A preparation method of high temperature resistant superheated water vapor coating

Abstract

The invention discloses a preparation method of a high temperature superheated water vapor resistant coating, comprising the following steps: step A, heating and stirring polymethylphenylsiloxane under water bath conditions to obtain polymethylphenylsiloxane fluid; step B, adding modified polysilsesquioxane to anhydrous ethanol for ultrasonic dispersion to obtain POSS dispersion; step C, adding POSS dispersion to polymethylphenylsiloxane fluid and continuing to stir until uniformly mixed under water bath conditions to obtain mixed dispersion A; step D, adding an organic solvent to the mixed dispersion A for dilution to obtain mixed dispersion B; step E, brushing the mixed dispersion B on a substrate, then placing it in a vacuum drying oven for vacuuming, and finally transferring it to a blast drying oven for curing to obtain a high temperature superheated water vapor resistant coating. The invention can solve the problem that the existing organic silicon coating has poor corrosion resistance and adhesion in high temperature superheated water vapor.

Description

Technical Field

[0001] The present invention relates to the technical field of high temperature resistant coatings, and more specifically to a method for preparing high temperature resistant superheated water vapor coatings. Background Art

[0002] At present, high-temperature pipelines, high-temperature boilers and other places are working in a high-temperature water vapor environment of 200℃-350℃ for a long time. High-temperature superheated water vapor resistant coatings are needed to prevent corrosion. High-temperature superheated water vapor resistant coatings are generally composed of ceramic materials or metal oxide films such as Cr2O3 and ZrO2. Although they have excellent high-temperature resistance, they have poor adhesion and are expensive, so they cannot be widely used. Silicone composite coatings show excellent thermal stability and oxidation resistance in dry air, but there is little research on their anti-corrosion ability in high-temperature and humid environments, especially in high-temperature superheated water vapor corrosive environments, which accelerates the corrosion of metal material surfaces. Si-O bonds are bound to ionized water molecules (H + OH - ) under the action of high temperature water vapor. On the other hand, oxygen, water, chlorine and other ions in the high temperature water vapor environment will form Si-OR active sites at the end of the organosilicon skeleton and the organic groups of the side chain, thereby reducing the thermal stability of the coating, and at the same time speeding up the speed at which the corrosive medium passes through the organosilicon coating, and weakening the adhesion between the coating and the metal substrate, resulting in the coating falling off. Therefore, it is crucial to improve the corrosion resistance and adhesion of organosilicon coatings in high temperature superheated water vapor. Summary of the invention

[0003] Therefore, the technical problem to be solved by the present invention is to provide a method for preparing a high-temperature superheated water vapor resistant coating, so as to solve the problem that the existing organic silicon coating has poor corrosion resistance and adhesion in high-temperature superheated water vapor.

[0004] In order to solve the above technical problems, the present invention provides the following technical solutions:

[0005] A preparation method of a high-temperature superheated water vapor resistant coating comprises the following steps: step A, heating and stirring polymethylphenylsiloxane in a water bath to obtain a polymethylphenylsiloxane fluid; step B, adding modified polysilsesquioxane into anhydrous ethanol for ultrasonic dispersion to obtain a POSS dispersion liquid; step C, adding the POSS dispersion liquid into the polymethylphenylsiloxane fluid and continuing to stir until the mixture is uniform under a water bath condition to obtain a mixed dispersion liquid A; step D, adding an organic solvent into the mixed dispersion liquid A for dilution to obtain a mixed dispersion liquid B; step E, brushing the mixed dispersion liquid B onto a substrate, then placing it in a vacuum drying oven for evacuation, and finally transferring it to a blast drying oven for curing to obtain the high-temperature superheated water vapor resistant coating.

[0006] In the preparation method of the above-mentioned high-temperature resistant superheated water vapor coating, in step A, the preparation method of polymethylphenylsiloxane is: step A-1, methyltrimethoxysilane, dimethyldimethoxysilane and phenyltrimethoxysilane are mixed evenly to obtain a mixed raw material liquid A; step A-2, the mixed raw material liquid A is added to a mixed solvent and mixed evenly, and transferred to a water bath condition while heating and dripping a hydrochloric acid solution, and the dripping of the hydrochloric acid solution is stopped when the mixture boils to obtain a mixed reaction system A; step A-3, the mixed reaction system A continues to reflux under water bath conditions, and after the reaction is completed, it is successively subjected to reduced pressure distillation and filtration to obtain polymethylphenylsiloxane after filtration.

[0007] The preparation method of the above-mentioned high-temperature superheated water vapor resistant coating, in step A-1, the molar ratio of methyltrimethoxysilane, dimethyldimethoxysilane and phenyltrimethoxysilane is (1.5-2):1:(2-4); in step A-2, the mixed solvent is formed by mixing xylene, n-butanol and deionized water in a volume ratio of 3:1:5; the mass volume ratio of the mixed raw material liquid A to the mixed solvent is 150-170g / 900mL; the water bath condition is 75-85°C, and the concentration of the hydrochloric acid solution is 0.5mol / L; in step A-3, the reflux reaction temperature is 75-85°C, and the reflux reaction time is 3-5h.

[0008] In the preparation method of the above-mentioned high-temperature superheated water vapor resistant coating, in step B, the preparation method of the modified polysilsesquioxane is: step B-1, mixing polysilsesquioxane and silane coupling agent KH560 and ultrasonically dispersing them to obtain a mixed raw material liquid B; step B-2, dropping the mixed raw material liquid B into an ethanol solution, heating and stirring during the dropping process, and continuing to heat and react under a nitrogen atmosphere after the dropping is completed. After the reaction is completed, a mixed reaction system B is obtained; step B-3, the mixed reaction system B is washed, centrifuged, dried and ground in sequence, and the modified polysilsesquioxane is obtained after the grinding is completed.

[0009] In the preparation method of the above-mentioned high-temperature resistant superheated water vapor coating, in step B-1, the mass ratio of polysilsesquioxane to silane coupling agent KH560 is 1:8; the ultrasonic dispersion time is 20 to 30 minutes; in step B-2, the volume fraction of the ethanol solution is 50%, the heating and stirring temperature is 60 to 80°C, the heating reaction temperature under a nitrogen atmosphere is 70 to 80°C, and the reaction time is 1 to 1.5 hours.

[0010] The preparation method of the above-mentioned high-temperature resistant superheated water vapor coating is as follows: in step A, the water bath heating temperature is 60-80°C, and the heating stirring time is 30-60min; in step B, the ultrasonic dispersion time is 20-40min; the mass fraction of the modified polysilsesquioxane in the POSS dispersion is 1-3wt%; in step C, the mass fraction of the modified polysilsesquioxane in the mixed dispersion A is 1-3wt%; the water bath condition is 60-80°C, and the heating stirring time is 30-60min; in step D, the organic solvent is a mixture of xylene and n-butanol in a mass ratio of 7:3; the amount of the organic solvent added is based on the standard that the viscosity of the mixed dispersion B reaches 100KU-120KU; in step E, the vacuuming time is 1h, the curing temperature is 60°C, and the curing time is 48h.

[0011] The preparation method of the above-mentioned high-temperature resistant superheated water vapor coating, step C also includes the following steps: step C-1, adding modified graphene oxide to anhydrous ethanol and ultrasonically dispersing it to obtain a PGO dispersion; step C-2, after the POSS dispersion is added to the polymethylphenylsiloxane fluid and stirred and mixed evenly under water bath conditions, the PGO dispersion is added and continued to be stirred and mixed evenly to obtain a mixed dispersion A.

[0012] The preparation method of the above-mentioned high-temperature superheated water vapor resistant coating, the preparation method of the modified graphene oxide in step C-1 is: step (1), ultrasonically dispersing graphene oxide in deionized water to obtain a graphene oxide dispersion; the mass fraction of the graphene oxide dispersion is 0.2 to 0.5wt%; step (2), mixing polyvinyl pyrrolidone and L-ascorbic acid in a mass ratio of 1:1 and adding them to the graphene oxide dispersion to mix evenly to obtain a mixed dispersion C; the polyvinyl pyrrolidone in the mixed dispersion C is 0.2 to 0.5wt%. The mass concentration is 2.5 to 5 mg / mL; step (3), heating and stirring the mixed dispersion C to 70 to 80° C., reacting at 70 to 80° C. for 3 to 5 hours, and centrifuging at 12000 rpm to discard the supernatant after the reaction is completed; step (4), repeatedly washing the lower layer liquid with deionized water and centrifuging it until it is neutral, transferring it to an evaporating dish and evaporating the solvent at 50 to 60° C. for 20 to 24 hours. After the solvent is evaporated, the obtained solid is ground into powder to obtain the modified graphene oxide.

[0013] The preparation method of the above-mentioned high-temperature superheated water vapor resistant coating, in step (1), the preparation method of graphene oxide is: step (1-1), adding graphite to a mixed concentrated acid, mixing and dispersing uniformly, to obtain a mixed dispersion D; the mixed concentrated acid is obtained by mixing concentrated phosphoric acid with a concentration of 83-90wt% and concentrated sulfuric acid with a concentration of 90-98wt% in a volume ratio of 1:3; the initial mass concentration of graphite in the mixed dispersion D is 5-8g / L; step (1-2), under ice-water bath conditions, adding potassium permanganate to the mixed dispersion D in 2-5 times, stirring until completely mixed, to obtain a mixed dispersion E; the amount of potassium permanganate added is the mixed dispersion D. 8 to 12 times the mass of graphite in dispersion D; step (1-3), transferring the mixed dispersion E to a water bath, heating it to 60 to 65° C. and stirring for reaction for 10 to 12 hours, and obtaining a mixed reaction system C after the reaction is complete; step (1-4), dripping a hydrogen peroxide solution with a mass fraction of 10 to 30 wt % into the mixed reaction system C until the reaction system turns golden yellow, to obtain a mixed reaction system D; step (1-5), repeatedly washing and centrifuging the mixed reaction system D with deionized water and a centrifuge until the aqueous solution is neutral; and then transferring the reaction product to a freeze dryer for freeze drying, and then collecting and grinding to obtain graphene oxide.

[0014] In the preparation method of the above-mentioned high-temperature resistant superheated water vapor coating, in step C-1, the mass fraction of modified graphene oxide in the PGO dispersion is 3 to 5 wt%; the conditions for ultrasonic dispersion are: ultrasonication at 150 W for 1 hour; in step C-2, the mass fraction of modified graphene oxide in the mixed dispersion A is 0.1 to 1 wt%.

[0015] The technical solution of the present invention achieves the following beneficial technical effects:

[0016] The invention synthesizes polymethylphenylsiloxane through three silane monomers, prepares GO through an improved Hummers method, uses PVP and L-ascorbic acid to perform hydrogen bonding and amino adsorption and grafting modification treatment to prepare modified graphene oxide, uses silane coupling agent KH560 to modify POSS to obtain modified POSS, and combines the modified graphene oxide, the modified POSS and polymethylphenylsiloxane to prepare a high-temperature superheated water vapor resistant coating; after the coating is circulated at 420°C for 100 hours, the low-frequency impedance modulus of the coating can reach up to 8.13×106Ωcm 2 The lowest self-corrosion current density is 13.607nA·cm -2 The minimum corrosion rate is 1.5422×10 -5 mpy; The addition of modified graphite oxide does not affect the adhesion of the coating. In a 430℃ high-temperature superheated steam environment, the coating can protect the metal substrate for 100h. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 Schematic diagram of the preparation process of POSS-polymethylphenylsiloxane high temperature superheated water vapor resistant coating in an embodiment of the present invention;

[0018] Figure 2 Infrared spectra of polymethylphenylsiloxane and modified POSS polymethylphenylsiloxane in the embodiments of the present invention;

[0019] Figure 3a and Figure 3b They are respectively the TG curve diagram and the DTG curve diagram of the POSS organosilicon high temperature superheated water vapor resistant coating in the embodiment of the present invention;

[0020] Figures 4a to 4f They are respectively macroscopic morphology pictures of the organic silicon high temperature resistant superheated water vapor coating after being treated by 420° C. cycle for 48 hours when the addition amount of POSS in the embodiment of the present invention is 0, 1.0wt%, 1.5wt%, 2.0wt%, 2.5wt% and 3.0wt%;

[0021] Figure 5a to Figure 5f They are SEM images of the organosilicon high temperature resistant superheated water vapor coating after being treated by 420° C. cycle for 48 hours when the addition amount of POSS in the embodiment of the present invention is 0, 1.0wt%, 1.5wt%, 2.0wt%, 2.5wt% and 3.0wt%;

[0022] Figures 6a to 6f They are respectively macroscopic morphology pictures of the organic silicon high temperature resistant superheated water vapor coating after being treated by 420° C. cycle for 100 h when the addition amount of POSS in the embodiment of the present invention is 0, 1.0wt%, 1.5wt%, 2.0wt%, 2.5wt% and 3.0wt%;

[0023] Figures 7a to 7f They are SEM images of the organic silicon high temperature resistant superheated water vapor coating after being treated by 420° C. cycle for 100 h when the addition amount of POSS in the embodiment of the present invention is 0, 1.0wt%, 1.5wt%, 2.0wt%, 2.5wt% and 3.0wt%;

[0024] Figure 8a and Figure 8b They are respectively low-frequency impedance diagrams of each POSS organosilicon high-temperature superheated water vapor resistant coating in the embodiment of the present invention after being circulated at 420°C for 48h and 100h;

[0025] Figure 9a and Figure 9b They are respectively the electrochemical impedance diagrams of each POSS organosilicon high temperature superheated water vapor resistant coating in the embodiment of the present invention after being circulated at 420°C for 48h and 100h;

[0026] Fig.10aand Fig.10b They are polarization curves of the POSS organosilicon high temperature superheated water vapor resistant coating in the embodiment of the present invention after being circulated at 420°C for 48h and 100h;

[0027] Fig.11a , Fig.11b and Fig.11c They are respectively the XPS spectra of the POSS organosilicon coating in the embodiment of the present invention before and after the high-temperature superheated water vapor is circulated for 100 hours, the C1s peak spectrum without circulation, and the C1s peak spectrum after circulation;

[0028] Fig.12a and Figure 12b They are respectively the adhesion and loss rate of the POSS organosilicon high temperature superheated water vapor resistant coating before and after the high temperature superheated water vapor 420°C cycle in the embodiment of the present invention;

[0029] Fig.13 XRD patterns of graphene oxide and modified graphene oxide in the embodiments of the present invention;

[0030] Fig.14 FT-IR images of graphene oxide and modified graphene oxide in the embodiments of the present invention;

[0031] Fig.15 Raman spectra of graphene oxide and modified graphene oxide in the embodiments of the present invention;

[0032] Figures 16a to 16c They are respectively the XPS full spectra of graphene oxide and modified graphene oxide in the embodiments of the present invention, the C1s peak spectrum of graphene oxide, and the C1s peak spectrum of modified graphene oxide;

[0033] Fig.17 TG curves of graphene oxide and modified graphene oxide in the embodiments of the present invention;

[0034] Figures 18a to 18d They are respectively a planar morphology diagram of graphene oxide, a graphene oxide height data diagram, a planar morphology diagram of modified graphene oxide, and a modified graphene oxide height data diagram in an embodiment of the present invention;

[0035] Figures 19a to 19d They are respectively a TEM image of graphene oxide (200 nm), a TEM image of graphene oxide (50 nm), a TEM image of modified graphene oxide (200 nm), and a TEM image of modified graphene oxide (50 nm) in an embodiment of the present invention;

[0036] Figure 20a to Figure 20b are electron diffraction patterns of graphene oxide and modified graphene oxide in the embodiments of the present invention, respectively;

[0037] Fig.21A flow chart of the preparation of the PVP-modified graphene oxide high temperature superheated water vapor resistant coating in an embodiment of the present invention;

[0038] Figure 22a to Figure 22b They are respectively a TG curve diagram and a DTG curve diagram of the modified graphene oxide high temperature superheated water vapor resistant coating in an embodiment of the present invention;

[0039] Figures 23a to 23d These are macroscopic morphology pictures of the coatings with modified graphene oxide addition amounts of 0.1wt%, 0.3wt%, 0.5wt% and 1.0wt% respectively after being treated with high-temperature superheated water steam at 420°C for 48h;

[0040] Figures 24a to 24d They are SEM images of the coatings with modified graphene oxide addition amounts of 0.1wt%, 0.3wt%, 0.5wt% and 1.0wt% respectively in the embodiments of the present invention after being treated with high-temperature superheated water steam at 420°C for 48h;

[0041] Figures 25a to 25d These are macroscopic morphology pictures of the coatings with modified graphene oxide addition amounts of 0.1wt%, 0.3wt%, 0.5wt% and 1.0wt% respectively after being treated with high-temperature superheated water steam at 420°C for 100h;

[0042] Figures 26a to 26d They are SEM images of the coatings with modified graphene oxide addition amounts of 0.1wt%, 0.3wt%, 0.5wt% and 1.0wt% respectively in the embodiments of the present invention after being treated with high-temperature superheated water steam at 420°C for 100h;

[0043] Figure 27a1 to Figure 27d1 These are macroscopic morphology pictures of the coatings with modified graphene oxide addition amounts of 0.1wt%, 0.3wt%, 0.5wt% and 1.0wt% respectively after being treated with high-temperature superheated water steam at 430°C for 100h;

[0044] Figure 27a2 to Figure 27d2 These are microscopic morphology images of the coatings in the embodiments of the present invention with the addition amounts of modified graphene oxide being 0.1wt%, 0.3wt%, 0.5wt% and 1.0wt% respectively after being treated with high-temperature superheated water steam at 430°C for 100h;

[0045] Figures 28a to 28d These are macroscopic morphology pictures of the coatings with modified graphene oxide addition amounts of 0.1wt%, 0.3wt%, 0.5wt% and 1.0wt% respectively after being treated with high-temperature superheated water steam at 430°C for 150h;

[0046] Fig.29a and Fig.29bThe low-frequency impedance modulus diagram of each coating with different modified graphene oxide addition amounts in the embodiment of the present invention after being circulated at 420°C high-temperature superheated steam for 48 hours and 100 hours respectively;

[0047] Fig.30a and Fig.30b The electrochemical impedance diagrams of the coatings with different modified graphene oxide addition amounts in the embodiments of the present invention after being circulated at 420°C for 48 hours and 100 hours respectively by high-temperature superheated water vapor;

[0048] Fig.31a and Fig.31b Polarization curves of various coatings with different modified graphene oxide addition amounts in the embodiment of the present invention after being circulated at 420°C high-temperature superheated steam for 48 hours and 100 hours respectively;

[0049] Figures 32a to 32e They are respectively the XPS full spectrum of the coating with a modified graphene oxide addition amount of 0.5wt% in the embodiment of the present invention before and after being cycled at 420°C for 100h by high-temperature superheated steam, the C1s peak before the cycle, the C1s peak after the cycle, the Si2p peak of the coating before the cycle, and the Si2p peak of the coating after the cycle;

[0050] Fig.33a and Figure 33b The adhesion and loss rate bar graphs of the coatings with different modified graphene oxide addition amounts in the embodiments of the present invention before and after being cycled by high-temperature superheated water vapor at 420°C are shown respectively;

[0051] Fig.34 Schematic diagram of the anti-corrosion mechanism of different coatings in the embodiments of the present invention;

[0052] Figures 35a to 35c They are schematic diagrams of the degradation mechanism of the coating in the embodiments of the present invention. DETAILED DESCRIPTION

[0053] Part I Preparation of POSS-polymethylphenylsiloxane high temperature superheated water vapor resistant coating

[0054] 1.1 Preparation of POSS-polymethylphenylsiloxane high temperature superheated water vapor resistant coating

[0055] 1.1.1 Preparation of polymethylphenylsiloxane

[0056] The performance of polymethylphenylsiloxane is related to two aspects, namely R / Si (the ratio of the amount of alkyl group to silicon atom) and Ph / R (the ratio of phenyl group to alkyl group). The larger the R / Si, the larger the contact angle, the better the hydrophobicity, the faster the curing speed, and the better the flexibility. The larger the Ph / R, the stronger the impact resistance of the silicone resin, the better the thermal stability, and the better the compatibility with the filler. However, the larger the R / Si, the more side chain organic groups, resulting in low temperature resistance of the silicone resin, and the larger the Ph / R, the greater the brittleness of the silicone resin. Therefore, controlling R / Si and Ph / R is crucial to the performance of the silicone resin, as shown in Table 1 and Table 2.

[0057] Table 1 Effect of R / Si on silicone resin

[0058]

[0059] Table 2 Effect of Ph / R on silicone resin

[0060]

[0061] According to the above analysis, the R / Si of polymethylphenylsiloxane is 1.2, and the Ph / R is 0.4. The calculation formula is as follows:

[0062]

[0063] Where a is methyltrimethoxysilane (C4H 12 O3Si), b is the molar mass of dimethyldimethoxysilane (C4H 12 O2Si), c is the molar mass of phenyltrimethoxysilane (C9H 14 O3Si). Assuming the total amount of monomers is 1 mol, the theoretical molar masses of the three organosilicon monomers can be obtained: C4H 12 O3Si=0.32mol,C4H 12 O2Si=0.2mol,C9H 14 O3Si=0.48 mol.

[0064] Add 300mL of xylene, 100mL of n-butanol and 500mL of deionized water into a three-necked flask, mix 43.5g of methyltrimethoxysilane, 24g of dimethyldimethoxysilane and 95g of phenyltrimethoxysilane, add them into a three-necked beaker, and place it in a water bath and heat it to 80°C. Slowly add 0.5mol / L of hydrochloric acid until the mixture boils, then stop adding. After reflux reaction for 4h, vacuum distillation is performed to evaporate the water and methanol generated by the reaction. The reaction ends when the reactant becomes viscous, cool to room temperature, and filter the reactant to obtain polymethylphenylsiloxane (PMPS).

[0065] 1.1.2 Preparation of KH560-modified POSS

[0066] The nitrogen was continuously circulated in the three-necked flask for 10 minutes, and the air was exhausted; 100 mL of deionized water and 100 mL of ethanol were added, and POSS (polysilsesquioxane) and silane coupling agent KH560 were mixed in a mass ratio of 1:8, and ultrasonic dispersion was performed for 30 minutes. In order to avoid rapid gelation, it was slowly added dropwise to the three-necked flask, and the mixture was stirred at 80°C with the help of a magnetic stirrer, while the system was kept sealed and protected with nitrogen, and the reaction was performed for 1 hour. A colorless transparent liquid was obtained, which was washed and centrifuged several times, dried, ground into powder, and collected for use to obtain KH560-modified POSS.

[0067] 1.2 Study on high temperature superheated water vapor resistant coatings with different POSS addition amounts

[0068] 1.2.1 Preparation of high temperature superheated water vapor resistant coatings with different POSS addition amounts

[0069] This embodiment adopts the method of solution blending to prepare the organosilicon high temperature superheated water vapor composite coating, and the preparation process is as follows: weigh a certain amount of polymethylphenylsiloxane, heat and stir in a water bath at 80°C. Then weigh the modified POSS powder with different addition amounts of 1.0wt%, 1.5wt%, 2.0wt%, 2.5wt% and 3.0wt% of the total mass, dissolve them in the organic solvent ethanol respectively, and ultrasonically disperse them for 30min to obtain the POSS dispersion liquid. The amount of ethanol is based on the mass fraction of the modified polysilsesquioxane in the POSS dispersion liquid being 1-3wt%, and is added to the polymethylphenylsiloxane to make the POSS uniformly dispersed in the polymethylphenylsiloxane. The polymethylphenylsiloxane high temperature superheated water vapor coating without POSS is used as a blank control. The xylene and n-butanol with a mass ratio of 7:3 are mixed and diluted, and the viscosity of the composite coating is adjusted until the viscosity that can be brushed (generally 100KU-120KU) is reached. The coated Q235 steel plate was placed in a vacuum drying oven for 1 hour to remove bubbles generated by ultrasound and stirring. Finally, the Q235 steel plate was placed in a blast drying oven for curing at 60°C for 48 hours to obtain the POSS polymethylphenylsiloxane high temperature superheated water vapor resistant coating. The coating preparation process is as follows: Figure 1 shown.

[0070] 1.2.2 Effect of different POSS addition amounts on the coating's resistance to high temperature superheated water vapor

[0071] (1) Fourier transform infrared spectroscopy (FT-IR)

[0072] Fourier transform infrared spectrometer (FT-IR) was used to analyze the bonding sites and functional group types of polymethylphenylsiloxane and modified POSS polymethylphenylsiloxane composites during the composite process. Figure 2 As shown. 1591cm -1 、1480cm -1 and 1429cm -1 The peak of the skeleton vibration on the C=C benzene ring is 779cm -1 and 740cm -1 It is the CH absorption peak on the benzene ring, 3391cm -1 、3051cm -1 and 3015cm -1 The CH stretching vibration peak on the methyl group is 1129 cm -1 、1066cm -1 is the Si-O absorption peak, 905cm -1 、849cm -1 The absorption peak of epoxy group proves that phenyl group is successfully introduced into polysiloxane and silane coupling agent exists in organosilicon. This result shows that after POSS is modified by KH560, epoxy group is successfully grafted into polymethylphenylsiloxane.

[0073] (2) High temperature resistance test

[0074] The thermal stability of the POSS organosilicon high temperature superheated steam resistant coating sample was analyzed by measuring the change of sample mass with temperature using a differential thermal gravimetric analyzer under program control. Under nitrogen conditions, the coating was heated from 25°C to 800°C at a heating rate of 10°C / min, and the thermogravimetric curve of the content of each component in the coating was measured. When the coating loses 5%, the corresponding temperature is the initial thermal decomposition temperature of the coating, recorded as T5. The temperature corresponding to the maximum weight loss rate of the coating is recorded as T max . Figure 3a and Figure 3b The mass loss and decomposition rate diagrams of the silicone high temperature superheated water vapor resistant coating samples with POSS addition of 0wt%, 1.0wt%, 1.5wt%, 2.0wt%, 2.5wt% and 3.0wt% at 30℃~800℃. Figure 3a and Figure 3bIt can be seen that the coating decomposition has two main stages. The first degradation stage is from 30℃ to 350℃, which is mainly the evaporation of water, such as the elimination of groups such as hydroxyl groups and unreacted low molecular weight substances or oligomers. The second stage is from 400℃ to 600℃, and the weight drops sharply, mainly due to the cleavage of the molecular chain and the collapse of the network during the pyrolysis process, the gradual degradation of the molecules on the main chain of the silicone and the oxidation of the methyl group, resulting in the rearrangement and depolymerization of the Si-O bond. The order of T5 of each coating sample from large to small is: 2.5wt%>3.0wt%>2.0wt%>1.5wt%>1.0wt%>0wt%. The initial thermal decomposition temperature of the silicone coating sample without POSS is T5=413.8℃, and the temperature at the maximum weight loss rate is 431.3℃. As the amount of POSS added increases, the initial thermal decomposition temperature of each coating sample gradually increases, and the temperature at the maximum weight loss rate also increases accordingly. When the addition amount of POSS is 2.5wt%, the initial decomposition temperature of the coating is T5=457.9℃, and the temperature at the maximum thermal weight loss efficiency is 561.9℃. Therefore, the results of the thermal stability test of the coating show that within the scope of this experiment, POSS can effectively improve the high temperature resistance of silicone resin. When the addition amount of POSS is 2.5wt%, the high temperature resistance of the high temperature superheated water vapor resistant coating is the best.

[0075] Table 3 Thermal decomposition parameters of POSS organosilicon high temperature superheated water vapor coating

[0076]

[0077]

[0078] (3) High temperature superheated steam resistance test

[0079] The organic silicon high temperature superheated water vapor resistant coating samples with POSS addition of 0wt%, 1.0wt%, 1.5wt%, 2.0wt%, 2.5wt% and 3.0wt% were tested for high temperature superheated water vapor resistance using a high temperature carbonization activation furnace. According to the initial decomposition temperature of each coating obtained from the TG graph, the temperature of the high temperature carbonization activation furnace was set to 420℃. Figures 4a to 4f The following are the surface macroscopic images of coatings with POSS addition of 0wt%, 1.0wt%, 1.5wt%, 2.0wt%, 2.5wt% and 3.0wt% respectively after being subjected to high temperature superheated steam cycle at 420℃ for 48h. Figure 4a It can be seen that when the amount of POSS added is 0wt%, the silicone coating sample used as the blank control has a large number of cracks and peeling on the surface, the coating begins to fall off, and the metal substrate is also corroded, with the greatest degree of corrosion. Figure 4b to Figure 4fIt can be seen that the surface of each coating sample turns black from the periphery to the middle, but the coating on the surface still exists, and no cracks, peeling or shedding is found, and there is no obvious difference on the surface of the samples.

[0080] SEM tests were performed on each sample, such as Figure 5a to Figure 5f As shown. Figure 5a It can be seen that when the addition amount of POSS is 0wt%, a large number of cracks and wrinkles appear on the surface of the coating. These cracks and wrinkles are mainly due to the thermal expansion of the surface coating after the high-temperature water vapor circulation, which causes the coating to be damaged. In the high-temperature water vapor environment, the corrosive medium can quickly pass through the coating and reach the metal substrate, reducing the adhesion between the coating and the substrate, causing the coating to fall off. Figure 5b and Figure 5c There are tiny cracks that are not visible to the naked eye. This is also due to cracks caused by thermal expansion. Figure 5d to Figure 5f The surface of the coating is still very smooth and flat, and the coating has good integrity. Figure 5a and Figure 5b to Figure 5f It can be found that the silicone coating after adding POSS can greatly improve the coating's resistance to high-temperature water vapor. With the increase in the amount of POSS added, the degree of high-temperature superheated water vapor corrosion of the coating gradually weakens, and the coating surface remains intact.

[0081] In order to further verify the effect of the amount of POSS added on the high temperature superheated water vapor resistance of the coating, the coating was subjected to a 100h high temperature superheated water vapor resistance test. Figures 6a to 6f The following are the surface macroscopic images of coatings with POSS addition of 0wt%, 1.0wt%, 1.5wt%, 2.0wt%, 2.5wt% and 3.0wt% respectively after being circulated at 420℃ for 100h by high temperature superheated steam. Figure 6a It can be seen that when the addition amount of POSS is 0wt%, the silicone coating begins to fall off on a large scale, the coating loses its protective effect and the metal substrate is corroded. Figure 6b to Figure 6c It can be seen that small cracks have begun to appear on the surface of the paint. Figure 6d to Figure 6f It can be seen that compared with the 420℃ cycle for 48h, the coating surface has become darker but has no cracks, peeling or shedding, and there is no obvious difference on the sample surface.

[0082] In order to further observe the coating surface, SEM tests were performed on each coating sample, such as Figures 7a to 7f As shown. From the SEM image, we can see that Figure 7a The paint surface has been completely destroyed and the metal substrate has been completely corroded. Figure 7b , Figure 7c and Figure 7fIt can be seen that the cracks on the coating surface gradually become larger and bubbles begin to appear. Figure 7d and Figure 7e It can be seen that the coating surface is still very smooth and flat. Through the macroscopic and microscopic images of the coating, it can be found that the addition of POSS has greatly improved the high-temperature water vapor resistance of the coating. With the increase of the amount of POSS added, the corrosion of high-temperature superheated water vapor of each coating sample gradually weakened, and the coating surface remained intact. When the amount of POSS added was 3.0wt%, the high-temperature water vapor resistance of the coating began to decline.

[0083] (4) Electrochemical experiments

[0084] The high-temperature carbonization activation furnace was used to test the high-temperature superheated water vapor resistance of each coating sample, and then the electrochemical workstation was used to test the electrochemical properties of each coating after the 420℃ cycle for 48h and 100h high-temperature superheated water vapor resistance test. After the high-temperature superheated water vapor cycle, the coating without POSS silicone fell off and the metal substrate was completely corroded, making it impossible to conduct electrochemical experiments.

[0085] Comparison of the low-frequency impedance modulus graphs (Bode curves) of POSS with addition amounts of 1.0wt%, 1.5wt%, 2.0wt%, 2.5wt% and 3.0wt% after high-temperature superheated steam circulation at 420°C for 48h and 100h, as shown in FIG. Figure 8a and Figure 8b As shown. Usually in the low-frequency impedance modulus curve, the larger the impedance modulus value corresponding to 0.01Hz in the low-frequency region, the better the corrosion resistance of the coating. Figure 8a and Figure 8b As can be seen from Table 4, after the high-temperature superheated water vapor test, the low-frequency impedance modulus values ​​of each POSS silicone coating sample showed a significant downward trend. As the amount of POSS added increased, the low-frequency impedance modulus increased. The order of the low-frequency impedance modulus values ​​of the coating samples from large to small is: 2.5wt%>3.0wt%>2.0wt%>1.5wt%>1.0wt%. Figure 8a After circulating at 420 °C for 48 h under high-temperature superheated steam, when the addition amount of POSS was 2.5 wt%, the impedance modulus value was the maximum |Z| f＝0.01Hz =9.22×10 6 Ωcm 2 .like Figure 8b After circulating at 420 °C for 100 h under high-temperature superheated steam, when the addition amount of POSS was 2.5 wt%, the impedance modulus value was the maximum |Z| f＝0.01Hz =8.05×10 6 Ωcm 2 This indicates that when the addition amount of POSS is 2.5wt%, the corrosion resistance of the silicone coating is the best.

[0086] Table 4 Comparison of low frequency impedance modulus of each coating sample after high temperature superheated steam 420℃ cycle (unit: Ωcm 2 )

[0087]

[0088] Comparison of electrochemical impedance diagrams (Nyquist curves) of POSS with addition amounts of 1.0wt%, 1.5wt%, 2.0wt%, 2.5wt% and 3.0wt% after high-temperature superheated steam circulation at 420℃ for 48h and 100h, as shown in Figure 9a and Figure 9b As shown. Generally, in the electrochemical impedance curve, the larger the radius of the arc, the greater the impedance value, the smaller the corrosion current, and the better the corrosion resistance. Figure 9a and Figure 9b It can be seen that in the electrochemical impedance diagram of the POSS silicone coating after being circulated at 420℃ for 48h and 100h, the order of the radius corresponding to the arc from large to small is: 2.5wt%>3.0wt%>2.0wt%>1.5wt%>1.0wt%. As the amount of POSS added increases, the impedance gradually increases. Among them, when the amount of POSS added is 2.5wt%, the corresponding curve arc radius is the largest, and the silicone coating has the best corrosion resistance.

[0089] Comparison of the polarization curves (Tafel curves) of the coatings with POSS addition amounts of 1.0wt%, 1.5wt%, 2.0wt%, 2.5wt% and 3.0wt% after being circulated at 420℃ for 48h and 100h, as shown in Fig. Fig.10a and Fig.10b As shown in Table 5. When the corrosion current density and corrosion rate are smaller, the polarization resistance is larger, indicating that the corrosion resistance of the coating is better. By fitting and calculating the polarization curves of different coating samples, the corrosion current density and corrosion rate of the coating after being circulated at 420℃ for 48h and 100h are obtained, as shown in Table 5. Fig.10a and Fig.10b As can be seen from Table 5, the order of corrosion current density and corrosion rate from large to small is: 2.5wt%>3.0wt%>2.0wt%>1.5wt%>1.0wt%. After 48h and 100h high-temperature superheated steam 420℃ cycle experiment, the results show that with the increase of POSS dosage, the self-corrosion current density and corrosion rate of all coating samples show a downward trend, and the corrosion resistance of all coating samples is gradually improved. When the POSS addition amount is 2.5wt%, the corrosion current of the cycle 48h and 100h is 2.565nA / cm 2 and 23.145nA / cm 2The corrosion rates are 1.1252×10 -5 mpy and 3.9267×10 -5 mpy, the corrosion current and corrosion rate of the coating sample are the lowest, and the corrosion resistance of the coating is the best. This is completely consistent with the conclusions obtained in the low-frequency impedance modulus value and electrochemical impedance diagram. The experiment shows that when the amount of POSS added is 2.5wt%, the dispersion effect of POSS in the coating is the best, which can effectively improve the corrosion resistance of the coating, better play the shielding effect in the coating, fill some tiny pores and defects in the coating, and prolong the time taken for the corrosive medium to reach the metal substrate through the coating, and the corrosion resistance of the coating is improved, thereby obtaining better corrosion resistance.

[0090] Table 5 Polarization curve fitting parameters of each coating after being circulated at 420℃ for different time periods by high temperature superheated steam

[0091]

[0092] (5) X-ray Photoelectron Spectrometer (XPS)

[0093] X-ray photoelectron spectrometer was used to characterize and analyze the changes in the content of various elements and the changes in chemical bonds of POSS silicone coating before and after high-temperature steam circulation for 100 hours. Figures 11a to 11c This is the XPS graph of POSS silicone coating before and after high-temperature superheated steam circulation for 100 hours. Fig.11a This is a broad peak full spectrum scan of silicone coating. Fig.11b It is the C1s peak of the coating before high-temperature water vapor circulation. Fig.11c It is the C1s peak after the coating is cycled through high-temperature steam. Table 6 shows the content of each element in the full spectrum of POSS silicone coating. It can be seen from the full spectrum that the POSS silicone coating only has O, C and Si elements, and the characteristic peaks appear at 533eV, 285eV and 100eV respectively. The carbon-oxygen content ratio of the POSS silicone coating without high-temperature steam cycle is 1.84. The carbon-oxygen content ratio of the POSS silicone coating after high-temperature steam cycle is 3.63. By comparing the carbon and oxygen content before and after the coating cycle, it can be found that during the high-temperature superheated water steam cycle, the Si content did not fluctuate significantly, the C content increased, and the oxygen content decreased, causing the carbon-oxygen content ratio to increase. This indicates that part of the oxygen element in the coating is consumed during the cycle, and at the same time, the organic groups in the side chains of the coating are broken and decomposed. The characteristic peaks of the carbon element in the silicone coating were separated and compared. Fig.11b and 11c It can be seen that the strength of Si-C bonds is enhanced. This is because the coating has been in a high temperature environment for a long time, and the composite coating has a SiC structure, which is cross-linked with the Si-O bonds, which can improve the stability of the coating in a high temperature environment.

[0094] Table 6 Content of each element in POSS silicone coating before and after high-temperature superheated steam circulation for 100h

[0095]

[0096] (6) Adhesion test

[0097] Paint adhesion refers to the mutual attraction between the paint and the metal substrate. When the corrosive medium passes through the paint, it will destroy the combination of the paint and the metal substrate. Under the influence of external environmental factors, it will accelerate the weakening of the adhesion between the paint and the metal substrate, so that the paint will fall off from the substrate, thereby destroying the integrity of the paint. The corrosion resistance of the paint will be reduced or even fail. Therefore, the adhesion of the paint directly affects the corrosion resistance of the paint and the service life of the paint.

[0098] The adhesion of the POSS silicone coating samples before and after the high-temperature superheated water vapor cycle at 420℃ for 48h and 100h was tested using a KS-V adhesion puller. After the organic silicone coating without POSS was cycled with high-temperature superheated water vapor, the coating fell off and the metal substrate was completely corroded, making it impossible to perform adhesion testing. The adhesion of the samples with POSS addition of 1.0wt%, 1.5wt%, 2.0wt%, 2.5wt% and 3.0wt% after the high-temperature superheated water vapor cycle at 420℃ for 48h and 100h was compared. Fig.12a and Figure 12b As shown. Fig.12a It can be seen that the adhesion of the coating sample that has not been circulated with high-temperature superheated steam is not affected by the increase in the amount of POSS added, and the adhesion of the coating is about 1.91MPa. The adhesion of the coating was tested after the coating was circulated with high-temperature superheated steam at 420℃ for 48h and 100h, and the adhesion of the coating dropped significantly. With the increase in the amount of POSS added, the adhesion and loss rate of the silicone coating gradually decreased. When the amount of POSS added was 2.5wt%, the adhesion of the coating sample was the best and the loss rate was the smallest, which were 1.41MPa and 1.19MPa respectively, and the adhesion loss rate was 23% and 34.9% respectively. When the amount of POSS added was 3.0wt%, the adhesion and loss rate of the coating increased.

[0099] 1.3 Summary of this section

[0100] A polysiloxane with phenyl groups was prepared using three silane monomers. The silane coupling agent KH560 was used as a modifier of POSS and added to polymethylphenylsiloxane to obtain an organic-inorganic high-temperature superheated water vapor resistant coating. The performance of the organic silicon high-temperature superheated water vapor resistant coating was evaluated using a variety of test methods, and the main conclusions are as follows:

[0101] (1) Polymethylphenylsiloxane with high temperature resistance was prepared by three silane monomers. The thermal decomposition temperature can reach up to 413.8℃. POSS was modified by silane coupling agent KH560 and added to polymethylphenylsiloxane to prepare a high temperature superheated water vapor resistant coating.

[0102] (2) The thermogravimetric comparison experiment of modified POSS polymethylphenylsiloxane high temperature superheated water vapor resistant coatings with different proportions showed that the thermal decomposition temperature of the coating could reach up to 457.9℃. After circulating the high temperature superheated water vapor at 420℃ for 48h, the low frequency impedance modulus of the coating could reach up to 9.22×10 6 Ωcm 2 The lowest self-corrosion current density is 2.565nA·cm -2 The minimum corrosion rate is 1.1252×10 -5 After circulating the high-temperature superheated steam at 420℃ for 100h, the low-frequency impedance modulus of the coating can reach up to 8.05×10 6 Ωcm 2 The lowest self-corrosion current density is 23.145nA·cm -2 The lowest corrosion rate is 3.9267×10 -5 mpy. XPS test found that the Si content of the coating remained unchanged and the C / O ratio increased before and after the high-temperature superheated steam cycle. Adhesion test showed that the addition of modified graphite oxide did not affect the adhesion of the coating. After 100 hours of high-temperature superheated steam cycle, the loss rate was 34.9%.

[0103] (3) The results of differential thermal gravimetric analysis, high temperature superheated water vapor experiment, electrochemical workstation and adhesion test show that KH560 modified POSS polymethylphenylsiloxane coating can improve the corrosion resistance of high temperature superheated water vapor resistant coating, and the optimal addition amount of POSS is 2.5wt%. After circulating high temperature superheated water vapor at 420℃ for 100h, the coating still maintains a good anti-corrosion effect on the metal substrate.

[0104] Part II Preparation of PVP-modified graphene oxide coating resistant to high temperature superheated water vapor

[0105] 2.1 Preparation and structural characterization of PVP-modified graphene oxide

[0106] 2.1.1 Preparation of graphene oxide

[0107] Graphene oxide (GO) was prepared using the improved Hummers method. First, 50 mL of concentrated H3PO4 and 150 mL of concentrated H2SO4 were weighed into a mixed solution, and then 1.5 g of graphite was added thereto. Then, 15 g of KMnO4 was slowly added in an ice-water bath and stirred. When the mixed solution was completely mixed, it was placed in a constant temperature water bath and heated to 60 ° C. The stirring reaction was continued for 10 hours to allow H2SO4 and KMnO4 to fully oxidize and intercalate the graphite. After the reaction was complete, H2O2 was slowly added with a rubber-tipped dropper to remove the unreacted KMnO4 until the solution was golden yellow. Subsequently, the solution was washed and centrifuged several times with deionized water and a centrifuge until the aqueous solution was neutral. Finally, the reaction product was placed in a freeze dryer for freeze drying, and then collected and ground to obtain graphene oxide.

[0108] 2.1.2 Preparation of PVP-modified graphene oxide

[0109] First, 0.5g of graphene oxide powder was weighed and dispersed in 200mL of deionized water, and ultrasonically treated at 150W for 1h to obtain a highly stable graphene oxide solution. Then 0.25g of PVP (polypyrrolidone) and 0.25g of L-ascorbic acid were weighed and mixed in a 250mL round-bottom bottle, and then 100mL of graphene oxide solution (2.5mg / mL) was added. The mixture was gradually heated to 80°C and stirred for 4h, and the color of the dispersion solution gradually changed from yellow to black. After that, it was centrifuged at 12000r / min using a centrifuge, washed with deionized water until neutral, poured into an evaporating dish, placed in a constant temperature blast drying oven at 60°C for drying, and dried in a constant temperature blast drying oven for 24h to obtain a modified graphite oxide solid. The dried PVP functionalized graphene oxide was ground into powder using an agate mortar, collected for later use, and the modified product modified graphene oxide was named PGO.

[0110] 2.1.3 Structural characterization of PVP-modified graphite oxide

[0111] (1) X-ray diffraction (XRD) analysis

[0112] The lattice structure and spatial distance of GO and PGO were analyzed by X-ray diffraction (XRD). Si standard samples were added to GO and PGO samples to eliminate the influence of external conditions on the measurement results. Fig.13 It can be seen that GO and PGO have three characteristic peaks at 2θ=28.4°, 2θ=47.3° and 2θ=56.1°. The XRD standard PDF comparison card shows that the characteristic peaks in PGO are the characteristic peaks of silicon, which completely coincide with the positions of the characteristic peaks of the Si standard sample. This shows that the disappearance of the (001) characteristic peak of PGO is caused by the amino-modified internal structure of GO and has nothing to do with other external factors. Fig.13 It can be seen that GO has corresponding lattice (001) and diffraction characteristic peaks at 2θ = 10.1°. According to the Bragg equation λ = 2d sinθ, (λ - incident wave wavelength, d - crystal plane spacing, θ - grazing angle). In this experiment, the X-ray source is Cu target Kα, whose characteristic wavelength λ = 0.1542nm. The GO interlayer spacing is calculated to be 0.866nm. This is related to the intercalation of oxygen-containing functional groups and water absorption, indicating that the interlayer spacing of GO is large, which can provide sufficient spacing and grafting points for the modification of GO. The (001) diffraction characteristic peak of PGO at the original position of GO disappears, and two relatively gentle and broad amorphous characteristic peaks are formed at 2θ = 12.4° and 2θ = 22.1°. The gentle broad peaks represent the decrease in the crystallinity of the two (001) and (002) characteristic peaks of PGO. This is the successful compounding of PVP and GO, which changes the spatial structure. The disappearance of the characteristic diffraction peak of GO also shows that GO has been successfully reduced.

[0113] (2) Fourier transform infrared spectroscopy (FT-IR)

[0114] Fourier transform infrared spectroscopy (FT-IR) was used to analyze the bonding sites and functional group types of graphene oxide (GO) and polyvinyl pyrrolidone (PVP) modified graphene oxide (PGO) composites during the composite process. Fig.14 It shows that GO is at 3475cm -1 、1738cm -1 、1624cm -1 and 1048cm -1 The characteristic peaks at 3467cm correspond to the stretching vibration peak of OH, the stretching vibration peaks of C=O and C=C in the carboxyl group, and the asymmetric bending vibration peak of CO. OH, C=O and CO are all produced by intercalation and oxidation of graphite with potassium permanganate and sulfuric acid, indicating that a large number of oxygen-containing functional groups were introduced in the process of preparing GO, proving that graphene oxide was successfully prepared. PVP at 3467cm -1 、1672cm -1 、1419cm -1 and 1286cm -1 The characteristic peaks at 3410cm correspond to the stretching vibration peak of OH, the stretching vibration peak of C=O in the pyrrolidone group, the absorption peak caused by the bending vibration of CH in the methylene group, and the stretching vibration peak of CN. -1 、1732cm -1 、1415cm -1 and 1291cm -1 The characteristic peaks at correspond to the stretching vibration peak of OH, the stretching vibration peak of C=O, the bending vibration absorption peak of CH, and the stretching vibration peak of C=O.

[0115] By comparing the three infrared spectra in the figure, it can be found that after the modification of graphene oxide, the absorption peaks of C=C and CO functional groups in the GO structure disappear, and the stretching vibration peak of C=O in the pyrrolidone group, the absorption peak of CH in the methylene group, and the stretching vibration peak of CN, three characteristic peaks of PVP, appear in the infrared spectrum of PGO. This is due to the formation of hydrogen bonds between PVP and the oxygen-containing functional groups on the surface of GO. Therefore, it is inferred that PVP molecules are adsorbed on the GO surface through hydrogen bonds and amino group interactions.

[0116] (3) Raman spectroscopy analysis

[0117] The structure of graphene oxide (GO) and polyvinyl pyrrolidone / graphene oxide (PGO) composites was characterized and analyzed by Raman spectroscopy. The Raman spectrum of graphene oxide has two characteristic peaks, D peak and G peak, which represent the disordered vibration peak of graphene oxide due to the defects of C atom lattice and the sp peak of C atom. 2 The hybrid stretching vibration peak expresses the order of the structure and is also the main characteristic peak of graphene oxide. The area ratio of the D peak to the G peak can characterize the degree of disorder and defect of the structure of graphene oxide and modified graphene oxide. Fig.15 This is the Raman spectrum of GO and PGO. From the GO spectrum, we can get the peak at 1345cm -1 D peak appears at 1585cm -1 The G peak appears at D / I G The ratio is an important indicator to measure the disorder and structural defect degree of carbon materials. The Raman spectrum is fitted using the Gauss function to obtain the peak area I D / I G The ratio is 1.26. From the PGO graph, we can see that the D peak is located at 1337cm -1 , the G peak is located at 1593cm -1 , I is obtained by fitting D / I G The ratio is 1.84. D / I G It can explain the reduction degree of graphene oxide to a certain extent. After GO is reduced by L-ascorbic acid, the oxygen-containing functional groups on the GO surface are removed. However, after being modified by PVP, PVP is adsorbed to the GO surface under the action of hydrogen bonds and amino groups, so that I D / I GThe PGO disorder and defect levels increased from 1.26 to 1.84. This is because the -NH2 and hydrogen bonds in the PVP molecules reacted with the oxygen-containing functional groups on the graphene oxide to generate new chemical bonds, which increased the overall disorder and defect levels of the composite material, proving that PVP modification of graphene oxide is successful.

[0118] (4) X-ray Photoelectron Spectroscopy (XPS)

[0119] The changes in the content of various elements and the changes in chemical bonds of graphene oxide (GO) and polyvinyl pyrrolidone-modified graphene oxide (PGO) composites were characterized and analyzed by X-ray photoelectron spectroscopy. Figures 16a to 16c This is the XPS graph of GO and PGO. Fig.16a This is the broad peak full spectrum scan of GO and PGO. Fig.16b is the C1s peak of GO, Fig.16c is the C1s peak of PGO. Table 7 is the content of each element in the XPS full spectrum of GO and PGO. From the full spectrum of GO, it can be found that GO only has C and O elements, and two characteristic peaks of C1s and O1s appear at 285eV and 532eV, and the carbon-oxygen content ratio is 2.4. From the full XPS spectrum of PGO, it can be found that in addition to the appearance of carbon and oxygen elements, there is a N1s characteristic peak at 399eV, and the carbon-oxygen content ratio is 3.5 at this time. By comparing the carbon and oxygen contents before and after graphene oxide modification, it can be found that the carbon content did not fluctuate greatly during the modification process, while the oxygen content decreased, causing the carbon-oxygen content ratio to increase, indicating that part of the oxygen element in the modification process of graphene oxide was consumed in the compound process, and at the same time, a new component, nitrogen, was introduced into graphene oxide. The characteristic peaks of the carbon element of GO were separated. Fig.16b It can be seen that the C1s spectrum of GO is composed of four fitting peaks, with binding energies of 284.8eV, 287eV, 287.5eV and 288.8eV corresponding to CC on the aromatic ring of GO, and CO, C=O and OC=O characteristic peaks on oxygen-containing functional groups. This indicates that a large number of oxygen-containing functional groups are distributed on the surface and edge of GO, providing modifiable grafting points for the modified material. Fig.16c It can be seen that the C1s spectrum of PGO is composed of four fitting peaks, corresponding to the characteristic peaks of CC, CN, CO and OC=O at binding energies of 284.8eV, 285.9eV, 286.9eV and 288.5eV, respectively. Compared with GO, the intensities of CO and OC=O are weakened, and the characteristic peak of CN appears, indicating that part of the oxygen-containing functional groups are consumed during the modification process.

[0120] Table 7 XPS full spectrum element content of graphene oxide and modified graphene oxide

[0121]

[0122] (5) Differential thermal gravimetric analyzer (TG)

[0123] The thermal stability of graphene oxide (GO) and polyvinyl pyrrolidone modified graphene oxide (PGO) materials was analyzed by differential thermal gravimetric analyzer. Under nitrogen protection, the samples were heated from room temperature to 800°C at a heating rate of 10°C / min, and the weight loss curve of the sample components changing with temperature was measured. Fig.17 The mass loss diagram of GO, PVP and PGO after heating from room temperature to 800℃ shows that GO starts to lose weight after 158℃, which can be attributed to the evaporation of residual water in GO and the decomposition of oxygen-containing functional groups. The decomposition temperature of PVP at 406℃ mainly corresponds to the oxidation and cleavage of the carbon chain on the main chain of PVP. Fig.17 It can be seen that PGO has two weight loss stages. The weight loss temperature of the first stage is 260℃, which is mainly due to high temperature dehydration and the decomposition of some oxygen-containing functional groups that have not been reduced. The second stage is at 395℃, where there is obvious thermal decomposition weight loss, which is caused by the breakage and decomposition of molecular bonds such as CH bonds and CN bonds generated during the PGO modification process. By comparing the TG graphs of GO, PVP and PGO, it can be found that GO modified by PVP has a higher pyrolysis temperature, thus showing better thermal stability.

[0124] (6) Atomic force microscopy (AFM)

[0125] Atomic force microscopy was used to observe the thickness of graphene oxide (GO) and polyvinyl pyrrolidone modified graphene oxide (PGO) materials. Figures 18a to 18d As shown. Fig.18a It can be seen that the GO flake diameters are relatively uniform with small differences. Fig.18a Three different positions in the height analysis, such as Fig.18b As shown, the height values ​​at the three positions are 2.26nm, 2.89nm, and 3.15nm, respectively, with an average value of 2.77nm. Fig.18c It can be seen that the PGO sheet diameter is significantly smaller than that of GO, but it still has a lamellar structure. Three different positions were selected for height analysis, such as Fig.18dAs shown, the height values ​​at the three positions are 5.12nm, 4.88nm and 4.91nm, respectively, with an average value of 4.97nm. The average height of PGO is higher than that of GO. This is because after PVP modifies GO, the PVP molecules are grafted to the surface of the GO sheets due to the action of hydrogen bonds and -NH2. When GO is reduced by L-ascorbic acid, the oxygen-containing functional groups on the surface of GO are eliminated, but the PVP adsorbed on the surface of GO can effectively prevent the stacking and agglomeration between GO sheets, thereby increasing the thickness of PGO and forming a stable and uniform PGO dispersion.

[0126] (7) Transmission electron microscopy (TEM)

[0127] The surface morphology of graphene oxide (GO) and polyvinyl pyrrolidone-modified graphene oxide (PGO) materials was observed using transmission electron microscopy. Figures 19a to 19d These are the TEM images of GO and PGO. Fig.19a and Fig.19b This is the TEM image and partial magnification of GO. From the image, we can see that GO has a clear lamellar structure, with a smooth surface in the middle and a few wrinkles around it. After observing the edge of GO with a high-power microscope, the single-layer structure of GO can be clearly seen. Fig.19c and Fig.19d This is the TEM image and local magnified image of PGO. It can be found that the surface of PGO is undulating, the irregular wrinkles become more numerous and rough, and the thickness of the edge increases. From the local magnified image, it can be seen that PGO is still a single-layer lamellar structure, which shows that after modification, the lamellar structure of GO is not destroyed. The increase in the surface roughness and wrinkles of PGO makes it more difficult for PGO to agglomerate, allowing PGO to be evenly dispersed in the silicone coating.

[0128] Fig.20a and Fig.20b It is the electron diffraction pattern of GO and PGO, which can characterize the sheet structure and lattice structure integrity of graphene oxide. Fig.20a This is the electron diffraction pattern of GO. Since the surface of GO contains more oxygen-containing functional groups and is not easily oxidized and graphitized, the diffraction spots in GO are difficult to observe. In addition, the density of oxygen-containing functional groups on the surface of GO is high, so the development of the diffraction spots in GO is also relatively blurred. Fig.20b This is the electron diffraction pattern of PGO. Compared with GO, the diffraction spots are more obvious and show a crystalline structure. This is because the oxygen-containing functional groups on GO react with the amino groups of PVP to increase the degree of graphitization.

[0129] 2.2 Preparation and performance study of composite coatings with different amounts of modified graphene oxide

[0130] 2.2.1 Preparation of composite coatings with different amounts of modified graphene oxide

[0131] This embodiment adopts the solution blending method to prepare the high temperature superheated water vapor resistant composite coating, the preparation process is as follows: weigh a certain amount of POSS-polymethylphenylsiloxane (POSS addition amount is 2.5wt%), heat and stir in a 60℃ water bath for 1h. Then weigh PGO powder with different addition amounts of 0.1wt%, 0.3wt%, 0.5wt% and 1wt.% of the total mass, dissolve them in organic solvent ethanol respectively, and ultrasonically disperse them for 1h to obtain PGO dispersion liquid, the mass fraction of modified graphene oxide is 3-5wt%, and then add it to the POSS-polymethylphenylsiloxane composite coating to make the modified graphene oxide uniformly dispersed in the high temperature superheated water vapor resistant composite coating. Prepare a mixture of xylene and n-butanol with a mass ratio of 7:3 to dilute, and adjust the viscosity of the composite coating until it reaches a brushable viscosity (100KU-120KU). Put the brushed Q235 steel plate in a vacuum drying oven for 1h to remove the bubbles generated by the ultrasonic stirring process. Finally, the Q235 steel plate was placed in a blast drying oven and cured at 60°C for 48h to obtain a PVP-modified graphene oxide high temperature superheated water vapor resistant coating. The preparation process is as follows: Fig.21 shown.

[0132] 2.2.2 Study on the performance of composite coatings with different amounts of modified graphene oxide

[0133] (1) High temperature resistance test

[0134] The thermal stability of the high temperature superheated water vapor resistant coating sample prepared by polyvinyl pyrrolidone modified graphene oxide (PGO) was analyzed by measuring the change of sample mass with temperature using a differential thermal gravimetric analyzer under program control. Under nitrogen conditions, the coating was heated from 25°C to 800°C at a heating rate of 10°C / min, and the thermogravimetric curves of the contents of each component in the coating were measured. Fig.22a and Figure 22b The mass loss and decomposition rate diagrams of high temperature superheated steam resistant coating samples with PGO addition of 0.1wt%, 0.3wt%, 0.5wt% and 1.0wt% at 30℃~800℃. It can be seen from the figure that with the increase of PGO content, the initial decomposition temperature of the coating continues to increase. The order of T5 of each coating sample from large to small is: 0.5wt%>1.0wt%>0.3wt%>0.1wt%. When the addition amount of PGO is 0.5wt%, the coating has the best high temperature resistance, T5=469.5℃, T max =571.9°C. Therefore, PGO can be used to improve the thermal stability of high temperature superheated water vapor resistant coatings.

[0135] Table 8 Thermal decomposition parameters of modified graphene oxide high temperature superheated water vapor resistant coating

[0136]

[0137] (2) High temperature superheated steam test

[0138] A high-temperature carbonization activation furnace was used to carry out a high-temperature superheated water vapor resistance test on four types of high-temperature superheated water vapor resistance coating samples prepared with 0.1wt%, 0.3wt%, 0.5wt% and 1wt% PVP-modified graphene oxide. Figures 23a to 23d The surface macroscopic morphology of the coatings with PVP modified graphene oxide addition of 0.1wt%, 0.3wt%, 0.5wt% and 1.0wt% after 48h of 420℃ cycle of high temperature superheated water vapor. It can be seen from the figure that after 48h of 420℃ cycle of high temperature superheated water vapor, the surface of the coating only turns black in the cured film, and the surface coating is still smooth and flat, and no cracks, peeling and shedding are found. It can be seen that there is no obvious difference in the surface of all samples.

[0139] SEM tests were performed on each coating sample, such as Figures 24a to 24d As shown. From the SEM image, we can see that Fig.24a The surface of the coating has slight undulations and wrinkles, which are mainly caused by the thermal expansion of the surface coating after the high-temperature water vapor circulation. Fig.24a compared to, Figures 24b to 24d As the amount of PVP-modified graphene oxide added increases, the surface of the coating remains very smooth, flat, and has good integrity.

[0140] In order to further verify the effect of PGO addition on the coating's resistance to high-temperature superheated water vapor, the coating was subjected to a high-temperature superheated water vapor resistance test. Figures 25a to 25d The surface macrographs of coatings with 0.1wt%, 0.3wt%, 0.5wt% and 1.0wt% PVP modified graphene oxide added after 100h of 420℃ superheated steam cycle. It can be seen from the figure that after 100h of 420℃ cycle, compared with 48h of 420℃ cycle, the coating surface becomes darker, but there are no cracks, peeling and shedding, and there is no obvious difference on the sample surface.

[0141] SEM test was performed on the coating samples after high temperature steam cycle for 100h. Figures 26a to 26d shown. Fig.26a It can be seen that there are obvious blistering and cracking on the coating surface. Figure 26b and 26d It can be seen that there are small cracks and bubbles on the surface of the coating, which are caused by the thermal expansion of the coating in the high-temperature water vapor environment. Fig.26c The coating surface is still smooth and flat, with good integrity, and has a protective effect on the metal substrate. Therefore, the results of the high-temperature superheated water vapor resistance test show that within the scope of this experiment, with the increase of the amount of PGO added, the corrosion of each coating sample by high-temperature superheated water vapor gradually weakens. When the amount of PGO added is 0.5wt%, the coating is least corroded and has the best corrosion resistance. The high-temperature superheated water vapor resistance coating has the best corrosion resistance and is still protective of the metal substrate after being circulated at 420℃ for 100h.

[0142] In order to test the limit temperature of the modified graphene oxide high temperature superheated water vapor resistant coating, the temperature and cycle time were increased and tested. Figure 27a1 to Figure 27d2 As shown, the surface macroscopic and microscopic morphology of the coatings with PVP-modified graphene oxide addition amounts of 0.1wt%, 0.3wt%, 0.5wt% and 1.0wt% after being circulated at 430°C for 100h with high-temperature superheated steam. Fig.27a1 It can be seen that a large area of ​​peeling occurs on the surface of the paint. Figure 27b1 to Figure 27d1 It can be seen that although the coating surface has not fallen off, it has begun to show cracks of varying degrees, but it still maintains a good state. Through the SEM image, it can be seen that each coating sample has obvious damage. Although the coating still exists on the metal substrate, it no longer has integrity.

[0143] Fig.28a and Fig.28b This is the surface macroscopic picture of PVP modified graphene oxide with addition of 0.1wt%, 0.3wt%, 0.5wt% and 1.0wt% after 150h of 430℃ high temperature superheated steam cycle. As can be seen from the figure, large areas of cracks and peeling appeared on the surface of the coating. In the environment of high temperature superheated steam, the coating began to decompose and the coating lost its protective effect on the substrate, indicating that the modified graphene oxide high temperature superheated steam coating briefly protected the metal substrate for 100h in the 430℃ high temperature steam environment. After 150h, the coating lost its effect and the substrate was damaged.

[0144] (3) Electrochemical experiments

[0145] The electrochemical performance of each coating after the 420℃ cycle for 48h and 100h high temperature superheated water vapor test was tested using an electrochemical workstation. The low frequency impedance modulus graph (Bode curve) of the coatings with PGO addition of 0.1wt%, 0.3wt%, 0.5wt% and 1.0wt% after the high temperature superheated water vapor cycle at 420℃ for 48h and 100h was compared. Fig.29a and Fig.29b As shown. Usually in the low-frequency impedance modulus curve, the larger the impedance modulus value corresponding to 0.01Hz in the low-frequency region, the better the corrosion resistance of the coating. Fig.29a and Fig.29b As can be seen from Table 9, after the high-temperature superheated water vapor test, the low-frequency impedance modulus values ​​of each PGO coating sample showed an obvious downward trend. Fig.29a As shown, after circulating at 420℃ for 48h under high-temperature superheated steam, the low-frequency impedance modulus values ​​of the coating samples are in the following order: 0.5wt%>1.0wt%>0.3wt%>0.1wt%. When the addition amount of PGO is 0.5wt%, the impedance modulus value is the largest, |Z| f＝0.01Hz =9.32×10 6 Ωcm 2 .like Fig.29b As shown, after circulating high-temperature superheated steam at 420 °C for 100 h, the low-frequency impedance modulus values ​​of the coating samples are in the following order: 0.5wt%>1.0wt%>0.3wt%>0.1wt%. When the addition amount of PGO is 0.5wt%, the impedance modulus value is the largest, |Z| f＝0.01Hz =8.13×10 6 Ωcm 2 This indicates that the corrosion resistance of the composite coating is the best when the addition amount of PGO composite material is 0.5wt%.

[0146] Table 9 Low frequency impedance modulus parameters of each coating sample after high temperature superheated steam 420℃ cycle (unit: Ωcm 2 )

[0147]

[0148] Comparison of the electrochemical impedance diagrams (Nyquist curves) of the coatings with PGO addition amounts of 0.1wt%, 0.3wt%, 0.5wt% and 1.0wt% after being cycled at 420℃ for 48h and 100h, as shown in Fig.30a and Fig.30b As shown. Generally, in the electrochemical impedance curve, the larger the radius of the arc, the greater the impedance value, the smaller the corrosion current, and the better the corrosion resistance. Fig.30a and Fig.30b It can be seen that in the electrochemical impedance diagrams of the four composite coatings after being cycled at 420℃ for 48h and 100h, the radius corresponding to the arc is in the following order from large to small: 0.5wt%>1.0wt%>0.3wt%>0.1wt%. When the addition amount of PGO is 0.5wt%, the corresponding arc radius of the curve is the largest, indicating that when the addition amount of PGO is 0.5wt%, the corrosion resistance of the coating is the best.

[0149] Comparison of the polarization curves (Tafel curves) of the coatings with PGO addition amounts of 0.1wt%, 0.3wt%, 0.5wt% and 1.0wt% after being circulated at 420℃ for 48h and 100h, as shown in Fig.31a and Fig.31b As shown in Table 10. When the corrosion current density and corrosion rate are smaller, the polarization resistance is larger, indicating that the corrosion resistance of the coating is better. By fitting and calculating the polarization curves of different coating samples, the corrosion current density and corrosion rate of the coating after being circulated at 420℃ for 48h and 100h are obtained, as shown in Table 10. Fig.31a and Fig.31b As can be seen from Table 10, the order of corrosion current density and corrosion rate from large to small is: 0.1wt%>0.3wt%>1.0wt%>0.5wt%. After 48h and 100h high-temperature superheated steam 420℃ cycle test, the results show that with the increase of POSS dosage, the self-corrosion current density and corrosion rate of each coating sample are on a downward trend, and the corrosion resistance of all coating samples is gradually improved. When the PGO addition is 0.5wt%, the corrosion current is 1.811nA / cm 2 and 13.607nA / cm 2 The corrosion rates are 8.315×10 -4 mpy and 1.5422×10 -5 mpy. The corrosion current and corrosion rate of the coating sample are both the lowest, and the corrosion resistance is the best. This is completely consistent with the conclusions obtained previously in the low-frequency impedance modulus value and the electrochemical impedance diagram. Experiments have shown that adding too much or too little PGO cannot make the high-temperature superheated water vapor resistant coating achieve the best performance. When the PGO addition amount is 0.5wt%, the dispersion effect of PGO in the coating is the best, which can effectively improve the corrosion resistance of the coating, better play the shielding effect in the coating, fill some tiny pores and defects in the coating, so that the time taken for the corrosive medium to reach the metal substrate through the coating is extended, and the corrosion resistance of the coating is improved, thereby obtaining better corrosion resistance.

[0150] Table 10 Polarization curve fitting parameters of coating samples after being circulated at 420℃ for different time periods by high temperature superheated steam

[0151]

[0152] (4) X-ray Photoelectron Spectroscopy (XPS)

[0153] X-ray photoelectron spectrometer was used to characterize and analyze the changes in the content of various elements and the changes in chemical bonds of PGO silicone coating before and after high-temperature steam circulation for 100 hours. Figures 32a to 32eThis is the XPS graph of PGO silicone coating after being circulated with high-temperature superheated steam for 100 hours. Fig.32a This is a broad peak full spectrum scan of the composite coating. Figure 32b and Fig.32c It is the C1s peak of the coating before and after high-temperature water vapor circulation. Fig.32d and Fig.32e It is the Si2p peak after the coating is circulated with high-temperature water vapor. Table 11 shows the content of each element in the full spectrum of PGO silicone coating. It can be seen from the full spectrum that PGO silicone coating only has O, N, C and Si elements, and the characteristic peaks appear at 533eV, 400eV, 288eV and 100eV respectively. It can be seen from Table 11 that the Si content did not fluctuate greatly during the high-temperature superheated water vapor cycle, the carbon content increased, and the oxygen content decreased. This indicates that part of the oxygen element in the coating is consumed during the cycle, and at the same time, the organic groups in the side chains of the coating are broken and decomposed. The characteristic peaks of the carbon and silicon elements in the silicone coating are separated and compared. Figure 32b and Fig.32e It can be seen that after 100 hours of high temperature cycling, the strength of the Si-C bond is enhanced. This is because the Si-O bond of the composite coating and the carbon-based structure of the modified graphene oxide are degraded to form Si x O y C z Ceramic-like carbon network structure, which acts as a special framework and enhances the degradation resistance of the nanocomposite.

[0154] Table 11 Content of each element in PGO silicone coating before and after high-temperature superheated steam circulation for 100h

[0155]

[0156] (5) Adhesion test

[0157] The adhesion of the coating samples was tested using a KS-V adhesion puller before and after the high-temperature superheated steam at 420℃ was circulated for 48h and 100h. Fig.33a It can be seen that the adhesion of the coating sample that has not been circulated with high-temperature superheated steam is not affected by the increase in the amount of PGO added, and the adhesion of the coating is about 1.79MPa. The results show that with the increase in the amount of PGO added, the adhesion and loss rate of each coating sample show a downward trend. When the PGO addition amount is 0.5wt%, the coating sample has the best adhesion and the smallest loss rate, which are 1.25MPa and

[0158] 1.05MPa, the loss rates are 29.8% and 41.2% respectively. When the amount of POSS added is 1.0wt%, the coating adhesion loss rate increases.

[0159] 2.3 Study on anti-corrosion mechanism

[0160] Single organic silicon material as high temperature superheated water vapor anticorrosion coating has the problem of poor high temperature resistance. During the curing process of organic silicon resin, the evaporation of solvent leads to the formation of micropores. These micropores are the way for the corrosive medium to penetrate into the coating and the substrate, which in turn leads to poor corrosion resistance of the coating. In the high temperature superheated water vapor environment, this process is accelerated. Doping nanoparticles in organic silicon coatings can improve the barrier properties and corrosion resistance of the coating. Nanofillers with different properties can give organic silicon coatings different properties and can effectively fill defects such as pores and cracks in the coating. The path of the corrosive medium through the coating is increased, reducing the diffusion of the corrosive medium to the coating / metal interface.

[0161] By introducing phenyl groups, polysiloxane containing phenyl groups was prepared, which improved its high temperature resistance. Then, POSS and polymethylphenylsiloxane were cross-linked with KH560 to further improve the high temperature resistance of silicone. Since POSS has good high temperature resistance and the uniformly dispersed POSS has good cross-linking properties, the thermal stability and heat shielding properties of the composite material are improved.

[0162] Due to the van der Waals forces between GO sheet structures, the sheets aggregate and accumulate, making them difficult to peel off, and they cannot be evenly dispersed in the silicone anti-corrosion coating, causing some corrosive media to quickly pass through the coating to reach the metal substrate, resulting in electrochemical reactions, which limits the application of GO. GO is modified and reduced with PVP and L-ascorbic acid, so that GO is evenly dispersed in the silicone coating and the hydrophilic oxygen-containing functional groups are removed. When applied to high-temperature superheated water vapor anti-corrosion coatings, a randomly distributed dense physical barrier layer can be constructed in the coating, which greatly increases the longitudinal thickness of the coating, inhibits the penetration of electrolyte ions into the interior of the coating, and plays a good "sealing" role for the electrolyte ions, thereby delaying the diffusion of corrosive media to the coating surface or the interior of the coating and the time for them to invade the substrate, so that they only stay on the coating surface. Schematic diagram of the anti-corrosion mechanism of single silicone coating, POSS silicone coating and PGO / POSS silicone coating, as shown in Fig.34 shown.

[0163] Due to the long-term exposure of the coating to high-temperature superheated water vapor, the Si-O bonds and organic groups in the coating sample degrade and oxidize, resulting in the rearrangement of the Si-O bonds in the composite coating. The modified graphene oxide is a two-dimensional material with a carbon-based structure. It can inhibit the rearrangement of the Si-O bonds in the silicone at high temperatures and block the formation of cyclic oligomers. In addition, the silicone degrades with the carbon-based structure of the modified graphene oxide at high temperatures to form Si x O y C zCeramic carbon network structure, as a special framework, enhances the degradation resistance of nanocomposites and further alleviates the degradation process of coatings. The structure is shown in the figure Figures 35a to 35c As shown. There are Si-O bonds in silicone coatings such as Fig.35a During the degradation process, a silicon and oxygen network can be formed to achieve a stable bond between the carbon layer and the matrix, thereby enhancing the integrity of the coating structure. Fig.35b and Fig.35c .

[0164] 2.4 Conclusion of this section

[0165] In this part, GO was prepared by the improved Hummers method, and PVP-modified graphene oxide was used for modification and grafting of amino groups and hydrogen bonds. PVP-modified graphene oxide organosilicon high temperature superheated water vapor resistant coating was prepared. The performance of PVP-modified graphene oxide high temperature superheated water vapor resistant coating was evaluated by various test methods. The main conclusions are as follows:

[0166] (1) The structures of GO and PGO were characterized by XRD, FT-IR, Raman and XPS, proving that the modified graphene oxide was successfully prepared. The surface morphology and sheet thickness of GO and PGO were observed by TEM and AFM, proving that GO still retained a complete sheet structure after being modified by PVP.

[0167] (2) The thermogravimetric comparison experiment of modified graphene oxide high temperature superheated water vapor resistant coatings with different proportions showed that the thermal decomposition temperature of the coating could reach up to 469.5℃. After circulating the high temperature superheated water vapor at 420℃ for 48h, the low frequency impedance modulus of the coating could reach up to 9.32×10 6 Ωcm 2 The lowest self-corrosion current density is 1.811nA·cm -2 The lowest corrosion rate is 8.315×10 -4 After circulating the high-temperature superheated steam at 420℃ for 100h, the low-frequency impedance modulus of the coating can reach up to 8.13×10 6 Ωcm 2 The lowest self-corrosion current density is 13.607nA·cm -2 The minimum corrosion rate is 1.5422×10 - 5 Adhesion test shows that the addition of modified graphite oxide does not affect the adhesion of the coating, and the loss rate is 41.2% after high-temperature superheated steam circulation.

[0168] (3) The test results of differential thermal gravimetric analyzer, high temperature superheated water vapor experiment, electrochemical workstation and adhesion puller show that PVP modified graphene oxide can improve the high temperature resistance and corrosion resistance of silicone high temperature superheated water vapor coating, and the optimal addition amount of PGO is 0.5wt%. After the high temperature superheated water vapor is circulated at 420℃ for 100h, the coating still maintains a good anti-corrosion effect on the metal substrate. In addition, in the high temperature superheated water vapor environment of 430℃, the coating can protect the metal substrate for 100h.

Claims

1. A method for preparing a high temperature superheated water vapor resistant coating, characterized in that: The steps include: Step A, heating and stirring polymethylphenylsiloxane in a water bath to obtain polymethylphenylsiloxane fluid; The preparation method of polymethylphenylsiloxane is: Step A-1, methyltrimethoxysilane, dimethyldimethoxysilane and phenyltrimethoxysilane are mixed uniformly to obtain a mixed raw material liquid A; Step A-2, adding the mixed raw material solution A to the mixed solvent and mixing evenly, transferring to a water bath and adding a hydrochloric acid solution dropwise while heating, and stopping the addition of the hydrochloric acid solution when the mixture boils, to obtain a mixed reaction system A; Step A-3, continuing the mixed reaction system A to reflux in a water bath, and after the reaction is completed, performing reduced pressure distillation and filtering in sequence to obtain polymethylphenylsiloxane after filtration; Step B, adding modified polysilsesquioxane to anhydrous ethanol for ultrasonic dispersion to obtain a POSS dispersion; the mass fraction of the modified polysilsesquioxane in the POSS dispersion is 1 to 3 wt %; The preparation method of modified polysilsesquioxane is: Step B-1, mixing polysilsesquioxane and silane coupling agent KH560 and dispersing them by ultrasonication to obtain a mixed raw material solution B; Step B-2, adding the mixed raw material liquid B dropwise to the ethanol solution, heating and stirring during the dropping process, and continuing to heat and react under a nitrogen atmosphere after the dropping is completed. After the reaction is completed, a mixed reaction system B is obtained; Step B-3, washing, centrifuging, drying and grinding the mixed reaction system B in sequence, and obtaining modified polysilsesquioxane after grinding; Step C, adding the POSS dispersion into the polymethylphenylsiloxane fluid and continuing to stir in a water bath until the mixture is uniformly mixed to obtain a mixed dispersion A; the mass fraction of the modified polysilsesquioxane in the mixed dispersion A is 1 to 3 wt %; Step C also includes the following steps: Step C-1, adding modified graphene oxide to anhydrous ethanol and ultrasonically dispersing to obtain a PGO dispersion; the mass fraction of the modified graphene oxide in the PGO dispersion is 3 to 5 wt%; Step C-2, after adding the POSS dispersion to the polymethylphenylsiloxane fluid and stirring and mixing evenly under water bath conditions, adding the PGO dispersion and continuing to stir and mix evenly to obtain a mixed dispersion A; the mass fraction of the modified graphene oxide in the mixed dispersion A is 0.1-1wt%; The preparation method of modified graphene oxide in step C-1 is: Step (1), ultrasonically dispersing graphene oxide in deionized water to obtain a graphene oxide dispersion; the mass fraction of the graphene oxide dispersion is 0.2 to 0.5 wt %; Step (2), mixing polyvinyl pyrrolidone and L-ascorbic acid in a mass ratio of 1:1, adding the mixture to the graphene oxide dispersion and mixing evenly to obtain a mixed dispersion C; the mass concentration of polyvinyl pyrrolidone in the mixed dispersion C is 2.5 to 5 mg / mL; Step (3), heating and stirring the mixed dispersion C to 70-80° C., reacting at 70-80° C. for 3-5 hours, and centrifuging at 12000 rpm to discard the supernatant after the reaction is completed; Step (4), repeatedly washing the lower layer of liquid with deionized water and centrifuging until it is neutral, transferring it to an evaporating dish and evaporating the solvent at a temperature of 50 to 60° C. for 20 to 24 hours. After the solvent is evaporated, the obtained solid is ground into powder to obtain the modified graphene oxide; Step D, adding an organic solvent to the mixed dispersion A for dilution to obtain a mixed dispersion B; Step E: Brush the mixed dispersion B onto the substrate, then place it in a vacuum drying oven to evacuate the substrate, and finally transfer it to a blast drying oven for curing to obtain a high-temperature superheated water vapor resistant coating.

2. The method for preparing the high temperature superheated water vapor resistant coating according to claim 1, characterized in that: In step A-1, the molar ratio of methyltrimethoxysilane, dimethyldimethoxysilane and phenyltrimethoxysilane is (1.5-2):1:(2-4); In step A-2, the mixed solvent is prepared by mixing xylene, n-butanol and deionized water in a volume ratio of 3:1:5; the mass volume ratio of the mixed raw material liquid A to the mixed solvent is 150-170 g / 900 mL; the water bath condition is 75-85° C., and the concentration of the hydrochloric acid solution is 0.5 mol / L; In step A-3, the reflux reaction temperature is 75 to 85° C., and the reflux reaction time is 3 to 5 h.

3. The method for preparing the high temperature superheated water vapor resistant coating according to claim 1, characterized in that: In step B-1, the mass ratio of polysilsesquioxane to silane coupling agent KH560 is 1:8; the ultrasonic dispersion time is 20 to 30 minutes; In step B-2, the volume fraction of the ethanol solution is 50%, the temperature of heating and stirring is 60 to 80° C., the temperature of heating reaction under nitrogen atmosphere is 70 to 80° C., and the reaction time is 1 to 1.5 h.

4. The method for preparing the high temperature superheated water vapor resistant coating according to any one of claims 1 to 3, characterized in that: In step A, the water bath heating temperature is 60-80° C., and the heating stirring time is 30-60 min; In step B, the ultrasonic dispersion time is 20 to 40 minutes; In step C, the water bath condition is 60-80° C., and the heating and stirring time is 30-60 min; In step D, the organic solvent is a mixture of xylene and n-butanol in a mass ratio of 7:3; the amount of the organic solvent added is such that the viscosity of the mixed dispersion B reaches 100KU to 120KU; In step E, the vacuuming time is 1 hour, the curing temperature is 60° C., and the curing time is 48 hours.

5. The method for preparing the high temperature superheated water vapor resistant coating according to claim 1, characterized in that: In step (1), the preparation method of graphene oxide is: Step (1-1), adding graphite to a mixed concentrated acid, mixing and dispersing the graphite uniformly, and obtaining a mixed dispersion D; the mixed concentrated acid is obtained by mixing concentrated phosphoric acid having a concentration of 83 to 90 wt % and concentrated sulfuric acid having a concentration of 90 to 98 wt % in a volume ratio of 1:3; the initial mass concentration of graphite in the mixed dispersion D is 5 to 8 g / L; Step (1-2), adding potassium permanganate to the mixed dispersion D in 2-5 portions under ice water bath conditions, stirring until completely mixed, to obtain a mixed dispersion E; the amount of potassium permanganate added is 8 to 12 times the mass of graphite in the mixed dispersion D; Step (1-3), transferring the mixed dispersion E to a water bath, heating it to 60-65°C and stirring it for 10-12 hours, and obtaining a mixed reaction system C after the reaction is complete; Step (1-4), adding a hydrogen peroxide solution with a mass fraction of 10 to 30 wt % to the mixed reaction system C until the reaction system turns golden yellow, to obtain a mixed reaction system D; Step (1-5), using deionized water and a centrifuge to repeatedly wash and centrifuge the mixed reaction system D until the aqueous solution is neutral; then transferring the reaction product to a freeze dryer for freeze drying, and then collecting and grinding to obtain graphene oxide.

6. The method for preparing a high temperature superheated water vapor resistant coating according to claim 1, characterized in that: In step C-1, the conditions for ultrasonic dispersion are: ultrasonication at 150 W for 1 h.

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