HIGH-TEMPERATURE-RESISTANT AND OXIDATION-RESISTANT LIGHT-WEIGHT HEAT-INSULATION FOAM MATERIAL AND PREPARATION METHOD THEREFOR

Abstract

A high-temperature-resistant and oxidation-resistant light-weight heat-insulation foam material and a preparation method thereof. The foam material is one of a SiBCN foam material, a SiHfBCN foam material, a SiBCN/C composite foam material and a SiHfBCN/C composite foam material. The foam material is prepared from a precursor solution through processes of template impregnation, curing, drying and cracking; wherein the precursor solution is a SiBCN precursor solution or a SiHfBCN precursor solution, and the template is a polyurethane foam or an organic carbon-modified polyurethane foam. The SiBCN foam material, SiHfBCN foam material, SiBCN/C composite foam material or SiHfBCN/C composite foam material obtained by the present application has the advantages of high temperature resistance, a low thermal conductivity, oxidation resistance, a low density and a high strength.

Claims

1. A high-temperature-resistant and oxidation-resistant light-weight heat-insulation foam material, being one selected from the group consisting of a SiBCN foam material, a SiHfBCN foam material, a SiBCN/C composite foam material and a SiHfBCN/C composite foam material, and prepared from a precursor solution through the processes of template impregnation, curing, drying and cracking; wherein, the precursor solution is a SiBCN precursor solution or a SiHfBCN precursor solution, the template is a polyurethane foam or an organic carbon-modified polyurethane foam, a SiBCN precursor for preparing the SiBCN precursor solution is polyborosilazane, a SiHfBCN precursor for preparing the SiHfBCN precursor solution is hafnium-containing polyborosilazane.

2. The high-temperature-resistant and oxidation-resistant light-weight heat-insulation foam material according to claim 1, wherein the SiBCN foam material has a density of equal to and greater than 0.07 g/cm.sup.3, a room temperature compressive strength of equal to and greater than 0.3 MPa, and a room temperature thermal conductivity of equal to and greater than 0.046 W/(m.Math.K); the SiHfBCN foam material has a density of equal to and greater than 0.11 g/cm.sup.3, a room temperature compressive strength of equal to and greater than 0.45 MPa, and a room temperature thermal conductivity of equal to and greater than 0.053 W/(m.Math.K); the SiBCN/C composite foam material has a density of equal to and greater than 0.09 g/cm.sup.3, a room temperature compressive strength of equal to and greater than 0.38 MPa, and a room temperature thermal conductivity of equal to and greater than 0.052 W/(m.Math.K); and the SiHfBCN/C composite foam material has a density of equal to and greater than 0.13 g/cm.sup.3, a room temperature compressive strength of equal to and greater than 0.68 MPa, and a room temperature thermal conductivity of equal to and greater than 0.062 W/(m.Math.K); preferably, the SiBCN foam material has a density of 0.17?0.6 g/cm.sup.3, a room temperature compressive strength of 0.8?7.2 MPa, and a room temperature thermal conductivity of 0.06?0.18 W/(m.Math.K); the SiHfBCN foam material has a density of 0.21?0.78 g/cm.sup.3, a room temperature compressive strength of 1.1?7.6 MPa, and a room temperature thermal conductivity of 0.067?0.22 W/(m.Math.K); the SiBCN/C composite foam material has a density of 0.23?0.68 g/cm.sup.3, a room temperature compressive strength of 1.0?7.4 MPa, and a room temperature thermal conductivity of 0.067?0.19 W/(m.Math.K); and the SiHfBCN/C composite foam has a density of 0.26?0.82 g/cm.sup.3, a room temperature compressive strength of 1.5?8.63 MPa, and a room temperature thermal conductivity of 0.074?0.25 W/(m.Math.K).

3. A preparation method of the high-temperature-resistant and oxidation-resistant light-weight heat-insulation foam material, comprising the following steps of: adopting a polyurethane foam or an organic carbon-modified polyurethane foam as a template and a SiBCN precursor solution or a SiHfBCN precursor solution as an impregnation solution, and sequentially carrying out impregnation process, curing process, drying process and cracking process to obtain the foam material; wherein, the SiBCN precursor solution or the SiHfBCN precursor solution is obtained by dissolving a SiBCN precursor or a SiHfBCN precursor in an organic solvent, adding a catalyst and mixing uniformly; the SiBCN precursor is polyborosilazane and the SiHfBCN precursor is hafnium-containing polyborosilazane.

4. The preparation method according to claim 3, wherein a mass fraction of the SiBCN precursor in the SiBCN precursor solution or a mass fraction of the SiHfBCN precursor in the SiHfBCN precursor solution is 5%?80%, and a mass of the catalyst is 0.5%?5% of a mass of the SiBCN precursor or the SiHfBCN precursor; preferably, the mass fraction of the SiBCN precursor in the SiBCN precursor solution or the mass fraction of the SiHfBCN precursor in the SiHfBCN precursor solution is 10%?30%.

5. The preparation method according to claim 3 or 4, wherein the organic solvent is liquid alkane; preferably, the organic solvent is selected from at least one of the group consisting of hexane, heptane, octane, nonane, decane, undecane, dodecane, tridecane and their isomers; more preferably, the organic solvent is selected from at least one of the group consisting of n-hexane, n-octane and n-nonane. preferably, the catalyst is selected from at least one of the group consisting of diisopropylbenzene peroxide, dibenzoyl peroxide, azo diisobutyronitrile, azo diisoprenonitrile and divinylbenzene; preferably, the catalyst is selected from at least one of the group consisting of diisopropylbenzene peroxide and divinylbenzene.

6. The preparation method according to any one of claims 3 to 5, wherein the organic carbon-modified polyurethane foam is prepared by immersing the polyurethane foam in an organic carbon source and then curing the organic carbon source attached to the polyurethane foam; preferably, the organic carbon source is selected from one of the group consisting of furfuryl alcohol, phenolic resin and resorcinol-formaldehyde sol; more preferably, in a process for preparing the organic carbon-modified polyurethane foam, the curing is to raise a temperature from room temperature to 50?200? C. at a heating rate of 0.01?10? C./min in an inert gas environment of nitrogen or argon, and then keep the temperature for 2?96 hours to cross-link and solidify the organic carbon source, so as to obtain the organic carbon-modified polyurethane foam.

7. The preparation method according to claim 6, wherein, when the organic carbon source is furfuryl alcohol, the process for preparing the organic carbon-modified polyurethane foam further includes adding formic acid or methyl p-toluenesulfonate as a catalyst into the furfuryl alcohol; preferably, when the catalyst is formic acid, a ratio of a mass of formic acid to a volume of furfuryl alcohol, is 40?65 g/L; preferably, when the catalyst is methyl p-toluenesulfonate, a mass ratio of the methyl p-toluenesulfonate to the furfuryl alcohol is (0.004?0.08):1; when the organic carbon source is a phenolic resin, the process for preparing the organic carbon-modified polyurethane foam further includes adding hexamethylenetetramine as a catalyst and anhydrous ethanol as a solvent into the phenolic resin; preferably, a mass ratio of the hexamethylenetetramine to the phenolic resin is 1:(4?9); preferably, a ratio of a mass of phenolic resin to a volume of anhydrous ethanol is 0.1?0.2 g/mL; when the organic carbon source is resorcinol-formaldehyde sol, the process for preparing the organic carbon-modified polyurethane foam further includes adding at least one selected from the group consisting of sodium carbonate, sodium hydroxide, and barium hydroxide as a catalyst and deionized water as a solvent into the resorcinol-formaldehyde sol; preferably, the molar ratio of the resorcinol to the formaldehyde is 1:2; preferably, the molar ratio of the resorcinol to the catalyst is (50?1000):1; and the molar ratio of the resorcinol to the deionized water is (0.01?0.5):1.

8. The preparation method according to claim 6 or 7, wherein, in the process for preparing the organic carbon-modified polyurethane foam, the used polyurethane foam has a reticulated open-cell structure with an average pore diameter of 1 ?m?1 mm; preferably, the polyurethane foam has a density of 0.025?0.1 g/cm.sup.3 and a porosity of more than 92%; preferably, in the process for preparing the organic carbon-modified polyurethane foam, a vacuum degree of the immersing is 10 Pa?10.sup.5 Pa, and an immersing time is 0.1?2 h.

9. The preparation method according to any one of claims 3 to 5, wherein, the polyurethane foam used directly as the template has a reticulated open-cell structure with an average pore size of 1 ?m?1 mm; preferably, the polyurethane foam has a density of 0.025?0.1 g/cm.sup.3 and a porosity of more than 92%.

10. The preparation method according to any one of claims 3 to 9, wherein, in the impregnation process, a vacuum degree is 10 Pa?10.sup.5 Pa and an impregnation time is 0.1?2 h; preferably, the curing process is to raise a temperature from room temperature to 100?280? C. at a heating rate of 0.01?5? C./min under a non-oxygen sealing condition, and to keep the temperature for 2?8 hours; preferably, the drying process is to raise a temperature from room temperature to 100?280? C. at a heating rate of 0.01?1? C./min in an inert atmosphere of nitrogen or argon, and then keep the temperature for 4?24 hours; preferably, the cracking process is to raise a temperature from room temperature to 800?1500? C. at a heating rate of 0.1?5? C./min in an inert atmosphere of nitrogen or argon, and then keep the temperature for 2?8 hours.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0055] FIG. 1 is a flow chart of the preparation process of a SiBCN foam material or a SiHfBCN foam material.

[0056] FIG. 2 is a flow chart of the preparation process of a SiBCN/C composite foam material or a SiHfBCN/C composite foam material.

[0057] FIG. 3 is an infrared spectrum of the SiBCN ceramic foam material sample prepared in Example 1 of the present application.

[0058] FIG. 4 is a XRD pattern of the SiHfBCN ceramic foam material sample prepared in Example 2 of the present application.

[0059] FIG. 5 is a microscopic topography diagram of the SiBCN foam material sample prepared in Example 1 of the present application.

[0060] FIG. 6 is a microscopic topography diagram of the SiBCN foam material sample prepared in Example 5 of the present application.

[0061] FIG. 7 is a microscopic topography diagram of the SiBCN foam material sample prepared in Example 6 of the present application.

DETAILED DESCRIPTION OF THE EMBODIMENTS

[0062] The high-temperature-resistant, oxidation-resistant, light-weight heat-insulation foam material and its preparation method of the present application will be described below with reference to the accompanying drawings and examples. It should be understood that these examples are only used to illustrate the present application and not to limit the scope of the present application. It should be understood that, after reading the content of the present application, those skilled in the art application make various changes and modifications to the present application, and these equivalent forms also fall within the scope defined by the appended claims of the present application.

[0063] The SiBCN precursor used in the following examples is polyborosilazane (the number-average molecular weight of polyborosilazane is 400?600 g/mol, and the viscosity at 80? C. is 100?300 cp), purchased from the Institute of Chemistry, Chinese Academy of Sciences, or Shandong Zibo Industry and Trade Co., Ltd. The SiHfBCN precursor (the number-average molecular weight of hafnium-containing polyborosilazane is 500?1000 g/mol, and the room temperature viscosity is 100?500 cp) was made in the laboratory (the specific preparation method is described below), wherein the polysilazane HTT1800 is a polysilazane containing vinyl active groups (its molecular structure is described below), purchased from Guangzhou Honghai Chemical Technology Co., Ltd., and the rest of the raw materials can be purchased from the market.

##STR00001##

[0064] Preparation of SiHfBCN precursor: at room temperature, toluene was pre-added in a Schlenk reactor filled with inert gas atmosphere, and polysilazane HTT1800 was dissolved in toluene to prepare a solution with volume fraction of 40%; then, the toluene solution of Hf (NEt.sub.2).sub.4 with volume fraction of 6% was added dropwise to the Schlenk reactor (wherein the volume ratio of Hf (NEt.sub.2).sub.4 to polysilazane HTT1800 is 1:9), and stirred for 2 h after mixing; the reaction system was cooled to ?50? C., and the toluene solution of borane dimethyl sulfide BH.sub.3.Math.(CH.sub.3).sub.2S with volume fraction of 6% was added dropwise to the mixture solution (wherein the volume ratio of BH.sub.3.Math.(CH.sub.3).sub.2S to polysilazane HTT1800 is 1:18), and stirred for 2 hours; then the reaction system was heated to room temperature for 24 hours; finally, the SiHfBCN precursor can be obtained by evaporating the toluene at 50-60? C. under vacuum.

[0065] The specific embodiment of the present application provides a high-temperature-resistant and oxidation-resistant light-weight heat-insulation foam material, wherein the preparation method of a SiBCN foam material or a SiHfBCN foam material, as shown in FIG. 1, includes the following steps: [0066] S1. Preparation of precursor solution: Dissolve a SiBCN precursor in an organic solvent to prepare a 5 wt %?80 wt % SiBCN precursor solution, add 0.5%?5% catalyst by mass of the SiBCN precursor thereto, and stir for a period of time until mix uniformly; or, dissolve a SiHfBCN precursor in an organic solvent to prepare a 5 wt %?80 wt % SiHfBCN precursor solution, adding 0.5%?5% catalyst by mass of the SiHfBCN precursor thereto, and stir for a period of time until the mixture is uniform. [0067] S2. Impregnation process: Impregnate a polyurethane foam template with an average pore size of 1 ?m?1 mm in the SiBCN precursor solution or the SiHfBCN precursor solution, wherein a vacuum degree for impregnation is 10 Pa?10.sup.5 Pa, and an impregnation time is 0.1?2 h. [0068] S3. Curing process: Under non-oxygen and sealing conditions, a temperature is raised from room temperature to 100?280? C. at a heating rate of 0.01?5? C./min, and then maintain the temperature for 2?8 hours to cure. [0069] S4. Drying process: Under an inert environment of nitrogen or argon, raise a temperature from room temperature to 100?280? C. at a heating rate of 0.01?1? C./min, then maintain the temperature for 4?24 hours to dry and remove the organic solvent, so as to obtain a SiBCN pre-solid foam or a SiHfBCN pre-solid foam. [0070] S5. Cracking process: Increase the temperature of the SiBCN pre-solid foam or the SiHfBCN pre-solid foam from room temperature to 800?1500? C. at a rate of 0.1?5? C./min under an inert environment of nitrogen or argon, and then maintain the temperature for 2?8 hours to obtain the SiBCN foam material or the SiHfBCN foam material.

[0071] Another specific embodiment of the present application provides a high-temperature-resistant and oxidation-resistant light-weight heat-insulation foam material, [0072] wherein the preparation method of a SiBCN/C composite foam material or a SiHfBCN/C composite foam material, as shown in FIG. 2, includes the following steps: [0073] S1. Preparation method of organic carbon-modified polyurethane foam template: A polyurethane foam with an average pore size of 1 ?m?1 mm is impregnated in an organic carbon source, wherein an impregnation vacuum degree is 10 Pa?10.sup.5 Pa, and an impregnation time is 0.1?2 h. Then increase a temperature from room temperature to 50?200? C. at a heating rate of 0.01?10? C./min, and keep the temperature for 2?96 hours to cross-link and solidify the organic carbon source, so as to obtain an organic carbon-modified polyurethane foam. [0074] S2. Precursor solution preparation: Dissolve a SiBCN precursor in an organic solvent to make a 5 wt %?80 wt % SiBCN precursor solution, then add 0.5%?5% catalyst by mass of the SiBCN precursor thereto and stir for a period of time until it is uniformly mixed; or, dissolve a SiHfBCN precursor in an organic solvent to prepare a 5 wt %?80 wt % SiHfBCN precursor solution, then add 0.5%?5% catalyst by mass of the SiHfBCN precursor thereto, and stir for a period of time until it is uniformly mixed. [0075] S3. Impregnation process: Impregnate the organic carbon-modified polyurethane foam template in the SiBCN precursor solution or the SiHfBCN precursor solution, wherein, a vacuum degree of impregnation is 10 Pa?10.sup.5 Pa, and an impregnation time is 0.1?2 h. [0076] S4. Curing process: Under non-oxygen and sealing conditions, raise a temperature from room temperature to 100?280? C. at a heating rate of 0.01?5? C./min, and then maintain the temperature for 2?8 hours to cure. [0077] S5. Drying process: Under an inert environment of nitrogen or argon, raise a temperature from room temperature to 100?280? C. at a heating rate of 0.01?1? C./min, and then keep the temperature for 4?24 h to dry and remove the organic solvent, so as to obtain a SiBCN/C pre-solid foam or a SiHfBCN/C pre-solid foam. [0078] S6. Cracking process: Increase a temperature of the above-mentioned SiBCN pre-solid foam or SiHfBCN pre-solid foam from room temperature to 800?1500? C. at a heating rate of 0.1?5? C./min under an inert environment of nitrogen or argon, and then maintain the temperature for 2?8 hours to obtain the SiBCN/C composite foam or the SiHfBCN/C composite foam.

Example 1

[0079] A SiBCN foam material, whose preparation method comprises the following steps: [0080] S1. Precursor solution preparation: Dissolve a SiBCN precursor in n-nonane to prepare a 10 wt % SiBCN precursor solution, add 0.5% dicumyl peroxide as catalyst by mass of the SiBCN precursor, and stir for 10 minutes under the condition of sealing until the mixture is uniform; [0081] S2. Impregnation process: impregnate a polyurethane foam template with a size of 200 mm?200 mm?35 mm, an average pore diameter of 300 ?m, a density of 0.032 g/cm.sup.3, and a porosity of 92.6% in the above-mentioned precursor solution at normal pressure, and an impregnation time is 10 minutes; [0082] S3. Curing process: Under non-oxygen and sealing conditions, raise a temperature from room temperature to 160? C. at a heating rate of 0.5? C./min, and then keep the temperature to cure for 4 hours; [0083] S4. Drying process: Increase a temperature from room temperature to 150? C. at a heating rate of 0.5? C./min, and then keep the temperature for 24 hours to dry and remove the n-nonane, so as to obtain a SiBCN pre-solid foam; [0084] S5.Cracking process: Increase a temperature of the SiBCN pre-solid foam from room temperature to 900? Cat a heating rate of 0.5? C./min under inert environment of argon, and then keep the temperature for 8 hours to obtain the SiBCN foam material.

[0085] The SiBCN foam material performance test are as follows: The density test is carried out in accordance with GB/T 17911-2006 (Refractory products-method of test for ceramic fibre products); the room temperature compressive strength test is carried out according to GB/T 1453-2005 (Test method for flatwise compression properties of sandwich constructions or cores); the thermal conductivity test is carried out in accordance with GB/T 10295-2008 (Thermal insulationDetermination of steady-state thermal resistance and related propertiesHeat flow meter apparatus).

[0086] The microscopic morphology of the prepared SiBCN foam material sample is shown in FIG. 5. The density of the material is 0.17 g/cm.sup.3, the compressive strength is 0.8 MPa at room temperature, and the thermal conductivity is 0.06 W/(m.Math.K) at room temperature. After the material was heat-treated in air at 1500? C. for 20 min, the weight loss rate was 1.01%, and the linear shrinkage rate was 0.67%.

Example 2

[0087] A SiHfBCN foam material, whose preparation method comprises the following steps: [0088] S1. Preparation of precursor solution: Dissolve a SiHfBCN precursor in n-tridecane to prepare a 10 wt % SiHfBCN precursor solution, add 0.5% dicumyl peroxide as catalyst by mass of the SiHfBCN precursor, and stir for 10 minutes under the condition of sealing until the mixture is uniform; [0089] S2. Impregnation process: Impregnate a polyurethane foam template with a size of 200 mm?200 mm?35 mm, an average pore diameter of 400 ?m, a density of 0.026 g/cm.sup.3, and a porosity of 94.2% in the above-mentioned precursor solution at normal pressure. a vacuum degree of impregnation is 10.sup.3 Pa, and an impregnation time is 30 minutes;. [0090] S3. Curing process: Under non-oxygen and sealing conditions, raise a temperature from room temperature to 230? C. at a heating rate of 1? C./min, and then keep the temperature for 2 hours to cure; [0091] S4. Drying process: Increase a temperature from room temperature to 230? C. at a heating rate of 1? C./min, and then keep the temperature for 8 hours to dry and remove the n-tridecane, so as to obtain a SiHfBCN pre-solid foam; [0092] S5.Cracking process: Increase a temperature of the SiHfBCN pre-solid foam from room temperature to 1200? C. at a heating rate of 1? C./min under an inert environment of argon, and then keep the temperature for 4 hours to obtain the SiHfBCN foam material.

[0093] The microscopic morphology of the prepared SiHfBCN foam material sample is not much different from that in FIG. 5. The density of the material is 0.21 g/cm.sup.3, the compressive strength is 1.1 MPa at room temperature, and the thermal conductivity is 0.067 W/(m.Math.K) at room temperature. After the material was heat-treated in air at 1600? C. for 1000 s, the weight loss rate was 1.69%, and the linear shrinkage rate was 1.36%.

Example 3

[0094] A SiBCN/C composite foam material, whose preparation method comprises the following steps: [0095] S1. Preparation of organic carbon-modified polyurethane foam template: Mix furfuryl alcohol and formic acid to form an organic carbon source solution with a formic acid concentration of 50 g/L and stir evenly; Immerse a polyurethane foam template with a size of 200 mm?200 mm?35 mm, an average pore diameter of 400 ?m, a density of 0.026 g/cm.sup.3 and a porosity of 94.2% in the above organic carbon source solution at atmospheric pressure (normal pressure), and an immersing time was 60 min; Then, under an inert gas environment of argon, raise a temperature from room temperature to 100? C. at a heating rate of 1? C./min, and then keep the temperature for 1 h to cross-link and solidify the organic carbon source, so as to obtain an organic carbon-modified polyurethane foam; [0096] S2. Preparation of precursor solution: Dissolve a SiBCN precursor in n-octane to prepare a 10 wt % SiBCN precursor solution, add 0.5% dicumyl peroxide as catalyst by mass of the SiBCN precursor, and stir for 10 minutes under the condition of sealing until the mixture is uniform; [0097] S3. Impregnation process: Impregnate the organic carbon-modified polyurethane foam in the SiBCN precursor solution for 50 min with the vacuum degree of 10 Pa; [0098] S4. Curing process: under non-oxygen and sealing conditions, raise a temperature from room temperature to 120? C. at a heating rate of 5? C./min, and then keep the temperature for 8 hours to cure; [0099] S5. Drying process: Under an inert environment of argon, raise a temperature from room temperature to 120? C. at a heating rate of 0.2? C./min, and keep the temperature for 24 hours, then dried, and remove the solvent n-octane to obtain a SiBCN/C pre-solid foam; [0100] S6.Cracking process: Raise a temperature of the SiBCN/C pre-solid foam from room temperature to 1500? C. at a heating rate of 0.5? C./min under an inert environment of argon, and then keep the temperature for 2 hours to obtain the SiBCN/Ccomposite foam material.

[0101] The microscopic morphology of the prepared SiBCN/Ccomposite foam material sample is not much different from that in FIG. 5. The density of the material is 0.23 g/cm.sup.3, the compressive strength is 1.0 MPa at room temperature, and the thermal conductivity is 0.067 W/(m.Math.K) at room temperature. After the material was heat-treated in air at 1500? C. for 20 min, the weight loss rate was 1.32%, and the linear shrinkage rate was 0.96%.

Example 4

[0102] A SiHfBCN/C composite foam material, whose preparation method comprises the following steps: [0103] S1. Preparation of organic carbon-modified polyurethane foam template: Mix furfuryl alcohol and formic acid to form an organic carbon source solution with a formic acid concentration of 50 g/L and stir evenly; Immerse a polyurethane foam template with a size of 200 mm?200 mm?35 mm, an average pore diameter of 400 ?m, a density of 0.026 g/cm.sup.3 and a porosity of 94.2% in the above organic carbon source solution at atmospheric pressure, and an immersing time was 60 min; Then, under an inert gas environment of argon, raise a temperature from room temperature to 80? C. at a heating rate of 0.5? C./min, and then keep the temperature for 2 hours to cross-link and solidify the organic carbon source, so as to obtain an organic carbon-modified polyurethane foam; [0104] S2. Preparation of precursor solution: Dissolve a SiHfBCN precursor in n-nonaneto prepare a 10 wt % SiHfBCN precursor solution, add 0.5% dicumyl peroxide as catalyst by mass of the SiHfBCN precursor, and stir for 10 minutes under the condition of sealing until the mixture is uniform; [0105] S3. Impregnation process: Under normal pressure conditions, impregnate the organic carbon-modified polyurethane foam in the SiHfBCN precursor solution for 20 min; [0106] S4. Curing process: Under non-oxygen and sealing conditions, raise a temperature from room temperature to 120? C. at a heating rate of 5? C./min, and then keep the temperature for 4 hours to cure; [0107] S5. Drying process: In an inert environment of argon, raise a temperature from room temperature to 120? C. at a heating rate of 0.2? C./min, and keep the temperature for 24 hours, then dried, and remove the solvent n-nonane to obtain a SiHfBCN/C pre-solid foam.

[0108] S6.Cracking process: Increase a temperature of the SiHfBCN/C pre-solid foam from room temperature to 1500? C. at a heating rate of 3? C./min under an inert environment of argon, and then keep the temperature for 2 hours to obtain the SiHfBCN/C composite foam material.

[0109] The microscopic morphology of the prepared SiHfBCN/C composite foam material sample is not much different from that in FIG. 5. The density of the material is 0.26 g/cm.sup.3, the compressive strength is 1.5 MPa at room temperature, and the thermal conductivity is 0.074 W/(m.Math.K) at room temperature. After the material was heat-treated in air at 1600? C. for 1000 s, the weight loss rate was 2.08%, and the linear shrinkage rate was 1.63%.

Example 5

[0110] Example 5 is the same as Example 1, except that the preparation of the precursor solution in S1 is different.

[0111] S1.Preparation of the precursor solution in Example 5: Dissolve a SiBCN precursor in n-nonane to prepare a 20 wt % SiBCN precursor solution, add 2.5% dicumyl peroxide as catalyst by mass of the SiBCN precursor, and stir for 20 minutes under the condition of sealing until the mixture is uniform.

[0112] The microscopic morphology of the prepared SiBCN foam material sample is shown in FIG. 6. The density of the material is 0.32 g/cm.sup.3, the compressive strength is 3.83 MPa at room temperature, and the thermal conductivity is 0.08 W/(m.Math.K) at room temperature. After the material was heat-treated in air at 1500? C. for 20 min, the weight loss rate was 0.95%, and the linear shrinkage rate was 0.68%.

Example 6

[0113] Example 6 is the same as Example 1, except that the preparation of the precursor solution in S1 is different.

[0114] S1.The preparation of the precursor solution in Example 6: Dissolve a SiBCN precursor in n-nonaneto prepare a 30 wt % SiBCN precursor solution, add 5% dicumyl peroxide as catalyst by mass of the SiBCN precursor, and stir for 30 minutes under the condition of sealing until the mixture is uniform.

[0115] The microscopic morphology of the prepared SiBCN foam material sample is shown in FIG. 7. The density of the material is 0.6 g/cm.sup.3, the compressive strength is 7.2 MPa at room temperature, and the thermal conductivity is 0.18 W/(m.Math.K) at room temperature. After the material was heat-treated in air at 1500? C. for 20 min, the weight loss rate was 0.84%, and the linear shrinkage rate was 0.59%.

Example 7

[0116] Example 7 is the same as Example 2, except that the preparation of the precursor solution in S1 is different.

[0117] S1. The preparation of the precursor solution in Example 7: Dissolve a SiHfBCN precursor in n-tridecane to prepare a 20 wt % SiHfBCN precursor solution, then add 2.5% dicumyl peroxide as catalyst by mass of the SiHfBCN precursor, and stir for 20 minutes under the condition of sealing until the mixture is uniform.

[0118] The microscopic morphology of the prepared SiHfBCN foam material sample is not much different from that in FIG. 6. The density of the material is 0.36 g/cm.sup.3, the compressive strength is 4.09 MPa at room temperature, and the thermal conductivity is 0.1 W/(m.Math.K) at room temperature. After the material was heat-treated in air at 1600? C. for 1000 s, the weight loss rate was 1.53%, and the linear shrinkage rate was 1.19%.

Example 8

[0119] Example 8 is the same as Example 2, except that the preparation of the precursor solution in S1 is different.

[0120] S1. The preparation of the precursor solution in Example 8: Dissolve a SiHfBCN precursor in n-tridecane to prepare a 30 wt % SiHfBCN precursor solution, then add 5% dicumyl peroxide as catalyst by mass of the SiHfBCN precursor, and stir for 30 minutes under the condition of sealing until the mixture is uniform.

[0121] The microscopic morphology of the prepared SiHfBCN foam material sample is not much different from that in FIG. 7. The density of the material is 0.78 g/cm.sup.3, the compressive strength is 7.6 MPa at room temperature, and the thermal conductivity is 0.22 W/(m.Math.K) at room temperature. After the material was heat-treated in air at 1600? C. for 1000 s, the weight loss rate was 1.07%, and the linear shrinkage rate was 0.85%.

Example 9

[0122] Example 9 is the same as Example 3, except that the preparation of the precursor solution in S2 is different. [0123] S2. The preparation of the precursor solution in Example 9: Dissolve a SiBCN precursor in n-octane to prepare a 20 wt % SiBCN precursor solution, add 2.5% dicumyl peroxide as catalyst by mass of the SiBCN precursor, and stir for 20 minutes under the condition of sealing until the mixture is uniform.

[0124] The microscopic morphology of the prepared SiBCN/C composite foam material sample is not much different from that in FIG. 6. The density of the material is 0.37 g/cm.sup.3, the compressive strength is 3.91 MPa at room temperature, and the thermal conductivity is 0.09 W/(m.Math.K) at room temperature. After the material was heat-treated in air at 1500? C. for 20 min, the weight loss rate was 1.21%, and the linear shrinkage rate was 0.92%.

Example 10

[0125] Example 10 is the same as Example 3, except that the preparation of the precursor solution in S2 is different. [0126] S2. The preparation of the precursor solution in Example 10: Dissolve a SiBCN precursor in n-octane to prepare a 30 wt % SiBCN precursor solution, add 5% dicumyl peroxide as catalyst by mass of the SiBCN precursor, and stir for 30 minutes under the condition of sealing until the mixture is uniform.

[0127] The microscopic morphology of the prepared SiBCN/C composite foam material sample is not much different from that in FIG. 7. The density of the material is 0.68 g/cm.sup.3, the compressive strength is 7.4 MPa at room temperature, and the thermal conductivity is 0.19 W/(m.Math.K) at room temperature. After the material was heat-treated in air at 1500? C. for 20 min, the weight loss rate was 1.08%, and the linear shrinkage rate was 0.77%.

Example 11

[0128] Example 11 is the same as Example 4, except that the preparation of the precursor solution in S2 is different. [0129] S2. The preparation of the precursor solution in Example 11: Dissolve a SiHfBCN precursor in n-nonane to prepare a 20 wt % SiHfBCN precursor solution, add 2.5% dicumyl peroxide as catalyst by mass of the SiHfBCN precursor, and stir for 20 minutes under the condition of sealing until the mixture is uniform.

[0130] The microscopic morphology of the prepared SiHfBCN composite foam material sample is not much different from that in FIG. 6. The density of the material is 0.41 g/cm.sup.3, the compressive strength is 4.15 MPa at room temperature, and the thermal conductivity is 0.12 W/(m.Math.K) at room temperature. After the material was heat-treated in air at 1600? C. for 1000 s, the weight loss rate was 1.87%, and the linear shrinkage rate was 1.46%.

Example 12

[0131] Example 12 is the same as Example 4, except that the preparation of the precursor solution in S2 is different. [0132] S2. The preparation of the precursor solution in Example 12: Dissolve a SiHfBCN precursor in n-nonane to prepare a 30 wt % SiHfBCN precursor solution, add 5% dicumyl peroxide as catalyst by mass of the SiHfBCN precursor, and stir for 30 minutes under the condition of sealing until the mixture is uniform.

[0133] The microscopic morphology of the prepared SiHfBCN composite foam material sample is not much different from that in FIG. 7. The density of the material is 0.82 g/cm.sup.3, the compressive strength is 8.63 MPa at room temperature, and the thermal conductivity is 0.25 W/(m.Math.K) at room temperature. After the material was heat-treated in air at 1600? C. for 1000 s, the weight loss rate was 1.59%, and the linear shrinkage rate was 1.37%.

[0134] The above descriptions are only the preferred embodiments of the present application and are not intended to limit the present application. Any modification, equivalent replacement, improvement and the like made within the spirit and principles of the present application shall fall within the scope of protection of the pending claims of the present application.