A hydrophobic silica aerogel based on desert sand and its preparation method and application

Abstract

This application relates to the technical field of silica aerogel preparation, and more particularly to a hydrophobic silica aerogel based on desert sand, its preparation method, and application. The preparation method comprises the following steps: S1, pretreatment; S2, calcination activation; S3, preparation of a water glass solution; S4, preparation of a wet gel; S5, replacement modification; and S6, atmospheric pressure drying to obtain a hydrophobic silica aerogel based on desert sand. This application provides a hydrophobic silica aerogel based on desert sand, its preparation method, and application, to address the problems of insufficient mechanical strength and low porosity in silica aerogels prepared from desert sand in related technologies.

Description

Technical Field

[0001] The present application relates to the technical field of silica aerogel preparation, and in particular to a hydrophobic silica aerogel based on desert sand, and a preparation method and application thereof. Background Art

[0002] Aerogels are open-cell, nanoporous materials typically made from a gel in which the liquid component is replaced by a gas. Their unique physical properties include low density, low thermal conductivity, large surface area, low refractive index, and low dielectric constant. These unique properties have attracted widespread attention due to their potential for application in a wide range of fields.

[0003] Silica aerogels are produced by removing the solvent from the wet gel while maintaining the integrity and high porosity of the gel. Supercritical fluid drying and atmospheric pressure drying are the most commonly used drying methods. Generally speaking, the surface tension of the fluid under supercritical pressure is almost zero. This avoids collapse and shrinkage caused by surface tension, thereby eliminating the fluid. However, supercritical drying involves high pressure, requires greater power and high-quality manufacturing equipment, and the supercritical drying process is cumbersome and time-consuming, which limits its commercial application. Therefore, in recent years, the synthesis of silica aerogels using atmospheric pressure drying technology has attracted much attention. In order to further reduce manufacturing costs and realize the commercial production of silica aerogels, it is very necessary to use a cheaper silicon source as a precursor and a new process for synthesizing hydrophobic silica aerogels in a reasonable method and cost.

[0004] Desertification is one of the most serious ecological and environmental issues facing the world today. It not only hinders the sustainable development of modern society but also causes the continuous deterioration of the ecological environment, thus affecting the environment for human survival and development. Northwest China has a considerable number of deserts with vast sand reserves and abundant resources. Desert sand is also rich in silica. Using desert sand as a precursor for aerogel production can not only reduce production costs but also have important significance for the green and sustainable development of the ecological environment.

[0005] However, due to the low specific surface area and mechanical strength of sand, the silica aerogel produced usually has insufficient mechanical strength and low porosity, which limits its application range. Summary of the Invention

[0006] The present application provides a hydrophobic silica aerogel based on desert sand, a preparation method thereof, and an application thereof, in order to solve the problems in the related art of insufficient mechanical strength and low porosity of the products prepared from silica aerogel using desert sand as raw material.

[0007] In a first aspect, a method for preparing a hydrophobic silica aerogel based on desert sand is provided, comprising the following steps:

[0008] S1. Preprocessing:

[0009] After washing the desert sand with water, immerse it in a 5% hydrochloric acid solution for 2-3 hours, filter it, and rinse it with deionized water until the rinse water is neutral.

[0010] The mixture was ball-milled through a 200-mesh sieve and subjected to magnetic separation to remove magnetic materials to obtain a powder. The powder was mixed with a dispersion solution and filtered to obtain a pretreated powder. The mass volume ratio of the powder to the dispersion solution was 1 g: (5-10) mL.

[0011] S2. Calcination and activation:

[0012] The pretreated powder and sodium sesquicarbonate were mixed uniformly in a mass ratio of 1:0.2, and then heated to 600-750°C at a heating rate of 5-10°C / min and kept at this temperature for 2 hours to complete calcination activation and obtain activated slag;

[0013] S3, preparing water glass solution:

[0014] The activated slag and sodium hydroxide were mixed in a mass ratio of 1:(0.5-0.8), deionized water was added to make the solid-liquid ratio reach 1:3, and after stirring at 80°C for 3-5h, a clear solution was obtained by filtration;

[0015] Adding 0.5 wt % of cetyltrimethylammonium bromide solution to the clear solution, letting it stand for 1 hour to obtain a water glass solution, wherein the mass ratio of the cetyltrimethylammonium bromide solution to the clear solution is 1:5;

[0016] S4. Preparation of wet gel:

[0017] Under stirring conditions, a 10 wt % hydrochloric acid solution is added dropwise to the water glass solution until the pH reaches 8-9, and then a 0.1 wt % sodium citrate solution is added dropwise, and the mixture is stirred for reaction for 1-2 hours. 5 wt % ammonia water is added dropwise to adjust the pH of the solution to 9-10, and the mixture is allowed to stand and age at room temperature for 12-24 hours to obtain a wet gel having a three-dimensional network skeleton structure;

[0018] The volume ratio of the sodium citrate solution to the water glass solution is 1:10;

[0019] S5, substitution modification:

[0020] The wet gel prepared by S4 was soaked in anhydrous ethanol for 3-4 hours, then taken out and soaked in dimethyl carbonate solution for another 3-4 hours;

[0021] Continue soaking in the modified solution for 3-4 hours, then take it out and wash it with anhydrous ethanol;

[0022] Continue to immerse in 2~5wt% trimethoxymethylsilane anhydrous ethanol solution and react at 50~60℃ for 3h to complete the replacement modification;

[0023] S6. Drying at normal pressure to obtain a hydrophobic silica aerogel based on desert sand:

[0024] Use filter paper to absorb the surface moisture of the wet gel after S5 replacement modification, place it in a drying oven, and slowly heat it to 60~120℃ at a heating rate of 1~2℃ / min. The drying time is 6h to obtain hydrophobic silica aerogel based on desert sand.

[0025] Preferably, in S1, the dispersion solution comprises 0.5 wt% lanolin ethanol solution and 0.5 wt% sodium chloroethylsulfonate solution in a volume ratio of 1:1.

[0026] Preferably, in S4, while adding the sodium citrate solution, the step also includes adding a modified suspension, and the volume ratio of the modified suspension to the water glass solution is 1:(10-20).

[0027] Preferably, the method for preparing the modified suspension comprises the following steps:

[0028] The fullerene derivative C60 is dissolved in anhydrous ethanol at a mass ratio of 0.1:100, and then cerium oxide nanoparticles are added to obtain a dispersion, wherein the mass ratio of the cerium oxide nanoparticles to the fullerene derivative C60 is 1:1;

[0029] Dopamine hydrochloride was dissolved in ammonia water to obtain a 0.1 wt % dopamine hydrochloride solution, which was added to the dispersion to obtain a modified suspension. The mass ratio of the dopamine hydrochloride solution to the dispersion was 1:5.

[0030] Preferably, the particle size of the cerium oxide nanoparticles is 5-20 nm.

[0031] Preferably, the modified solution is a mixed solution of lithium stearate and sodium dodecylbenzenesulfonate, the concentration of lithium stearate is 1 wt %, and the mass ratio of lithium stearate to sodium dodecylbenzenesulfonate is 1:1.

[0032] Preferably, in S1, when the powder and the dispersed solution are mixed, ultrasonic treatment is adopted, with an ultrasonic frequency of 40-60 kHz, a power of 200-300 W, and a time of 20-30 min.

[0033] Preferably, in S6, the drying oven includes a normal pressure drying oven and a blast drying oven;

[0034] After using filter paper to absorb the surface moisture of the wet gel after S5 replacement modification, the following steps are also included:

[0035] First, dry in a normal pressure drying oven at room temperature with ventilation for 12 hours, and then dry at 60-120℃;

[0036] When drying at 60-120°C, the following steps are also included:

[0037] The samples were dried in a forced air drying oven at temperatures of 60°C, 90°C and 120°C, respectively, and the drying time at each temperature was 2 h.

[0038] In a second aspect, a desert sand-based hydrophobic silica aerogel is provided, which is prepared by any of the above methods for preparing a desert sand-based hydrophobic silica aerogel.

[0039] In a third aspect, a use of the above-mentioned desert sand-based hydrophobic silica aerogel in a composite thermal insulation material is provided.

[0040] The beneficial effects of the technical solution provided by this application include:

[0041] The present application provides a hydrophobic silica aerogel based on desert sand, a preparation method thereof, and an application thereof. Desert sand, which is abundant in reserves and inexpensive, is used as a raw material. In a pretreatment step, hydrochloric acid is first reacted with impurities such as calcium carbonate that may be present to remove the impurities. Then, a dispersing liquid is used to disperse the desert sand particles to ensure the dispersibility of the desert sand particles during calcination activation. Sodium sesquicarbonate decomposes during calcination to produce carbon dioxide and sodium carbonate. The carbon dioxide gas forms tiny pores in the material and provides an alkaline environment to promote the dissolution of silica in the desert sand. When preparing the wet gel, sodium citrate and the modified suspension are added. The sodium citrate undergoes complexation with the metal ions in the solution, slowing down the hydrolysis rate of the sodium silicate and avoiding excessive local hydrolysis that leads to uneven gelation, thereby controlling the sol-gel reaction rate. The modified suspension enhances the mechanical strength of the aerogel, and then the aerogel is modified through displacement to form a uniform pore structure, thereby improving the surface hydrophobicity and water resistance of the aerogel. Finally, the cost is further reduced by drying at normal pressure, thereby reducing the problem of desert sand accumulation and production costs. At the same time, the obtained aerogel material has good mechanical strength, broadening the application field of desert sand. Therefore, it can solve the related problems mentioned in the background technology to a certain extent. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without any creative work.

[0043] Figure 1 A flow chart of the method for preparing hydrophobic silica aerogel based on desert sand provided in this application;

[0044] Figure 2 This is a photo of the hydrophobic silica aerogel based on desert sand prepared in Example 1 provided in this application;

[0045] Figure 3 This is a scanning electron microscope image of the hydrophobic silica aerogel based on desert sand prepared in Example 1 provided in this application;

[0046] Figure 4 This is a hydrophobic angle diagram of the hydrophobic silica aerogel based on desert sand prepared in Example 1 provided in this application;

[0047] Figure 5 This is a Fourier transform infrared spectrum of the hydrophobic silica aerogel based on desert sand prepared in Example 1 provided in this application;

[0048] Figure 6 Schematic diagram of thermal conductivity and compressive strength of composite insulation materials with different dosages of hydrophobic silica aerogel based on desert sand provided in this application. DETAILED DESCRIPTION

[0049] To make the purpose, technical solutions, and advantages of the embodiments of this application more clear, the technical solutions in the embodiments of this application will be clearly and completely described below in conjunction with the drawings in the embodiments of this application. Obviously, the described embodiments are part of the embodiments of this application, not all of the embodiments. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of this application.

[0050] See also Figures 1 to 6 As shown, the present application provides a hydrophobic silica aerogel based on desert sand and its preparation method and application.

[0051] Example 1

[0052] The method for preparing the hydrophobic silica aerogel based on desert sand provided in this embodiment comprises the following steps:

[0053] S101, pre-processing:

[0054] After washing the desert sand with water, immerse it in a 5% hydrochloric acid solution for 2 hours, filter it, and rinse it with deionized water until the rinse water is neutral;

[0055] The mixture was ball-milled through a 200-mesh sieve and magnetically separated to remove magnetic materials to obtain a powder. 500 g of the powder was ultrasonically mixed with 4 L of the dispersion solution and filtered to obtain a pretreated powder. The ultrasonic frequency was 50 kHz, the power was 200 W, and the time was 25 min.

[0056] S102, calcination activation:

[0057] 500 g of pretreated powder was mixed evenly with 100 g of sodium sesquicarbonate, and then heated to 650 ° C at a heating rate of 5 ° C / min and kept at this temperature for 2 h to complete the calcination activation and obtain activated slag;

[0058] S103, preparing water glass solution:

[0059] 500 g of activated slag was mixed with 300 g of sodium hydroxide, and 2.4 L of deionized water was added to make the solid-liquid ratio reach 1:3. After stirring at 80 °C for 4 h, a clear solution was obtained by filtration.

[0060] 640 mL of 0.5 wt% hexadecyltrimethylammonium bromide solution was added to the clear solution, and the solution was allowed to stand for 1 h to obtain a water glass solution.

[0061] S104, preparing wet gel:

[0062] Under stirring conditions, 10 wt % hydrochloric acid solution was added dropwise to 2 L of the water glass solution prepared by S103 above until the pH reached 8, and then 200 mL of 0.1 wt % sodium citrate solution and 125 mL of the modified suspension were added dropwise. The reaction was stirred for 2 h, and 5 wt % ammonia water was added dropwise to adjust the solution pH to 9. The solution was allowed to stand and age at room temperature for 24 h to obtain a wet gel with a three-dimensional network skeleton structure.

[0063] S105, substitution modification:

[0064] The wet gel prepared by S104 was soaked in anhydrous ethanol for 3 h, then taken out and soaked in dimethyl carbonate solution for another 3 h;

[0065] After continuing to soak in the modified solution for 4 hours, take it out and wash it with anhydrous ethanol;

[0066] The product was then immersed in a 3 wt% trimethoxymethylsilane anhydrous ethanol solution and reacted at 55°C for 3 h to complete the replacement modification.

[0067] S106, drying at normal pressure to obtain a hydrophobic silica aerogel based on desert sand:

[0068] Use filter paper to absorb the surface moisture of the wet gel after S105 replacement modification, first ventilate and dry it in a normal pressure drying oven at room temperature for 12 hours, and then dry it step by step in a blast drying oven, heating it to three temperatures at a heating rate of 2°C / min, namely 60°C, 90°C, and 120°C, and pause the heating at 60°C, 90°C, and 120°C for drying, and the drying time at each temperature is 2 hours.

[0069] The S101 dispersion solution is a mixture of 2 L of 0.5 wt% lanolin ethanol solution and 2 L of 0.5 wt% sodium chloroethylsulfonate solution.

[0070] The method for preparing the modified suspension in S104 comprises the following steps:

[0071] 0.12 g of fullerene derivative C60 was dissolved in 120 g of anhydrous ethanol, and then 0.12 g of cerium oxide nanoparticles (particle size 8-10 nm) was added to obtain a dispersion;

[0072] 0.05 g of dopamine hydrochloride was dissolved in 50 g of 25% ammonia water to obtain a 0.1 wt% dopamine hydrochloride solution. 24 g of the dopamine hydrochloride solution was added to the above dispersion to obtain a modified suspension.

[0073] The modified solution in S105 is a mixture of 2 L of 1 wt % lithium stearate solution and 2 L of 1 wt % sodium dodecylbenzenesulfonate solution.

[0074] Example 2

[0075] The difference from Example 1 is that S6 includes the following steps:

[0076] Using filter paper, the surface moisture of the wet gel after S5 replacement modification was absorbed, and then placed in a drying oven, slowly heated to 100°C at a heating rate of 2°C / min, and dried for 6 hours to obtain a hydrophobic silica aerogel based on desert sand.

[0077] Example 3

[0078] The difference from Example 1 is that no modification suspension is added to S4.

[0079] Example 4

[0080] The method for preparing the hydrophobic silica aerogel based on desert sand provided in this embodiment comprises the following steps:

[0081] S401, pre-processing:

[0082] After washing the desert sand with water, immerse it in a 5% hydrochloric acid solution for 3 hours, filter it, and rinse it with deionized water until the rinse water is neutral;

[0083] The mixture was ball-milled through a 200-mesh sieve and subjected to magnetic separation to remove magnetic materials to obtain a powder. 500 g of the powder was ultrasonically mixed with 2.5 L of the dispersion solution and filtered to obtain a pretreated powder. The ultrasonic frequency was 60 kHz, the power was 200 W, and the time was 20 min.

[0084] S402, calcination activation:

[0085] 500 g of pretreated powder was mixed evenly with 100 g of sodium sesquicarbonate, and then heated to 750 ° C at a heating rate of 8 ° C / min and kept at this temperature for 2 h to complete the calcination activation and obtain activated slag;

[0086] S403, preparing water glass solution:

[0087] 500 g of activated slag was mixed with 250 g of sodium hydroxide, and 2.25 L of deionized water was added to make the solid-liquid ratio reach 1:3. After stirring at 80 °C for 3 h, a clear solution was obtained by filtration.

[0088] 600 mL of 0.5 wt% hexadecyltrimethylammonium bromide solution was added to the clear solution, and the solution was allowed to stand for 1 h to obtain a water glass solution.

[0089] S404, preparing wet gel:

[0090] Under stirring conditions, 10 wt % hydrochloric acid solution was added dropwise to 2 L of the water glass solution prepared by S403 above until the pH reached 9, and then 200 mL of 0.1 wt % sodium citrate solution and 100 mL of the modified suspension were added dropwise. The reaction was stirred for 1 h, and 5 wt % ammonia water was added dropwise to adjust the solution pH to 10. The solution was allowed to stand and age at room temperature for 20 h to obtain a wet gel with a three-dimensional network skeleton structure.

[0091] S405, substitution modification:

[0092] The wet gel prepared by S404 was soaked in anhydrous ethanol for 3 h, then taken out and soaked in dimethyl carbonate solution for another 3 h;

[0093] After continuing to soak in the modified solution for 3 hours, take it out and wash it with anhydrous ethanol;

[0094] The product was then immersed in a 5 wt% trimethoxymethylsilane anhydrous ethanol solution and reacted at 50°C for 3 h to complete the replacement modification.

[0095] S406, drying at normal pressure to obtain a hydrophobic silica aerogel based on desert sand:

[0096] Use filter paper to absorb the surface moisture of the wet gel after S405 replacement modification, first ventilate and dry it at room temperature in a normal pressure drying oven for 12 hours, and then dry it step by step in a blast drying oven, heating it to three temperatures at a heating rate of 2°C / min, namely 60°C, 90°C, and 120°C, and pause the heating at 60°C, 90°C, and 120°C for drying, and the drying time at each temperature is 2 hours.

[0097] The dispersed solution in S401, the modified suspension in S404, and the modified solution in S405 are the same as those in Example 1.

[0098] Example 5

[0099] The method for preparing the hydrophobic silica aerogel based on desert sand provided in this embodiment comprises the following steps:

[0100] S501, pre-processing:

[0101] After washing the desert sand with water, immerse it in a 5% hydrochloric acid solution for 2 hours, filter it, and rinse it with deionized water until the rinse water is neutral;

[0102] The mixture was ball-milled through a 200-mesh sieve and magnetically separated to obtain a powder. 500 g of the powder was ultrasonically mixed with 5 L of the dispersion solution and filtered to obtain a pretreated powder. The ultrasonic frequency was 40 kHz, the power was 300 W, and the time was 30 min.

[0103] S502, calcination activation:

[0104] 500 g of pretreated powder was mixed evenly with 100 g of sodium sesquicarbonate, and then heated to 600 ° C at a heating rate of 10 ° C / min and kept at this temperature for 2 h to complete the calcination activation and obtain activated slag;

[0105] S503, preparing water glass solution:

[0106] 500 g of activated slag was mixed with 400 g of sodium hydroxide, and 2.7 L of deionized water was added to make the solid-liquid ratio reach 1:3. After stirring at 80 °C for 5 h, a clear solution was obtained by filtration.

[0107] 600 mL of 0.5 wt% hexadecyltrimethylammonium bromide solution was added to the clear solution, and the solution was allowed to stand for 1 h to obtain a water glass solution.

[0108] S504, preparing wet gel:

[0109] Under stirring conditions, 10 wt % hydrochloric acid solution was added dropwise to 2 L of the water glass solution prepared in S503 above until the pH reached 8, and then 200 mL of 0.1 wt % sodium citrate solution and 200 mL of the modified suspension were added dropwise. The reaction was stirred for 1 h, and 5 wt % ammonia water was added dropwise to adjust the solution pH to 9. The solution was allowed to stand and age at room temperature for 12 h to obtain a wet gel with a three-dimensional network skeleton structure.

[0110] S505, replacement modification:

[0111] The wet gel prepared by S504 was immersed in anhydrous ethanol for 4 h, and then taken out and immersed in dimethyl carbonate solution for another 4 h;

[0112] After continuing to soak in the modified solution for 3 hours, take it out and wash it with anhydrous ethanol;

[0113] The product was then immersed in a 2 wt% trimethoxymethylsilane anhydrous ethanol solution and reacted at 60°C for 3 h to complete the replacement modification.

[0114] S506, drying at normal pressure to obtain a hydrophobic silica aerogel based on desert sand:

[0115] Use filter paper to absorb the surface moisture of the wet gel after S505 replacement modification, first ventilate and dry it at room temperature in a normal pressure drying oven for 12 hours, and then dry it step by step in a blast drying oven, heating it to three temperatures at a heating rate of 2°C / min, namely 60°C, 90°C, and 120°C, and pause the heating at 60°C, 90°C, and 120°C for drying, and the drying time at each temperature is 2 hours.

[0116] The modified solution in S505 is consistent with that in Example 1.

[0117] The dispersion solution in S501 is a mixture of 2.5 L of a 0.5 wt % lanolin ethanol solution and 2.5 L of a 0.5 wt % sodium chloroethylsulfonate solution.

[0118] The preparation method of the modified suspension in S504 comprises the following steps:

[0119] 0.2 g of fullerene derivative C60 was dissolved in 200 g of anhydrous ethanol, and then 0.2 g of cerium oxide nanoparticles (particle size 10-20 nm) was added to obtain a dispersion;

[0120] 0.05 g of dopamine hydrochloride was dissolved in 50 g of 25% ammonia water to obtain a 0.1 wt% dopamine hydrochloride solution. 40 g of the dopamine hydrochloride solution was added to the above dispersion and mixed evenly to obtain a modified suspension.

[0121] Comparative Example 1

[0122] The difference from Example 1 is that S101 is replaced by the following steps:

[0123] After washing the desert sand with water, immerse it in a 5% hydrochloric acid solution for 2 hours, filter it, and rinse it with deionized water until the rinse water is neutral;

[0124] The pretreated powder was obtained by ball milling, passing through a 200-mesh sieve, and magnetic separation to remove magnetic substances.

[0125] Comparative Example 2

[0126] The difference from Example 1 is that S102 is replaced by the following steps:

[0127] 500 g of pretreated powder was taken, heated to 650° C. at a heating rate of 5° C. / min, and kept warm for 2 h to complete calcination activation and obtain activated slag.

[0128] Comparative Example 3

[0129] The difference from Example 1 is that S104 and S105 are replaced by the following steps:

[0130] Under magnetic stirring, 1 mol / L sulfuric acid was added to 2 L of the prepared water glass solution to adjust its pH to 8, and the wet gel was obtained after gelation. After the wet gel was aged for 24 h, it was placed in a 45 ° C water bath for washing to remove the Na + , obtaining a wet gel;

[0131] The wet gel is immersed in anhydrous ethanol for 3 hours for replacement, and the replacement is repeated 3 times to obtain an alcohol gel; a modification mixture is prepared, and the alcohol gel is placed in the modification mixture for surface modification and replacement, thereby completing the replacement modification.

[0132] The modified mixed solution includes n-hexane, ethanol, and trimethylchlorosilane (TMCS), the amount of n-hexane is 50 mL, the molar ratio of TMCS to ethanol is 1, and the amount of TMCS is 75% of the volume of the alcohol gel.

[0133] The hydrophobic silica aerogels based on desert sand (hereinafter referred to as aerogels) prepared by the preparation methods of Examples 1 to 5 and Comparative Examples 1 to 3 were tested.

[0134] Bending strength test:

[0135] With reference to GB / T232-2024 “Metallic Material Bending Test Method”, the aerogel was cut into 10mm×10mm×50mm rectangular specimens (the length direction is the force direction), ensuring that the surface is flat and free of cracks; a universal material testing machine (Instron5967) was used to fix the three-point bending fixture (loading head radius 2mm) on the testing machine, and the distance between the two support points of the three-point bending fixture was adjusted to 40mm. The specimen was placed flat on the two support points, ensuring that the axis of the specimen was perpendicular to the support points. The loading head was aligned with the center of the specimen, and a preload of 0.01N was applied. Then, a vertical downward load was applied at a rate of 0.1mm / min until the specimen broke, and the maximum failure load P was recorded. max and the displacement at fracture. The flexural strength is calculated as follows:

[0136]

[0137] Where MOR is the bending strength (MPa), L is the support point distance (40mm), b is the specimen width (10mm), h is the specimen thickness (10mm), P max is the maximum failure load when the specimen breaks.

[0138] Tap density test:

[0139] Grind the aerogel into a powder with a particle size of 500 μm; weigh the weight of the measuring cylinder and record it as m1, and pour the aerogel powder into the measuring cylinder to half its volume; fix the measuring cylinder to a tap density meter and vibrate it at an amplitude of 3 mm and a frequency of 250 times / min for 10 minutes. After the vibration, record the volume V of the aerogel powder and the weight m2 of the measuring cylinder + aerogel powder. The tap density is calculated as follows:

[0140]

[0141] Where ρ is the tap density (g / cm 3 ).

[0142] The specific test results are shown in Table 1.

[0143] Table 1

[0144]

[0145] The aerogel prepared in Example 1 has high flexural strength and low tap density, indicating that the desert sand is evenly dispersed during pretreatment and calcination activation, resulting in well-developed pores in the gel network. In the modified suspension added when preparing the wet gel, the fullerene derivative C60 and cerium oxide nanoparticles form a composite reinforced network. At the same time, dopamine hydrochloride and the modified solution undergo replacement cross-linking and curing to enhance the toughness of the skeleton and form stable hydrophobic channels. In the final drying step, the gradual increase in temperature also avoids pore collapse.

[0146] Compared with Example 1, Example 2 uses a different method of normal pressure drying, has a similar porosity, and has a slightly higher tap density. This indicates, to a certain extent, that long-term constant temperature drying causes the gel network to shrink slightly, resulting in increased pore closure and decreased skeleton uniformity, which in turn leads to slightly lower flexural strength.

[0147] Compared with Example 1, Example 3 does not add a modified suspension to S4, lacks C60 and cerium oxide nanoparticle reinforcement, and the gel skeleton is composed only of silica, which is fragile and easy to break. Therefore, the flexural strength is significantly reduced, the porosity is reduced, and the tap density is increased.

[0148] Compared with Example 1, in the pretreatment step, the ratio of desert sand to dispersion liquid in Example 4 is increased (more desert sand), which leads to powder agglomeration. Due to the increase in the calcination activation temperature, the formed silica aerogel particles are denser and more tightly packed, which increases the tap density and reduces the porosity.

[0149] Compared with Example 1, in Example 5, the ratio of desert sand to dispersion is reduced (too much dispersion), the powder concentration is low, and the ratio of sodium hydroxide is too high when preparing the water glass solution, the gelation process is difficult to control, and there are many skeleton defects; at the same time, the ratio of the modified suspension to the water glass solution is reduced, the nanoparticles are less supported, and the pores are easy to shrink, resulting in a decrease in porosity and an increase in tap density.

[0150] The flexural strength of the aerogels produced in Comparative Examples 1 to 3 was significantly lower than that in Example 1. The tap density of Comparative Examples 1 and 2 was significantly increased, while the porosity was significantly decreased. Because the pretreatment in Comparative Example 1 was not dispersed with a dispersing solution, the pretreated powder obtained was severely agglomerated, and the calcined product was blocky, with a relatively loose structure and large interparticle pores. In Comparative Example 2, sodium hemicarbonate was not added during calcination and activation, resulting in insufficient activation of the quartz sand in the desert sand and insufficient dissolution of the silica, leading to insufficient activation. Comparative Example 3 replaced the modification with MCS. While the hydrophobic effect was good, the 1:1 molar ratio of TMCS to ethanol resulted in an uneven modified layer and insufficient skeleton crosslinking, which in turn led to lower flexural strength.

[0151] Furthermore, the aerogel prepared in Example 1 was characterized and analyzed, and the results are shown in Figures 2 to 5 As shown, Figure 2 This is a photo of the aerogel prepared in Example 1. Figure 3 For its microscopic picture, Figure 4 Its hydrophobic angle diagram, Figure 5 Its Fourier infrared spectrum.

[0152] In the hydrophobic angle diagram, the left and right contact angles are 141.4° and 141.3° respectively, with a difference of only 0.1°, indicating that the hydrophobicity of the aerogel surface is uniform, with no obvious local hydrophilic area, and the contact angle of about 141° belongs to the high hydrophobicity category (usually >120° is strongly hydrophobic), indicating that the aerogel surface has excellent hydrophobic properties. Figure 5 It can be seen that the strong absorption peak of Si-O-Si indicates that the aerogel has a typical silica network skeleton and a high structural density.

[0153] Furthermore, the present application provides a use of the above-prepared desert sand-based hydrophobic silica aerogel in a composite thermal insulation material. The composite thermal insulation material comprises cement, water, a silane coupling agent, and the desert sand-based hydrophobic silica aerogel.

[0154] The water-cement ratio is 0.35 (mass of water / mass of cement = 0.35), the silane coupling agent is γ-aminopropyltriethoxysilane, and the mass of the hydrophobic silica aerogel based on desert sand is 0.5-3% of the mass of the cement.

[0155] Cement and water form a hardened matrix, providing structural support; silane coupling agents improve interfacial bonding; and hydrophobic silica aerogel based on desert sand fills the pores, reducing thermal conductivity and improving water resistance.

[0156] See also Figure 6 , which is a thermal conductivity diagram and compressive strength diagram of composite thermal insulation materials with different amounts of hydrophobic silica aerogel based on desert sand. The hydrophobic silica aerogel based on desert sand used is prepared in Example 1 above. It can be seen that with the increase in the amount of hydrophobic silica aerogel based on desert sand, the compressive strength of the composite thermal insulation material decreases and the thermal conductivity is improved. This application maximizes the thermal insulation effect without significantly reducing the strength of the matrix. It is finally believed that when the addition ratio of hydrophobic silica aerogel based on desert sand is 0.5%, the effect is best. At this time, the composite thermal insulation material is suitable for building walls, pipeline insulation and other fields. While utilizing the low thermal conductivity and hydrophobicity of the aerogel, the construction performance and structural strength are guaranteed by the cement matrix.

[0157] The foregoing is merely a list of specific embodiments of the present application, intended to enable those skilled in the art to understand or implement the present application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present application. Therefore, the present application is not limited to the embodiments shown herein, but is intended to conform to the broadest scope consistent with the principles and novel features of the present application.

Claims

1. A method for preparing hydrophobic silica aerogel based on desert sand, characterized in that: It includes the following steps: S1. Preprocessing: After washing the desert sand with water, immerse it in a 5% hydrochloric acid solution for 2-3 hours, filter it, and rinse it with deionized water until the rinse water is neutral. The mixture was ball-milled through a 200-mesh sieve and subjected to magnetic separation to remove magnetic materials to obtain a powder. The powder was mixed with a dispersion solution and filtered to obtain a pretreated powder. The mass volume ratio of the powder to the dispersion solution was 1 g: (5-10) mL. S2. Calcination and activation: The pretreated powder and sodium sesquicarbonate were mixed uniformly in a mass ratio of 1:0.2, and then heated to 600-750°C at a heating rate of 5-10°C / min and kept at this temperature for 2 hours to complete calcination activation and obtain activated slag; S3, preparing water glass solution: The activated slag and sodium hydroxide were mixed in a mass ratio of 1:(0.5-0.8), deionized water was added to make the solid-liquid ratio reach 1:3, and after stirring at 80°C for 3-5h, a clear solution was obtained by filtration; Adding 0.5 wt % of cetyltrimethylammonium bromide solution to the clear solution, letting it stand for 1 hour to obtain a water glass solution, wherein the mass ratio of the cetyltrimethylammonium bromide solution to the clear solution is 1:5; S4. Preparation of wet gel: Under stirring conditions, a 10 wt % hydrochloric acid solution is added dropwise to the water glass solution until the pH reaches 8-9, and then a 0.1 wt % sodium citrate solution is added dropwise, and the mixture is stirred for reaction for 1-2 hours. 5 wt % ammonia water is added dropwise to adjust the pH of the solution to 9-10, and the mixture is allowed to stand and age at room temperature for 12-24 hours to obtain a wet gel having a three-dimensional network skeleton structure; The volume ratio of the sodium citrate solution to the water glass solution is 1:10; S5, substitution modification: The wet gel prepared by S4 was soaked in anhydrous ethanol for 3-4 hours, then taken out and soaked in dimethyl carbonate solution for another 3-4 hours; After continuing to soak in the modification solution for 3 to 4 hours, take it out and wash it with anhydrous ethanol. The modification solution is a mixed solution of lithium stearate and sodium dodecylbenzene sulfonate, the concentration of lithium stearate is 1wt%, and the mass ratio of lithium stearate to sodium dodecylbenzene sulfonate is 1:1; Continue to immerse in 2~5wt% trimethoxymethylsilane anhydrous ethanol solution and react at 50~60℃ for 3h to complete the replacement modification; S6. Drying at normal pressure to obtain a hydrophobic silica aerogel based on desert sand: Use filter paper to absorb the surface moisture of the wet gel after S5 replacement modification, place it in a drying oven, and slowly heat it to 60~120℃ at a heating rate of 1~2℃ / min. The drying time is 6h to obtain hydrophobic silica aerogel based on desert sand.

2. The method for preparing a hydrophobic silica aerogel based on desert sand according to claim 1, wherein: In S1, the dispersion solution includes 0.5 wt% lanolin ethanol solution and 0.5 wt% sodium chloroethylsulfonate solution in a volume ratio of 1:

1.

3. The method for preparing a hydrophobic silica aerogel based on desert sand according to claim 1, wherein: In said S4, while adding the sodium citrate solution, it also includes adding a modified suspension, and the volume ratio of the modified suspension to the water glass solution is 1: (10-20); The preparation method of the modified suspension comprises the following steps: The fullerene derivative C60 is dissolved in anhydrous ethanol at a mass ratio of 0.1:100, and then cerium oxide nanoparticles are added to obtain a dispersion, wherein the mass ratio of the cerium oxide nanoparticles to the fullerene derivative C60 is 1:1; Dopamine hydrochloride was dissolved in ammonia water to obtain a 0.1 wt % dopamine hydrochloride solution, which was added to the dispersion to obtain a modified suspension. The mass ratio of the dopamine hydrochloride solution to the dispersion was 1:

5.

4. The method for preparing a hydrophobic silica aerogel based on desert sand according to claim 3, wherein: The particle size of the cerium oxide nanoparticles is 5-20 nm.

5. The method for preparing a hydrophobic silica aerogel based on desert sand according to claim 1, wherein: In the above-mentioned S1, when the powder and the dispersed solution are mixed, ultrasonic treatment is adopted, and the ultrasonic frequency is 40-60kHz, the power is 200-300W, and the time is 20-30min.

6. The method for preparing a hydrophobic silica aerogel based on desert sand according to claim 1, wherein: In S6, the drying oven includes a normal pressure drying oven and a blast drying oven; After using filter paper to absorb the surface moisture of the wet gel after S5 replacement modification, the following steps are also included: First, dry in a normal pressure drying oven at room temperature with ventilation for 12 hours, and then dry at 60-120℃; When drying at 60-120°C, the following steps are also included: The samples were dried in a forced air drying oven at temperatures of 60°C, 90°C and 120°C, respectively, and the drying time at each temperature was 2 h.

7. A desert sand-based hydrophobic silica aerogel, prepared by the method for preparing a desert sand-based hydrophobic silica aerogel according to any one of claims 1 to 6.

8. Use of the desert sand-based hydrophobic silica aerogel according to claim 7 in composite thermal insulation materials.

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