CN114832741B - Preparation method of heat-conducting wave-absorbing composite aerogel and heat-conducting wave-absorbing composite aerogel - Google Patents

Preparation method of heat-conducting wave-absorbing composite aerogel and heat-conducting wave-absorbing composite aerogel Download PDF

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CN114832741B
CN114832741B CN202210483516.0A CN202210483516A CN114832741B CN 114832741 B CN114832741 B CN 114832741B CN 202210483516 A CN202210483516 A CN 202210483516A CN 114832741 B CN114832741 B CN 114832741B
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sio
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CN114832741A (en
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秦文波
郭晶晶
黄飞
舒登峰
孙佳晨
陈昊
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Huijing New Material Technology Hangzhou Co ltd
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    • B01J13/00—Colloid chemistry, e.g. the production of colloidal materials or their solutions, not otherwise provided for; Making microcapsules or microballoons
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Abstract

The embodiment of the disclosure discloses a preparation method of heat-conducting wave-absorbing composite aerogel and the heat-conducting wave-absorbing composite aerogel, wherein the method comprises the following steps: the method comprises the following steps: silicon dioxide SiO 2 Coating on MWCNTs to obtain SiO 2 @ MWCNTs nano composite material, and surface modification is carried out; step two: weighing polyvinylpyrrolidone, glycol and ferric chloride hexahydrate, and mixing to obtain Fe 3+ Precursor solution is added with SiO after surface modification 2 @ MWCNTs nano composite material to obtain mixed solution, then transferring the mixed solution into a reaction kettle to react, and drying to obtain Fe 3 O 4 @SiO 2 @ MWCNTs ternary nanocomposite; step three: mixing Fe 3 O 4 @SiO 2 Carrying out surface modification on the @ MWCNTs ternary nano composite material, then adding the material into water, and carrying out ultrasonic dispersion to prepare a suspension; step four: adding phytic acid PA and alginate into the suspension under stirring, and then adding glucolactone to obtain a composite gel solution; step five: and (4) introducing the composite gel solution into a mold, and freeze-drying to obtain the composite aerogel.

Description

Preparation method of heat-conducting wave-absorbing composite aerogel and heat-conducting wave-absorbing composite aerogel
Technical Field
The invention relates to the field of heat conduction and wave absorption materials, in particular to a preparation method of heat conduction and wave absorption composite aerogel and the heat conduction and wave absorption composite aerogel.
Background
With the development of modern science and technology, the requirements on materials are further improved, the materials with single functions cannot meet the requirement of multi-functionalization, how to realize that the materials with single functions have multiple functions so as to meet the requirements of light weight, miniaturization and high reliability of electronic equipment, aerospace, weaponry and the like is realized, and the research is developed towards the direction of integration of composite and multifunctional structures and functions into the inevitable trend of future development. With the rapid development of aerospace technologies, weaponry and anti-reconnaissance radars, aircrafts and the like progress towards high Mach number, the surfaces of the aircrafts are subjected to the requirements of thermal radiation generated by strong pneumatic heating action and radar stealth technologies, and the requirements on thermal protection and electromagnetic shielding of materials are extremely high. The heat insulation and wave absorption functions have important significance for improving the technical indexes of the aircraft, the composite functions are integrated into a whole body, the passive structural quality can be effectively reduced, the space utilization rate of an instrument chamber is improved, the structural function integration is well realized, and the requirements of the aircraft on high speed, high overload, high maneuverability and super stealth are met. In addition, for the civil field, heat radiation and electromagnetic waves generated by the operation of household high-power appliances (such as an induction cooker, a refrigerator, an oven and the like) and large medical examination equipment (such as an X-ray diffractometer, nuclear magnetic resonance and the like) cause great harm to human bodies and the environment. Therefore, how to prepare a light interlayer material with high heat insulation performance and strong wave absorption becomes an important field of research at present.
The aerogel material serving as a highly-crosslinked net-shaped porous material has the advantages of low density, high porosity, low thermal conductivity and the like. The low density and complex three-dimensional structure of the aerogel can effectively prolong the heat transfer path to realize excellent heat insulation. Meanwhile, the high porosity characteristic of the aerogel enables the material to have excellent impedance matching characteristic, and the aerogel is a high-quality wave-absorbing base material with high performance. Therefore, the development of the aerogel material integrating heat insulation and wave absorption has important practical significance. After the research on inorganic aerogels such as oxides, carbides and nitrides and traditional polymer-based organic aerogels, the biomass-based organic aerogel attracts great attention by virtue of the advantages of wide distribution of raw materials, simple acquisition mode and the like. Meanwhile, the biomass-based raw materials are usually green and nontoxic, and generally have the characteristics of biocompatibility, biodegradability and the like, so that the biomass-based raw materials are very in line with the current green chemical concept and also are the development concept of actively responding to the carbon neutralization planning and implementation of the country. The alginate is a randomly arranged polymeric polysaccharide with a linear structure extracted from seaweed, consists of beta-D-mannuronic acid (M unit) and alpha-L-guluronic acid (G unit), and has the advantages of biodegradability, abundant resources, low price and environmental friendliness. However, the pure alginate-based aerogel has the problems of poor wave-absorbing performance, large contractibility in the preparation process, easy structural collapse, poor mechanical properties, poor flame retardant property and the like, thereby causing the reduction of the comprehensive properties of the pure alginate-based aerogel. And the heat insulation/wave absorption research of most of the aerogel shows excellent performance in a single direction, and the research on the aerogel integrating heat insulation and wave absorption is relatively less.
Disclosure of Invention
In order to solve the technical problems, the invention provides a preparation method of a heat-conducting wave-absorbing composite aerogel, which comprises the following steps:
the method comprises the following steps: siO silicon dioxide 2 Coating on MWCNTs to obtain SiO 2 @ MWCNTs nano composite material, and SiO 2 Processing the @ MWCNTs nano composite material at high temperature to perform surface modification;
step two: weighing polyvinylpyrrolidone, glycol and ferric chloride hexahydrate, and mixing to obtain Fe 3+ Precursor solution, then adding surface modified SiO 2 The preparation method comprises the following steps of obtaining a mixed solution from the @ MWCNTs nano composite material, adjusting the pH value of the mixed solution to 10-12, performing ultrasonic dispersion under stirring, transferring the mixed solution into a reaction kettle for reaction, cooling to room temperature after the reaction is finished, collecting a reaction product by using a magnet, washing the reaction product, and drying to obtain Fe 3 O 4 @SiO 2 @ MWCNTs ternary nanocomposite;
step three: mixing Fe 3 O 4 @SiO 2 The @ MWCNTs ternary nano composite material is subjected to surface modification to obtain Fe with the surface rich in hydrophilic groups such as hydroxyl groups and oxygen-containing functional groups 3 O 4 @SiO 2 The @ MWCNTs ternary nano composite material is added into water and is subjected to ultrasonic dispersion to prepare suspension;
step four: adding phytic acid PA and alginate into the suspension prepared in the third step under stirring, then adding glucolactone, and uniformly stirring to obtain a composite gel solution;
step five: and (4) introducing the composite gel solution into a mold, and freeze-drying to obtain the composite aerogel.
According to one embodiment of the invention, the improvement utilized in step one
Figure BDA0003628471110000031
Process for preparing SiO 2 2 The shell is coated on the MWCNTs of the multi-walled carbon nano-tube to prepare tubular SiO with a core-shell structure 2 @ MWCNTs nanocomposite. Specifically, MWCNTs, deionized water and ethanol are weighed and mixed to obtain a suspension, ammonia water is added under stirring to be mixed uniformly, tetraethoxysilane is added to be mixed uniformly, reaction is carried out under the water bath condition, and after the reaction is finished, obtained powder is centrifuged, washed and dried to obtain SiO 2 @ MWCNTs nanocomposite.
In the present disclosure, the volume ratio of the mixed solution of deionized water and ethanol is 4:1. the bath temperature may be 60 ℃. The washing conditions were deionized water 3 times and then ethanol 3 times. The drying condition is drying time 24h in a vacuum oven at 60 ℃.
According to an embodiment of the invention, the surface modification in the first step is performed by heating to 300-500 ℃ and maintaining for 2-4h, and then heating to 550-750 ℃ and maintaining for 2-4h, wherein the heating rate can be 3-5 ℃/min.
In step two, ferric chloride hexahydrate and SiO 2 The mass ratio of the @ MWCNTs nano composite material is 2:2-4.
According to one embodiment of the present invention, the surface modification in step three is performed under the condition that Fe is added 3 O 4 @SiO 2 The @ MWCNTs ternary nano composite material is put into mixed solution of sulfuric acid and nitric acid for acidification modification, and then washed to be neutral by water. Specifically, the volume ratio of sulfuric acid to nitric acid is 1:1, the concentration of sulfuric acid may be 45-65% and the concentration of nitric acid may be 45-65%.
According to one embodiment of the invention, in the third step, ultrasonic and slow electric stirring are firstly carried out for 30min, then fast stirring is carried out for 30min (ultrasonic power 1200W, stirring speed is 200r/min and 500 r/min), then standing is carried out for 30min, and the uniformly dispersed suspension of the upper layer is taken. And adding deionized water into the residual precipitated mixed solution, ultrasonically and electrically stirring uniformly according to the steps, and repeating the steps until the powder is completely dispersed to obtain the suspension.
According to one embodiment of the invention, the concentration of phytic acid PA in step four is from 40wt% to 50wt%. The stirring is ultrasonic and electric stirring to a uniform gel state.
According to an embodiment of the present invention, the alginate in step four is selected from one or more of ammonium alginate, potassium alginate and sodium alginate. Specifically, phytic acid PA, alginate and Fe 3 O 4 @SiO 2 The mass ratio of the @ MWCNTs ternary nano composite material is 1-4:5:1-7. Preferably, phytic acid PA, alginate, fe 3 O 4 @SiO 2 The mass ratio of the @ MWCNTs ternary nano composite material is 4:5:5.
according to one embodiment of the invention, the freeze-drying conditions in step five are two-way liquid nitrogen freezing at-20-40 ℃ and drying in a freeze-drying oven for 1-3 days. The freeze drying method is to use solvent as medium, to grow crystal through the solvent medium, to rearrange the solute in the slurry, and to remove the solvent by means of low temperature sublimation, etc. to obtain the porous material with anisotropic or isotropic pore structure. In the present disclosure, a liquid nitrogen freeze-drying method is adopted, as shown in fig. 2, freezing is performed in both directions from the X-axis direction and from the Z-axis direction, and the supercooling degree is increased to promote the refinement of ice crystals, thereby obtaining a fine and uniform pore structure. Under the high vacuum state, the ice state is sublimated directly into water vapor by utilizing the sublimation principle, so that the aim of freeze drying is fulfilled.
According to an embodiment of the present invention, before the introducing the composite gel solution into the mold in the fifth step, the method further comprises: and (3) placing the composite gel solution in a two-dimensional magnetic field or a three-dimensional magnetic field for directional treatment. Specifically, a two-dimensional magnetic field is formed by utilizing vertical orthogonal electromagnets, and two-dimensional (X and Y axes) orientation treatment is carried out on the composite gel solution; or on the basis of a two-dimensional magnetic field, a solenoid magnetic field in the Z-axis direction is added to form a three-dimensional magnetic field, and the composite gel solution is subjected to three-dimensional (X, Y and Z axes) orientation treatment.
The invention also provides a heat-conducting wave-absorbing composite aerogel prepared by adopting any one of the methods.
Compared with the prior art, the invention has the following beneficial effects:
the preparation method of the heat-conducting wave-absorbing composite aerogel provided by the disclosure selects porous Fe rich in oxygen defects 3 O 4 @SiO 2 The @ MWCNTs ternary nano composite material is used as a reinforcing material to prepare the double-network structure composite aerogel, namely Fe is utilized 3 O 4 @SiO 2 The high length-diameter ratio characteristic of the @ MWCNTs ternary nanocomposite interpenetrates and bridges in the aerogel network matrix, so that the aerogel has a strong cross-linked structure, and the volume shrinkage of the aerogel can be effectively inhibited. Meanwhile, a network structure formed inside the aerogel improves the absorption performance of electromagnetic waves and provides more multilayer reflection effects, and the energy of incident electromagnetic waves is effectively attenuated. Under the action of high-intensity electromagnetic wave, fe 3 O 4 @SiO 2 The internal defects and the good impedance matching of the @ MWCNTs ternary nanocomposite provide good channels for electron transfer, improve dielectric loss and magnetic loss, and simultaneously, siO 2 And the PA has double flame-retardant and heat-insulating properties, effectively reduces the heat energy converted by electromagnetic waves and has better flame-retardant and heat-insulating properties.
Drawings
Other features, objects, and advantages of the present disclosure will become more apparent from the following detailed description of non-limiting embodiments when taken in conjunction with the accompanying drawings. In the drawings:
FIG. 1 shows a schematic diagram of a two-dimensional magnetic field orientation treatment of a composite gel solution;
fig. 2 shows a schematic diagram of three-dimensional magnetic field orientation treatment of a composite gel solution.
Detailed Description
The present invention will be further described with reference to the following examples.
Thermal conductivity of the material was measured according to ASTM D5470;
and measuring the electromagnetic parameters of the material in the frequency range of 2-18 GHz on a vector network analyzer.
The compression performance of the material is measured on a universal testing machine.
Example 1:
porous magnetic Fe 3 O 4 @SiO 2 Preparation of the @ MWCNTs ternary nanocomposite:
(1) 1g of MWCNTs is added into a mixed solution of 20mL of deionized water and 80mL of ethanol, and ultrasonic stirring is carried out for 30min to obtain a suspension. 10mL of ammonia water is added dropwise to the suspension, the reaction is continued for 20min under stirring, and subsequently 2.083g of ethyl orthosilicate are slowly added dropwise with stirring and mixed, and the reaction is continued for 12h under the condition of a water bath. Then, the obtained powder is centrifuged, washed and dried to obtain the tubular SiO with the core-shell structure 2 @ MWCNTs nanocomposite. Prepared SiO 2 The @ MWCNTs nano composite material is put into a muffle furnace for high-temperature heat treatment, the temperature is firstly raised to 400 ℃ and is preserved for 3h, then the temperature is raised to 650 ℃ and is preserved for 3h, the temperature raising speed is 3-5 ℃/min, then the temperature is rapidly cooled to room temperature, and the porous tubular SiO with the core-shell structure and the surface rich in defects is obtained 2 @ MWCNTs nanocomposite.
(2) Dissolving 0.3g of polyvinylpyrrolidone in 80mL of ethylene glycol to obtain a mixed solution, and taking 2g of FeCl 3 ·6H 2 Adding O powder into the mixed solution, and stirring for 30min under ultrasonic condition until the powder is completely dissolved to obtain Fe 3+ And (3) precursor solution. 2g of SiO are taken 2 @ MWCNTs nano composite material added with Fe 3+ And (3) in the precursor solution, carrying out ultrasonic and electric stirring for 30min, adjusting the pH value to 12 by using a concentrated NaOH solution, and continuously stirring for reacting for 30min. Then transferring the mixed solution into a 100mL stainless steel autoclave with a polytetrafluoroethylene lining, reacting for 12h at a constant temperature of 180 ℃, naturally cooling to room temperature, collecting a sample by using a permanent magnet, washing (washing with deionized water for 3 times and washing with ethanol for 3 times), and drying in an oven at 60 ℃ for 24h to obtain porous magnetic Fe 3 O 4 @SiO 2 @ MWCNTs ternary nanocomposite.
Example 2
Porous magnetic Fe 3 O 4 @SiO 2 Preparation of the @ MWCNTs ternary nanocomposite:
(1) 1g of MWCNTs is added into a mixed solution of 20mL of deionized water and 80mL of ethanol, and ultrasonic stirring is carried out for 30min to obtain a suspension. 10mL of ammonia water is added dropwise to the suspension, the reaction is continued for 20min under stirring, and subsequently 2.083g of ethyl orthosilicate are slowly added dropwise with stirring and mixed, and the reaction is continued for 12h under the condition of a water bath. Then, the obtained powder is centrifuged, washed and dried to obtain the tubular SiO with the core-shell structure 2 @ MWCNTs nanocomposite. Prepared SiO 2 The @ MWCNTs nano composite material is put into a muffle furnace for high-temperature heat treatment, the temperature is firstly raised to 400 ℃ and is preserved for 3h, then the temperature is raised to 650 ℃ and is preserved for 3h, the temperature raising speed is 3-5 ℃/min, then the temperature is rapidly cooled to room temperature, and the porous tubular SiO with the core-shell structure and the oxygen-rich defect on the surface is obtained 2 @ MWCNTs nanocomposite.
(2) Dissolving 0.3g of polyvinylpyrrolidone in 80mL of ethylene glycol to obtain a mixed solution, and taking 2g of FeCl 3 ·6H 2 Adding O powder into the mixed solution, and stirring for 30min under ultrasonic condition until the powder is completely dissolved to obtain Fe 3+ And (3) precursor solution. Take 4g of SiO 2 The @ MWCNTs nano composite material is added with Fe 3+ And (3) in the precursor solution, carrying out ultrasonic and electric stirring for 30min, adjusting the pH value to 12 by using a concentrated NaOH solution, and continuously stirring for reacting for 30min. Then transferring the mixed solution into a 100mL stainless steel autoclave with a polytetrafluoroethylene lining, reacting for 12h at a constant temperature of 180 ℃, naturally cooling to room temperature, collecting a sample by using a permanent magnet, washing (washing with deionized water for 3 times and washing with ethanol for 3 times), and drying in an oven at 60 ℃ for 24h to obtain porous magnetic Fe 3 O 4 @SiO 2 @ MWCNTs ternary nanocomposite.
Example 3
Preparation of SA-PA aerogel:
1g phytic acid PA (50 wt%) solution was added to 150mL deionized water and stirred under ultrasonic agitation for 30min to give a uniform suspension. And adding 5g of sodium alginate SA into the suspension, stirring vigorously for 1h until the powder is completely dissolved to obtain a uniform SA-PA sol solution, then adding 0.2g of gluconolactone into the sol solution, and stirring vigorously for 30min to disperse uniformly to obtain a precursor composite gel solution. And pouring the precursor composite gel solution into a mold, performing two-way liquid nitrogen freezing at-30 ℃, and drying in a freeze drying oven for 3 days to obtain the SA-PA aerogel.
Example 4
Preparation of SA-PA aerogel:
2g phytic acid PA (50 wt%) solution was added to 150mL deionized water and stirred under ultrasonic agitation for 30min to give a uniform suspension. And adding 5g of sodium alginate SA into the suspension, stirring vigorously for 1h until the powder is completely dissolved to obtain a uniform SA-PA sol solution, then adding 0.2g of gluconolactone into the sol solution, and stirring vigorously for 30min to disperse uniformly to obtain a precursor composite gel solution. And pouring the precursor composite gel solution into a mold, performing two-way liquid nitrogen freezing at-30 ℃, and drying in a freeze drying oven for 3 days to obtain the SA-PA aerogel.
Example 5
Preparation of SA-PA aerogel:
adding 3g phytic acid PA (50 wt%) solution into 150mL deionized water, and stirring for 30min by ultrasonic addition to obtain a uniform suspension. And adding 5g of sodium alginate SA into the suspension, stirring vigorously for 1h until the powder is completely dissolved to obtain a uniform SA-PA sol solution, then adding 0.2g of gluconolactone into the sol solution, and stirring vigorously for 30min to disperse uniformly to obtain a precursor composite gel solution. And pouring the precursor composite gel solution into a mold, performing bidirectional liquid nitrogen freezing at-30 ℃, and drying in a freeze-drying oven for 3 days to obtain the SA-PA aerogel.
Example 6
Preparation of SA-PA aerogel:
4g phytic acid PA (50 wt%) solution was added to 150mL deionized water and stirred under ultrasonic agitation for 30min to give a uniform suspension. And adding 5g of sodium alginate SA into the suspension, stirring vigorously for 1h until the powder is completely dissolved to obtain a uniform SA-PA sol solution, then adding 0.2g of gluconolactone into the sol solution, and stirring vigorously for 30min to disperse uniformly to obtain a precursor composite gel solution. And pouring the precursor composite gel solution into a mold, performing two-way liquid nitrogen freezing at-30 ℃, and drying in a freeze drying oven for 3 days to obtain the SA-PA aerogel.
Example 7
Preparing a composite aerogel:
(1) Porous magnetic Fe prepared in example 1 3 O 4 @SiO 2 The @ MWCNTs ternary nanocomposite is put into a mixed solution of 50% sulfuric acid and 60% nitric acid (the volume ratio of sulfuric acid to nitric acid is 1 3 O 4 @SiO 2 @ MWCNTs ternary nanocomposite.
(2) Taking 1g of modified Fe 3 O 4 @SiO 2 @ MWCNTs is added into 150mL deionized water and stirred uniformly, ultrasonic and slow electric stirring is carried out for 30min, then rapid stirring is carried out for 30min (the ultrasonic power is 1200W, the stirring speed is 200r/min and 500 r/min), then standing is carried out for 30min, and the suspension with uniformly dispersed upper layer is taken. And adding deionized water into the residual precipitated mixed solution, performing ultrasonic addition and stirring uniformly according to the steps, and repeating the steps until the powder is completely suspended to obtain a uniformly dispersed suspension.
(3) Slowly dripping 4g phytic acid PA (50 wt%) solution into the suspension under stirring, and rapidly stirring for 30min to uniformly distribute phytic acid PA in Fe 3 O 4 @SiO 2 @ MWCNTs surface to obtain PA-Fe 3 O 4 @SiO 2 @ MWCNTs mixed solution. 5g sodium alginate SA was added to the above PA-Fe 3 O 4 @SiO 2 In the @ MWCNTs mixed solution, the mixture is stirred vigorously by ultrasonic for 1h until the powder is completely dissolved, and then the uniform SA-PA-Fe is obtained 3 O 4 @SiO 2 @ MWCNTs sol solution, then 0.2g of gluconolactone is added, and the mixture is stirred vigorously for 30min to be dispersed evenly, so that composite gel solution is obtained. And pouring the composite gel solution into a mold, performing two-way liquid nitrogen freezing at-30 ℃, and drying in a freeze-drying oven for 3 days to obtain the composite aerogel.
Example 8
Preparing the composite aerogel:
(1) Will implement the embodiments1 porous magnetic Fe prepared in 3 O 4 @SiO 2 The method comprises the following steps of putting a @ MWCNTs ternary nano composite material into a mixed solution of 50% sulfuric acid and 60% nitric acid (the volume ratio of sulfuric acid to nitric acid is 1 3 O 4 @SiO 2 @ MWCNTs composites.
(2) Taking 3g of modified Fe 3 O 4 @SiO 2 @ MWCNTs is added into 150mL deionized water and stirred uniformly, ultrasonic and slow electric stirring is carried out for 30min, then rapid stirring is carried out for 30min (the ultrasonic power is 1200W, the stirring speed is 200r/min and 500 r/min), then standing is carried out for 30min, and the evenly dispersed suspension of the upper layer is taken. And adding deionized water into the residual precipitated mixed solution, performing ultrasonic addition and stirring uniformly according to the steps, and repeating until the powder is completely suspended to obtain a uniformly dispersed suspension.
(3) Slowly dripping 4g of phytic acid PA (50 wt%) solution into the suspension under stirring, and rapidly stirring for 30min to uniformly distribute phytic acid in Fe 3 O 4 @SiO 2 @ MWCNTs surface to obtain PA-Fe 3 O 4 @SiO 2 @ MWCNTs mixed solution. 5g sodium alginate SA was added to the above PA-Fe 3 O 4 @SiO 2 In the @ MWCNTs mixed solution, the mixture is stirred vigorously by ultrasonic for 1h until the powder is completely dissolved, and then the uniform SA-PA-Fe is obtained 3 O 4 @SiO 2 @ MWCNTs sol solution, then 0.2g of gluconolactone is added, and the mixture is stirred vigorously for 30min to be dispersed evenly, so that composite gel solution is obtained. And pouring the composite gel solution into a mold, performing two-way liquid nitrogen freezing at-30 ℃, and drying in a freeze-drying oven for 3 days to obtain the composite aerogel.
Example 9
Preparing the composite aerogel:
(1) Porous magnetic Fe prepared in example 1 3 O 4 @SiO 2 The @ MWCNTs ternary nano composite material is put into a mixed solution of 50% sulfuric acid and 60% nitric acid (the volume ratio of the sulfuric acid to the nitric acid is 1Washing the powder to be neutral by deionized water to obtain Fe with the surface rich in hydrophilic groups 3 O 4 @SiO 2 @ MWCNTs composite material.
(2) Taking 5g of modified Fe 3 O 4 @SiO 2 @ MWCNTs is added into 150mL deionized water and stirred uniformly, ultrasonic and slow electric stirring is carried out for 30min, then rapid stirring is carried out for 30min (the ultrasonic power is 1200W, the stirring speed is 200r/min and 500 r/min), then standing is carried out for 30min, and the suspension with uniformly dispersed upper layer is taken. And adding deionized water into the residual precipitated mixed solution, performing ultrasonic addition and stirring uniformly according to the steps, and repeating the steps until the powder is completely suspended to obtain a uniformly dispersed suspension.
(3) Slowly dripping 4g of phytic acid PA (50 wt%) solution into the suspension under stirring, and rapidly stirring for 30min to uniformly distribute phytic acid in Fe 3 O 4 @SiO 2 @ MWCNTs surface to obtain PA-Fe 3 O 4 @SiO 2 @ MWCNTs mixed solution. 5g sodium alginate SA was added to the above PA-Fe 3 O 4 @SiO 2 In the @ MWCNTs mixed solution, the mixture is stirred vigorously by ultrasonic for 1h until the powder is completely dissolved, and then the uniform SA-PA-Fe is obtained 3 O 4 @SiO 2 @ MWCNTs sol solution, then 0.2g of gluconolactone is added, and the mixture is stirred vigorously for 30min to be dispersed evenly, so that composite gel solution is obtained. And pouring the composite gel solution into a mold, performing two-way liquid nitrogen freezing at-30 ℃, and drying in a freeze-drying oven for 3 days to obtain the composite aerogel.
Example 10
Preparing the composite aerogel:
(1) Porous magnetic Fe prepared in example 1 3 O 4 @SiO 2 The method comprises the following steps of putting a @ MWCNTs ternary nano composite material into a mixed solution of 50% sulfuric acid and 60% nitric acid (the volume ratio of sulfuric acid to nitric acid is 1 3 O 4 @SiO 2 @ MWCNTs composite material.
(2) Taking 7g of modified Fe 3 O 4 @SiO 2 @MWCNTs is added into 150mL deionized water and stirred evenly, ultrasonic and slow electric stirring is firstly carried out for 30min, then fast stirring is carried out for 30min (ultrasonic power is 1200W, stirring speed is 200r/min and 500 r/min), then standing is carried out for 30min, and the suspension with evenly dispersed upper layer is taken. And adding deionized water into the residual precipitated mixed solution, performing ultrasonic addition and stirring uniformly according to the steps, and repeating until the powder is completely suspended to obtain a uniformly dispersed suspension.
(3) Slowly dripping 4g of phytic acid PA (50 wt%) solution into the suspension under stirring, and rapidly stirring for 30min to uniformly distribute phytic acid in Fe 3 O 4 @SiO 2 @ MWCNTs surface to obtain PA-Fe 3 O 4 @SiO 2 @ MWCNTs mixed solution. 5g sodium alginate SA was added to the above PA-Fe 3 O 4 @SiO 2 In the @ MWCNTs mixed solution, the mixture is stirred vigorously by ultrasonic for 1h until the powder is completely dissolved, and then the uniform SA-PA-Fe is obtained 3 O 4 @SiO 2 @ MWCNTs sol solution, then 0.2g of gluconolactone is added, and the mixture is stirred vigorously for 30min to be dispersed evenly, so that composite gel solution is obtained. And pouring the composite gel solution into a mold, performing two-way liquid nitrogen freezing at-30 ℃, and drying in a freeze-drying oven for 3 days to obtain the composite aerogel.
Example 11
Preparing a composite aerogel:
(1) Porous magnetic Fe prepared in example 1 3 O 4 @SiO 2 The method comprises the following steps of putting a @ MWCNTs ternary nano composite material into a mixed solution of 50% sulfuric acid and 60% nitric acid (the volume ratio of sulfuric acid to nitric acid is 1 3 O 4 @SiO 2 @ MWCNTs composite material.
(2) 5g of modified Fe 3 O 4 @SiO 2 @ MWCNTs is added into 150mL deionized water and stirred uniformly, ultrasonic and slow electric stirring is carried out for 30min, then rapid stirring is carried out for 30min (the ultrasonic power is 1200W, the stirring speed is 200r/min and 500 r/min), then standing is carried out for 30min, and the evenly dispersed suspension of the upper layer is taken. Precipitating the restAdding deionized water into the mixed solution, performing ultrasonic addition and stirring uniformly according to the steps, and repeating the steps until the powder is completely suspended to obtain uniformly dispersed suspension.
(3) Slowly dripping 4g of phytic acid PA (50 wt%) solution into the suspension under stirring, and rapidly stirring for 30min to uniformly distribute phytic acid in Fe 3 O 4 @SiO 2 @ MWCNTs surface to obtain PA-Fe 3 O 4 @SiO 2 @ MWCNTs mixed solution. 5g sodium alginate SA was added to the above PA-Fe 3 O 4 @SiO 2 In the @ MWCNTs mixed solution, stirring vigorously by ultrasonic for 1h until the powder is completely dissolved to obtain uniform SA-PA-Fe 3 O 4 @SiO 2 @ MWCNTs sol solution. Then 0.2g of gluconolactone is added, the mixture is stirred vigorously for 30min to be dispersed evenly, then a container containing the sol solution (B in the figure) is vertically placed in a two-dimensional magnetic field formed by an upper electromagnet and a lower electromagnet as shown in figure 1, two-dimensional (X and Y axes) directional treatment is carried out, and the composite gel solution is obtained by low-power ultrasonic vibration for 30min. And then pouring the composite gel solution into a mold, performing two-way liquid nitrogen freezing at-30 ℃, and drying in a freeze-drying oven for 3 days to obtain the composite aerogel.
Example 12
Preparing the composite aerogel:
(1) Porous magnetic Fe prepared in example 1 3 O 4 @SiO 2 The method comprises the following steps of putting a @ MWCNTs ternary nano composite material into a mixed solution of 50% sulfuric acid and 60% nitric acid (the volume ratio of sulfuric acid to nitric acid is 1 3 O 4 @SiO 2 @ MWCNTs composite material.
(2) Taking 5g of modified Fe 3 O 4 @SiO 2 @ MWCNTs is added into 150mL deionized water and stirred uniformly, ultrasonic and slow electric stirring is carried out for 30min, then rapid stirring is carried out for 30min (the ultrasonic power is 1200W, the stirring speed is 200r/min and 500 r/min), then standing is carried out for 30min, and the suspension with uniformly dispersed upper layer is taken. Adding the rest precipitate into deionized water, and performing the above stepsAnd (4) stirring uniformly by sound adding, and repeating until the powder is completely suspended to obtain a uniformly dispersed suspension.
(3) Slowly dripping 4g of phytic acid PA (50 wt%) solution into the suspension under stirring, and rapidly stirring for 30min to uniformly distribute phytic acid in Fe 3 O 4 @SiO 2 @ MWCNTs surface to obtain PA-Fe 3 O 4 @SiO 2 @ MWCNTs mixed solution. 5g of sodium alginate SA was added to the above PA-Fe 3 O 4 @SiO 2 In the @ MWCNTs mixed solution, stirring vigorously by ultrasonic for 1h until the powder is completely dissolved to obtain uniform SA-PA-Fe 3 O 4 @SiO 2 @ MWCNTs sol solution. Adding 0.2g of gluconolactone into the sol solution, vigorously stirring for 30min to uniformly disperse the gluconolactone, placing a container containing the sol solution (B in the figure) in a central area of a three-dimensional electromagnet (vector electromagnet A2) as shown in figure 2, setting the magnetic field intensity (800-1600 Gs), performing three-dimensional orientation treatment, and forming a two-dimensional magnet pair Fe in a plane by two pairs of vertically orthogonal electromagnets 3 O 4 @SiO 2 The @ MWCNTs composite material is subjected to two-dimensional (X-axis and Y-axis) orientation treatment, and then a solenoid magnetic field in the Z-axis direction is added on the basis of a two-dimensional magnet to form a three-dimensional magnet, and Fe is subjected to orientation treatment 3 O 4 @SiO 2 And (3) performing orientation treatment on the Z axis on the @ MWCNTs composite material to obtain a composite gel solution. And then pouring the composite gel solution into a mold, performing two-way liquid nitrogen freezing at-30 ℃, and drying in a freeze-drying oven for 3 days to obtain the composite aerogel.
The thermal conductivity, wave absorption and mechanical properties of the materials prepared in the above examples 1-12 are shown in the following table 1:
Figure BDA0003628471110000121
as can be seen from Table 1, example 1 has an increased SiO content compared to example 2 2 The amount of @ MWCNTs results in Fe 3 O 4 The particle loading is reduced, the heat-conducting property of the particles is not changed greatly, and the wave-absorbing property is obviously improved (the reflection loss is-43.37 dB).
The test results of the SA-PA aerogel prepared in examples 3, 4, 5, and 6 show that the thermal conductivity of the SA-PA aerogel gradually decreases, the wave-absorbing property gradually increases, and the mechanical properties gradually increase with the increase of the phytic acid amount. Among them, example 6 has better flame retardancy (36.13 mW/m · K), and the phytic acid molecules are uniformly coated on the macromolecular chain of the sodium alginate, so that the aerogel structure is reinforced, and the aerogel has better mechanical properties and flame retardant and heat insulation properties.
In examples 7, 8, 9, and 10, parameters of low thermal conductivity, large compressive strength, and good wave-absorbing performance are selected, that is, the composite aerogel is prepared by adding the phytic acid PA and the sodium alginate SA in example 6.
As can be seen from Table 1, with Fe 3 O 4 @SiO 2 The filling amount of the @ MWCNTs composite material is increased, the heat conductivity of the aerogel is gradually increased, the wave-absorbing performance and the compressive strength are increased firstly and then reduced, and the Fe 3 O 4 @SiO 2 The excessive filling amount of the @ MWCNTs composite material can lead to uneven dispersion and agglomeration of the composite material in the gel, lead to the destruction of the internal network structure of the gel, and cause the reduction of the comprehensive properties such as wave-absorbing performance, compressive strength and the like (embodiment 10), so that the proper filling amount (embodiment 9) is the key for improving the comprehensive properties.
On the basis of the embodiment 9, the embodiment 11 performs two-dimensional orientation on the sol solution, and the test results in table 1 show that compared with the embodiment 9, the embodiment 11 has the advantages that the thermal conductivity of the aerogel is reduced, the wave-absorbing performance is improved, but the mechanical performance in the Z-axis direction is obviously reduced; in example 12, the tubular composite material with different length-diameter ratios is subjected to three-dimensional orientation treatment due to the tubular Fe 3 O 4 @SiO 2 The @ MWCNTs have different particle sizes, in magnetic field orientation, under the condition that two-dimensional orientation is uniformly distributed, the composite material with the short particle size is reversed under the action of strong magnetic force and is lapped and crossed with the composite material with the long particle size to form a uniform, regular and compact three-dimensional crossed three-dimensional network structure, and the cross-linking effect of the three-dimensional structure is further strengthened by the bidirectional freezing process. The unique structure not only provides the multilayer reflection effect for the absorption of the electromagnetic wave and improves the absorption performance of the electromagnetic wave, but also improvesThe mechanical property (compression property 421.76 kPa) of the material. While Fe 3 O 4 @SiO 2 The internal defects of the @ MWCNTs and good impedance matching provide a good channel for electron transfer, improve dielectric loss and magnetic loss, and are the key for improving the wave absorbing performance (-75.69 dB).
The above description is only a preferred embodiment of the disclosure and is illustrative of the principles of the technology employed. It will be appreciated by those skilled in the art that the scope of the invention in the present disclosure is not limited to the specific combination of the above-mentioned features, but also encompasses other embodiments in which any combination of the above-mentioned features or their equivalents is possible without departing from the inventive concept. For example, the above features and (but not limited to) the features disclosed in this disclosure having similar functions are replaced with each other to form the technical solution.

Claims (10)

1. A preparation method of the heat-insulating wave-absorbing composite aerogel comprises the following steps:
the method comprises the following steps: siO silicon dioxide 2 Coating on MWCNTs to obtain SiO 2 @ MWCNTs nano composite material, and SiO 2 Processing the @ MWCNTs nano composite material at high temperature to carry out surface modification;
step two: weighing polyvinylpyrrolidone, glycol and ferric chloride hexahydrate, and mixing to obtain Fe 3+ Precursor solution is added with SiO after surface modification 2 The preparation method comprises the following steps of obtaining a mixed solution from the @ MWCNTs nano composite material, adjusting the pH value of the mixed solution to 10-12, performing ultrasonic dispersion under stirring, transferring the mixed solution into a reaction kettle for reaction, cooling to room temperature after the reaction is finished, collecting a reaction product by using a magnet, washing the reaction product, and drying to obtain Fe 3 O 4 @ SiO 2 @ MWCNTs ternary nanocomposite;
step three: mixing Fe 3 O 4 @ SiO 2 The surface of the @ MWCNTs ternary nano composite material is modified to obtain Fe with the surface being rich in hydrophilic groups 3 O 4 @ SiO 2 The @ MWCNTs ternary nano composite material is added into water to make the above-mentioned material pass throughPerforming acoustic dispersion to prepare a suspension;
step four: adding phytic acid PA and alginate into the suspension prepared in the third step under stirring, then adding glucolactone, and uniformly stirring to obtain a composite gel solution;
step five: and (4) introducing the composite gel solution into a mold, and freeze-drying to obtain the composite aerogel.
2. The preparation method of the heat-insulating wave-absorbing composite aerogel according to claim 1, wherein the surface modification conditions in the first step are that the temperature is raised to 300-500 ℃ and is preserved for 2-4h, and then the temperature is raised to 550-750 ℃ and is preserved for 2-4 h.
3. The preparation method of the heat-insulating wave-absorbing composite aerogel according to claim 1, wherein in the second step, ferric chloride hexahydrate and SiO 2 The mass ratio of the @ MWCNTs nano composite material is 2:2-4.
4. The preparation method of the heat-insulating wave-absorbing composite aerogel according to claim 1, wherein the surface modification in the third step is carried out under the condition that Fe is added 3 O 4 @ SiO 2 The @ MWCNTs ternary nano composite material is put into mixed solution of sulfuric acid and nitric acid for acidification modification, and then washed to be neutral by water.
5. The preparation method of the heat-insulating wave-absorbing composite aerogel of claim 1, wherein the concentration of the phytic acid PA in the step four is 40-50 wt%.
6. The preparation method of the heat-insulating wave-absorbing composite aerogel according to claim 1, wherein the alginate in the step four is selected from one or more of ammonium alginate, potassium alginate and sodium alginate.
7. The preparation method of the heat-insulating wave-absorbing composite aerogel of claim 6, wherein the phytic acid PA, the alginate and the Fe are adopted in the fourth step 3 O 4 @ SiO 2 The mass ratio of the @ MWCNTs ternary nano composite material is 1-4:5:1-7.
8. The preparation method of the heat-insulating wave-absorbing composite aerogel of claim 1, wherein the freeze-drying condition in the fifth step is bidirectional liquid nitrogen freezing at-20 to-40 ℃, and drying in a freeze-drying oven for 1 to 3 days.
9. The preparation method of the heat-insulating and wave-absorbing composite aerogel according to any one of claims 1 to 8, wherein before the composite gel solution is introduced into the mold in the fifth step, the method further comprises: and (3) placing the composite gel solution in a two-dimensional magnetic field or a three-dimensional magnetic field for directional treatment.
10. A heat-insulating wave-absorbing composite aerogel prepared by the preparation method of any one of claims 1 to 9.
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