A method for preparing a fibrous MAX phase powder

Abstract

The application discloses a kind of fibrous MAX phase powder preparation methods, comprising the following steps: carbon nanofiber preliminary pretreatment, and obtain primary modified carbon nanofiber;Primary modified carbon nanofiber is mixed in first mixed salt solution, after ultrasonic dispersion freeze-drying, and obtain first mixed fiber material;Prepare first mixed solution;The first mixed solution includes Ti powder and Si powder;First mixed fiber material is added in first mixed solution dispersion, then dry, and obtain second mixed fiber material;Second mixed fiber material surface is covered with second mixed salt, then segmented heating is carried out, then segmented cooling is carried out to obtain the mixture of fibrous MAX phase powder and salt;Fibrous MAX phase powder and salt mixture is washed, dried, and obtain fibrous MAX phase powder;Realize that the internal structure of fibrous MAX phase powder is uniform, high in purity, and the problem that length-diameter ratio is obviously reduced is avoided.

Description

Technical Field

[0001] This invention relates to the field of MAX phase powder technology, and more particularly to a method for preparing fibrous MAX phase powder. Background Technology

[0002] MAX phase materials (such as Ti3SiC2) have attracted much attention in fields such as high-temperature structural materials and electromagnetic shielding due to their unique layered structure and excellent mechanical and electrical properties.

[0003] Traditional synthesis of MAX phase materials relies on high-temperature, long-duration reactions, and the products are prone to problems such as coarse grains and low purity. Furthermore, when carbon nanofibers (CNFs) are used as a carbon source, their surface inertness leads to poor interfacial bonding with metal powders (such as Ti and Si), affecting the uniformity and performance of the final product. In existing technologies, CNFs exhibit insufficient dispersibility and reactivity, resulting in inhomogeneous structures and low purity in the final product.

[0004] Therefore, how to prepare a fibrous MAX phase powder that has a uniform internal structure, high purity, and avoids a significant reduction in aspect ratio has become a pressing problem to be solved in this field. Summary of the Invention

[0005] To address the aforementioned technical problems, this invention provides a method for preparing fibrous MAX phase powder, which achieves uniform internal structure and high purity of the fibrous MAX phase powder while avoiding the problem of a significant reduction in aspect ratio.

[0006] This invention provides a method for preparing fibrous MAX phase powder, comprising the following steps: The carbon nanofibers were pretreated to obtain primary modified carbon nanofibers. Primary modified carbon nanofibers are mixed in a first mixed salt solution, ultrasonically dispersed, and then freeze-dried to obtain a first mixed fiber material. The first mixed fiber material includes primary modified carbon nanofibers, a first mixed salt coating the surface of the primary modified carbon nanofibers, and a first mixed salt dispersed between the primary modified carbon nanofibers. A first mixture is prepared; the first mixture comprises Ti powder and Si powder; The first mixed fiber material is added to the first mixed liquid and dispersed, and then dried to obtain the second mixed fiber material; the second mixed fiber material includes primary modified carbon nanofibers, a first mixed salt, Ti powder and Si powder coated on the surface of the primary modified carbon nanofibers and dispersed between the primary modified carbon nanofibers; After covering the surface of the second mixed fiber material with the second mixed salt, it is heated in stages and then cooled in stages to obtain a mixture of fibrous MAX phase powder and salt. The fibrous MAX phase powder was washed and dried to obtain the fibrous MAX phase powder.

[0007] Compared with the prior art, the present invention has the following beneficial effects: by pre-treating carbon nanofibers to obtain primary modified carbon nanofibers, it is beneficial to improve the dispersion performance of primary modified carbon nanofibers and the bonding strength between primary modified carbon nanofibers and metal powders. This helps to avoid the problem of low aspect ratio caused by the shortening of carbon nanofibers in subsequent preparation processes, and also helps to achieve the purity of the prepared fibrous MAX phase powder. By mixing primary modified carbon nanofibers in a first mixed salt solution, ultrasonically dispersing them, and then freeze-drying them, a first mixed fiber material is obtained. This achieves uniform mixing of the first mixed salt and the primary modified carbon nanofibers, which is beneficial for the melting of the first mixed salt during subsequent heating to ensure uniform heating of the carbon nanofibers. Furthermore, the ultrasonic method achieves uniform dispersion while avoiding the problem of carbon nanofibers becoming shorter during dispersion. The first mixture includes Ti powder and Si powder; the first mixed fiber material is added to the first mixture and dispersed, and then dried to obtain the second mixed fiber material, so as to achieve uniform mixing of modified carbon nanofibers with Ti powder and Si powder, which is beneficial to achieving uniform internal structure. By covering the surface of the second mixed fiber material with the second mixed salt, the second mixed salt is buried and burned into the second mixed fiber material, which helps to avoid the volatilization of Si powder. At the same time, the second mixed salt melts during the heating process, which further helps to achieve uniform mixing of carbon nanofibers with Ti powder and Si powder, and helps to achieve uniform internal structure. By covering the surface of the second mixed fiber material with the second mixed salt and then heating it in stages, segmented temperature control is achieved, and the intermediate products generated during each heating process are controlled, resulting in a fibrous MAX phase powder with a uniform internal structure and high purity.

[0008] Furthermore, the initial pretreatment process for carbon nanofibers includes the following steps: Carbon nanofibers were added to a mixed acid solution of nitric acid and sulfuric acid in a volume ratio of 2.5-3.5:1, and the mixed acid solution was heated under reflux at 55-65℃ for 1.8-2.5 hours. Then the carbon nanofibers were removed from the mixed acid solution, washed and dried at a temperature of 98-110℃ for 2-3 hours. The concentration of nitric acid is 66-70%, and the concentration of sulfuric acid is 70-80%.

[0009] The beneficial effect of the previous step is that it introduces hydroxyl groups on the surface of carbon nanofibers, which is conducive to subsequent bonding with Si powder and Ti powder, and helps to achieve a uniform internal structure of fibrous MAX phase powder.

[0010] Furthermore, the initial pretreatment process for carbon nanofibers also includes the following steps: Place anhydrous ethanol at 0-5°C, then add tetrabutyl titanate dropwise to the anhydrous ethanol. Mix; Then add acetylacetone and continue stirring for 8-20 minutes to obtain a clear, light yellow solution; Then, add ethanol solution dropwise to the transparent light yellow solution and stir, controlling the temperature of the transparent light yellow solution at 5-10℃; the stirring time is 1-2 hours. Then add the washed and dried carbon nanofibers, and ultrasonically impregnate for 0.5-1 h. After stopping the ultrasonic impregnation, let it stand for 1.8-2.2 h and then filter under reduced pressure. Then, the carbon nanofibers after vacuum filtration are vacuum dried for ≥8 hours. Then, an initial pretreatment heating process is performed, which includes: Heat at 115-125℃ for 0.8-1.2 hours; Heat at 235-260℃ for 0.8-1.2 hours; The mass ratio of tetrabutyl titanate, acetylacetone, and carbon nanofibers is (5-8):(3-6):100.

[0011] The beneficial effect of the previous step is that by placing anhydrous ethanol at 0-5℃, then adding tetrabutyl titanate dropwise to the anhydrous ethanol and mixing, and then adding acetylacetone and continuing to stir for 8-20 min, a transparent light yellow solution is obtained, which inhibits the rapid hydrolysis of tetrabutyl titanate through complexation. By adding ethanol solution dropwise to a transparent light yellow solution and stirring, the temperature of the transparent light yellow solution is controlled at 5-10℃; the stirring time is 1-2h; then the washed and dried carbon nanofibers are added and ultrasonically impregnated for 0.5-1h to achieve carbon nanofiber coating of tetrabutyl titanate and acetylacetone. The process involves initial pretreatment heating, which includes heating at 115-125℃ for 0.8-1.2 hours and at 235-260℃ for 0.8-1.2 hours to achieve carbon nanofiber coating of tetrabutyl titanate. This is beneficial for the high bonding strength between carbon nanofibers and Ti during subsequent segmented heating processes, which is conducive to the reaction between carbon nanofibers and Ti.

[0012] Furthermore, the first mixed salt comprises NaCl in a molar ratio of (0.8-1.2):1. and KCl; The second mixed salt comprises NaCl, KCl, and LiF in a molar ratio of (2.8-3.2):(0.8-1.2):(0.8-1.2); and / or The molar ratio of Ti powder, Si powder, and carbon nanofibers is 3:(1.2-1.3):2; The mass ratio of carbon nanofibers to the second mixed salt is 1:(38-43). Preferably, the aspect ratio of the carbon nanofiber is (300-500):1.

[0013] The beneficial effect of the previous step is that the second mixed salt comprises NaCl, KCl, and LiF in a molar ratio of (2.8-3.2):(0.8-1.2):(0.8-1.2), and the LiF helps to significantly reduce the melting temperature of the mixed salt. By using a molar ratio of Ti powder, Si powder, and carbon nanofibers of 3:(1.2-1.3):2, the Si powder content in the raw materials is slightly higher, which is beneficial for promoting the forward reaction and obtaining fibrous MAX phase powder with high purity. Furthermore, the excess Si powder is volatilized without affecting the high purity of the fibrous MAX phase powder.

[0014] Furthermore, the preparation process of the first hybrid fiber material includes the following steps: The first mixed salt is added to ethylene glycol, and then the primary modified carbon nanofibers are added to ethylene glycol; Then, the first mixed salt and carbon nanofibers were dispersed into ethylene glycol by ultrasonic dispersion. After ultrasound for 20-50 minutes, freeze-drying is then performed. Freezing temperature is -15 to -13℃; drying temperature after freezing is 0-20℃; The mass ratio of primary modified carbon nanofibers to the first mixed salt is 1:(9-11).

[0015] The beneficial effect of the previous step is that the first mixed salt and carbon nanofibers are dispersed in ethylene glycol by ultrasonic dispersion. After ultrasonication for 20-50 minutes, freeze-drying is carried out at a freezing temperature of -15 to -13℃. The drying temperature after freezing is 0-20℃, which achieves uniform mixing of the first mixed salt and carbon nanofibers without causing a significant reduction in the aspect ratio of the carbon nanofibers.

[0016] Furthermore, the process of preparing the first mixture includes the following steps: Ti powder and Si powder were added to ethylene glycol, and the solution temperature was maintained at [temperature value] using a cold water bath. At 20-30℃, ultrasonic dispersion was performed simultaneously to obtain the first mixture.

[0017] Furthermore, the preparation process of the second hybrid fiber material includes the following steps: The first mixed fiber material is added to the first mixed solution, and the solution temperature is maintained at 20-30℃ by a cold water bath; at the same time, ultrasonic dispersion is performed for 20-25 minutes. Then, while maintaining ultrasonic dispersion, the solution temperature was adjusted to 60-65℃, and the second mixed fiber material was obtained after 0.5-1h.

[0018] The advantage of the previous step is that it achieves uniform mixing of the first mixed salt, carbon nanofibers, Si powder, and carbon powder, without causing a significant reduction in the aspect ratio of the carbon nanofibers.

[0019] Furthermore, the process of segmented heating after coating the surface of the second mixed fiber material with the second mixed salt includes the following steps: First stage of heating: Increase the temperature to 300-500℃ at a rate of 5-9℃ / min, and hold at 300-500℃ for 0.5-1h; Second stage heating: Increase the temperature to 770-820℃ at a rate of 3-4℃ / min, and hold at 770-820℃ for 1.4-2 hours; The third stage of heating: the temperature is increased to 900-950℃ at a rate of 2.2-2.6℃ / min, and then held at 900-950℃ for 1.2-2.2 hours; Fourth stage heating: Increase the temperature to 1100-1150℃ at a rate of 1.5-1.8℃ / min, and hold at 900-950℃ for 2.8-3.2 hours; Fifth stage of heating: Increase the temperature to 1250-1300℃ at a rate of 0.8-1.3℃ / min, and hold at 1250-1300℃ for 2.5-4 hours; and / or The segmented cooling process includes the following steps: After segmented heating, the temperature is reduced from 1200-1300℃ to 580-650℃ at a rate of 0.8-1.2℃ / min. Then allow it to cool naturally to room temperature.

[0020] The beneficial effect of the previous step is that, through the first stage of heating: heating to 300-500℃ at 5-9℃ / min and holding at 300-500℃ for 0.5-1h, the organic matter in the second mixed fiber material is volatilized, thereby enabling the carbon nanofibers to contact with Ti powder and Si powder. The second stage of heating involves raising the temperature to 770-820℃ at a rate of 3-4℃ / min and holding it at 770-820℃ for 1.4-2 hours. This allows for the partial reaction of Ti powder and Si powder to produce trisilicon (Ti5Si3), avoiding the problem of silicon evaporation caused by temperature increases during subsequent heating. At the same time, carbon nanofibers and Ti powder do not react with Si at this temperature range. The third stage of heating involves raising the temperature to 900-950℃ at a rate of 2.2-2.6℃ / min and holding it at 900-950℃ for 1.2-2.2 hours. This process allows the remaining Ti to react with some carbon nanofibers to form titanium carbide. Some carbon nanofibers do not participate in the reaction, which helps to avoid the generation of other impurities. By heating to 1100-1150℃ at a rate of 1.5-1.8℃ / min and holding at 1000-1050℃ for 2.8-3.2h, unreacted carbon nanofibers react with pentatidium trisilide at 1100-1150℃ to generate TiC and TiSi, and the generated TiC and TiSi have high activity. By heating to 1250-1300℃ at a rate of 0.8-1.3℃ / min and holding at 1250-1300℃ for 2.5-4h, TiC and TiSi react under high activity to obtain fibrous MAX phase powder. Through the above segmented heating, the segmented reaction is fully realized, the generation of side reactions is avoided, and the obtained fibrous MAX phase powder (Ti3SiC2 powder) has high purity.

[0021] Furthermore, before mixing the primary modified carbon nanofibers in the first mixed salt solution to prepare the first mixed solution, the primary modified carbon nanofibers undergo a secondary pretreatment. The secondary preprocessing process includes: Paraffin wax was added to acetone and dissolved to obtain a second mixture; the mass ratio of paraffin wax to acetone was 18:(785-820). Then, the primary modified carbon nanofibers were added to the second mixture and ultrasonically dispersed. Then, a second pretreatment heating is performed at a temperature of 60-65℃ for 0.5-1h to obtain the primary modified carbon nanofibers after the second pretreatment. The mass ratio of paraffin wax to carbon nanofibers is (2-5):100; The preparation process of the second mixed fiber material includes the following steps: The first mixed fiber material is added to the first mixed solution, and the solution temperature is maintained at 20-30℃ by a cold water bath; at the same time, ultrasonic dispersion is performed for 20-25 minutes. Then, while maintaining ultrasonic dispersion, the solution temperature is adjusted to 60-65℃ and heated for 0.5-1h to obtain the second mixed fiber material.

[0022] The beneficial effect of the previous step is that by adding paraffin to acetone and dissolving it, a second mixture is obtained; the mass ratio of paraffin to acetone is 18:(785-820), and a second pretreatment is carried out by heating at a temperature of 60-65℃ for 0.5-1h. This allows paraffin to adhere to the surface of the primary modified carbon nanofibers after the second pretreatment, thereby improving the strength of the primary modified carbon nanofibers after the second pretreatment and helping to avoid a significant reduction in the aspect ratio of the nano-quartz fibers. By adding the first mixed fiber material to the first mixed solution and maintaining the solution temperature at 20-30℃ in a cold water bath, while simultaneously performing ultrasonic dispersion for 20-25 minutes, and then maintaining ultrasonic dispersion while adjusting the solution temperature to 60-65℃ and heating for 0.5-1 hours, it is beneficial to achieve the adhesion of Ti powder and Si powder on the surface of the carbon nanofibers of the second mixed fiber material, and to achieve a uniform internal structure of the prepared fibrous MAX phase powder.

[0023] Furthermore, the mixture of fibrous MAX phase powder and salt is first washed with deionized water and dried to obtain fibrous MAX phase powder; the drying temperature is 100-120℃; and / or the fibrous MAX phase powder has a diameter of 50-100 nm and a length of 5-15 μm.

[0024] The advantage of the previous step is that it removes the mixed salts; and the fibrous MAX phase powder with a diameter of 50-100 nm and a length of 5-15 μm is relatively long. Attached Figure Description

[0025] Figure 1 The image shows the XRD pattern of the fibrous MAX phase powder (Ti3SiC2 powder) from Example 1. Figure 2 SEM images and surface scan analysis of the fibrous MAX phase powder (Ti3SiC2 powder) of Example 1. Detailed Implementation

[0026] To better understand the technical solution of the present invention, the present invention will be further described below with reference to specific embodiments.

[0027] Example 1: This embodiment provides a method for preparing fibrous MAX phase powder, characterized by comprising the following steps: Carbon nanofibers are pretreated to obtain primary modified carbon nanofibers; the aspect ratio of the carbon nanofibers is 400:1. The initial pretreatment process for carbon nanofibers includes the following steps: Carbon nanofibers were added to a mixed acid solution of nitric acid and sulfuric acid in a volume ratio of 3:1, and the mixed acid solution was heated under reflux at 60°C for 3.1 h. The carbon nanofibers were then removed from the mixed acid solution, washed, and dried at 100°C for 2.5 hours. The concentration of nitric acid is 68%, and the concentration of sulfuric acid is 75%.

[0028] Primary modified carbon nanofibers are mixed in a first mixed salt solution, ultrasonically dispersed, and then freeze-dried to obtain a first mixed fiber material. The first mixed fiber material includes primary modified carbon nanofibers, a first mixed salt coating the surface of the primary modified carbon nanofibers, and a first mixed salt dispersed between the primary modified carbon nanofibers. The first mixed salt includes NaCl and KCl in a molar ratio of 1:1. The preparation process of the first hybrid fiber material includes the following steps: The first mixed salt was added to ethylene glycol, and then the primary modified carbon nanofibers were added to ethylene glycol. Then, the first mixed salt and carbon nanofibers were dispersed into ethylene glycol by ultrasonic dispersion. After ultrasound for 35 minutes, freeze-drying was performed. The freezing temperature is -14℃; the drying temperature after freezing is 10℃. The mass ratio of primary modified carbon nanofibers to the first mixed salt is 1:10.

[0029] Preparation of a first mixture; the first mixture comprises Ti powder and Si powder; the process of preparing the first mixture includes the following steps: Ti powder and Si powder were added to ethylene glycol and the solution temperature was maintained at 25°C by a cold water bath; at the same time, ultrasonic dispersion was performed to obtain the first mixture.

[0030] The first mixed fiber material is added to the first mixed liquid and dispersed, and then dried to obtain the second mixed fiber material; the second mixed fiber material includes primary modified carbon nanofibers, a first mixed salt, Ti powder and Si powder coated on the surface of the primary modified carbon nanofibers and dispersed between the primary modified carbon nanofibers; The second mixed salt comprises NaCl, KCl, and LiF in a molar ratio of 3:1:1; the preparation process of the second mixed fiber material includes the following steps: The first mixed fiber material was added to the first mixed solution, and the solution temperature was maintained at 25°C by a cold water bath; at the same time, ultrasonic dispersion was performed for 23 minutes to obtain the second mixed fiber material. The molar ratio of Ti powder, Si powder, and carbon nanofibers is 3:1.25:2; The mass ratio of carbon nanofibers to the second mixed salt is 1:40.

[0031] After covering the surface of the second mixed fiber material with the second mixed salt, it is heated in stages and then cooled in stages to obtain a mixture of fibrous MAX phase powder and salt. The process of segmented heating after the surface of the second mixed fiber material is coated with the second mixed salt includes the following steps: First stage heating: Increase the temperature to 400℃ at a rate of 7℃ / min, and hold at 400℃ for 0.6h; Second stage heating: Increase the temperature to 815℃ at 3.5℃ / min, and hold at 815℃ for 1.6h; The third stage of heating: the temperature is increased to 940℃ at a rate of 2.4℃ / min, and then held at 940℃ for 1.5 hours; Fourth stage heating: Increase the temperature to 1140℃ at a rate of 1.6℃ / min, and hold at 1140℃ for 2.9 hours; Fifth stage of heating: Increase the temperature to 1280℃ at a rate of 1℃ / min, and hold at 1280℃ for 2.7 hours; The segmented cooling process includes the following steps: After segmented heating, the temperature is reduced from 1280℃ to 600℃ at a rate of 1℃ / min; then it is allowed to cool naturally to room temperature.

[0032] The mixture of fibrous MAX phase powder and salt was washed and dried to obtain fibrous MAX phase powder. The mixture of fibrous MAX phase powder and salt was first washed with deionized water and then dried to obtain fibrous MAX phase powder; the drying temperature was 110℃. The fibrous MAX phase powder has a diameter of 60 nm and a length of 6 μm.

[0033] Example 2: The same content as in Example 1 will not be repeated here; the different aspects of this embodiment compared to Example 1 are as follows: This embodiment provides a method for preparing fibrous MAX phase powder; The initial pretreatment process for carbon nanofibers also includes the following steps: Anhydrous ethanol was placed at 3°C, and then tetrabutyl titanate was added dropwise to the anhydrous ethanol and mixed. Then add acetylacetone and continue stirring for 14 minutes to obtain a clear, light yellow solution; Then, ethanol solution was added dropwise to the transparent light yellow solution while stirring, and the temperature of the transparent light yellow solution was controlled at 8℃; the stirring time was 1.5h. Then add the washed and dried carbon nanofibers, and ultrasonically impregnate for 0.5-1 h. After stopping the ultrasonic impregnation, let it stand for 2 h and then filter under reduced pressure. Then, the carbon nanofibers after vacuum filtration were vacuum dried for 10 hours. Then, an initial pretreatment heating process is performed, which includes: Heat at 120℃ for 1 hour; heat at 246℃ for 1 hour; The mass ratio of tetrabutyl titanate, acetylacetone, and carbon nanofibers is 6.5:4.5:100.

[0034] The aspect ratio of the carbon nanofibers is 380:1; The first mixed salt comprises NaCl and KCl in a molar ratio of 0.85:1; The mass ratio of primary modified carbon nanofibers to the first mixed salt is 1:9.5.

[0035] The second mixed salt comprises NaCl, KCl, and LiF in a molar ratio of 2.9:0.9:0.9; The first mixed fiber material was added to the first mixed solution, and the solution temperature was maintained at 22°C by a cold water bath; at the same time, ultrasonic dispersion was performed for 22 minutes to obtain the second mixed fiber material. The molar ratio of Ti powder, Si powder, and carbon nanofibers is 3:1.22:2; The mass ratio of carbon nanofibers to the second mixed salt is 1:39.

[0036] The process of segmented heating after the surface of the second mixed fiber material is coated with the second mixed salt includes the following steps: First stage heating: Increase the temperature to 450℃ at a rate of 6℃ / min, and hold at 450℃ for 0.8h; Second stage heating: Increase the temperature to 810℃ at 3.2℃ / min, and hold at 810℃ for 1.7h; The third stage of heating: the temperature is increased to 930℃ at a rate of 2.3℃ / min, and then held at 930℃ for 1.6 hours; Fourth stage heating: Increase the temperature to 1130℃ at a rate of 1.55℃ / min, and hold at 1130℃ for 3.0h; Fifth stage of heating: Increase the temperature to 1270℃ at a rate of 0.9℃ / min, and hold at 1270℃ for 2.6 hours; The segmented cooling process includes the following steps: After segmented heating, the temperature was reduced from 1270℃ to 620℃ at a rate of 0.9℃ / min; then it was allowed to cool naturally to room temperature.

[0037] The fibrous MAX phase powder has a diameter of 70 nm and a length of 10 μm.

[0038] Example 3: The same content as in Example 1 will not be repeated here; the different aspects of this embodiment compared to Example 1 are as follows: This embodiment provides a method for preparing fibrous MAX phase powder; The initial pretreatment process for carbon nanofibers also includes the following steps: Anhydrous ethanol was placed at 4°C, and then tetrabutyl titanate was added dropwise to the anhydrous ethanol and mixed. Then add acetylacetone and continue stirring for 18 minutes to obtain a clear, light yellow solution; Then, ethanol solution was added dropwise to the transparent light yellow solution while stirring, and the temperature of the transparent light yellow solution was controlled at 8℃; the stirring time was 1.2h. Then add the washed and dried carbon nanofibers, and ultrasonically impregnate for 0.5-1h. After stopping the ultrasonic impregnation, let it stand for 2.1 hours and then filter under reduced pressure. The carbon nanofibers after vacuum filtration were then vacuum dried for 8.5 hours. Then, an initial pretreatment heating process is performed, which includes: Heating at 122℃ for 0.9 hours; heating at 256℃ for 0.9 hours; The mass ratio of tetrabutyl titanate, acetylacetone, and carbon nanofibers is 7.5:5.5:100.

[0039] Before preparing the first mixture by mixing the primary modified carbon nanofibers in the first mixed salt solution, the primary modified carbon nanofibers are subjected to a second pretreatment. The secondary preprocessing process includes: Paraffin wax was added to acetone and dissolved to obtain a second mixture; the mass ratio of paraffin wax to acetone was 18:800. Then, the primary modified carbon nanofibers were added to the second mixture and ultrasonically dispersed. Then, a second pretreatment heating was performed at a temperature of 63℃ for 0.8 hours to obtain the primary modified carbon nanofibers after the second pretreatment. The mass ratio of paraffin wax to carbon nanofibers is 3.5:100; The preparation process of the second mixed fiber material includes the following steps: The first mixed fiber material was added to the first mixed solution, and the solution temperature was maintained at 22°C by a cold water bath; at the same time, ultrasonic dispersion was performed for 24 minutes. Then, while maintaining ultrasonic dispersion, the solution temperature was adjusted to 63℃ for 0.8 hours to obtain the second mixed fiber material.

[0040] The aspect ratio of the carbon nanofibers is 480:1; The first mixed salt comprises NaCl and KCl in a molar ratio of 1.1:1; The mass ratio of primary modified carbon nanofibers to the first mixed salt is 1:10.5.

[0041] The second mixed salt comprises NaCl, KCl, and LiF in a molar ratio of 3.1:1.1:1.05; The molar ratio of Ti powder, Si powder, and carbon nanofibers is 3:1.28:2; The mass ratio of carbon nanofibers to the second mixed salt is 1:42.

[0042] The process of segmented heating after the surface of the second mixed fiber material is coated with the second mixed salt includes the following steps: First stage heating: Increase the temperature to 480℃ at a rate of 8.5℃ / min, and hold at 480℃ for 0.7h; Second stage heating: Increase the temperature to 780℃ at a rate of 3.8℃ / min, and hold at 780℃ for 1.8 hours; The third stage of heating: the temperature is increased to 910℃ at a rate of 2.5℃ / min, and then held at 910℃ for 2.1 hours; Fourth stage heating: Increase the temperature to 1110℃ at a rate of 1.7℃ / min, and hold at 1110℃ for 3.1 hours; Fifth stage of heating: Increase the temperature to 1260℃ at a rate of 1.2℃ / min, and hold at 1260℃ for 3.8 hours; The segmented cooling process includes the following steps: After segmented heating, the temperature was reduced from 1260℃ to 590℃ at a rate of 1.1℃ / min; then it was allowed to cool naturally to room temperature.

[0043] The fibrous MAX phase powder has a diameter of 80 nm and a length of 14 μm.

[0044] The above description is merely a preferred embodiment of this application and an explanation of the technical principles employed. Those skilled in the art should understand that the scope of the invention involved in this application is not limited to the technical solutions formed by specific combinations of the above-described technical features, but should also cover other technical solutions formed by arbitrary combinations of the above-described technical features or their equivalents without departing from the inventive concept. For example, the above-described features have similar functions to (but are not limited to) those disclosed in this application.

Claims

1. A method for preparing fibrous MAX phase powder, characterized in that, Includes the following steps: The carbon nanofibers were pretreated to obtain primary modified carbon nanofibers. Primary modified carbon nanofibers are mixed in a first mixed salt solution, ultrasonically dispersed, and then freeze-dried to obtain a first mixed fiber material. The first mixed fiber material includes primary modified carbon nanofibers, a first mixed salt coating the surface of the primary modified carbon nanofibers, and a first mixed salt dispersed between the primary modified carbon nanofibers. A first mixture is prepared; the first mixture comprises Ti powder and Si powder; The first mixed fiber material is added to the first mixed liquid and dispersed, and then dried to obtain the second mixed fiber material; the second mixed fiber material includes primary modified carbon nanofibers, a first mixed salt, Ti powder and Si powder coated on the surface of the primary modified carbon nanofibers and dispersed between the primary modified carbon nanofibers; After covering the surface of the second mixed fiber material with the second mixed salt, it is heated in stages and then cooled in stages to obtain a mixture of fibrous MAX phase powder and salt. The fibrous MAX phase powder was washed and dried to obtain the fibrous MAX phase powder.

2. The method for preparing fibrous MAX phase powder according to claim 1, characterized in that, The initial pretreatment process for carbon nanofibers includes the following steps: Carbon nanofibers were added to a mixed acid solution of nitric acid and sulfuric acid in a volume ratio of 2.5-3.5:1, and the mixed acid solution was heated under reflux at 55-65℃ for 1.8-2.5 hours. Then the carbon nanofibers were removed from the mixed acid solution, washed and dried at a temperature of 98-110℃ for 2-3 hours. The concentration of nitric acid is 66-70%, and the concentration of sulfuric acid is 70-80%.

3. The method for preparing fibrous MAX phase powder according to claim 2, characterized in that, The initial pretreatment process for carbon nanofibers also includes the following steps: Place anhydrous ethanol at 0-5°C, then add tetrabutyl titanate dropwise to the anhydrous ethanol and mix. Then add acetylacetone and continue stirring for 8-20 minutes to obtain a clear, light yellow solution; Then, add ethanol solution dropwise to the transparent light yellow solution and stir, controlling the temperature of the transparent light yellow solution at 5-10℃; the stirring time is 1-2 hours. Then add the washed and dried carbon nanofibers, and ultrasonically impregnate for 0.5-1 h. After stopping the ultrasonic impregnation, let it stand for 1.8-2.2 h and then filter under reduced pressure. Then, the carbon nanofibers after vacuum filtration are vacuum dried for ≥8 hours. Then, an initial pretreatment heating process is performed, which includes: Heat at 115-125℃ for 0.8-1.2 hours; Heat at 235-260℃ for 0.8-1.2 hours; The mass ratio of tetrabutyl titanate, acetylacetone, and carbon nanofibers is (5-8):(3-6):

100.

4. The method for preparing fibrous MAX phase powder according to claim 1, characterized in that, The first mixed salt comprises NaCl and KCl in a molar ratio of (0.8-1.2):1; The second mixed salt comprises NaCl, KCl, and LiF in a molar ratio of (2.8-3.2):(0.8-1.2):(0.8-1.2); and / or The molar ratio of Ti powder, Si powder, and carbon nanofibers is 3:(1.2-1.3):2; The mass ratio of carbon nanofibers to the second mixed salt is 1:(38-43).

5. The method for preparing fibrous MAX phase powder according to claim 1, characterized in that, The preparation process of the first hybrid fiber material includes the following steps: The first mixed salt was added to ethylene glycol, and then the primary modified carbon nanofibers were added to ethylene glycol. Then, the first mixed salt and carbon nanofibers were dispersed into ethylene glycol by ultrasonic dispersion. After ultrasound for 20-50 minutes, freeze-drying is then performed. Freezing temperature is -15 to -13℃; drying temperature after freezing is 0-20℃; The mass ratio of primary modified carbon nanofibers to the first mixed salt is 1:(9-11).

6. The method for preparing fibrous MAX phase powder according to claim 1, characterized in that, The process of preparing the first mixture includes the following steps: Ti powder and Si powder were added to ethylene glycol and the solution temperature was maintained at 20-30℃ by a cold water bath; at the same time, ultrasonic dispersion was performed to obtain the first mixture.

7. The method for preparing fibrous MAX phase powder according to claim 1, characterized in that, The preparation process of the second hybrid fiber material includes the following steps: The first mixed fiber material is added to the first mixed solution, and the solution temperature is maintained at 20-30℃ by a cold water bath; at the same time, ultrasonic dispersion is performed for 20-25 minutes to obtain the second mixed fiber material.

8. The method for preparing fibrous MAX phase powder according to claim 1, characterized in that, The process of segmented heating after the surface of the second mixed fiber material is coated with the second mixed salt includes the following steps: First stage of heating: Increase the temperature to 300-500℃ at a rate of 5-9℃ / min, and hold at 300-500℃ for 0.5-1h; Second stage heating: Increase the temperature to 770-820℃ at a rate of 3-4℃ / min, and hold at 770-820℃ for 1.4-2 hours; The third stage of heating: the temperature is increased to 900-950℃ at a rate of 2.2-2.6℃ / min, and then held at 900-950℃ for 1.2-2.2 hours; Fourth stage heating: Increase the temperature to 1100-1150℃ at a rate of 1.5-1.8℃ / min, and hold at 1100-1150℃ for 2.8-3.2 hours; Fifth stage of heating: Increase the temperature to 1250-1300℃ at a rate of 0.8-1.3℃ / min, and hold at 1250-1300℃ for 2.5-4 hours; and / or The segmented cooling process includes the following steps: After segmented heating, the temperature is reduced from 1250-1300℃ to 580-650℃ at a rate of 0.8-1.2℃ / min. Then allow it to cool naturally to room temperature.

9. The method for preparing fibrous MAX phase powder according to claim 1, characterized in that, Before preparing the first mixture by mixing the primary modified carbon nanofibers in the first mixed salt solution, the primary modified carbon nanofibers are subjected to a second pretreatment. The secondary preprocessing process includes: Paraffin wax was added to acetone and dissolved to obtain a second mixture; the mass ratio of paraffin wax to acetone was 18:(785-820). Then, the primary modified carbon nanofibers were added to the second mixture and ultrasonically dispersed. Then, a second pretreatment heating is performed at a temperature of 60-65℃ for 0.5-1h to obtain the primary modified carbon nanofibers after the second pretreatment. The mass ratio of paraffin wax to carbon nanofibers is (2-5):100; The preparation process of the second mixed fiber material includes the following steps: The first mixed fiber material is added to the first mixed solution, and the solution temperature is maintained at 20-30℃ by a cold water bath; at the same time, ultrasonic dispersion is performed for 20-25 minutes. Then, while maintaining ultrasonic dispersion, the solution temperature is adjusted to 60-65℃ and heated for 0.5-1h to obtain the second mixed fiber material.

10. The method for preparing fibrous MAX phase powder according to claim 1, characterized in that, The mixture of fibrous MAX phase powder and salt is first washed with deionized water and then dried to obtain fibrous MAX phase powder; the drying temperature is 100-120℃. and / or The fibrous MAX phase powder has a diameter of 50-100 nm and a length of 5-15 μm.

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