfate bath of ions to be plated, wherein the concentration of zinc sulfate is 50-300g/L, and the concentration of cerium sulfate is 0.2~4g/L; add rare earth complexing agent sodium citrate 5~60g/L, add sodium hypophosphite 5~60g/L; use dilute sulfuric acid to adjust the pH value of the plating solution to 1~4; the temperature of the plating solution The control is 15~60°C. (2) Electroplating is carried out by the method of direct current electrodeposition; in the electroplating tank filled with the above-mentioned plating solution, the material to be plated is carbon steel as the cathode and platinum sheet as the anode, and a direct current is applied with a current density of 0.6~4A/cm ^2. The electroplating time is 1~6min; the content of cerium in the final coating is 0.05~0.3wt%. This method is aimed at the sulfate system of direct current electrodeposited zinc coating, adopts sodium citrate and sodium hypophosphite as the material that promotes cerium deposition, can improve the cathodic polarization behavior during cerium deposition, finally obtains the zinc coating containing trace cerium, makes the coating The corrosion resistance performance has been significantly improved.

Description

A kind of preparation method of cerium-containing zinc coating

technical field

The invention relates to a method for preparing a cerium-containing zinc coating by direct current electrodeposition in an acidic sulfate solution, in particular a method for preparing a cerium-containing zinc coating, which belongs to the technical field of surface engineering and surface anti-corrosion treatment.

Background technique

Corrosion of metal materials such as iron and steel not only leads to the scrapping of materials and equipment, but also causes huge indirect losses such as shutdown and production reduction, material loss, and environmental pollution, which hinders the development of the national economy. The surface treatment of materials is one of the most economical and effective means to solve the corrosion and protection of materials. Due to the advantages of simple process equipment, easy operation, and low cost, electroplating technology has become one of the most commonly used surface treatment technologies.

At present, the process of electro-galvanizing is relatively mature. Zinc coating is the most widely used protective coating on steel. Contact, and the method of sacrificial anode can be used to electrochemically protect the substrate to achieve the purpose of preventing steel corrosion. Due to the deterioration of the environment and the improvement of application requirements, in order to meet the actual production needs, the corrosion resistance of the zinc coating must be improved.

Rare earth elements have excellent properties due to their unique structures and are called "industrial vitamins". In the 1990s, rare earths began to be used in the surface chemical treatment of zinc coatings, which not only enhanced the corrosion resistance of the galvanized steel coating, but also avoided the environmental problems caused by the traditional chemical treatment of hexavalent chromium. Cerium salts among rare earths are popular because of factors such as price and performance. Adding rare earth cerium salt into the acidic electroplating zinc solution, adopting the method of direct current electrodeposition, obtains the zinc coating containing cerium, which makes the rare earth modification of the zinc coating more convenient and quick, and the existence of trace cerium has a positive effect on the corrosion resistance of the zinc coating. significantly improved.

Lokhande et al. reported the results of direct electrodeposition of La and Sm thin films from aqueous solution for the first time, and discussed the influence of different ligands and substrates on the precipitation potential of La. In acidic medium, oxalic acid, EDTA and sodium citrate were selected as ligands. Polarization curves of lanthanum electrodeposition were measured on different substrates (copper, brass, stainless steel, titanium, ITO) by potentiostatic method. The experimental results show that in the electrolyte without ligands, the hydrogen evolution potential on the substrate (except ITO) is about -1.0V (relative to SCE), and E°La ³⁺ =-2.52V, so the precipitation of lanthanum is affected by La cannot be electrodeposited due to the interference of hydrogen evolution. When the ligand is added to the plating solution, the copper, brass, and stainless steel cathodes start to have a La reduction current at -0.7 to -0.8V (relative to SCE), and the hydrogen evolution potential is about -1.2V, so hydrogen can be excluded The interference of precipitation enables La ⁺ to electrodeposit La from aqueous solution.

In the 1990s, Li Shijia and others in China began to add rare earth compounds to ordinary galvanizing solutions, and introduced trace rare earths into zinc coatings to study the deposition state and coating properties of rare earths. Subsequently, taking cerium as a representative, 0.1-0.2 g/L cerium salt was added to the potassium chloride plating solution, the content of cerium in the coating was tested, and the effect of cerium on the corrosion resistance of zinc coating was studied. The results show that: in the actual bright potassium chloride galvanized electrolyte, with the increase of the concentration of cerium salt in the bath, the content of cerium in the coating also increases. The presence of cerium can effectively improve the corrosion resistance of the zinc coating, and the maximum degree of improvement is about 35%. When the cerium content in the coating is between 10ppm and 20ppm, the coating has high corrosion resistance, and when it exceeds this value, the corrosion resistance of the coating decreases instead.

Chu Dewei and others studied the electroplating Zn system in the alkaline zincate system, using appropriate cerium salt complexing agents and electroplating additives, and determined the process conditions for electroplating Zn-Ce alloys. The existence of Ce in the coating was deduced by XRD analysis method. When the content of Ce ₂ (SO ₄ ) ₃ in the plating solution was 1g/L, the corrosion resistance of the Zn-Ce alloy coating and the pure Zn coating in NaCl solution were compared, and the corrosion resistance of the Zn-Ce alloy coating was found to be It is more than 3 times that of pure zinc coating with the same thickness.

At present, there are very few studies and literature introductions on the introduction of rare earths into zinc coatings, and the application in acid sulfate galvanizing systems has not been involved. The main problem is that the equilibrium potential of rare earth is far negative than the precipitation potential of zinc and hydrogen, which makes the preparation of rare earth in zinc coating more difficult; the complexing agent in different solutions has different deposition effects on rare earth, and further research is needed. further research. the

Contents of the invention

In view of the defects in the prior art, the purpose of the present invention is to provide a method for preparing a cerium-containing zinc coating, which is a method for preparing a cerium-containing zinc coating by direct current electrodeposition in an acidic sulfate solution.

To achieve the above object, the present invention adopts the following technical solutions:

The invention is a method for preparing a cerium-containing zinc coating, which is characterized in that it has the following preparation process and process conditions:

a. Prepare the sulfate solution of the ion to be plated, in which the concentration of zinc sulfate is 50~300g/L, and the concentration of cerium sulfate is 0.2~4g/L;

b. Add rare earth complexing agent sodium citrate to the above sulfate solution, the concentration is 5~60g/L; then add sodium hypophosphite, the concentration is 5~60g/L; use dilute sulfuric acid to adjust the pH value of the plating solution 1~4; the temperature of the bath is controlled at 15~60°C;

c. Electroplating is carried out by direct current electrodeposition; in the electroplating tank filled with the above plating solution, the carbon steel to be plated is used as the cathode, and the platinum sheet is used as the anode, and a direct current is applied with a current density of 0.6~4A/cm2. The electroplating time is 1-6 minutes; the content of rare earth cerium in the finally prepared coating is 0.05-0.3wt%.

Compared with the prior art, the features of the present invention are as follows:

(1) Using acidic sulfate system without adding other conductive salts, the current efficiency is high, and the maintenance of the plating solution is easy; (2) The complexing agent sodium citrate is added to the plating solution to form a complex cation with cerium, changing the cerium The cathodic polarization behavior makes the precipitation of cerium possible; (3) sodium hypophosphite is added to the plating solution to provide phosphorus with strong electronegativeness to promote the deposition of cerium (4) the corrosion resistance of the zinc coating containing cerium is improved Very obvious improvement.

Description of drawings

Fig. 1 is the scanning topography figure of cerium-containing zinc coating;

Figure 2 is the EDS spectrum of the surface micro-region of the cerium-containing zinc coating.

Detailed ways

    Specific embodiments of the present invention are described below.

Example 1

The preparation process and steps in this example are as follows:

a. First prepare the sulfate solution of the ion to be plated, and dissolve 60g of crystalline zinc sulfate and 2g of cerous sulfate in distilled water to prepare a 1L plating solution.

b. Then add 20g of sodium citrate and 20g of sodium hypophosphite to dissolve completely; add dilute sulfuric acid to adjust the pH value to 2, and control the temperature of the plating solution to 55°C.

c. Electrodeposition is carried out by DC electroplating method; in the electroplating tank filled with the above-mentioned sulfate plating solution, the steel plate to be plated is used as the cathode and the platinum sheet is used as the anode, and a DC current of 0.6A/ ^cm2 is passed through for 2 minutes; finally The Ce content in the coating was measured by AES to be 0.1wt%.

Example 2

The preparation process and steps in this embodiment are as follows:

a. First prepare the sulfate solution of the ion to be plated, dissolve 100g of crystalline zinc sulfate and 2g of cerous sulfate in distilled water to prepare a 1L plating solution.

b. Then add 20g of sodium citrate and 20g of sodium hypophosphite to dissolve completely; add dilute sulfuric acid to adjust the pH value to 2, and control the temperature of the bath to 55°C.

c. Use DC electroplating method for electrodeposition; in the electroplating tank filled with the above-mentioned sulfate plating solution, use the steel plate to be plated as the cathode and the platinum sheet as the anode, feed a DC current of 1A/ ^cm2 , and electroplate for 2 minutes; The final AES measured Ce content in the coating was 0.065wt%.

Example 3

The preparation process and steps in this embodiment are as follows:

a. First prepare the sulfate solution of the ion to be plated, dissolve 350g of crystalline zinc sulfate and 2g of cerous sulfate in distilled water to prepare a 1L plating solution.

b. Then add 30g of sodium citrate and 30g of sodium hypophosphite to dissolve completely; add dilute sulfuric acid to adjust the pH value to 2, and control the temperature of the plating solution to 25°C.

c. Use DC electroplating method for electrodeposition; in the electroplating tank filled with the above-mentioned sulfate plating solution, use the steel plate to be plated as the cathode and the platinum sheet as the anode, feed a DC current of 2A/ ^cm2 , and electroplate for 2 minutes; The final AES measured Ce content in the coating was 0.05wt%.

Claims (1)

1., containing a preparation method for cerium zinc coating, it is characterized in that there are following steps:

A. preparation is plated the sulfate liquor of ion, and wherein sulfuric acid zinc concentration is 50 ~ 300g/L, and the concentration of cerous sulfate is 0.2 ~ 4g/L;

B. in above-mentioned sulfate liquor, add rare-earth enveloping agent natrium citricum, concentration is 5 ~ 60g/L; Add inferior sodium phosphate again, concentration is 5 ~ 60g/L; Dilute sulfuric acid is adopted to regulate the pH value of plating solution to be 1 ~ 4; The temperature of plating solution controls to be 15 ~ 60 DEG C;

C. the method for DC electrodeposition is adopted to electroplate; In the electroplating bath filling above-mentioned plating solution, with plated material carbon steel for negative electrode, be anode, pass into DC current with platinized platinum, current density is 0.6 ~ 4A/cm ², electroplating time is 1 ~ 6min; The content of final obtained coating middle rare earth cerium is 0.05 ~ 0.3wt%.