CN101876071B - Environmentally-friendly black chrome-silver-free zinc-plating passivation solution and preparation method thereof - Google Patents

Abstract

The invention provides a black passivation solution for post-galvanizing treatment, which consists of the following components: sodium silicate 10-20g/L, copper sulfate 20-30g/L, nickel sulfate 0.5-1.5g/L, sulfuric acid Ferrous iron 0.5-1.5g/L, sodium acetate 1-3g/L, glacial acetic acid 20-40mL/L, sulfuric acid (98%) 3-7mL/L, and the rest is water. The galvanized material treated by this passivation solution presents a uniform, bright and black appearance, and has excellent corrosion resistance. After the neutral salt spray test, the rusting time can reach more than 200 hours, and the appearance and performance can reach the current level. It has the effect of black passivation process containing chromium and silver. The present invention uses silicate instead of chromium salt as the main film-forming substance, and uses copper salt, nickel salt, and iron salt instead of silver salt as the blackening agent, which fundamentally solves the problem caused by the use of chromium salt in the existing galvanizing black passivation process. At the same time, the use of silver salt is canceled, and the cost of passivation solution is greatly reduced. The passivation solution is stable and reliable, and the film-forming efficiency is high.

Description

A kind of chromium-free and silver-free galvanized black passivation solution and preparation method thereof

technical field

The invention relates to the technical field of material surface treatment, in particular to a chromium-free and silver-free environment-friendly galvanized black passivation solution used as a post-treatment solution for electrogalvanized iron and steel parts and a preparation method thereof.

Background technique

Material corrosion and material anticorrosion engineering are directly related to economic development and people's life safety. Surface engineering technology is the most economical and effective means and method to solve the corrosion and protection of mechanical parts and materials.

Electrogalvanizing is an effective way to improve the corrosion resistance of the surface of steel materials, and is currently widely used in many fields such as construction, transportation, machinery, electronics, and aviation. However, in a humid environment, especially in a hot and humid environment, the galvanized layer is prone to corrosion, causing the surface of the coating to form a dark gray or white loose corrosion product - white rust; after a long time, red rust will appear, thus losing the anti-corrosion effect. In order to improve the corrosion resistance of the coating, it is necessary to passivate the coating after the surface of the steel material is galvanized, so as to form a dense passivation film on the surface of the galvanized layer, thereby further improving the corrosion resistance of the material and prolonging the service life of the material. service life.

At present, almost all post-treatment processes of galvanized materials such as galvanized sheets adopt passivation treatment with hexavalent chromium or trivalent chromium as the main component. Restrict its use and emissions, especially in the EU RoHS Directive, which clearly prohibits the use of any parts and products treated with hexavalent chromium passivation technology; although the trivalent chromium passivation process is much less polluting than hexavalent chromium, it is passed Trivalent chromium passivated galvanized materials will still be oxidized to hexavalent chromium after a period of time, which means that the toxicity of hexavalent chromium has not really been solved, so many countries and regions have begun to restrict the use of trivalent chromium passivation process. In addition, since the chromium-containing passivation process is widely used in the galvanized black passivation process in our country, a large number of products that need galvanized and black passivated products in the electronics, machinery, hardware and other industries cannot be exported, which seriously affects my country's foreign trade. trading.

Therefore, the development of a chromium-free passivation solution that meets environmental protection requirements will inevitably become a future development trend. At present, the research on chromium-free passivation solution for zinc coating at home and abroad mainly includes molybdate system, titanium salt system, rare earth system, silicate system, phytic acid system and organic system, etc., but these chromium-free passivation systems only It can form a (blue) white or colored passivation film on the surface of the galvanized layer. For many black passivated galvanized parts used in production, it still completely relies on hexavalent chromium or trivalent chromium passivation process.

In addition, in many black passivation processes of galvanized parts, in addition to using chromium salt as the main film-forming substance, it is usually necessary to add silver salt to the passivation solution as a blackening agent. The production cost has a great impact on the economic benefits of galvanizing enterprises. Therefore, when developing a chromium-free passivation process, it is also necessary to consider how to reduce or even eliminate the use of silver salts.

Contents of the invention

The present invention is just to overcome the deficiencies of the existing passivation solution in the prior art, and provides a chrome-free and silver-free environmentally friendly galvanized black passivation solution, which has excellent performance, low cost, and high efficiency, and can meet the requirements of electroplating galvanized iron and steel parts. The silicate passivation solution required for black passivation and its preparation method.

The technical solution of the present invention is: on the basis of the existing chromium salt passivation process, use silicate instead of chromium salt as the main film-forming substance, and use copper sulfate, nickel sulfate, ferrous sulfate and other substances instead of silver salt as the blackening agent. At the same time, various other auxiliary film-forming substances were selected and optimized, and the invention was a completely chrome-free and silver-free black passivation solution for galvanizing post-treatment, consisting of the following components:

Described sodium silicate, copper sulfate, nickel sulfate, ferrous sulfate, sodium acetate, glacial acetic acid, sulfuric acid are commercially available chemically pure products.

Described silicate black passivation solution is prepared by the following methods:

A, sodium silicate is dissolved in a small amount of water to obtain a completely dissolved aqueous solution of sodium silicate;

B, add sulfuric acid in the sodium silicate aqueous solution of A step, mix well;

C, copper sulfate is added in the mixed solution of B step, mixes evenly;

D, nickel sulfate is added in the mixed solution of C step, mixes evenly;

E, ferrous sulfate is added in the mixed liquor of D step, mixes evenly;

F, sodium acetate is added in the mixed liquor of E step, mix well;

G, glacial acetic acid is added in the mixed liquor of F step, mixes evenly;

H. Add water to the mixed solution in step G to the required volume, and adjust the pH value to 2.0-2.5 with dilute H ₂ SO ₄ or dilute NaOH solution according to conventional methods to obtain a silicate black passivation solution.

The method of using the silicate black passivation solution to passivate the electro-galvanized parts is as follows: clean the electro-galvanized steel parts with water, perform light treatment according to the conventional method, take out the parts and wash them in water, and then immerse the parts in After soaking in the silicate black passivation solution at room temperature for 1 to 2 minutes, take it out, wash it with water, and then dry it.

The electro-galvanizing process is obtained by using the existing mature technology.

The light-emitting treatment is as follows: put the galvanized parts into the light-emitting liquid composed of HNO ₃ and H ₂ O, soak at room temperature for 3 to 5 seconds, and then take it out. The specific ratio of the light-emitting liquid is: mass The concentration is 65% HNO ₃ 5-15mL/L, the rest is H ₂ O.

The cleaning method of the galvanized, polished and passivated parts is as follows: washing with tap water, or rinsing in a tank or pool filled with clean water until the surface of the plated parts is cleaned.

The drying method of the passivated galvanized parts is as follows: drying naturally, or drying with a hair dryer, or drying in an oven.

The water used in each process involved in the present invention is tap water or distilled water.

Compared with the prior art, the present invention has the following advantages and effects: using the above scheme, sodium silicate is used as the main component, and auxiliary components such as copper sulfate, nickel sulfate, ferrous sulfate, sodium acetate, glacial acetic acid, sulfuric acid, etc. are added. The film material is formulated into a clean silicate black passivation solution, which is used for subsequent passivation treatment of electro-galvanized products, which can make the appearance of galvanized products present a good visual effect that is black and bright, and at the same time significantly improve the quality of galvanized products. Or the corrosion resistance of the material, after the salt spray test, the rusting time can reach more than 200 hours, and the appearance and performance can reach the effect of the existing chromium-containing black passivation process. In addition, because the passivation solution of the present invention does not contain hexavalent chromium and trivalent chromium, it fundamentally solves the problem of environmental pollution by the existing chromium-containing passivation process, and fully complies with China's national sewage comprehensive discharge standard (GB 8978-1996 ) and the EU RoHS Directive and other environmental standards, it is a true chromium-free passivation solution, which can greatly improve the clean production of the passivation process of electro-galvanized products; at the same time, relatively cheap copper salts, nickel salts, Iron salt replaces the traditional blackening passivation process of silver salt, and greatly reduces the preparation cost of passivation solution. The passivation solution is stable and reliable, and has high film forming efficiency. It can completely replace the existing black passivation solution containing chromium and silver. , is also easily accepted by manufacturers in terms of cost and passivation efficiency, and is an environmentally friendly passivation solution with great application prospects.

Detailed ways

The present invention will be further described below in conjunction with embodiment.

Example 1:

1) Prepare materials according to the following formula: sodium silicate 10g/L, copper sulfate 20g/L, nickel sulfate 0.5g/L, ferrous sulfate 0.5g/L, sodium acetate 1g/L, glacial acetic acid 20mL/L, sulfuric acid (98 %) 3mL/L, the rest is water, the raw materials used are commercially available chemically pure products, and _H2O is tap water;

2) The silicate black passivation solution is prepared by the following method for subsequent use:

A, 10g of sodium silicate is dissolved in a small amount of water to obtain a completely dissolved aqueous solution of sodium silicate;

B, 3mL sulfuric acid (98%) is added in the sodium silicate aqueous solution of A step, mixes evenly;

C, 20g copper sulfate is added in the mixed solution of B step, mixes evenly;

D, 0.5g nickel sulfate is added in the mixed solution of C step, mixes evenly;

E, 0.5g ferrous sulfate is added in the mixed liquor of D step, mixes evenly;

F. Add 1g of sodium acetate to the mixed solution in step E, and mix well;

G. Add 20mL of glacial acetic acid to the mixture in step F, and mix well;

H. Add water to the mixed solution in step G to adjust the _volume to 1 liter, adjust the pH value to about 2.0 with dilute _H2SO4 or dilute NaOH solution according to the conventional method, and obtain the silicate black passivation solution;

3) The electro-galvanized steel plate is obtained by the following method: the low-carbon steel plate of 80 mm × 40 mm × 1.5 mm is subjected to pre-treatments such as rust removal, degreasing, activation, etc. before electroplating, and then placed in a conventional electroplating solution for electroplating treatment. The bath composition and operating conditions of the galvanizing process are: ZnCl ₂ : 50g/L, KCl: 200g/L, No. 1 additive of zinc chloride 12mL/L, No. 2 additive of zinc chloride 6mL/L, and the pH of the bath is 6.0, the current density is 1.0A/dm ² , the temperature is room temperature, and the electroplating time is 25 minutes, the electroplated galvanized steel sheet is obtained, and it is ready for use;

4) Preparation of light-emitting liquid: chemically pure HNO ₃ (concentration of 65% by mass) was mixed with tap water at 10 mL/L to make light-emitting liquid (add 10 mL of HNO ₃ per liter of water), and set aside;

5) Clean the electrogalvanized steel sheet after 3) with tap water, then immerse it in the light-emitting solution of 4), stay at room temperature for 5 seconds, take it out, clean it with tap water, and then immerse it in the passivation solution of 2), and soak it at room temperature for 1 After a few minutes, take it out, rinse it with tap water and dry it with a hair dryer.

The galvanized steel plate treated with this passivation solution presents a uniform, bright and black appearance. After the neutral salt spray test, the white rust time can reach 200 hours.

Example 2:

1) Prepare materials according to the following formula: sodium silicate 15g/L, copper sulfate 25g/L, nickel sulfate 1.0g/L, ferrous sulfate 1.0g/L, sodium acetate 2g/L, glacial acetic acid 30mL/L, sulfuric acid (98 %) 5mL/L, the rest is water, the raw materials used are commercially available chemically pure products, and the H ₂ O is distilled water.

2) through the method identical with embodiment 1, be mixed with the silicate black passivation solution that pH value is about 2.2, for subsequent use:

3) The electrogalvanized steel plate is obtained by the following method: the Q235 steel plate of 100mm×60mm×2mm is subjected to pretreatment such as derusting, degreasing, activation, etc. The plating solution composition and operating conditions of the treatment process are: ZnO: 10g/L, NaOH: 120g/L, Z50 alkaline zinc plating additive 8mL/L, the pH value of the plating solution is 12, and the current density is 2.0A/dm ² , The temperature is room temperature, and the electroplating time is 15 minutes to obtain an electro-galvanized steel sheet for subsequent use;

4) Preparation of light-emitting liquid: chemically pure HNO ₃ (mass percentage concentration 65%) was mixed with tap water at 15mL/L to make light-emitting liquid (add 15mL of HNO ₃ per liter of water), and set aside;

5) Immerse the galvanized steel sheet of 3) in the light-emitting solution of 4), stay at room temperature for 3 seconds, take it out, clean it with tap water, put it in the passivation solution of 2), soak it for 2 minutes at room temperature, and then take out the Steel plates were dried at 80°C in a blast oven.

The galvanized steel plate treated with this passivation solution presents a uniform, bright and black appearance. After the neutral salt spray test, the white rust time can reach 280 hours.

Example 3:

1) Prepare materials according to the following formula: sodium silicate 20g/L, copper sulfate 30g/L, nickel sulfate 1.5gg/L, ferrous sulfate 1.5g/L, sodium acetate 3g/L, glacial acetic acid 40mL/L, sulfuric acid (98 %) 7mL/L, the rest is water, the raw materials used are commercially available chemically pure products, and H ₂ O is tap water.

2) Prepare a silicate color passivation solution with a pH value of about 2.5 through the same method as in Example 1, for subsequent use;

3) Alkaline electro-galvanizing treatment of a steel shell of a certain machine: Electroplating is carried out after the steel shell of a certain machine is subjected to conventional derusting, degreasing, weak etching, pre-soaking, etc., and the composition of the plating solution of the galvanizing process and The operating conditions are: ZnO 10g/L, NaOH 120g/L, Z50 alkaline galvanizing additive 8mL/L, current density 2.5A/dm ² , temperature at room temperature, and electroplating time of 30 minutes to obtain an electroplated galvanized shell for use;

4) Preparation of light emitting liquid: chemically pure HNO ₃ (concentration of 65% by mass) was mixed with tap water at 5 mL/L to make light emitting liquid (5 mL of HNO ₃ per liter of water), and set aside;

5) After cleaning the electro-galvanized steel shell of 3) with tap water, put it into the light-emitting solution of 4), soak it for 5 seconds at room temperature, take it out, rinse it with tap water, then put it into the passivation solution of 2), and put it in the passivation solution at room temperature. Soak for 90 seconds, take it out, wash it with tap water, and let it dry naturally.

The galvanized steel shell treated with this passivation solution presents a uniform, bright and black appearance. After the neutral salt spray test, the white rust time can reach 240 hours.

Claims (1)

1. a chromium-free and silver-free galvanized black passivation solution is characterized in that it is made up of the following components:

the rest is water; The preparation method of the described chromium-free and silver-free galvanized black passivation solution is prepared according to the following steps: A, sodium silicate is dissolved in a small amount of water to obtain a completely dissolved aqueous solution of sodium silicate; B, the sulfuric acid of concentration 98% is added in the sodium silicate aqueous solution of A step, mixes; C, copper sulfate is added in the mixed solution of B step, mixes evenly; D, nickel sulfate is added in the mixed solution of C step, mixes evenly; E, ferrous sulfate is added in the mixed liquor of D step, mixes evenly; F, sodium acetate is added in the mixed liquor of E step, mix well; G, glacial acetic acid is added in the mixed liquor of F step, mixes evenly; H. Add water to the mixed solution in step G to the required volume, and adjust the pH value to 2.0-2.5 with dilute H ₂ SO ₄ or dilute NaOH solution according to conventional methods to obtain a silicate black passivation solution.