WO2017152587A1 - Method for fabricating composite sio2 aerogel blanket - Google Patents

Abstract

Provided is a method for fabricating a composite SiO₂ aerogel blanket; an inexpensive sodium silicate is used as a starting material; a silica sol is formed under catalysis conditions; during the sol-gel process, a fiber mat is added and, following aging, acidogenesis, surface modification, and drying at atmospheric pressure, a composite SiO₂ aerogel blanket having a superhydrophobic function, ultra-low thermal conductivity, and high mechanical strength is fabricated; the method for fabricating the above is simple, safe, and low-cost, and is advantageous to large-scale fabrication of SiO₂ aerogel blankets.

Description

Method for preparing composite SiO2 aerogel felt Technical field

The invention belongs to the technical field of thermal insulation materials, and in particular relates to a method for preparing a composite SiO ₂ aerogel felt.

Background technique

With the development of the global economy, energy shortage has become one of the major issues that cannot be ignored in the sustainable development of society. Conventional fiber insulation materials are mostly prepared by wet or dry processes. These products have high mechanical strength and are widely used in applications. However, the thermal conductivity of these products is relatively high (≥0.35W/m·K), and their thermal insulation effect is general. As a new type of nano-porous, low-density, amorphous material, aerogel has many unique properties: low density (minimum 30kg/m ³ ), high porosity (up to 97%), It has a large specific surface area (up to 1000m ² /g) and low thermal conductivity (as low as 0.013W/m·K), so it has broad application prospects in energy, chemical metallurgy, building energy conservation and aerospace. SiO ₂ aerogel has a unique nano-three-dimensional network structure, which has an ultra-low solid thermal conductivity and a thermal conductivity. It is the most solid material for thermal insulation. However, the pure SiO ₂ aerogel has low mechanical strength and is difficult to form a complete monolithic material, which restricts its practicability and makes it difficult to promote its application. In addition, the conventional supercritical drying process for manufacturing SiO ₂ aerogel has high cost, complicated operation process and high risk, which further limits the large-scale preparation of SiO ₂ aerogel.

Chinese patent application 201410787165.8 discloses a preparation process of a glass fiber composite silica aerogel insulation felt, which mainly utilizes a glass fiber felt saturated absorption silica aerogel glue and gels under specific conditions, supercritical fluid The CO _{2 is} dried to form an enhanced aerogel material. The glass fiber composite silica aerogel insulation felt prepared by the invention has excellent heat preservation performance, mechanical property, fireproof performance and waterproof performance. However, the preparation process disclosed by the invention avoids the complicated solvent replacement step, thereby making it have the advantages of relatively simple operation, controllable process and continuous preparation, but the preparation method adopts a conventional supercritical CO ₂ drying method. The use of expensive silicone raw materials makes it relatively expensive, increases the complexity of its operation, and reduces the safety of production.

Summary of the invention

In order to make up for the deficiencies of the prior art, the present invention provides a method for preparing a composite SiO ₂ aerogel felt, which can use a low cost water glass as a silicon source to recombine the fiber mat with a silica sol formed by water glass. The composite is subjected to aging, acidification, surface modification and atmospheric drying steps to prepare a composite SiO ₂ aerogel felt with superhydrophobic function, ultra-low thermal conductivity and high mechanical strength. The preparation method is simple and the preparation cost is relatively high. Low, is conducive to the large-scale preparation of adiabatic aerogel felt.

In one aspect, the present invention provides a method of preparing a composite SiO ₂ aerogel felt, comprising the steps of:

A) sol-gel: a silicon source is mixed with deionized water to obtain a diluted solution, and an aqueous solution containing an acidic catalyst is added to the diluted solution to adjust the pH of the mixed solution to 3.0-8.0, and the mixed solution is stirred to obtain uniformity. Silica sol;

B) integrated soaking: soaking the fiber mat into the silica sol obtained in step A), or adding the silica sol to the fiber mat, sealing and standing to obtain a fiber mat-SiO ₂ gel composite;

C) aging: the fiber mat-SiO ₂ gel composite obtained in step B) is aged at room temperature for 2-72h, then placed in an ethanol solution, aged at 40-80 ° C for 2-72h;

D) acidification: the fiber mat-SiO ₂ gel composite obtained in step C) is immersed in a strong acid solution for 20-180min, wherein the concentration of hydrogen ions in the strong acid solution is not less than 4.5mol / L;

E) Surface modification treatment: the fiber mat-SiO ₂ gel composite after acidification in step D) is placed in a mixture consisting of a nonionic surfactant and a silane coupling agent at 25-80 ° C The surface modification is carried out under conditions, and then the surface-modified fiber mat-SiO ₂ gel composite is washed with a mixture of ethanol and n-hexane in a volume ratio of 1:5 for 5-8 h;

F) Normal pressure drying: The fiber mat-SiO ₂ gel composite treated by the step E) is dried under normal pressure to obtain a composite SiO ₂ aerogel felt.

In order to enable those skilled in the art to further understand the technical solutions provided by the present invention, a general explanation of the principles of the above six steps will be made below.

In the sol-gel step A), the silicon source is uniformly dispersed in the solvent of deionized water and hydrolyzed to form a silica sol, and then the silica sol reactive monomer is polymerized under the action of the acidic catalyst to generate a certain space. Structure of the gel. However, it will be understood by those skilled in the art that the formation of the gel takes a long time, and therefore the aerogel structure of the aerogel felt produced by the method provided by the present invention is not completely formed in this step. The main purpose of this step is to generate a silica sol, but it is not excluded that a portion of the silica sol will form a silicone gel during this step.

In the integral soaking step B), the fiber mat and the silica sol formed in the sol-gel step are thoroughly mixed, and the silica sol continues to undergo polymerization under the action of an acidic catalyst to form a silicone gel; The silicone gel is interspersed with the fibers on the fiber mat to form a fiber mat-SiO ₂ gel composite. It should be noted that the length of the integrated immersion mainly depends on the specifications of the fiber mat. When the thickness of the fiber mat is larger, the fiber length is longer or the density is larger, the immersion time is longer.

In the aging step C), part of the remaining silica sol continues to undergo polymerization to form a silica gel, and the silicon gel formed in this step further increases the number of pores and pore radius of the previously formed gel network. The pore distribution is narrowed, so that the skeleton strength of the fiber mat-SiO ₂ gel composite becomes large. It is foreseeable that the aging time is too short, and the fiber mat-SiO ₂ gel composite has insufficient strength; if the aging time is too long, the number of pores of the fiber mat-SiO ₂ gel composite is reduced, and the transparency thereof is lowered. And its density increases, which leads to a decrease in the thermal insulation of the composite SiO ₂ aerogel felt. In addition, the temperature of the aging and the concentration of the soaking solvent have an effect on the properties of the final product of the preparation process, i.e., the properties of the composite SiO ₂ aerogel felt, and the present invention will further explain the effects of these parameters.

In the acidification step D), the hydrogen ions in the strong acid solution are combined with the surface of the fiber mat-SiO ₂ gel composite, which can effectively control the reaction rate of surface modification in the subsequent surface modification step, thereby avoiding surface modification. The aerogel is broken and pulverized in the fiber mat-SiO ₂ gel composite due to the excessive rate.

After the sol-gel, aging and acidification steps, the surface of the silica gel aggregates a large amount of incompletely reacted hydroxyl groups. These hydroxyl groups undergo a polycondensation reaction in the subsequent atmospheric drying step, resulting in cracking or even collapse of the gel structure. The phenomenon. In the surface modification step E), a nonionic surfactant and a silane coupling agent are used to modify the fiber mat-SiO ₂ gel composite skeleton, which can effectively prevent the silanol groups on the surface of the gel pores from being The polymerization occurs in the subsequent atmospheric drying step, thereby improving the mechanical properties and thermal insulation properties of the fiber mat-SiO ₂ gel composite.

In the atmospheric pressure drying step F), the surface-modified fiber mat-SiO ₂ gel composite is dried under normal pressure conditions to dehydrate the silicon gel to form a SiO ₂ aerogel, and finally form a composite SiO. ₂ aerogel felt.

In the following, some preferred embodiments of the invention are further described.

It should be noted that the preparation method provided by the present invention is applicable to a plurality of silicon sources including but not limited to one of methyl orthosilicate, tetraethyl orthosilicate, polysiloxane, methyltriethoxysilane or A variety. In some embodiments, in order to reduce the preparation cost of the composite SiO ₂ aerogel felt on the basis of ensuring the thermal insulation performance and mechanical properties of the aerogel felt, the present invention selects Na ₂ O·nSiO ₂ , that is, water glass, as Silicon source and limit n to 3-5. Deionized water acts as a solvent for the sol-gel reaction, and its volume ratio to the reactant silicon source has a significant effect on the density of the fiber mat-SiO ₂ gel composite. If the volume ratio is too large, the amount of the solvent having a low surface tension in the subsequent acidification step is increased, resulting in an increase in the preparation cost of the preparation method and a long preparation period; if the volume ratio is too small, the hydrolysis and polycondensation reaction of the silicon source are not Completely, it will result in a decrease in the yield of the preparation method. For this reason, in some embodiments, the present invention limits the volume ratio of silicon source to deionized water to 1:1-8. In order to form a finer pore network structure, in some preferred embodiments of the invention, the volume ratio is selected to be 1:3-5, and in some preferred embodiments the volume ratio is selected to be 1:3.

The hydrolysis and polycondensation reactions in the sol-gel process of the silicon source can be carried out under the catalysis of acid and base, respectively. Among them, the polycondensation reaction of the acidic catalyst in the silica sol acts to adjust the pH of the reaction environment, thereby controlling the polycondensation rate of the silica sol, and thereby controlling the structure of the silica gel polycondensation reaction product-silicon gel. In general, the rate of polycondensation is faster under neutral or acidic conditions. For this reason, the present invention, in some embodiments, selects the acidic catalyst as sulfuric acid or hydrochloric acid, and in some more preferred embodiments, the acidic catalyst is selected as 0.5 mol/L sulfuric acid. For the same reason, the present invention also adjusts the pH of the sol-gel reaction environment to 3.0-8.0. In some more preferred embodiments, the pH of the above reaction environment is adjusted to 4.0.

The mechanical properties of the composite SiO ₂ aerogel felt are mainly derived from the mechanical properties of the fiber mat itself. Therefore, the better the mechanical properties of the selected fiber mat, the better the mechanical properties of the composite SiO ₂ aerogel felt prepared. In addition, although the aerogel formed by the silicon source is dominant in the thermal conductivity of the composite SiO ₂ aerogel felt, the fiber mat also has a certain influence on the thermal conductivity of the composite SiO ₂ aerogel felt. It is foreseeable that under the conditions of using the same aerogel powder, the lower the thermal conductivity of the selected fiber mat, the better the thermal insulation performance of the prepared composite SiO ₂ aerogel felt. In summary of the above, in some preferred embodiments, the fiber mat is selected from the group consisting of fiberglass mats, ceramic fiber mats, and rock wool mats. Generally, the glass fiber mat used in the present invention has a thickness of 3-25 mm, a density of 110-200 kg/m ³ , a glass fiber length of 6-10 cm, and a glass fiber diameter of 6-13 μm; The rock wool felt used has a density of 60-100 kg/m ³ and a thickness of 40-75 mm; the ceramic fiber mat used in the present invention has a density of 96-128 kg/m ³ and a thickness of 10-50 mm. In some embodiments, the fiber mat is selected as a glass wool felt in a glass fiber mat having a thickness of 3-10 mm, a density of 150-200 kg/m ³ , a glass fiber length of 6-9 cm, and a glass thereof. The fibers have a diameter of 8-10 μm.

In some preferred embodiments, the duration of the aging treatment with the ethanol solution in step C) is 24 h and the aging temperature is 40 °C. The fiber mat-SiO ₂ gel composite formed under this condition has a more porous and smaller aerogel structure, and the corresponding composite SiO ₂ aerogel felt also has good mechanical properties and thermal insulation properties. .

The aging of the fiber mat-SiO ₂ gel composite in a liquid reaction environment has a respiratory effect, that is, as the silica sol polycondensation reaction occurs, the fiber mat-SiO ₂ gel composite will have a large volume shrinkage, and then The newly formed silicone gel-attached fiber mat-SiO ₂ gel composite gradually expanded. The liquid reaction environment in which the fiber mat-SiO ₂ gel composite is located in the aging step was found to have a certain control effect on the above volume change. When the reaction environment, that is, the volume fraction of the ethanol solution is 70-95%, the fiber mat-SiO ₂ gel composite has a small volume change during aging. Thus, in some preferred embodiments, the volume fraction of the ethanol solution in step C) is 70-95%. When the volume fraction of the ethanol solution is 95%, the fiber mat-SiO ₂ gel composite has the smallest volume change during aging. Thus, in some more preferred embodiments, the volume fraction of the ethanol solution in step C) is 95%.

In some preferred embodiments, the strong acid in step D) is selected from the group consisting of sulfuric acid, nitric acid and hydrochloric acid; the concentration of hydrogen ions in the strong acid solution is preferably from 4.5 to 15 mol/L. Under such conditions, the surface of the fiber mat-SiO ₂ gel composite can combine a sufficient amount of hydrogen ions to control the reaction in the subsequent surface treatment step, thereby preparing an aerogel felt excellent in thermal insulation performance. It can fully reduce the cost and time of aerogel felt production, making the preparation method more competitive in the market. In some preferred embodiments, the concentration of hydrogen ions in the strong acid solution is from 10 to 13 mol/L.

In some preferred embodiments, the nonionic surfactant in step E) is selected from the group consisting of polyethylene glycol. The reason is that polyethylene glycol can increase the size of the silicone gel pores and reduce the capillary pressure on the surface of the silicone gel.

In some preferred embodiments, the silane coupling agent in step E) is selected from the group consisting of trimethylchlorosilane, hexamethyldisilazane, 3-aminopropyltriethoxysilane, and hexamethyldiene. One of the siloxanes. The reason is that these silane coupling agents can effectively react with the hydroxyl groups on the surface of the silicone gel to silanize the surface of the silicone gel, exhibiting hydrophobicity, and increasing the contact angle of the corresponding solvent with the surface of the gel. According to the Young-Laplace equation, the capillary pressure is thus reduced, which is advantageous for atmospheric drying of the aerogel. Trimethylchlorosilane has the characteristics of non-toxicity, unsatisfactory reaction conditions and good reaction effect with respect to the above other silane coupling agents, and trimethylchlorosilane can adjust the fiber mat-SiO ₂ gel composite to some extent. The polycondensation reaction is carried out to obtain a porous structure of a silica gel having a uniform pore size and a structural order. Thus, in some more preferred embodiments, the silane coupling agent is trimethylchlorosilane.

The concentration of the surfactant and the silane coupling agent in the reaction system and the ratio between them are important factors affecting the surface modification. If their concentration is too small or the ratio is not suitable, and the reaction with the hydroxyl group on the surface of the silicone gel is insufficient, the surface modification effect will not be achieved; if their concentration is too large or the ratio is not suitable, it will be given to the subsequent The aerogel washing process is inconvenient, making the entire preparation cycle lengthy while wasting reagents. In addition, an excessive amount of the silane coupling agent may even react with the silicone gel. For example, an excessive amount of trimethylchlorosilane may cause the silicone gel to dissolve. Therefore, in some preferred embodiments, the weight ratio of the nonionic surfactant to the silane coupling agent in the step E) is 1:0.23-0.33, and the fiber mat-SiO ₂ gel composite and The weight ratio of the silane coupling agent is preferably from 1:0.01 to 0.03. In some preferred embodiments, the weight ratio of the nonionic surfactant to the silane coupling agent in the step E) is 1:0.23, the fiber mat-SiO ₂ gel composite and the silane coupling The weight ratio of the crosslinking agent is preferably from 1:0.01 to 0.03, more preferably 1:0.03. The surface modification of the fiber mat-SiO ₂ gel composite is more complete with the surfactant and the silane coupling agent under the above weight ratio conditions.

In some preferred embodiments, the surface modification process in step E) is carried out in an environment of 40-60 ° C for a modification time of 10-24 h; in some more preferred embodiments, the modification temperature is 50 ° C. The modification time is 12h. Under such conditions of reaction temperature and reaction time, the surfactant can be reacted with more hydroxyl groups remaining on the surface of the silicone gel, and other reactions of the surfactant with the silica gel solid skeleton can be avoided.

In some preferred embodiments, the atmospheric pressure drying in the step F) is performed by first drying the fiber felt-SiO ₂ gel composite sample obtained by the step E) at 40-80 ° C for 4-7 h, and then drying. Dry at 120-200 ° C for 1-3 h. Since the fiber mat-SiO ₂ gel composite is dried at normal temperature and pressure, the occurrence of void collapse is unavoidable, but the graded drying employed in these preferred embodiments can minimize cracking or collapse. degree.

In another aspect, the present invention provides a composite SiO ₂ aerogel felt characterized by being produced by one of the various methods described above.

Compared with the prior art, the present invention has the following technical advantages:

The method for preparing a composite SiO ₂ aerogel felt provided by the invention particularly improves the formulation of the surfactant and the silane coupling agent in the surface modification step, and adopts acidification means before the surface modification treatment to make the preparation process The volume shrinkage of the fiber mat-SiO ₂ gel composite is small and the aerogel pores in the composite are fine, so that the prepared composite SiO ₂ aerogel felt can have more excellent heat insulating properties and mechanical properties. In addition, the method disclosed in the present invention can use a cheap water glass as a silicon source, add the fiber mat to a silica sol formed by water glass to form a composite, and then subject the composite to aging, acidification, surface modification, and atmospheric drying. The steps are to prepare an aerogel felt, and the composite SiO ₂ aerogel felt prepared has the advantages of super hydrophobic function, ultra-low thermal conductivity, high tensile strength, compression resistance and bending strength. In addition, the preparation method disclosed in the present invention is simple, and is advantageous for large-scale preparation of the composite SiO ₂ aerogel felt.

detailed description

Those skilled in the art will appreciate that the techniques disclosed in the examples which follow represent techniques discovered by the inventors in the practice of the invention. However, many modifications may be made in the particular embodiments disclosed, and the same or similar results can be obtained without departing from the spirit and scope of the invention.

Unless otherwise specified, the concentration of the ethanol solution involved in the present invention is a volume percentage concentration, and the ethanol involved in the present invention is industrial grade ethanol.

Example 1: Method for preparing composite SiO ₂ aerogel felt

A) Sol-gel: 10 mL of industrial water glass with a mass fraction of 34% and 30 mL of deionized water were mixed in a beaker, stirred for 10 min, and the above solution was added to a 0.5 mol/L sulfuric acid solution, and Adjusting the pH of the mixed solution to 4.0, stirring for 5 min, to obtain a uniform silica sol;

B) Integrated immersion: soaking a glass wool felt having a density of 150-200 kg/m ³ , a thickness of 3-10 mm, a glass fiber length of 6-9 cm, and a glass fiber diameter of 8-10 μm into the silica sol obtained in the step A) , sealing and standing for 24h to obtain a fiber mat-SiO ₂ gel composite;

C) aging: the fiber mat-SiO ₂ gel composite obtained in step B) is aged at room temperature for 24 h, placed in a 95% ethanol solution, aged at 40 ° C for 24 h;

D) acidification: the fiber mat-SiO ₂ gel composite obtained in step C) is immersed in a hydrochloric acid solution having a hydrogen ion concentration of 10-10.5 mol / L for 40-45 min;

E) Surface modification treatment: The fiber mat-SiO ₂ gel composite treated in step D) is placed in a mixture of polyethylene glycol and trimethylchlorosilane in a weight ratio of 1:0.23, at 50 Surface modification at °C for 12 h, wherein the weight ratio of fiber mat-SiO ₂ gel composite to trimethylchlorosilane was 1:0.03, and then a mixture of ethanol and n-hexane in a volume ratio of 1:5 The liquid is washed on the surface modified fiber mat-SiO ₂ gel composite for 6 h;

F) Atmospheric pressure drying: the fiber mat-SiO ₂ gel composite sample treated by the step E) is dried at 80 ° C for 5 h, and then dried at 150 ° C for 2 h to obtain a composite SiO ₂ aerogel felt. .

Example 2: Method for preparing composite SiO ₂ aerogel felt

A) Sol-gel: 10 mL of a mass concentration of 34% industrial water glass, 50 mL of deionized water, mixed in a beaker, stirred for 10 min, the above solution was added to a 0.5 mol/mL hydrochloric acid solution, and adjusted Mixing the pH of the solution to 3.5, adding 0.5 mL of formamide, stirring for 5 min to obtain a uniform silica sol;

B) integrated soaking: a ceramic fiber mat having a density of 96-128 kg/m ³ and a thickness of 10-20 mm is immersed in the silica sol obtained in the step A), and sealed for 24 hours to obtain a fiber mat-SiO ₂ gel composite;

C) aging: the fiber mat-SiO ₂ gel composite obtained in step B) is aged at room temperature for 48h, placed in a 95% ethanol solution, aged at 45 ° C for 24h;

D) acidification: the fiber mat-SiO ₂ gel composite obtained in step C) is immersed in a nitric acid solution having a hydrogen ion concentration of 8-9.5 mol / L for 45-50 min;

E) Surface modification treatment: the fiber mat-SiO ₂ gel composite treated by the step D) is placed at a weight ratio of 1.5:0.5 (ie 1:0.33) from polyethylene glycol and trimethylchlorosilane. In the mixture, the surface modification was carried out at 40 ° C. The weight ratio of the fiber mat-SiO ₂ gel composite to trimethylchlorosilane was 1:0.02, and the volume was modified by ethanol solution and n-hexane. Washing mixture for a ratio of 1:5; 7h;

F) Atmospheric pressure drying: the fiber mat-SiO ₂ gel composite sample treated by the step E) is dried at 60 ° C for 6 h, and then dried at 200 ° C for 1 h to obtain a composite SiO ₂ aerogel felt. .

Example 3: Method for preparing composite SiO ₂ aerogel felt

A composite SiO ₂ aerogel felt was prepared in the same manner as in Example 1 except that the temperature of the aging treatment was 45 ° C and the aging time was 72 h.

Example 4: Method for preparing composite SiO ₂ aerogel felt

A composite SiO ₂ aerogel felt was prepared in the same manner as in Example 1 except that the temperature of the aging treatment was 50 ° C and the aging time was 24 h.

Example 5: Method for preparing composite SiO ₂ aerogel felt

A composite SiO ₂ aerogel felt was prepared in the same manner as in Example 1 except that the temperature of the aging treatment was 80 ° C and the aging time was 6 h.

The composite SiO ₂ aerogel felt prepared in the above Examples 1-5 was tested for its density, mechanical strength, thermal conductivity and appearance. The test results are shown in Table 1.

Table 1

Test items	Example 1	Example 3	Example 4	Example 5
Density (g/cm 3 )	0.15	0.16	0.16	0.17
Tensile strength (MPa)	0.301	0.306	0.308	0.311
Bending strength (MPa)	0.513	0.528	0.534	0.563
Compressive strength (MPa)	1.546	1.549	1.585	1.598
Thermal conductivity (w/(m·k))	0.020	0.022	0.022	0.024
Exterior	Blocky, good overall	Blocky, good overall	Blocky, good overall	Blocky, good overall

It can be seen from Table 1 that the aging time and the aging temperature have a certain influence on the mechanical properties and thermal insulation properties of the composite SiO ₂ aerogel felt. In the aging temperature range of 40-80 ° C, the lower the aging temperature, the finer the aerogel gap of the aerogel felt obtained, and the thermal conductivity and mechanical properties of the aerogel felt will also become better. In the range of aging time of 2-72h, the number of aerogel pores in the aerogel felt will fall after reaching the peak at around 24h, and the corresponding thermal conductivity and mechanical properties will also decrease. Therefore, it is preferred to set the duration of the aging treatment to 24 h and the aging temperature to 40 °C.

Example 6: Method for preparing composite SiO ₂ aerogel felt

A composite SiO ₂ aerogel felt was prepared in the same manner as in Example 1 except that the volume fraction of the ethanol solution used in the step C) was 40%.

Example 7: Method for preparing composite SiO ₂ aerogel felt

A composite SiO ₂ aerogel felt was prepared in the same manner as in Example 1 except that the volume fraction of the ethanol solution used in the step C) was 60%.

Example 8: Method for preparing composite SiO ₂ aerogel felt

A composite SiO ₂ aerogel felt was prepared in the same manner as in Example 1 except that the volume fraction of the ethanol solution used in the step C) was 80%.

Example 9: Method for preparing composite SiO ₂ aerogel felt

A composite SiO ₂ aerogel felt was prepared in the same manner as in Example 1 except that the volume fraction of the ethanol solution used in the step C) was 90%.

The composite SiO ₂ aerogel felt prepared in the above Example 1 and Examples 6-9 was tested for its density, mechanical strength, thermal conductivity and appearance. The test results are shown in Table 2.

Table 2

It can be seen from Table 2 that the volume fraction of the ethanol solution used in the step C) has an effect on the mechanical properties and thermal insulation properties of the composite SiO ₂ aerogel felt: the higher the volume fraction of ethanol in the ethanol solution, the gas obtained by the preparation thereof The higher the density of the gel felt, the better the mechanical properties and thermal conductivity of the aerogel felt. For the above reasons, it is preferred to set the volume fraction of the ethanol solution in step C) to 95%.

Example 10: Method for preparing composite SiO ₂ aerogel felt

A composite SiO ₂ aerogel felt was prepared in the same manner as in Example 1 except that the silane coupling agent used in the step E) was hexamethyldisilazane.

Example 11: Method for preparing composite SiO ₂ aerogel felt

A composite SiO ₂ aerogel felt was prepared in the same manner as in Example 1 except that the silane coupling agent used in the step E) was 3-aminopropyltriethoxysilane.

Example 12: Method for preparing composite SiO ₂ aerogel felt

A composite SiO ₂ aerogel felt was prepared in the same manner as in Example 1 except that the silane coupling agent used in the step E) was hexamethyldisiloxane.

The composite SiO ₂ aerogel felt prepared in the above Example 1 and Examples 10-12 was tested for its density, mechanical strength, thermal conductivity, contact angle and appearance. The test results are shown in Table 3.

table 3

It can be seen from Table 3 that different silane coupling agents have different modification effects on the aerogel felt, resulting in differences in density, mechanical properties and thermal conductivity of the corresponding aerogel felt. Among the above four kinds of silane coupling agents, trimethylchlorosilane and hexamethyldisiloxane have a better modification effect on the aerogel felt. However, since hexamethyldisiloxane has a certain toxicity, trimethylchlorosilane is preferred.

Example 13: Method for preparing composite SiO ₂ aerogel felt

A composite SiO ₂ aerogel felt was prepared in the same manner as in Example 1 except that the weight ratio of polyethylene glycol to trimethylchlorosilane in the step E) was 3:1 (i.e., 1:0.33).

Comparative Example 1: Method for preparing composite SiO ₂ aerogel felt

A composite SiO ₂ aerogel felt was prepared in the same manner as in Example 1 except that the weight ratio of polyethylene glycol to trimethylchlorosilane in the step E) was 1:1.

Comparative Example 2: Method for preparing composite SiO ₂ aerogel felt

A composite SiO ₂ aerogel felt was prepared in the same manner as in Example 1 except that the weight ratio of polyethylene glycol to trimethylchlorosilane in the step E) was 4:1.

Comparative Example 3: Method for preparing composite SiO ₂ aerogel felt

A composite SiO ₂ aerogel felt was prepared in the same manner as in Example 1 except that polyethylene glycol was used alone in the step E) without using any silane coupling agent.

Comparative Example 4: Method for preparing composite SiO ₂ aerogel felt

A composite SiO ₂ aerogel felt was prepared in the same manner as in Example 1 except that trimethylchlorosilane was used alone in the step E) without using any nonionic surfactant.

The obtained composite SiO ₂ aerogel felt was prepared in the above Example 1, Example 13 and Comparative Examples 1-4, and tested for density, mechanical strength, thermal conductivity, contact angle and appearance, and the test results are shown in Table 4.

Table 4

It can be seen from Table 4 that the composite SiO ₂ aerogel felt obtained by using polyethylene glycol and trimethylchlorosilane in combination of 1:0.23-0.33 has excellent mechanical properties and thermal insulation properties, among which polyethylene-2 The performance of the obtained composite SiO ₂ aerogel felt was best when the alcohol and trimethylchlorosilane were combined in a weight ratio of 1:0.23.

Comparative Example 5: Method for preparing composite SiO ₂ aerogel felt

In addition to the step D), the fiber mat-SiO ₂ gel composite obtained in the step C) is immersed in a hydrochloric acid solution having a hydrogen ion concentration of 1-1.5 mol/L for 40-45 minutes, and the same as in the first embodiment. A composite SiO ₂ aerogel felt was prepared in a manner.

Comparative Example 6: Method for preparing composite SiO ₂ aerogel felt

A composite SiO ₂ aerogel felt was prepared in the same manner as in Example 1 except that the step D) was omitted.

Comparative Example 7: Method for preparing composite SiO ₂ aerogel felt

A composite SiO ₂ aerogel felt was prepared in the same manner as in Example 1 except that the amount of water glass was increased to 20 mL.

The obtained composite SiO ₂ aerogel felts were prepared in the above Examples 1-2 and Comparative Examples 5-7, and their densities, mechanical strength, thermal conductivity, hydrophobic properties and appearance were tested. The test results are shown in Table 5.

table 5

It can be seen from Table 5 that the SiO ₂ aerogel felt prepared by the preparation method of the invention has good integrity, low density, low thermal conductivity, high tensile, compressive and flexural strength, and good hydrophobic properties.

Comparative Example 5 Compared with Example 1, the hydrogen ion concentration of the hydrochloric acid solution was lowered to 1-1.5 mol/L, and the prepared aerogel felt was observed to have a slightly pulverized aerogel powder in appearance, and The performance of the obtained composite SiO ₂ aerogel felt has a large difference from the performance of the aerogel felt obtained in Example 1.

Comparative Example 6 had no acidification step compared with Example 1, and the surface of the finished product was broken, and a large amount of aerogel powder was dispersed in the fiber mat, and an effective aerogel-fiber mat composite structure could not be formed. It is impossible to effectively test the mechanical properties of its finished products. However, since the finished product prepared in Comparative Example 6 did not form an effective aerogel-fiber mat composite structure, the heat insulating performance of the finished product was greatly reduced.

Comparative Example 7 increased the amount of water glass, and the resulting composite SiO ₂ aerogel felt did not perform as well as the aerogel felt prepared in Example 1.

Comparative Example 8: Method for preparing composite SiO ₂ aerogel felt

Except for the atmospheric pressure drying described in the step F), the fiber SiO ₂ gel composite sample treated by the step E) was dried at 70-80 ° C for 12-16 h, and the composite was prepared in the same manner as in Example 1. SiO ₂ aerogel felt.

Comparative Example 9: Method for preparing composite SiO ₂ aerogel felt

The composite SiO was prepared in the same manner as in Example 1 except that the atmospheric pressure drying in the step F) was carried out by subjecting the fiber SiO ₂ gel composite sample treated in the step E) to drying at 100 to 150 ° C for 5 to 6 hours. ₂ aerogel felt.

The composite SiO ₂ aerogel felt prepared in the above Example 1 and Comparative Examples 8-9 was tested for apparent density, mechanical strength, thermal conductivity and appearance, and the test results are shown in Table 6.

Table 6

Test items	Example 1	Comparative example 8	Comparative example 9
Density (g/cm 3 )	0.15	0.17	0.16
Tensile strength (MPa)	0.301	0.271	0.257
Bending strength (MPa)	0.513	0.499	0.486
Compressive strength (MPa)	1.546	1.531	1.501
Thermal conductivity (w/(m·k))	0.020	0.025	0.024
Exterior	Blocky, good overall	Blocky, good overall	Blocky, good overall

It can be seen from Table 6 that the aerogel felt obtained by using the staged drying than the single temperature drying condition is superior in mechanical properties and heat insulation. It can be seen that the density of the aerogel felt obtained in Example 1 is smaller than that of Comparative Examples 8 and 9, which can prove from the side that the classification drying can effectively reduce the void reduction caused by collapse or cracking of the aerogel hole, thereby Its internal block heat transfer function is guaranteed.

Since the present invention has been described by the above preferred embodiments, it is obvious to those skilled in the art that the present invention can be practiced without departing from the spirit and/or scope of the invention. And is included in the present invention.

Claims (13)

1. A method for preparing a composite SiO ₂ aerogel felt, comprising the steps of:

   A) sol-gel: a silicon source is mixed with deionized water to obtain a diluted solution, and an aqueous solution containing an acidic catalyst is added to the diluted solution to adjust the pH of the mixed solution to 3.0-8.0, and the mixed solution is stirred to obtain uniformity. Silica sol;

   B) integral soaking: soaking the fiber mat to the silica sol obtained in step A), or adding the silica sol to the fiber mat to seal and let stand to obtain the fiber mat-SiO ₂ gel composite;

   C) aging: the fiber mat-SiO ₂ gel composite obtained in step B) is aged at room temperature for 2-72h, then placed in an ethanol solution, aged at 40-80 ° C for 2-72h;

   D) acidification: the fiber mat-SiO ₂ gel composite obtained in step C) is immersed in a strong acid solution for 20-180min, wherein the concentration of hydrogen ions in the strong acid solution is not less than 4.5mol / L;

   E) Surface modification treatment: the fiber mat-SiO ₂ gel composite after acidification in step D) is placed in a mixture consisting of a nonionic surfactant and a silane coupling agent at 25-80 ° C The surface modification is carried out under conditions, and then the surface-modified fiber mat-SiO ₂ gel composite is washed with a mixture of ethanol and n-hexane in a volume ratio of 1:5 for 5-8 h;

   F) Normal pressure drying: The fiber mat-SiO ₂ gel composite treated by the step E) is dried under normal pressure to obtain a composite SiO ₂ aerogel felt.
2. The method for preparing a composite SiO ₂ aerogel felt according to claim 1, wherein the volume ratio of the silicon source to the deionized water in the step A) is 1:1-8, and the silicon source is Na. ₂ O·nSiO ₂ , n is 3-5; wherein the volume ratio of the 0 silicon source to the deionized water is preferably 1:3-5, more preferably the volume ratio is 1:3.
3. A method of producing a composite SiO ₂ aerogel felt according to claim ₂ , wherein the acidic catalyst in the step A) is selected from the group consisting of sulfuric acid and hydrochloric acid.
4. The method for preparing a composite SiO ₂ aerogel felt according to claim 1, wherein the fiber mat in step B) is selected from the group consisting of glass fiber mat, ceramic fiber mat and rock wool felt; wherein the glass fiber mat is preferably Glass wool felt.
5. The method for preparing a composite SiO ₂ aerogel felt according to claim 1, wherein the aging treatment of the fiber mat-SiO ₂ gel composite with the ethanol solution in step C) is 24 hours, correspondingly aging The temperature is 40 °C.
6. The method of preparing a composite SiO ₂ aerogel felt according to claim 5, wherein the volume fraction of the ethanol solution in the step C) is 70 to 95%; wherein the volume fraction is preferably 95%.
7. The method for preparing a composite SiO ₂ aerogel felt according to claim 1, wherein the strong acid in the step D) is selected from the group consisting of sulfuric acid, nitric acid and hydrochloric acid; and the concentration of hydrogen ions in the strong acid solution is 4.5-15 mol /L, preferably 10-13 mol/L.
8. The method of preparing a composite SiO ₂ aerogel felt according to claim 1, wherein the nonionic surfactant in the step E) is polyethylene glycol.
9. The method for preparing a composite SiO ₂ aerogel mat according to claim 8, wherein the silane coupling agent in the step E) is selected from the group consisting of trimethylchlorosilane, hexamethyldisilazane, and 3- Aminopropyltriethoxysilane and hexamethyldisiloxane; preferably, the silane coupling agent is trimethylchlorosilane.
10. The method for preparing a composite SiO ₂ aerogel mat according to claim 9, wherein the weight ratio of the nonionic surfactant to the silane coupling agent in the step E) is 1:0.23-0.33 Preferably, the weight ratio is 1:0.23.
11. The method for preparing a composite SiO ₂ aerogel felt according to claim 10, wherein the surface modification process in the step E) is carried out in an environment of 40-60 ° C, and the modification time is 10-24 h; preferably The ambient temperature is 50 ° C and the modification time is 12 h.
12. The method for preparing a composite SiO ₂ aerogel felt according to claim 11, wherein the atmospheric pressure drying in the step F) is a fiber mat-SiO ₂ gel composite after the step E). The sample was dried at 40-80 ° C for 4-7 h, and then dried at 120-200 ° C for 1-3 h to obtain a composite SiO ₂ aerogel felt.
13. A composite SiO ₂ aerogel felt obtained by the method of any one of claims 1-12.