Preparation method of magnesium alloy surface super-hydrophobic high-temperature-resistant composite film

Abstract

The application discloses a preparation method of a magnesium alloy surface super-hydrophobic high-temperature-resistant composite film and belongs to the technical field of metal material surface modification. The method comprises the following steps: S1, polishing the magnesium alloy to be bright and cleaning the magnesium alloy with acetone until the surface is clean; S2, placing the polished and cleaned magnesium alloy in a composite oxidizing solution with a mass fraction of 1-20%, stirring the magnesium alloy at 25-45 DEG C for 5-30 min, and obtaining the magnesium alloy with an oxide film layer at a stirring speed of 50-100 r / min; and S3, placing the magnesium alloy with the oxide film layer in a mixed solution of fluorosilane, stearic acid and ethanol, washing and drying the magnesium alloy after immersion at room temperature for 1 h. The super-hydrophobic high-temperature-resistant layer is established on the surface of the magnesium alloy through the composite oxidation / modification approach, the static contact angle of the prepared composite film can reach 150 DEG, and the composite film has excellent temperature resistance and corrosion resistance and other performances.

Description

Technical Field

[0001] This invention belongs to the field of surface modification technology of metal materials, and specifically relates to a method for preparing a superhydrophobic and high-temperature resistant composite film on the surface of magnesium alloy. Background Technology

[0002] Magnesium alloys are the lightest metallic engineering materials used in industrial applications, with a density only 2 / 3 that of aluminum and 1 / 4 that of iron. They possess high specific strength and specific stiffness, excellent damping and electromagnetic shielding properties, good heat dissipation and electrical conductivity, and are easy to process, recyclable, and abundant in reserves. Therefore, their applications in the automotive, electronics, biomedical, defense, and aerospace industries are increasing, earning them the reputation of being a green engineering metal structural material for the 21st century. However, magnesium alloys also have drawbacks such as poor corrosion resistance, poor wear resistance, flammability, and difficulty in room temperature plastic deformation. In particular, their poor high-temperature resistance and poor corrosion resistance significantly limit the full realization of their performance advantages and their widespread application.

[0003] Currently, research on high-temperature resistant magnesium alloys in my country is mainly at the experimental stage, and there are relatively few industrially viable and high-performance high-temperature resistant magnesium alloy grades. Although high-rare-earth content high-temperature resistant magnesium alloys possess good room-temperature mechanical properties and high-temperature heat resistance, the high rare-earth content leads to reduced casting performance and higher costs, hindering commercial application. Therefore, surface modification treatment of formed magnesium alloys to improve their comprehensive properties such as high-temperature resistance, corrosion resistance, and wear resistance, thereby enhancing the application value of magnesium alloy substrates, has become an urgent problem to be solved. Summary of the Invention

[0004] The purpose of this invention is to provide a method for preparing a superhydrophobic high-temperature resistant composite film on the surface of magnesium alloys, so as to solve the problem of poor high-temperature resistance and corrosion resistance of existing magnesium alloys.

[0005] The objective of this invention can be achieved through the following technical solutions:

[0006] A method for preparing a superhydrophobic and high-temperature resistant composite film on a magnesium alloy surface includes the following steps:

[0007] S1. Magnesium alloy surface pretreatment: Polish the magnesium alloy to a bright finish and clean it with acetone until the surface is clean.

[0008] S2. Composite oxidation treatment: The polished and cleaned magnesium alloy is placed in a composite oxidation solution with a mass fraction of 1%-20%, and stirred for 5-30 minutes at 25-45℃ and a stirring rate of 50-100 r / min to obtain a magnesium alloy with an oxide film layer.

[0009] S3. Surface hydrophobic modification treatment: The magnesium alloy with oxide film is placed in a mixed solution of fluorosilane, stearic acid and ethanol, soaked at room temperature (25-30℃) for 1 hour, washed with deionized water, and then dried in a 60℃ forced-air drying oven for 40 minutes.

[0010] Furthermore, the preparation method of the composite oxidation liquid includes the following steps: adding waterborne organosilicon resin, dispersant and modified graphene oxide to water in sequence, stirring at 500 r / min for 2 h at room temperature, and then adding molybdate, silicate, sodium sulfide, coumarin, rare earth salt and potassium fluorozirconate in sequence at 60°C, and continuing to stir at a constant temperature for 2 h to obtain the composite oxidation liquid.

[0011] Furthermore, the solid-liquid ratio of the aqueous organosilicon resin, molybdate, silicate, sodium sulfide, coumarin, rare earth salt, potassium fluorozirconate, modified graphene oxide, dispersant, and water is 20-50g:40-80g:30-50g:10-30g:3-10g:0.75-1.2g:1-3g:0.5-1.5g:0.01-0.1g:1L.

[0012] Furthermore, the molybdate is any one or any two of sodium molybdate, ammonium molybdate, and potassium molybdate mixed in a mass ratio of 1:1, or sodium molybdate, ammonium molybdate, and potassium molybdate mixed in a mass ratio of 1:1:1.

[0013] Furthermore, the silicate is any one or any two of sodium silicate, polysodium silicate, sodium aluminum silicate, potassium silicate, and potassium aluminum silicate mixed in a mass ratio of 1:1.

[0014] Furthermore, the rare earth salt is any one of cerium acetate and lanthanum acetate, or a mixture of cerium acetate and lanthanum acetate in a mass ratio of 1:1.

[0015] Furthermore, the dispersant is any one or any two of polyvinylpyrrolidone, sodium dodecyl sulfonate, polysulfonic acid, and gelatin mixed in a mass ratio of 1:1, or any three of them mixed in a mass ratio of 1:1:1.

[0016] Furthermore, the method for preparing the modified graphene oxide includes the following steps:

[0017] Step A. Add 3g of APTES (3-aminopropyltriethoxysilane) to 100g of a 50% (w / w) aqueous ethanol solution, adjust the pH to 4-5 with glacial acetic acid, and stir magnetically at 40℃ for 0.5h at a stirring rate of 1000r / min; then add 0.1g of SiO2, heat to 60℃, and stir magnetically at 1500r / min for 8h; after filtration, wash the filter residue with ethanol, and dry at 60℃ for 24h to obtain product a;

[0018] Step B. Add 0.05g of product a and 0.15g of GO (graphene oxide) to 100mL of DMF (N,N-dimethylformamide), sonicate for 5min, and magnetically stir at 105℃ for 6h at a stirring rate of 1500r / min. After filtration, wash the filter residue with ethanol and dry at 60℃ for 24h to obtain modified graphene oxide.

[0019] Furthermore, the fluorosilane, stearic acid and ethanol mixed solution is composed of fluorosilane, stearic acid and ethanol in a mass ratio of 1:15:84.

[0020] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0021] 1. This invention provides a method for preparing a superhydrophobic and high-temperature resistant composite film on a magnesium alloy surface. A superhydrophobic and high-temperature resistant layer is established on the surface of a magnesium alloy (AZ series) through a composite oxidation / modification process. The prepared composite film has a static contact angle of up to 150° and also has excellent temperature resistance (500℃) and corrosion resistance.

[0022] 2. In this invention, the composite oxidation solution formulation design utilizes water-based organosilicon resin and SiO2-modified graphene oxide to improve the temperature resistance and corrosion resistance of the composite film. Inorganic corrosion inhibitors, natural corrosion inhibitors, and rare earth salts are combined, creating a synergistic effect to enhance the coating's corrosion resistance. During the composite oxidation film formation process, micro-stirring (50-100 r / min) increases the coating thickness, thereby increasing its corrosion resistance. Furthermore, based on the composite oxidation, hydrophobic modification with a mixture of fluorosilane, stearic acid, and ethanol is applied to improve the static contact angle of the composite film, achieving the goal of enhancing the coating's corrosion resistance through the synergistic effect of the composite oxide layer and the hydrophobic layer. Detailed Implementation

[0023] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0024] Example 1

[0025] The preparation method of modified graphene oxide includes the following steps:

[0026] Step A. Add 3g APTES to 100g of 50% ethanol aqueous solution, adjust the pH to 4.5 with glacial acetic acid, and stir magnetically at 40℃ for 0.5h at a stirring rate of 1000r / min; then add 0.1g SiO2, heat to 60℃, and stir magnetically at 1500r / min for 8h; after filtration, wash the filter residue with ethanol, and dry at 60℃ for 24h to obtain product a;

[0027] Step B. Add 0.05g of product a and 0.15g of GO to 100mL of DMF, sonicate for 5min, and magnetically stir at 105℃ for 6h at a stirring rate of 1500r / min. After filtration, wash the filter residue with ethanol and dry at 60℃ for 24h to obtain modified graphene oxide.

[0028] The modified graphene oxide described in the following examples was prepared according to the above preparation method.

[0029] Example 2

[0030] The preparation method of the composite oxidation liquid includes the following steps:

[0031] Add 50g of waterborne silicone resin, 0.1g of dispersant (0.05g of polyvinylpyrrolidone and 0.05g of polysulfonic acid) and 1.5g of modified graphene oxide (prepared in Example 1) to 1L of water in sequence. Stir at 500r / min for 2h at room temperature, and then add 60g of molybdate (20g of ammonium molybdate, 20g of potassium molybdate, and 20g of sodium molybdate), 50g of silicate (25g of sodium polysilicate and 25g of potassium silicate), 30g of sodium sulfide, 10g of coumarin, 1.2g of rare earth salt (lanthanum acetate) and 3.0g of potassium fluorozirconate in sequence at 60℃. Continue stirring at constant temperature for 2h to obtain a composite oxidation solution.

[0032] Examples 3-4

[0033] The preparation method of the composite oxidation liquid is the same as in Example 2, except that the proportions of each component are shown in Table 1.

[0034] Table 1

[0035]

[0036] Examples 5-7

[0037] The preparation method of the composite oxidation liquid is the same as in Example 2, except that the proportions of each component are shown in Table 2.

[0038] Table 2

[0039]

[0040]

[0041] Comparative Example 1

[0042] The preparation method of the composite oxidation liquid is the same as that in Example 2, except that the water-based organosilicon resin is replaced with water-soluble acrylic resin, while the other component parameters remain unchanged.

[0043] Comparative Example 2

[0044] The preparation method of the composite oxidation liquid is the same as that in Example 2, except that no modified graphene oxide is added, while the parameters of the other components remain unchanged.

[0045] Comparative Example 3

[0046] The preparation method of the composite oxidation liquid is the same as that in Example 2, except that coumarin is not added, while the parameters of the other components remain unchanged.

[0047] Example 8

[0048] A method for preparing a superhydrophobic and high-temperature resistant composite film on a magnesium alloy surface includes the following steps:

[0049] S1. Magnesium alloy surface pretreatment: Grind the magnesium alloy (AZ type) to a bright finish and clean it with acetone until the surface is clean;

[0050] S2. Composite oxidation treatment: The polished and cleaned magnesium alloy was placed in a composite oxidation solution with a mass fraction of 18% prepared in Example 2, and stirred for 18 min at 35°C and a stirring rate of 100 r / min to obtain a magnesium alloy with an oxide film layer.

[0051] S3. Surface hydrophobic modification treatment: The magnesium alloy with oxide film layer is placed in a solution of fluorosilane, stearic acid and ethanol in a mass ratio of 1:15:85, soaked at room temperature for 1 hour, washed with deionized water, and then dried in a 60℃ forced-air drying oven for 40 minutes.

[0052] Example 9

[0053] A method for preparing a superhydrophobic and high-temperature resistant composite film on a magnesium alloy surface includes the following steps:

[0054] S1. Magnesium alloy surface pretreatment: Grind the magnesium alloy (AZ type) to a bright finish and clean it with acetone until the surface is clean;

[0055] S2. Composite oxidation treatment: The polished and cleaned magnesium alloy was placed in a composite oxidation solution with a mass fraction of 12% prepared in Example 2, and stirred for 8 minutes at 28°C with a stirring rate of 50 r / min to obtain a magnesium alloy with an oxide film layer.

[0056] S3. Surface hydrophobic modification treatment: The magnesium alloy with oxide film layer is placed in a solution of fluorosilane, stearic acid and ethanol in a mass ratio of 1:15:85, soaked at room temperature for 1 hour, washed with deionized water, and then dried in a 60℃ forced-air drying oven for 40 minutes.

[0057] Example 10

[0058] A method for preparing a superhydrophobic and high-temperature resistant composite film on a magnesium alloy surface includes the following steps:

[0059] S1. Magnesium alloy surface pretreatment: Grind the magnesium alloy (AZ type) to a bright finish and clean it with acetone until the surface is clean;

[0060] S2. Composite oxidation treatment: The polished and cleaned magnesium alloy was placed in a composite oxidation solution prepared in Example 2 with a mass fraction of 2%, and stirred for 30 min at 45°C and a stirring rate of 80 r / min to obtain a magnesium alloy with an oxide film layer.

[0061] S3. Surface hydrophobic modification treatment: The magnesium alloy with oxide film layer is placed in a solution of fluorosilane, stearic acid and ethanol in a mass ratio of 1:15:85, soaked at room temperature for 1 hour, washed with deionized water, and then dried in a 60℃ forced-air drying oven for 40 minutes.

[0062] Example 11

[0063] A method for preparing a superhydrophobic and high-temperature resistant composite film on a magnesium alloy surface, the specific preparation steps and parameters are the same as in Example 8, the difference being that the composite oxidation liquid is prepared in Example 3.

[0064] Example 12

[0065] A method for preparing a superhydrophobic and high-temperature resistant composite film on a magnesium alloy surface, the specific preparation steps and parameters are the same as in Example 8, the difference being that the composite oxidation liquid is prepared in Example 4.

[0066] Example 13

[0067] A method for preparing a superhydrophobic and high-temperature resistant composite film on a magnesium alloy surface, the specific preparation steps and parameters are the same as in Example 8, the difference being that the composite oxidation liquid is prepared in Example 5.

[0068] Example 14

[0069] A method for preparing a superhydrophobic and high-temperature resistant composite film on a magnesium alloy surface, the specific preparation steps and parameters are the same as in Example 8, the difference being that the composite oxidation liquid is prepared in Example 6.

[0070] Example 15

[0071] A method for preparing a superhydrophobic and high-temperature resistant composite film on a magnesium alloy surface, the specific preparation steps and parameters are the same as in Example 8, the difference being that the composite oxidation liquid is prepared in Example 7.

[0072] Comparative Example 4

[0073] A method for preparing a superhydrophobic and high-temperature resistant composite film on a magnesium alloy surface, the specific preparation steps and parameters are the same as in Example 8, the difference being that the composite oxidation liquid is prepared by Comparative Example 1.

[0074] Comparative Example 5

[0075] A method for preparing a superhydrophobic and high-temperature resistant composite film on a magnesium alloy surface, the specific preparation steps and parameters are the same as in Example 8, the difference being that the composite oxidation liquid is prepared by Comparative Example 2.

[0076] Comparative Example 6

[0077] A method for preparing a superhydrophobic and high-temperature resistant composite film on a magnesium alloy surface, the specific preparation steps and parameters are the same as in Example 8, the difference being that the composite oxidation liquid is prepared by Comparative Example 3.

[0078] Comparative Example 7

[0079] A method for preparing a superhydrophobic high-temperature resistant composite film on a magnesium alloy surface, the specific preparation steps are the same as in Example 8, the difference being that the stirring rate in S2 is 0 r / min, and the other parameters are the same as in Example 8.

[0080] Comparative Example 8

[0081] A method for preparing a superhydrophobic high-temperature resistant composite film on a magnesium alloy surface is described. The specific preparation steps are the same as in Example 8, except that the stirring rate in S2 is 150 r / min, and the other parameters are the same as in Example 8.

[0082] Comparative Example 9

[0083] A method for preparing a composite film on a magnesium alloy surface includes the following steps:

[0084] S1. Magnesium alloy surface pretreatment: Grind the magnesium alloy (AZ type) to a bright finish and clean it with acetone until the surface is clean;

[0085] S2. Composite oxidation treatment: The polished and cleaned magnesium alloy was placed in a composite oxidation solution with a mass fraction of 18% prepared in Example 2, and stirred for 20 min at 35°C and a stirring rate of 100 r / min to obtain a magnesium alloy with an oxide film. After washing with deionized water, it was placed in a forced-air drying oven at 60°C for 40 min to dry.

[0086] Performance tests were conducted on Examples 8-15 and Comparative Examples 4-9, using the following methods:

[0087] Corrosion resistance test method: According to the GB / T 1771-1991 test standard, after 400h test, the coating surface is considered qualified if no rust appears;

[0088] The test and evaluation method for temperature resistance is as follows: According to GB / T 1735-2009, the muffle furnace is adjusted to 500℃, and three surface-treated magnesium alloy samples are placed in it. After 5 hours, the magnesium alloy samples are taken out, cooled to room temperature, and compared with the pre-reserved magnesium alloy samples. If there is no crack or discoloration in appearance, it is judged as qualified.

[0089] Hydrophobicity test method: The static contact angle was measured using a semi-automatic water droplet contact angle meter. The test results are shown in Table 3.

[0090] Table 3

[0091]

[0092] As shown in Table 3:

[0093] Examples 8, 9, and 10 show the test results of the composite films on the surface of magnesium alloy plates obtained by treating the same composite oxidizing solution (prepared in Example 2) under different parameters; Examples 11, 12, 13, 14, and 15 show the test results of the composite films on the surface of magnesium alloy plates obtained by treating composite oxidizing solutions with different component concentrations (prepared in Examples 3, 4, 5, 6, and 7, respectively) under the same parameters. The results show that the composite films on the surface of magnesium alloys obtained by the surface modification method of the present invention have excellent hydrophobicity, temperature resistance, and corrosion resistance.

[0094] As shown in Example 8 and Comparative Example 4, the aqueous organosilicon resin in the composite oxidation solution is beneficial to improving the temperature resistance and corrosion resistance of the composite film; as shown in Example 8 and Comparative Example 5, the modified graphene oxide is beneficial to improving the temperature resistance and corrosion resistance of the composite film; as shown in Example 8 and Comparative Example 6, the natural corrosion inhibitor coumarin is beneficial to improving the corrosion resistance of the composite film, because coumarin combined with inorganic corrosion inhibitors and rare earth salts can produce a synergistic effect that promotes the improvement of corrosion resistance.

[0095] A comparison of Example 8 with Comparative Examples 7 and 8 shows that when using a composite oxide solution to surface treat magnesium alloys, mechanical disturbance can improve coating performance. When micro-stirring (<100 r / min) is present in the composite oxide film-forming system, the corrosion resistance of the film can be improved. This is because micro-stirring facilitates the film-forming process and increases the thickness of the film. However, when the stirring rate continues to increase (>100 r / min), the corrosion resistance of the film decreases. This is because when the stirring rate reaches a certain level, the dissolution process of the film accelerates with increasing stirring rate, ultimately leading to a thinner film and even cracks. Preferably, a rotation speed in the range of 50-100 r / min yields better results.

[0096] As can be seen from Example 8 and Comparative Example 9, the treatment with a mixture of fluorosilane, stearic acid and ethanol can further improve the hydrophobicity of the oxide layer, thereby achieving corrosion resistance of the composite oxide layer.

[0097] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus.

[0098] 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 alterations 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 method for preparing a super-hydrophobic high-temperature-resistant composite film on a magnesium alloy surface, characterized in that, It comprises the following steps: S1. Polishing the magnesium alloy to bright and cleaning the surface with acetone; S2. Placing the polished magnesium alloy in a composite oxidizing solution with a mass fraction of 1%-20%, stirring at 25-45℃ for 5-30min, and the stirring rate is 50-100r / min, to obtain the magnesium alloy with an oxide film layer; S3. Placing the magnesium alloy with an oxide film layer in a mixed solution of fluorosilane, stearic acid and ethanol, soaking at room temperature for 1h, then washing with deionized water and drying. The preparation method of the composite oxidizing solution comprises the following steps: adding water-based silicone resin, dispersant and modified graphene oxide into water in sequence, stirring at 500r / min for 2h at room temperature, then adding molybdate, silicate, sodium sulfide, coumarin, rare earth salt and potassium fluorozirconate in sequence at 60℃, and continuing to stir for 2h at constant temperature to obtain the composite oxidizing solution. The dosage of the water-based silicone resin, molybdate, silicate, sodium sulfide, coumarin, rare earth salt, potassium fluorozirconate, modified graphene oxide, dispersant and water is 20-50g:40-80g:30-50g:10-30g:3-10g:0.75-1.2g:1-3g:0.5-1.5g:0.01-0.1g:1L.

2. The method according to claim 1, wherein the magnesium alloy surface superhydrophobic high-temperature resistant composite film is prepared by the following steps: (1) preparing a magnesium alloy substrate; (2) preparing a magnesium alloy surface superhydrophobic high-temperature resistant composite film on the magnesium alloy substrate by a chemical vapor deposition method. The preparation method of the modified graphene oxide comprises the following steps: Step A. Adding 3g APTES into 100g ethanol aqueous solution with a mass fraction of 50%, adjusting the pH value to 4-5 with glacial acetic acid, stirring at 40℃ for 0.5h, and the stirring rate is 1000r / min; then adding 0.1g SiO2, increasing the temperature to 60℃, and stirring for 8h, and the stirring rate is 1500r / min; filtering the residue, washing with ethanol, and drying at 60℃ for 24h to obtain product a; Step B. Adding 0.05g product a and 0.15g GO into 100mL DMF, ultrasonic dispersion for 5min, stirring at 105℃ for 6h, and the stirring rate is 1500r / min; filtering the residue, washing with ethanol, and drying at 60℃ for 24h to obtain the modified graphene oxide.

3. The method according to claim 1, wherein the magnesium alloy surface superhydrophobic high-temperature resistant composite film is prepared by the following steps: 1) preparing a magnesium alloy substrate; 2) preparing a magnesium alloy surface superhydrophobic high-temperature resistant composite film on the magnesium alloy substrate by a sol-gel method. The molybdate is any one of sodium molybdate, ammonium molybdate and potassium molybdate, or any two of them mixed in a mass ratio of 1:1, or sodium molybdate, ammonium molybdate and potassium molybdate mixed in a mass ratio of 1:1:

1.

4. The method according to claim 1, wherein the magnesium alloy surface superhydrophobic high-temperature resistant composite film is prepared by the following steps: 1) preparing a magnesium alloy substrate; 2) preparing a magnesium alloy surface superhydrophobic high-temperature resistant composite film on the magnesium alloy substrate by a chemical vapor deposition method. The silicate is any one of sodium silicate, sodium polysilicate, sodium aluminum silicate, potassium silicate and potassium aluminum silicate, or any two of them mixed in a mass ratio of 1:

1.

5. The method according to claim 1, wherein the magnesium alloy surface superhydrophobic high-temperature resistant composite film is prepared by the following steps: 1) preparing a magnesium alloy substrate; 2) preparing a magnesium alloy surface superhydrophobic high-temperature resistant composite film on the magnesium alloy substrate by a chemical vapor deposition method. The rare earth salt is any one of cerium acetate and lanthanum acetate, or cerium acetate and lanthanum acetate mixed in a mass ratio of 1:

1.

6. The method according to claim 1, wherein the magnesium alloy surface superhydrophobic high-temperature resistant composite film is prepared by the following steps: 1) preparing a magnesium alloy substrate; 2) preparing a magnesium alloy surface superhydrophobic high-temperature resistant composite film on the magnesium alloy substrate by a chemical vapor deposition method. The dispersant is any one of polyvinylpyrrolidone, sodium dodecyl sulfonate, polysulfonic acid and gelatin, or any two of them mixed in a mass ratio of 1:1, or any three of them mixed in a mass ratio of 1:1:

1.

7. The method according to claim 1, wherein the magnesium alloy surface superhydrophobic high-temperature resistant composite film is prepared by the following steps: 1) preparing a magnesium alloy substrate; 2) preparing a magnesium alloy surface superhydrophobic high-temperature resistant composite film on the magnesium alloy substrate by a chemical vapor deposition method. The fluorosilane, stearic acid and ethanol in the mixed solution are mixed in a mass ratio of 1:15:84.

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