Methanol mediated ammonium fluoride assisted acetic acid etched zeolite adsorption thermal control coating and controllable preparation method thereof

Abstract

The invention discloses a controllable preparation method of a methanol-mediated ammonium fluoride-assisted acetic acid etching zeolite adsorption thermal control coating, and belongs to the field of special functional coatings. The invention aims to solve the problems that a zeolite adsorption coating is low in adsorption capacity in an extreme environment and a microporous structure limits diffusion. Zeolite defects are introduced through ammonium fluoride / methanol etching, and then the hierarchical pore zeolite attached thermal control coating is prepared through acetic acid etching. Methanol is adopted as an etching medium, so that ammonium fluoride can be freely transported in a zeolite channel, in-situ hydrolysis and etching of zeolite are carried out until the ammonium fluoride is in contact with water molecules adsorbed in the zeolite channel, and uniform and controllable etching of the outer surface and the interiors of pores of the zeolite is achieved; and meanwhile, the graded zeolite molecular adsorption coating can realize self-balance of body temperature thermal control by virtue of the strong control capability of the layered and three-dimensional space graded pore channel structure on spectral absorption or emission, so that the heat dissipation capability is greatly enhanced, and the thermal control application of the graded zeolite molecular adsorption coating in spacecrafts is facilitated by virtue of the low-absorption-high-emission performance of the graded zeolite molecular adsorption coating.

Description

Technical Field

[0001] The present invention belongs to the field of special functional coatings, and specifically relates to a methanol-mediated ammonium fluoride-assisted acetic acid-etched zeolite adsorption thermal control coating and a controllable preparation method thereof. The present invention plays an important role in aerospace, construction, electronics, automobiles, energy, industry, medical treatment and other fields, and has a very broad application prospect. Background Art

[0002] After the spacecraft is in orbit, it is in a high vacuum environment. The materials used will release volatile organic gas molecules, which will cause serious contamination to sensitive surfaces such as optics, electronics, detectors, and thermal control. With the increasingly stringent requirements for the quality and reliability of spacecraft, contamination control has gradually become one of the key factors for the success of most space missions. At present, the effective solution for contamination control is adsorption. Molecular adsorption coating (MAC) as an emerging sprayable coating can replace the use of molecular adsorbers and can be directly sprayed onto the surface of internal instruments. It has the advantages of easy implementation, customizability, wide range, light weight, and low cost. However, the single micropore structure (<2nm) of the narrow micropores of the key adsorption material zeolite in the coating limits the mass transfer process of molecular pollutants with larger diameters, which will result in low adsorption of large molecular pollutants and easy desorption, which seriously affects the actual use of the adsorption coating. Therefore, it is of great significance to develop a preparation method for a graded pore zeolite molecular adsorption coating.

[0003] The construction methods of hierarchical pores of zeolites mainly include in-situ synthesis and post-treatment synthesis. The post-treatment synthesis method including acid etching and ammonium fluoride etching has the advantages of simple operation and low cost, and has become a feasible method for preparing hierarchical pores of zeolites. Small-pore low-silicon zeolites have small pore sizes, and it is difficult for the etchant to effectively diffuse into the interior; and the skeleton has poor stability and is prone to collapse during the preparation of hierarchical pores. It is difficult to effectively obtain hierarchical pore 5A zeolites using traditional single etching methods. The use of acid etchants alone can help zeolites to dealumen and form mesopores, but it is very easy to over-etch and cause the collapse of the zeolite skeleton. Ammonium fluoride etching can remove silicon atoms and aluminum atoms in the zeolite skeleton to introduce defects, help acid etchants to etch at low concentrations to produce mesopores, and avoid the problem of easy collapse of the zeolite skeleton. However, ammonium fluoride etching often uses water as the etching medium. Using water as the medium is prone to the phenomenon that zeolite etching only occurs on the outer surface and cannot penetrate into the interior of the zeolite.

[0004] The microporous structure of zeolite in existing molecular adsorption coatings is limited by diffusion, and the adsorption capacity needs to be further improved. The adsorption performance of the coating can be improved by preparing a hierarchical pore zeolite coating. For small-pore low-silicon zeolite, it is difficult for the etchant to effectively diffuse into the interior and the zeolite is prone to collapse during the etching process to prepare hierarchical pores. It is difficult to effectively obtain hierarchical pore zeolite by traditional single etching methods. Summary of the invention

[0005] The present invention obtains hierarchical pore 5A zeolite with a complete microporous structure through a two-step etching method of ammonium fluoride / methanol-acetic acid, solves the problem of restricted diffusion by the micropores of zeolite, and at the same time breaks through the limitation of the conventional etching method on the destruction of the zeolite framework structure. The present invention aims to solve the problems of low adsorption capacity of the zeolite adsorption coating in extreme environments and restricted diffusion by the microporous structure, and provides a preparation method for a two-step etched hierarchical pore zeolite coating of ammonium fluoride / methanol-acetic acid. The present invention uses methanol as an etching medium, which allows ammonium fluoride to freely transport within the zeolite channels and only undergoes in-situ hydrolysis etching of the zeolite when it comes into contact with the water molecules adsorbed within the zeolite channels, achieving uniform and controllable etching on the outer surface and the interior pores of the zeolite.

[0006] In order to achieve the above technical problems, the present invention adopts the following technical solutions:

[0007] The object of the present invention is to provide a controllable preparation method for an adsorption thermal control coating of zeolite etched by acetic acid assisted by ammonium fluoride mediated by methanol, which is carried out according to the following steps:

[0008] Step 1: Etch the zeolite molecular sieve with an ammonium fluoride methanol solution, filter, and wash to remove fluoride ions;

[0009] Step 2: Then etch with an acetic acid aqueous solution, wash, dry and grind, pre-treat, and add a binder in batches to obtain a slurry;

[0010] Step 3: After roughening the surface of the substrate, ultrasonically clean it with anhydrous ethanol, wipe it clean, coat the slurry, and cure it in segments after natural drying to obtain the adsorption coating.

[0011] Further defined, the types of zeolites used in the present invention include but are not limited to 5A, 13X, USY, and ZSM-5.

[0012] Further defined, in Step 1, the mass ratio of the zeolite to the ammonium chloride methanol solution is 1:(5 - 20).

[0013] Further defined, in Step 1, the concentration of the ammonium fluoride methanol solution is 0.1 wt% - 5 wt%; the preparation method of the ammonium fluoride methanol solution is to add ammonium fluoride solid to methanol and stir well to dissolve it under the condition of 50°C.

[0014] Further defined, in Step 1, the etching temperature is 50°C - 80°C.

[0015] Further defined, in Step 1, the etching time of ammonium fluoride is controlled within 1 minute - 10 minutes.

[0016] Further defined, in Step 2, the mass ratio of the zeolite to the acetic acid aqueous solution is 1:(5 - 10).

[0017] Further defined, in Step 2, the concentration of the acetic acid aqueous solution is 0.5 wt% - 3 wt%.

[0018] Further limitation: in step 2, the acetic acid etching temperature is 50°C to 80°C.

[0019] Further limitation: in step 2, the acetic acid etching time is controlled within 20 - 40 minutes.

[0020] Further limitation: in step 2, the specific operation process of the pretreatment is as follows: Place the zeolite molecular sieve powder in a tube furnace for heating, and set the heating rate to: heat to 100°C - 200°C within 1 h, evacuate to -0.1 MPa, keep warm for 2 h - 4 h, and then naturally cool to room temperature.

[0021] Further limitation: in step 2, the binder is silica sol.

[0022] Even further limitation: the mass fraction of the silica sol is 30 wt%.

[0023] Further limitation: in step 2, the mass ratio of the pretreated zeolite to the silica sol is 1∶(1 - 3), and the stirring and mixing time is 2 h - 5 h;

[0024] Further limitation: the coating substrate used in step 3 can be a metal substrate such as aluminum alloy, or a resin substrate, an organic - inorganic composite substrate;

[0025] Further limitation: the coating preparation process used in step 3 includes, but is not limited to, spraying, brushing, scraping, spin - coating and other processes;

[0026] Further limitation: in step 3, the coating is composed of multiple layers, and the thickness can be 50 - 500 microns;

[0027] Further limitation: in step 3, by adjusting process parameters such as spraying pressure, spraying speed and gun distance, hierarchical pore zeolite coatings with different morphological structures can be prepared.

[0028] The coating of the present invention includes two parts: functional fillers and binders; the functional fillers are composed of hierarchical zeolite powders, the binder is silica sol, and the composite coating is formed by a room - temperature spraying process.

[0029] For small - pore low - silica zeolites, their pore diameters are small, and it is difficult for the etchant to effectively diffuse into the interior; moreover, the framework stability is poor and it is easy to collapse during the preparation of hierarchical pores. The traditional single - etching method is difficult to effectively obtain hierarchical - pore zeolites. The present invention first etches with ammonium fluoride / methanol and then etches with acetic acid to prepare a multi - hierarchical pore zeolite - attached thermal - control coating. The key improvement point of the present invention lies in using the methanol - mediated ammonium fluoride - assisted acetic acid etching strategy to regulate the pore structure of small - pore low - silica zeolites to prepare hierarchical - pore zeolites, and further constructing a hierarchical - pore molecular adsorption coating. The addition of hierarchical zeolites in the coating improves the mass transfer and diffusion rate, solves the problem of pore blockage, and can efficiently adsorb large - molecule organic pollutants in a targeted manner.

[0030] Compared with the prior art, the present invention has the following beneficial effects:

[0031] The present invention uses an ammonium fluoride / methanol-acetic acid two-step etching method to obtain hierarchical pore zeolites with a complete microporous structure. The introduction of mesopores in the zeolites makes their pore structures more diverse, which is conducive to improving the adsorption, catalytic and other properties of the zeolites.

[0032] The hierarchical zeolite molecular adsorption coating prepared by the method of the present invention has a hierarchical pore structure composed of abundant micropores and mesopores, which increases the transport and diffusion rate of organic molecular pollutants, avoids the failure problem caused by the blockage of organic pollutants in the molecular adsorption coating, improves the adsorption capacity of macromolecular pollutants, and promotes the storage of pollutant molecules.

[0033] The hierarchical zeolite molecular adsorption coating prepared by the method of the present invention can achieve the self-balance of body temperature thermal control by virtue of its strong control ability of spectral absorption or emission for its own layered and three-dimensional space hierarchical pore structure, greatly enhancing the heat dissipation ability. The low absorption-high emission performance is conducive to its thermal control application in spacecraft.

[0034] In order to further understand the features and technical content of the present invention, please refer to the following detailed description of the present invention and the attached drawings. However, the attached drawings are only for reference and illustration, and are not used to limit the present invention. Description of the Drawings

[0035] Figure 1 is the XRD of the hierarchical zeolite molecular adsorption coating prepared by the method of Example 1;

[0036] Figure 2 is the 77.3K nitrogen adsorption / desorption isotherm of the hierarchical zeolite molecular adsorption coating prepared by the method of Example 1;

[0037] Figure 3 is the NLDFT differential integral logarithmic pore volume pore size distribution diagram of the hierarchical pore molecular adsorption coating prepared by the method of Example 1;

[0038] Figure 4 is the SEM image of the cross-section of the hierarchical pore molecular adsorption coating prepared by the method of Example 1;

[0039] Figure 5 is the test result of the ultraviolet-visible spectrometer of the hierarchical pore molecular adsorption coating prepared by the method of Example 1;

[0040] Figure 6 is the emissivity curve of the hierarchical pore molecular adsorption coating prepared by the method of Example 1;

[0041] Figure 7It is a physical picture before and after the thermal cycling experiment of the hierarchical pore molecular adsorption coating prepared by the method of Example 1. Detailed implementation manners

[0042] The present invention will be described in detail below with reference to specific embodiments. The following embodiments will help those skilled in the art to further understand the present invention, and at the same time do not limit the present invention in any form. It should be noted that for those of ordinary skill in the art, without departing from the inventive concept of the present invention, several modifications and improvements can be made. These all belong to the protection scope of the present invention.

[0043] Example 1: In this example, the controllable preparation method of the methanol-mediated ammonium fluoride-assisted acetic acid etched zeolite adsorption thermal control coating is carried out according to the following steps:

[0044] (1) Preparation of hierarchical pore 5A zeolite molecular sieve

[0045] Accurately weigh 0.5 g of ammonium fluoride solid and add it to 49.5 g of methanol (1 wt%), and the ammonium fluoride methanol solution is stirred and fully dissolved at a high temperature of 50 °C for standby;

[0046] Accurately weigh 5.0 g of 5A zeolite and quickly add it to the uniformly stirred ammonium fluoride etching solution (liquid: solid = 10), and carry out an etching reaction under high-speed stirring at a high temperature of 50 °C. During this period, keep stirring at a rate of 1000 rpm;

[0047] After reacting for 5 minutes, immediately carry out solid-liquid separation by suction filtration, and wash it thoroughly with normal temperature distilled water 3-5 times to remove fluoride ions in the solution to obtain a solid etching product;

[0048] Accurately weigh 0.5 g of acetic acid and add it to 49.5 g of water (1 wt%), and the acetic acid solution is stirred and fully prepared at a high temperature of 50 °C;

[0049] Quickly add the above solid etching product to the uniformly stirred acetic acid etching solution, and carry out an etching reaction under high-speed stirring at a high temperature of 50 °C. During this period, keep stirring at a rate of 1000 rpm;

[0050] After reacting for 30 minutes, immediately carry out solid-liquid separation by suction filtration, and wash it thoroughly with normal temperature distilled water 3-5 times to obtain a solid etching product;

[0051] The hierarchical pore zeolite obtained by the two-step etching method is dried at 373 K for 8 hours, and fully ground to obtain hierarchical pore 5A zeolite powder. Repeat the above steps according to experimental requirements to prepare a sufficient amount of hierarchical pore 5A zeolite powder.

[0052] (2) Preparation of spraying slurry

[0053] Before preparing the spraying slurry, the hierarchical pore zeolite molecular sieve is pretreated: The zeolite molecular sieve powder is placed in a tubular furnace and heated at a heating rate of heating to 150 °C within 1 h, evacuating to -0.1 MPa, then holding for 3 h, and naturally cooling to room temperature;

[0054] Accurately weigh 15 g of hierarchical pore 5A zeolite powder and add it to 50 g of silica sol (30 wt% silica sol). Note that in order to prevent poor dispersion or agglomeration due to too fast addition speed of zeolite, the hierarchical pore 5A zeolite is added to the silica sol in batches and slowly. After mixing, continue to stir at high speed for 3 hours to obtain the coating spraying slurry.

[0055] (3) The slurry is coated on the surface of the substrate by using the normal temperature spraying technology

[0056] An aluminum alloy thin plate is used as the substrate. The surface of the substrate is polished with 500-mesh sandpaper. After roughening the surface, it is ultrasonically cleaned with absolute ethanol for 30 min. After cleaning, use a dust-free cloth dipped in absolute ethanol to wipe the surface clean.

[0057] The spraying slurry is sprayed on the surface of the aluminum alloy substrate by using a pneumatic spray gun. Spraying conditions: The nozzle diameter is 3 mm, the liquid supply pressure is 0.8 Mpa, the moving speed of the spray gun is 100 cm / s, and the spraying distance is 15 cm. To prevent cracking caused by poor coating adhesion, the coating is prepared by the multiple spraying method. The interval between each spraying is 10 minutes, and the thickness of each spraying does not exceed 20 μm until the spraying thickness reaches 200 μm.

[0058] (5) Curing and forming

[0059] After spraying, the hierarchical pore 5A coating is placed at room temperature of 25 °C and naturally air-dried for 6 h. Then the hierarchical pore 5A zeolite molecular adsorption coating is placed in a vacuum oven for programmed heating and curing to ensure a strong bonding force between the coating and the substrate and prevent the coating from cracking. The specific heating conditions are: first heating to 100 °C at a rate of 1 °C / min and holding for 1 h, then heating to 150 °C at a rate of 5 °C / min and holding for 6 h, and a hierarchical pore 5A zeolite molecular adsorption thermal control coating with good performance can be obtained.

[0060] The XRD test results of the hierarchical pore 5A zeolite molecular adsorption coating obtained in this example are as Figure 1 shown, which is consistent with the 5A zeolite standard spectrum (PFD#11-0589). By comparison, it can be seen that the positions of the diffraction peaks are basically consistent, indicating that it has the crystal structure of 5A zeolite and has good crystallinity.

[0061] The test result diagram of the 77.3K nitrogen adsorption-desorption isotherm of the hierarchical pore 5A zeolite molecular adsorption coating obtained in this example is as Figure 2As shown, it has a high adsorption capacity in the range of p / p0 less than 0.01, indicating that it has a rich microporous structure and the phenomenon of micropore filling of nitrogen molecules occurs; an obvious hysteresis loop appears in the range of p / p0 of 0.6 - 0.8, indicating that it has a mesoporous structure, and the hierarchical pore structure of micropores - mesopores is conducive to the transport and diffusion of molecular substances. According to the BET method, its specific surface area is 326.74m 2 / g, and the high specific surface area is conducive to the adsorption of pollutant molecules.

[0062] The obtained hierarchical pore 5A zeolite molecular adsorption coating in this example uses the NLDFT method to calculate the measured nitrogen isothermal adsorption - desorption curve, and the obtained pore size - pore volume distribution diagram is as Figure 3 shown. From the data, it can be seen that the micropore volume of this coating is 0.0785 mL / g, the mesopore volume is 0.2127 mL / g, and the total pore volume is 0.2612 mL / g. The pore size distribution diagram shows that the molecular adsorption coating is a hierarchical pore structure containing both micropores and mesopores.

[0063] The SEM test results of the obtained hierarchical pore 5A zeolite molecular adsorption coating in this example are as Figure 4 shown. It can be seen from the figure that the zeolite particles are wrapped by silica sol to form a coating, and the surface and cross - section of the coating are relatively flat.

[0064] The ultraviolet - visible spectrometer test results of the obtained hierarchical pore 5A zeolite molecular adsorption coating in this example are as Figure 5 shown. After calculation, in the wavelength range of 200 - 2500 nm, the average solar absorptance is 29.9%.

[0065] The emissivity curve of the obtained hierarchical pore 5A zeolite molecular adsorption coating in this example is as Figure 6 shown. After calculation, in the wavelength range of 2 - 16 μm, the average emissivity of this coating reaches 96.4%, showing a quite high infrared emissivity, which is extremely conducive to the heat dissipation of the coating and achieves the temperature control effect.

[0066] The obtained hierarchical pore adsorption coating in this example is subjected to a thermal - cold cycle test. The specific test process is as follows: The coating is placed in a vacuum high - low temperature tester for thermal - cold alternating tests at - 170 - 130 °C. From Figure 7 it can be seen that after the test, there are no phenomena such as cracking and powder falling on the substrate of the coating, and it still has excellent interfacial bonding strength.

[0067] The vacuum adsorption test of pollutants was carried out using dioctyl phthalate. The specific test process was as follows: The hierarchical pore 5A molecular adsorption coating material obtained in Example 1 and dioctyl phthalate were placed in a space molecular contamination vacuum test system, and the temperature of the heating table was set at 80 °C. The adsorption experiment was carried out on the heating table, and samples were taken every 30 minutes and weighed at a different position on a precision balance. The adsorption amount was obtained by calculating the difference before and after weighing. The results are shown in the following table:

[0068] Table 1

[0069] Adsorption time (min) <![CDATA[Adsorption capacity (mg / cm 2 )]]> 30 1.4123 60 2.5076 90 3.2287 120 3.9286 150 4.1895 180 4.2777

[0070] As can be seen from Table 1, the adsorption capacity of the hierarchical pore 5A adsorption coating is very strong within 3 hours, and its adsorption amount can reach 4.2777 mg / cm at 3 hours 2 .

[0071] The specific embodiments of the present invention have been described above. It should be noted that the present invention is not limited to the above specific embodiments, and those skilled in the art can make various deformations or modifications within the scope of the claims, which do not affect the essence of the present invention.

Claims

1. A controllable preparation method for a zeolite adsorption thermal control coating etched by acetic acid assisted by ammonium fluoride mediated by methanol, characterized in that, It includes the following steps: Step 1: Etch the zeolite molecular sieve with an ammonium fluoride methanol solution, filter, and wash to remove fluoride ions; Step 2: Then etch with an acetic acid aqueous solution, clean, dry, grind, pretreat, and add the binder in batches to obtain a slurry; Step 3: After roughening the surface of the substrate, ultrasonically clean with anhydrous ethanol, wipe clean, coat the slurry, air-dry naturally, and cure in segments to obtain the adsorption coating.

2. The method according to claim 1, wherein The concentration of the ammonium fluoride methanol solution is 0.1 wt% to 5 wt%.

3. The method according to claim 1, characterized in that, The types of zeolites are 5A, 13X, USY, and ZSM-5.

4. The method according to claim 1, wherein In Step 1, etch at 50°C to 80°C for 1 min to 10 min.

5. The method according to claim 1, characterized in that, The concentration of the acetic acid aqueous solution is 0.5 wt% to 3 wt%.

6. The method according to claim 1, wherein In Step 2, etch at 50°C to 80°C for 20 min to 40 min.

7. The method according to claim 1, wherein The pretreatment is to heat to 100°C - 200°C within 1 h, evacuate to -0.1 MPa, keep warm for 2 h - 4 h, and naturally cool to room temperature.

8. The method according to claim 1, wherein The binder is silica sol, and the mass ratio of the pretreated zeolite to the binder is 1:(1 - 3).

9. The method according to claim 1, characterized in that, The curing is to raise the temperature to 100°C at a rate of 1°C / min, hold for 1 h, then raise the temperature to 150°C at a rate of 5°C / min, and hold for 6 h.

10. A coating prepared by the method according to any one of claims 1 - 9.

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