Boron nitride composite fiber material and preparation method thereof

Abstract

The invention discloses a boron nitride composite fiber material and a preparation method thereof. The boron nitride composite fiber material comprises a plurality of boron nitride fiber layers, a heat insulation layer is arranged between every two adjacent fiber layers; the boron nitride fiber layer comprises boron nitride fibers which are arranged in a staggered manner; interlaced silicon nitride short fibers are filled among grids formed by the interlaced boron nitride fibers; silicon oxide is attached to the surface of the boron nitride fiber, and silicon oxide is attached to the surface of the silicon nitride short fiber; a boron nitride layer attached to the outermost surface of the boron nitride fiber is arranged on the joint surface of the boron nitride fiber layer and the heat insulation layer; the heat insulation layer comprises silicon dioxide aerogel. The boron nitride composite fiber material is 0.1-0.5 g / cm < 3 >, still has good heat insulation performance at the high temperature of 1500 DEG C or above, and does not deform.

Description

Technical Field

[0001] The present invention relates to the field of boron nitride composite materials, and particularly to the field of a boron nitride composite fiber material and a preparation method thereof. Background Art

[0002] For the large-area thermal protection of the fuselage of new aircraft, the heat preservation of civil high-temperature kilns, microwave smelting equipment and other fields, there is a wide need for lightweight, efficient, rigid, high-temperature resistant and heat-insulating materials;

[0003] Traditional lightweight, efficient, rigid, high-temperature resistant and heat-insulating materials generally use quartz fiber and alumina fiber with low thermal conductivity, corrosion resistance, high temperature resistance and stable performance as the main raw materials, and are porous rigid heat-insulating materials obtained by wet forming and high-temperature sintering. This material has excellent properties such as lightweight, low thermal conductivity, high strength and high temperature resistance; however, with the development of technologies such as hypersonic speed and long endurance of modern aircraft, the total amount of aerodynamic heating on the surface of the aircraft during flight is increasing, and the existing material system is difficult to meet the service requirements of high temperature resistance and ablation resistance in this service environment.

[0004] Therefore, how to prepare a lightweight, efficient, rigid, high-temperature resistant and heat-insulating material, so that the lightweight material still has good heat-insulating performance above 1500 °C and does not deform has become an urgent problem to be solved in this field. Summary of the Invention

[0005] The purpose of the present invention is to provide a boron nitride composite fiber material and a preparation method thereof, so that the boron nitride composite fiber material has a density of 0.1-0.5 g / cm 3 , and still has good heat-insulating performance above 1500 °C and does not deform.

[0006] According to one aspect of the present invention, a boron nitride composite fiber material is provided, which includes a plurality of layers of boron nitride fiber layers; an insulating layer is provided between adjacent two fiber layers;

[0007] The boron nitride fiber layer includes boron nitride fibers arranged in an interleaved manner; silicon nitride short fibers arranged in an interleaved manner are filled in the grids formed by the interleaved arrangement of the boron nitride fibers;

[0008] Silicon oxide is attached to the surface of the boron nitride fibers, and silicon oxide is attached to the surface of the silicon nitride short fibers; a boron nitride layer attached to the outermost surface of the boron nitride fibers is provided on the interface between the boron nitride fiber layer and the insulating layer;

[0009] The insulating layer includes silica aerogel. Preferably, the surface of the intersection points of the boron nitride fibers is coated with silicon nitride, and the intersection points of the boron nitride short fibers are attached with silicon nitride.

[0010] The beneficial effects of the present invention compared with the prior art are as follows. Through several layers of boron nitride fiber layers, and an insulating layer is provided between adjacent two fiber layers, the boron nitride fiber layer is on the outer surface, and its maximum temperature resistance in an oxygen-free environment can reach above 2000 °C. Therefore, it is beneficial to achieve a temperature resistance of about 2000 °C in an oxygen-free environment. By providing an insulating layer in the middle and including silica aerogel, good heat insulation performance is achieved. And through the insulating layer in the middle, the problem that the heat conduction coefficient decreases due to the damage of the aerogel structure at a high external temperature above 1500 °C is effectively avoided. Thus, it is beneficial to achieve that the finished material still has good heat insulation performance when the external high temperature environment is greater than 1500 °C.

[0011] Through the boron nitride fiber layer including staggered boron nitride fibers, and the grid formed by the staggered boron nitride fibers is filled with staggered silicon nitride short fibers, the external boron nitride fiber layer has high strength and toughness. At the same time, through the interface between the boron nitride fiber layer and the insulating layer, a boron nitride layer attached to the outermost layer of boron nitride is provided, realizing that the boron nitride fiber layer has controllable pores and a pore gradient change. The pores of the boron nitride fiber layer gradually decrease from the outside to the inside, the porosity is high at the position far from the insulating layer, and gradually decreases when approaching the insulating layer. Thus, the boron nitride fiber layer itself has high heat insulation performance and effectively blocks the entry of external gas into the insulating layer, further avoiding the structural change of the insulating layer directly affected by external high-temperature gas.

[0012] Most importantly, by attaching silica to the surface of the boron nitride fiber and attaching silica to the surface of the silicon nitride short fiber, the problems that the boron nitride fiber and the silicon nitride short fiber are oxidized in a high-temperature aerobic environment are solved, and it is beneficial to achieve controllable and realizable pore rate gradient change of the boron nitride fiber layer. Because silica, in an aerobic environment at a high temperature above 1500 °C, although its spatial structure does not change, it will not be oxidized and decomposed. Therefore, it will not essentially change the structure of silica attached to the surface of the boron nitride fiber and the silicon nitride short fiber in an aerobic environment at a high temperature above 1500 °C. Thus, the boron nitride fiber and the silicon nitride short fiber effectively isolate air and prevent them from being oxidized.

[0013] By attaching silica to the surface of the boron nitride fiber and attaching silica to the surface of the silicon nitride short fiber, the connection strength between the fibers is increased, thus realizing the stability of the fiber network structure inside the finished material, and improving the compressive strength of the finished material.

[0014] Further, the boron nitride composite fiber material is 0.1 - 0.5 g / cm 3, with a compressive strength of 1.2 - 5 MPa, a temperature resistance of ≥ 2000 °C, and a thermal conductivity of 0.036 - 0.048 W / (m·K) at 1500 °C; preferably, the thermal conductivity is 0.036 - 0.04 W / (m·K) at 1500 °C.

[0015] Furthermore, the boron nitride composite fiber material includes two layers of boron nitride fiber layers; the length of the boron nitride fibers is 5 - 10 mm; the length of the silicon nitride fibers is 0.2 - 3 mm.

[0016] According to one aspect of the present invention, there is provided a method for preparing a boron nitride composite fiber material, which is characterized by including the following steps

[0017] Modify the boron nitride fibers to obtain modified boron nitride fibers;

[0018] Modify the short silicon nitride fibers to obtain modified short silicon nitride fibers;

[0019] Prepare a primary boron nitride fiber layer preform with a network structure through the modified boron nitride fibers;

[0020] Add the modified short silicon nitride fibers into the network pores of the primary boron nitride fiber layer preform to obtain a secondary boron nitride fiber layer preform;

[0021] Immerse one side of the secondary boron nitride fiber layer preform in a borazane precursor solution, and then obtain a tertiary boron nitride fiber layer preform through vacuum treatment and drying;

[0022] Pyrolyze the borazane precursor in the tertiary boron nitride fiber layer preform to obtain a quaternary boron nitride fiber layer preform;

[0023] Place a number of quaternary boron nitride fiber layer preforms in parallel, and leave a accommodation space between adjacent two layers of quaternary boron nitride fiber layers;

[0024] Inject a silica sol precursor into the accommodation space, and at the same time, a negative pressure environment is created on the side of the quaternary boron nitride fiber layer away from the accommodation space, and then the silica sol precursor is subjected to sol-gelation to obtain a boron nitride composite fiber material precursor;

[0025] Perform replacement and critical drying on the boron nitride composite fiber material precursor to obtain the boron nitride composite fiber material.

[0026] The beneficial effect of the present invention compared with the prior art is that by preparing a primary boron nitride fiber layer preform with a network structure through the modified boron nitride fibers, it is realized that the boron nitride fiber layer includes the boron nitride fibers with silicon oxide attached to the surface;

[0027] By adding the modified silicon nitride short fibers into the reticular pores of the primary boron nitride fiber layer preform, it is achieved that the boron nitride fiber layer includes the silicon nitride short fibers with silica attached to the surface; and the silicon nitride short fibers are filled between the grids formed by the staggered arrangement of the boron nitride fibers;

[0028] By pyrolyzing the borazane precursor in the tertiary boron nitride fiber layer preform, a quaternary boron nitride fiber layer preform is obtained; and a plurality of quaternary boron nitride fiber layer preforms are placed in parallel, and a accommodating space is left between adjacent two layers of quaternary boron nitride fiber layers, and a silica sol precursor is injected into the accommodating space; it is achieved that there is a heat insulation layer including silica aerogel between adjacent two fiber layers, and a boron nitride layer attached to the outermost surface of the boron nitride fibers is provided on the interface between the boron nitride fiber layer and the heat insulation layer;

[0029] At the same time, by first modifying the boron nitride fibers and silicon nitride short fibers and then manufacturing the boron nitride fiber layer preform, the problem of filling redundant silica inside the boron nitride fiber layer preform is avoided, thereby avoiding the uncontrollability of the pores of the boron nitride fiber layer and the problems of reduction of the thermal coefficient and reduction of the high-temperature resistance of the surface layer;

[0030] At the same time, boron nitride has excellent wave-transmitting performance and can be well applied to the field of radomes.

[0031] Further, the preparation process of the modified boron nitride fibers is as follows: prepare a modified solution; impregnate the boron nitride fibers with the modified solution, and then dry the boron nitride fibers to obtain the modified boron nitride fibers;

[0032] The modified solution includes silica sol, organic binder, and water in a mass ratio of (30 - 60):(10 - 20):(80 - 100);

[0033] The preparation process of the modified silicon nitride short fibers is as follows: prepare a modified solution; impregnate the silicon nitride short fibers with the modified solution, and then dry the silicon nitride short fibers to obtain the modified silicon nitride short fibers;

[0034] The organic binder includes one or more of starch, PEO, cellulose, and polyacrylic acid;

[0035] The length of the boron nitride fibers is 5 - 10 mm; the length of the silicon nitride fibers is 0.2 - 3 mm;

[0036] The drying temperature is 80 - 150 °C, and the drying time is 0.5 - 2.5 h.

[0037] The beneficial effect of the previous step is to achieve the modification of the boron nitride fibers, with silica attached to the surface of the modified boron nitride fibers, to achieve the modification of the silicon nitride short fibers, and with silica attached to the surface of the modified silicon nitride short fibers;

[0038] By attaching silicon oxide to the fiber surface, oxidation resistance is achieved by isolating air on the surfaces of boron nitride fibers and chopped silicon nitride fibers, and meanwhile, it is beneficial for the borazane precursor attached to the surface of the subsequent intersection points to react with silicon oxide during the pyrolysis process to generate silicon nitride and attach it to the surface of the intersection points;

[0039] The length of the boron nitride fiber is 5 - 10 mm; the length of the silicon nitride fiber is 0.2 - 3 mm. The silicon nitride fibers are dispersed among the pores of the boron nitride fibers, enabling the pores of the boron nitride fiber layer to be controllable and vary in a gradient manner. Meanwhile, on the premise of meeting high temperature resistance, the pores gradually decrease from the outside to the inside; at the same time, silicon nitride is beneficial for increasing the bonding strength with the thermal insulation layer.

[0040] Furthermore, the modified boron nitride fibers are dispersed into a solvent to obtain a primary boron nitride fiber layer slurry; the primary boron nitride fiber layer slurry is filtered through a first filter screen to obtain a primary boron nitride fiber layer preform; the solid content of the primary boron nitride fiber layer slurry is 30 - 40%;

[0041] The preparation process of the secondary boron nitride fiber layer preform includes the following steps: the modified short silicon nitride fibers are dispersed into a solvent to obtain a secondary boron nitride fiber layer slurry; the secondary boron nitride fiber layer slurry is added to the first filter screen containing the primary boron nitride fiber layer preform and filtered to obtain the secondary boron nitride fiber layer preform;

[0042] The solid content of the secondary boron nitride fiber layer slurry is 40 - 60%.

[0043] The beneficial effect of the previous step is to achieve a gradient change and controllability of the pores inside the boron nitride fiber layer preform.

[0044] Furthermore, the preparation process of the tertiary boron nitride fiber layer preform includes: preparing a borazane precursor solution, impregnating one side of the secondary boron nitride fiber layer preform with the borazane precursor solution through vacuum, and then drying it at a temperature of 75 - 85°C under a negative pressure environment to obtain the tertiary boron nitride fiber layer preform;

[0045] The mass fraction of the borazane precursor solution is 20 - 50%; the borazane precursor solution includes monomeric cycloborazane or polymeric polyborazane.

[0046] The beneficial effect of the previous step is to achieve that the borazane precursor is provided on one side and in some pores of the tertiary boron nitride fiber layer preform.

[0047] Further, the preparation process of the four - level boron nitride fiber layer preform is as follows: heat the three - level boron nitride fiber layer preform in an atmosphere of ammonia and nitrogen. Heat from room temperature to 280 - 320 °C at a heating rate of 0.3 - 0.6 °C / min; then heat from 280 - 320 °C to 580 - 620 °C at a heating rate of 0.5 - 2 °C / min; then heat from 580 - 620 °C to 990 - 1000 °C at a heating rate of 5 - 10 °C / min, and keep the temperature at 990 - 1000 °C for 1 - 3 h. The total flow rate of ammonia and nitrogen is 0.15 - 0.25 m 3 / h;

[0048] Then heat in a nitrogen atmosphere. Heat from 990 - 1000 °C to 1550 - 1650 °C at a heating rate of 5.5 - 6.5 °C / min, and keep the temperature at 1550 - 1650 °C for 1.8 - 2.2 h. The nitrogen flow rate is 0.15 - 0.25 m 3 / h;

[0049] The beneficial effect of the previous step is that boron nitride formed by the pyrolysis of borazane precursor is provided on one side of the three - level boron nitride fiber layer preform and in some pores, and at the same time, the sintering strength between fibers is increased. Passing a certain amount of nitrogen as a carrier gas is beneficial for the discharge of pyrolysis by - products to obtain boron nitride, and continuously passing nitrogen subsequently can prevent the decomposition of boron nitride during high - temperature ceramization.

[0050] Further, the preparation process of the boron nitride composite fiber material precursor includes placing the two four - level boron nitride fiber layer preforms in mold one and mold two respectively. Mold one and mold two are arranged opposite to each other, forming a sealed accommodation cavity between the two four - level boron nitride fiber layer preforms. Inject the silica sol precursor into the accommodation cavity through the grouting holes arranged on the side of mold one and / or mold two, and then place mold one and mold two in a negative - pressure environment;

[0051] The sides of the two four - level boron nitride fiber layer preforms impregnated with the borazane precursor solution are arranged opposite to each other;

[0052] Then subject the silica sol precursor to sol - gelation to obtain the boron nitride composite fiber material precursor.

[0053] The beneficial effect of the previous step is that a silica aerogel thermal insulation layer is connected between adjacent boron nitride fiber layers, and at the same time, a boron nitride layer attached to the outermost surface of the boron nitride fiber is provided on the interface between the boron nitride fiber layer and the thermal insulation layer.

[0054] Further, disperse the modified silicon nitride short fibers into a solvent to obtain a thermal insulation layer skeleton slurry. The solid content of the thermal insulation layer skeleton slurry is 15 - 20%; the solvent is water;

[0055] Before cracking the borazane precursor of the three - layer boron nitride fiber layer preform before ammonia, place the two three - layer boron nitride fiber layer preforms in mold one and mold two respectively. Set mold one and mold two opposite to each other to form a sealed accommodation cavity between the two three - layer boron nitride fiber layer preforms. Then, inject the heat - insulating layer skeleton slurry between the two three - layer boron nitride fiber layers through the grouting holes arranged on the side of mold one and / or mold two. Then, freeze - treat mold one, mold two and the intermediate materials.

[0056] After freezing, perform the first - stage heat treatment in a nitrogen atmosphere. Then, perform the second - stage heat treatment in an ammonia and nitrogen atmosphere to obtain two four - layer boron nitride fiber layers with a three - dimensional reticulated heat - insulating layer skeleton sandwiched in the middle. The three - dimensional reticulated heat - insulating layer skeleton includes three - dimensional silicon nitride fibers. The thickness of the three - dimensional reticulated heat - insulating layer skeleton is 0.5 - 1.5 cm.

[0057] In a negative - pressure environment, then inject the silica sol precursor and the boron nitride composite fiber material precursor into the three - dimensional reticulated heat - insulating layer skeleton sandwiched between the two four - layer boron nitride fiber layers through the grouting holes arranged on the side of mold one and / or mold two.

[0058] The first - stage heat - treatment process includes, in a negative - pressure environment, heating from room temperature to 80 - 120 °C at a heating rate of 0.3 - 0.6 °C / min.

[0059] The second - stage heat - treatment process includes, in an ammonia and nitrogen atmosphere, heating from 80 - 120 °C to 280 - 320 °C at a heating rate of 0.3 - 0.6 °C / min; heating from 280 - 320 °C to 580 - 620 °C at a heating rate of 0.5 - 2 °C / min; heating from 580 - 620 °C to 990 - 1000 °C at a heating rate of 5 - 10 °C / min, and holding at 990 - 1000 °C for 1 - 3 h. The total flow rate of ammonia and nitrogen is 0.15 - 0.25 m 3 / h;

[0060] Then, heat in a nitrogen atmosphere, heating from 990 - 1000 °C to 1550 - 1650 °C at a heating rate of 5.5 - 6.5 °C / min, and holding at 1550 - 1650 °C for 1.8 - 2.2 h. The nitrogen flow rate is 0.15 - 0.25 m 3 / h.

[0061] The beneficial effect of adopting the previous step is that the heat insulation layer skeleton slurry is injected between the two layers of three-stage boron nitride fiber layers through the grouting holes arranged on the sides of the first mold and / or the second mold, and then the first mold, the second mold and the intermediate materials are frozen to solidify the heat insulation layer skeleton slurry of the two layers of three-stage boron nitride fiber layers, and then slowly depressurized to heat and volatilize the solvent and sinter and form, so that the heat insulation layer between adjacent boron nitride fiber layers includes silicon nitride short fibers with a large-pore network structure; by injecting a silica sol precursor, silica aerogel is uniformly filled between the silicon nitride short fibers, and the silica aerogel inside the heat insulation layer has a high bonding strength with the silicon nitride short fibers, and there are no obvious gaps and defects; at the same time, the bonding strength between the silicon nitride short fibers of the heat insulation layer and the fibers inside the boron nitride fiber layer is high, which significantly increases the strength of the boron nitride fiber layer and the heat insulation layer, and the overall material has a small density and is light in weight. Detailed implementation mode

[0062] In order to better understand the technical solution of the present invention, the present invention will be further described below in conjunction with specific embodiments.

[0063] Example 1:

[0064] One aspect of this embodiment provides a boron nitride composite fiber material, which includes two layers of boron nitride fiber layers; a heat insulation layer is provided between adjacent two layers of fiber layers;

[0065] The boron nitride fiber layer includes boron nitride fibers arranged in an interleaved manner; the grid formed by the interleaved arrangement of the boron nitride fibers is filled with interleaved silicon nitride short fibers; the length of the boron nitride fibers is 7 mm; the length of the silicon nitride fibers is 1.6 mm;

[0066] Silica is attached to the surface of the boron nitride fibers, and silica is attached to the surface of the silicon nitride short fibers; a boron nitride layer attached to the outermost surface of the boron nitride fibers is provided on the interface between the boron nitride fiber layer and the heat insulation layer; the heat insulation layer includes silica aerogel;

[0067] The boron nitride composite fiber material is 0.3 g / cm 3 , the compressive strength is 3 MPa, the temperature resistance is ≥2000 °C, the thermal conductivity at 1500 °C is 0.037 W / (m·K); the thermal conductivity at 1500 °C is 0.039 W / (m·K).

[0068] Another aspect of this embodiment provides a method for preparing a boron nitride composite fiber material, which includes the following steps: modifying the boron nitride fibers to obtain modified boron nitride fibers;

[0069] The preparation process of the modified boron nitride fiber is as follows: prepare a modified solution; impregnate the boron nitride fiber with the modified solution, and then dry the boron nitride fiber to obtain the modified boron nitride fiber;

[0070] The modified solution includes silica sol, organic binder, and water in a mass ratio of 45:15:90; the length of the boron nitride fiber is 7 mm;

[0071] Modify the silicon nitride short fiber to obtain a modified silicon nitride short fiber; the preparation process of the modified silicon nitride short fiber is as follows: prepare a modified solution; impregnate the silicon nitride short fiber with the modified solution, and then dry the silicon nitride short fiber to obtain the modified silicon nitride short fiber; the length of the silicon nitride fiber is 1.6 mm;

[0072] The organic binder includes polyacrylic acid; the drying temperature is 120 °C and the drying time is 1.5 h.

[0073] Prepare a primary boron nitride fiber layer preform with a network structure from the modified boron nitride fiber; disperse the modified boron nitride fiber into a solvent to obtain a primary boron nitride fiber layer slurry; the primary boron nitride fiber layer slurry is filtered through a first filter screen to obtain a primary boron nitride fiber layer preform; the solid content of the primary boron nitride fiber layer slurry is 35%;

[0074] Add the modified silicon nitride short fiber into the network pores of the primary boron nitride fiber layer preform to obtain a secondary boron nitride fiber layer preform; the preparation process of the secondary boron nitride fiber layer preform includes the following steps: disperse the modified silicon nitride short fiber into a solvent to obtain a secondary boron nitride fiber layer slurry; add the secondary boron nitride fiber layer slurry into the first filter screen containing the primary boron nitride fiber layer preform, and after filtration, obtain the secondary boron nitride fiber layer preform;

[0075] The solid content of the secondary boron nitride fiber layer slurry is 50%.

[0076] Impregnate one side of the secondary boron nitride fiber layer preform with a borazane precursor solution, and then obtain a tertiary boron nitride fiber layer preform through vacuum treatment and drying; the preparation process of the tertiary boron nitride fiber layer preform includes: prepare a borazane precursor solution, impregnate one side of the secondary boron nitride fiber layer preform with the borazane precursor solution through vacuum, and then dry it at a temperature of 80 °C under a negative pressure environment to obtain the tertiary boron nitride fiber layer preform;

[0077] The mass fraction of the borazane precursor solution is 25%; the borazane precursor solution includes monomeric borazine.

[0078] Pyrolyze the borazane precursor in the three - stage boron nitride fiber layer preform to obtain a four - stage boron nitride fiber layer preform; heat the three - stage boron nitride fiber layer preform in an ammonia and nitrogen atmosphere, raise the temperature from room temperature to 290 °C at a heating rate of 0.55 °C / min; raise the temperature from 290 °C to 590 °C at a heating rate of 0.19 °C / min; raise the temperature from 590 °C to 991 °C at a heating rate of 9.5 °C / min, and hold at 991 °C for 1.2 h; the total flow rate of ammonia and nitrogen is 0.16 m 3 / h;

[0079] Then heat in a nitrogen atmosphere, raise the temperature from 990 - 1000 °C to 1550 - 1650 °C at a heating rate of 5.5 - 6.5 °C / min, and hold at 1550 - 1650 °C for 1.8 - 2.2 h; the nitrogen flow rate is 0.16 m 3 / h;

[0080] Place two four - stage boron nitride fiber layer preforms in parallel, and leave a accommodation space between adjacent two - layer four - stage boron nitride fiber layers; the preparation process of the boron nitride composite fiber material precursor includes placing the two four - stage boron nitride fiber layer preforms in mold one and mold two respectively, with mold one and mold two arranged oppositely, forming a sealed accommodation cavity between the two four - stage boron nitride fiber layer preforms, injecting a silica sol precursor into the accommodation cavity through the grouting holes arranged on the side of mold one and / or mold two, and then placing mold one and mold two in a negative pressure environment;

[0081] The sides of the two four - stage boron nitride fiber layer preforms impregnated with the borazane precursor solution are arranged oppositely;

[0082] Then carry out sol - gelation on the silica sol precursor to obtain the boron nitride composite fiber material precursor.

[0083] Inject the silica sol precursor into the accommodation space, and at the same time, keep the side of the four - stage boron nitride fiber layer away from the accommodation space in a negative pressure environment, then carry out sol - gelation on the silica sol precursor to obtain the boron nitride composite fiber material precursor; carry out replacement and critical drying on the boron nitride composite fiber material precursor to obtain the boron nitride composite fiber material.

[0084] Example 2:

[0085] The same content as in Example 1 will not be repeated here; the different solutions in this example compared with Example 1 are as follows:

[0086] One aspect of this embodiment provides a boron nitride composite fiber material. The heat insulation layer includes silica aerogel and a three-dimensional network heat insulation layer framework. The three-dimensional network heat insulation layer framework includes three-dimensional silicon nitride fibers. The thickness of the three-dimensional network heat insulation layer framework is 1 cm. The silica aerogel is uniformly dispersed in the three-dimensional network heat insulation layer framework. The surfaces of the intersection points of the boron nitride fibers are coated with silicon nitride, and silicon nitride adheres to the intersection points of the boron nitride short fibers. The boron nitride composite fiber material includes two layers of boron nitride fiber layers. The length of the boron nitride fibers is 9 mm. The length of the silicon nitride fibers is 2.5 mm.

[0087] The boron nitride composite fiber material is 0.15 g / cm 3 , with a compressive strength of 2.8 MPa, a temperature resistance of ≥2000 °C, a thermal conductivity of 0.042 W / (m·K) at 1500 °C; and a thermal conductivity of 0.045 W / (m·K) at 1500 °C.

[0088] Another aspect of this embodiment provides a method for preparing a boron nitride composite fiber material, which further includes preparing a heat insulation layer framework slurry, specifically including the following steps: dispersing the modified silicon nitride short fibers into a solvent to obtain a heat insulation layer framework slurry. The solid content of the heat insulation layer framework slurry is 16%. The solvent is water.

[0089] Before pyrolyzing the borazane precursor of the three-stage boron nitride fiber layer preform in ammonia, place the two three-stage boron nitride fiber layer preforms in mold one and mold two respectively. Set mold one and mold two opposite to each other to form a sealed accommodation cavity between the two three-stage boron nitride fiber layer preforms. Then, inject the heat insulation layer framework slurry between the two three-stage boron nitride fiber layers through the grouting holes provided on the sides of mold one and / or mold two. Then, freeze the mold one, mold two, and the intermediate material.

[0090] After freezing, perform a first-stage heat treatment in a nitrogen atmosphere. Then, perform a second-stage heat treatment in an ammonia and nitrogen atmosphere to obtain two four-stage boron nitride fiber layers with a three-dimensional network heat insulation layer framework sandwiched in the middle. The three-dimensional network heat insulation layer framework includes three-dimensional silicon nitride fibers. The thickness of the three-dimensional network heat insulation layer framework is 1 cm.

[0091] In a negative pressure environment, then inject a silica sol precursor, a boron nitride composite fiber material precursor, into the three-dimensional network heat insulation layer framework sandwiched between the two four-stage boron nitride fiber layers through the grouting holes provided on the sides of mold one and / or mold two.

[0092] The first-stage heat treatment process includes, in a negative pressure environment, heating from room temperature to 100 °C at a heating rate of 0.45 °C / min.

[0093] The second-stage heat treatment process includes heating from 100°C to 300°C at a heating rate of 0.45°C / min in an ammonia and nitrogen atmosphere; heating from 300°C to 600°C at a heating rate of 1.3°C / min; heating from 600°C to 995°C at a heating rate of 7.5°C / min, and holding at 995°C for 2 h; the total flow rate of ammonia and nitrogen is 0.2 m 3 / h;

[0094] Then, heating is carried out in a nitrogen atmosphere, heating from 995°C to 1600°C at a heating rate of 6°C / min, and holding at 1600°C for 2 h; the nitrogen flow rate is 0.2 m 3 / h.

[0095] The modified solution includes silica sol, organic binder, and water in a mass ratio of 35:12:85; the length of the boron nitride fiber is 9 mm;

[0096] The length of the silicon nitride fiber is 2.5 mm; the solid content of the primary boron nitride fiber layer slurry is 32%;

[0097] The organic binder includes PEO and cellulose;

[0098] The drying temperature is 140°C and the drying time is 2 h.

[0099] The solid content of the secondary boron nitride fiber layer slurry is 43%.

[0100] Prepare a borazane precursor solution, impregnate one side of the preform of the secondary boron nitride fiber layer with the borazane precursor solution by vacuum, and then dry it at a temperature of 78°C under a negative pressure environment to obtain the preform of the tertiary boron nitride fiber layer; the mass fraction of the borazane precursor solution is 35%; the borazane precursor solution includes the polymer polyborazane.

[0101] Example 3:

[0102] The content that is the same as that in Example 1 will not be elaborated here; the different solutions from Example 1 are as follows:

[0103] One aspect of this example provides a boron nitride composite fiber material, the heat insulation layer includes silica aerogel and a three-dimensional network heat insulation layer framework; the three-dimensional network heat insulation layer framework includes three-dimensional silicon nitride fibers; the thickness of the three-dimensional network heat insulation layer framework is 0.8 cm; the silica aerogel is uniformly dispersed in the three-dimensional network heat insulation layer framework; the surface of the intersection points of the boron nitride fibers is coated with silicon nitride, and the intersection points of the boron nitride short fibers are attached with silicon nitride; the boron nitride composite fiber material includes two layers of boron nitride fiber layers; the length of the boron nitride fibers is 6 mm; the length of the silicon nitride fibers is 0.5 mm;

[0104] The boron nitride composite fiber material has a density of 0.35 g / cm 3 , a compressive strength of 4.5 MPa, a temperature resistance of ≥2000 °C, a thermal conductivity of 0.038 W / (m·K) at 1500 °C; and a thermal conductivity of 0.039 W / (m·K) at 1500 °C.

[0105] Another aspect of this embodiment provides a method for preparing a boron nitride composite fiber material, which further includes preparing a heat-insulating layer skeleton slurry, specifically including the following steps: dispersing the modified silicon nitride short fibers into a solvent to obtain a heat-insulating layer skeleton slurry; the solid content of the heat-insulating layer skeleton slurry is 18%; the solvent is water;

[0106] Before cracking the borazane precursor of the three-stage boron nitride fiber layer preform before ammonia, place the two three-stage boron nitride fiber layer preforms in mold one and mold two respectively, set mold one and mold two opposite to each other to form a closed accommodation cavity between the two three-stage boron nitride fiber layer preforms; then inject the heat-insulating layer skeleton slurry between the two three-stage boron nitride fiber layers through the grouting holes provided on the side of mold one and / or mold two; then freeze-treat mold one, mold two and the intermediate materials;

[0107] After freezing, perform a first-stage heat treatment in a nitrogen atmosphere; then perform a second-stage heat treatment in an ammonia and nitrogen atmosphere; obtain two four-stage boron nitride fiber layers with a three-dimensional reticulated heat-insulating layer skeleton sandwiched in the middle; the three-dimensional reticulated heat-insulating layer skeleton includes three-dimensional silicon nitride fibers; the thickness of the three-dimensional reticulated heat-insulating layer skeleton is 0.8 cm;

[0108] In a negative pressure environment, then inject a silica sol precursor and a boron nitride composite fiber material precursor into the three-dimensional reticulated heat-insulating layer skeleton sandwiched between the two four-stage boron nitride fiber layers through the grouting holes provided on the side of mold one and / or mold two;

[0109] The first-stage heat treatment process includes, in a negative pressure environment, heating from room temperature to 85 °C at a heating rate of 0.35 °C / min;

[0110] The second-stage heat treatment process includes, in an ammonia and nitrogen atmosphere, heating from 115 °C to 310 °C at a heating rate of 0.35 °C / min; heating from 310 °C to 610 °C at a heating rate of 0.7 °C / min; heating from 610 °C to 998 °C at a heating rate of 6 °C / min, and holding at 998 °C for 1 - 3 h; the total flow rate of ammonia and nitrogen is 0.22 m 3 / h;

[0111] Then, heating is carried out in a nitrogen atmosphere, heating from 998 °C to 1630 °C, with a heating rate of 6.2 °C / min, and holding at 1630 °C for 2.1 h; the nitrogen flow rate is 0.22 m 3 / h.

[0112] The modified solution includes silica sol, organic binder, and water in a mass ratio of 55:18:95; the length of the boron nitride fiber is 6 mm;

[0113] The length of the silicon nitride fiber is 0.5 mm; the solid content of the primary boron nitride fiber layer slurry is 38%;

[0114] The organic binder includes PEO and polyacrylic acid;

[0115] The drying temperature is 85 °C and the drying time is 0.8 h.

[0116] The solid content of the secondary boron nitride fiber layer slurry is 58%.

[0117] Prepare a borazane precursor solution, impregnate one side of the preform of the secondary boron nitride fiber layer with the borazane precursor solution by vacuum, and then dry it at a temperature of 82 °C in a negative pressure environment to obtain the preform of the tertiary boron nitride fiber layer; the mass fraction of the borazane precursor solution is 46%; the borazane precursor solution includes the polymer polyborazane.

[0118] The above description is only the preferred embodiment of the present application and the explanation of the applied technical principles. Those skilled in the art should understand that the scope of the invention involved in the present application is not limited to the technical solution formed by the specific combination of the above technical features, and should also cover other technical solutions formed by any combination of the above technical features or their equivalent features without departing from the inventive concept. For example, the above features have similar functions to those disclosed in the present application (but not limited to).

Claims

1. A boron nitride composite fiber material, characterized in that, It includes several layers of boron nitride fiber layers; a heat insulation layer is provided between adjacent two fiber layers; The boron nitride fiber layer includes boron nitride fibers arranged in a staggered manner; the meshes formed by the staggered arrangement of the boron nitride fibers are filled with silicon nitride short fibers arranged in a staggered manner; Silicon oxide is attached to the surface of the boron nitride fibers, and silicon oxide is attached to the surface of the silicon nitride short fibers; On the interface where the boron nitride fiber layer is connected to the heat insulation layer, there is a boron nitride layer attached to the outermost surface of the boron nitride fibers; The heat insulation layer includes silica aerogel.

2. The boron nitride composite fiber material according to claim 1, wherein The boron nitride composite fiber material has a density of 0.1 - 0.5 g / cm 3 , a compressive strength of 1.2 - 5 MPa, a temperature resistance of ≥ 2000 °C, and a thermal conductivity of 0.036 - 0.048 W / (m·K) at 1500 °C.

3. The boron nitride composite fiber material according to claim 1, characterized in that The boron nitride composite fiber material includes two layers of boron nitride fiber layers; The length of the boron nitride fibers is 5 - 10 mm; the length of the silicon nitride fibers is 0.2 - 3 mm.

4. A method for preparing a boron nitride composite fiber material, characterized in that, It includes the following steps, Modify the boron nitride fibers to obtain modified boron nitride fibers; Modify the silicon nitride short fibers to obtain modified silicon nitride short fibers; Prepare a primary boron nitride fiber layer preform with a network structure from the modified boron nitride fibers; Add the modified silicon nitride short fibers into the network pores of the primary boron nitride fiber layer preform to obtain a secondary boron nitride fiber layer preform; Immerse one side of the secondary boron nitride fiber layer preform in a borazane precursor solution, and then obtain a tertiary boron nitride fiber layer preform through vacuum treatment and drying; Pyrolyze the borazane precursor in the tertiary boron nitride fiber layer preform to obtain a quaternary boron nitride fiber layer preform; Place several quaternary boron nitride fiber layer preforms in parallel, and leave a accommodation space between adjacent two quaternary boron nitride fiber layers; Inject a silica sol precursor into the accommodation space, and at the same time, a negative pressure environment is maintained on the side of the quaternary boron nitride fiber layer away from the accommodation space, and then the silica sol precursor is subjected to sol-gelation to obtain a boron nitride composite fiber material precursor; Perform replacement and critical drying on the boron nitride composite fiber material precursor to obtain the boron nitride composite fiber material.

5. The preparation method of the boron nitride composite fiber material according to claim 4, characterized in that, The preparation process of the modified boron nitride fibers is as follows: prepare a modification solution; Immerse the boron nitride fibers with the modification solution, and then dry the boron nitride fibers to obtain the modified boron nitride fibers; The modification solution includes silica sol, organic binder, and water in a mass ratio of (30 - 60):(10 - 20):(80 - 100); The preparation process of the modified silicon nitride short fibers is as follows: prepare a modification solution; Immerse the silicon nitride short fibers with the modification solution, and then dry the silicon nitride short fibers to obtain the modified silicon nitride short fibers; The organic binder includes one or more of starch, PEO, cellulose, and polyacrylic acid; The length of the boron nitride fibers is 5 - 10 mm; the length of the silicon nitride fibers is 0.2 - 3 mm; The drying temperature is 80 - 150 °C, and the drying time is 0.5 - 2.5 h.

6. The method for preparing the boron nitride composite fiber material according to claim 4, characterized in that The preparation process of the primary boron nitride fiber layer preform includes the following steps: disperse the modified boron nitride fibers into a solvent to obtain a primary boron nitride fiber layer slurry; the primary boron nitride fiber layer slurry is filtered through a first filter screen to obtain a primary boron nitride fiber layer preform; the solid content of the primary boron nitride fiber layer slurry is 30 - 40%; The preparation process of the secondary boron nitride fiber layer preform includes the following steps: dispersing the modified silicon nitride short fibers into a solvent to obtain a secondary boron nitride fiber layer slurry; Adding the secondary boron nitride fiber layer slurry into a first filter screen containing a primary boron nitride fiber layer preform, and after filtration, obtaining a secondary boron nitride fiber layer preform; The solid content of the secondary boron nitride fiber layer slurry is 40-60%.

7. The preparation method of the boron nitride composite fiber material according to claim 4, wherein, The preparation process of the tertiary boron nitride fiber layer preform includes: preparing a borazane precursor solution, impregnating one side of the secondary boron nitride fiber layer preform with the borazane precursor solution through vacuum, and then drying it at a temperature of 75-85 °C under a negative pressure environment to obtain the tertiary boron nitride fiber layer preform; The mass fraction of the borazane precursor solution is 20-50%; the borazane precursor solution includes monomeric borazine or polymeric polyborazylene.

8. The method for preparing the boron nitride composite fiber material according to claim 4, wherein, The preparation process of the four - stage boron nitride fiber layer preform is as follows: heat the three - stage boron nitride fiber layer preform in an atmosphere of ammonia and nitrogen. Raise the temperature from room temperature to 280 - 320 °C at a heating rate of 0.3 - 0.6 °C / min; then raise the temperature from 280 - 320 °C to 580 - 620 °C at a heating rate of 0.5 - 2 °C / min; then raise the temperature from 580 - 620 °C to 990 - 1000 °C at a heating rate of 5 - 10 °C / min, and hold the temperature at 990 - 1000 °C for 1 - 3 h; the total flow rate of ammonia and nitrogen is 0.15 - 0.25 m 3 / h; Then heat in a nitrogen atmosphere, raise the temperature from 990 to 1000 °C to 1550 to 1650 °C, with a heating rate of 5.5 to 6.5 °C / min, and hold at 1550 to 1650 °C for 1.8 to 2.2 h; the nitrogen flow rate is 0.15 to 0.25 m 3 / h.

9. The preparation method of the boron nitride composite fiber material according to claim 4, characterized in that, The preparation process of the boron nitride composite fiber material precursor includes placing the two layers of quaternary boron nitride fiber layer preforms in mold one and mold two respectively, with mold one and mold two arranged opposite to each other, forming a closed accommodation cavity between the two quaternary boron nitride fiber layer preforms, injecting a silica sol precursor into the accommodation cavity through the grouting holes arranged on the side of mold one and / or mold two, and then placing mold one and mold two in a negative pressure environment; The sides of the two quaternary boron nitride fiber layer preforms impregnated with the borazane precursor solution are arranged opposite to each other; Then, the silica sol precursor is subjected to sol-gelation to obtain the boron nitride composite fiber material precursor.

10. The preparation method of the boron nitride composite fiber material according to claim 4, characterized in that, It also includes preparing an insulating layer skeleton slurry, specifically including the following steps: dispersing the modified silicon nitride short fibers into a solvent to obtain an insulating layer skeleton slurry; the solid content of the insulating layer skeleton slurry is 15-20%; the solvent is water; Before the borazane precursor of the tertiary boron nitride fiber layer preform is cracked in ammonia, place the two layers of tertiary boron nitride fiber layer preforms in mold one and mold two respectively, with mold one and mold two arranged opposite to each other, forming a closed accommodation cavity between the two tertiary boron nitride fiber layer preforms; then inject the insulating layer skeleton slurry between the two layers of tertiary boron nitride fiber layers through the grouting holes arranged on the side of mold one and / or mold two; then freeze the mold one, mold two and the intermediate materials; After freezing, perform a first-stage heat treatment in a nitrogen atmosphere; then perform a second-stage heat treatment in an ammonia and nitrogen atmosphere; Obtain two layers of quaternary boron nitride fiber layers with a three-dimensional reticulated insulating layer skeleton sandwiched in the middle; the three-dimensional reticulated insulating layer skeleton includes three-dimensional silicon nitride fibers; the thickness of the three-dimensional reticulated insulating layer skeleton is 0.5-1.5 cm; In a negative pressure environment, then inject a silica sol precursor and a boron nitride composite fiber material precursor into the three-dimensional reticulated insulating layer skeleton sandwiched between the two layers of quaternary boron nitride fiber layers through the grouting holes arranged on the side of mold one and / or mold two; The first-stage heat treatment process includes, under a negative pressure environment, heating from room temperature to 80-120 °C, with a heating rate of 0.3-0.6 °C / min; The second-stage heat treatment process includes heating from 80 to 120 °C to 280 to 320 °C at a heating rate of 0.3 to 0.6 °C / min in an atmosphere of ammonia and nitrogen; heating from 280 to 320 °C to 580 to 620 °C at a heating rate of 0.5 to 2 °C / min; heating from 580 to 620 °C to 990 to 1000 °C at a heating rate of 5 to 10 °C / min, and holding at 990 to 1000 °C for 1 to 3 h; the total flow rate of ammonia and nitrogen is 0.15 to 0.25 m 3 / h; Then, heating is carried out in a nitrogen atmosphere, the temperature is raised from 990 to 1000 °C to 1550 to 1650 °C, the heating rate is 5.5 to 6.5 °C / min, and it is kept at 1550 to 1650 °C for 1.8 to 2.2 h; the nitrogen flow rate is 0.15 to 0.25 m 3 / h.