A method for preparing an aluminum-containing SiBCN ceramic fiber

Abstract

This invention discloses a method for preparing aluminum-containing SiBCN ceramic fibers. The method involves mixing a precursor, polyaluminosilane carbosilane (PACS), and boron nitride powder to obtain a uniform, pale yellow PACS / BN hybrid precursor. This hybrid precursor is then sequentially subjected to melt spinning, air-insoluble treatment, high-temperature pyrolysis, and sintering to achieve densification, resulting in black, dense aluminum-containing SiBCN ceramic fibers. This invention differs from existing methods for preparing SiBCN ceramic fibers by avoiding the use of toxic organic monomers (such as boron trichloride, chlorosilanes, and hexamethyldisilazane) or difficult-to-synthesize polyborosilicate (PBSZ, a precursor for SiBCN ceramic fibers). It offers advantages such as safe and simple operation, economy, mild reaction conditions, and adjustable boron and nitrogen content.

Description

Technical Field

[0001] This invention belongs to the field of precursor conversion ceramic fiber technology, and specifically relates to a method for preparing aluminum-containing SiBCN ceramic fibers. Background Technology

[0002] Continuous fiber-reinforced ceramic matrix composites possess excellent properties such as high specific strength, high specific modulus, high toughness, high temperature resistance, and ablation resistance, and are widely used in high-tech fields such as aerospace. With the development of space exploration technology, the requirements for the performance of ceramic matrix composites (such as high temperature resistance and oxidation resistance) are becoming increasingly stringent, making ceramic fibers crucial for the preparation of high-performance ceramic matrix composites. Silicon boron carbon nitride (SiBCN) fibers have attracted widespread attention in both military and civilian fields due to their good high-temperature thermal stability and excellent high-temperature oxidation resistance. However, in high-temperature oxidizing environments, boron (B) in SiBCN ceramic materials will volatilize to form boron oxide (B₂O₃) gas, thereby weakening its high-temperature resistance and oxidation resistance. Introducing elements such as aluminum (Al), zirconium (Zr), and hafnium (Hf) into SiBCN ceramic materials to form a multi-element system can improve the overall performance of the ceramic material.

[0003] Currently, the key to preparing SiBCN ceramic fibers containing heterogeneous elements lies in the synthesis of precursors. Polyborosilazane (PBSZ) precursors containing heterogeneous elements are generally obtained through two routes: (1) reacting the raw materials for synthesizing PBSZ with reagents containing specific elements; (2) reacting PBSZ directly with reagents containing specific elements.

[0004] Among them, PBSZ containing heterogeneous elements is obtained by reacting the raw materials for synthesizing PBSZ with reagents containing specific elements. For example, Liu Yong et al. (patent application publication number: CN107500766A) disclosed a method for preparing amorphous silicon boron carbon nitride zirconium ceramic fibers. The method for synthesizing the precursor is as follows: under a nitrogen atmosphere and at a temperature below -10℃, a mixed solution of boron trichloride and chlorosilane is first added to a hexamethyldisilazane solution and stirred for 8-16 hours, then stirred at 120-150℃ for 3-4 hours, and cooled to room temperature to obtain a pale yellow liquid; zirconium dichlorocerocene (Zr(AcAc)3) is added to the pale yellow liquid, the temperature is raised to 170-190℃ and stirred for 4-6 hours, and then the temperature is raised to 220-250℃ and stirred for 4-6 hours to obtain a yellow precursor. This method of synthesizing precursors requires toxic organic raw materials, has a long reaction time, harsh reaction conditions, and is cumbersome to operate; while PBSZ directly reacts with reagents containing specific elements to obtain PBSZ containing heterogeneous elements. For example, Du Liang et al. (patent application publication number: CN105801866A) disclosed a method for preparing an aluminum-containing polyborosilazane ceramic precursor. The method involves first dissolving solid PBSZ in xylene, then adding an organometallic aluminum reagent (such as aluminum sec-butoxide, aluminum acetylacetonate, etc.), heating to 100–130°C for 2–3 hours, and then refluxing at 150°C for 2–3 hours. After the reaction, the solvent is removed to obtain a yellow solid aluminum-containing PBSZ. However, this invention does not address whether it can be spun into aluminum-containing SiBCN ceramic fibers. Wu Baolin et al. (Patent Application Publication No.: CN109825901A) disclosed aluminum-zirconium co-doped silicon carbide / boron nitride fibers and their preparation method. The precursor preparation method involved thoroughly mixing aluminum acetate, Zr(AcAc)3, and PBSZ in a high-pressure reactor, then injecting polydimethylsilane (PDMS) and uniformly covering the surface of the mixture. The mixture was heated to 180°C and held for 2 hours to obtain a coarse material. The coarse material was dissolved in xylene, filtered, and distilled under reduced pressure to obtain fine aluminum-zirconium co-doped silicon carbide / boron nitride precursors. The entire reaction was carried out in a high-pressure system, and PBSZ is difficult to synthesize.

[0005] In summary, there are still some technical difficulties in preparing SiBCN ceramic fibers by using organic raw materials or PBSZ to prepare precursors containing heterogeneous elements. These difficulties are mainly manifested in the following aspects: (1) Organic raw materials are highly toxic; (2) The operation is complicated and the reaction time is long; (3) The reaction conditions are harsh (low temperature or high pressure environment); and (4) PBSZ is difficult to obtain. Summary of the Invention

[0006] To address the problems existing in the background art, the present invention aims to provide a method for preparing aluminum-containing SiBCN ceramic fibers. This method has the advantages of simple operation, mild reaction conditions, avoidance of using highly toxic organic reagents (such as boron trichloride, chlorosilane, and hexamethyldisilazane) or using hard-to-obtain PBSZ as raw material for aluminum doping modification, and adjustable boron and nitrogen content and densification in ceramic fibers.

[0007] The technical solution adopted in this invention is as follows:

[0008] I. A method for preparing aluminum-containing SiBCN ceramic fibers:

[0009] (1) Preparation of hybrid precursor: A certain proportion of polyaluminum carbosilane PACS is dissolved in a solvent to form a polyaluminum carbosilane solution. Boron nitride powder (BN) is added and the solution is placed in a ball mill jar and ball-milled for a certain time. After the boron nitride powder is evenly dispersed in the polyaluminum carbosilane solution, the solvent is removed by distillation to obtain a uniform light yellow PACS / BN hybrid precursor.

[0010] (2) The PACS / BN hybrid precursor in step (1) is subjected to four processes in sequence: melt spinning, non-melting treatment, high-temperature pyrolysis and sintering densification to obtain black aluminum-containing SiBCN ceramic fibers.

[0011] The polyaluminosilane in step (1) is obtained by direct polymerization of low molecular weight polyaluminosilane and aluminum acetylacetonate under nitrogen at 420-450°C. It is a brown, semi-transparent thermoplastic brittle solid with a softening point of 170-220°C and an aluminum content of 0.5-1 wt%.

[0012] The polycarbosilane has a number-average molecular weight of 450–800 Da.

[0013] The particle diameter of the boron nitride powder is typically in the nanometer range, but is not limited thereto.

[0014] The boron nitride powder in step (1) is hexagonal boron nitride nanosheets or rod-shaped boron nitride.

[0015] The solvent in step (1) is either n-hexane or xylene.

[0016] In step (1), the polyaluminosilicate, boron nitride, and solvent are in a mass ratio of 20:0.1-2:5-10.

[0017] The ball milling conditions in step (1) are: ball milling time of 8 to 24 hours and turntable speed of 300 rpm.

[0018] The melt spinning process in step (2) is as follows: the spinning temperature is 320-380℃, and the atmosphere is nitrogen.

[0019] In step (2), the non-melting treatment is air thermal oxidation cross-linking at a temperature of 150-220°C and a non-melting time of 2-4 hours, that is, the heating treatment is carried out in an air atmosphere at a temperature of 150-220°C for 2-4 hours.

[0020] In step (2), the high-temperature pyrolysis treatment is as follows: under a nitrogen atmosphere, the temperature is raised to 1100℃ at a heating rate of 2-5℃ / min and held for 0.5-2h; the sintering densification treatment is as follows: under an argon atmosphere, the temperature is raised to 1700-1900℃ at a heating rate of 5-10℃ / min and held for 0.5-2h.

[0021] This invention prepares silicon-boron-carbon-nitrogen-aluminum ceramic fibers by using polyaluminosilane and boron nitride powder as raw materials in the presence of a solvent, and preparing a PACS / BN hybrid precursor through ball milling and blending. This method not only ensures uniform dispersion of BN in the PACS, but also borrows from the preparation route of aluminum-containing SiC ceramic fibers to achieve the preparation of aluminum-containing SiBCN ceramic fibers, and the preparation process is relatively mature. Therefore, the steps described in this method, such as ball milling, melt spinning, non-melting treatment, and high-temperature pyrolysis, can all be operated using conventional methods.

[0022] The beneficial effects of this invention are as follows:

[0023] (1) This invention uses ball milling to uniformly disperse boron nitride in polyaluminum carbide silane, and then melt spinning, non-melting treatment and high-temperature pyrolysis to successfully prepare aluminum-containing SiBCN ceramic fibers. This avoids the use of highly toxic organic raw materials and difficult-to-synthesize PBSZ in conventional preparation methods. The reaction conditions are mild and the operation is simple.

[0024] (2) The amount of boron nitride powder added takes into account both the precursor molding performance and the temperature resistance of the final ceramic fiber, so as to achieve adjustable boron and nitrogen content in the ceramic fiber.

[0025] (3) The present invention uses aluminum-doped sintering aids combined with high-temperature sintering process to achieve densification of aluminum-containing SiBCN ceramic fibers. Attached Figure Description

[0026] Figure 1 The following are SEM images of two forms of boron nitride powder in specific embodiments of the present invention: (a) flakes; (b) rods;

[0027] Figure 2 These are optical photographs of the precursors in specific embodiments of the present invention: (a) PACS; (b) PACS / BN-0.5%; (c) PACS / BN-2%; (d) PACS / BN-5%;

[0028] Figure 3 These are the infrared spectra of each precursor in a specific embodiment of the present invention;

[0029] Figure 4 These are optical photographs of the precursor fiber in a specific embodiment of the present invention: (a) PACS; (b) PACS / BN-8%;

[0030] Figure 5 Optical photographs and SEM images of ceramic fibers obtained by pyrolysis at 1100℃ and sintering at 1850℃ in specific embodiments of the present invention: (a)(b)(c) 1100℃; (d)(e)(f) 1850℃;

[0031] Figure 6 This is a SEM image of the Si-C-Al(O) ceramic fibers in the comparative example of this invention. Detailed Implementation

[0032] The invention will be further illustrated below with specific examples.

[0033] Specific embodiments of the present invention are as follows:

[0034] Example 1

[0035] Preparation of hybrid precursor PACS / BN (sheet-like) - 8%: 20g of polyaluminum carbosilane with a softening point of 170–220℃ was dissolved in 9g of n-hexane to form a polyaluminum carbosilane solution. 1.6g of hexagonal boron nitride nanosheets (whose SEM images are shown below) were then added. Figure 1 (As shown in a) The mixture was then placed in a ball mill jar and ball-milled for 24 hours. After the boron nitride powder was uniformly dispersed in the polyaluminum carbide silane solution, the solvent was removed by distillation to obtain a uniform, pale yellow PACS / BN (flake) - 8% hybrid precursor.

[0036] PACS / BN (sheet-like) - 8% hybrid precursor was melt-spun at 370℃ under a nitrogen atmosphere to obtain hybrid precursor fiber precursor (optical photograph of the precursor is shown in the image). Figure 4 As shown in b, the fiber diameter distribution is relatively uniform; the precursor fiber is treated in air at 180℃ for 4 hours to obtain infusible fiber; the infusible fiber is then heated to 1100℃ at a heating rate of 5℃ / min under a nitrogen atmosphere and pyrolyzed for 1 hour to obtain sintered fiber (optical photographs and SEM images of the sintered fiber are shown in Figure b). Figure 5 (As shown in a, 5b, and 5c); the sintered fibers were heated to 1850℃ and held for 0.5h at a heating rate of 10℃ / min under an argon atmosphere to obtain black, relatively dense aluminum-containing SiBCN ceramic fibers (their optical photographs and SEM images are shown in a, 5b, and 5c). Figure 5 (As shown in d, 5e, and 5f). The addition of boron nitride results in the final aluminum-containing SiBCN ceramic fibers being black, matte filament bundles with a diameter of approximately 32 μm and a uniform and dense structure, further demonstrating the good dispersibility of boron nitride in polyaluminosilane.

[0037] Example 2

[0038] Preparation of the hybrid precursor PACS / BN-5%: 20g of polyaluminum carbosilane with a softening point of 170–220℃ was dissolved in 8g of n-hexane to form a polyaluminum carbosilane solution. 1g of hexagonal boron nitride nanosheets were added, and the solution was ball-milled for 24 hours. After the boron nitride powder was uniformly dispersed in the polyaluminum carbosilane solution, the solvent was removed by distillation, yielding a uniform, pale yellow PACS / BN-5% hybrid precursor (its optical photograph is shown in Figure 1). Figure 2 As shown in d, the precursor has a uniform color, indicating that boron nitride is relatively uniformly dispersed in polyaluminosilane; Figure 3 It can be seen that, apart from the infrared characteristic peak of BN, no other characteristic peaks appeared in the prepared hybrid precursor PACS / BN-5%, indicating that the mixture of polyaluminosilane and boron nitride is only a simple physical mixture.

[0039] After melt spinning of PACS / BN-5% hybrid precursor at 330℃ under nitrogen atmosphere, hybrid precursor fiber filaments were obtained. The filaments were then subjected to non-melting treatment at 180℃ in air for 4 hours to obtain non-melting fibers. The non-melting fibers were then heated to 1100℃ at a heating rate of 5℃ / min under nitrogen atmosphere and pyrolyzed for 1 hour to obtain sintered fibers. The sintered fibers were then heated to 1850℃ at a heating rate of 10℃ / min under argon atmosphere and held for 0.5 hours to obtain black, dense aluminum-containing SiBCN ceramic fibers.

[0040] Example 3

[0041] Preparation of the hybrid precursor PACS / BN-2%: 20g of polyaluminum carbosilane with a softening point of 170–220℃ was dissolved in 7g of n-hexane to form a polyaluminum carbosilane solution. 0.4g of hexagonal boron nitride nanosheets were added, and the solution was ball-milled for 24 hours. After the boron nitride powder was uniformly dispersed in the polyaluminum carbosilane solution, the solvent was removed by distillation, yielding a uniform, pale yellow PACS / BN-2% hybrid precursor (its optical photograph is shown in the image). Figure 2 (as shown in c);

[0042] After melt spinning of PACS / BN-2% hybrid precursor at 310℃ under nitrogen atmosphere, hybrid precursor fiber filaments were obtained. The filaments were then subjected to non-melting treatment at 180℃ in air for 4 hours to obtain non-melting fibers. The non-melting fibers were then heated to 1100℃ at a heating rate of 5℃ / min under nitrogen atmosphere and pyrolyzed for 1 hour to obtain sintered fibers. The sintered fibers were then heated to 1850℃ at a heating rate of 10℃ / min under argon atmosphere and held for 0.5 hours to obtain black, dense aluminum-containing SiBCN ceramic fibers.

[0043] Example 4

[0044] Preparation of the hybrid precursor PACS / BN-0.5%: 20g of polyaluminum carbosilane with a softening point of 170–220℃ was dissolved in 5g of n-hexane to form a polyaluminum carbosilane solution. 0.1g of hexagonal boron nitride nanosheets were added, and the solution was ball-milled for 24 hours. After the boron nitride powder was uniformly dispersed in the polyaluminum carbosilane solution, the solvent was removed by distillation, yielding a uniform, pale yellow PACS / BN-0.5% hybrid precursor (its optical photograph is shown in Figure 1). Figure 2 (as shown in b);

[0045] PACS / BN-0.5% hybrid precursor was melt-spun at 290℃ under a nitrogen atmosphere to obtain hybrid precursor fiber filaments; the filaments were treated in air at 180℃ for 4 hours to obtain infusible fibers; the infusible fibers were heated to 1100℃ at a heating rate of 5℃ / min under a nitrogen atmosphere and pyrolyzed for 1 hour to obtain sintered fibers; the sintered fibers were heated to 1850℃ at a heating rate of 10℃ / min under an argon atmosphere and held for 0.5 hours to obtain black, dense aluminum-containing SiBCN ceramic fibers.

[0046] Example 5

[0047] Preparation of hybrid precursor PACS / BN (rod-shaped) - 8%: 20g of polyaluminum carbosilane with a softening point of 170–220℃ was dissolved in 9g of n-hexane to form a polyaluminum carbosilane solution. 1.6g of rod-shaped boron nitride powder (SEM image) was then added. Figure 1 (As shown in b) The mixture was then placed in a ball mill jar and ball-milled for 24 hours. After the boron nitride powder was uniformly dispersed in the polyaluminum carbide silane solution, the solvent was removed by distillation to obtain a uniform pale yellow PACS / BN (rod-shaped) - 8% hybrid precursor;

[0048] PACS / BN (rod-shaped) - 8% hybrid precursor was melt-spun at 370℃ under a nitrogen atmosphere to obtain hybrid precursor fiber filaments; the filaments were treated in air at 180℃ for 4 hours to obtain infusible fibers; the infusible fibers were heated to 1100℃ at a heating rate of 5℃ / min under a nitrogen atmosphere and pyrolyzed for 1 hour to obtain sintered fibers; the sintered fibers were heated to 1850℃ at a heating rate of 10℃ / min under an argon atmosphere and held for 0.5 hours to obtain black, dense aluminum-containing SiBCN ceramic fibers.

[0049] Comparative Example 1

[0050] 20g of polyaluminum carbide silane with a softening point of 170–220℃ was dissolved in 9g of n-hexane to form a polyaluminum carbide silane solution. Without adding boron nitride powder, the solution was ball-milled in a ball mill jar for 24 hours to obtain a homogeneous and transparent PACS solution. After distilling to remove the n-hexane, a brownish-red transparent precursor PACS was obtained (its optical photograph is shown below). Figure 2 (as shown in a).

[0051] After the precursor PACS was melt-spun at 320℃ under nitrogen protection, precursor fiber precursor filaments were obtained (optical photographs of the precursor filaments are shown in the image). Figure 4 (As shown in a). The precursor fiber was treated in air at 180℃ for 4 hours to obtain infusible fibers; the infusible fibers were heated to 1100℃ at a heating rate of 5℃ / min under a nitrogen atmosphere and pyrolyzed for 1 hour to obtain sintered fibers; the sintered fibers were heated to 1900℃ at a heating rate of 10℃ / min under an argon atmosphere and held for 0.5 hours to obtain porous Si-C-Al(O) ceramic fibers with a diameter of approximately 8μm (the SEM of which is shown in figure a). Figure 6 (As shown).

[0052] Comparative Example 2

[0053] Preparation of the hybrid precursor PACS / BN-10%: 20g of polyaluminum carbosilane with a softening point of 170–220℃ was dissolved in 10g of n-hexane to form a polyaluminum carbosilane solution. 2g of hexagonal boron nitride nanosheets were added, and the solution was ball-milled in a ball mill jar for 24 hours. After the boron nitride powder was uniformly dispersed in the polyaluminum carbosilane solution, the solvent was removed by distillation to obtain a uniform, pale yellow PACS / BN-10% hybrid precursor.

[0054] PACS / BN-10% hybrid precursor can be melt-spun at 360°C in a nitrogen atmosphere to extrude precursor fibers. However, due to the presence of boron nitride and its large addition amount, the precursor fibers are brittle and cannot be wound.

[0055] As can be seen from the above, the present invention introduces boron nitride uniformly dispersed in polyaluminum carbide silane, and then processes it through specific steps such as melt spinning, non-melting treatment and high-temperature pyrolysis, successfully realizing the preparation of aluminum-containing SiBCN ceramic fibers, improving the precursor forming performance and the temperature resistance of the final ceramic fibers, and achieving adjustable and densified boron and nitrogen content of ceramic fibers.

[0056] Therefore, this invention uses a hybrid precursor of PACS and BN to prepare aluminum-containing SiBCN ceramic fibers. By using aluminum-doped sintering aids, air-insoluble processes, and high-temperature sintering, the ceramic fibers are made dense. This avoids the use of toxic organic raw materials (such as boron trichloride, chlorosilanes, and hexamethyldisilazane) or difficult-to-synthesize polyborosilicates (PBSZ, a SiBCN ceramic fiber precursor) as raw materials. It has the advantages of safe and simple operation, economy, mild reaction conditions, and adjustable boron and nitrogen content, and has achieved outstanding technical effects and advantages.

[0057] The above specific embodiments are used to explain and illustrate the present invention, but not to limit the present invention. Any modifications and changes made to the present invention within the spirit and scope of the claims shall fall within the protection scope of the present invention.

[0058] The above description is only a preferred embodiment of the present invention. Therefore, all equivalent changes or modifications made to the structure, features and principles described in the claims of this patent application are included in the scope of this patent application.

Claims

1. A method for preparing aluminum-containing SiBCN ceramic fibers, characterized in that: (1) Preparation of hybrid precursor: Polyalumina carbosilane was dissolved in a solvent to form a polyalumina carbosilane solution. Boron nitride powder was added and the solution was ball-milled in a ball mill jar. After the boron nitride powder was evenly dispersed in the polyalumina carbosilane solution, the solvent was removed by distillation to obtain a uniform light yellow PACS / BN hybrid precursor. (2) The PACS / BN hybrid precursor in step (1) is subjected to four processes in sequence: melt spinning, non-melting treatment, high-temperature pyrolysis and sintering densification to obtain black aluminum-containing SiBCN ceramic fibers. The melt spinning process in step (2) is as follows: the spinning temperature is 320~380 ℃, and the atmosphere is nitrogen. In step (2), the non-melting treatment is air thermal oxidation cross-linking at a temperature of 150~220 ℃ and a non-melting time of 2~4h; In step (2), the high-temperature pyrolysis treatment is as follows: under a nitrogen atmosphere, the temperature is raised to 1100 ℃ at a heating rate of 2~5 ℃ / min and held for 0.5~2 h; the sintering densification treatment is as follows: under an argon atmosphere, the temperature is raised to 1700~1900 ℃ at a heating rate of 5~10 ℃ / min and held for 0.5~2 h.

2. The method for preparing aluminum-containing SiBCN ceramic fibers according to claim 1, characterized in that: The polyaluminosilicate in step (1) is obtained by direct polymerization of polyaluminosilicate and aluminum acetylacetonate under nitrogen at 420~450 °C.

3. The method for preparing aluminum-containing SiBCN ceramic fibers according to claim 1, characterized in that: The boron nitride powder in step (1) is hexagonal boron nitride nanosheets or rod-shaped boron nitride.

4. The method for preparing aluminum-containing SiBCN ceramic fibers according to claim 1, characterized in that: The solvent in step (1) is either n-hexane or xylene.

5. The method for preparing aluminum-containing SiBCN ceramic fibers according to claim 1, characterized in that: In step (1), the polyaluminosilicate, boron nitride, and solvent are in a mass ratio of 20:0.1-2:5-10.

6. The method for preparing aluminum-containing SiBCN ceramic fibers according to claim 1, characterized in that: The ball milling conditions in step (1) are: ball milling time of 8~24 h and turntable speed of 300 rpm.

7. An aluminum-containing SiBCN ceramic fiber, characterized in that: It is made by any of the methods described in claims 1-6.

Images