阅读说明：本技术 一种锌表面无铬钝化液及钝化方法 (Zinc surface chromium-free passivation solution and passivation method ) 是由 魏中华 陈小平 赵栋梁 卢泽琴 王向东 黄涛 汪兵 刘清友 贾书君 于 2021-06-29 设计创作，主要内容包括：本发明涉及一种锌表面无铬钝化液及钝化方法,属于电镀锌表面处理技术领域,本发明的锌表面无铬钝化液,含有可溶性硅酸盐和可溶性铈(Ⅳ)盐,其中可溶性硅酸盐为成膜剂,可溶性铈(Ⅳ)盐为氧化成膜剂。解决了现有技术中硅酸盐镀锌层钝化膜易于脱落,在钕铁硼工件浸渍翻动过程中存在破损和脱落；钝化膜钝化速度快则钝化膜变薄,厚度不足；钝化过程中钝化膜不够致密,导致耐腐蚀性下降的问题。实现了对钕铁硼工件镀锌层的无铬化钝化耐腐蚀保护。(The invention relates to a zinc surface chromium-free passivation solution and a passivation method, belonging to the technical field of electrogalvanizing surface treatment. The problems that in the prior art, a silicate zinc coating passive film is easy to fall off, and the neodymium iron boron workpiece is damaged and falls off in the dipping and turning process are solved; when the passivation speed of the passivation film is high, the passivation film becomes thin and is insufficient in thickness; the passive film is not compact enough in the passivation process, which causes the problem of the reduction of the corrosion resistance. The chromium-free passivation corrosion-resistant protection of the zinc coating of the neodymium iron boron workpiece is realized.)

1. The zinc surface chromium-free passivation solution is characterized by comprising soluble silicate and soluble cerium (IV) salt, wherein the soluble silicate is a film forming agent, and the soluble cerium (IV) salt is an oxidized film forming agent; the pH value of the passivation solution is 2.0-3.0.

2. The zinc surface chromium-free passivation solution of claim 1, wherein the concentration of soluble cerium (IV) salt in the passivation solution is 5 g/L-20 g/L.

3. The chromium-free passivation solution for zinc surface according to claim 2, characterized in that the soluble cerium (IV) salt is ceric sulfate.

4. The zinc surface chromium-free passivation solution according to claim 1, characterized in that the concentration of soluble silicate in the passivation solution is 5 g/L-35 g/L.

5. The zinc surface chromium-free passivation solution according to claim 4, characterized in that the soluble silicate in the passivation solution is one or a combination of sodium silicate and potassium silicate.

6. The zinc surface chromium-free passivation solution according to claim 1, characterized in that the passivation solution further comprises a film forming auxiliary agent and/or an auxiliary oxidant, wherein the film forming auxiliary agent is soluble cobalt salt and soluble copper salt, and the auxiliary oxidant is hydrogen peroxide.

7. The zinc surface chromium-free passivation solution of claim 6, wherein the concentration of the soluble cobalt salt in the passivation solution is 0.1 g/L-1.0 g/L, the concentration of the soluble copper salt is 0.1 g/L-1.0 g/L, and the concentration of the hydrogen peroxide is 5 mL/L-20 mL/L.

8. The zinc surface chromium-free passivation solution according to claim 6, characterized in that the passivation solution further comprises an acidifying agent, and the acidifying agent is sulfuric acid.

9. A zinc surface chromium-free passivation method is characterized in that zinc surface workpieces are soaked by the zinc surface chromium-free passivation solution as claimed in claims 1 to 8, and the zinc surface workpieces are turned over simultaneously in the soaking process.

10. The method for the chromium-free passivation of the zinc surface according to claim 9, characterized in that the passivation treatment temperature is normal temperature, and the immersion time is 10 seconds to 120 seconds.

Technical Field

The invention relates to the technical field of electrogalvanizing surface treatment, in particular to a zinc surface chromium-free passivation solution and a passivation method.

Background

The common active metal is placed in the air, and is very easy to oxidize and rust particularly under the conditions of water vapor, salt mist, insolation and the like, a plurality of metals such as the most common copper, iron and the like are oxidized to destroy the original structure of the metal surface and can be further oxidized and rusted more easily, the metal surface which is easy to corrode is treated by a galvanizing process, and passivation treatment is carried out on the surface of a galvanizing coat.

The passivation technology of zinc coating has been developed for three generations, the first being hexavalent chromate passivation. The second generation of trivalent chromium passivation has been developed over two decades and has been a substantial replacement for hexavalent chromium passivation, and the salt spray corrosion resistance of trivalent chromium passivation is comparable to that of hexavalent chromium passivation. The toxicity of the trivalent chromium is 1 percent of that of the hexavalent chromium, and the trivalent chromium framework film with excellent performance can be reserved, so that the corrosion resistance of the passivation film is ensured, and the passivation of the trivalent chromium is rapidly developed and basically replaces the passivation of the hexavalent chromium. However, a small amount of hexavalent chromium is often included in the trivalent chromium passivation film layer, and the possibility of converting trivalent chromium into hexavalent chromium also exists in the long-term use process.

Therefore, the search for environmentally friendly chromium-free surface protection technologies to replace chromate passivation has become one of the hot technologies actively being studied and studied in the electrogalvanizing industry. The third-generation inorganic salt chromium-free passivation has great advantages due to environmental protection, and has extremely wide technical application prospect. The prior inorganic salt chromium-free passivation mainly comprises molybdate passivation, titanate passivation, silicate passivation, rare earth metal salt passivation and the like. Therefore, the development of new chromium-free passivation solutions has been the direction of research by those skilled in the art.

Disclosure of Invention

In view of the above analysis, the present invention aims to provide a chromium-free passivation solution for zinc surface and a passivation method thereof, which can solve at least one of the following technical problems in the prior art: (1) hexavalent chromium and trivalent chromium passivation solutions have high toxicity; (2) oxidizing agent must be added in the process of forming the chromium-free passivation film for oxidation.

The invention provides a zinc surface chromium-free passivation solution which contains soluble silicate and soluble cerium (IV) salt, wherein the soluble silicate is a film forming agent, the soluble cerium (IV) salt is an oxidized film forming agent, and the pH value of the passivation solution is 2.0-3.0.

Furthermore, the concentration of the soluble cerium (IV) salt in the passivation solution is 5 g/L-20 g/L.

Further, the soluble cerium (IV) salt is ceric sulfate.

Furthermore, the concentration of the soluble silicate in the passivation solution is 5 g/L-35 g/L.

Further, in the passivation solution, the soluble silicate is one or a combination of sodium silicate and potassium silicate.

Furthermore, the passivation solution also contains a film forming auxiliary agent and/or an auxiliary oxidant, wherein the film forming auxiliary agent is soluble cobalt salt and soluble copper salt, and the auxiliary oxidant is hydrogen peroxide.

Furthermore, in the passivation solution, the concentration of the soluble cobalt salt is 0.1-1.0 g/L, the concentration of the soluble copper salt is 0.1-1.0 g/L, and the concentration of the hydrogen peroxide is 5-20 mL/L.

Further, the passivation solution also contains an acidifying agent, and the acidifying agent is sulfuric acid.

The invention also provides a zinc surface chromium-free passivation method, which is characterized in that the zinc surface chromium-free passivation solution is used for dipping the zinc surface workpiece, and the zinc surface workpiece is turned over simultaneously in the dipping process.

Further, the passivation treatment temperature is normal temperature, and the immersion time is 10 seconds to 120 seconds.

Compared with the prior art, the invention can realize at least one of the following beneficial effects:

1. the zinc surface chromium-free passivation solution provided by the invention comprises soluble silicate and soluble cerium (IV) salt, wherein the silicate and the soluble cerium (IV) salt are jointly used as film forming agents, the soluble cerium (IV) salt is a film forming agent and an oxidant, and zinc is oxidized by the cerium (IV) and then converted into cerium (III) to participate in film forming. The metal ion salt in the existing chromium-free passivation solution plays the role of a passivator and needs to be added with an oxidant for oxidation. Different from the prior chromium-free passivation solution, the invention can form a passivation film on the surface of zinc without adding an oxidant.

2. The pH value of the passivation solution is 2.0-3.0, so that the reduction of corrosion resistance caused by the over-coarse passivation film due to over-high pH can be effectively prevented, and meanwhile, the phenomenon that the passivation film becomes thin and has insufficient thickness due to over-low pH and over-high passivation dissolution speed can be prevented; the invention realizes the preparation of the passive film by accurately controlling the pH value.

3. The zinc surface chromium-free passivation solution can also be added with hydrogen peroxide as an auxiliary oxidant to improve the formation speed of a passivation film and improve the compactness of the passivation film. In contrast to the prior art, where hydrogen peroxide is used as the primary oxidant, the hydrogen peroxide that can be added in the present invention acts as an oxidant to assist the soluble cerium (iv) salt.

In the invention, the technical schemes can be combined with each other to realize more preferable combination schemes. Additional features and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objectives and other advantages of the invention will be realized and attained by the structure particularly pointed out in the written description and drawings.

Drawings

FIG. 1 is a macroscopic view of a galvanized product after chromium-free passivation;

FIG. 2 is a graph showing the macroscopic morphology of a galvanized product after chromium-free passivation;

FIG. 3 is a macroscopic view of a galvanized product of comparative example II after chromium-free passivation;

FIG. 4 shows the macroscopic morphology of the galvanized product of example two after chromium-free passivation.

Detailed Description

The most common method for improving the corrosion resistance of metal is to plate zinc on the surface of the metal and utilize the compactness of zinc, but the activity of zinc is higher than that of common metals such as copper, iron and the like, so the chromate passivation treatment is most widely used on the surface of the metal zinc, and the chromate passivation is compact and uniform and has excellent corrosion resistance so as to prevent the zinc from being oxidized and corroded to realize the corrosion resistance of the metal or alloy. But the chromium passivation solution still is not an ideal galvanizing passivation solution because of the existence of carcinogenic hexavalent chromium Cr (VI). The toxicity of the subsequently developed Cr (III) is 1 percent of that of hexavalent chromium, and a trivalent chromium framework film with excellent performance can be reserved, so that the corrosion resistance of the passive film is ensured. However, a small amount of hexavalent chromium is often included in the trivalent chromium passivation film layer, and the possibility of converting trivalent chromium into hexavalent chromium also exists in the long-term use process. At present, inorganic salt chromium-free passivation mainly comprises molybdate passivation, titanate passivation, silicate passivation, rare earth metal salt passivation and the like.

The invention provides a novel zinc surface chromium-free passivation solution. And different from the prior chromium-free passivation solution, the invention does not need to separately add an oxidant.

The invention provides a zinc surface chromium-free passivation solution which can meet the special requirement of zinc surface chromium-free passivation. The zinc surface chromium-free passivation solution contains soluble silicate and soluble cerium (IV) salt, wherein the soluble silicate is a film forming agent, the soluble cerium (IV) salt is an oxidized film forming agent, and the pH value of the passivation solution is 2.0-3.0. The soluble silicate and soluble cerium (iv) salt may be dissolved in water to form an aqueous solution.

Compared with the prior passivation solution, the invention has the following remarkable characteristics:

(1) the zinc surface chromium-free passivation solution comprises two main components of film forming, namely a film forming agent and an oxidation film forming agent, wherein soluble silicate can form a silicon film, and soluble cerium (IV) salt can oxidize a zinc coating and form a cerium film, so that the zinc surface chromium-free passivation solution can simultaneously form two films in the process of passivating the zinc coating, and the two films are not formed independently and are not two films in a covering relationship but are mixed films which are simultaneously formed on the zinc coating and are uniformly dispersed and integrated with each other.

(2) The soluble cerium (IV) salt adopted by the invention is an oxidant and a film-forming agent, and in the passivation solution, the oxidant mainly has the effect of oxidizing galvanized metal zinc to form a film. The soluble cerium (IV) salt is an oxidation film-forming agent, namely the soluble cerium (IV) salt has oxidation property and oxidizes zinc on the surface of the galvanized layer. The oxidation principle of the soluble cerium (iv) salt is that the soluble cerium (iv) salt oxidizes zinc, which is itself reduced to cerium (iii) by zinc. The cerium (III) is directly involved in the film-forming process and is converted to an insoluble cerium (III) compound. Therefore, the soluble cerium (IV) salt can be used as an oxidant for oxidation, and cerium (III) after the oxidation reaction can be used as a film-forming agent for film formation.

(3) Through research, the passivation process of the zinc surface and the passivation solution is a solid-liquid heterogeneous reaction process, and the reaction only occurs at the interface of the solid and the liquid, namely, the passivation reaction process only occurs at the contact interface of the passivation solution and a zinc coating. Therefore, oxidant molecules in the passivation solution need to move to the interface of the passivation solution and the zinc coating through molecular motion to oxidize zinc, and meanwhile, film forming agent molecules need to move to the interface of the passivation solution and the zinc coating through molecular motion to form a film. In the traditional mode of combining the oxidant and the film forming agent, after the oxidant molecules are oxidized, the oxidant molecules need to move away from an interface where the passivation solution is contacted with the zinc coating layer, and the film forming agent molecules need to move to reach the interface where the passivation solution is contacted with the zinc coating layer. The soluble cerium (IV) salt of the oxidation film-forming agent reduces zinc into cerium (III) after zinc is oxidized when molecules move to an interface where passivation solution and a zinc coating are contacted, and the cerium (III) is formed into a film in situ after being generated in situ at the interface where the passivation solution and the zinc coating are contacted, so that the speed of passivation film formation is accelerated, the influence caused by the molecular motion of other components of the passivation solution in the process of bonding oxidation and film formation is effectively prevented, and the uniformity and compactness of passivation film formation are improved.

The pH value of the passivation solution needs to be strictly controlled within 2.0-3.0. Through research, the passivation solution utilizes an oxidation film-forming agent to carry out oxidation passivation on the surface of zinc, and the reaction is carried out in an acidic environment. However, tests show that the effect is best when the pH value of the passivation solution is within the range of 2.0-3.0, if the pH value of the passivation solution is too high, namely the pH value is more than 3.0, the passivation film is rough, the corrosion resistance of the passivation film is reduced, if the pH value of the passivation solution is too low, namely the pH value is less than 2.0, the composite film of cerium and silicate generated after passivation is easily and partially dissolved by acid again, the generated passivation film is thinned, and the high-quality passivation film is difficult to form. Therefore, in order to obtain a compact passivation film, the pH value of the passivation solution is controlled within the range of 2.0-3.0, so that a compact passivation film with proper thickness is obtained in the passivation process, and the requirement on corrosion resistance is met.

Specifically, the concentration of the soluble silicate in the passivation solution is 5 g/L-35 g/L.

The soluble silicate is a film forming agent in the passivation solution, and forms a film together with the soluble cerium (IV) salt of the oxidized film forming agent. Two films are formed simultaneously in the process of passivating the zinc coating by the zinc surface chromium-free passivation solution, and the two films are not formed independently, are not two films in a covering relationship, and are mixed films which are formed simultaneously on the zinc coating surface and are uniformly dispersed into a whole. According to research, the silicate concentration can influence the component proportion of the formed mixed film, if the silicate concentration is too low, the proportion of silicon in the passive film formed by the passivation solution is low, the corrosion resistance of the film is reduced, and if the silicate concentration is too high, the proportion of cerium in the passive film formed by the passivation solution is reduced, and the compactness of the passive film is also influenced. Tests show that when the concentration of the soluble silicate is lower than 5g/L, the formed passivation film has insufficient compactness and corrosion resistance, and when the concentration of the soluble silicate is higher than 35g/L, the proportion of silicon and the proportion of cerium in the formed passivation film are too high and too low due to too high concentration of the silicate, so that the requirement of corrosion resistance cannot be met.

Specifically, the soluble silicate is one or a combination of sodium silicate and potassium silicate.

In particular, the soluble cerium (iv) salt may be ceric sulfate.

The soluble cerium (iv) salt of the present invention is an oxidation film-forming agent, and oxidizes the zinc coating layer by using the oxidation ability of cerium (iv), which is completely different from the principle of adding cerium as an auxiliary agent in the prior art.

Specifically, the concentration of the soluble cerium (IV) salt in the passivation solution is 5 g/L-20 g/L.

Because the soluble cerium (IV) salt is an oxidation film-forming agent, the zinc coating is oxidized by utilizing the oxidation capability of the cerium (IV) and also participates in film formation as the film-forming agent, the addition amount of the soluble cerium (IV) salt is used as a main component and is far higher than that of the cerium (III) added as an auxiliary agent in the prior art. Through research, the concentration of the soluble cerium (IV) salt is lower than 5g/L, and the content of cerium in the formed passivation film is insufficient, so that the requirement on corrosion resistance cannot be met. A concentration of the soluble cerium (IV) salt higher than 20g/L causes waste and increases the cost. Therefore, the concentration of the soluble cerium (IV) salt in the passivation solution is 5g/L to 20 g/L.

Specifically, the passivation solution also comprises a film-forming auxiliary agent, wherein the film-forming auxiliary agent is soluble cobalt salt and soluble copper salt.

In one possible embodiment, the soluble cobalt salt is cobalt sulfate and the soluble copper salt is copper sulfate.

The soluble cobalt salt has obvious effect on improving the corrosion resistance of the passive film and inhibiting the generation and the expansion of the pitting corrosion of the passive film.

The corrosion resistance of the passive film can be further improved by the soluble copper salt, and the color of the passive film can be adjusted due to the obvious color of copper ions.

Specifically, in the passivation solution, the concentration of soluble cobalt salt is 0.1 g/L-1.0 g/L, preferably, the concentration of soluble cobalt salt is 0.5g/L, the concentration of soluble copper salt is 0.1 g/L-1.0 g/L, preferably, the concentration of soluble copper salt is 0.5 g/L.

The cobalt salt and the copper salt play an auxiliary role, and are the same as the soluble cerium (IV) salt which reduces zinc into cerium (III) after oxidation, insoluble copper and insoluble cobalt are formed by copper ions and cobalt ions, and the insoluble copper and the insoluble cobalt are simultaneously formed into a film by film forming agents, namely silicate and cerium (III) to form a silicon-cerium-cobalt-copper mixed film, so that a passivation film formed by the passivation solution has better corrosion resistance. However, tests show that when the concentrations of the copper salt and the cobalt salt are too high and are more than 1.0g/L, the auxiliary film-forming agent and the oxidized film-forming agent interfere with the film formation of the silicate of the film-forming agent and the cerium (III) oxidized into the film-forming agent due to the too high content of copper ions and cobalt ions when the auxiliary film-forming agent and the oxidized film-forming agent form a film, so that the compactness of the formed film is poor. And when the concentration of the copper salt and the cobalt salt is too low and is less than 0.1g/L, the auxiliary film forming effect cannot be realized.

Specifically, the passivation solution further comprises an auxiliary oxidant, and the auxiliary oxidant is hydrogen peroxide.

The hydrogen peroxide belongs to an auxiliary oxidant, namely the hydrogen peroxide also participates in oxidation as an oxidant, but the auxiliary soluble cerium (IV) salt is mainly embodied in two aspects: firstly, the soluble cerium salt is consumed greatly as an oxidant, but the soluble silicate and cerium form a film together as the film forming agent, so the consumption of cerium as the film forming agent is less than that of cerium as the oxidant, and if the soluble cerium (IV) salt is added in excess, the cost is seriously increased, so hydrogen peroxide is added for assisting oxidation, and the content part of the soluble cerium (IV) salt which is used as the oxidant is supplemented; secondly, the hydrogen peroxide can improve the oxidation potential of the whole passivation solution, even if the whole passivation solution is in an oxidation environment, other reductive impurities or other reductive substances in the air are prevented from consuming cerium (IV), the oxidation efficiency is improved, and the density reduction of a passivation film caused by the uneven oxidation rate of the interface of the passivation solution and a zinc coating is prevented.

In one possible embodiment, the concentration of hydrogen peroxide in the passivating solution is from 5mL/L to 20mL/L, such as 8mL/L, 10mL/L, 12mL/L, 14mL/L, 16mL/L, 18 mL/L. Preferably, the hydrogen peroxide concentration is 10 mL/L.

Through tests, the concentration of hydrogen peroxide is lower than 5mL/L, the content of hydrogen peroxide is insufficient, and the zinc on the surface of the galvanized layer cannot be completely oxidized or the oxidation rate is slowed down when the zinc is matched with the soluble cerium (IV) salt. When the content of the hydrogen peroxide is too high, waste is caused, so that the concentration of the hydrogen peroxide is below 20 mL/L.

Specifically, the passivating solution also comprises an acidifying agent, and the acidifying agent can be sulfuric acid.

The acidifying agent provides an acidic environment during passivation, and the concentration of the sulfuric acid is 5 mL/L-20 mL/L.

In one possible embodiment, in order to achieve the desired pH of the passivation solution, the pH needs to be adjusted by adding a suitable amount of sodium hydroxide.

The invention also provides a zinc surface chromium-free passivation method, which is characterized in that the zinc surface chromium-free passivation solution is used for dipping zinc surface workpieces, and the zinc surface workpieces are rolled simultaneously in the dipping process.

Specifically, the passivation treatment temperature of the zinc surface chromium-free passivation method is normal temperature, and the immersion time is 10-120 seconds.

The passivation method can be processed at normal temperature, does not need heating, and is convenient for industrial popularization. Meanwhile, the dipping time is 10-120 seconds, and experiments show that the passivating solution provided by the invention has two film forming agents, the dipping time is less than 10 seconds, so that the film forming effect is poor, and the corrosion resistance does not meet the requirements, but the dipping time is not too long, when the dipping time exceeds 120 seconds, the passivating film is completely formed, and the too long dipping can generate acid to dissolve the passivating film again, so that the passivating film is roughened, and the corrosion resistance is reduced.

The following detailed description of the preferred embodiments of the invention is provided to illustrate the principles of the invention and not to limit the scope of the invention.

Example one

The invention discloses a zinc surface chromium-free passivation solution and a passivation method.

At normal temperature, 25g of sodium silicate, 10g of ceric sulfate and 10mL of sulfuric acid (98 wt%) are stirred uniformly to be completely dissolved, a solution with a constant volume is prepared into 1L, and a proper amount of sodium hydroxide is added to adjust the pH value to 2.5 for later use. The obtained passivation solution comprises the following main components in percentage by weight:

25g/L of sodium silicate;

ceric sulfate 10 g/L;

sulfuric acid 10 mL/L.

The steel products on the surface of zinc are soaked in 3% nitric acid solution and then washed by water, then soaked in passivation solution for passivation for 20 seconds, continuously turned over in the passivation process to ensure that each product is passivated uniformly, and then the products are washed by water and dried after being passivated.

Comparative example 1

At normal temperature, 10g of ceric sulfate and 10mL of sulfuric acid (98 wt%) are added into deionized water, stirred uniformly to be completely dissolved, the volume is constant to prepare 1L of solution, and a proper amount of sodium hydroxide is added to adjust the pH value to 2.5 for later use. The steel products on the surface of zinc are soaked in 3% nitric acid solution and then washed by water, then soaked in passivation solution for passivation for 20 seconds, continuously turned over in the passivation process to ensure that each product is passivated uniformly, and then the products are washed by water and dried after being passivated.

Comparative example No. two

At normal temperature, 25g of sodium silicate and 10mL of sulfuric acid (98 wt%) are added into deionized water, the mixture is stirred uniformly to be completely dissolved, a solution with the volume constant is prepared into 1L, and a proper amount of sodium hydroxide is added to adjust the pH value to 2.5 for later use. The steel products on the surface of zinc are soaked in 3% nitric acid solution and then washed by water, then soaked in passivation solution for passivation for 20 seconds, continuously turned over in the passivation process to ensure that each product is passivated uniformly, and then the products are washed by water and dried after being passivated.

Example two

The invention discloses a zinc surface chromium-free passivation solution and a passivation method.

At normal temperature, 25g of sodium silicate, 10g of ceric sulfate, 0.5g of cobalt sulfate, 0.5g of copper sulfate, 10mL of sulfuric acid (98 wt%) and 10mL of hydrogen peroxide (30 wt%) are added into deionized water, stirred uniformly to be completely dissolved, the volume is constant to prepare 2L solution, and a proper amount of sodium hydroxide is added to adjust the pH value to 2.5 for later use. The obtained passivation solution comprises the following main components in percentage by weight:

25g/L of sodium silicate;

ceric sulfate 10 g/L;

0.5g/L of cobalt sulfate;

copper sulfate 0.5 g/L;

10mL/L of sulfuric acid;

10mL/L of hydrogen peroxide.

And (3) soaking the zinc surface product in a 3% nitric acid solution at normal temperature, washing with water, then soaking the zinc surface product in a passivation solution for passivation for 20 seconds, continuously turning over the product in the passivation process to ensure that each product is uniformly passivated, and washing and drying the passivated product with water to obtain a uniform and compact colored passivation film.

By way of comparison:

the passivation solution of the first embodiment is not added with an oxidizing agent, and the soluble cerium (iv) salt in the passivation solution is both a film forming agent and an oxidizing agent, and can still form a film, as shown in fig. 1. No white rust was observed in the salt spray test for 12 hours.

The passivation solution of comparative example one is not added with sodium silicate, which is one of the main film forming agents in the passivation solution, and because the passivation film lacks the main film forming agent, although the soluble cerium (IV) salt can also be reduced to form a film, the film component is single, the formed passivation film is obviously not dense and rough, and the passivation film is a rough gray blue passivation film as seen from the appearance, as shown in fig. 2. Due to the fact that the corrosion resistance of the passivation film is poor due to the fact that the passivation film is rough, white rust appears in 4 hours of a salt spray experiment.

The passivating solution of comparative example two is not added with ceric sulfate, which is both an oxidant and a main film forming agent in the passivating solution, and because the main film forming agent is lacked in the passivating film, the formed passivating film is dark and rough and has obvious scratches only by forming a silicon film by sodium silicate, and the passivating film is a rough blue-yellow passivating film as observed from the appearance, as shown in fig. 3. The film forming standard is not met due to direct scratch on the surface of the passivation film.

In the second embodiment, the passivation solution is added with the auxiliary film-forming agents of soluble cobalt salt and soluble copper salt, and the auxiliary oxidant of hydrogen peroxide, and the passivation solution passivates the zinc surface product, the passivation film is bright, dense and scratch-free, and the passivation film is a bright and dense color passivation film as shown in fig. 4. Compared with the first embodiment, the film forming speed is higher, and the compactness of the passivation film is higher. The passive film does not corrode in 24 hours of neutral salt spray test, and has more excellent corrosion resistance.

The above description is only for the preferred embodiment of the present invention, but the scope of the present invention is not limited thereto, and any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope of the present invention are included in the scope of the present invention.