Preparation method of nanofiber reinforced aerogel inorganic fiber composite material

Abstract

The present invention provides a method for preparing a nanofiber-reinforced aerogel inorganic fiber composite material. By chemically etching the inorganic fiber material, the surface energy of the material is increased, and the adhesion and adhesiveness of the inorganic fiber material are improved. Then, the surface of the inorganic fiber material is subjected to plasma treatment. When the plasma generated by the inert gas bombards to further increase the surface roughness of the material, the plasma generated by the hydrocarbon gas forms a C-containing light-shielding layer with a nanoscale thickness on the surface of the inorganic fiber material, solving the problem of powder shedding of the aerogel composite material, and enabling the finally prepared aerogel composite material to have a smaller thickness and excellent mechanical properties and heat insulation properties.

Description

Technical Field

[0001] The invention relates to the field of nano aerogel materials, and in particular to a hydrophobic aerogel composite material with excellent thermal insulation and mechanical properties and a preparation method thereof. Background Art

[0002] Aerogel is a nanoporous solid material with a three-dimensional network structure formed by cross-linking of colloidal particles or polymer molecules. With its extremely low density, high specific surface area, high porosity and low thermal conductivity, aerogel has been used in aerospace, military, petrochemical, automobile and train industries.

[0003] The high porosity of silica aerogel leads to its low strength and poor toughness, and its application scenarios are greatly limited. At present, there have been many studies on the preparation technology of aerogel composite materials to overcome the disadvantages of aerogel itself: CN107208355A provides a sol-gel method to prepare a felt containing silica aerogel, which uses a supercritical method for drying, which is difficult to industrialize, and the adhesion between the fiber and the aerogel in the aerogel composite material is poor, so that the aerogel particles are separated during processing such as cutting and bending, resulting in dust and poor durability; in order to improve the composite strength of aerogel and fiber felt, CN1196035A provides a method of mixing aerogel powder with an organic or inorganic adhesive for pressing and molding. The material prepared by this method has a certain mechanical strength, but the addition of the adhesive has a negative impact on the thermal insulation performance of the aerogel; CN110870395A improves the strength of the material by compounding a multilayer sheet with a coating, but its durability, thermal insulation, mechanical strength and processing performance are all subject to the thickness of the material, and it is difficult to achieve large-scale production. Summary of the invention

[0004] In order to solve the above technical problems, the present invention provides a method for preparing a nanofiber reinforced aerogel inorganic fiber composite material, comprising the following steps:

[0005] (1) Silicon source pretreatment: Add silicon source dropwise to the acid catalyst, then add alcohol solvent, cool and lower the temperature to precipitate impurities, and obtain high-purity silica sol after impurities removal;

[0006] (2) Nanofiber doping: adding hydrophilic nanofibers to high-purity silica sol, stirring and dispersing the hydrophilic nanofibers to obtain hydrophilic nanofiber doped silica sol;

[0007] (3) Surface treatment of inorganic fiber materials: ① chemically etching the inorganic fiber materials, then cleaning and drying them to obtain inorganic fiber materials with a high specific surface area; ② plasma treating the surface of the inorganic fiber materials with a high specific surface area until the surface roughness is further increased and a C-containing sunscreen layer is formed to obtain a surface-treated inorganic fiber material;

[0008] (4) Sol-gel - inorganic fiber composite: Adjust the pH value of the hydrophilic nanofiber-doped silica sol in (2), and composite and age it with the surface-treated inorganic fiber material in (3) under vacuum negative pressure conditions to obtain a composite material;

[0009] (5) Hydrophobization modification: Add saturated concentrated hydrochloric acid to the composite material obtained in (4) for solvent replacement, and then carry out hydrophobization modification;

[0010] (6) Atmospheric drying: Alkaline wash the surface of the hydrophobically modified composite material, and dry it under atmospheric pressure to obtain a nanofiber-reinforced aerogel inorganic fiber composite material.

[0011] The mass ratio of the silicon source: deionized water: alcohol solvent: acid catalyst in (1) is 1:(0.8 - 1):(1.5 - 2):(0.8 - 1.2).

[0012] The silicon source in (1) is commercially available acidic silica sol, neutral silica sol or water glass.

[0013] The alcohol solvent in (1) is methanol, ethanol, propanol or isopropanol, preferably ethanol.

[0014] The acidic catalyst in (1) is hydrochloric acid, nitric acid, hydrofluoric acid or sulfuric acid;

[0015] The temperature for cooling down in (1) is -10 to 10 °C.

[0016] The mass ratio of the high-purity silica sol: hydrophilic nanofibers in (2) is 1:(0.001 - 0.004).

[0017] The hydrophilic nanofibers in (2) are one or more of PBO fibers, aramid fibers, and graphene carbon fibers with a high aspect ratio, having a diameter of 10 - 100 nm and a length of 30 - 300 μm.

[0018] The stirring in (2) is high-speed stirring, and the stirring speed ≥ 1500 r / min.

[0019] The inorganic fiber material in (3) is glass fiber felt, ceramic fiber felt or carbon fiber felt.

[0020] The chemical etching in (3) includes the following steps:

[0021] ① Etching solution preparation: The described etching solution is composed of hydrochloric acid and sulfuric acid, where the molar concentration of hydrochloric acid is 0.1 - 0.4 mol / L and the molar concentration of sulfuric acid is 0.05 - 0.2 mol / L;

[0022] ② Substrate etching: Place the inorganic fiber material in the etching solution and completely immerse it for etching, where the etching temperature is 10 - 50 °C and the etching time is 0.5 - 7 h;

[0023] ③ Substrate cleaning: The etched inorganic fiber material is rinsed with deionized water and dried at 80 - 300 °C.

[0024] The plasma treatment in (3) includes the following steps:

[0025] The process of the plasma treatment in (3) is as follows: Under vacuum conditions, the surface of the chemically etched inorganic fiber material is bombarded with plasma gas and a uniform C-containing light-shielding agent layer is deposited on its surface.

[0026] More specifically, this plasma treatment includes the following steps:

[0027] ① Place the chemically etched inorganic fiber substrate in a plasma reaction device and use a vacuum pump to reduce the internal pressure of the device, and the pressure is ≤ 0.1 Pa.

[0028] ② Introduce plasma gas: Fill the device with plasma gas, lead it out from the other end of the device through a vacuum pump to form a flowing state, and maintain a certain vacuum degree in the system. The vacuum degree is 1 - 10 3 Pa. The plasma gas is a mixture of an inert gas and an organic gas vapor. The inert gas is argon, and the organic gas vapor is one or several of ethylene, cyclic compounds, saturated hydrocarbon compounds, and aromatic compounds. The volume ratio of the inert gas to the organic gas vapor is 1:(1 - 9).

[0029] ③ Plasma film coating: Turn on the power of the device to ionize the gas to form plasma. The plasma bombards the inorganic fiber substrate and deposits a uniform C-containing light-shielding agent layer on its surface.

[0030] The input power during the plasma treatment process is 10 - 55 W, and the plasma treatment time is 10 - 120 mins.

[0031] The addition of an alkali catalyst in (4) adjusts the pH range to 3.8 - 5.8.

[0032] The thickness of the inorganic fiber material in (4) is 0.1 - 15 mm.

[0033] The alkali catalyst in (4) is sodium hydroxide, potassium hydroxide, aluminum hydroxide, ammonia water, basic silica sol or basic water glass solution.

[0034] The aging in (4) can be achieved by microwave heating aging in a microwave reactor. The microwave power of the microwave reactor is 0 - 800 W, and the time of microwave heating aging is 2 - 48 h.

[0035] The volume ratio of the composite material in (5) to saturated concentrated hydrochloric acid is 1:(1.7-8).

[0036] The time for solvent replacement in (5) is 2 to 4 hours.

[0037] The modifier in (5) is one or more of trimethylethoxysilane, dimethyldiethoxysilane, dimethyldimethoxysilane, methyltriethoxysilane, hexamethyldisilazane, trimethylchlorosilane or hexamethyldisiloxane.

[0038] The temperature of the modification heating in the step (5) is 45 to 85° C., and the modification time is 4 to 18 hours.

[0039] The reagent for alkali washing in (6) is one or more of sodium hydroxide, potassium hydroxide, aluminum hydroxide, ammonia water or sodium bicarbonate.

[0040] The atmospheric pressure drying in (6) is graded drying, and the graded drying process is to first dry the composite material with nitrogen hot air at 70°C for 1 to 3 hours, then dry it with nitrogen hot air at 100°C for 1 to 3 hours, then dry it with nitrogen hot air at 130°C for 1 to 3 hours, and finally dry it with nitrogen hot air at 160°C for 1 to 3 hours.

[0041] Since fiber felt is usually prepared by extruding and drawing the corresponding raw materials after melting, and then stacking and needle-punching to form a slightly dense felt, the fiber surface is relatively rough, and it is loose and flexible after stacking. Simple plasma bombardment surface treatment will lead to poor deposition effect and cannot significantly improve the powder loss problem of aerogel fiber felt composite materials. On the one hand, the present invention first uses chemical etching to make the fiber felt surface have better roughness and strength, which can provide a foundation for the subsequent plasma treatment. On the other hand, plasma etching to form a C-containing thin layer fills the defects of chemical etching to a certain extent while keeping the surface of the inorganic fiber material rough, and has a mutually complementary effect. Compared with the prior art, the present invention has the following beneficial effects:

[0042] (1) The present invention increases the surface energy of the material and improves the adhesion and cohesion of the inorganic fiber material by chemically etching the inorganic fiber material, thereby effectively solving the problem of powder loss caused by poor adhesion between conventional aerogel and inorganic fiber, and can meet various processing requirements and dust-free requirements in specific scenarios;

[0043] (2) There are many easily enriched metal oxides in the inorganic fiber, which occupy a certain space in the continuous phase of inorganic oxide to form a phase separation. The metal oxides are chemically dissolved by etching solution, thereby forming a rough structure with depressions on the surface of the inorganic fiber. When the glass fiber is compounded with the gel, some gel enters the cavities, producing an anchoring effect and enhancing the bonding force between the two phases.

[0044] (3) By subjecting the surface of the inorganic fiber material to plasma film coating treatment, when the plasma bombarded by inert gas further increases the surface roughness of the material, the plasma generated by hydrocarbon gas forms a C-containing light-shielding agent layer with a nanoscale thickness on the surface of the inorganic fiber material, which can effectively reduce the heat transfer in the form of thermal radiation under high-temperature conditions, and solve the problem of the reduction of the heat insulation performance of the composite material in a high-temperature environment;

[0045] (4) By incorporating nanofibers into the aerogel to form a three-dimensional network interpenetrating structure, the strength and toughness of the aerogel material are greatly enhanced, solving the problems of poor mechanical strength, poor processability, and limited size specifications of the aerogel composite material. The prepared aerogel composite material has a small thickness and excellent mechanical properties, greatly expanding its application scenarios. Detailed implementation manners

[0046] 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, but 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 concept of the present invention, several deformations and improvements can still be made. These all belong to the protection scope of the present invention.

[0047] Example 1: 1mm nanofiber-reinforced aerogel glass fiber composite ultra-thin felt.

[0048] Take 2.5 kg of sulfuric acid solution (wt% = 20%) and place it in a reaction kettle. Start stirring, and slowly drip diluted water glass (water glass: water = 2.5 kg: 2.5 kg) into the kettle. After the dripping is completed, keep stirring for 2 h. After sufficient hydrolysis, add 4 kg of ethanol into the kettle, start the condensation cycle of the reaction kettle, stir at a low speed of 100 r / min, keep the system at 0 °C, and carry out condensation and crystallization for 6 h. Transfer the above-mentioned liquid material to a centrifuge for centrifugal filtration to obtain the purified sol.

[0049] Accurately weigh 1 kg of aramid fiber (solid content 3.2%), and directly put it into the purified silica sol obtained in the previous step. Stir with a high-speed dispersion disk at 1800 r / min for 30 mins to make it fully mixed and uniform, and obtain a sol doped with aramid fiber.

[0050] Place a 10 m long, 0.5 m wide, 1 mm thick glass fiber ultra-thin felt completely immersed in the etching solution (mHCl = 0.1 mol / L, mH2SO4 = 0.05 mol / L), start the circulation and treat at room temperature. After reacting for 3 h, drain all the etching solution, and introduce deionized water into the kettle to rinse the glass fiber ultra-thin felt until the pH of the cleaning residue is 6. Take out the glass fiber ultra-thin felt and transfer it to an oven for drying at 120 °C for later use.

[0051] Place the glass fiber ultra-thin felt after the previous drying step into the plasma reaction device. Wait until the vacuum pump reduces the pressure in the device to 0.1 Pa, then fill the device with ethylene / argon = 3:1 and adjust the pressure in the system to 20 Pa. Turn on the power input of 15 W and process for 30 minutes.

[0052] Wind the plasma-treated glass fiber ultra-thin felt and place it in a vacuum container. Drop the alkaline sodium silicate solution into the doped silica sol, adjust the pH of the system to 4 to obtain a sol solution. Use the pressure difference to pump the sol solution into the vacuum container until it completely submerges the wound glass fiber ultra-thin felt, and maintain a negative pressure. Turn on the microwave generator outside the vacuum device, set the microwave power to 200 W to accelerate gel formation, and continuously turn it on for 6 hours to accelerate gel aging.

[0053] After aging is completed, transfer the obtained aged composite material to a reaction kettle. Add 20 L of concentrated hydrochloric acid (wt% = 36%) to the kettle, turn on the circulation device for solvent replacement for 3 hours, drain the replaced waste liquid, add 20 L of hexamethyldisiloxane to the kettle, turn on the circulation device and heating device, and keep the system temperature at 70 °C for hydrophobic modification for 12 hours.

[0054] After the modification is completed, drain the liquid in the kettle, use a 5% (wt%) sodium bicarbonate solution to rinse the surface of the composite material to remove the residual acid solution and modifier. Transfer the composite material to a hot air drying device, and set the stepwise drying temperatures at 70 °C, 100 °C, 130 °C, and 160 °C for 2 hours each. After drying is completed, the aramid fiber-reinforced aerogel glass fiber composite ultra-thin felt is obtained.

[0055] Example 2: 2 mm nanofiber-reinforced aerogel ceramic fiber composite felt.

[0056] Take 2.5 kg of sulfuric acid solution (wt% = 20%) and place it in a reaction kettle. Turn on the stirring, and slowly drop the diluted sodium silicate (sodium silicate: water = 2.5 kg: 2.5 kg) into the kettle. After dropping, keep stirring for 2 hours. After sufficient hydrolysis, add 4 kg of ethanol to the kettle, turn on the condensation cycle of the reaction kettle, stir at a low speed of 100 r / min, keep the system at 0 °C, and condense and crystallize for 6 hours. Transfer the above-mentioned liquid material to a centrifuge for centrifugal filtration to obtain the impurity-removed sol.

[0057] Accurately weigh 1 kg of aramid fiber (solid content 3.2%) and directly add it to the impurity-removed silica sol obtained in the previous step. Stir it at 1800 r / min with a high-speed dispersion disk for 30 minutes to make it fully mixed and uniform, and prepare a sol doped with aramid fiber.

[0058] Place a 10m long, 0.5m wide, and 2mm thick ceramic fiber felt completely immersed in the etching solution (mHCl = 0.1mol / L, mH2SO4 = 0.05mol / L), start the circulating room temperature treatment. After reacting for 3h, drain all the etching solution, and introduce deionized water into the autoclave to rinse the ceramic fiber felt until the pH of the cleaning residue is 6. Take out the ceramic fiber felt, transfer it to an oven, dry it at 120°C, and set it aside for use.

[0059] Place the dried ceramic fiber felt from the previous step in the plasma reaction device. Wait for the vacuum pump to reduce the pressure in the device to 0.1Pa, and then fill the device with ethylene / argon = 3:1, and adjust the pressure in the system to 20Pa. Turn on the power input power of 15W and the treatment time of 30 minutes.

[0060] After winding the plasma-treated ceramic fiber felt, place it in a vacuum container. Drop the alkaline water glass solution into the doped silica sol, adjust the pH of the system to 4 to obtain a sol solution. Use the pressure difference to pump the sol solution into the vacuum container until it completely submerges the ceramic fiber felt roll, and maintain a negative pressure. Turn on the microwave generator outside the vacuum device, set the microwave power to 200W to accelerate gel formation, and continuously turn it on for 6h to accelerate gel aging.

[0061] After aging is completed, transfer the obtained aged composite material to the autoclave. Add 20L of concentrated hydrochloric acid (wt% = 36%) to the autoclave, turn on the circulating device for solvent replacement for 3h, drain the replaced waste liquid, add 20L of hexamethyldisiloxane to the autoclave, turn on the circulating device and heating device, and maintain the system temperature at 70°C for hydrophobic modification for 12h.

[0062] After the modification is completed, drain the liquid in the autoclave, and use a 5% (wt%) sodium bicarbonate solution to rinse the surface of the composite material to remove the residual acid solution and modifier. Transfer the composite material to a hot air drying device, and set the grading drying temperature at 70°C, 100°C, 130°C, and 160°C for 2h each. After drying is completed, the aramid fiber-reinforced aerogel ceramic fiber composite felt is obtained.

[0063] Example 3: 10mm nanofiber-reinforced aerogel glass fiber composite felt

[0064] Take 2.5kg of sulfuric acid solution (wt% = 20%) and place it in the autoclave. Start stirring, and slowly drip the diluted water glass (water glass: water = 2.5kg: 2.5kg) into the autoclave. After dripping, keep stirring for 2h. After sufficient hydrolysis, add 4kg of ethanol to the autoclave, turn on the condensation cycle of the autoclave, stir at a low speed of 100r / min, maintain the system at 0°C, and carry out condensation crystallization for 6h. Transfer the above-mentioned feed liquid to a centrifuge for centrifugal filtration to obtain the impurity-removed sol.

[0065] Accurately weigh 1 kg of aramid fiber (solid content 3.2%), and directly put it into the impurity-removed silica sol obtained in the previous step. Stir it at 1800 r / min with a high-speed dispersion disk for 30 minutes to make it fully and evenly mixed, and obtain a sol doped with aramid fiber.

[0066] Place a 10 m long, 0.5 m wide, and 10 mm thick glass fiber mat completely immersed in the etching solution (mHCl = 0.1 mol / L, mH2SO4 = 0.05 mol / L), start the circulating room temperature treatment. After reacting for 3 h, drain all the etching solution, and introduce deionized water into the kettle to wash the glass fiber mat until the pH of the cleaning residue is 6. Take out the glass fiber mat and transfer it to an oven for drying at 120 °C for later use.

[0067] Place the dried glass fiber mat from the previous step into the plasma reaction device. Wait until the pressure in the device is reduced to 0.1 Pa by the vacuum pump, and then fill the device with ethylene / argon = 3:1, and adjust the pressure in the system to 20 Pa. Turn on the power input power of 15 W and the treatment time of 30 minutes.

[0068] Wind the plasma-treated glass fiber mat and place it in a vacuum container. Drop the alkaline water glass solution into the doped silica sol, and adjust the pH of the system to 4 to obtain a sol solution. Use the pressure difference to pump the sol solution into the vacuum container until it completely submerges the glass fiber mat roll, and maintain a negative pressure. Turn on the microwave generator outside the vacuum device, set the microwave power to 200 W, accelerate the gel formation, and continuously turn it on for 6 h to accelerate the gel aging.

[0069] After the aging is completed, transfer the obtained aged composite material to the reaction kettle, add 20 L of concentrated hydrochloric acid (wt% = 36%) into the kettle, turn on the circulation device for solvent replacement for 3 h, drain the replacement waste liquid, add 20 L of hexamethyldisiloxane into the kettle, turn on the circulation device and the heating device, and keep the system temperature at 70 °C for hydrophobic modification for 12 h.

[0070] After the modification is completed, drain the liquid in the kettle, and use a wt% = 5% sodium bicarbonate solution to wash the surface of the composite material to remove the residual acid solution and the modifier. Transfer the composite material to the hot air drying device, and set the grading drying temperature to 70 °C, 100 °C, 130 °C, and 160 °C for 2 h each. After drying is completed, the aramid fiber-reinforced aerogel glass fiber composite mat is obtained.

[0071] Example 4: 5 mm nanofiber-reinforced aerogel ceramic fiber composite mat

[0072] Take 2.5 kg of sulfuric acid solution (wt% = 20%) and place it in a reaction kettle. Start stirring, and slowly drip diluted sodium silicate solution (sodium silicate: water = 2.5 kg: 2.5 kg) into the kettle. After the dripping is completed, keep stirring for 2 h. After sufficient hydrolysis, add 4 kg of ethanol into the kettle, start the condensation cycle of the reaction kettle, stir at a low speed of 100 r / min, keep the system at 0 °C, and carry out condensation crystallization for 6 h. Transfer the above-mentioned liquid material to a centrifuge for centrifugal filtration to obtain the purified sol.

[0073] Accurately weigh 1 kg of aramid fiber (solid content 3.2%) and directly put it into the purified silica sol obtained in the previous step. Stir with a high-speed dispersion disk at 1800 r / min for 30 mins to make it fully and evenly mixed, and prepare the sol doped with aramid fiber.

[0074] Place a 10 m long, 0.5 m wide, and 5 mm thick ceramic fiber felt completely immersed in the etching solution (mHCl = 0.1 mol / L, mH2SO4 = 0.05 mol / L). Start the circulation and treat it at room temperature. After reacting for 3 h, drain all the etching solution, and introduce deionized water into the kettle to wash the ceramic fiber felt until the pH of the residual cleaning solution is 6. Take out the ceramic fiber felt and transfer it to an oven for drying at 120 °C for later use.

[0075] Place the dried ceramic fiber felt in a plasma reaction device. Wait for the vacuum pump to reduce the pressure in the device to 0.1 Pa, and then fill the device with methane / argon = 3:1, and adjust the pressure in the system to 20 Pa. Turn on the power input power of 15 W and treat for 30 mins.

[0076] Wind the plasma-treated ceramic fiber felt and place it in a vacuum container. Drop the alkaline sodium silicate solution into the doped sol, adjust the pH of the system to 4 to obtain a sol liquid. Use the pressure difference to pump the sol liquid into the vacuum container until it completely submerges the wound ceramic fiber felt, and maintain negative pressure. Turn on the microwave generator outside the vacuum device, set the microwave power to 200 W to accelerate gel formation, and keep it on for 6 h to accelerate gel aging.

[0077] After aging is completed, transfer the obtained aged composite material to a reaction kettle. Add 20 L of concentrated hydrochloric acid (wt% = 36%) into the kettle, start the circulation device for solvent replacement for 3 h, drain the replaced waste liquid, add 20 L of hexamethyldisiloxane into the kettle, start the circulation device and heating device, and keep the system temperature at 70 °C for hydrophobic modification for 12 h.

[0078] After the modification is completed, drain the liquid in the kettle, and use a 5% (wt%) sodium bicarbonate solution to wash the surface of the composite material to remove the residual acid liquid and modifier. Transfer the composite material to a hot air drying device, and set the stepwise drying temperatures at 70 °C, 100 °C, 130 °C, and 160 °C for 2 h each. After drying is completed, the aramid fiber-reinforced aerogel ceramic fiber composite felt is obtained.

[0079] Example 5: 2mm nanofiber-reinforced aerogel carbon fiber composite felt

[0080] Take 2.5 kg of sulfuric acid solution (wt% = 20%) and place it in a reaction kettle. Start stirring, and slowly drip diluted sodium silicate (sodium silicate: water = 2.5 kg: 2.5 kg) into the kettle. After dripping, keep stirring for 2 h. After sufficient hydrolysis, add 4 kg of ethanol into the kettle. Start the condensation cycle of the reaction kettle, stir at a low speed of 100 r / min, keep the system at 0 °C, and carry out condensation crystallization for 6 h. Transfer the above-mentioned liquid material to a centrifuge for centrifugal filtration to obtain the purified sol.

[0081] Accurately weigh 1 kg of aramid fiber (solid content 3.2%), and directly put it into the purified silica sol obtained in the previous step. Stir with a high-speed dispersion disk at 1800 r / min for 30 mins to make it fully and evenly mixed, and prepare the sol doped with aramid fiber.

[0082] Place a carbon fiber felt with a length of 10 m, a width of 0.5 m, and a thickness of 2 mm completely immersed in the etching solution (mHCl = 0.1 mol / L, mH2SO4 = 0.05 mol / L). Start the circulating room temperature treatment. After reacting for 3 h, drain all the etching solution, and introduce deionized water into the kettle to wash the carbon fiber felt until the pH of the cleaning residual liquid is 6. Take out the carbon fiber felt and transfer it to an oven for drying at 120 °C for later use.

[0083] Place the dried carbon fiber felt in a plasma reaction device. Wait for the vacuum pump to reduce the pressure in the device to 0.1 Pa, and then fill the device with methane / argon = 3:1, and adjust the pressure in the system to 20 Pa. Turn on the power input power of 15 W and the treatment time of 30 mins.

[0084] Wind the plasma-treated carbon fiber felt and place it in a vacuum container. Drop the alkaline sodium silicate solution into the doped silica sol, adjust the pH of the system to 4 to obtain the sol liquid. Use the pressure difference to pump the sol liquid into the vacuum container until the carbon fiber felt roll is completely immersed, and keep negative pressure. Turn on the microwave generator outside the vacuum device, set the microwave power to 200 W, accelerate the gel formation, and continuously turn on for 6 h to accelerate the gel aging.

[0085] After aging is completed, transfer the obtained aged composite material to a reaction kettle. Add 20 L of concentrated hydrochloric acid (wt% = 36%) into the kettle, start the circulating device for solvent replacement for 3 h, drain the replaced waste liquid, add 20 L of hexamethyldisiloxane into the kettle, start the circulating device and the heating device, and keep the system temperature at 70 °C for hydrophobic modification for 12 h.

[0086] After the modification is completed, drain the liquid in the kettle, and use a 5 wt% sodium bicarbonate solution to rinse the surface of the composite material to remove the residual acid solution and the modifier. Transfer the composite material to a hot air drying device, and set the classification drying temperatures at 70 °C, 100 °C, 130 °C, and 160 °C for 2 hours each. After drying is completed, the aramid fiber-reinforced aerogel carbon fiber composite felt is obtained.

[0087] Example 6: 10 mm nanofiber-reinforced aerogel glass fiber composite felt

[0088] Take 2.5 kg of sulfuric acid solution (wt% = 20%) and place it in a reaction kettle. Start stirring, and slowly drip diluted sodium silicate solution (sodium silicate: water = 2.5 kg: 2.5 kg) into the kettle. After dripping is completed, keep stirring for 2 hours. After sufficient hydrolysis, add 4 kg of ethanol into the kettle, start the condensation cycle of the reaction kettle, stir at a low speed of 100 r / min, keep the system at 0 °C, and carry out condensation crystallization for 6 hours. Transfer the above-mentioned feed liquid to a centrifuge for centrifugal filtration to obtain the purified sol.

[0089] Accurately weigh 1 kg of aramid fiber (solid content 3.2%), and directly put it into the purified silica sol obtained in the previous step. Stir with a high-speed dispersion disk at 1800 r / min for 30 minutes to make it fully mixed and uniform, and prepare a sol doped with aramid fiber.

[0090] Place a 10 m long, 0.5 m wide, and 10 mm thick glass fiber felt completely immersed in the etching solution (mHCl = 0.1 mol / L, mH2SO4 = 0.05 mol / L). Start the circulation and treat it at room temperature. After reacting for 3 hours, drain all the etching solution, and introduce deionized water into the kettle to rinse the glass fiber felt until the pH of the cleaning residual liquid is 6. Take out the glass fiber felt, transfer it to an oven, and dry it at 120 °C for later use.

[0091] Place the dried glass fiber felt in a plasma reaction device. Wait for the vacuum pump to reduce the pressure in the device to 0.1 Pa, and then fill the device with methane / argon = 9:1, and adjust the pressure in the system to 20 Pa. Turn on the power input power of 15 W and the treatment time of 30 minutes.

[0092] Wind up the plasma-treated glass fiber felt and place it in a vacuum container. Drop the alkaline sodium silicate solution into the doped silica sol, adjust the pH of the system to 4 to obtain a sol liquid. Use the pressure difference to pump the sol liquid into the vacuum container until it completely submerges the glass fiber felt roll, and maintain negative pressure. Turn on the microwave generator outside the vacuum device, set the microwave power to 200 W, accelerate the gel formation, and continuously turn it on for 6 hours to accelerate the gel aging.

[0093] After the aging is completed, transfer the aged composite material obtained to a reaction kettle, add 20 L of concentrated hydrochloric acid (wt% = 36%) into the kettle, start the circulation device for solvent replacement for 3 h, drain the replaced waste liquid, add 20 L of hexamethyldisiloxane into the kettle, start the circulation device and heating device, and keep the system temperature at 70 °C for hydrophobic modification for 12 h.

[0094] After the modification is completed, drain the liquid in the kettle, and use a sodium bicarbonate solution with wt% = 5% to rinse the surface of the composite material to remove the residual acid solution and modifier. Transfer the composite material to a hot air drying device, and set the grading drying temperatures at 70 °C, 100 °C, 130 °C, and 160 °C for 2 h each. After drying is completed, the aramid fiber-reinforced aerogel glass fiber composite felt is obtained.

[0095] Comparative Example 1: 10 mm nanofiber-reinforced aerogel glass fiber composite felt

[0096] Put 2.5 kg of sulfuric acid solution (wt% = 20%) into a reaction kettle, start stirring, and slowly drip diluted water glass (water glass: water = 2.5 kg: 2.5 kg) into the kettle. After dripping is completed, keep stirring for 2 h. After sufficient hydrolysis, add 4 kg of ethanol into the kettle, start the condensation cycle of the reaction kettle, stir at a low speed of 100 r / min, keep the system at 0 °C, and carry out condensation crystallization for 6 h. Transfer the above-mentioned liquid material to a centrifuge for centrifugal filtration to obtain the purified sol.

[0097] Accurately weigh 1 kg of aramid fiber (solid content 3.2%), directly put it into the purified silica sol obtained in the previous step, and stir it at 1800 r / min with a high-speed dispersion disk for 30 mins to make it fully mixed evenly, thus obtaining the sol doped with aramid fiber.

[0098] Place a glass fiber felt with a length of 10 m, a width of 0.5 m, and a thickness of 10 mm completely immersed in the etching solution (mHCl = 0.1 mol / L, mH2SO4 = 0.05 mol / L), start the circulation and treat it at room temperature. After reacting for 3 h, drain all the etching solution, and pass deionized water into the kettle to rinse the glass fiber felt until the pH of the cleaning residual liquid is 6. Take out the glass fiber felt and transfer it to an oven for drying at 120 °C for later use.

[0099] Wind the chemically etched glass fiber felt and place it in a vacuum container. Drop the alkaline water glass solution into the doped silica sol, adjust the system pH = 4 to obtain the sol liquid. Use the pressure difference to pump the sol liquid into the vacuum container until the glass fiber felt roll is completely immersed, and keep negative pressure. Start the microwave generator outside the vacuum device, set the microwave power at 200 W to accelerate gel formation, and continuously turn it on for 6 h to accelerate gel aging.

[0100] After aging is completed, transfer the aged composite material obtained to a reaction kettle, add 20 L of concentrated hydrochloric acid (wt% = 36%) into the kettle, start the circulation device for solvent replacement for 3 h, drain the replaced waste liquid, add 20 L of hexamethyldisiloxane into the kettle, start the circulation device and heating device, and maintain the system temperature at 70 °C for hydrophobic modification for 12 h.

[0101] After the modification is completed, drain the liquid in the kettle, and use a sodium bicarbonate solution with wt% = 5% to rinse the surface of the composite material to remove the residual acid liquid and modifier. Transfer the composite material to a hot air drying device, and set the grading drying temperatures at 70 °C, 100 °C, 130 °C, and 160 °C for 2 h each. After drying is completed, the aramid fiber-reinforced aerogel glass fiber composite felt is obtained.

[0102] Comparative Example 2: 10 mm nanofiber-reinforced aerogel glass fiber composite felt

[0103] Put 2.5 kg of sulfuric acid solution (wt% = 20%) into a reaction kettle, start stirring, and slowly add diluted sodium silicate (sodium silicate: water = 2.5 kg: 2.5 kg) into the kettle dropwise. After the dropping is completed, keep stirring for 2 h. After sufficient hydrolysis, add 4 kg of ethanol into the kettle, start the condensation cycle of the reaction kettle, stir at a low speed of 100 r / min, keep the system at 0 °C, and carry out condensation crystallization for 6 h. Transfer the above-mentioned slurry to a centrifuge for centrifugal filtration to obtain the impurity-removed sol.

[0104] Accurately weigh 1 kg of aramid fiber (solid content 3.2%), and directly add it into the impurity-removed silica sol obtained in the previous step. Stir with a high-speed dispersion disk at 1800 r / min for 30 mins to make it fully mixed evenly, and prepare a sol doped with aramid fiber.

[0105] Place a 10 m long, 0.5 m wide, and 10 mm thick glass fiber felt in a plasma reaction device. Wait until the pressure in the device is reduced to 0.1 Pa by a vacuum pump, and then fill the device with methane / argon = 9:1, and adjust the pressure in the system to 20 Pa. Turn on the power input power of 15 W and the treatment time of 30 mins.

[0106] After winding the plasma-treated glass fiber felt, place it in a vacuum container. Dropwise add an alkaline sodium silicate solution into the doped silica sol, adjust the pH of the system to 4 to obtain a sol solution. Use the pressure difference to pump the sol solution into the vacuum container until the glass fiber felt roll is completely immersed, and maintain negative pressure. Turn on the microwave generator outside the vacuum device, set the microwave power to 200 W, accelerate gel formation, and continuously turn it on for 6 h to accelerate gel aging.

[0107] After the aging is completed, transfer the aged composite material obtained to a reaction kettle, add 20 L of concentrated hydrochloric acid (wt% = 36%) into the kettle, start the circulation device for solvent replacement for 3 h, drain the replaced waste liquid, add 20 L of hexamethyldisiloxane into the kettle, start the circulation device and heating device, and maintain the system temperature at 70 °C for hydrophobic modification for 12 h.

[0108] After the modification is completed, drain the liquid in the kettle, and use a sodium bicarbonate solution with wt% = 5% to rinse the surface of the composite material to remove the residual acid solution and modifier. Transfer the composite material to a hot air drying device, and set the grading drying temperatures at 70 °C, 100 °C, 130 °C, and 160 °C for 2 h each. After drying is completed, the aramid fiber-reinforced aerogel glass fiber composite felt is obtained.

[0109] Comparative Example 3: 10 mm nanofiber-reinforced aerogel glass fiber composite felt

[0110] Place 2.5 kg of sulfuric acid solution (wt% = 20%) in a reaction kettle, start stirring, and slowly add diluted sodium silicate (sodium silicate: water = 2.5 kg: 2.5 kg) into the kettle. After the addition is completed, keep stirring for 2 h. After sufficient hydrolysis, add 4 kg of ethanol into the kettle, start the condensation cycle of the reaction kettle, stir at a low speed of 100 r / min, maintain the system at 0 °C, and carry out condensation crystallization for 6 h. Transfer the above-mentioned slurry to a centrifuge for centrifugal filtration to obtain the purified sol.

[0111] Accurately weigh 1 kg of aramid fiber (solid content 3.2%), and directly add it into the purified silica sol obtained in the previous step. Use a high-speed dispersing disk to stir at 1800 r / min for 30 mins to make it fully mixed uniformly, and prepare a sol doped with aramid fiber.

[0112] Wind a ceramic fiber felt with a length of 10 m, a width of 0.5 m, and a thickness of 10 mm and place it in a vacuum container. Drop an alkaline sodium silicate solution into the doped silica sol to adjust the pH of the system to 4 to obtain a sol liquid. Use the pressure difference to pump the sol liquid into the vacuum container until it completely submerges the wound ceramic fiber felt, and maintain a negative pressure. Turn on the microwave generator outside the vacuum device, set the microwave power to 200 W, accelerate the gel formation, and continuously turn it on for 6 h to accelerate the gel aging.

[0113] After the aging is completed, transfer the aged composite material obtained to a reaction kettle, add 20 L of concentrated hydrochloric acid (wt% = 36%) into the kettle, start the circulation device for solvent replacement for 3 h, drain the replaced waste liquid, add 20 L of hexamethyldisiloxane into the kettle, start the circulation device and heating device, and maintain the system temperature at 70 °C for hydrophobic modification for 12 h.

[0114] After the modification is completed, drain the liquid in the kettle, and use a sodium bicarbonate solution with wt% = 5% to rinse the surface of the composite material to remove the residual acid solution and the modifier. Transfer the composite material to a hot air drying device, and set the classification drying temperatures at 70 °C, 100 °C, 130 °C, and 160 °C for 2 hours each. After drying is completed, the aramid fiber-reinforced aerogel glass fiber composite felt is obtained.

[0115] Test results

[0116]

[0117]

[0118] In the embodiment of the present invention, the inorganic material is first chemically etched, then plasma-treated and then compounded with silica sol. In the comparative example, the inorganic fiber material is subjected to limited treatment or no surface treatment. The test results of the prepared nanofiber-reinforced aerogel inorganic fiber composite material show that the nanofiber-reinforced aerogel inorganic fiber composite material prepared by the preparation method of the present invention has excellent heat insulation effect even at high temperatures, and the thickness range of the composite material can be extended downward, and the problem of powder falling can be solved.

Claims

1. A preparation method of a nanofiber-reinforced aerogel inorganic fiber composite material, characterized in that, It includes the following steps: (1) Pretreatment of silicon source: Drop silicon source into an acid catalyst, then add an alcohol solvent, cool down to precipitate impurities, and obtain high-purity silica sol after impurity removal; (2) Nanofiber doping: Add aramid fibers with a diameter of 10 - 100 nm and a length of 30 - 300 μm into the high-purity silica sol, stir and disperse evenly to obtain aramid fiber-doped silica sol; (3) Surface treatment of inorganic fiber material: ① Chemically etch the inorganic fiber material, then wash and dry it to obtain an inorganic fiber material with a high specific surface area; ② Then perform plasma treatment on the surface of the inorganic fiber material with a high specific surface area until the surface roughness is further increased and a C-containing light-shielding agent layer is formed to obtain the surface-treated inorganic fiber material; (4) Sol-inorganic fiber composite: Adjust the pH value of the aramid fiber-doped silica sol in (2), and composite and age it with the surface-treated inorganic fiber material in (3) under a vacuum negative pressure condition to obtain a composite material; (5) Hydrophobic modification: Add saturated concentrated hydrochloric acid to the composite material obtained in (4) for solvent replacement, and then perform hydrophobic modification; (6) Atmospheric drying: Alkaline wash the surface of the hydrophobically modified composite material and dry it under atmospheric pressure to prepare a nanofiber-reinforced aerogel inorganic fiber composite material; The process of the plasma treatment in (3) is: Under vacuum conditions, bombard the surface of the chemically etched inorganic fiber material with plasma gas and deposit a uniform C-containing light-shielding agent layer on its surface; The plasma gas is a mixture of an inert gas and an organic gas vapor.

2. The preparation method of a nanofiber-reinforced aerogel inorganic fiber composite material as described in claim 1, characterized in that, In (2), the mass ratio of the high-purity silica sol to the aramid fiber is 1:(0.001 - 0.004).

3. The preparation method of a nanofiber-reinforced aerogel inorganic fiber composite material according to claim 1, characterized in that, In (3), the inorganic fiber material is one of a glass fiber mat, a ceramic fiber mat, or a carbon fiber mat.

4. The preparation method of a nanofiber-reinforced aerogel inorganic fiber composite material according to claim 1, characterized in that, The chemical etching in (3) includes the following steps: ① Etching solution preparation: The etching solution is composed of hydrochloric acid and sulfuric acid, where the molar concentration of hydrochloric acid is 0.1 - 0.4 mol / L and the molar concentration of sulfuric acid is 0.05 - 0.2 mol / L; ② Substrate etching: Place the inorganic fiber material in the etching solution and soak it completely for etching, where the etching temperature is 10 - 50 °C and the etching time is 0.5 - 7 h; ③ Substrate cleaning: Rinse the etched inorganic fiber material with deionized water and dry it at 80 - 300 °C.

5. The preparation method of a nanofiber-reinforced aerogel inorganic fiber composite material as described in claim 1, characterized in that, The vacuum condition is that the pressure ≤ 0.1 Pa and the vacuum degree is 1 - 103 Pa.

6. The preparation method of a nanofiber-reinforced aerogel inorganic fiber composite material according to claim 1, characterized in that, The inert gas is argon, and the organic gas vapor is one or several of ethylene, cyclic compounds, saturated hydrocarbon compounds, and aromatic compounds; and the volume ratio of the inert gas to the organic gas vapor is 1:(1 - 9).

7. The preparation method of a nanofiber-reinforced aerogel inorganic fiber composite material as described in claim 1, characterized in that, In (4), the thickness of the inorganic fiber material is 0.1 - 15 mm.

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