A method for preparing an ordered structure ceramicizable aerogel

Abstract

The application belongs to the field of preparation process of nanoporous materials, and particularly relates to a preparation method of ordered structure ceramicizable aerogel. The application utilizes directional casting combined with a sol-gel method to prepare excellent high-temperature stable ceramicizable aerogel materials, which are expected to meet the needs of the current aerospace ablation materials and other fields. Meanwhile, the simple preparation method of the ordered structure ceramicizable aerogel is conducive to promoting the development of aerogel industrialization and solving the problems such as complex application process of the current ceramicizable aerogel.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of preparation process of nanoporous materials, and particularly relates to a preparation method of ordered structure ceramicizable aerogel. BACKGROUND

[0002] Ablation heat protection materials are widely used in hypersonic vehicles, and provide heat protection and heat shielding in the aerodynamic heating environment through self-sacrifice. Among aerogel materials, phenolic aerogel is widely used in thermal insulation of hypersonic vehicles due to its high carbon residue rate, high temperature resistance, good heat preservation performance and other unique advantages.

[0003] Phenolic aerogel is synthesized from small molecule phenols and aldehydes, and the preparation cycle is more than 7 days. In addition, the wet gel will produce significant capillary pressure during the drying process, resulting in the collapse, wrinkling or shrinkage of the aerogel, so that the wet gel must be subjected to expensive supercritical drying. Therefore, the preparation cost of pure phenolic aerogel is high, and the process is difficult, which seriously hinders large-scale industrial production. Moreover, the mechanical properties and ablation / oxidation resistance of phenolic aerogel are poor, which is difficult to adapt to complex and challenging working environments. In view of the above problems, researchers consider adding ceramic fillers to phenolic aerogel to improve its oxidation resistance, for example, adding nanoparticles such as zirconium dioxide, multi-walled carbon nanotubes and nanoclay. However, it cannot effectively improve the ablation resistance and mechanical properties, and the structural stability is significantly deteriorated over time at high temperatures, and the pore structure is prone to collapse.

[0004] And based on the research results of the current porous fiber skeleton composite aerogel material, it can be found that the strength of the aerogel composite material is improved, the temperature resistance is improved, and the thermal conductivity is also increased to a certain extent, which causes the common problem that the strength and heat insulation performance of the aerogel material are difficult to be compatible.

[0005] The composite material prepared by the prior art (CN111349267A) has a minimum weight loss rate of 30.7% at 1000℃, and the inorganic wrapping organic material achieves the effect of oxidation resistance. The prior art CN110467742A uses an initiator to form a wet gel at room temperature under normal pressure after 2-5 days. The above methods have the problems of complex preparation steps, long cycle, high weight loss rate and poor performance, which need to be further improved. SUMMARY

[0006] In order to overcome the problems existing in the above-mentioned existing phenolic composite aerogel technology, the purpose of the present application is to provide a simple operation of the preparation method of the ordered structure of the ceramicizable aerogel, improve the temperature resistance of the matrix, use directional casting to control the ordered structure of the ceramic filler, use graphene, carbon nanofiber and the like as the heat-conducting filler, composite the phenolic aerogel with the ordered inorganic aerogel, and obtain the ceramicizable aerogel material through normal pressure drying. In the use process, a part is ablated to take away the heat, and at the same time, a high-temperature-resistant coating is formed, and the temperature resistance is further improved. The present application solves the problems such as complex and tedious preparation process, and prepares the ablation-resistant ceramic aerogel material. The material is expected to meet the needs of the fields of aviation, aerospace and the like.

[0007] The technical scheme of the present application is as follows: a preparation method of an ordered structure ceramicizable aerogel, characterized by the following specific steps:

[0008] (1) The inorganic salt is weighed and added to a mixed solution of anhydrous ethanol and deionized water, and stirred until completely dissolved; then the template agent is added and stirred, and then the silicon source is added and stirred, finally obtaining an aerogel precursor solution;

[0009] (2) The functionalized heat-conducting filler is added to the aerogel precursor solution obtained in step (1) and stirred, and then placed in an electric field induction directional instrument, after the directional process is completed, the gelling agent is added, and after room temperature gelation, aging and solvent replacement, supercritical drying is carried out, and finally calcination is carried out in an air atmosphere to obtain an ordered structure ceramic aerogel;

[0010] (3) The phenolic resin is weighed and added to anhydrous ethanol, and after stirring and completely dissolving, the curing agent is added, and after dissolving, the phenolic solution is poured into the ordered structure ceramic aerogel prepared in step (2), and after completely impregnating, it is placed in an oven for normal pressure drying, and finally an ordered structure ceramicizable aerogel is prepared.

[0011] Preferably, the inorganic salt in step (1) is at least one of a nitrate of Zr, Gd or Tm or a chloride salt of Zr, Gd or Tm.

[0012] Preferably, the template agent in step (1) is one of propionamide, polyacrylic acid, phenolic resin, 3-carboxyl-3-hydroxy glutaric acid or amino formaldehyde.

[0013] Preferably, the silicon source in step (1) is one of tetraethyl silicate, tetramethyl silicate, tetrabutyl silicate, methyl trimethoxysilane, methyl triethoxysilane, hexamethyl disilazane or sodium silicate; and the stirring time is preferably 10-120 min.

[0014] Preferably, the mass ratio of the inorganic salt to the silicon source in step (1) is 1:(1-1.5); and the mass ratio of the inorganic salt: deionized water: anhydrous ethanol: template agent is 1:(8-22):(9-20):(2-10).

[0015] The gelatin in step (2) is preferably propylene oxide; the mass ratio of the inorganic salt to the gelatin is 1:(1.5-8).

[0016] The solvent replacement and aging time in step (2) is preferably 2-6 days, the solvent is anhydrous ethanol, and the replacement is performed every 4-12 hours; the calcination time is 0.5-4 hours, the calcination temperature is 900-1400℃, and the heating rate is 1-10℃ / min.

[0017] The mass ratio of the phenolic resin, the curing agent and ethanol in step (3) is preferably 1:(0.1-0.8):(1-5).

[0018] The curing agent in step (3) is preferably one of ethylenediamine, diethylenetriamine, triethylenetetramine, m-phenylenediamine, m-xylylenediamine or hexamethylenetetramine.

[0019] The temperature of the normal pressure drying in step (3) is preferably 50-150℃.

[0020] Beneficial effects:

[0021] (1) Compared with the existing preparation technology, the aerogel matrix prepared by the directional casting method has an ordered structure, which can enhance the mechanical properties and reduce the thermal conductivity;

[0022] (2) Compared with other phenolic materials, the ordered ceramicizable aerogel material prepared by the present application has a more excellent controllable structure, which is more conducive to the later modification;

[0023] (3) The ordered ceramicizable aerogel material described in the present application breaks through the existing ablation-resistant materials which only resist oxidation by loading inorganic matter on the surface of organic matter, and can be directly used and form an oxidation-resistant coating during use. Not only solves the oxidation problem, but also improves the temperature resistance. Expands its application field and has potential application prospect in the field of heat insulation and high temperature resistance. BRIEF DESCRIPTION OF DRAWINGS

[0024] Figure 1 The macroscopic sample diagram of the ordered ceramicizable aerogel prepared in Example 1;

[0025] Figure 2 The pore size distribution diagram of the ordered ceramicizable aerogel prepared in Example 2;

[0026] Figure 3 The thermogravimetric diagram of the ordered ceramicizable aerogel prepared in Example 3. DETAILED DESCRIPTION

[0027] The present application will be further described below in conjunction with examples, but the protection scope is not limited thereto.

[0028] Example 1

[0029] (1) 1 g of GdCl3·6H2O was weighed and added to 9 g of anhydrous ethanol and 8 g of deionized water, and stirred until completely dissolved. Then 1 g of tetraethyl orthosilicate and 2 g of propionamide were added and stirred for 10 min to obtain an aerogel precursor solution;

[0030] (2) The functionalized thermally conductive filler was added to the obtained aerogel precursor solution and stirred, and then placed in an electric field induction orientation instrument (model: WT2-ZMC-10kV). After the orientation was completed, 1.5 g of propylene oxide was added, and the gel was formed at room temperature. Then, solvent replacement and aging were performed with anhydrous ethanol for 2 days (replaced every 4 h). An ordered structure aerogel was obtained by supercritical drying, and an ordered structure ceramic aerogel was finally prepared by calcining at 900°C under an air atmosphere at a temperature rising rate of 1°C / min for 4 h.

[0031] (3) 2 g of phenolic resin was weighed and added to 3 g of anhydrous ethanol, and stirred until completely dissolved. Then 1.5 g of hexamethylenetetramine was added and dissolved as a single uniform solution to obtain a phenolic solution. The solution was poured into the ordered structure ceramic aerogel prepared in step (2) and allowed to completely immerse. Then, the sample was placed in a 60°C oven for normal pressure drying, and an ordered structure ceramifiable aerogel was finally prepared.

[0032] The sample diagram of the prepared ordered ceramifiable aerogel is shown in Figure 1 The sample diagram of the prepared ordered ceramifiable aerogel is shown in

[0033] Example 2

[0034] (1) 1 g of TmCl3·6H2O was weighed and added to 15 g of anhydrous ethanol and 16 g of deionized water, and stirred until completely dissolved. Then 1.2 g of tetraethyl orthosilicate and 6 g of propionamide were added and stirred for 50 min to obtain an aerogel precursor solution;

[0035] (2) The functionalized thermally conductive filler was added to the obtained aerogel precursor solution and stirred, and then placed in an electric field induction orientation instrument (model: WT2-ZMC-10kV). After the orientation was completed, 5 g of propylene oxide was added, and the gel was formed at room temperature. Then, solvent replacement and aging were performed with anhydrous ethanol for 4 days (replaced every 8 h). An ordered structure aerogel was obtained by supercritical drying, and an ordered structure ceramic aerogel was finally prepared by calcining at 1200°C under an air atmosphere at a temperature rising rate of 3°C / min for 0.6 h.

[0036] (3) Take 2g phenolic resin into 8g anhydrous ethanol, after stirring and completely dissolving, add 1g m-xylylenediamine, and after dissolving into a single uniform, obtain a phenolic solution, pour into the ordered structure ceramic aerogel prepared in step (2), make it completely immersed, and then put into a 100℃ oven for normal pressure drying, finally obtain an ordered structure ceramicizable aerogel.

[0037] The prepared ordered ceramicizable aerogel is in the form of a complete block, with a porosity of 95%, and the pore size distribution is shown in Figure 2 The pore size is mainly distributed in the range of 10-90nm. The weight loss rate is less than 45%, the compressive strength is 9.7MPa, the room temperature thermal conductivity is 0.027W / (m·K), and the back temperature is ≤205℃.

[0038] Example 3

[0039] (1) Take 1g ZrCl4, add 20g anhydrous ethanol and 22g deionized water, and stir until completely dissolved. Then add 1.5g tetraethyl orthosilicate and 10g propionamide, stir for 120min, and obtain an aerogel precursor solution;

[0040] (2) After stirring, the obtained aerogel precursor solution is added to an electric field induction directional instrument (model: WT2-ZMC-10kV), and after the orientation is completed, 8g propylene oxide is added, and then gelled at room temperature. Then use anhydrous ethanol for solvent replacement and aging for 4 days to obtain an aerogel precursor gel (replace every 12h). Through supercritical drying, an ordered structure aerogel is obtained, which is calcined at 1400℃ under air atmosphere at a temperature rising rate of 10℃ / min for 1h, and finally an ordered structure ceramic aerogel is obtained.

[0041] (3) Take 2g phenolic resin into 10g anhydrous ethanol, after stirring and completely dissolving, add 0.2g diethylenetriamine, and after dissolving into a single uniform, obtain a phenolic solution, pour into the ordered structure ceramic aerogel prepared in step (2), make it completely immersed, and then put into a 150℃ oven for normal pressure drying, finally obtain an ordered structure ceramicizable aerogel.

[0042] The thermogravimetric diagram of the prepared ordered ceramicizable aerogel is shown in Figure 3 There are three weight loss stages in total, and the final weight loss rate is less than 40%. The porosity is 96%, the pore size is mainly distributed in the range of 15-90nm, the compressive strength is 11.7MPa, the room temperature thermal conductivity is 0.026W / (m·K), and the back temperature is ≤210℃.

[0043] Example 4

[0044] (1) 1 g TmCl3·6H2O was weighed and added to 13 g of anhydrous ethanol and 20 g of deionized water, and stirred until completely dissolved. Then 1.2 g of tetraethyl orthosilicate and 6 g of propionamide were added and stirred for 90 min to obtain an aerogel precursor solution;

[0045] (2) The functionalized thermally conductive filler was added to the obtained aerogel precursor solution and stirred, and then placed in an electric field induction orientation instrument (model: WT2-ZMC-10kV). After the orientation was completed, 5 g of propylene oxide was added, and the gel was obtained at room temperature. Then, solvent replacement and aging were performed with anhydrous ethanol for 3 days (replaced every 6 h). The ordered structure aerogel was obtained by supercritical drying, and the ordered structure ceramic aerogel was finally prepared by calcining at 1300°C under an air atmosphere at a heating rate of 5°C / min for 2.5 h.

[0046] (3) 2 g of phenolic resin was weighed and added to 6 g of anhydrous ethanol, and stirred until completely dissolved. Then 0.8 g of m-phenylenediamine was added and dissolved as a single uniform solution to obtain a phenolic solution. The ordered structure ceramic aerogel prepared in step (2) was poured into the solution and completely immersed, and then placed in a 120°C oven for normal pressure drying. The ordered structure ceramifiable aerogel was finally prepared.

[0047] The ordered structure ceramifiable aerogel prepared has a weight loss rate of less than 47%, a porosity of 94%, a pore size mainly distributed in the range of 20-94 nm, a compressive strength of 11 MPa, a room temperature thermal conductivity of 0.028 W / (m·K), and a back temperature of ≤203°C.

[0048] Example 5

[0049] (1) 1 g of ZrCl4 was weighed and added to 13 g of anhydrous ethanol and 16 g of deionized water, and stirred until completely dissolved. Then 1.3 g of tetraethyl orthosilicate and 6 g of propionamide were added and stirred for 100 min to obtain an aerogel precursor solution;

[0050] (2) The functionalized thermally conductive filler was added to the obtained aerogel precursor solution and stirred, and then placed in an electric field induction orientation instrument (model: WT2-ZMC-10kV). After the orientation was completed, 8 g of propylene oxide was added, and the gel was obtained at room temperature. Then, solvent replacement and aging were performed with anhydrous ethanol for 3 days (replaced every 9 h). The ordered structure aerogel was obtained by supercritical drying, and the ordered structure ceramic aerogel was finally prepared by calcining at 1000°C under an air atmosphere at a heating rate of 8°C / min for 3.5 h.

[0051] (3) Take 2g phenolic resin into 9g anhydrous ethanol, after stirring and completely dissolving, add 1.5g triethylene tetramine, and after dissolving into a single uniform, obtain a phenolic solution, pour into the ordered structure ceramic aerogel prepared in step (2), make it completely impregnated, and then put into a 130℃ oven for normal pressure drying, finally obtain an ordered structure ceramicizable aerogel.

[0052] The prepared ordered structure ceramicizable aerogel has a weight loss rate of less than 42%, a porosity of 93%, a pore size mainly distributed in the range of 18-96nm, a compressive strength of 10MPa, a room temperature thermal conductivity of 0.031W / (m·K), and a back temperature of ≤195℃.

[0053] Example 6

[0054] (1) Take 1g GdCl4, add 10g anhydrous ethanol and 16g deionized water, and stir until completely dissolved. Then add 1.4g tetraethyl orthosilicate and 7g propionamide, stir for 80min, and obtain an aerogel precursor solution;

[0055] (2) After adding the functionalized thermal conductive filler to the obtained aerogel precursor solution and stirring, put it into an electric field induction directional instrument (model: WT2-ZMC-10kV), after the orientation is completed, add 5g propylene oxide, then gel at room temperature, and then use anhydrous ethanol for solvent replacement and aging for 3 days (replace every 5h). Through supercritical drying, obtain an ordered structure aerogel, calcine at 1250℃ under air atmosphere, at a heating rate of 4℃ / min for 2h, and finally obtain an ordered structure ceramic aerogel.

[0056] (3) Take 2g phenolic resin into 6g anhydrous ethanol, after stirring and completely dissolving, add 1.2g ethylenediamine, and after dissolving into a single uniform, obtain a phenolic solution, pour into the ordered structure ceramic aerogel prepared in step (2), make it completely impregnated, and then put into a 120℃ oven for normal pressure drying, finally obtain an ordered structure ceramicizable aerogel.

[0057] The prepared ordered structure ceramicizable aerogel has a weight loss rate of less than 46%, a porosity of 92%, a pore size mainly distributed in the range of 23-96nm, a compressive strength of 8.7MPa, a room temperature thermal conductivity of 0.033W / (m·K), and a back temperature of ≤190℃.

Claims

1. A method for preparing an ordered, ceramic-like aerogel, characterized in that... The specific steps are as follows: (1) Weigh the inorganic salt and add it to the mixed solution of anhydrous ethanol and deionized water, and stir until completely dissolved; then add the template agent and stir, then add the silicon source and continue stirring to finally obtain the aerogel precursor solution; (2) Add functionalized thermally conductive filler to the aerogel precursor solution obtained in step (1), stir and place it in an electric field-induced orientation instrument. After orientation, add gelling agent, and after gelation, aging and solvent replacement, perform supercritical drying and finally calcine in air atmosphere to obtain ordered structure ceramic aerogel. (3) Weigh the phenolic resin and add it to anhydrous ethanol. After stirring until completely dissolved, add the curing agent. After dissolving, pour the phenolic solution into the ordered ceramic aerogel prepared in step (2). After completely impregnating it, place it in an oven and dry it under normal pressure to finally obtain the ordered ceramic aerogel.

2. The preparation method according to claim 1, characterized in that... The inorganic salt mentioned in step (1) is at least one of the following: a nitrate of Zr, Gd or Tm, or a chloride of Zr, Gd or Tm.

3. The preparation method according to claim 1, characterized in that... The template agent mentioned in step (1) is one of propionamide, polyacrylic acid, phenolic resin, 3-carboxy-3-hydroxyglutaric acid or aminoformaldehyde.

4. The preparation method according to claim 1, characterized in that... The silicon source mentioned in step (1) is one of tetraethyl silicate, tetramethyl silicate, tetrabutyl silicate, methyltrimethoxysilane, methyltriethoxysilane, hexamethyldisilazane, or sodium silicate.

5. The preparation method according to claim 1, characterized in that... The mass ratio of inorganic salt to silicon source in step (1) is 1:(1~1.5); the mass ratio of inorganic salt:deionized water:anhydrous ethanol:template agent is 1:(8~22):(9~20):(2~10).

6. The preparation method according to claim 1, characterized in that... The gelling agent mentioned in step (2) is propylene oxide; the mass ratio of inorganic salt to gelling agent is 1:(1.5-8).

7. The preparation method according to claim 1, characterized in that... The solvent replacement and aging time in step (2) is 2 to 6 days, the solvent is anhydrous ethanol, and it is replaced every 4 to 12 hours; the calcination time is 0.5 to 4 hours, the calcination temperature is 900 to 1400℃, and the heating rate is 1 to 10℃ / min.

8. The preparation method according to claim 1, characterized in that... The mass ratio of phenolic resin, curing agent and ethanol in step (3) is 1:(0.1-0.8):(1-5).

9. The preparation method according to claim 1, characterized in that... The curing agent mentioned in step (3) is one of ethylenediamine, diethylenetriamine, triethylenetetramine, m-phenylenediamine, m-phenylenediamine or hexamethylenetetramine.

10. The preparation method according to claim 1, characterized in that... The temperature for atmospheric pressure drying in step (3) is 50 to 150°C.

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