Method for preparing bulk C—AlN composite aerogel with high strength and high temperature resistance

Abstract

Provided is a method for preparing a bulk CAlN composite aerogel with high strength and high temperature resistance, which includes: evenly stirring aluminum chloride crystals, water, ethanol and epoxy propane, to obtain a clear aluminum oxide sol solution, then adding formaldehyde and resorcinol to the solution and performing even stirring, to obtain an RF/Al.sub.2O.sub.3 composite aerogel sol solution, leaving the gel to stand, treating the sample by using a supercritical CO.sub.2 drying method, and finally heat-treating the sample at a high temperature under the condition of nitrogen, to obtain the bulk CAlN composite aerogel with high strength and high temperature resistance. The composite aerogel prepared by using this method has advantages of high integrity, high specific surface area, intact structure, low heat conductivity, low density, and high strength.

Claims

1. A method for preparing a bulk CAlN composite aerogel with high strength and high temperature resistance, the method comprising the following steps: (1) evenly stirring aluminum chloride crystals, distilled water, anhydrous ethanol and epoxy propane, to obtain a clear aluminum oxide sol solution; (2) adding formaldehyde (referred to as F for short) and resorcinol (referred to as R for short) to the aluminum oxide sol solution obtained in Step (1) and performing even stirring, to obtain an RF/Al.sub.2O.sub.3 composite aerogel sol solution; (3) pouring the RF/Al.sub.2O.sub.3 composite aerogel sol solution in Step (2) into a mold for reaction to form a gel; (4) adding at least one of anhydrous ethanol and deionized water to the gel obtained in Step (3) for aging replacement; (5) placing the wet gel after aging replacement in Step (4) in an oven at 60 C. to 75 C., aging the wet gel for 5 to 10 d, and then drying the wet gel using a supercritical CO.sub.2 drying method; and (6) heat-treating the sample after drying in Step (5) under the condition of nitrogen, to obtain the bulk CAlN composite aerogel with high strength and high temperature resistance; wherein: in Step (1), a molar ratio of aluminum chloride crystals, distilled water, anhydrous ethanol and epoxy propane is 1:(50 to 70):(20 to 30):(8 to 13); in Step (2), a molar ratio of aluminum chloride crystals:resorcinol:formaldehyde is (1 to 5):1:2; in the supercritical CO.sub.2 drying method of Step (5), CO.sub.2 is used for protection, a reaction temperature is 45 C. to 50 C., pressure of a high pressure reactor is controlled at 8 to 12 MPa, and reaction time is 2 to 3 d; and in Step (6), a heat treatment temperature ranges from 1500 C. to 1700 C., and heat treatment time is 1 h to 10 h.

2. The preparation method according to claim 1, wherein in Step (3), time for reaction to form a gel is 2 to 10 h.

3. The preparation method according to claim 1, wherein in Step (4), the number of times of replacement of the anhydrous ethanol and/or deionized water in the process of aging replacement is 3 to 5, and replacement time is 12 to 24 h each time.

4. The preparation method according to claim 1, wherein: in Step (1), the molar ratio of aluminum chloride crystals, distilled water, anhydrous ethanol and epoxy propane is 1:(50 to 70):(20 to 30):(9 to 13); in the supercritical CO.sub.2 drying method of Step (5), the pressure of the high pressure reactor is controlled at 8 to 11 MPa; and in Step (6), the heat treatment time is 2 h to 5 h.

5. The preparation method according to claim 1, wherein: in Step (3), time for reaction to form a gel is 2 to 10 h; and in Step (4), the number of times of replacement of the anhydrous ethanol and/or deionized water in the process of aging replacement is 3 to 5, and replacement time is 12 to 24 h each time.

6. The preparation method according to claim 4, wherein: in Step (3), time for reaction to form a gel is 2 to 10 h; and in Step (4), the number of times of replacement of the anhydrous ethanol and/or deionized water in the process of aging replacement is 3 to 5, and replacement time is 12 to 24 h each time.

7. A method for preparing a bulk CAlN composite aerogel with high strength and high temperature resistance, the method comprising the following steps: (1) evenly stirring aluminum chloride crystals, distilled water, anhydrous ethanol and epoxy propane, to obtain a clear aluminum oxide sol solution; (2) adding formaldehyde (referred to as F for short) and resorcinol (referred to as R for short) to the aluminum oxide sol solution obtained in Step (1) and performing even stirring, to obtain an RF/Al.sub.2O.sub.3 composite aerogel sol solution; (3) pouring the RF/Al.sub.2O.sub.3 composite aerogel sol solution in Step (2) into a mold for reaction to form a gel; (4) adding at least one of anhydrous ethanol and deionized water to the gel obtained in Step (3) for aging replacement; (5) placing the wet gel after aging replacement in Step (4) in an oven at 60 C. to 75 C., aging the wet gel for 5 to 10 d, and then taking the wet gel out for drying; and (6) heat-treating the sample after drying in Step (5) under the condition of nitrogen, to obtain the bulk CAlN composite aerogel with high strength and high temperature resistance; wherein: in Step (1), a molar ratio of aluminum chloride crystals, distilled water, anhydrous ethanol and epoxy propane is 1:(50 to 70):(20 to 30):(8 to 13); and in Step (2), a molar ratio of aluminum chloride crystals:resorcinol:formaldehyde is (3 to 5):1:2..

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The disclosure will become more fully understood from the detailed description given herein below for illustration only, and thus are not limitative of the disclosure, and wherein:

(2) FIG. 1 is an SEM photo of a bulk CAlN composite aerogel with high strength and high temperature resistance prepared in Example 1.

DETAILED DESCRIPTION

Example 1

(3) Aluminum chloride crystals, resorcinol and formaldehyde are weighted at a molar ratio of 1:1:2 to prepare a bulk CAlN composite aerogel with high strength and high temperature resistance. First step: 0.1 mol aluminum chloride crystals are weighted and poured into a 500 ml beaker, and then 151.4 ml ethanol (Al/EtOH=1:26), 90 ml deionized water (Al/H.sub.2O=1:50) and 63 ml epoxy propane (Al/PO=9) are added to the beaker, which are fully and evenly stirred, to obtain a clear aluminum oxide sol solution. Second step: 0.1 mol resorcinol (white needle-like crystals) and 15 ml formaldehyde are added to the aluminum oxide sol solution in the first step, which are fully and evenly stirred until the solution completely turns into a clear reddish sol solution, so as to obtain an RF/Al.sub.2O.sub.3 composite aerogel sol solution, which is poured into a mold for gelation. Gelation time at room temperature is about 8 h, and after gelation, ethanol is used as an aging solution to replace impurity ions in the wet gel three times and each time for 24 h. Finally, the wet gel in the mold is placed in an oven at 75 C. and aged at a high temperature for 10 d for full reaction. The RF/Al.sub.2O.sub.3 composite wet gel is placed in a high-temperature high-pressure reactor, and the sample is dried by using a supercritical CO.sub.2 drying method, where pressure of CO.sub.2 is controlled at 10 MPa, a temperature is controlled at 50 C., and supercritical drying time is 48 h. Finally, the sample is heat-treated for 2 h at a high temperature of 1500 C. under the condition of nitrogen, to obtain the bulk CAlN composite aerogel with high strength and high temperature resistance. It is found from an SEM photo of the prepared bulk CAlN composite aerogel with high strength and high temperature resistance by characterization that, the specific surface area of the aerogel is 596 m.sup.2/g, and the compressive strength is 5.22 MPa.

Example 2

(4) Aluminum chloride crystals, resorcinol and formaldehyde are weighted at a molar ratio of 2:1:2 to prepare a bulk CAlN composite aerogel with high strength and high temperature resistance. First step: 0.2 mol aluminum chloride crystals are weighted and poured into a 1000 ml beaker, and then 349.9 ml ethanol (Al/EtOH=1:30), 252 ml deionized water (Al/H.sub.2O=1:70) and 126 ml epoxy propane (Al/PO=9) are added to the beaker, which are fully and evenly stirred, to obtain a clear aluminum oxide sol solution. Second step: 0.1 mol resorcinol (white needle-like crystals) and 15 ml formaldehyde are added to the aluminum oxide sol solution in the first step, which are fully and evenly stirred until the solution completely turns into a clear reddish sol solution, so as to obtain an RF/Al.sub.2O.sub.3 composite aerogel sol solution, which is poured into a mold for gelation. Gelation time at room temperature is about 6 h, and after gelation, a mixed solution of ethanol and deionized water is used as an aging solution to replace impurity ions in the wet gel five times and each time for 12 h. Finally, the wet gel in the mold is placed in an oven at 60 C. and aged at a high temperature for 7 d for full reaction. The RF/Al.sub.2O.sub.3 composite wet gel is placed in a high-temperature high-pressure reactor, and the sample is dried by using a supercritical CO.sub.2 drying method, where pressure of CO.sub.2 is controlled at 12 MPa, a temperature is controlled at 45 C., and supercritical drying time is 72 h. Finally, the sample is heat-treated for 1 h at a high temperature of 1650 C. under the protection of argon, to obtain the bulk CAlN composite aerogel with high strength and high temperature resistance. It is found by characterization that, the specific surface area of the aerogel is 503 m.sup.2/g, and the compressive strength is 5.95 MPa.

Example 3

(5) Aluminum chloride crystals, resorcinol and formaldehyde are weighted at a molar ratio of 5:1:2 to prepare a bulk CAlN composite aerogel with high strength and high temperature resistance. First step: 0.5 mol aluminum chloride crystals are weighted and poured into a 2000 ml beaker, and then 583.16 ml ethanol (Al/EtOH=1:20), 450 ml deionized water (Al/H.sub.2O=1:50) and 345 ml epoxy propane (Al/PO=1:10) are added to the beaker, which are fully and evenly stirred, to obtain a clear aluminum oxide sol solution. Second step: 0.1 mol resorcinol (white needle-like crystals) and 15 ml formaldehyde are added to the aluminum oxide sol solution in the first step, which are fully and evenly stirred until the solution completely turns into a clear reddish sol solution, so as to obtain an RF/Al.sub.2O.sub.3 composite aerogel sol solution, which is poured into a mold for gelation. Gelation time at room temperature is about 2 h, and after gelation, deionized water is used as an aging solution to replace impurity ions in the wet gel three times and each time for 18 h. Finally, the wet gel in the mold is placed in an oven at 65 C. and aged at a high temperature for 5 d for full reaction. The RF/Al.sub.2O.sub.3 composite wet gel is placed in a high-temperature high-pressure reactor, and the sample is dried by using a supercritical CO.sub.2 drying method, where pressure of CO.sub.2 is controlled at 8 MPa, a temperature is controlled at 50 C., and supercritical drying time is 60 h. Finally, the sample is heat-treated for 5 h at a high temperature of 1550 C. under the condition of nitrogen, to obtain the bulk CAlN composite aerogel with high strength and high temperature resistance. It is found by characterization that, the specific surface area of the aerogel is 526 m.sup.2/g, and the compressive strength is 4.14 MPa.

Example 4

(6) Aluminum chloride crystals, resorcinol and formaldehyde are weighted at a molar ratio of 1:1:2 to prepare a bulk CAlN composite aerogel with high strength and high temperature resistance. First step: 0.1 mol aluminum chloride crystals are weighted and poured into a 500 ml beaker, and then 151 ml ethanol (Al/EtOH=1:26), 126 ml deionized water (Al/H.sub.2O=1:70) and 91 ml epoxy propane (Al/PO=1:13) are added to the beaker, which are fully and evenly stirred, to obtain a clear aluminum oxide sol solution. Second step: 0.1 mol resorcinol (white needle-like crystals) and 15 ml formaldehyde are added to the aluminum oxide sol solution in the first step, which are fully and evenly stirred until the solution completely turns into a clear reddish sol solution, so as to obtain an RF/Al.sub.2O.sub.3 composite aerogel sol solution, which is poured into a mold for gelation. Gelation time at room temperature is about 9 h, and after gelation, ethanol is used as an aging solution to replace impurity ions in the wet gel four times and each time for 15 h. Finally, the wet gel in the mold is placed in an oven at 70 C. and aged at a high temperature for 10 d for full reaction. The RF/Al.sub.2O.sub.3 composite wet gel is placed in a high-temperature high-pressure reactor, and the sample is dried by using a supercritical CO.sub.2 drying method, where pressure of CO.sub.2 is controlled at 10 MPa, a temperature is controlled at 45 C., and supercritical drying time is 48 h. Finally, the sample is heat-treated for 3 h at a high temperature of 1600 C. under the condition of nitrogen, to obtain the bulk CAlN composite aerogel with high strength and high temperature resistance. It is found by characterization that, the specific surface area of the aerogel is 555 m.sup.2/g, and the compressive strength is 5.17 MPa.

Example 5

(7) Aluminum chloride crystals, resorcinol and formaldehyde are weighted at a molar ratio of 4:1:2 to prepare a bulk CAlN composite aerogel with high strength and high temperature resistance. First step: 0.4 mol aluminum chloride crystals are weighted and poured into a 2000 ml beaker, and then 699.8 ml ethanol (Al/EtOH=1:30), 504 ml deionized water (Al/H.sub.2O=1:70) and 307.9 ml epoxy propane (Al/PO=1:11) are added to the beaker, which are fully and evenly stirred, to obtain a clear aluminum oxide sol solution. Second step: 0.1 mol resorcinol (white needle-like crystals) and 15 ml formaldehyde are added to the aluminum oxide sol solution in the first step, which are fully and evenly stirred until the solution completely turns into a clear reddish sol solution, so as to obtain an RF/Al.sub.2O.sub.3 composite aerogel sol solution, which is poured into a mold for gelation. Gelation time at room temperature is about 7 h, and after gelation, deionized water is used as an aging solution to replace impurity ions in the wet gel four times and each time for 20 h. Finally, the wet gel in the mold is placed in an oven at 70 C. and aged at a high temperature for 10 d for full reaction. The RF/Al.sub.2O.sub.3 composite wet gel is placed in a high-temperature high-pressure reactor, and the sample is dried by using a supercritical CO.sub.2 drying method, where pressure of CO.sub.2 is controlled at 11 MPa, a temperature is controlled at 45 C., and supercritical drying time is 60 h. Finally, the sample is heat-treated for 4 h at a high temperature of 1550 C. under the condition of nitrogen, to obtain the bulk CAlN composite aerogel with high strength and high temperature resistance. It is found by characterization that, the specific surface area of the aerogel is 506 m.sup.2/g, and the compressive strength is 4.57 MPa.

Example 6

(8) Aluminum chloride crystals, resorcinol and formaldehyde are weighted at a molar ratio of 2:1:2 to prepare a bulk CAlN composite aerogel with high strength and high temperature resistance. First step: 0.2 mol aluminum chloride crystals are weighted and poured into a 1000 ml beaker, and then 233.27 ml ethanol (Al/EtOH=1:20), 216 ml deionized water (Al/H.sub.2O=1:60) and 84 ml epoxy propane (Al/H.sub.2O=1:12) are added to the beaker, which are fully and evenly stirred, to obtain a clear aluminum oxide sol solution.

(9) Second step: 0.1 mol resorcinol (white needle-like crystals) and 15 ml formaldehyde are added to the aluminum oxide sol solution in the first step, which are fully and evenly stirred until the solution completely turns into a clear reddish sol solution, so as to obtain an RF/Al.sub.2O.sub.3 composite aerogel sol solution, which is poured into a mold for gelation. Gelation time at room temperature is about 5 h, and after gelation, a mixed solution of ethanol and deionized water is used as an aging solution to replace impurity ions in the wet gel four times and each time for 18 h. Finally, the wet gel in the mold is placed in an oven at 60 C. and aged at a high temperature for 7 d for full reaction. The RF/Al.sub.2O.sub.3 composite wet gel is placed in a high-temperature high-pressure reactor, and the sample is dried by using a supercritical CO.sub.2 drying method, where pressure of CO.sub.2 is controlled at 10 MPa, a temperature is controlled at 50 C., and supercritical drying time is 48 h. Finally, the sample is heat-treated for 5 h at a high temperature of 1700 C. under the condition of nitrogen, to obtain the bulk CAlN composite aerogel with high strength and high temperature resistance. It is found by characterization that, the specific surface area of the aerogel is 525 m.sup.2/g, and the compressive strength is 588 MPa.

Example 7

(10) Aluminum chloride crystals, resorcinol and formaldehyde are weighted at a molar ratio of 3:1:2 to prepare a bulk CAlN composite aerogel with high strength and high temperature resistance. First step: 0.3 mol aluminum chloride crystals are weighted and poured into a 1000 ml beaker, and then 454.2 ml ethanol (Al/EtOH=1:26), 324 ml deionized water (Al/H2O=1:60) and 207 ml epoxy propane (Al/PO=1:10) are added to the beaker, which are fully and evenly stirred, to obtain a clear aluminum oxide sol solution. Second step: 0.1 mol resorcinol (white needle-like crystals) and 15 ml formaldehyde are added to the aluminum oxide sol solution in the first step, which are fully and evenly stirred until the solution completely turns into a clear reddish sol solution, so as to obtain an RF/Al.sub.2O.sub.3 composite aerogel sol solution, which is poured into a mold for gelation. Gelation time at room temperature is about 6 h, and after gelation, ethanol is used as an aging solution to replace impurity ions in the wet gel five times and each time for 12 h. Finally, the wet gel in the mold is placed in an oven at 70 C. and aged at a high temperature for 10 d for full reaction. The RF/Al.sub.2O.sub.3 composite wet gel is placed in a high-temperature high-pressure reactor, and the sample is dried by using a supercritical CO.sub.2 drying method, where pressure of CO.sub.2 is controlled at 8 MPa, a temperature is controlled at 50 C., and supercritical drying time is 72 h. Finally, the sample is heat-treated for 5 h at a high temperature of 1600 C. under the condition of nitrogen, to obtain a bulk carbon-supported Al.sub.2O.sub.3Al.sub.4C.sub.3 composite aerogel. It is found by characterization that, the specific surface area of the aerogel is 505 m.sup.2/g, and the compressive strength is 5.18 MPa.

Example 8

(11) Aluminum chloride crystals, resorcinol and formaldehyde are weighted at a molar ratio of 3:1:1 to prepare a bulk CAlN composite aerogel with high strength and high temperature resistance. First step: 0.3 mol aluminum chloride crystals are weighted and poured into a 1000 ml beaker, and then 524.85 ml ethanol (Al/EtOH=1:30), 270 ml deionized water (Al/H.sub.2O=1:50) and 252 ml epoxy propane (Al/PO=1:12) are added to the beaker, which are fully and evenly stirred, to obtain a clear aluminum oxide sol solution. Second step: 0.1 mol resorcinol (white needle-like crystals) and 15 ml formaldehyde are added to the aluminum oxide sol solution in the first step, which are fully and evenly stirred until the solution completely turns into a clear reddish sol solution, so as to obtain an RF/Al.sub.2O.sub.3 composite aerogel sol solution, which is poured into a mold for gelation. Gelation time at room temperature is about 4 h, and after gelation, deionized water is used as an aging solution to replace impurity ions in the wet gel three times and each time for 20 h. Finally, the wet gel in the mold is placed in an oven at 75 C. and aged at a high temperature for 5 d for full reaction. The RF/Al.sub.2O.sub.3 composite wet gel is placed in a high-temperature high-pressure reactor, and the sample is dried by using a supercritical CO.sub.2 drying method, where pressure of CO.sub.2 is controlled at 10 MPa, a temperature is controlled at 45 C., and supercritical drying time is 60 h. Finally, the sample is heat-treated for 10 h at a high temperature of 1650 C. under the condition of nitrogen, to obtain the bulk CAlN composite aerogel with high strength and high temperature resistance. It is found by characterization that, the specific surface area of the aerogel is 426 m.sup.2/g, and compressive strength is 5.31 MPa.