CN112265998B - Large-size silica aerogel with ultralow density and low thermal conductivity and preparation method thereof - Google Patents
Large-size silica aerogel with ultralow density and low thermal conductivity and preparation method thereof Download PDFInfo
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Abstract
The invention discloses a large-size silica aerogel with ultralow density and low thermal conductivity and a preparation method thereof, wherein the preparation method comprises the following steps: (1) preparing a sol precursor a; (2) preparing a solvent 1; (3) preparing a mixed solution 2; (4) preparing a sol precursor b; (5) preparing silica sol; (6) preparing a wet gel composite; (7) preparing the large-size silica aerogel material with ultralow density and low thermal conductivity. Solves the defects of high density, poor thermal conductivity and small size of the existing silica aerogel.
Description
Technical Field
The invention belongs to the technical field of aerogel preparation, and particularly relates to a large-size silica aerogel with ultralow density and low thermal conductivity and a preparation method thereof.
Background
The airship is a low-speed aircraft capable of flying in stratosphere space for a long time, and has the advantages of continuous power propulsion, fixed-point controllable flight, long dead time, strong loading capacity, high cost-effectiveness ratio and the like. The flexible thin-film solar cell is selected for a common stratospheric airship energy system, has the characteristics of high technical maturity, high photoelectric conversion efficiency, customization according to shape and the like, and when the flexible solar cell is used for supplying power to an airship, the surface temperature of the flexible solar cell panel can reach 150-180 ℃ in a working state, and if heat insulation is not carried out, other instruments and equipment on the back of the panel can be burnt. Traditional heat insulation materials, such as polyurethane foam, polyimide, inorganic fiber cotton, low-density heat insulation boards and the like, cannot meet the heat insulation requirement of the flexible solar cell panel due to the fact that the traditional heat insulation materials are not resistant to high temperature aging, low in heat insulation efficiency, high in density and the like.
Aerogel is a nano-porous material with low density and low thermal conductivity, and the density is generally 0.07-0.1g/cm3About, the most common application at present is a silica aerogel system, and as the preparation technology is relatively mature, the aerogel product has good mechanical property, mature preparation process and stable product performance, and is widely usedThe thermal insulation of some aircraft key parts is widely applied. However, for a part of space detectors, because of the limitation of installation space requirements, the thickness of the heat insulation material is generally less than 3 mm; meanwhile, the thermal control surface is large, and the size of the heat insulation component is more than 1000 multiplied by 1000mm in a single piece; or the weight of the heat insulation material is strictly controlled, and the density is less than 0.17g/cm3. If the insulation material is heavily loaded, it will affect the performance and flight distance of the aircraft, and if it is undersized, it will result in a high product count, potential heat leak and safety risks. If the quantity of the heat insulation products is large, the number of seams is large, and the processing difficulty of splicing positions is high.
For example, chinese patent 201710357894.3 discloses a flexible silica aerogel material and a method for preparing the same, wherein a silane coupling agent containing amino groups is added to a frozen acidic silica sol, and the silane coupling agent containing amino groups is controlled to react with the silica sol, so as to introduce active amino groups into the surface of a silica wet gel; and then soaking the modified silica wet gel into a solution containing organic epoxy molecules, introducing a flexible organic molecular layer on the surface of the silica wet gel through an addition reaction of amino groups on the surface of the silica wet gel and epoxy organic molecules, and finally performing purification and drying processes to obtain the dry flexible silica aerogel material.
For another example, chinese patent 201110382030.X is a silica aerogel material and a preparation method thereof, comprising the steps of: (1) sol-gel preparation: 1520g of methyl orthosilicate is taken, the methyl orthosilicate, methanol and deionized water are uniformly mixed according to the molar ratio of 1:10:10, then polyethylene glycol 1000 accounting for 1 wt% of the total weight of the methyl orthosilicate, the methanol and the deionized water is gradually added as a gel particle structure cross-linking agent, N-dimethylformamide accounting for 10 wt% of the total weight of the methyl orthosilicate, the methanol and the deionized water is gradually added as a gel pore modifying agent, the mixture is uniformly stirred, and then ammonia water is added according to the molar ratio of the methyl orthosilicate to the catalyst of 1:0.05 and the mixture is uniformly stirred to obtain silica sol; then filling the silica sol into a flat plate mould of 400x400mm, sealing, standing at 20 ℃, and forming gel after 2 hours; (2) gel aging, hydrophobization, solvent replacement: aging the gel prepared in the step (1) for 72h at room temperature; adding 3000g of 5 wt% methanol solution of hexamethyldisilazane into the flat plate mold to completely immerse the gel, sealing, and standing at room temperature for 72h for hydrophobization; pouring out the methanol solvent in the container, pouring anhydrous methanol solvent to immerse the gel, and performing solvent replacement; after 2 days, the methanol solvent is replaced, and the solvent replacement is repeated for 5 times; (3) supercritical drying treatment
Because the traditional silica aerogel heat insulation composite material has higher density and cannot meet the use requirement, the development of an ultralow-density large-size-formable silica aerogel composite material is urgent.
Disclosure of Invention
The invention aims to solve the technical problem of providing the large-size silica aerogel with ultralow density and low thermal conductivity and the preparation method thereof aiming at the defects of high density, poor thermal conductivity and small size of the existing silica aerogel.
The preparation method of the large-size silica aerogel with ultralow density and low thermal conductivity comprises the following steps:
(1) preparing a sol precursor a: adding a silicon source and solvent mixed solution into a container, stirring for 3-6h at the temperature of 30-50 ℃, and adjusting the pH to 3-5 to form a sol precursor a;
(2) preparation of solvent 1: adding hydrochloric acid into ethanol, and adjusting the pH value to 2-3 to obtain a solvent 1;
(3) preparing a mixed solution 2: mixing ethanol, water and alkali liquor, adding acetylated distarch phosphate which is 0.01-0.02% of the weight of the alkali liquor, stirring, and adjusting the pH to 8-10 to obtain a mixed solution 2;
(4) preparing a sol precursor b: mixing the sol precursor a with the solvent 1 according to the mass ratio of (1-2) to (2-3), and fully stirring to obtain a sol precursor b;
(5) preparing a silica sol: mixing one or more of oxalic acid, glycol and formamide in a concentration of 0.1mol/L to obtain a mixed solution c, mixing the mixed solution c with a sol precursor b and the mixed solution 2 according to a volume ratio of (1-2) to (2-4) to (1-3), and controlling the pH value to 7-8 to obtain silica sol;
(6) preparing a wet gel composite material: mixing the silica sol obtained in the step with the fiber reinforced prefabricated part according to the mass ratio of (1-2) to (2-3), ageing after gelling, and soaking by using a soaking solution to obtain a wet gel composite material;
(7) preparing a large-size silicon oxide aerogel material with ultralow density and low thermal conductivity: and (3) putting the wet gel composite material obtained in the step (a) into an ethanol supercritical drying kettle for supercritical drying to obtain the large-size silica aerogel material with ultralow density and low thermal conductivity.
The silicon source in step (1) of the present invention is selected from methyl orthosilicate or ethyl orthosilicate.
The solvent mixed solution in the step (1) is a mixed solution of ethanol and glycol, and the adding amount of the glycol is 0.2-0.5 times, preferably 0.3 times of the mass of the ethanol; or the mixed solution of ethanol and formamide, wherein the addition amount of the formamide is 0.2-0.5 time of the mass of the ethanol; or mixed solution of ethanol and oxalic acid, with acid concentration of (2-3) × 10-3mol/L, preferably 2.1X 10-3mol/L。
The silicon source and solvent mixed solution in the step (1) is prepared, wherein the mass ratio of the silicon source to water to ethanol is 1:4 (10-20).
The whole reaction in the step (1) is carried out in a water bath or an oil bath.
The alkali liquor in the step (3) is selected from ammonia water or sodium hydroxide, and the concentration of the ammonia water or the sodium hydroxide is 3 multiplied by 10- 3mol/L。
And (5) mixing the mixed solution c with the sol precursor b and the mixed solution 2, namely slowly dropwise adding the mixed solution c into the sol precursor b and the mixed solution 2 while stirring, wherein the dropwise adding speed is 5-10ml/min, and the dropwise adding process is carried out in a water bath kettle at the temperature of 30-50 ℃.
The fiber reinforced prefabricated member in the step (6) is selected from glass wool fibers, rock wool fibers, aluminum silicate fibers, mullite fibers, quartz fibers and carbon felts; the density of the fiber reinforced preform is 0.05-0.12g/cm3(ii) a By adjusting the density and/or type of the reinforcement matrix, the aerogel density, temperature resistance and integrity of the composite material can be ensured; stainless steel is selected for use in forming of fiber reinforced prefabricated partThe thickness of the die is 6mm, the length and width dimensions are 650mm multiplied by 700mm, the thickness of the prefabricated part is controlled by the positioning cushion block, the size of the prepared maximum product is 600mm multiplied by 650mm, the thickness is 1mm-3mm, and the large-size aerogel composite material has no defects of loose surface, uniform hole and the like and has uniform thickness.
And (3) aging for 3 days, wherein solvent replacement is adopted in the aging process, the solvent replacement is selected from one or two or more of ethanol, acetone, normal hexane and n-pentane, the solvent replacement is a mixed solution of ethanol, acetone, normal hexane and n-pentane, the solvent replacement is carried out at any ratio when the solvent replacement is carried out, and the replacement temperature is controlled to be 25-35 ℃. Applicants have discovered that increasing the frequency of the substitution and extending the time of the substitution can improve the post-supercritical integrity of the material.
The purpose of aging is to make SiO2The degree of crosslinking of the gel is increased to strengthen the network structure thereof because although the raw material apparently changes from the sol state to the gel state, the hydrolysis reaction and the polycondensation reaction are not 100% completed, and SiO2There are still a lot of alkoxide groups on the network skeleton of the gel which do not participate in the reaction, and it is necessary to leave time for these groups to continue the hydrolysis and polycondensation processes to form a more rigid gel network. Theoretically, the longer the gel aging time, the better, so as to lead the reaction of forming Si-O bonds by condensation polymerization of-OH on the surface of the gel network skeleton to be more thorough, thereby greatly increasing the SiO2The skeleton strength and toughness of the gel are usually achieved by using raw material mother liquor, alcohol solution, mixed solvent of water and alcohol and the like as an aging agent.
The solvent replacement is to replace water and alcohol in the pores with a solution with a smaller surface tension so as to reduce the capillary pressure generated during drying, and a gel network prepared by a sol-gel method contains a large amount of water and alcohol with a larger surface tension, so that the gel is easy to break due to the existence of a larger capillary additional pressure during the drying process. After the aging is finished, a large number of groups with strong polarity are attached to the gel skeleton, so that the surface modifier is difficult to approach to Si-OH groups on the gel skeleton, and the surface modification process is difficult, therefore, nonpolar solvents are required to replace polar water, ethanol and the like.
Soaking with the soaking solution in the step (6) is to mix ethanol, ethyl orthosilicate and trimethylchlorosilane according to the volume ratio of (1-2) to (2-3) to (0.2-0.5) to form the soaking solution for soaking for 6 times, wherein each time lasts for 12 hours; the soaking with the steeping liquor is carried out by adopting a vacuumizing mode, and the vacuum degree of vacuum glue injection is-0.5 MPa-0.7 MPa.
And (6) carrying out moisture-proof treatment on the obtained wet gel composite material, wherein the moisture-proof treatment specifically comprises the following steps: and (3) carrying out hydrophobic modification treatment on the dried silica aerogel material by using a hydrophobic agent to obtain the hydrophobic aerogel.
Surface modification: the organosilicon water repellent is commonly used for hydrophobic modification of the surface of a material and has obvious effect because of strong chemical affinity with inorganic silicate, and the surface characteristics of the material can be effectively changed to achieve the hydrophobic effect.
Drying Control additives, DCCA (drying Control Chemical additives), which is a common class of organic liquids with low vapor pressure, are formamide, glycerol (glycerin), oxalic acid, and the like. Because of their low volatility, the inhomogeneous evaporation of alcohol solvent in different pore sizes can be greatly reduced, so that the drying stress can be reduced, and in addition, DCCA of formamide and oxalic acid can make the structure of gel uniform, and can reduce the inhomogeneity of pore structure to form gel with narrow pore size distribution. DCCA is used as an organic matter with low surface tension, the DCCA can be added to inhibit the growth of gel particles, so that the network structure of the gel is more uniform, and meanwhile, the DCCA can also increase the skeleton strength, so that the DCCA can better resist the action of capillary force, and the shrinkage and cracking of the aerogel in the normal-pressure drying process are reduced and avoided, thereby obtaining an ideal porous light aerogel structure.
The invention also relates to a large-size silica aerogel material with ultralow density and low thermal conductivity, which is prepared by adopting the preparation method.
The invention also relates to an application of the large-size silica aerogel material with ultralow density and low thermal conductivity, and the silica aerogel material is applied to preparation of a solar cell thermal insulation board.
Preferably, the prepared solar cell thermal insulation board has a single size of 1300mm × 1200 mm.
Further preferably, the manufactured solar cell thermal insulation board is a flat plate with good bending performance, the periphery of the solar cell thermal insulation board is reinforced by using an adhesive tape, and the four solar cell thermal insulation boards are connected by using fiber wires to form a whole, so that the production efficiency is improved, corner damage in the assembling process can be prevented, and the solar cell thermal insulation board has good assembling performance.
Compared with the prior art, the invention has the following advantages:
1. the research of the invention finds that the phenomenon of uneven evaporation of alcohol solvents in different apertures can be greatly reduced by adjusting the proportion of methyl orthosilicate or ethyl orthosilicate, ethanol and hydrochloric acid and using ethylene glycol as a drying control chemical additive; meanwhile, acetylated distarch phosphate is added in the reaction, acetylated distarch phosphate is a variable starch substance, the molecular structure of acetylated distarch phosphate has hydrophilic group and hydrophobic group, which makes it present a certain property of surfactant, when it contacts with water, micelle is formed, micelle and polymer particle are associated to form network structure, and one molecule has several micelles, which reduces the mobility of water molecule, makes the size distribution of pore in gel more centralized, viscosity is also increased, reduces drying stress and improves the integrity of aerogel, in this process, it is matched with glycol to play the main role, the solubility of glycol is good, at the same time, it is very large, after adding, the reaction rate of hydrolytic polycondensation can be reduced, adding glycol, when aging at 50 deg.C, the time can be controlled at 90-120min, if no ethylene glycol is added, the gel time is 40-60 min.
2. According to the invention, the particle size distribution of the sol precursor is controlled, the concentration of catalyst ammonia water or sodium hydroxide is adjusted, the gelation speed can be controlled, so that the crosslinking degree of colloidal particles is controlled, and the aperture of the aerogel is increased, thereby realizing the preparation of the low-density aerogel.
Drawings
FIG. 1 is a 50 μm electron microscope magnification diagram of a large-sized silica aerogel with ultra-low density and low thermal conductivity prepared in example 1 of the present invention.
FIG. 2 is a 100 μm electron microscope magnification diagram of the ultra-low density, low thermal conductivity, large size silica aerogel prepared in example 1 of the present invention.
FIG. 3 is a 50 μm electron microscope magnification diagram of the ultra-low density, low thermal conductivity, large size silica aerogel prepared in example 2 of the present invention.
FIG. 4 is a 100 μm electron micrograph of the ultra-low density, low thermal conductivity, large size silica aerogel prepared in example 3 of the present invention.
FIG. 5 is a 100 μm electron micrograph of a silica aerogel prepared in comparative example 1 of the present invention.
FIG. 6 is a 100 μm electron micrograph of a silica aerogel prepared according to comparative example 2 of the present invention.
FIG. 7 is a 100 μm electron micrograph of a prior art silica aerogel product.
Detailed Description
The present invention is described in further detail below by way of examples, which should not be construed as limiting the invention thereto.
Example 1:
the preparation method of the ultra-low density and low thermal conductivity large-size silica aerogel comprises the following steps:
(1) preparing a sol precursor a: adding a silicon source and solvent mixed solution into a container, stirring for 6 hours in a water bath at the temperature of 30 ℃, and adjusting the pH value to 3 to form a sol precursor a;
the silicon source is selected from methyl orthosilicate; the solvent mixed solution is a mixed solution of ethanol and ethylene glycol, and the addition amount of the ethylene glycol is 0.3 times of the mass of the ethanol; in the solvent mixed solution, the mass ratio of the silicon source to the water to the ethanol is 1:4: 10; the whole reaction in the step (1) is carried out in a water bath;
(2) preparation of solvent 1: adding hydrochloric acid into ethanol, and adjusting the pH value to 2 to obtain a solvent 1;
(3) preparing a mixed solution 2: mixing ethanol, water and alkali liquor, adding acetylated distarch phosphate which is 0.01 percent of the weight of the alkali liquor, stirring, and adjusting the pH value to 8 to obtain a mixed solution 2;
the alkali liquor is selected from ammonia water with the concentration of3×10-3mol/L；
(4) Preparing a sol precursor b: mixing the sol precursor a with a solvent 1 according to a mass ratio of 1:2, and fully stirring to obtain a sol precursor b;
(5) preparing a silica sol: slowly dripping 0.1mol/L oxalic acid into the sol precursor b and the mixed solution 2 according to the volume ratio of 1:2:3, continuously stirring, wherein the dripping speed is 5-10ml/min, the dripping process is carried out in a water bath kettle at the temperature of 30 ℃, and the pH is controlled to be 7 to obtain silica sol;
(6) preparing a wet gel composite material: mixing the silica sol obtained in the above step with fiber reinforced preform (glass wool fiber, density of 0.05 g/cm)3) Mixing according to the mass ratio of 1:2, aging for 3 days after gelation, adopting solvent replacement in the aging process, wherein the solvent replacement is selected from ethanol, and the replacement temperature is controlled at 25 ℃;
the fiber reinforced prefabricated part is formed by a stainless steel mold, the thickness of the mold is 6mm, the length and width of the mold are 650mm multiplied by 700mm, the thickness of the formed prefabricated part is controlled by a positioning cushion block, the size of the prepared maximum product is 600mm multiplied by 650mm, the thickness of the prepared maximum product is 1mm-3mm, and the large-size aerogel composite material has no defects such as loose surface, holes and the like and has uniform thickness;
mixing ethanol, ethyl orthosilicate and trimethylchlorosilane according to a volume ratio of 1:2:0.2 to form an impregnation solution, and soaking the obtained gel for 6 times (12 hours each time) by adopting a vacuumizing mode, wherein the vacuum degree of vacuum glue injection is-0.5 Mpa to obtain a wet gel composite material;
and (3) obtaining a wet gel composite material, and carrying out moisture-proof treatment, wherein the moisture-proof treatment specifically comprises the following steps: carrying out hydrophobic modification treatment on the dried silica aerogel material by using a hydrophobic agent to obtain hydrophobic aerogel;
(7) preparing a large-size silicon oxide aerogel material with ultralow density and low thermal conductivity: and (3) putting the wet gel composite material obtained in the step (a) into an ethanol supercritical drying kettle for supercritical drying to obtain the large-size silica aerogel material with ultralow density and low thermal conductivity.
Table 1 thermal conductivity test results of aerogel thermal insulation composite material obtained in this example under different air pressures
Example 2:
the preparation method of the ultra-low density and low thermal conductivity large-size silica aerogel comprises the following steps:
(1) preparing a sol precursor a: adding a silicon source and solvent mixed solution into a container, stirring for 4 hours at 40 ℃ in an oil bath, and adjusting the pH to 5 to form a sol precursor a;
the silicon source is selected from ethyl orthosilicate; the solvent mixed solution is a mixed solution of ethanol and formamide, and the addition amount of the formamide is 0.2 time of the mass of the ethanol; in the solvent mixed solution, the mass ratio of the silicon source to the water to the ethanol is 1:4: 20; the whole reaction in the step (1) is carried out in an oil bath;
(2) preparation of solvent 1: adding hydrochloric acid into ethanol, and adjusting the pH value to 3 to obtain a solvent 1;
(3) preparing a mixed solution 2: mixing ethanol, water and alkali liquor, adding acetylated distarch phosphate which is 0.02% of the weight of the alkali liquor, stirring, and adjusting the pH value to 9 to obtain a mixed solution 2;
the concentration of the alkali liquor, the sodium hydroxide and the sodium hydroxide is 3 multiplied by 10-3mol/L；
(4) Preparing a sol precursor b: mixing the sol precursor a with a solvent 1 according to a mass ratio of 1:3, and fully stirring to obtain a sol precursor b;
(5) preparing a silica sol: mixing 0.1mol/L oxalic acid and ethylene glycol in equal volume to obtain a mixed solution c, slowly dropwise adding the mixed solution c into the sol precursor b and the mixed solution 2 according to the volume ratio of 2:2:3, continuously stirring, wherein the dropwise adding speed is 5-10ml/min, the dropwise adding process is carried out in a water bath kettle at 50 ℃, and the pH is controlled to be 8 to obtain silica sol;
(6) preparing a wet gel composite material: mixing the silica sol obtained in the above step with a fiber-reinforced preform (rock wool fiber, density of 0.12 g/cm)3) Mixing at a mass ratio of 1:3, aging for 3 days, and replacing solvent with ethanol or acetoneVolume of the mixed solution, and replacement temperature is controlled at 35 ℃;
the fiber reinforced prefabricated part is formed by a stainless steel mold, the thickness of the mold is 6mm, the length and width of the mold are 650mm multiplied by 700mm, the thickness of the formed prefabricated part is controlled by a positioning cushion block, the size of the prepared maximum product is 600mm multiplied by 650mm, the thickness of the prepared maximum product is 1mm-3mm, and the large-size aerogel composite material has no defects such as loose surface, holes and the like and has uniform thickness;
mixing ethanol, ethyl orthosilicate and trimethylchlorosilane according to a volume ratio of 1:3:0.5 to form an impregnation solution, and soaking the obtained gel for 6 times (12 hours each time) by adopting a vacuumizing mode, wherein the vacuum degree of vacuum glue injection is-0.7 Mpa to obtain a wet gel composite material;
and (3) obtaining a wet gel composite material, and carrying out moisture-proof treatment, wherein the moisture-proof treatment specifically comprises the following steps: carrying out hydrophobic modification treatment on the dried silica aerogel material by using a hydrophobic agent to obtain hydrophobic aerogel;
(7) preparing a large-size silicon oxide aerogel material with ultralow density and low thermal conductivity: and (3) putting the wet gel composite material obtained in the step (a) into an ethanol supercritical drying kettle for supercritical drying to obtain the large-size silica aerogel material with ultralow density and low thermal conductivity.
Table 2 thermal conductivity test results of the aerogel thermal insulation composite material obtained in this embodiment under different air pressures
Example 3:
the preparation method of the ultra-low density and low thermal conductivity large-size silica aerogel comprises the following steps:
(1) preparing a sol precursor a: adding a silicon source and solvent mixed solution into a container, stirring for 3 hours in a water bath at 50 ℃, and adjusting the pH to 4 to form a sol precursor a;
the silicon source is selected from methyl orthosilicate; the solvent mixed solution is a mixed solution of ethanol and oxalic acid, and the acid concentration is 2.1 multiplied by 10-3mol/L; in the solvent mixed solution, the mass ratio of silicon source to water to ethanolIs 1:4: 15;
(2) preparation of solvent 1: adding hydrochloric acid into ethanol, and adjusting the pH value to 2 to obtain a solvent 1;
(3) preparing a mixed solution 2: mixing ethanol, water and alkali liquor, adding acetylated distarch phosphate equivalent to 0.015% of the mass of the alkali liquor, stirring, and adjusting the pH value to 10 to obtain a mixed solution 2;
the concentration of the alkali liquor, the sodium hydroxide and the sodium hydroxide is 3 multiplied by 10-3mol/L；
(4) Preparing a sol precursor b: mixing the sol precursor a with a solvent 1 according to a mass ratio of 2:3, and fully stirring to obtain a sol precursor b;
(5) preparing a silica sol: mixing 0.1mol/L oxalic acid, glycol and formamide in an equal volume ratio to obtain a mixed solution c, slowly dropwise adding the mixed solution c into the sol precursor b and the mixed solution 2 according to a volume ratio of 4:4:3, continuously stirring, wherein the dropwise adding speed is 5-10ml/min, the dropwise adding process is carried out in a water bath kettle at 40 ℃, and the pH is controlled to 7 to obtain silica sol;
(6) preparing a wet gel composite material: mixing the silica sol obtained in the above step with a fiber-reinforced preform (quartz fiber, density of 0.10 g/cm)3) Mixing according to the mass ratio of 2:3, aging for 3 days after gelation, adopting solvent replacement in the aging process, wherein the solvent replacement is selected from mixed liquor of acetone and n-hexane in the volume ratio of 1:3, and the replacement temperature is controlled at 30 ℃;
the fiber reinforced prefabricated part is formed by a stainless steel mold, the thickness of the mold is 6mm, the length and width of the mold are 650mm multiplied by 700mm, the thickness of the formed prefabricated part is controlled by a positioning cushion block, the size of the prepared maximum product is 600mm multiplied by 650mm, the thickness of the prepared maximum product is 1mm-3mm, and the large-size aerogel composite material has no defects such as loose surface, holes and the like and has uniform thickness;
mixing ethanol, ethyl orthosilicate and trimethylchlorosilane according to a volume ratio of 2:2:0.4 to form an impregnation solution, and soaking the obtained gel for 6 times (12 hours each time) by adopting a vacuumizing mode, wherein the vacuum degree of vacuum glue injection is-0.6 Mpa to obtain a wet gel composite material;
and (3) obtaining a wet gel composite material, and carrying out moisture-proof treatment, wherein the moisture-proof treatment specifically comprises the following steps: carrying out hydrophobic modification treatment on the dried silica aerogel material by using a hydrophobic agent to obtain hydrophobic aerogel;
(7) preparing a large-size silicon oxide aerogel material with ultralow density and low thermal conductivity: and (3) putting the wet gel composite material obtained in the step (a) into an ethanol supercritical drying kettle for supercritical drying to obtain the large-size silica aerogel material with ultralow density and low thermal conductivity.
Table 3 thermal conductivity test results of aerogel thermal insulation composite material obtained in this example under different air pressures
Example 4:
the silica aerogel material obtained in example 1 is applied to the preparation of the solar cell thermal insulation board, preferably, the size of a single piece of the prepared solar cell thermal insulation board is 1300mm × 1200mm, the prepared solar cell thermal insulation board is a flat plate with better bending property, the periphery of the solar cell thermal insulation board is reinforced by using an adhesive tape, and the solar cell thermal insulation boards are connected by using fiber wires to form a whole, so that the production efficiency is improved, the corner damage in the assembly process can be prevented, and the assembly performance is better.
Comparative example 1: step 5) lacks ethylene glycol as compared to example 1, otherwise as in example 1.
TABLE 4 thermal conductivity test results under different air pressures for aerogel thermal insulation composite obtained in this comparative example
As can be seen from the drawing of comparative example 1, cracks were found in the microstructure observed after the aerogel was aged.
Comparative example 2: compared to example 1, step 3) lacks acetylated distarch phosphate, otherwise as in example 1.
TABLE 5 thermal conductivity test results under different air pressures for aerogel thermal insulation composite obtained in this comparative example
As can be seen from the drawing of comparative example 1, cracks were found in the microstructure observed after the aerogel was aged.
Comparative example 3: aerogel density of existing silica aerogel is 0.1g/cm3Left and right;
table 6 test results of thermal conductivity of the conventional ordinary glass fiber aerogel thermal insulation felt under different air pressures
Experimental example: gel time
And (4) analyzing results:
1. the examples compare to comparative example 1 to illustrate that ethylene glycol is a key component of the present invention. The nonuniformity of the pore structure of the microporous structure with large and small pores distributed in the gel is the main reason of stress generated during gel drying, the gel shrinks due to the capillary action during drying, the large pores are dried faster than the small pores due to the difference between the saturated vapor pressure and the capillary force between the large pores and the small pores with different pore diameters, the small pores are gradually dried and shrunk after the large pores are dried, so that the stress is necessarily generated between the large pore area and the small pore area, the gel cracks when the stress is large enough, and the gel is easy to crack during the drying process when the pore diameter distribution in the gel is wide. The invention adds glycol as surfactant, which reduces capillary force of gel in drying process and reduces surface tension of liquid phase.
2. Compared with the comparative example 2, the method shows that the acetylated distarch phosphate is added in the reaction, the acetylated distarch phosphate is a variable starch substance, the molecular structure of the acetylated distarch phosphate has hydrophilic groups and hydrophobic groups, so that the acetylated distarch phosphate has certain surfactant properties, when the acetylated distarch phosphate is contacted with water, micelles are formed, the micelles are associated with polymer particles to form a network structure, and one molecule has a plurality of micelles, so that the mobility of water molecules is reduced, the pore size distribution of the gel is more concentrated, the viscosity is also improved, the drying stress is reduced, and the integrity of the aerogel is improved.
3. Compared with the existing silica aerogel represented by comparative example 3, the ultra-low-density and low-thermal-conductivity large-size silica aerogel obtained in the embodiment has the advantages that the density of the aerogel is low, the aerogel can be uniformly mixed with reinforcing fibers, cracking is avoided after gelation, the large-size component can be formed due to small supercritical post-shrinkage, and the aerogel has industrial application capability.
4. Through the comparison of the gel time of the embodiment and the gel time of the comparative example, the embodiment can control the gel speed by controlling the particle size distribution of the sol precursor and adjusting the concentration of catalyst ammonia water or sodium hydroxide, thereby controlling the crosslinking degree of colloidal particles and increasing the pore diameter of the aerogel to realize the preparation of the low-density aerogel.
By comparing the basic properties of the examples and comparative examples, the preparation process of the examples is significantly superior to the comparative examples.
Claims (10)
1. The preparation method of the large-size silica aerogel with ultra-low density and low thermal conductivity is characterized by comprising the following steps of: the method comprises the following steps:
(1) preparing a sol precursor a: adding a silicon source and solvent mixed solution into a container, stirring for 3-6h at the temperature of 30-50 ℃, and adjusting the pH to 3-5 to form a sol precursor a;
(2) preparation of solvent 1: adding hydrochloric acid into ethanol, and adjusting the pH value to 2-3 to obtain a solvent 1;
(3) preparing a mixed solution 2: mixing ethanol, water and alkali liquor, adding acetylated distarch phosphate which is 0.01-0.02% of the weight of the alkali liquor, stirring, and adjusting the pH to 8-10 to obtain a mixed solution 2;
(4) preparing a sol precursor b: mixing the sol precursor a with the solvent 1 according to the mass ratio of (1-2) to (2-3), and fully stirring to obtain a sol precursor b;
(5) preparing a silica sol: mixing one or more of oxalic acid, glycol and formamide in a concentration of 0.1mol/L to obtain a mixed solution c, mixing the mixed solution c with a sol precursor b and the mixed solution 2 according to a volume ratio of (1-2) to (2-4) to (1-3), and controlling the pH value to 7-8 to obtain silica sol;
(6) preparing a wet gel composite material: mixing the silica sol obtained in the step with the fiber reinforced prefabricated part according to the mass ratio of (1-2) to (2-3), ageing after gelling, and soaking by using a soaking solution to obtain a wet gel composite material;
(7) preparing a large-size silicon oxide aerogel material with ultralow density and low thermal conductivity: and (3) putting the wet gel composite material obtained in the step (a) into an ethanol supercritical drying kettle for supercritical drying to obtain the large-size silica aerogel material with ultralow density and low thermal conductivity.
2. The method of preparing an ultra-low density, low thermal conductivity, large size silica aerogel according to claim 1, wherein:
the silicon source in the step (1) is selected from methyl orthosilicate or ethyl orthosilicate;
the solvent mixed solution in the step (1) is a mixed solution of ethanol and glycol, and the addition amount of the glycol is 0.2-0.5 times of the mass of the ethanol; or the mixed solution of ethanol and formamide, wherein the addition amount of the formamide is 0.2-0.5 time of the mass of the ethanol; or mixed solution of ethanol and oxalic acid, with acid concentration of (2-3) × 10-3mol/L。
3. The method of preparing an ultra-low density, low thermal conductivity, large size silica aerogel according to claim 1, wherein: the whole reaction in the step (1) is carried out in a water bath or an oil bath.
4. The super set of claim 1The preparation method of the large-size silica aerogel with low density and low thermal conductivity is characterized by comprising the following steps: the alkali liquor in the step (3) is selected from ammonia water or sodium hydroxide, and the concentration of the ammonia water or the sodium hydroxide is 3 multiplied by 10- 3mol/L。
5. The method of preparing an ultra-low density, low thermal conductivity, large size silica aerogel according to claim 1, wherein: and (5) mixing the mixed solution c with the sol precursor b and the mixed solution 2, namely slowly dropwise adding the mixed solution c into the sol precursor b and the mixed solution 2 while continuously stirring, wherein the dropwise adding speed is 5-10ml/min, and the dropwise adding process is carried out in a water bath kettle at the temperature of 30-50 ℃.
6. The method of preparing an ultra-low density, low thermal conductivity, large size silica aerogel according to claim 1, wherein: the fiber reinforced prefabricated member in the step (6) is selected from glass wool fibers, rock wool fibers, aluminum silicate fibers, mullite fibers, quartz fibers and carbon felts; the density of the fiber reinforced preform is 0.05-0.12g/cm3。
7. The method of preparing an ultra-low density, low thermal conductivity, large size silica aerogel according to claim 1, wherein:
aging for 3 days in the step (6), wherein solvent replacement is adopted in the aging process, the solvent replacement is selected from one or more of ethanol, acetone, normal hexane and n-pentane, and when the solvent replacement is mixed, the solvent replacement is in any proportion, and the replacement temperature is controlled to be 25-35 ℃;
soaking with the soaking solution in the step (6) is to mix ethanol, ethyl orthosilicate and trimethylchlorosilane according to the volume ratio of (1-2) to (2-3) to (0.2-0.5) to form the soaking solution for soaking for 6 times, wherein each time lasts for 12 hours; the soaking with the impregnation liquid is carried out in a vacuumizing mode, and the vacuum degree of vacuum glue injection is-0.5 MPa to-0.7 MPa.
8. The method of preparing an ultra-low density, low thermal conductivity, large size silica aerogel according to claim 1, wherein: and (6) carrying out moisture-proof treatment on the obtained wet gel composite material, wherein the moisture-proof treatment specifically comprises the following steps: and (3) carrying out hydrophobic modification treatment on the dried silica aerogel material by using a hydrophobic agent to obtain the hydrophobic aerogel.
9. A large-size silica aerogel with ultra-low density and low thermal conductivity is characterized in that: the ultra-low density, low thermal conductivity, large size silica aerogel of any of claims 1-7.
10. The use of an ultra-low density, low thermal conductivity, large size silica aerogel material according to claim 9, wherein: the silica aerogel material is applied to the preparation of a solar cell thermal insulation board.
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| KR20190129596A (en) * | 2018-05-11 | 2019-11-20 | 주식회사 엘지화학 | Manufacturing process silica aerogel blanket using recycled solvent |
| CN111847463A (en) * | 2020-08-04 | 2020-10-30 | 中国科学技术大学 | Preparation method of silicon dioxide nano aerogel fiber |
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| CN104496402A (en) * | 2014-12-18 | 2015-04-08 | 贵州航天乌江机电设备有限责任公司 | Process for preparing glass fiber composite type silicon dioxide aerogel insulation quilt |
| KR20190129596A (en) * | 2018-05-11 | 2019-11-20 | 주식회사 엘지화학 | Manufacturing process silica aerogel blanket using recycled solvent |
| CN111847463A (en) * | 2020-08-04 | 2020-10-30 | 中国科学技术大学 | Preparation method of silicon dioxide nano aerogel fiber |
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