CN101899660B - Processing technology of dark green passivating film of galvanized workpiece - Google Patents

Abstract

The invention discloses a process for processing a dark green passivation film on a galvanized workpiece. The process is to put the light-exposed workpiece into a dark green passivation solution for passivation, and then wash, scald, blow dry or dry it. The components of the dark green passivation solution are chromic anhydride, phosphoric acid, nitric acid, sulfuric acid, glacial acetic acid and silver nitrate. The passivation film formed by the present invention on galvanized workpieces has an elegant appearance, bright oil, soft luminosity, black in the green tone, just like a paint layer, which is completely different from army green passivation film and black passivation film, and the passivation film has a Good adhesion, strong hydrophobicity on the surface, good corrosion resistance.

Description

A processing technology of dark green passivation film on galvanized workpiece

technical field

The invention belongs to the technical field of electroplating, and specifically relates to a processing technology for a dark green passivation film of a galvanized workpiece. the

Background technique

Because the steel substrate is easy to rust, it is usually protected by electro-galvanizing in industry, that is, the steel substrate is protected by the sacrifice of zinc. However, zinc is a chemically active metal. If the workpiece is not post-treated after galvanizing, the coating will soon become dark and white corrosion will appear one after another. In order to avoid this phenomenon, a passivation solution is often used to passivate the galvanized layer of the workpiece, so that a passivation film is formed on the surface of the galvanized layer to improve its corrosion resistance. After the passivation film is formed, not only the corrosion resistance of the galvanized layer can be greatly improved, but also the appearance of the galvanized layer becomes colorful. Depending on the passivation solution, the appearance of the galvanized layer can be iridescent, white, blue-white, army green, black, golden yellow, etc. At present, there is no relevant report on the processing technology of dark green passivation film on galvanized workpieces. the

Contents of the invention

The object of the present invention is to provide a processing technology for a dark green passivation film on a galvanized workpiece. The passivation film formed by this process has good gloss, good adhesion and strong corrosion resistance. the

To achieve the above object, the feature of the technical solution of the present invention is to take the following steps:

a. Take the galvanized workpiece out of the electroplating tank, wash it with water, and remove the remaining electroplating solution on the workpiece;

b. Put the cleaned workpiece into a certain concentration of nitric acid solution to emit light;

c. Use deionized water to clean the remaining light-emitting liquid on the workpiece after light-emitting, and then put the workpiece into the dark green passivation solution for passivation;

d. After the passivation is completed, take the workpiece out of the passivation solution, and let it stand in the air for a period of time, so that the reaction between the passivation solution and the zinc layer can fully proceed;

e. Wash the workpiece quickly with deionized water, then quickly scald it with high-temperature deionized water, and finally dry it with cold air or constant temperature. the

In the present invention, said nitric acid solution in the b step is 1% nitric acid solution, and the time of light emission is 1s; in the passivation process of c step, the workpiece will be shaken slightly, and the time of staying in the dark green passivation solution is 30-50s; d The time of standing in the air in the step is 60-120s; the time of quick cleaning with deionized water in the step e is 1s; said high-temperature deionized water refers to deionized water at 60°C, and the scalding time is 1s; Constant temperature drying means that the temperature is 60°C and the drying time is 15-20min. the

According to 1 liter of passivation solution, the components of said dark green passivation solution are:

Chromic anhydride 20-25(g/L);

Phosphoric acid/(d=1.7) 10-11(ml/L)

Nitric acid/(d=1.4) 2-2.5(ml/L)

Sulfuric acid/(d=1.84) 2-2.5(ml/L)

Glacial acetic acid 4-5(ml/L)

Silver nitrate 0.007-0.008(g/L)

The balance is deionized water. the

The preparation method of the above-mentioned dark green passivation solution is: pre-inject an appropriate amount of deionized water in the passivation tank, then add the required amount of chromic anhydride, phosphoric acid, nitric acid, sulfuric acid, glacial acetic acid and silver nitrate in sequence; Add deionized water to the predetermined liquid level and stir evenly. After adding chromic anhydride, it should be fully stirred to make it fully dissolved before adding other components; the added silver nitrate should be dissolved in deionized water first and then added to the passivation tank; add all raw materials and add deionized After the water is stirred evenly to the predetermined liquid level, the pH value of the solution is measured with pH test paper, and adjusted with glacial acetic acid so that the pH value of the solution is not higher than 1.5. the

The galvanized dark green passivation film formed by the present invention is composed of basic chromate hydrate colloids of divalent zinc, trivalent chromium and hexavalent chromium, and black metal particles and phosphate are also embedded in the skeleton structure of the film. , to maintain the dark green appearance of the membrane. The divalent zinc ions in the formed passivation film originate from the zinc layer. When the zinc layer enters the passivation solution, in the interface layer between the metal and the passivation solution, due to the presence of acid and the oxidation of chromic anhydride, the metal zinc is dissolved. In this interface layer film, the pH value increases rapidly, and the hexavalent chromium is reduced to trivalent chromium at the same time, and the trivalent chromium forms the colloidal skeleton of the film in the alkaline film. At this time, the acidity of the solution should not be too high, otherwise the colloidal film will It will be dissolved by hydrogen ions, so the pH value must be strictly controlled within the range of 1 to 1.5 to form a pH gradient in the film layer to balance the dissolution of the film on the solution side and the formation of the film on the zinc surface. At this time, black The metal particles simultaneously diffuse into the passivation film. This process is completed within 30 to 50 seconds. If the time is continued to be extended, the zinc layer will continue to be consumed, resulting in unnecessary losses. After the workpiece leaves the passivation solution, the passivation film should properly stay in the air for 60-120s, which is conducive to the continuous film formation reaction of the passivation film on the surface of the passivation film, making the film thicker, and removing the excess passivation solution at the same time. Then enter the deionized water for quick dipping and scalding, and finally dry with cold wind or at a constant temperature of 60°C. the

Specifically, in an acidic solution, chromic anhydride is dissolved in water to mainly generate Cr ₂ O ₇ ^2- , and the following ion balance exists:

2CrO ₄ ^2- +2H ⁺ →Cr ₂ O ₇ ^2- +H ₂ O Formula (1)

Cr ₂ O ₇ ^2- is a strong oxidizing agent. When the galvanized parts are immersed in the passivation solution, a chemical reaction occurs on the surface:

Anode reaction: Zn→Zn ²⁺ +2e

Cathode reaction: CrO ₄ ^2- +14H ⁺ +6e→2Cr ³⁺ +7H ₂ O

2H ⁺ +2e→H ₂ ↑

Phosphoric acid is also present in the solution, and the following equilibrium exists:

H ₃ PO ₄ →H ₂ PO ₄ ^- +H ⁺

H ₂ PO ₄ ^- →HPO ₄ ^2- +H ⁺

HPO ₄ ^2- → PO ₄ ^3- +H ⁺

At the same time, the Zn ²⁺ generated by the anode reaction will react with the phosphate and hydrogen phosphate on the interface to generate some insoluble phosphate. The Cr ³⁺ produced by the cathodic reaction will also react with the phosphate to form insoluble chromium phosphate.

On the other hand, due to the electrochemical reaction on the surface of the zinc layer, the pH value of the reaction interface increases, which prompts the balance of the reaction formula (1) to shift to the left, that is, some Cr ₂ O ₇ ^2- ions at the reaction interface generate CrO ₄ ^{2 -} ions, Cr ³⁺ and Zn ²⁺ cations react with PO ₄ ^3- , CrO ₄ ^2- , HPO ₄ ^2- , SO ₄ ^2- , and H ₂ O to form gel compounds with large network molecules . At this time, the acidity of the solution should not be too high, otherwise the colloidal film will be dissolved by H ⁺ , so the pH value must be strictly controlled between 1 and 1.5 to form a pH gradient in the film, so that the dissolution process of the film occurs on one side of the solution This is in equilibrium with the film formation process that occurs on the zinc surface side. At this time, the dyed particles Ag diffuse into the passivation film at the same time, so as to ensure the dark green appearance of the film layer.

The present invention has the following beneficial effects:

1. Use the method of the present invention to passivate the galvanized workpiece, and the formed passivation film has good effect. After the galvanized workpiece is passivated, the formed passivation film has an elegant appearance, glossy appearance, soft luminosity, black in the green tone, just like a paint layer, which is completely different from the army green passivation film and black passivation film, and the passivation film It has good adhesion, strong hydrophobicity on the surface and good corrosion resistance. The adhesion test was carried out according to the experimental method specified in GB9791-2003. The passivation film formed by the present invention can withstand 90 times of manual reciprocating wiping with a grain-free soft eraser without revealing the bottom. The corrosion resistance test is carried out according to the test method specified in GB/T6458-86. Using the passivation film formed by the present invention, no white corrosion products appear after 400 hours through the neutral salt spray test. the

2. The present invention has better social benefits. In the current electroplating process, the acid potassium chloride galvanizing process is one of the few green environmental protection processes, and the process of the present invention is particularly suitable for use in combination with the galvanizing process. Tests show that the present invention can show its unique advantages when passivating workpieces using the acid potassium chloride galvanizing process. The passivation film formed not only has strong corrosion resistance, but also has bright colors and good gloss. the

3. The process of the present invention is simple, the raw materials are easy to obtain, the design is reasonable, and the implementation is convenient. the

Description of drawings

Figure 1 is the XRD spectrum of the dark green passivated sample. the

Detailed ways

Embodiment 1, the processing technology of the dark green passivation film of the galvanized workpiece of the present embodiment is as follows:

①Preparation of dark green passivation solution

According to the amount of 1 liter of solution, the components of the dark green passivation solution are:

Chromic anhydride 20(g/L);

Phosphoric acid/(d=1.7) 11(ml/L);

Nitric acid/(d=1.4) 2.5(ml/L);

Sulfuric acid/(d=1.84) 2.5(ml/L);

Glacial acetic acid 5(ml/L);

Silver nitrate 0.008(g/L);

The balance is deionized water. The preparation method is as follows: pre-inject an appropriate amount of deionized water into the passivation tank, add the required amount of chromic anhydride according to the proportion of the above components, stir fully to make it fully dissolved, and then add the required amount of phosphoric acid and nitric acid in sequence , sulfuric acid, glacial acetic acid and silver nitrate, the added silver nitrate should be dissolved in deionized water first and then added to the passivation tank; add deionized water to the predetermined liquid level in the passivation tank, and stir evenly ; Use pH test paper to measure the pH value of the solution, and adjust it with glacial acetic acid so that the pH value of the solution is not higher than 1.5. the

②Passivate the galvanized workpiece

a. Take the galvanized workpiece out of the electroplating tank, wash it with water, and remove the remaining electroplating solution on the workpiece;

b. Put the cleaned workpiece into 1% nitric acid solution for 1s;

c. Use deionized water to clean the residual light-emitting liquid on the workpiece after light-emitting, and then put it into the dark green passivation solution prepared above for passivation. Note that the workpiece should be slightly shaken during the passivation process. The time to stay in the liquid is 30-50s;

d. After the passivation is finished, take the workpiece out of the passivation solution, and let it stand in the air for 60-120s, so that the reaction between the passivation solution and the zinc layer can fully proceed;

e. Wash the workpiece quickly with deionized water for 1 second, then quickly scald it with high-temperature deionized water at 60°C for 1 second, and finally dry it with cold wind, or dry it at a constant temperature at 60°C Dry for 15-20min. the

In this embodiment, the dark green passivation film formed on the galvanized workpiece has been tested and found that its adhesion and corrosion resistance are much higher than the requirements of the national standard. The INCAx-sight energy spectrometer (EDS) of Oxford, UK was used to analyze the surface of the dark green passivation film, and the distribution of elements on the surface of the dark green passivation film was measured as shown in the following table:

elements o P S Cr Zn Fe wt% 35.73 4.42 2.24. 8.35 48.06 1.21 at% 66.41 4025 2.07 4.78 21.86 0.64

Adopting the X-ray diffractometer of D/max-rB that the model that Japan Science and Technology Corporation produces is copper target (Cu-K α), tube pressure 40kV, tube flow 100mA, sweep speed 6 °/min at test condition 1. Under the condition of scanning range of 30°-90°, the phase composition of the passivation layer was analyzed, and the XRD spectrum of the dark green passivation sample was obtained as shown in FIG. 1 . The contained substances are marked with different symbols in the figure. The XRD analysis results show that in addition to the Zn crystal (galvanized layer), other substances appear, which are CrPO ₄ , Cr(OH) ₃ , CrOOH, Cr ₂ O _3. Zn(OH) ₂ , 2ZnO.CrO ₃ .H2O and Zn ₃ (PO ₄ ) ₂ .4H ₂ O.

Embodiment 2, the component of every liter of dark green passivation solution of the present embodiment is:

Chromic anhydride 25(g/L);

Phosphoric acid/(d=1.7) 10(ml/L);

Nitric acid/(d=1.4) 2(ml/L);

Sulfuric acid/(d=1.84) 2(ml/L);

Glacial acetic acid 4(ml/L);

Silver nitrate 0.007(g/L);

The balance is deionized water. Other technical characteristics are the same as embodiment 1. the

Claims (6)

1. a processing technology of galvanized workpiece dark green passivation film, it is characterized in that taking the following steps: a. Take the galvanized workpiece out of the electroplating tank, wash it with water, and remove the remaining electroplating solution on the workpiece; b. Put the cleaned workpiece into a certain concentration of nitric acid solution to emit light; c. Use deionized water to clean the residual light-emitting liquid on the workpiece after light-emitting, and then put the workpiece into the dark green passivation solution for passivation; the preparation method of the dark-green passivation solution is: in the passivation tank Inject an appropriate amount of deionized water in advance, and then add the required amount of chromic anhydride, phosphoric acid, nitric acid, sulfuric acid, glacial acetic acid and silver nitrate in sequence; add deionized water to the predetermined liquid level in the passivation tank, and stir evenly; press 1 liter The amount of passivation solution, the amount of each component contained in the dark green passivation solution is:

d. After the passivation is completed, take the workpiece out of the passivation solution, and let it stand in the air for a period of time, so that the reaction between the passivation solution and the zinc layer can fully proceed; e. Wash the workpiece quickly with deionized water, then quickly scald it with high-temperature deionized water, and finally dry it with cold air or constant temperature. 2. the processing technology of dark green passivation film of galvanized workpiece as claimed in claim 1, it is characterized in that said nitric acid solution in the b step is the nitric acid solution of 1%, and the light emitting time is 1s. 3. The processing technology of the dark green passivation film of galvanized workpiece as claimed in claim 1, it is characterized in that in the passivation process of step c, the workpiece will be shaken slightly, and the time of staying in the dark green passivation solution is 30-50s. 4. The processing technology of dark green passivation film of galvanized workpiece as claimed in claim 1, it is characterized in that in the preparation process of dark green passivation liquid, fully stir after first adding chromic anhydride, make it fully dissolve and then add other Components; the added silver nitrate should be dissolved in deionized water first and then added to the passivation tank; add all raw materials and add deionized water to the predetermined liquid level and stir evenly, then measure the pH value of the solution with pH test paper , and adjusted with glacial acetic acid to make the pH of the solution not higher than 1.5. 5. The processing technology of dark green passivation film of galvanized workpiece as claimed in claim 1, it is characterized in that the time left standing in the air is 60-120s in d step. 6. The processing technology of the dark green passivation film of galvanized workpiece as claimed in claim 1, it is characterized in that the time of quick cleaning with deionized water is 1s in the e step; Said high temperature deionized water refers to the temperature of 60 ℃. Deionized water, scalding time is 1s; constant temperature drying means that the temperature is 60°C, and the drying time is 15-20min.

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