Zirconium tungstate fiber reinforced insulating coating for oriented silicon steel and preparation method of zirconium tungstate fiber reinforced insulating coating

Abstract

The invention relates to the technical field of coatings, in particular to a zirconium tungstate fiber reinforced insulating coating for oriented silicon steel and a preparation method of the zirconium tungstate fiber reinforced insulating coating. The preparation method of the coating comprises the following steps: S1, uniformly mixing aluminum dihydrogen phosphate, silica sol, molybdenum hydroxide hexahydrate, nickel hydroxide and deionized water, then adding zirconium tungstate nanofibers, and uniformly stirring to obtain high-tension coating liquid for oriented silicon steel; and S2, the surface of the oriented silicon steel is coated with the high-tension coating liquid for the oriented silicon steel, baking is conducted at the temperature of 430-470 DEG C in the protective atmosphere, then heat preservation is conducted for a period of time at the temperature of 620-650 DEG C, and the fiber-reinforced coating for the oriented silicon steel is prepared. The prepared high-tension coating for the oriented silicon steel has good adhesiveness and high interlayer resistivity, not only meets the requirement for insulation performance, but also has good heat resistance and corrosion resistance.

Description

Technical Field

[0001] The invention relates to the technical field of coatings, and in particular to a zirconium tungstate fiber reinforced insulating coating for oriented silicon steel and a preparation method thereof. Background Art

[0002] Oriented silicon steel has the excellent properties of high magnetic induction and low iron loss, and is an important soft magnetic material in the power and electronics industries. In the production process, in order to improve the insulation performance, oxidation resistance, surface brightness of oriented silicon steel and reduce the stress between the coating and the substrate, a layer of insulating coating needs to be applied to the silicon steel unit to protect the silicon steel sheet from erosion and rust by various corrosive media during storage, transportation and use, increase the surface resistivity, and reduce the eddy current loss of oriented silicon steel. In the actual application of silicon steel sheets, magnetostriction will occur due to the high-frequency changing induced magnetic field, which will cause the conversion of electrical energy into mechanical energy and thermal energy, resulting in energy loss and noise.

[0003] In order to prevent this energy loss, the study uses coatings with different thermal expansion coefficients. During the cooling process after high-temperature treatment, the coating shrinks less and applies tensile stress to the oriented silicon steel along the rolling direction. The tension can greatly eliminate the surface closed domains in the oriented silicon steel, reduce the domain wall spacing, and help reduce abnormal eddy current losses. The type, process and quality of the insulating coating will have a great impact on the insulation, punching and corrosion resistance of oriented silicon steel, and thus affect the total loss and other magnetic properties of the electrical steel itself. At present, oriented silicon steel widely uses two systems: semi-inorganic and semi-organic coatings or inorganic phosphate coatings. However, in the actual production process, the existing tension coatings have problems such as no obvious improvement in iron loss, unstable insulation performance, easy to fall off, and containing harmful substances such as chromium.

[0004] In the prior art, for example, "A Phosphate Coating Solution and Preparation Method Thereof" (CN201510020371.0) proposes a formula for an insulating coating solution: using aluminum dihydrogen phosphate, magnesium dihydrogen phosphate, chromic anhydride and silica sol as raw materials, and adding 0.5-1.5wt% polyether modified silicone oil to improve leveling, and forming a coating through baking and high-temperature sintering. However, oriented silicon steel needs to be stress-relieved annealed at high temperature before use to reduce iron loss. The organic part in the coating solution is easy to decompose at high temperature and volatilize harmful gases, resulting in a decrease in the heat resistance and weldability of the coating, slow film formation, and a long processing process.

[0005] "An environmentally friendly insulating coating for oriented silicon steel and its preparation method" (CN116731543B) proposes an insulating coating using aluminum dihydrogen phosphate, magnesium dihydrogen phosphate, zirconium oxychloride, magnesium aluminate, sodium tungstate, boric acid, silica gel, nano-tantalum oxide, titanate, alkali metal phosphate, and water as raw materials, which can improve the insulation, adhesion, corrosion resistance, magnetic properties, and glossiness of the oriented silicon steel coated with the coating. However, there are problems with the raw materials used in this coating. First, the magnesium dihydrogen phosphate used will hydrate to form particles, which will increase the roughness of the coating and reduce the stacking coefficient; secondly, a large amount of alkali metal tungstates, titanates, and phosphates are used in the coating, which will reduce the resistance of the coating. At the same time, the alkali metal elements will corrode the silicon steel body. Therefore, this coating will cause a lot of problems during use.

[0006] The patented technology of "Method for forming chromium-free topcoat insulating coating" (JP2005068493A) uses aluminum dihydrogen phosphate, silica sol, sulfate, aluminum borate, aluminum oxide and zirconium oxide solid particles as raw materials to prepare oriented silicon steel insulating coating. Although the appearance and corrosion resistance of the prepared coating are good, the adhesion of the coating is general, and the addition of solid particles affects the stability of the coating liquid, which is prone to precipitation and agglomeration. Summary of the invention

[0007] The object of the present invention is to provide a zirconium tungstate fiber reinforced insulating coating for oriented silicon steel with rapid film formation, low iron loss and high insulation and a preparation method thereof in view of the above-mentioned deficiencies in the prior art.

[0008] The present invention provides a method for preparing a zirconium tungstate fiber reinforced insulating coating for oriented silicon steel, comprising the following steps:

[0009] S1. Mix aluminum dihydrogen phosphate, silica sol, molybdenum hydroxide hexahydrate, nickel hydroxide and deionized water, add zirconium tungstate nanofibers, and stir evenly to obtain a high-tension coating solution for oriented silicon steel;

[0010] S2, coating the surface of the oriented silicon steel with a high tension coating liquid, baking at 430-470° C. under a protective atmosphere, and then keeping the temperature at 620-650° C. for a period of time to obtain a fiber-reinforced coating for the oriented silicon steel;

[0011] Among them, the mass ratio of aluminum dihydrogen phosphate, silica sol, molybdenum hydroxide hexahydrate, nickel hydroxide, deionized water and zirconium tungstate nanofibers is 20-40:25-45:2-4:1-3:80-120:2-11.

[0012] Furthermore, in the high tension coating solution for oriented silicon steel, the solid content is maintained at 30% to 40%, and the P / Si ratio is maintained at 1:0.8 to 1.

[0013] Furthermore, in step S2, baking is performed for 25 to 35 seconds.

[0014] Furthermore, in step S2, the temperature is kept at 150 to 200 seconds.

[0015] Furthermore, the zirconium tungstate nanofiber is prepared by the following preparation method: firstly, ammonium tungstate and zirconium acetate solution are mixed, heated and stirred until the water is completely evaporated to obtain zirconium tungstate nanopowder, and the zirconium tungstate nanopowder is slowly heated to promote crystal growth to form zirconium tungstate nanowires.

[0016] Furthermore, the zirconium tungstate nanopowder is slowly heated to 1300° C. at 5° C. / s in a heating furnace on a silicon oxide substrate and kept at this temperature for 5 to 10 hours to grow zirconium tungstate nanofibers.

[0017] Furthermore, the mass ratio of ammonium tungstate to zirconium acetate in the zirconium acetate solution is 1.8-6.4:0.8-4, and the zirconium content in the zirconium acetate solution is 15-16%.

[0018] Furthermore, the aluminum dihydrogen phosphate is a colorless viscous liquid; in the aluminum dihydrogen phosphate, the P2O5 content is 32-34wt%, and the Al2O3 content is 8-9wt%.

[0019] Furthermore, in the silica sol, the SiO2 content is 29-31wt%, the pH value is 8.5-10.5; and the average particle size of the silica sol is 10-20nm.

[0020] A zirconium tungstate fiber reinforced insulating coating for oriented silicon steel prepared by the above preparation method.

[0021] Zirconium tungstate nanofibers added to the coating can act as a skeleton to adsorb and promote the phosphate and silica sol in the coating to grow directional along the zirconium tungstate nanofibers. The two-dimensional characteristics of the fiber material are used to form a woven cross-linked network on the surface of the oriented silicon steel. After curing, the P and Si oxide tetrahedrons grow along the fibers to form a dense network structure. This fiber network provides a large specific surface area and has a strong adsorption capacity, which can increase the curing speed of the coating and effectively improve the processing line speed.

[0022] Zirconium tungstate nanofibers themselves have high toughness and extremely low thermal expansion coefficient. As a skeleton, they can reduce the thermal expansion coefficient of the coating, increase the tensile stress applied by the high-tension coating on the oriented silicon steel, pull the surface magnetic chips, reduce the magnetostrictive deformation rate, and reduce the steel loss of the oriented silicon steel.

[0023] Aluminum dihydrogen phosphate is colorless, tasteless and viscous, solidifies at room temperature, has high bonding strength, and has the characteristics of high temperature resistance, shock resistance, anti-stripping and good insulation performance. The use of aluminum dihydrogen phosphate in the present invention is conducive to the close combination of the coating and the substrate, and can significantly improve the adhesion between the high-tension coating for oriented silicon steel and the magnesium silicate bottom layer.

[0024] Silica sol is a milky white colloidal solution of nano-scale ultrafine silicon dioxide particles dispersed in water. There are a large number of active groups such as water and hydroxyl groups on the surface of silicon dioxide, which can cross-link with phosphates through active hydroxyl groups to promote the formation of a network structure of the coating. After curing, phosphorus-oxygen tetrahedrons will be formed, which will cross-link with the network structure and effectively improve the bonding and wear resistance of high-tension coatings for oriented silicon steel.

[0025] Molybdenum hydroxide hexahydrate can improve the wettability of the coating solution and stabilize the free phosphoric acid in the phosphate. The molybdenum hydroxide hexahydrate used in the present invention can improve the stability and moisture absorption resistance of the high-tension coating for oriented silicon steel and improve the appearance of the coating.

[0026] On the one hand, nickel hydroxide can be evenly dissolved in the solution. During the film-forming process, it can form a nickel oxide layered structure with a higher resistivity, thereby improving the resistivity of the coating. On the other hand, the addition of nickel hydroxide can have the effect of dyeing and concealing blemishes, filling in the gaps in the magnesium silicate below, covering up the defects of the magnesium silicate layer, and improving the product qualification rate.

[0027] The high-tension coating solution for oriented silicon steel prepared by the present invention does not contain harmful substances, thus avoiding the volatilization of harmful gases, which leads to reduced heat resistance and weldability of the coating. It also does not contain boric acid, thus not causing the problem of moisture absorption and stickiness.

[0028] The present invention performs double-sided coating on oriented silicon steel, and after baking and high-temperature curing, the formed high-tension coating for oriented silicon steel has uniform appearance and moderate surface hardness, so that it is not easy to peel off and powder in the subsequent processing process.

[0029] The high-tension coating for oriented silicon steel prepared by the present invention has good adhesion and high interlayer resistivity, not only meets the requirements of insulation performance, but also has good heat resistance and corrosion resistance.

[0030] Therefore, the present invention has the characteristics of low cost, simple process and easy industrial production, and the prepared high-tension coating for oriented silicon steel has good tension effect and excellent performance.

[0031] The ammonium tungstate and zirconium acetate used in the preparation of zirconium tungstate nanofibers are both water-soluble substances. After heating, the ammonium ions will be converted into ammonia and volatilized into the air, while the acetate ions will be oxidized into water and carbon dioxide. That is, after the two substances are synthesized into nanofibers, the byproducts will not pollute the coating components. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 This is a SEM image of the zirconium tungstate nanofibers prepared in Example 1;

[0033] Figure 2 This is a SEM image of the zirconium tungstate fiber reinforced insulation coating for oriented silicon steel prepared in Example 1;

[0034] Figure 3 The electrode potential experimental results of coatings with different P / Si ratios. DETAILED DESCRIPTION

[0035] The following are specific embodiments of the present invention and the accompanying drawings to further describe the technical solution of the present invention, but the present invention is not limited to these embodiments.

[0036] Embodiment 1:

[0037] Step 1: Synthetic fiber reinforced coating solution

[0038] First, the ammonium tungstate and zirconium acetate solutions are mixed, stirred at 300 rpm for 8 hours, heated and stirred until the water is completely evaporated to obtain zirconium tungstate nanopowder, and the zirconium tungstate nanopowder is slowly heated to 1300° C. at 5° C. / s in a heating furnace on a silicon oxide substrate and kept at this temperature for 8 hours to grow zirconium tungstate nanofibers;

[0039] Step 2: adding aluminum dihydrogen phosphate, silica sol, molybdenum oxide and nickel hydroxide into a reaction kettle and mixing them evenly to obtain a mixed solution; then adding 3wt% of zirconium tungstate nanofibers into the mixed solution in sequence and stirring evenly to obtain a high-tension coating solution for oriented silicon steel;

[0040] Step three, coating the surface of the oriented silicon steel by roll coating, the oriented silicon steel is a semi-finished oriented silicon steel sheet with a thickness of 0.28 mm, baking at 450°C for 35 seconds under an argon protection atmosphere, and then keeping warm at 650°C for 200 seconds to obtain a zirconium tungstate fiber reinforced insulating coating for the oriented silicon steel.

[0041] The components and contents of the coating solution are: 33 parts of aluminum dihydrogen phosphate, 30 parts of silica sol, 4 parts of molybdenum hydroxide hexahydrate, 3 parts of nickel hydroxide, 120 parts of deionized water, and 3 wt% of zirconium tungstate nanofibers. The product exhibits good adhesion, insulation and a smooth appearance. The iron loss (P 17 / 50 ) is 1.048W / kg.

[0042] Embodiment 2:

[0043] The same preparation steps as in Example 1 were used to adjust the composition and content of the coating solution: 28 parts of aluminum dihydrogen phosphate, 25 parts of silica sol, 2 parts of molybdenum hydroxide hexahydrate, 1 part of nickel hydroxide, 4.5 parts of ammonium tungstate, 2 parts of zirconium acetate, 80 parts of deionized water, and 3% of zirconium tungstate nanofibers. The product showed good adhesion, insulation and smooth appearance, and the iron loss (P 17 / 50 ) is 1.062W / kg.

[0044] Embodiment 3:

[0045] The same preparation steps as in Example 1 were used to adjust the composition and content of the coating solution: 33 parts of aluminum dihydrogen phosphate, 30 parts of silica sol, 4 parts of molybdenum hydroxide hexahydrate, 3 parts of nickel hydroxide, 120 parts of deionized water, and 0.8% of zirconium tungstate nanofibers. The product showed good adhesion, insulation and smooth appearance, and the iron loss (P 17 / 50 ) is 1.079W / kg.

[0046] The amount of zirconium tungstate nanofiber added was reduced, the fiber structure in the coating was reduced, and the pulling effect on the surface of oriented silicon steel was reduced, resulting in an increase in iron loss. This shows that zirconium tungstate nanofiber plays an important role in optimizing the iron loss performance of the coating.

[0047] Comparative Example 1

[0048] Without using insulating coating, the 0.28mm oriented silicon steel semi-finished product was directly tested. The surface of the product showed that the magnesium silicate oxide film had fallen off and the appearance was uneven. The insulation performance was average, and the iron loss (P 17 / 50 ) is 1.109W / kg.

[0049] Comparative Example 2

[0050] No zirconium tungstate nanofibers were added, and the other aspects were exactly the same as in Example 1. The obtained product had good adsorption performance and slightly fell off. However, due to the lack of zirconium tungstate nanofibers, the phosphate and silica sol in the coating could not be promoted to grow in an oriented manner, resulting in a loose structure of the cured coating and a low iron loss (P 17 / 50 ) is 1.120W / kg.

[0051] Comparative Example 3

[0052] Using some relevant components of "An environmentally friendly oriented silicon steel insulating coating and its preparation method" (CN116731543B), in the product production process, 33 parts of aluminum dihydrogen phosphate, 4 parts of zirconium oxychloride, 6.4 parts of sodium tungstate, 30 parts of silica gel, 3 parts of sodium phosphate, and 120 parts of water are mixed as raw materials for the insulating coating, sprayed, and cured. The product shows good adhesion and a smooth appearance, but the insulation performance is average, and the iron loss (P 17 / 50) is 1.113W / kg.

[0053] This is mainly due to the use of a large amount of alkali metal elements, such as sodium salt, in the raw materials. After curing at high temperature, ionic compounds still exist, which reduces the insulation performance of the coating. At the same time, since no nanofiber structure is formed, the coating cannot optimize the iron loss performance of oriented silicon steel.

[0054] Comparative Example 4

[0055] The same preparation steps as in Example 1 were used to adjust the components and contents of the coating solution: 20 parts of aluminum dihydrogen phosphate, 40 parts of silica sol, 0.5 parts of molybdenum hydroxide hexahydrate, 1 part of nickel hydroxide, 4.5 parts of ammonium tungstate, 2 parts of zirconium acetate, 80 parts of deionized water, and 3% of zirconium tungstate nanofibers. The product showed good adhesion, but the material insulation was insufficient, the coating appearance was uneven, and the iron loss (P 17 / 50 ) is 1.126W / kg.

[0056] This is mainly because the P / Si ratio of the coating is not maintained normally, the PO tetrahedron and Si-O tetrahedron do not form a paired structure, and the excess silicate tends to remain as an ionic compound after curing, thus affecting the insulation performance of the coating. At the same time, the content of hexahydrated molybdenum oxide is too low, resulting in poor film-forming performance of the coating, and the coating cannot maintain a complete and dense structure, and cannot form a dense fiber structure around the nanofibers. The loose structure cannot exert traction on the silicon steel surface, resulting in a large iron loss result.

[0057] Performance measurement of coating: The smoothness of coating appearance is evaluated by SEM; the adhesion, insulation and magnetic properties are measured in accordance with GB2522-2017 [Test method for insulation resistance and adhesion of coating on electrical steel strip (sheet)].

[0058] The coating properties prepared in Examples 1-3 and Comparative Examples 1-4 are shown in Table 1;

[0059] It can be seen from Table 1 that after the coating prepared by the present invention is applied, the iron loss of the oriented silicon steel is reduced from 1.109 W / kg to 1.048 W / kg, and the iron loss improvement rate is 5.5%. Therefore, the specific implementation method has the characteristics of low cost, simple process and easy industrial production, and the prepared high-tension coating for oriented silicon steel has good tension effect and excellent performance.

[0060] Table 1 Coating properties

[0061]

[0062] Figure 1 This is a SEM image of the zirconium tungstate nanofibers prepared in Example 1. These fibers have a diameter of about 20 nanometers and a length of 700 to 900 nanometers.

[0063] Figure 2 This is an SEM image of the cross-section of the zirconium tungstate fiber reinforced insulating coating for oriented silicon steel prepared in Example 1. It can be seen from the figure that the coating is applied to the surface of the oriented silicon steel sheet. After heating and curing, silicon oxide and aluminum polyphosphate gather on the fiber surface to form a network structure, connecting each magnetic chip to increase the strength of the coating, improve the internal traction of the coating, and thus reduce the steel loss of silicon steel.

[0064] According to the method of Example 1, only the amount of deionized water added was changed to adjust the solid content to study the effect of the iron loss and iron loss improvement rate of oriented silicon steel. The research range of solid content was 30-41%. The iron loss and iron loss improvement rate reached the lowest when the solid content was 38.1%. Therefore, the present invention can select a solid content of 30-40%.

[0065] According to the method of Example 1, the amount of aluminum dihydrogen phosphate added was maintained and only the amount of silica sol added was changed to prepare the coating, and the coating surface electrode potential experiment was carried out to study the effect of changing the P / Si ratio of the coating on the coating polarization curve.

[0066] Figure 3 The results of the electrode potential experiment of coatings with different P / Si ratios show that the maximum electrode potential can be reached when the P / Si ratio inside the coating is 1:0.9, which means that the coating under this ratio can obtain the optimal interlayer resistance and corrosion resistance. The surface of the coating with a P / Si ratio of 1:0.8 has many protrusions. Properly reducing the P / Si ratio can improve the density of the coating surface, and the corrosion resistance is therefore improved. When the P / Si ratio is further reduced, the content of the film-forming substance aluminum dihydrogen phosphate decreases, and tiny pores are generated on the surface, which has an adverse effect on the corrosion resistance of the coating. Therefore, the P / Si ratio can be controlled at 1:0.8~1.

[0067] For matters not mentioned above, the prior art applies.

[0068] Although some specific embodiments of the present invention have been described in detail through examples, those skilled in the art should understand that the above examples are for illustration only and are not intended to limit the scope of the present invention. Those skilled in the art to which the present invention belongs may make various modifications or supplements to the specific embodiments described or replace them in a similar manner, but they will not deviate from the direction of the present invention or exceed the scope defined by the attached claims. Those skilled in the art should understand that any modifications, equivalent substitutions, improvements, etc. made to the above embodiments based on the technical essence of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for preparing a zirconium tungstate fiber reinforced insulating coating for oriented silicon steel, characterized in that: The steps include: S1. Mix aluminum dihydrogen phosphate, silica sol, molybdenum hydroxide hexahydrate, nickel hydroxide and deionized water, add zirconium tungstate nanofibers, and stir evenly to obtain a high-tension coating solution for oriented silicon steel; S2, coating the surface of the oriented silicon steel with a high tension coating liquid, baking at 430-470° C. under a protective atmosphere, and then keeping the temperature at 620-650° C. for a period of time to obtain a fiber-reinforced coating for the oriented silicon steel; Among them, the mass ratio of aluminum dihydrogen phosphate, silica sol, molybdenum hydroxide hexahydrate, nickel hydroxide, deionized water and zirconium tungstate nanofibers is 20-40:25-45:2-4:1-3:80-120:2-11.

2. The preparation method according to claim 1, characterized in that: In the high tension coating liquid for oriented silicon steel, the solid content is maintained at 30% to 40%, and the P / Si ratio is maintained at 1:0.8 to 1.

3. The preparation method according to claim 1, characterized in that: In step S2, baking is performed for 25 to 35 seconds.

4. The preparation method according to claim 1, characterized in that: In step S2, the temperature is kept at 150 to 200 seconds.

5. The preparation method according to claim 1, characterized in that: The zirconium tungstate nanofiber is prepared by the following preparation method: firstly, ammonium tungstate and zirconium acetate solution are mixed, heated and stirred until the water is completely evaporated to obtain zirconium tungstate nanopowder, and the zirconium tungstate nanopowder is slowly heated to promote crystal growth to form zirconium tungstate nanowires.

6. The preparation method according to claim 5, characterized in that: The zirconium tungstate nanopowder is slowly heated to 1300°C at 5°C / s in a heating furnace on a silicon oxide substrate and kept at this temperature for 5 to 10 hours to grow zirconium tungstate nanofibers.

7. The preparation method according to claim 5, characterized in that: The mass ratio of ammonium tungstate to zirconium acetate in the zirconium acetate solution is 1.8-6.4:0.8-4. In the zirconium acetate solution, the zirconium content is 15-16%.

8. The preparation method according to claim 1, characterized in that: The aluminum dihydrogen phosphate is a colorless viscous liquid; in the aluminum dihydrogen phosphate, the P2O5 content is 32-34wt%, and the Al2O3 content is 8-9wt%.

9. The preparation method according to claim 1, characterized in that: The silica sol has a SiO2 content of 29-31 wt %, a pH value of 8.5-10.5, and an average particle size of 10-20 nm.

10. A zirconium tungstate fiber reinforced insulating coating for oriented silicon steel prepared by the preparation method according to any one of claims 1 to 9.

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