Passivation solution, preparation method thereof and construction process of metal composite coating

Abstract

The invention discloses a passivation solution, a preparation method of the passivation solution and a construction process of a metal composite coating, and aims to solve the problem of effective passivation treatment on the surface of an exposed steel substrate after thermal spraying of an anode metal coating. Aiming at the problem of bimetal primary battery effect occurring in the passivation stage of a thermal spraying anode metal coating simultaneously existing on a steel substrate and the surface of the steel substrate, the passivation solution comprehensively utilizes the film-forming properties of phytic acid, silane and polyaniline, is supplemented with a metal accelerant, an oxidizing agent and titanium salt, and optimizes the pH value of the passivation solution to be faintly acid of 5-6; the thermal spraying anode metal coating is protected to the maximum extent, meanwhile, the passivation effect on an exposed steel base body is effectively achieved, the corrosion resistance of the exposed metal base body under the thermal spraying anode metal composite coating is achieved, and therefore the long-acting protection life of the thermal spraying anode metal composite coating is greatly prolonged.

Description

Technical Field

[0001] This invention relates to the field of metal passivation technology, specifically to a passivation liquid and its preparation method, as well as the construction process of metal composite coatings. Background Technology

[0002] Thermal spraying technology utilizes a heat source to heat the spraying material to a molten or semi-molten state, and then sprays it at a certain speed onto a pre-treated substrate surface to form a coating. The resulting thermal spray coating can possess a variety of functions, including corrosion resistance, wear resistance, friction reduction, high-temperature resistance, oxidation resistance, heat insulation, electrical insulation, conductivity, and microwave radiation protection. Thermal spray anodic metal composite coatings primarily use zinc and its alloys, aluminum and its alloys, and other anodic metal materials. The anodic metal coating is thermally sprayed onto a cleaned steel substrate surface, followed by a paint coating process to form a thermal spray anodic metal composite coating. The thermally sprayed anodic metal coating contains significant porosity, typically around 10%. Therefore, current technologies generally require sealing treatment to plug these porosity gaps. Since epoxy primers are commonly used for sealing, the resin and filler molecules in these primers are relatively large, and the primers are quite viscous, making it difficult for them to penetrate the steel substrate surface. This results in exposed areas on the steel substrate surface, which are highly susceptible to small-molecule corrosive media (such as Cl). - The corrosion of steel matrix is ​​caused by the erosion of H2O and other substances, which then spreads continuously.

[0003] Before thermal spraying, the anolyte steel substrate needs to be cleaned to a cleanliness level of Sa2½ or higher. Therefore, the surface of the steel substrate exhibits the original elemental form of the metal, which is highly reactive. Due to the significant porosity of the thermally sprayed anolyte metal coating, corrosive media can directly contact the exposed elemental form of the steel substrate in the gaps of the thermally sprayed anolyte metal coating, forming a rapid oxidation reaction and causing corrosion of the steel substrate. The common phenomenon of rust return in thermally sprayed aluminum coatings is an example of this. To address these issues, the industry has researched passivation technology for thermally sprayed anolyte metal coatings, but these technologies are all specifically designed for thermally sprayed anolyte metal coatings. The pH value of the passivation solution is either too high or too low (for example, Chinese invention patent CN111621775B discloses a passivation solution for alloy anti-corrosion coatings and its preparation method, specifically for alloy anti-corrosion coatings, with a pH of 2-4; for example, Chinese invention patent CN116377366A discloses an aqueous chromium-free alkaline passivation solution with a pH of 9-11). Passivation solutions with a low pH value are strongly acidic. While sealing the thermally sprayed anolyte coating, they also create a bimetallic contact between the steel substrate and the coating. The resulting galvanic effect not only accelerates the sacrificial wear of the anolyte coating but also affects the passivation effect on its surface and fails to passivate the steel substrate. Conversely, passivation solutions with a high pH value are strongly alkaline. Although they can provide good passivation for the anolyte coating, they cannot passivate the steel substrate. Summary of the Invention

[0004] The purpose of this invention is to provide a passivation liquid and its preparation method, as well as a construction process for metal composite coatings, to solve the problems mentioned in the background art.

[0005] To achieve the above objectives, the present invention provides the following technical solution: a passivation solution, comprising, by weight percentage: 3%–6% phytic acid, 0.2%–0.5% silane, 0.01%–0.02% emulsifier, 0.01%–0.02% titanium salt; 0.05%–1% metal accelerator, 0.1%–1% polyaniline aqueous solution, 0.2%–2% oxidant, with the balance being deionized water, and the pH value adjusted to 5–6 using 0.5 mol / L NaOH solution.

[0006] This invention also includes a method for preparing a passivation solution, comprising the following steps: (1) Preparing polyaniline aqueous solution: The polyaniline aqueous solution is prepared as follows: Weigh 4-6 parts of 50% phytic acid aqueous solution, 0.3-0.5 parts of p-phenylenediamine, 5-10 parts of ethanol, 2-5 parts of dodecylbenzenesulfonic acid, and 50 parts of deionized water according to a total weight of 100 parts. Place them in a three-necked flask, stir and mix evenly, then add 0.3-0.5 parts of aniline and the remainder of deionized water. Place the three-necked flask in an ice-water bath at 0℃, and add 1-2 parts of ammonium persulfate dropwise while stirring and mixing. During the dropwise addition, control the temperature of the liquid in the three-necked flask at 0℃-2℃. After the dropwise addition is completed, keep the temperature of the liquid in the three-necked flask at 0℃-2℃ and continue the reaction for 12-24 hours to obtain the polyaniline aqueous solution. (2) Preparation of passivation solution: According to the raw material composition of the passivation solution, weigh out deionized water, phytic acid, silane, titanium salt, metal accelerator, oxidant and polyaniline aqueous solution in sequence. While stirring, first add phytic acid to deionized water, then add emulsifier, silane, titanium salt, metal accelerator and oxidant in sequence. Stir at room temperature for 1 to 2 hours. Finally, add the pre-prepared polyaniline aqueous solution of S1, stir evenly, and then add 0.5 mol / L NaOH solution dropwise to adjust the pH value of the passivation solution to 5 to 6.

[0007] The present invention also includes a construction process for a metal composite coating, comprising the following steps: after cleaning and treating the metal substrate and completing the thermal spraying of the anodic metal coating, the steel substrate coated with the thermal sprayed anodic metal coating is passivated using the above-mentioned passivation liquid, a passivation layer is formed on the exposed gaps of the anodic metal coating on the surface of the metal substrate, and a coating is covered on the anodic metal coating.

[0008] Compared with existing technologies, the beneficial effects of this invention are: it effectively solves the negative effects caused by the bimetallic effect between the thermally sprayed anodic metal coating and the steel substrate, while reducing damage to the anodic metal coating and achieving effective passivation of the exposed steel substrate under the thermally sprayed anodic metal coating. Furthermore, this passivation technology can be used to produce thermally sprayed anodic metal composite coating products with excellent corrosion resistance, such as thermally sprayed composite coated steel bars and thermally sprayed high-strength bolt friction surfaces. Attached Figure Description

[0009] Figure 1 This is a schematic diagram of the composite coating structure; Figure 2 The appearance changes of Example 1 and the control group after 240 hours of salt spray test are shown. Figure 3 The appearance changes of Example 2 and the control group after 1000h of salt spray test are shown.

[0010] In the diagram: 1. Steel substrate; 2. Anode metal coating; 3. Overlay coating; 4. Passivation layer. Detailed Implementation

[0011] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.

[0012] This invention provides a technical solution: a passivation solution, comprising, by weight percentage: 3%–6% phytic acid, 0.2%–0.5% silane, 0.01%–0.02% emulsifier, 0.01%–0.02% titanium salt; 0.05%–1% metal accelerator, 0.1%–1% polyaniline aqueous solution, 0.2%–2% oxidant, with the balance being deionized water, and the pH adjusted to 5–6 using 0.5 mol / L NaOH solution. The phytic acid is a 50% phytic acid aqueous solution; the emulsifier is OP-10 or sodium dodecylbenzenesulfonate; the titanium salt is titanium oxysulfate or titanium nitrate; the metal accelerator is any one or any combination of zirconium sulfate, manganese dihydrogen phosphate, and zinc oxide; the silane is KH560 or KH791; and the oxidant is H2O2 or NaNO2.

[0013] A method for preparing a passivation solution includes the following steps: (1) Preparing polyaniline aqueous solution: The polyaniline aqueous solution is prepared as follows: Weigh 4-6 parts of 50% phytic acid aqueous solution, 0.3-0.5 parts of p-phenylenediamine, 5-10 parts of ethanol, 2-5 parts of dodecylbenzenesulfonic acid, and 50 parts of deionized water according to a total weight of 100 parts. Place them in a three-necked flask, stir and mix evenly, then add 0.3-0.5 parts of aniline and the remainder of deionized water. Place the three-necked flask in a 0℃ ice-water bath, and add 1-2 parts of ammonium persulfate dropwise while stirring and mixing. During the dropwise addition, control the liquid temperature in the three-necked flask to 0℃-2℃. After the dropwise addition is completed, keep the liquid temperature in the three-necked flask at 0℃-2℃ and continue the reaction for 12-24 hours to obtain the polyaniline aqueous solution; set aside for later use.

[0014] (2) Preparation of passivation solution: According to the raw material composition of the passivation solution, weigh out deionized water, phytic acid, silane, titanium salt, metal accelerator, oxidant and polyaniline aqueous solution in sequence. While stirring, first add phytic acid to deionized water, then add emulsifier, silane, titanium salt, metal accelerator and oxidant in sequence. Stir at room temperature for 1 to 2 hours. Finally, add the pre-prepared polyaniline aqueous solution of S1, stir evenly, and then add 0.5 mol / L NaOH solution dropwise to adjust the pH value of the passivation solution to 5 to 6.

[0015] A construction process for a metal composite coating includes the following steps: After cleaning the steel substrate and applying the thermal spray anodic metal coating, the substrate temperature is generally between 60℃ and 80℃. At this temperature, passivation is performed on the steel substrate coated with the thermal spray anodic metal coating while it is still hot. Passivation can be performed using high-pressure airless spraying or immersion methods. If high-pressure airless spraying is used, the passivation solution dosage is 50–200 g / m³. 2 For steel substrates with thermally sprayed anodic metal coatings, the spraying time is 2 to 10 seconds, followed by indoor air drying. If dip coating is used, the entire steel substrate with thermally sprayed anodic metal coating is immersed in the passivation solution for 1 to 5 seconds, then immediately removed and air dried indoors.

[0016] This passivation solution is not limited to the passivation treatment of anodic metal coatings. For example, it can also be used for anti-corrosion and anti-rust treatment of friction surfaces of high-strength bolts and steel reinforcement base materials.

[0017] The formulation tables for the control experiment on the passivation solution effect, including the examples and the control group, are as follows. For the above test specimens, the corrosion resistance of their metal composite coatings was tested and compared using GB / T 6807-2001 "Technical Conditions for Phosphating Treatment of Steel Workpieces Before Coating" and salt spray testing equipment. The results of the 240h salt spray test are as follows: Figure 2 As shown (the left half of the upper steel bar specimen is silane impregnation, and the right half is silane impregnation + coating; the left half of the lower steel bar specimen is Example 1, and the right half is Example 1 + coating), the passivation film formed in the control group has significantly lower resistance to salt spray corrosion than that in Example 1. Firstly, existing passivation solutions target the passivation of metal coatings, without considering the exposed steel substrate surface in the gaps beneath the metal coating. Secondly, passivating the exposed steel substrate surface in the gaps beneath the metal coating is extremely difficult, as it is locally a bimetallic environment, and the composition of the passivation solution, pH level, etc., all affect the formation and quality of the passivation film.

[0018] The passivation solution used in Example 2 was applied, and the results of the 1000-hour salt spray test are shown below. Figure 3(The left half of the upper steel reinforcement specimen is silane impregnated, and the right half is silane impregnated with a coating; the left half of the lower steel reinforcement specimen is Example 2, and the right half is Example 2 with a coating). It can be concluded that this invention has a significant effect compared to existing silane composite coating anti-corrosion technologies. While the difference in 1000h salt spray test results between the two technologies with coatings is not significant, the difference in anti-corrosion performance is significant without coatings. The silane impregnation area shows that, to resist the erosion of the steel substrate by salt spray, the metal coating is severely sacrificed, and its surface is covered with a large amount of white anodic metal oxide formed due to the sacrifice of the anodic metal protecting the cathode steel reinforcement substrate. In contrast, the control group, due to the excellent protective performance of the passivation layer, does not require the sacrificial protection of the anodic metal coating to activate the steel reinforcement substrate.

[0019] After passivation treatment, a good composite passivation film can be formed on the exposed steel substrate under the thermally sprayed anodic metal coating, significantly improving the corrosion resistance of the entire thermally sprayed anodic metal coating. The salt spray test time after passivation is tens of times longer than that without passivation and existing passivation technologies for thermally sprayed anodic metal coatings. The passivation solution is weakly acidic. By utilizing the composite passivation components, the exposed steel substrate under the thermally sprayed anodic metal coating is effectively protected while minimizing the negative effects of galvanic cells caused by bimetallic contact between the thermally sprayed anodic metal coating and the steel substrate.

[0020] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and variations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A passivation liquid, characterized by, The raw material composition includes, by weight percentage, 3-6% of phytic acid, 0.2-0.5% of silane, 0.01-0.02% of emulsifier, 0.01-0.02% of titanium salt, 0.05-1% of metal accelerator, 0.1-1% of polyaniline aqueous solution, 0.2-2% of oxidant, and the rest is deionized water, and the PH value is adjusted to 5-6 by using 0.5 mol / L NaOH solution.

2. The passivation solution according to claim 1, characterized in that: The phytic acid is a 50% content phytic acid aqueous solution; the emulsifier is OP-10 or sodium dodecyl benzene sulfonate; the titanium salt is titanyl sulfate or titanium nitrate; the metal accelerator is any one of zirconium sulfate, manganese dihydrogen phosphate, and zinc oxide or any combination thereof; the silane is KH560 or KH791; and the oxidant is H2O2 or NaNO2.

3. A method for producing a passivation liquid, characterized by, The method comprises the following steps: S1, preparing a polyaniline aqueous solution The polyaniline aqueous solution is prepared as follows: 4-6 parts of 50% content phytic acid aqueous solution, 0.3-0.5 parts of p-phenylenediamine, 5-10 parts of ethanol, 2-5 parts of dodecyl benzene sulfonic acid, and 50 parts of deionized water are weighed according to a total of 100 parts by weight, and are placed in a three-necked flask, stirred and mixed uniformly, then 0.3-0.5 parts of aniline is added, and the rest parts of deionized water is added, the three-necked flask is placed in an ice water bath at 0℃, 1-2 parts of ammonium persulfate is added dropwise under stirring and mixing, the liquid temperature in the three-necked flask is controlled at 0-2℃ during the dropwise addition, the liquid temperature in the three-necked flask is maintained at 0-2℃ after the dropwise addition is completed, and the reaction is continued for 12-24 hours to obtain the polyaniline aqueous solution; S2, preparing a passivation solution According to the raw material composition of the passivation solution, deionized water, phytic acid, silane, titanium salt, metal accelerator, oxidant, and polyaniline aqueous solution are weighed in sequence, the phytic acid is added to the deionized water under stirring, then the emulsifier, silane, titanium salt, metal accelerator, and oxidant are added in sequence, stirring is performed at room temperature for 1-2 hours, the polyaniline aqueous solution prepared in S1 is finally added, stirring is performed until uniform, and then 0.5 mol / L NaOH solution is added dropwise to adjust the PH value of the passivation solution to 5-6.

4. A process for applying a metallic composite coating, characterized in that The steps are as follows: After the metal substrate (1) is cleaned and a thermal spraying anode metal coating (2) is formed, the steel substrate (1) with the thermal spraying anode metal coating (2) is passivated using the passivation solution, a passivation layer (4) is formed on the surface of the metal substrate (1) by the exposed gaps of the anode metal coating (2), and a coating layer (3) is formed on the upper side of the anode metal coating (2) by spraying.

5. A process for applying a metallic composite coating according to claim 4, characterized in that: The temperature of the steel substrate (1) is controlled at 60-80℃ during the passivation operation, and the passivation operation can be performed by high-pressure airless spraying or immersion.

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