A basic magnesium sulfate aerogel and a method for its preparation

Abstract

The application relates to a basic magnesium sulfate aerogel and a preparation method thereof. The technical scheme is as follows: first, M0 mass parts of basic magnesium sulfate whiskers and M1 mass parts of deionized water are mixed to obtain 100 mass parts of a basic magnesium sulfate whisker solution; the mass parts M0 of the basic magnesium sulfate whiskers is 8-12; then, M0 mass parts of the basic magnesium sulfate whiskers and M2 mass parts of aluminum dihydrogen phosphate are mixed according to a mass ratio of 1:0.2-1, the aluminum dihydrogen phosphate is mixed with the basic magnesium sulfate whisker solution, and the wet gel is obtained after being left to stand; then, the wet gel is subjected to first drying under the condition that the temperature is 70-90 DEG C and the humidity is 85-95% rh, and is subjected to second drying under the condition of normal pressure, so that the basic magnesium sulfate aerogel is prepared. The application has the characteristics of simple process, short production cycle, low cost, safety and environmental protection; the basic magnesium sulfate aerogel prepared by the method has the advantages of large size, small volume shrinkage, small volume density and good heat preservation and heat insulation performance.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of aerogels. Specifically relates to a basic magnesium sulfate aerogel and a preparation method thereof. BACKGROUND

[0002] Aerogels have the characteristics of high porosity, low density, large specific surface area, and low thermal conductivity. Due to the nanoscale size of the solid skeleton and internal pores of the aerogel, its heat transfer efficiency is very low, and the heat transfer amount is very small, so the thermal conductivity of the aerogel is very low, and it has good heat insulation effect. In the preparation of aerogels, drying determines the pore structure of the aerogel. At present, the three common drying methods for preparing aerogels are supercritical drying, vacuum freeze drying and atmospheric drying. Aerogels prepared by supercritical drying have high porosity, large specific surface area and small volume shrinkage, but the equipment for supercritical drying is expensive, the operation is complex, and the danger is relatively large. In the process of vacuum freeze drying, there is no gas-liquid interface, which reduces the surface energy interaction between the liquid solvent and the solid skeleton structure, but due to the slow solid sublimation, the product size and production efficiency also have great limitations. Compared with supercritical drying and freeze drying, atmospheric drying can realize large-scale preparation of aerogels. However, there is still a lot of water solution remaining in the pores of the untreated wet gel. If direct atmospheric drying is performed, the capillary force generated will exceed the bearing limit of the skeleton structure, resulting in a large shrinkage rate of the aerogel or even collapse, and a dramatic increase in thermal conductivity. Therefore, how to further improve the atmospheric drying technology is one of the focuses of attention.

[0003] Einarsrud MA (Einarsrud MA, Haereid S. Preparation of transparent, monolithic silica xerogels with low density: Code: HP9 [J]. Journal of Sol-Gel Science and Technology, 1994, 2: 903-906.) et al. prepared SiO2 wet gel with tetramethyl orthosilicate (TMOS) as precursor, used different concentrations of tetraethyl orthosilicate (TEOS) and methanol mixed solution as aging liquid, and aged the SiO2 wet gel for 48h, dried at 60℃ for 1 week, and then heat-treated the gel in air atmosphere at 500℃ for 4h to prepare SiO2 aerogel. Studies have shown that as the concentration of tetraethyl orthosilicate solution increases from 30vol% to 70vol%, the linear shrinkage of the sample decreases from 30% to 22%, and the bulk density decreases from 0.65g / cm 3 to 0.5g / cm 3Although aging treatment can effectively enhance the network skeleton structure and reduce the shrinkage rate during ambient pressure drying, the pore size decreases and some small pores disappear due to the accumulation and thickening of particles in the skeleton, resulting in a larger bulk density and a lower porosity. In addition, the use of TMOS is costly, and the methanol generated during hydrolysis is harmful to the environment and human body, which does not meet the environmental protection requirements.

[0004] Rao A P(Rao A P, Rao AV, Pajonk G M. Hydrophobic and physical properties of the two step processed ambient pressure dried silica aerogels with various exchanging solvents [J]. Journal of Sol-Gel Science and Technology, 2005, 36: 285-292.) et al. used tetraethyl orthosilicate (TEOS) and hexamethyldisilazane (HMDZ) methylating reagent as the silicon source, prepared SiO2 gel after oxalic acid hydrolysis and ammonia condensation, and selected hexane, cyclohexane, heptane, benzene, toluene and xylene as different organic solvents for solvent replacement. SiO2 aerogels were prepared by ambient pressure drying. The results show that the shrinkage rate of the sample using heptane for solvent replacement is as low as 4%, the porosity is 97%, and the thermal conductivity is 0.07 W / (m·K). Solvent replacement can effectively alleviate the problem of skeleton collapse during ambient pressure drying, but the process of solvent replacement is time-consuming and complex.

[0005] Wu X, Zhong K, Ding J, et al. Facile synthesis of flexible and hydrophobic polymethylsilsesquioxane based silica aerogel via the co-precursor method and ambient pressure drying technique[J]. Journal of Non-Crystalline Solids, 2020, 530: 119826. Wu et al. used methyltrimethoxysilane (MTMS) and tetraethyl orthosilicate (TEOS) as co-precursors, hydrochloric acid and ammonia as acid-base catalysts, cetyltrimethylammonium chloride (CTAC) as a surfactant, exchanged solvents with ethanol and ethane after aging for 24 h, modified the surface with 10 vol% trimethylchlorosilane (TMCS) / ethane solution for 24 h, washed the wet gel with ethane three times, and prepared flexible SiO2 aerogel with hydrophobic properties by ambient pressure drying. Studies have shown that the sample shrinks greatly during ambient pressure drying, but the aerogel will quickly recover to its original size due to the "rebound" effect. When the volume percentage of MTMS is 60%, the sample has the lowest volume density of 0.12 g / cm 3 , and a specific surface area of 364.5 m 2 / g. Although the performance of SiO2 aerogel prepared by surface hydrophobic modification is good, it has hydrophobicity, but the process is complicated, the preparation period is long, and a large amount of organic solvent is consumed, which limits its actual application.

[0006] The heat of ambient pressure drying is transferred from the surface of the material to the inside, and the heat distribution is uneven, causing the skeleton to shrink and collapse. The energy of microwave drying is transmitted through the material, and the interaction with the material is in the form of heat, and the heat distribution is uniform. Bonnardel P, Chausson S. Process for producing aerogels by dielectric heating: U.S. Patent 10,058,836 [P]. 2018-8-28. Bonnardel et al. prepared SiO2 aerogel with a thermal conductivity as low as 0.0135 W / (m·K) by microwave drying using tetraethyl orthosilicate (TEOS) as the silicon source. Microwave energy helps to more accurately control the drying process, most of the liquid has evaporated before leaving the gel, shortening the drying time and saving production costs. However, its drying process is not mature enough, it is difficult to dry larger blocks of gel, and further research is needed. SUMMARY

[0007] The application aims to overcome the shortcomings of the prior art, and aims to provide a preparation method of basic magnesium sulfate aerogel, which has the advantages of simple process, short production cycle, low cost, safety and environmental protection, and the basic magnesium sulfate aerogel prepared by the method has the advantages of large size, small volume shrinkage, small bulk density and good heat preservation and heat insulation performance.

[0008] To achieve the above-mentioned purpose, the technical scheme adopted by the application is:

[0009] Step 1, mix M0 mass parts of basic magnesium sulfate whiskers and M1 mass parts of deionized water to obtain 100 mass parts of a basic magnesium sulfate whisker solution.

[0010] The mass parts M0 of the basic magnesium sulfate whiskers is 8-12.

[0011] Step 2, mix the aluminum dihydrogen phosphate and the basic magnesium sulfate whisker solution according to a mass ratio of M0 mass parts of the basic magnesium sulfate whiskers to M2 mass parts of the aluminum dihydrogen phosphate of 1:0.2-1, and then stand to obtain a wet gel.

[0012] Step 3, dry the wet gel for the first time under the conditions of a temperature of 70-90 DEG C and a humidity of 85-95% rh to obtain a basic magnesium sulfate aerogel precursor.

[0013] Step 4, dry the basic magnesium sulfate aerogel precursor for the second time under normal pressure to obtain a basic magnesium sulfate aerogel.

[0014] The content of MgSO4·5Mg(OH)2·3H2O in the basic magnesium sulfate whiskers is greater than or equal to 90wt%, and the aspect ratio of the basic magnesium sulfate whiskers is greater than or equal to 5.

[0015] The content of Al(H2PO4)3 in the aluminum dihydrogen phosphate is greater than or equal to 90wt%.

[0016] The standing time is 0.5-5 min.

[0017] The first drying time is 24-48 h.

[0018] The second drying temperature is 70-90 DEG C, and the second drying time is 10-12 h.

[0019] The volume shrinkage of the basic magnesium sulfate aerogel is 0-8.9%.

[0020] Due to the above technical scheme, the application has the following positive effects compared with the prior art:

[0021] 1. This invention uses basic magnesium sulfate whiskers and aluminum dihydrogen phosphate as raw materials. By reasonably controlling the raw material ratio, the mixture is uniformly mixed with deionized water, and after molding, it is dried twice to obtain basic magnesium sulfate aerogel. The process is simple, the operation is controllable and safe, and it can produce basic magnesium sulfate aerogels with larger blocks.

[0022] 2. The raw materials used in this invention are basic magnesium sulfate whiskers and aluminum dihydrogen phosphate, which are inexpensive and have low production costs. The aerogel structure is constructed using basic magnesium sulfate whiskers and aluminum dihydrogen phosphate, and basic magnesium sulfate aerogel is prepared by a constant temperature and humidity method and a normal pressure drying method, without the need for other treatments; it has the advantages of simple process, easy operation, and short production cycle.

[0023] 3. This invention employs a constant temperature and humidity method to treat basic magnesium sulfate aerogel. High humidity reduces gas pressure and slows the drying process, thus preventing shrinkage and collapse of the basic magnesium sulfate aerogel during drying and greatly preserving its porous structure. In the prior art, products obtained by direct drying under normal pressure under the same conditions have a volume shrinkage rate of 10.9–37.1%; under the same conditions, the volume shrinkage rate of the products prepared using the method of this invention is reduced to 0–8.9%. The prepared basic magnesium sulfate aerogel has a low density and is in a complete block shape, effectively overcoming the problem of high shrinkage rate in existing aerogels dried under normal pressure.

[0024] The basic magnesium sulfate aerogel prepared by this invention was tested and found to have the following characteristics: volume shrinkage rate of 0–8.9%; bulk density ≤0.23 g / cm³. 3 Porosity ≥ 90%; Thermal conductivity ≤ 0.088 W / (m·K).

[0025] Therefore, the present invention has the characteristics of simple process, short production cycle, low cost and safety and environmental protection. The basic magnesium sulfate aerogel prepared by this method has large size, small volume shrinkage rate, low bulk density and good thermal insulation performance. Attached Figure Description

[0026] Figure 1 A photograph of a basic magnesium sulfate aerogel prepared according to the present invention;

[0027] Figure 2 for Figure 1 SEM image of the prepared basic magnesium sulfate aerogel. Detailed Implementation

[0028] The present invention will now be further described in conjunction with the accompanying drawings and specific embodiments, but this is not intended to limit the scope of protection thereof.

[0029] A basic magnesium sulfate aerogel and its preparation method. The steps of the preparation method described in this specific embodiment are as follows:

[0030] Step 1, mix M0 mass parts of basic magnesium sulfate whiskers and M1 mass parts of deionized water to obtain 100 mass parts of a basic magnesium sulfate whisker solution.

[0031] The mass parts M0 of the basic magnesium sulfate whiskers is 8-12.

[0032] Step 2, mix the aluminum dihydrogen phosphate and the basic magnesium sulfate whisker solution according to a mass ratio of M0 mass parts of the basic magnesium sulfate whiskers: M2 mass parts of the aluminum dihydrogen phosphate of 1:0.2-1, and stand to obtain a wet gel.

[0033] Step 3, dry the wet gel for the first time under conditions of a temperature of 70-90°C and a humidity of 85-95% rh to obtain a basic magnesium sulfate aerogel precursor.

[0034] Step 4, dry the basic magnesium sulfate aerogel precursor for the second time under normal pressure to obtain a basic magnesium sulfate aerogel.

[0035] The standing time is 0.5-5 min.

[0036] The first drying time is 24-48 h.

[0037] The second drying temperature is 70-90°C, and the second drying time is 10-12 h.

[0038] The volume shrinkage rate of the basic magnesium sulfate aerogel is 0-8.9%.

[0039] In the specific embodiment:

[0040] The content of MgSO4·5Mg(OH)2·3H2O in the basic magnesium sulfate whiskers is ≥90wt%, and the aspect ratio of the basic magnesium sulfate whiskers is ≥5.

[0041] The content of Al(H2PO4)3 in the aluminum dihydrogen phosphate is ≥90wt%.

[0042] The embodiments are not described again.

[0043] Embodiment 1

[0044] A basic magnesium sulfate aerogel and a preparation method thereof. The preparation method in the embodiment is:

[0045] Step 1, mix M0 mass parts of basic magnesium sulfate whiskers and M1 mass parts of deionized water to obtain 100 mass parts of a basic magnesium sulfate whisker solution.

[0046] The mass parts M0 of the basic magnesium sulfate whiskers is 8.

[0047] Step 2, the mass ratio of M0 mass parts of magnesium hydroxide sulfate whisker: M2 mass parts of aluminum dihydrogen phosphate is 1:0.2, the aluminum dihydrogen phosphate is mixed with the magnesium hydroxide sulfate whisker solution, and standing is performed to obtain a wet gel.

[0048] Step 3, the wet gel is subjected to first drying under the condition that the temperature is 70 DEG C and the humidity is 85% rh, and a magnesium hydroxide sulfate aerogel precursor is obtained.

[0049] Step 4, the magnesium hydroxide sulfate aerogel precursor is subjected to second drying under the condition of normal pressure, and a magnesium hydroxide sulfate aerogel is prepared.

[0050] The standing time is 5 min.

[0051] The first drying time is 24 h.

[0052] The second drying temperature is 70 DEG C, and the second drying time is 10 h.

[0053] The magnesium hydroxide sulfate aerogel prepared in the embodiment is detected: the volume shrinkage rate is 8.9%, the volume density is 0.14 g / cm 3 , the porosity is 93.1%, and the thermal conductivity is 0.070 W / (m.K). While the sample obtained by directly performing normal pressure drying under the same condition in the prior art: the volume shrinkage rate is 37.1%, the volume density is 0.23 g / cm 3 , the porosity is 90.0%, and the thermal conductivity is 0.101 W / (m.K).

[0054] Example 2

[0055] A magnesium hydroxide sulfate aerogel and a preparation method thereof. The preparation method in the embodiment is:

[0056] Step 1, M0 mass parts of magnesium hydroxide sulfate whisker and M1 mass parts of deionized water are mixed to obtain 100 mass parts of a magnesium hydroxide sulfate whisker solution.

[0057] The mass parts M0 of the magnesium hydroxide sulfate whisker is 10.

[0058] Step 2, the mass ratio of M0 mass parts of magnesium hydroxide sulfate whisker: M2 mass parts of aluminum dihydrogen phosphate is 1:0.6, the aluminum dihydrogen phosphate is mixed with the magnesium hydroxide sulfate whisker solution, and standing is performed to obtain a wet gel.

[0059] Step 3, the wet gel is subjected to first drying under the condition that the temperature is 80 DEG C and the humidity is 90% rh, and a magnesium hydroxide sulfate aerogel precursor is obtained.

[0060] Step 4, the basic magnesium sulfate aerogel precursor is secondarily dried under normal pressure to obtain a basic magnesium sulfate aerogel.

[0061] The standing time is 2 min.

[0062] The first drying time is 36 h.

[0063] The second drying temperature is 80℃, and the second drying time is 11 h.

[0064] The basic magnesium sulfate aerogel prepared in this embodiment is detected: the volume shrinkage rate is 0%, the volume density is 0.17 g / cm 3 , the porosity is 91.9%, and the thermal conductivity is 0.082 W / (m·K); while the sample obtained by directly drying under normal pressure under the same conditions in the prior art: the volume shrinkage rate is 21.2%, the volume density is 0.24 g / cm 3 , the porosity is 90.0%, and the thermal conductivity is 0.096 W / (m·K).

[0065] Example 3

[0066] A basic magnesium sulfate aerogel and a preparation method thereof. The preparation method in this embodiment is:

[0067] Step 1, mix M0 mass parts of basic magnesium sulfate whiskers and M1 mass parts of deionized water to obtain 100 mass parts of a basic magnesium sulfate whisker solution.

[0068] The mass parts M0 of the basic magnesium sulfate whiskers is 12.

[0069] Step 2, mix the aluminum dihydrogen phosphate and the basic magnesium sulfate whisker solution according to the mass ratio of M0 mass parts of the basic magnesium sulfate whiskers to M2 mass parts of the aluminum dihydrogen phosphate is 1:1, and stand to obtain a wet gel.

[0070] Step 3, the wet gel is first dried under the condition of a temperature of 90℃ and a humidity of 95% rh to obtain a basic magnesium sulfate aerogel precursor.

[0071] Step 4, the basic magnesium sulfate aerogel precursor is secondarily dried under normal pressure to obtain a basic magnesium sulfate aerogel.

[0072] The standing time is 0.5 min.

[0073] The first drying time is 48 h.

[0074] The second drying temperature is 90℃, and the second drying time is 12 h.

[0075] The basic magnesium sulfate aerogel prepared in the embodiment is detected to have a volume shrinkage of 0%, a volume density of 0.23 g / cm 3 , a porosity of 90.0%, and a thermal conductivity of 0.088 W / (m·K). The sample obtained by directly performing normal pressure drying under the same conditions in the prior art has a volume shrinkage of 10.9%, a volume density of 0.32 g / cm 3 , a porosity of 84.0%, and a thermal conductivity of 0.092 W / (m·K).

[0076] Compared with the prior art, the specific embodiment has the following positive effects:

[0077] 1. The specific embodiment uses basic magnesium sulfate whiskers and aluminum dihydrogen phosphate as raw materials, uniformly mixes the raw materials with deionized water, and obtains the basic magnesium sulfate aerogel by twice drying after molding. The process is simple, the operation process is controllable and safe, and a large block of basic magnesium sulfate aerogel can be prepared.

[0078] 2. The raw materials used in the specific embodiment are basic magnesium sulfate whiskers and aluminum dihydrogen phosphate, which are low in price and low in production cost. The basic magnesium sulfate aerogel is prepared by building an aerogel structure with basic magnesium sulfate whiskers and aluminum dihydrogen phosphate, and by using the constant temperature and humidity method and the normal pressure drying method without other treatment. The process is simple, easy to operate, and short in production cycle.

[0079] 3. In the specific embodiment, the basic magnesium sulfate aerogel is treated by the constant temperature and humidity method, the pressure is reduced and the drying process is slowed down by high humidity, so as to avoid the shrinkage and collapse of the basic magnesium sulfate aerogel during the drying process, and the pore structure of the basic magnesium sulfate aerogel is greatly preserved. The volume shrinkage of the product obtained by directly performing normal pressure drying in the prior art is 10.9-37.1%; under the same conditions, the volume shrinkage of the product prepared by using the preparation method of the specific embodiment is reduced to 0-8.9%. The prepared basic magnesium sulfate aerogel is low in density and in the form of a complete block, which effectively overcomes the problem of large shrinkage of the existing aerogel during normal pressure drying.

[0080] The basic magnesium sulfate aerogel prepared in the specific embodiment is shown in the following figures: Figure 1 is a real photo of the basic magnesium sulfate aerogel prepared in Example 1; Figure 2 is a SEM image of the basic magnesium sulfate aerogel shown in Figure 1 From Figure 1 , it can be seen that the prepared basic magnesium sulfate aerogel does not deform the petals when placed on fresh flowers, indicating that the prepared basic magnesium sulfate aerogel is small in quality and low in density; from Figure 2It can be seen that the microstructure of the basic magnesium sulfate aerogel is that aluminum phosphate wraps and bonds the basic magnesium sulfate whiskers to build the porous structure of the basic magnesium sulfate aerogel, which can effectively improve the thermal insulation performance.

[0081] The basic magnesium sulfate aerogel prepared in the embodiment is detected to have a volume shrinkage rate of 0-8.9%, a volume density of ≤0.23 g / cm 3 , a porosity of ≥90%, and a thermal conductivity of ≤0.088 W / (m·K).

[0082] Therefore, the embodiment has the characteristics of simple process, short production cycle, low cost and high safety, and the prepared basic magnesium sulfate aerogel has large size, small volume shrinkage rate, small volume density and good thermal insulation performance.

Claims

1. A method for preparing basic magnesium sulfate aerogel, characterized by The specific steps of the preparation method are: Step 1, mixing M0 mass parts of basic magnesium sulfate whiskers and M1 mass parts of deionized water to obtain 100 mass parts of a basic magnesium sulfate whisker solution; The mass parts M0 of the basic magnesium sulfate whisker is 8-12; Step 2, mixing the aluminum dihydrogen phosphate and the basic magnesium sulfate whisker solution according to a mass ratio of M0 mass parts of the basic magnesium sulfate whisker: M2 mass parts of aluminum dihydrogen phosphate of 1:0.2-1, and standing to obtain a wet gel; Step 3, performing first drying on the wet gel under conditions of a temperature of 70-90℃ and a humidity of 85-95% rh to obtain a basic magnesium sulfate aerogel precursor; Step 4, performing second drying on the basic magnesium sulfate aerogel precursor under normal pressure to obtain a basic magnesium sulfate aerogel.

2. The method of preparation of basic magnesium sulfate aerogel according to claim 1, characterized by The content of MgSO4·5Mg(OH)2·3H2O in the basic magnesium sulfate whisker is ≥90wt%, and the length-diameter ratio of the basic magnesium sulfate whisker is ≥5.

3. The method of claim 1, wherein the magnesium hydroxy sulfate aerogel is prepared by The content of Al(H2PO4)3 in the aluminum dihydrogen phosphate is ≥90wt%.

4. The method of claim 1, wherein the magnesium hydroxy sulfate aerogel is prepared by The standing time is 0.5-5min.

5. The method for preparing basic magnesium sulfate aerogel according to claim 1, characterized in that... The first drying time is 24-48h.

6. The method of claim 1, wherein the basic magnesium sulfate aerogel is prepared by the steps of The second drying temperature is 70-90℃, and the second drying time is 10-12h.

7. A basic magnesium sulfate aerogel, characterized in that The basic magnesium sulfate aerogel is prepared according to the preparation method of the basic magnesium sulfate aerogel in any one of claims 1-6.

8. The basic magnesium sulfate aerogel according to claim 7, characterized in that The volume shrinkage rate of the basic magnesium sulfate aerogel is 0-8.9%.

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