CN112661482A - Fiber composite aerogel material and preparation method and application thereof - Google Patents
Fiber composite aerogel material and preparation method and application thereof Download PDFInfo
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Abstract
The invention relates to a fiber composite aerogel material and a preparation method and application thereof. The preparation method of the fiber composite aerogel material comprises the following steps: hydrolyzing part of the silicon source to prepare a silicon hydrolysate, mixing the silicon hydrolysate with a polymer, and performing electrostatic spinning to prepare a nanofiber membrane; heat treating the nanofiber membrane to remove the polymer; mixing the residual silicon source with water and an alcohol solvent to prepare silica sol; soaking the nanofiber membrane subjected to heat treatment in silica sol, and mixing under a negative pressure condition to prepare nanofiber sol; and carrying out gel aging treatment on the nanofiber sol, and then drying to prepare the fiber composite aerogel material. The preparation method of the fiber composite aerogel material can simultaneously improve the heat preservation performance and the flexibility of the fiber composite aerogel material and prevent powder falling.
Description
Technical Field
The invention relates to the field of aerogel materials, in particular to a fiber composite aerogel material and a preparation method and application thereof.
Background
The silica aerogel material has poor mechanical property and brittle quality, and is difficult to be directly applied to actual engineering. Compounding aerogel materials with fibers is a main modification method for improving the mechanical properties of silica aerogel at present. However, the heat conduction effect of the commonly used modified fibers is large, and the heat insulation performance of the aerogel material is greatly reduced.
The traditional technology discloses a method for preparing a high-efficiency aerogel fibrofelt by compounding a fibrofelt and aerogel through siphoning, wherein the fibrofelt with specific density and diameter is selected to ensure the processing performance and the heat insulation performance of the material, and the combination effect of the aerogel material and fibers is enhanced through siphoning. However, it is difficult to simultaneously achieve flexibility and thermal insulation performance of the material with the conventional fiber mat. In addition, another technology discloses a preparation method of the fiber composite aerogel, which is used for soaking the fibers in the alcohol sol and then gelling and drying the fibers. However, in this method, the aerogel is not sufficiently bonded to the fibers, which results in a material that is susceptible to "dusting". In addition, another technology discloses a method for preparing the electrostatic spinning nanofiber reinforced silica aerogel by taking electrostatic spinning nanofibers as a reinforcement through a composite process, solvent exchange, surface modification and normal-pressure drying. The nano-fiber prepared by the method contains more organic components, and the organic components can be oxidized and decomposed at high temperature, so that the mechanical and heat-insulating properties of the material are reduced.
Disclosure of Invention
Based on the above, there is a need for a method for preparing a fiber composite aerogel material, which can simultaneously improve the thermal insulation performance and flexibility of the fiber composite aerogel material and prevent the fiber composite aerogel material from falling off powder.
In addition, there is a need to provide a fiber composite aerogel material and applications.
A preparation method of a fiber composite aerogel material comprises the following steps:
hydrolyzing part of the silicon source to prepare a silicon hydrolysate, mixing the silicon hydrolysate with a polymer, and performing electrostatic spinning to prepare a nanofiber membrane;
heat treating the nanofiber membrane to remove the polymer;
mixing the residual silicon source with water and an alcohol solvent to prepare silica sol;
soaking the nanofiber membrane subjected to heat treatment in the silica sol, and mixing under a negative pressure condition to prepare nanofiber sol; and
and carrying out gel aging treatment on the nanofiber sol, and then drying to prepare the fiber composite aerogel material.
In one embodiment, the temperature of the heat treatment is 300-900 ℃, the time of the heat treatment is 0.5-5 h, and the heat treatment is carried out under vacuum condition or under the protection of inert gas.
In one embodiment, in the step of electrospinning, the spinning voltage is 10kV to 20kV, the receiving distance is 5cm to 25cm, and the injection flow rate is 0.3mL/h to 3 mL/h.
In one embodiment, the drying mode is carbon dioxide supercritical drying.
In one embodiment, the temperature of the carbon dioxide supercritical drying is 32-50 ℃, and the pressure is 7.4-18 MPa.
In one embodiment, the step of mixing the remaining silicon source with water and an alcohol reagent further comprises adding a rare earth nitrate or a rare earth oxide.
In one embodiment, the rare earth element is lanthanum, cerium, neodymium, or gadolinium; and/or the presence of a catalyst in the reaction mixture,
the mass ratio of the nitrate of the rare earth element or the oxide of the rare earth element to the rest of the silicon source is (1-35) to 100.
In one embodiment, in the step of mixing the silicon hydrolysate with a polymer, the polymer is polyvinyl alcohol; and/or the presence of a catalyst in the reaction mixture,
in the step of mixing the silicon hydrolysate with the aqueous solution of the polymer, the mass ratio of the silicon hydrolysate to the aqueous solution of the polymer is 1: 0.6-1.4, and the mass percentage concentration of the aqueous solution of the polymer is 5% -15%.
In one embodiment, in the step of performing gel aging treatment on the nanofiber sol, the nanofiber sol is kept still for 0.5 to 3 hours to prepare the nanofiber gel, and then the nanofiber gel is placed in an alcohol reagent and subjected to aging treatment at 60 to 70 ℃ for 1 to 3 days.
In one embodiment, the step of hydrolyzing a portion of the silicon source comprises: mixing part of the silicon source and water according to the molar ratio of 1: 2-10, then adjusting the pH value to 2-5, and stirring for 1-10 h.
In one embodiment, the step of mixing the remaining silicon source with water and an alcohol reagent, and adjusting the pH comprises: dispersing the rest silicon source in the alcohol reagent, adding water, adjusting the pH to 2-5, stirring for 1-10 h, and adjusting the pH to 6-9.
In one embodiment, in the step of mixing the remaining silicon source with water and the alcohol reagent, the molar ratio of the remaining silicon source to the alcohol reagent to the water is 1: 5-20: 2-10.
In one embodiment, the silicon source is ethyl orthosilicate, methyl orthosilicate or butyl orthosilicate; and/or the alcohol solvent is ethanol, methanol or propanol.
The fiber composite aerogel material is prepared by the preparation method of the fiber composite aerogel material.
The fiber composite aerogel material is applied to preparation of nuclear power heat-insulating materials.
The preparation method of the fiber composite aerogel material is based on the characteristic that inorganic fibers can obtain enhanced flexibility when the inorganic fibers have a nanoscale diameter and are uniformly distributed, the flexible fibers with the nanoscale diameter and are uniformly distributed are prepared by using an electrostatic spinning method and serve as fiber reinforcements of the aerogel material, and polymers in the nanofibers are removed through heat treatment, so that the fiber structure is inorganic, the polymers are prevented from being oxidized and decomposed at high temperature to reduce the mechanical and heat insulation properties of the material, and the material has better high temperature resistance and heat insulation properties. The nanofiber membrane after heat treatment is soaked in the silica sol and mixed under the negative pressure condition, so that the nanofiber membrane is fully soaked in the silica sol, the silica sol is fully dispersed in a nanofiber framework and gaps, and the silica gel and fibers form stronger binding force in the gelling and aging processes, so that the mechanical property is enhanced, and the phenomenon of powder falling is avoided. Meanwhile, the dispersion effect effectively reduces the content of macropores in the composite material, thereby further improving the heat insulation performance of the material. Therefore, the preparation method of the fiber composite aerogel material can simultaneously improve the heat preservation performance and the flexibility of the fiber composite aerogel material and prevent powder falling.
Drawings
Fig. 1 is a process flow diagram of a method for preparing a fiber composite aerogel material according to an embodiment.
Detailed Description
In order that the invention may be more fully understood, reference will now be made to the following description taken in conjunction with the accompanying drawings. The detailed description sets forth the preferred embodiments of the invention. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete.
Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. The terminology used in the description of the invention herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention.
Referring to fig. 1, a method for preparing a fiber composite aerogel material according to an embodiment includes the following steps:
step S110: hydrolyzing part of the silicon source to prepare silicon hydrolysate, mixing the silicon hydrolysate with the polymer, and performing electrostatic spinning to prepare the nanofiber membrane.
Wherein the silicon source is tetraethoxysilane, methyl orthosilicate or butyl orthosilicate.
The step of hydrolyzing a portion of the silicon source comprises: mixing part of silicon source and water according to the molar ratio of 1: 2-10, then adjusting the pH value to 2-5, and stirring for 1-10 h. Preferably, hydrochloric acid is added to adjust the pH value in the step of adjusting the pH value to 2-5. It can be understood that in the step of adjusting the pH to 2-5, other acidic reagents can be added to adjust the pH.
Specifically, in the step of mixing the silicon hydrolysate with the polymer, the silicon hydrolysate is mixed with the aqueous solution of the polymer, the mass ratio of the silicon hydrolysate to the aqueous solution of the polymer is 1: 0.6-1.4, and the mass percentage concentration of the aqueous solution of the polymer is 5% -15%.
In one embodiment, the polymer is polyvinyl alcohol.
The preparation of the aqueous solution of the polymer comprises the following steps: the polymer was mixed with water and stirred to dissolve the polymer. Specifically, during the mixing and stirring, heat may be applied to accelerate the dissolution rate.
Specifically, in the step of electrostatic spinning, the spinning voltage is 10kV to 20kV, the receiving distance is 5cm to 25cm, and the injection flow is 0.3mL/h to 3 mL/h. Preferably, in the step of electrospinning, the receiving distance is 8cm to 15 cm.
The nanofiber prepared by electrostatic spinning has the characteristics of small fiber diameter, large specific surface area and uniform fiber diameter distribution, and can be well dispersed in the silica sol to form a uniform and complex three-dimensional network structure, so that the composite material has good mechanical property and good flexibility.
The inorganic silica nanofiber has a large influence on the performance of the fiber composite aerogel, and the inventor finds that the performance of the prepared inorganic silica nanofiber is better by adjusting the proportion and spinning parameters of a spinning precursor solution and matching with a subsequent heat treatment process through a large number of experiments. The inorganic fiber can obtain the characteristic of enhancing flexibility when the inorganic fiber has a nano-scale diameter and is uniform in size distribution, and the flexible fiber with the nano-scale diameter is prepared by an electrostatic spinning method and used as a fiber reinforcement body of an aerogel material. Silica nanofiber has with silica aerogel compatibility good, specific surface area is big, the pliability is good, characteristics such as heat conduction coefficient is little, with nanofiber and aerogel material complex, flexible fiber material not only can bear the certain degree of buckling, can also effectively prevent aerogel material at the expansion of deformation in-process crackle, and then reinforcing aerogel material's mechanical properties, simultaneously, nanometer fiber diameter is thinner, and heat conduction effect is lower, makes the material have stronger heat-proof quality.
Step S120: the nanofiber membrane is heat treated to remove the polymer.
Specifically, the temperature of the heat treatment is 300-900 ℃, the time of the heat treatment is 0.5-5 h, and the heat treatment is carried out under the vacuum condition or under the protection of inert gas. The nanofiber prepared by the electrostatic spinning method contains more organic components, and the organic components are oxidized and decomposed at high temperature, so that the mechanical and heat-insulating properties of the material are reduced. In this embodiment, the nanofiber membrane is heat-treated to make the fiber structure inorganic and remove organic components without destroying the fiber structure, so that the material has better high-temperature resistance and heat insulation performance.
Specifically, the temperature of the heat treatment may be adjusted according to the cracking temperature of the polymer.
In one embodiment, the inert gas is nitrogen or argon.
Step S130: and mixing the residual silicon source with water and an alcohol solvent to prepare the silica sol.
Specifically, the step of mixing the remaining silicon source with water and an alcohol reagent comprises: dispersing the rest silicon source in an alcohol reagent, adding water, adjusting the pH to 2-5, stirring for 1-10 h, and adjusting the pH to 6-9.
Preferably, hydrochloric acid is added to adjust the pH value in the step of adjusting the pH value to 2-5. It can be understood that in the step of adjusting the pH to 2-5, other acidic reagents can be added to adjust the pH.
Preferably, in the step of adjusting the pH to 6-8, ammonia water is added to adjust the pH. It can be understood that other alkaline reagents can be added to adjust the pH in the step of adjusting the pH to 6-8.
Preferably, in the step of mixing the remaining silicon source with water and the alcohol reagent, the molar ratio of the remaining silicon source to the alcohol reagent to the water is 1: (5-20): (2-10). The inventor finds that the time for generating the silica sol into the gel is controlled by controlling the molar ratio of the silicon source, the alcohol reagent and the water and the pH value of the reaction, so that the condition that the silica sol gel is too fast to influence the subsequent mixing and dipping process with the nanofiber membrane under the negative pressure condition is avoided.
In one embodiment, the alcoholic solvent is ethanol, methanol or propanol. Preferably, the alcoholic solvent is ethanol.
Further, in the step of mixing the remaining silicon source with water and an alcohol reagent, a nitrate of a rare earth element or an oxide of a rare earth element is added. The nuclear power plant primary circuit shell has strong neutron irradiation, and the neutron irradiation can accelerate the aging of the conventional aerogel material, so that the material performance is degraded. Therefore, in the embodiment, in the method of adding the nitrate of the rare earth element or the oxide of the rare earth element in the preparation process of the silica sol, the rare earth element has strong absorption and shielding effects on neutron irradiation, so that the material has higher neutron tolerance, and the application of the aerogel thermal insulation material in a nuclear power thermal insulation scene is expanded.
In one embodiment, the mass ratio of the nitrate or oxide of the rare earth element to the rest of the silicon source is (1-35) to 100.
Specifically, the rare earth element is lanthanum, cerium, neodymium or gadolinium. Preferably, the rare earth element is gadolinium. In the step of mixing the remaining silicon source with water and an alcohol reagent, gadolinium nitrate or gadolinium oxide is also added.
Specifically, the nitrate salt of the rare earth element is mixed with the remaining silicon source, water and alcohol solvent in the form of an aqueous solution. The oxide of the rare earth element is mixed with the rest silicon source, water and alcohol solvent in an ultrasonic dispersion mode.
Further, step S130 and step S120 are not in sequence, and step S130 may be performed first, and then step S120 may be performed, or step S120 may be performed first, and then step S130 may be performed, or step S120 and step S130 may be performed simultaneously.
Step S140: and soaking the nanofiber membrane subjected to heat treatment in silica sol, and mixing under a negative pressure condition to prepare nanofiber sol.
Specifically, the silica sol is placed at the lower layer of the mold, and the nanofiber membrane is placed at the upper layer of the mold, so that the silica sol completely submerges the nanofiber membrane. It is understood that the mold may be a mold commonly used in the art and will not be described herein.
It can be understood that, in the process of immersing the nanofiber membrane after the heat treatment in the silica sol in step S140, the nanofiber membrane may be one or more layers, and may be specifically adjusted according to the thickness, mechanical properties and other conditions of the fiber aerogel material to be actually obtained. The one-layer or multi-layer nanofiber membrane can play a role in improving the heat insulation performance, high temperature resistance and mechanical performance of the fiber composite aerogel material, and the number of the layers of the nanofiber membrane has little influence on the heat conductivity and the high temperature resistance of the prepared fiber composite aerogel material.
Different from a simple dipping gel method, the bottom-pouring type negative pressure dipping method is adopted in the embodiment to enable the nanofiber membrane to be fully dipped by the silica sol, the silica sol is fully dispersed in a nanofiber framework and gaps, and the silica gel and the fibers form stronger bonding force in the process of gelling and aging, so that the mechanical property is enhanced, and the phenomenon of powder falling is avoided. Meanwhile, the dispersion effect effectively reduces the content of macropores in the composite material, thereby further improving the heat insulation performance of the material.
Step S150: and carrying out gel aging treatment on the nanofiber sol, and then drying to prepare the fiber composite aerogel material.
In the step of carrying out gel aging treatment on the nanofiber sol, standing the nanofiber sol for 0.5-3 h to prepare the nanofiber gel, then placing the nanofiber gel in an alcohol reagent, and carrying out aging treatment for 1-3 days at 60-70 ℃.
Specifically, the alcohol solvent is ethanol, methanol or propanol. Preferably, the alcoholic solvent is ethanol.
The drying mode is carbon dioxide supercritical drying. The temperature of the supercritical drying of the carbon dioxide is 32-50 ℃, and the pressure is 7.4-18 MPa. Compared with vacuum drying and normal-pressure drying methods, the carbon dioxide supercritical drying method saves the period of material surface modification, reduces collapse of the pore diameter in the material in the drying process, and enables the material to have better heat insulation and mechanical properties.
The preparation method of the fiber composite aerogel material at least has the following advantages:
(1) the preparation method of the fiber composite aerogel material is based on the characteristic that inorganic fibers can obtain enhanced flexibility when the inorganic fibers have nanometer-scale diameters and are uniformly distributed, the flexible fibers with the nanometer-scale diameters are prepared by using an electrostatic spinning method and serve as fiber reinforcements of the aerogel material, polymers in the nanofibers are removed through heat treatment, the fiber structure is inorganic, the polymers are prevented from being oxidized and decomposed at high temperature to reduce the mechanical and heat insulation performance of the material, and therefore the material has better high-temperature resistance and heat insulation performance. The inorganic silica nanofiber has the characteristics of good compatibility with silica aerogel, large specific surface area, good flexibility, small heat conduction coefficient and the like, the nanofiber is compounded with the aerogel material, the flexible fiber material can bear bending to a certain degree, the expansion of cracks of the aerogel material in the deformation process can be effectively prevented, and further the mechanical performance of the aerogel material is enhanced. The nanofiber membrane after heat treatment is soaked in the silica sol and mixed under the negative pressure condition, so that the nanofiber membrane is fully soaked in the silica sol, the silica sol is fully dispersed in a nanofiber framework and gaps, and the silica gel and fibers form stronger binding force in the gelling and aging processes, so that the mechanical property is enhanced, and the phenomenon of powder falling is avoided. Meanwhile, the dispersion effect effectively reduces the content of macropores in the composite material, thereby further improving the heat insulation performance of the material. Therefore, the preparation method of the fiber composite aerogel material can simultaneously improve the heat preservation performance and the flexibility of the fiber composite aerogel material and prevent powder falling.
(2) Rare earth elements are added in the preparation process of the fiber composite aerogel material, so that the rare earth elements are dispersed in the fiber composite aerogel material, and the rare earth elements have strong absorption and shielding effects on neutron irradiation, so that the material has higher neutron tolerance and can be applied to nuclear power heat-insulating materials.
(3) Compared with vacuum drying and normal-pressure drying methods, the carbon dioxide supercritical drying method saves the period of material surface modification, reduces collapse of the pore diameter in the material in the drying process, and enables the material to have better heat insulation and mechanical properties.
The fiber composite aerogel material of an embodiment is prepared by the preparation method of the fiber composite aerogel material. The fiber composite aerogel material has good heat preservation and insulation performance and flexibility, and has good high temperature resistance, no powder falling and neutron radiation resistance.
The application of the fiber composite aerogel material of one embodiment in preparing nuclear power thermal insulation materials. The fiber composite aerogel material has good heat insulation performance and flexibility, is good in high temperature resistance, does not fall powder, is resistant to neutron radiation, and can be applied to nuclear power heat insulation materials.
The following are specific examples:
example 1
The preparation process of the fiber composite aerogel material of the embodiment is specifically as follows:
(1) uniformly mixing tetraethoxysilane and deionized water (the molar ratio is 1: 8), adjusting the pH value to 3 by using hydrochloric acid, uniformly mixing the mixture with a PVA solution (the mass percentage concentration is 10%) according to the mass ratio of 1: 1 after stirring for 12 hours, and then carrying out electrostatic spinning on the mixed solution to prepare the nanofiber membrane, wherein the technological parameters in the spinning process are as follows: the voltage was 10kV, the receiving distance was 12cm, and the injection flow rate was 2 mL/h.
(2) And (2) preserving the temperature of the nanofiber membrane prepared in the step (1) for 1.5h at 700 ℃ in a vacuum environment, and preparing the high-temperature-resistant nanofiber membrane.
(3) The ethyl orthosilicate, the ethanol and the water (the molar ratio is 1: 10: 5) are uniformly mixed, the pH is adjusted to 3 by hydrochloric acid, the mixture is continuously and slowly stirred for 6 hours, and then the pH is adjusted to 7 by ammonia water to prepare the silica sol.
(4) And (3) placing the multilayer high-temperature-resistant nanofiber membrane prepared in the step (2) on the upper layer of a mold, placing the silica sol solution prepared in the step (3) on the lower layer of the mold, and mixing the multilayer nanofiber membrane with the silica sol under the negative pressure condition to prepare the nanofiber sol.
(5) And (4) standing the nanofiber sol prepared in the step (4) in a constant-temperature water bath in a closed environment for 2 hours, and after the nanofiber sol is gelled, placing the gelled material in a container containing ethanol and aging in a constant-temperature water bath at 70 ℃ for 3 days. And then drying the aged nanofiber gel by using supercritical carbon dioxide to prepare the fiber composite aerogel. The drying temperature is 40 ℃ and the pressure is 10 MPa.
Example 2
The preparation process of the fiber composite aerogel material of the embodiment is specifically as follows:
(1) uniformly mixing tetraethoxysilane and deionized water (the molar ratio is 1: 8), adjusting the pH value to 3 by using hydrochloric acid, uniformly mixing the mixture with a PVA solution (the mass percentage concentration is 10%) according to the mass ratio of 1: 1 after stirring for 12 hours, and then carrying out electrostatic spinning on the mixed solution to prepare the nanofiber membrane, wherein the technological parameters in the spinning process are as follows: the voltage was 10kV, the receiving distance was 12cm, and the injection flow rate was 2 mL/h.
(2) And (2) preserving the temperature of the nanofiber membrane prepared in the step (1) for 1h at 700 ℃ in a vacuum environment, and preparing the high-temperature-resistant nanofiber membrane.
(3) 10mL of ethyl orthosilicate (9.3g, 0.045mol) and 40mL of ethanol (31.56g, 0.685mol) were uniformly mixed to prepare a solution A, 4.5mL (4.5g, 0.25mol) (the molar ratio of ethyl orthosilicate, ethanol and water is 1: 15: 5.5) of an aqueous solution containing 0.5g of gadolinium nitrate was added dropwise to the solution A, the pH was adjusted to 3 with hydrochloric acid, stirring was continued slowly for 6 hours, and then the pH was adjusted to 7 with aqueous ammonia to prepare a silica sol.
(4) And (3) placing the multilayer high-temperature-resistant nanofiber membrane prepared in the step (2) on the upper layer of a mold, placing the silica sol solution prepared in the step (3) on the lower layer of the mold, and mixing the multilayer nanofiber membrane with the silica sol under the negative pressure condition to prepare the nanofiber sol.
(5) And (4) standing the nanofiber sol prepared in the step (4) in a constant-temperature water bath in a closed environment for 2 hours, and after the nanofiber sol is gelled, placing the gelled material in a container containing ethanol and aging in a constant-temperature water bath at 70 ℃ for 3 days. And then drying the aged nanofiber gel by using supercritical carbon dioxide to prepare the fiber composite aerogel. The drying temperature is 40 ℃ and the pressure is 10 MPa.
Example 3
The process for making the fiber composite aerogel material of this example is similar to the process for making the fiber composite aerogel material of example 1, except that: the sol in the step (3) has different proportions. Specifically, the step (3) is as follows: the ethyl orthosilicate, the ethanol and the water (the molar ratio is 1: 5) are uniformly mixed, the pH is adjusted to 3 by hydrochloric acid, the mixture is continuously and slowly stirred for 6 hours, and then the pH is adjusted to 7 by ammonia water to prepare the silica sol.
Example 4
The process for making the fiber composite aerogel material of this example is similar to the process for making the fiber composite aerogel material of example 1, except that: the sol in the step (3) has different proportions. Specifically, the step (3) is as follows: the ethyl orthosilicate, the ethanol and the water (the molar ratio is 1: 20: 5) are uniformly mixed, the pH is adjusted to 3 by hydrochloric acid, the mixture is continuously and slowly stirred for 6 hours, and then the pH is adjusted to 7 by ammonia water to prepare the silica sol.
Example 5
The process for making the fiber composite aerogel material of this example is similar to the process for making the fiber composite aerogel material of example 2, except that: the proportion of the rare earth elements in the step (3) is different. Specifically, the step (3) is as follows: uniformly mixing 10mL of ethyl orthosilicate and 40mL of ethanol to obtain a solution A, dropwise adding 4.5mL of a dissolving solution containing 1g of gadolinium nitrate into the solution A, adjusting the pH to 3 by hydrochloric acid, continuously and slowly stirring for 6 hours, and adjusting the pH to 7 by using ammonia water to prepare silica sol.
Example 6
The process for making the fiber composite aerogel material of this example is similar to the process for making the fiber composite aerogel material of example 2, except that: the proportion of the rare earth elements in the step (3) is different. Specifically, the step (3) is as follows: uniformly mixing 10mL of ethyl orthosilicate and 40mL of ethanol to obtain a solution A, dropwise adding 4.5mL of a dissolving solution containing 3g of gadolinium nitrate into the solution A, adjusting the pH to 3 by hydrochloric acid, continuously and slowly stirring for 6 hours, and adjusting the pH to 7 by using ammonia water to prepare silica sol.
Comparative example 1
The process for making the fiber composite aerogel material of comparative example 1 is similar to the process for making the fiber composite aerogel material of example 1, except that: the heat treatment of step (2) was not performed in comparative example 1.
Comparative example 2
The process for making the fiber composite aerogel material of comparative example 2 is similar to the process for making the fiber composite aerogel material of example 1, except that: the heat treatment temperature in comparative example 2 was 1200 ℃.
Comparative example 3
The preparation process of the fiber composite aerogel material of comparative example 3 is specifically as follows:
(1) the ethyl orthosilicate, the ethanol and the water (the molar ratio is 1: 10: 5) are uniformly mixed, the pH is adjusted to 3 by hydrochloric acid, and the mixture is continuously and slowly stirred for 12 hours to prepare the silica sol.
(2) Carrying out electrostatic spinning on 10% of PVA solution by mass fraction to prepare the nanofiber membrane, wherein the technological parameters in the spinning process are as follows: the voltage is 10KV, the receiving distance is 12cm, and the injection flow rate is 2 mL/h.
(3) And (3) collecting and dispersing the PVA fiber membrane in the step (2) through the silica sol in the step (1), and adding a certain amount of ammonia water to enable the silica sol to form gel.
(4) And (4) placing the gel obtained in the step (3) in ethanol, and aging the gel for 3 days at 70 ℃. And then drying the aged nanofiber gel by using supercritical carbon dioxide to prepare the fiber composite aerogel. The drying temperature is 40 ℃ and the pressure is 10 MPa.
The following are test sections:
the fiber composite aerogel materials prepared in the examples and the comparative examples were tested for temperature resistance, thermal conductivity at 25 ℃, density and other parameters, and the experimental data shown in the following table were obtained. The specific test method is as follows: the high temperature resistance test adopts that after calcination is carried out at 750 ℃ for not less than 6 hours, various properties of the material still meet the performance index requirements. And testing the normal-temperature thermal conductivity of the fiber composite aerogel material by adopting GB/T10295-2008 test standard. The density of the fiber composite aerogel material is tested by GB/T17911-2006.
TABLE 1 Performance data for fiber composite aerogel materials of the examples and comparative examples
As can be seen from Table 1, the fiber composite aerogel materials prepared in examples 1 to 6 have good temperature resistance, can reach 750 ℃, have room-temperature thermal conductivity of 0.022mW/(m.K) -0.025 mW/(m.K), and have density of 0.08-0.16 g/cm3. While the temperature resistance of the fiber composite aerogel materials of comparative example 1 and comparative example 3 is only 350 ℃, the temperature resistance is poor, and the cracking of the spinning fibers at higher temperature leads to the fragmentation of the materials. The heat conductivity at normal temperature is 0.028-0.032mW/(m.K), and the heat preservation performance is poorer than that of the embodiment. The temperature of the heat treatment in comparative example 2 was too high, resulting in brittle fracture of the electrospun fiber and failure to form.
The technical features of the embodiments described above may be arbitrarily combined, and for the sake of brevity, all possible combinations of the technical features in the embodiments described above are not described, but should be considered as being within the scope of the present specification as long as there is no contradiction between the combinations of the technical features.
The above-mentioned embodiments only express several embodiments of the present invention, and the description thereof is more specific and detailed, but not construed as limiting the scope of the invention. It should be noted that, for a person skilled in the art, several variations and modifications can be made without departing from the inventive concept, which falls within the scope of the present invention. Therefore, the protection scope of the present patent shall be subject to the appended claims.
Claims (15)
1. The preparation method of the fiber composite aerogel material is characterized by comprising the following steps:
hydrolyzing part of the silicon source to prepare a silicon hydrolysate, mixing the silicon hydrolysate with a polymer, and performing electrostatic spinning to prepare a nanofiber membrane;
heat treating the nanofiber membrane to remove the polymer;
mixing the residual silicon source with water and an alcohol solvent to prepare silica sol;
soaking the nanofiber membrane subjected to heat treatment in the silica sol, and mixing under a negative pressure condition to prepare nanofiber sol; and
and carrying out gel aging treatment on the nanofiber sol, and then drying to prepare the fiber composite aerogel material.
2. The preparation method of the fiber composite aerogel material according to claim 1, wherein the temperature of the heat treatment is 300-900 ℃, the time of the heat treatment is 0.5-5 h, and the heat treatment is performed under vacuum condition or under inert gas protection.
3. The method for preparing the fiber composite aerogel material according to claim 1, wherein in the step of electrospinning, the spinning voltage is 10kV to 20kV, the receiving distance is 5cm to 25cm, and the injection flow rate is 0.3mL/h to 3 mL/h.
4. The method for preparing a fiber composite aerogel material according to claim 1, wherein the drying manner is carbon dioxide supercritical drying.
5. The preparation method of the fiber composite aerogel material according to claim 4, wherein the temperature of the carbon dioxide supercritical drying is 32-50 ℃, and the pressure is 7.4-18 MPa.
6. The method of claim 1, wherein a rare earth nitrate or a rare earth oxide is added during the step of mixing the remaining silicon source with water and an alcohol reagent.
7. The method of claim 6, wherein the rare earth element is lanthanum, cerium, neodymium, or gadolinium; and/or the presence of a catalyst in the reaction mixture,
the mass ratio of the nitrate of the rare earth element or the oxide of the rare earth element to the rest of the silicon source is (1-35) to 100.
8. The method of preparing a fiber composite aerogel material of claim 1, wherein the polymer is polyvinyl alcohol; and/or the presence of a catalyst in the reaction mixture,
in the step of mixing the silicon hydrolysate with the polymer, the silicon hydrolysate is mixed with the aqueous solution of the polymer, the mass ratio of the silicon hydrolysate to the aqueous solution of the polymer is 1: 0.6-1.4, and the mass percentage concentration of the aqueous solution of the polymer is 5% -15%.
9. The method for preparing the fiber composite aerogel material according to claim 1, wherein in the step of subjecting the nanofiber sol to gel aging treatment, the nanofiber sol is allowed to stand for 0.5 to 3 hours to prepare nanofiber gel, and then the nanofiber gel is placed in an alcohol reagent and subjected to aging treatment at 60 to 70 ℃ for 1 to 3 days.
10. The method of preparing a fiber composite aerogel material according to any of claims 1 to 9, wherein the step of hydrolyzing a portion of the silicon source comprises: mixing part of the silicon source and water according to the molar ratio of 1: 2-10, then adjusting the pH value to 2-5, and stirring for 1-10 h.
11. The method of any one of claims 1-9, wherein the step of mixing the remaining silicon source with water and an alcohol reagent comprises: dispersing the rest silicon source in the alcohol reagent, adding water, adjusting the pH to 2-5, stirring for 1-10 h, and adjusting the pH to 6-9.
12. The method for preparing the fiber composite aerogel material according to claim 11, wherein in the step of mixing the remaining silicon source with water and the alcohol reagent, the molar ratio of the remaining silicon source to the alcohol reagent to the water is 1: 5-20: 2-10.
13. The preparation method of the fiber composite aerogel material according to any one of claims 1 to 9 and 11, wherein the silicon source is ethyl orthosilicate, methyl orthosilicate or butyl orthosilicate; and/or the alcohol solvent is ethanol, methanol or propanol.
14. A fiber composite aerogel material, characterized by being prepared by the method for preparing the fiber composite aerogel material according to any one of claims 1 to 13.
15. Use of the fiber composite aerogel material of claim 14, in the preparation of nuclear power insulation.
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