Aluminum dihydrogen phosphate-based inorganic coating and method for protecting stone cultural relics

Abstract

The invention discloses an aluminum dihydrogen phosphate-based inorganic coating and method for stone cultural relic protection, and belongs to the technical field of multifunctional super-hydrophobic inorganic coatings, and the method comprises the following steps: adding aluminum hydroxide powder into a phosphoric acid aqueous solution, fully stirring, and carrying out a constant temperature reaction to obtain an aluminum dihydrogen phosphate film-forming agent; the preparation method comprises the following steps: dispersing a siloxane series modifier into a mixed solution of ethanol and isopropanol, adding inorganic nanoparticles under ultrasonic treatment, and homogenizing to obtain a silanization modified inorganic nanoparticle dispersion solution; and adding an aluminum dihydrogen phosphate film-forming agent into the silanization modified inorganic nanoparticle dispersion liquid, carrying out homogenate treatment, spraying on the surface of a stone base material, and drying at normal temperature to obtain the aluminum dihydrogen phosphate-based inorganic coating for stone cultural relic protection. The aluminum dihydrogen phosphate film-forming agent can improve the compatibility and adhesive force of the coating and the stone cultural relics, the inorganic nanoparticles improve the hydrophobic, water-permeable, air-permeable, light-heat-resistant and anti-microbial constant values, and a new thought is provided for improving the weather resistance of the stone cultural relic protection coating.

Description

Technical Field

[0001] The present invention belongs to the technical field of multifunctional superhydrophobic inorganic coatings, and particularly relates to an aluminum dihydrogen phosphate-based inorganic coating for the protection of stone cultural relics and a method therefor. Background Art

[0002] In the field of restoration and protection of cultural heritage, the protection of outdoor stone cultural heritage such as grotto temples, cliffside statues, stone carvings, and stele inscriptions is of crucial importance. After thousands of years of the influence of natural and human activities, stone cultural relics are affected by different degrees and types of diseases due to the physical and chemical changes of internal factors (mineralogy and chemical composition, texture and porous structure) and the long-term action of external factors (pollutants, humidity, wind, temperature, and biological growth), seriously affecting the preservation and cultural value of the cultural relics.

[0003] At present, the surface coating protection technology for stone cultural relics mainly uses organic polymers to form a dense coating on the surface of stone cultural relics to prevent the influence and damage of external factors on stone cultural relics, and inorganic nanoparticles are also added to improve the functionality of the coating. However, the dense coating formed by organic polymers hinders the material exchange (mainly water) inside and outside the stone cultural relics, destroys its air permeability, and causes large-area peeling of the loose layer on the surface of the stone cultural relics. At the same time, the organic polymer coating serves as a substrate for bacteria and fungi to colonize on the coating surface and form a biofilm, thereby causing certain damage to the cultural relics themselves. The inorganic nanoparticles in the polymer will accelerate the decomposition and oxidation of the polymer coating under the action of light, reducing the protection effect of the coating on the stone, thus limiting its application in the protection of stone cultural relics.

[0004] In view of the fact that the dense coating of the organic polymer coating system in the existing stone cultural relic protection technology can block environmental pollutants, but due to excessive hindrance to the diffusion of moisture inside the stone and gas exchange, the surface loose layer of the cultural relics peels off due to humidity imbalance; the problem of biofilm growth on the coating surface and the phenomenon of photocatalysis acceleration of coating aging by inorganic nanoparticles form a dual damage mechanism, which not only weakens the protection efficiency but also introduces new biological corrosion risks. Therefore, it is necessary to develop a new type of protection material system with functions of breathable regulation, anti-biofouling properties, and light stability to achieve the synergistic optimization of the protection of stone cultural relics and the balance of the microenvironment. Summary of the Invention

[0005] In order to overcome the above-mentioned disadvantages of the prior art, the purpose of the present invention is to provide an aluminum dihydrogen phosphate-based inorganic coating for the protection of stone cultural relics and a preparation method therefor, so as to solve the technical problems of poor air permeability, easy aging and decomposition, biofilm growth, and low environmental compatibility existing in the traditional organic polymer coating in the protection of stone cultural relics.

[0006] To achieve the above purpose, the present invention adopts the following technical solutions: The present invention discloses a preparation method of an aluminum dihydrogen phosphate-based inorganic coating for the protection of stone cultural relics, including: 1) Adding aluminum hydroxide powder into phosphoric acid aqueous solution, fully stirring and reacting at a constant temperature, to obtain an aluminum dihydrogen phosphate film-forming agent; 2) Dispersing a siloxane series modifier into a mixed solution of ethanol and isopropanol, adding inorganic nanoparticles under ultrasonic treatment, and after homogenization treatment, obtaining a silanized modified inorganic nanoparticle dispersion; 3) Adding the aluminum dihydrogen phosphate film-forming agent prepared in step 1) into the silanized modified inorganic nanoparticle dispersion prepared in step 2), and after homogenization treatment, obtaining a precursor coating. Spraying the precursor coating on the surface of the stone substrate and drying at room temperature, to obtain an aluminum dihydrogen phosphate-based inorganic coating for the protection of stone cultural relics.

[0007] Preferably, in step 1), the dosage ratio of aluminum hydroxide powder to phosphoric acid aqueous solution is (5 - 10) g﹕(50 - 80) mL; the mass percentage concentration of the phosphoric acid aqueous solution is 60 wt%.

[0008] Preferably, in step 1), the temperature of the constant temperature reaction is 100 - 120 °C, and the time of the constant temperature reaction is 180 - 240 min.

[0009] Preferably, in step 2), the dosage ratio of the siloxane series modifier: the mixed solution of ethanol and isopropanol: inorganic nanoparticles is (2 - 5) mL﹕(50 - 80) mL﹕(0.5 - 1) g; in the mixed solution of ethanol and isopropanol, the volume ratio of ethanol to isopropanol is 1:1.

[0010] Preferably, in step 2), the siloxane series modifier includes at least one of cetyltrimethoxysilane and polydimethylsiloxane; the inorganic nanoparticles include any one of titanium dioxide, silicon dioxide and zinc oxide; the particle size of the inorganic nanoparticles is 50 - 300 nm.

[0011] Preferably, in step 2), the time of ultrasonic treatment is 15 - 30 min; the rotation speed of homogenization treatment is 12000 - 15000 rpm, and the time of homogenization treatment is 10 - 30 min.

[0012] Preferably, in step 3), the rotation speed of homogenization treatment is 12000 - 15000 rpm, and the time of homogenization treatment is 10 - 30 min.

[0013] Preferably, in step 3), the stone substrate is natural sandstone or marble.

[0014] Preferably, in step 3), the spraying conditions include: the nozzle diameter is 0.6 - 0.8 mm, the spraying pressure is 35 - 45 psi, the moving speed of the spray gun is 3 - 6 cm / s, and the spraying volume is 120 - 150 mL / m 2 , the nozzle sprays at a position 15 - 20 cm directly above the stone substrate, the spraying time for one time lasts for 2 - 5 s, and the sprayed stone substrate is dried at normal temperature for 6 - 12 h.

[0015] The present invention also discloses an aluminum dihydrogen phosphate - based inorganic coating for stone cultural relic protection prepared by using the above - mentioned preparation method of the aluminum dihydrogen phosphate - based inorganic coating for stone cultural relic protection.

[0016] Compared with the prior art, the present invention has the following beneficial effects: The present invention discloses a preparation method of an aluminum dihydrogen phosphate - based inorganic coating for stone cultural relic protection. Aluminum dihydrogen phosphate is used to replace the organic polymer as the film - forming agent, and inorganic nanoparticles are used as functional components to construct a multifunctional super - hydrophobic inorganic coating for stone cultural relic protection based on a hydrophobic surface. The dispersibility and solid content of the film - forming agent and functional components are regulated and optimized to prepare a multifunctional super - hydrophobic inorganic coating with good compatibility with the stone cultural relic matrix, good air - permeability and water - permeability, high adhesion, strong self - cleaning ability, good light and heat resistance, and the ability to inhibit microbial growth. Replacing the organic polymer with inorganic aluminum dihydrogen phosphate as the film - forming agent further improves the compatibility of the coating with the stone cultural relic body material and functional inorganic nanoparticles, and the coating has excellent mechanical stability, hydrophobicity, air - permeability, acid - alkali resistance, thermal stability, wear resistance, and anti - aging performance, which can significantly improve the protection effect of stone cultural relics and has positive significance for expanding the application of inorganic materials in the protection of stone cultural relics. The raw materials of the present invention are easily available, the preparation conditions are mild, the use method is simple and convenient, it has good compatibility with the stone matrix, extremely strong weather resistance, obvious protection effect, is green and environmentally friendly, pollution - free, and does not involve any toxic solvents in the treatment of raw materials. Only by simply homogenizing and spraying on the surface of stone cultural relics and drying at normal temperature can a protective coating with excellent performance be obtained.

[0017] Furthermore, ensuring that the molar ratio of phosphoric acid to aluminum hydroxide is close to the reaction stoichiometry can avoid the influence of excessive acid residue or unreacted aluminum hydroxide on the purity of the film - forming agent; the 60 wt% phosphoric acid solution not only provides sufficient reaction activity but also avoids too high a concentration resulting in too fast a reaction or too high a system viscosity, which affects subsequent dispersibility.

[0018] Furthermore, 100 - 120 °C is the appropriate temperature range for the reaction of phosphoric acid and aluminum hydroxide, which can promote the complete reaction and avoid the over - dehydration of phosphoric acid to form pyrophosphoric acid, affecting the stability of the film - forming agent; 3 - 4 h ensures that the reaction proceeds fully to generate high - purity aluminum dihydrogen phosphate and avoids the residue of intermediate products caused by short - time reaction.

[0019] Furthermore, the amount of siloxane is sufficient to cover the surface of the nanoparticles, forming a dense hydrophobic layer, while avoiding excessive amounts that would lead to too high a viscosity of the dispersion. The equal-volume mixture of ethanol and isopropanol is used as the solvent, which can not only dissolve the siloxane modifier but also facilitate the uniform dispersion of the nanoparticles.

[0020] Furthermore, the long-chain alkyl group of cetyltrimethoxysilane provides high hydrophobicity, and polydimethylsiloxane imparts flexibility to the coating and enhances mechanical stability. Both are silanes with high hydrolytic stability, avoiding the degradation of the coating due to environmental humidity.

[0021] Furthermore, titanium dioxide has photocatalytic antibacterial properties, generating reactive oxygen species under ultraviolet light to inhibit microbial colonization; silicon dioxide has high hardness to enhance wear resistance, and its micro-nano structure improves superhydrophobic performance; zinc oxide has broad-spectrum antibacterial properties and can absorb ultraviolet light to delay photoaging; 50 - 300 nm particles can construct a micro-nano composite rough structure to achieve a superhydrophobic effect in cooperation with silane modification.

[0022] Furthermore, the cavitation effect is used to break the nanoparticle aggregates, promoting the uniform coating of siloxane molecules on the particle surface; high rotational speed further ensures the uniform dispersion of the nanoparticles in the solvent and film-forming agent, avoiding cracks or defects in the coating after drying.

[0023] Furthermore, the porous structure of sandstone is prone to water absorption, leading to weathering. The high gas permeability of the coating allows water vapor to pass through but blocks the penetration of liquid water, avoiding the blistering effect; the calcium carbonate matrix of marble is vulnerable to acid rain corrosion, and the acid and alkali resistance of the coating can provide double protection.

[0024] Furthermore, a distance of 15 - 20 cm ensures uniform atomization of the coating, avoiding running caused by being too close or coating waste caused by being too far away; spraying in multiple times for a short period instead of a single thick coating can form a uniform thin film, reducing the drying shrinkage stress. Drying at room temperature avoids thermal stress cracking of the stone matrix caused by high temperature, and a drying time of 6 - 12 h ensures sufficient curing of the coating. Aluminum dihydrogen phosphate forms a three-dimensional network structure through a polycondensation reaction.

[0025] The present invention also discloses an aluminum dihydrogen phosphate-based inorganic coating for the protection of stone cultural relics prepared by the above preparation method. Through the synergistic effect of the aluminum dihydrogen phosphate film-forming agent and the silylated inorganic nanoparticles, the multifunctional integration of hydrophobicity, high gas permeability, antibacterial property and weather resistance is realized. Its inorganic nature has excellent chemical compatibility with the stone matrix (such as sandstone, marble), avoiding the peeling problem caused by the difference in thermal expansion coefficient of the organic coating. At the same time, the micro-nano rough structure and the silane hydrophobic layer formed on the surface endow the coating with self-cleaning ability, which can effectively resist rain erosion, acid rain corrosion and microbial erosion. The room-temperature curing characteristic of the coating avoids the damage to the cultural relics caused by construction thermal stress. The spraying process is suitable for complex surfaces, and the raw materials are non-toxic, environmentally friendly and free of volatile organic compound release, meeting the ethical requirements of cultural relic protection, and providing a long-term, green and engineerable comprehensive protection solution for outdoor stone cultural relics. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 It is a super-depth-of-field optical photograph of the Al(H2PO4)3-HDTMS-SiO2 coating prepared in Example 1 of the present invention; Figure 2 It is a hydrophobic optical photograph of the Al(H2PO4)3-HDTMS-TiO2 coating prepared in Example 2 of the present invention; Figure 3 It is a gas permeability test curve of the Al(H2PO4)3-PDMS-SiO2 coating prepared in Example 3 of the present invention; Figure 4 It is a photo of the growth inhibition of Staphylococcus aureus by the Al(H2PO4)3-PDMS-ZnO coating prepared in Example 4 of the present invention; among them, (a) is without the inorganic coating covered; (b) is with the Al(H2PO4)3-PDMS-ZnO coating covered. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0027] The technical solutions of the present invention will be described clearly and completely below. Obviously, the described embodiments are some but not all of the embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0028] In the present invention, if there is no special description, all the embodiments and preferred implementation methods mentioned in this article can be combined with each other to form a new technical solution.

[0029] In the present invention, if there is no special description, all the technical features and preferred features mentioned in this article can be combined with each other to form a new technical solution.

[0030] In the present invention, unless otherwise specified, percentage (%) or part refers to the weight percentage or weight part relative to the composition.

[0031] In the present invention, unless otherwise specified, the components or preferred components involved can be combined with each other to form a new technical solution.

[0032] In the present invention, unless otherwise specified, the numerical range "a~b" represents an abbreviation of any real number combination between a and b, where a and b are real numbers. For example, the numerical range "6~22" means that all real numbers between "6~22" have been listed in this document, and "6~22" is just an abbreviation of these numerical combinations.

[0033] The “range” disclosed in the present invention is in the form of a lower limit and an upper limit, which can be one or more lower limits, and one or more upper limits, respectively.

[0034] In the present invention, the term "and / or" used herein refers to any combination and all possible combinations of one or more of the associated listed items, and includes these combinations.

[0035] In the present invention, unless otherwise specified, each reaction or operation step can be carried out sequentially or in accordance with the sequence. Preferably, the reaction method herein is carried out sequentially.

[0036] Unless otherwise specified, the professional and scientific terms used herein have the same meanings as those familiar to those skilled in the art. In addition, any method or material similar or equivalent to the described content may also be applied to the present invention.

[0037] The present invention proposes a method for preparing an aluminum dihydrogen phosphate-based inorganic coating for protecting stone cultural relics. By constructing a multifunctional inorganic coating for protecting stone cultural relics based on a hydrophobic surface, the problems of organic polymer coatings being water permeable, poor air permeability, poor light and heat resistance, and easy colonization of microorganisms on the coating surface can be solved.

[0038] The present invention discloses a method for preparing an aluminum dihydrogen phosphate-based inorganic coating for protecting stone cultural relics, which is specifically implemented according to the following steps: Step 1: Add aluminum hydroxide powder to phosphoric acid aqueous solution, stir thoroughly and react in an oil bath at a constant temperature to obtain aluminum dihydrogen phosphate Al(H2PO4)3 film-forming agent; The phosphoric acid aqueous solution is a 60 wt% phosphoric acid aqueous solution obtained by diluting 85 wt% phosphoric acid with a certain amount of water; the volume ratio of the mass of the aluminum hydroxide powder to the phosphoric acid aqueous solution is (5-10) g: (50-80) mL, the isothermal reaction temperature is 100-120 °C, and the reaction time is 180-240 min; Step 2: Disperse the siloxane series modifiers into an equal-volume mixture of ethanol and isopropanol, add inorganic nanoparticles with a size of 50 - 300 nm under ultrasonic conditions, and homogenize the dispersion to obtain a silanized modified inorganic nanoparticle dispersion; Among them, the siloxane modifier refers to one or a mixture of hexadecyltrimethoxysilane (HDTMS) and polydimethylsiloxane (PDMS); the inorganic nanoparticles refer to one of titanium dioxide (TiO2), silicon dioxide (SiO2), and zinc oxide (ZnO); the volume ratio of the siloxane series modifier, the volume of the ethanol and isopropanol mixture, and the mass ratio of the inorganic nanoparticles is (2 - 5) mL﹕(50 - 80) mL﹕(0.5 - 1) g, the ultrasonic treatment time is 15 - 30 min; the rotation speed of the homogenization treatment is 12000 - 15000 rpm, and the homogenization treatment time is 10 - 30 min; Step 3: Add the Al(H2PO4)3 film-forming agent prepared in Step 1 to the silanized modified inorganic nanoparticle dispersion prepared in Step 2, homogenize to obtain a precursor coating, and spray the coating on the surface of the stone substrate using a spraying process. After drying at room temperature, an Al(H2PO4)3-based inorganic coating is obtained.

[0039] Among them, the rotation speed of the homogenization treatment is 12000 - 15000 rpm, and the time is 10 - 30 min; the stone substrate is natural sandstone or marble, the substrate is in the shape of a cuboid block, with dimensions of 50×20×5 mm, and the coating spraying area is 50×20 mm 2 ; the spraying process is that the nozzle diameter is 0.6 - 0.8 mm, the spraying pressure is 35 - 45 psi, the moving speed of the spray gun is about 3 - 6 cm / s, and the coating ejection volume is 120 - 150 mL / m 2 . During the spraying process, the nozzle sprays at a position 15 - 20 cm directly above the substrate, the spraying time for one time lasts 2 - 5 s, and the sprayed stone substrate is dried at room temperature for 6 - 12 h.

[0040] The invention discloses a method for preparing an aluminum dihydrogen phosphate-based inorganic coating for protecting stone cultural relics. Aluminum hydroxide powder is added to a phosphoric acid aqueous solution, and then the mixture is stirred thoroughly and then subjected to an oil bath constant temperature reaction to obtain an aluminum dihydrogen phosphate film-forming agent; a siloxane series modifier is dispersed in an equal volume mixed solution of ethanol and isopropanol, and inorganic nanoparticles are added under an ultrasonic state, and the dispersion liquid is homogenized to obtain a silanized modified inorganic nanoparticle dispersion liquid; the prepared aluminum dihydrogen phosphate film-forming agent is added to the silanized modified inorganic nanoparticle dispersion liquid, and a precursor coating is obtained after homogenization, and the coating is sprayed on the surface of a stone substrate by a spraying process, and then dried at room temperature to obtain an aluminum dihydrogen phosphate-based inorganic coating. The aluminum dihydrogen phosphate film-forming agent is used to improve the compatibility and adhesion of the coating with the stone cultural relic body, and the inorganic nanoparticles are functional components, so that the hydrophobic, water-permeable and air-permeable, light-heat-resistant and anti-microbial fixed value properties of the inorganic coating are improved, and a new idea is provided for improving the weather resistance of the stone cultural relic protection coating. The inorganic coating has good compatibility with the stone cultural relic body, good mechanical stability, thermal stability, wear resistance and anti-aging performance, and exhibits hydrophobicity, air permeability and antibacterial functionality, and has certain potential application value as a stone cultural relic protection coating. At the same time, the preparation process of the invention is simple and easy, which is conducive to outdoor construction and has special practical significance for the protection of stone cultural relics that are mostly outdoors.

[0041] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all of the embodiments. The components of the embodiments of the present invention described and shown in the drawings here can usually be arranged and designed in various different configurations. Therefore, the following detailed description of the embodiments of the present invention provided in the drawings is not intended to limit the scope of the claimed invention, but merely represents selected embodiments of the present invention. Based on the embodiments in the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0042] Example 1 A method for preparing an aluminum dihydrogen phosphate-based inorganic coating for protecting stone cultural relics, comprising: 5 g of aluminum hydroxide powder was added to 80 mL of 60 wt% phosphoric acid aqueous solution. After sufficient stirring, the reaction was carried out at a constant temperature of 100 °C in an oil bath for 180 min to obtain the Al(H2PO4)3 film-forming agent; 5 mL of HDTMS modifier was dispersed in a 50 mL equal-volume mixture of ethanol and isopropanol. Then, 1 g of SiO2 with a particle size of 30 was dispersed in the mixture under ultrasonic conditions. After ultrasonic treatment for 30 min, the dispersion was homogenized to achieve the silanization modification of nano-SiO2. The rotation speed of the homogenization treatment was 15,000 rpm and the time was 30 min to obtain the HDTMS-SiO2 dispersion; 5 g of the prepared Al(H2PO4)3 film-forming agent was added to 50 mL of the prepared HDTMS-SiO2 dispersion. After homogenization treatment at a rotation speed of 12,000 rpm for 30 min, a precursor coating was obtained. The coating was sprayed on the surface of the natural sandstone substrate by a spraying process, where the nozzle diameter was 0.6 mm, the spraying pressure was 35 psi, the moving speed of the spray gun was 3 cm / s, and the coating ejection volume was 120 mL / m 2 . During the spraying process, the nozzle was sprayed 15 cm directly above the substrate, and the spraying time for one time lasted for 2 s. The sprayed stone substrate was dried at room temperature for 6 h to obtain the Al(H2PO4)3-HDTMS-SiO2 coating.

[0043] Figure 1 This is the ultra-depth-of-field optical photograph of the Al(H2PO4)3-HDTMS-SiO2 coating prepared in Example 1 of the present invention. It can be seen from the figure that a uniform and dense coating was formed on the surface of the natural sandstone substrate.

[0044] Example 2 A preparation method of an aluminum dihydrogen phosphate-based inorganic coating for the protection of stone cultural relics, including: Add 10 g of aluminum hydroxide powder to 50 mL of 60 wt% phosphoric acid aqueous solution. After stirring well, react at a constant temperature of 120 °C in an oil bath for 240 min to obtain an Al(H2PO4)3 film-forming agent. Disperse 2 mL of HDTMS modifier in an equal-volume mixture of 80 mL of ethanol and isopropyl alcohol. Then, under ultrasonic conditions, disperse 0.5 g of TiO2 with a particle size of 100 nm in the mixture and ultrasonically treat for 15 min. Subsequently, perform homogenization treatment on the dispersion to achieve silanization modification of the nano-TiO2 particles. The rotation speed of the homogenization treatment is 12,000 rpm and the time is 10 min to obtain an HDTMS-TiO2 dispersion. Take 5 g of the prepared Al(H2PO4)3 film-forming agent and add it to 80 mL of the prepared HDTMS-TiO2 dispersion. After homogenization treatment at a rotation speed of 12,000 rpm for 10 min, a precursor coating is obtained. The coating is sprayed on the surface of a natural sandstone substrate using a spraying process, where the nozzle diameter is 0.8 mm, the spraying pressure is 45 psi, the moving speed of the spray gun is 6 cm / s, and the coating ejection volume is 150 mL / m 2 . During the spraying process, the nozzle sprays at a position 20 cm directly above the substrate, and the spraying time for one time lasts for 5 s. The sprayed stone substrate is dried at room temperature for 12 h to obtain an Al(H2PO4)3-HDTMS-TiO2 coating.

[0045] Figure 2 This is a hydrophobic optical photograph of the Al(H2PO4)3-HDTMS-TiO2 coating prepared in Example 2 of the present invention. As can be seen from the figure, water droplets appear spherical on the coating surface, and the water droplets easily roll off from the surface of the natural sandstone substrate, thereby reducing the harm of external water to stone cultural relics and achieving self-cleaning.

[0046] Example 3 A preparation method of an aluminum dihydrogen phosphate-based inorganic coating for the protection of stone cultural relics, including: 8 g of aluminum hydroxide powder was added to 80 mL of 60 wt% phosphoric acid aqueous solution. After sufficient stirring, the reaction was carried out at a constant temperature of 120 °C in an oil bath for 180 min to obtain an Al(H2PO4)3 film-forming agent. 5 mL of PDMS modifier was dispersed in an 80 mL equal-volume mixture of ethanol and isopropanol. Then, 0.5 g of SiO2 with a particle size of 200 nm was dispersed in the mixture under ultrasonic conditions, and ultrasonic treatment was carried out for 20 min. Subsequently, the dispersion was homogenized to achieve the silanization modification of the nano-SiO2 particles. The rotation speed of the homogenization treatment was 13,000 rpm, and the time was 15 min to obtain a PDMS-SiO2 dispersion. 8 g of the prepared Al(H2PO4)3 film-forming agent was added to 80 mL of the prepared PDMS-SiO2 dispersion. After homogenization treatment at a rotation speed of 15,000 rpm for 30 min, a precursor coating was obtained. The coating was sprayed on the surface of the marble substrate by a spraying process. Among them, the nozzle diameter was 0.7 mm, the spraying pressure was 42 psi, the moving speed of the spray gun was about 5 cm / s, and the coating ejection volume was 140 mL / m 2 . During the spraying process, the nozzle was sprayed 18 cm directly above the substrate, and the spraying time for one time lasted for 3 s. The sprayed stone substrate was dried at room temperature for 8 h to obtain an Al(H2PO4)3-PDMS-SiO2 coating.

[0047] Figure 3 Figure 6 is the air permeability performance test curve of the Al(H2PO4)3-PDMS-SiO2 coating prepared in Example 3 of the present invention. After calculation, the water vapor flow rate of the marble substrate covered with the inorganic coating during the test period was 9.2×10 -3 g / h, indicating that the sample has good air permeability performance and is not prone to problems such as coating peeling and flaking caused by poor material exchange inside and outside the coating compared with polymer coatings.

[0048] Example 4 A preparation method of an aluminum dihydrogen phosphate-based inorganic coating for the protection of stone cultural relics, comprising: 6 g of aluminum hydroxide powder was added to 80 mL of 60 wt% phosphoric acid aqueous solution, and after sufficient stirring, the mixture was reacted at a constant temperature of 110 °C in an oil bath for 180 min to obtain an Al(H2PO4)3 film-forming agent; 5 mL of PDMS modifier was dispersed in 60 mL of a mixed solution of equal volumes of ethanol and isopropanol, and then 1 g of ZnO with a particle size of 100 nm was dispersed in the mixed solution under ultrasound, and the mixture was ultrasonically treated for 25 min. The dispersion was then homogenized to achieve silanization modification of nano-ZnO. The homogenization speed was 13000 rpm for 30 min to obtain a PDMS-ZnO particle dispersion; 6 g of the prepared Al(H2PO4)3 was added to 50 mL of the prepared PDMS-ZnO dispersion, and the precursor coating was obtained after homogenization at a speed of 15000 rpm for 20 min. The coating was sprayed on the surface of the natural sandstone substrate by a spraying process, wherein the nozzle diameter was 0.8 mm and the spraying pressure was 42 psi, the spray gun moves at a speed of about 5 cm / s, and the paint spray volume is 120 mL / m 2 During the spraying process, the nozzle was sprayed at a distance of 20 cm above the substrate, and the spraying time lasted for 3 s. The sprayed stone substrate was dried at room temperature for 12 h to obtain the Al(H2PO4)3-PDMS-ZnO coating.

[0049] Figure 4 The photograph of the growth inhibition of Staphylococcus aureus by the Al(H2PO4)3-PDMS-ZnO coating prepared in Example 4 of the present invention is shown. It can be seen from the figure that the growth and diffusion of Staphylococcus aureus on the surface of natural sandstone without coating is obvious, while no growth of Staphylococcus aureus is found on the surface of natural sandstone covered with Al(H2PO4)3-PDMS-ZnO coating, indicating that the prepared aluminum dihydrogen phosphate-based inorganic coating has a certain antibacterial effect, which can effectively prevent the enrichment and growth of fungal organisms on the surface of stone cultural relics and prevent the harm of biological colonization to stone cultural relics.

[0050] Example 5 A method for preparing an aluminum dihydrogen phosphate-based inorganic coating for protecting stone cultural relics, comprising: Add 7 g of aluminum hydroxide powder to 60 mL of 60 wt% phosphoric acid aqueous solution. After stirring well, react at a constant temperature of 115 °C in an oil bath for 200 min to obtain the Al(H2PO4)3 film-forming agent. Disperse 2 mL of HDTMS modifier and 2 mL of PDMS modifier into a 70 mL equal-volume mixture of ethanol and isopropanol. Then, under ultrasonic conditions, disperse 0.8 g of TiO2 with a particle size of 300 nm in the mixture and ultrasonically treat for 20 min. Subsequently, perform homogenization treatment on the dispersion to achieve the silanization modification of nano-TiO2 particles. The rotation speed of the homogenization treatment is 14,000 rpm and the time is 20 min to obtain the HDTMS-PDMS-TiO2 dispersion. Take 7 g of the prepared Al(H2PO4)3 film-forming agent and add it to 60 mL of the prepared HDTMS-PDMS-TiO2 dispersion. After homogenization treatment at a rotation speed of 14,000 rpm for 25 min, obtain the precursor coating. Use the spraying process to spray the coating on the surface of the marble substrate. Among them, the nozzle diameter is 0.8 mm, the spraying pressure is 42 psi, the moving speed of the spray gun is about 4 cm / s, and the coating ejection volume is 120 mL / m 2 . During the spraying process, the nozzle sprays at a position 20 cm directly above the substrate, and the spraying time for one time lasts for 3 s. The sprayed stone substrate is dried at room temperature for 12 h to obtain the Al(H2PO4)3-HDTMS-PDMS-TiO2 coating.

[0051] In summary, a dihydrogen phosphate-based inorganic coating and method for stone cultural relic protection disclosed by the present invention controls the dosages of dihydrogen phosphate film-forming agent, inorganic nanoparticles, siloxane modifiers, etc., and simultaneously controls the coating mixing process and spraying process to obtain a dihydrogen phosphate-based multifunctional inorganic coating for stone cultural relic protection. Using inorganic dihydrogen phosphate as the film-forming agent improves the compatibility between the coating and the stone cultural relic body as well as functional inorganic nanoparticles. The addition of functional components further improves the mechanical stability, hydrophobicity, air permeability, etc. of the coating. Moreover, the coating is basically composed of inorganic components, and the thermal stability, wear resistance, and anti-aging performance can be significantly improved compared with organic coatings, thereby significantly enhancing the protection effect of stone cultural relics. The raw materials used in the present invention are inexpensive, green, and pollution-free. The treatment of raw materials does not involve any toxic solvents, and only simple homogenization and spraying on the surface of stone cultural relics followed by drying at room temperature can obtain a protective coating with excellent performance. The present invention uses a simple spraying process to prepare an inorganic coating. The preparation method is simple and feasible, and with a slight adjustment, it can be not affected by the surface morphology of the stone substrate. The good hydrophobic and breathable performance and the characteristic of forming a film at room temperature are conducive to outdoor construction and other characteristics, which have special practical significance for the protection of most stone cultural relics located outdoors.

[0052] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements on some or all of the technical features; and these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A preparation method of an aluminum dihydrogen phosphate-based inorganic coating for the protection of stone cultural relics, characterized in that, Comprising: 1) Adding aluminum hydroxide powder into phosphoric acid aqueous solution, fully stirring and reacting at a constant temperature, to obtain an aluminum dihydrogen phosphate film-forming agent; 2) Dispersing a siloxane series modifier into a mixed solution of ethanol and isopropanol, adding inorganic nanoparticles under ultrasonic treatment, and after homogenization treatment, obtaining a silanized modified inorganic nanoparticle dispersion; 3) Adding the aluminum dihydrogen phosphate film-forming agent prepared in step 1) into the silanized modified inorganic nanoparticle dispersion prepared in step 2), and after homogenization treatment, obtaining a precursor coating. Spraying the precursor coating on the surface of a stone substrate and drying at room temperature, to obtain an aluminum dihydrogen phosphate-based inorganic coating for stone cultural relic protection.

2. The preparation method of the aluminum dihydrogen phosphate-based inorganic coating for stone cultural relic protection according to claim 1, characterized in that, In step 1), the dosage ratio of the aluminum hydroxide powder to the phosphoric acid aqueous solution is (5 - 10) g﹕(50 - 80) mL; the mass percentage concentration of the phosphoric acid aqueous solution is 60 wt%.

3. The preparation method of the aluminum dihydrogen phosphate-based inorganic coating for stone cultural relic protection according to claim 1, wherein In step 1), the temperature of the constant temperature reaction is 100 - 120 °C, and the time of the constant temperature reaction is 180 - 240 min.

4. The preparation method of the aluminum dihydrogen phosphate-based inorganic coating for stone cultural relic protection according to claim 1, characterized in that In step 2), the dosage ratio of the siloxane series modifier: the mixed solution of ethanol and isopropanol: the inorganic nanoparticles is (2 - 5) mL﹕(50 - 80) mL﹕(0.5 - 1) g; in the mixed solution of ethanol and isopropanol, the volume ratio of ethanol to isopropanol is 1:

1.

5. The preparation method of the aluminum dihydrogen phosphate-based inorganic coating for stone cultural relic protection according to claim 1, characterized in that In step 2), the siloxane series modifier includes at least one of cetyltrimethoxysilane and polydimethylsiloxane; the inorganic nanoparticles include any one of titanium dioxide, silicon dioxide, and zinc oxide; the particle size of the inorganic nanoparticles is 50 - 300 nm.

6. The preparation method of the aluminum dihydrogen phosphate-based inorganic coating for stone cultural relic protection according to claim 1, wherein In step 2), the time of the ultrasonic treatment is 15 - 30 min; the rotation speed of the homogenization treatment is 12000 - 15000 rpm, and the time of the homogenization treatment is 10 - 30 min.

7. The preparation method of the aluminum dihydrogen phosphate-based inorganic coating for stone cultural relic protection according to claim 1, characterized in that, In step 3), the rotation speed of the homogenization treatment is 12000 - 15000 rpm, and the time of the homogenization treatment is 10 - 30 min.

8. The preparation method of the aluminum dihydrogen phosphate-based inorganic coating for stone cultural relic protection according to claim 1, characterized in that, In step 3), the stone substrate is natural sandstone or marble.

9. The preparation method of the aluminum dihydrogen phosphate-based inorganic coating for stone cultural relic protection according to claim 1, characterized in that, In step 3), the conditions for spraying include: the nozzle diameter is 0.6 - 0.8 mm, the spraying pressure is 35 - 45 psi, the moving speed of the spray gun is 3 - 6 cm / s, and the spraying volume is 120 - 150 mL / m 2 , the nozzle sprays at a position 15 - 20 cm directly above the stone substrate, the duration of one spraying is 2 - 5 s, and the sprayed stone substrate is dried at room temperature for 6 - 12 h.

10. An aluminum dihydrogen phosphate-based inorganic coating for the protection of stone cultural relics, characterized in that, Prepared by using the preparation method of the aluminum dihydrogen phosphate-based inorganic coating for stone cultural relic protection according to any one of claims 1 - 9.

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