Preparation method of aluminum nitride coated silicon carbide composite ceramic whisker and product thereof

Abstract

The application discloses a preparation method of aluminum nitride coated silicon carbide composite ceramic whisker and a product thereof. Alumina, silicon oxide, carbon black and ice crystal as a whisker forming agent are used as raw materials, the slurry is uniformly mixed through ball milling, the mixed slurry is dried in a drying box, a mixed powder containing aluminum nitride coated silicon carbide composite ceramic whisker and carbon is prepared through a carbothermic reduction reaction, and finally, AlN coated SiC whisker is obtained by removing the excess carbon. The composite ceramic whisker prepared by the method is obtained by synthesizing SiC whisker and coating AlN on the surface of the whisker in one step, AlN coated SiC composite ceramic whisker is formed, SiC is used as a core, and AlN is used as a shell, the length of the final product is 20-200 mu m, the diameter is 0.8-2.5 mu m, and the length-diameter ratio is 40-150.

Description

Technical Field

[0001] This invention belongs to the field of ceramic composite material preparation technology, and provides a method for preparing aluminum nitride-coated silicon carbide composite ceramic whiskers and the product thereof. Background Technology

[0002] One-dimensional silicon carbide (SiC) nanomaterials (such as SiC whiskers, microstructures, and nanowires (NW)) possess excellent structural and functional properties, including wide bandgap, high thermal conductivity, and good mechanical strength. Furthermore, one-dimensional SiC nanomaterials can also be used to prepare ceramic matrix composites. Due to grain refinement and whisker / fiber toughening mechanisms, such as crack deflection, grain pull-out, and whisker bridging, the fracture strength, Vickers hardness, and fracture toughness of ceramic matrix composites can all be improved. In the preparation of aluminum nitride ceramics, AlN-coated SiCw composites offer advantages such as increased interfacial bonding and thermal conductivity, making them a promising candidate for high-strength, high-heat-dissipation ceramic substrates used in high-performance power modules.

[0003] For the synthesis of SiC whiskers, there are currently various catalytic growth-based preparation methods, including chemical vapor deposition, laser ablation, growth from carbon nanotube templates, and arc discharge. However, the industrialization of these methods still faces obstacles, such as the use of expensive material precursors, costly proprietary equipment, and low yields. Meanwhile, the carbothermic reduction (CR) of silica and alumina to prepare silicon carbide and aluminum nitride powder particles has been industrialized on a large scale, with relatively mature processes and equipment. Patent CN201710875873.0 discloses a process for synthesizing AlN-SiC solid solution whiskers on the surface of a preform using Al4SiC4 powder and nano-nickel powder as raw materials, pressed into shape, and then using nitrogen as the nitrogen source. This method can prepare AlN-SiC solid solution whiskers, but the synthesized whiskers are generated on the surface of the preform and are a solid solution product of a uniform mixture of AlN and SiC.

[0004] Currently, there is no publicly available research on aluminum nitride coating on the surface of silicon carbide whiskers. This invention uses ultrafine alumina and silicon oxide as raw materials and cryolite as a whisker generating agent. By controlling the carbothermal reduction synthesis process, a new process method for aluminum nitride coating silicon carbide composite ceramic whiskers is obtained, which is convenient to obtain raw powder, simple in process, and produces a large number of whiskers. Summary of the Invention

[0005] The purpose of this invention is to provide a method for preparing aluminum nitride-coated silicon carbide composite ceramic whiskers and the resulting product, addressing the limitations of existing synthesis processes.

[0006] The present invention adopts the following technical solution:

[0007] In a first aspect, the present invention provides a method for preparing aluminum nitride-coated silicon carbide composite ceramic whiskers, the method comprising the following steps:

[0008] Silica, alumina, carbon black, and a whisker-forming agent were added to a ball mill jar, and deionized water was used as the dispersion medium. The mixture was ball-milled until homogeneous to obtain a viscous slurry A. The whisker-forming agent was cryolite (Na3AlF6).

[0009] The viscous slurry A is placed in a drying oven and dried to obtain the mixed powder B;

[0010] Mixed powder B is placed in a graphite sintering furnace and synthesized by carbothermic reduction under flowing nitrogen to obtain nitrided powder C;

[0011] The nitrided powder C is placed in a high-temperature box furnace to remove excess carbon, resulting in aluminum nitride-coated silicon carbide composite ceramic whiskers.

[0012] Preferably, the median diameter of the alumina is 20 nm to 1 nm. m, the median diameter of the silicon oxide is 10 nm to 1 m. m, wherein the median diameter of the carbon black is 10–100 nm.

[0013] Preferably, the mass ratio of silicon oxide, aluminum oxide, carbon black and whisker-forming agent is 100:(20-50):(120-160):(5-100).

[0014] Preferably, the ball milling speed is 100-250 r / min and the ball milling time is 2-8 h.

[0015] Preferably, the drying temperature of the viscous mixed slurry A is 70-100°C.

[0016] Preferably, the carbothermic reduction synthesis temperature is 1500–1600℃, and the synthesis time is 2–8 h; wherein the heating rate from 1200℃ to the synthesis temperature is 2–8℃ / min.

[0017] Preferably, the reaction conditions of the high-temperature box furnace are to maintain a temperature of 600-700°C in dry air for 4-8 hours.

[0018] Secondly, the present invention provides aluminum nitride-coated silicon carbide composite ceramic whiskers.

[0019] The composite ceramic whiskers consist of SiC whiskers as the core, with AlN coated on the surface of the SiC whiskers in the form of particles or thin films.

[0020] The composite ceramic whiskers have a whisker length of 20–200 μm, a diameter of 0.8–2.5 μm, and an aspect ratio of 40–150.

[0021] Compared with the prior art, the present invention has the following advantages:

[0022] (1) Compared with other processes for preparing AlN-SiC solid solutions with various forms such as whiskers by adding Al powder, Si3N4, Al2O3 raw powder, the present invention uses Al2O3 and SiO2 as raw powders, and introduces cryolite as a generating agent to generate O'sialon and β-sialon intermediate phases at low temperature. Then, the intermediate phases cause AlN to be generated in situ on the surface of SiC whiskers to form a coating, and the two have a tight bond.

[0023] (2) In this invention, cryolite (Na3AlF6) is introduced as a generating agent for composite ceramic whiskers. Firstly, it can provide the CO or carbon vapor necessary for the synthesis of SiC at a lower temperature, thereby enabling the generation of SiC whiskers at a lower temperature. Secondly, the AlF3 decomposed by cryolite at high temperature can also provide an additional aluminum source for the reaction.

[0024] (3) Current research on whiskers mainly focuses on single SiC or AlN whiskers. The composite ceramic whiskers prepared in this invention are synthesized by simultaneously coating AlN onto the surface of SiC whiskers in one step, forming AlN-coated SiC composite ceramic whiskers with SiC as the core and AlN as the shell. This is unprecedented in the current field. The AlN-SiC composite ceramic whiskers combine the unique properties of SiC whiskers and AlN, and are used to prepare aluminum nitride ceramic matrix composites. While having high thermal conductivity and insulation, they provide a fully compatible AlN bonding interface, which is beneficial for enhancing and toughening the product. Attached Figure Description

[0025] Figure 1 This is a morphology diagram of the synthesized powder in Example 1.

[0026] Figure 2 This is a morphology diagram of the synthesized powder in Example 2.

[0027] Figure 3 These are morphology images of the synthesized powder in Example 3, where (a) shows the specific morphology of the whiskers under high magnification, and (b) shows the distribution morphology of the whiskers under low magnification.

[0028] Figure 4 These are the energy dispersive spectroscopy (EDS) spectra of the composite ceramic whiskers in the synthesized powder in Example 3, where (a) is the morphology of the composite ceramic whiskers in Example 3, (b) represents Al, (c) represents N, (d) represents Si, and (e) represents C.

[0029] Figure 5 This is a morphology diagram of the synthesized powder in Example 4.

[0030] Figure 6This is a morphology diagram of the synthesized powder in Comparative Example 1.

[0031] Figure 7 This is a morphology diagram of the synthesized powder in Comparative Example 2.

[0032] Figure 8 These are XRD patterns of the synthesized powders from Examples 1, 2, 3, 4 and Comparative Example 1. Detailed Implementation

[0033] As mentioned above, in view of the shortcomings of the prior art, the inventors of this case, through long-term research and extensive practice, have proposed the technical solution of this invention, which includes at least: (1) using Al2O3 and SiO2 as raw powders, and introducing cryolite as a generating agent to generate O'sialon and β-sialon intermediate phases at low temperature, and then using the intermediate phase to generate AlN in situ on the surface of SiC whiskers to form a coating, with a tight bond between the two. (2) Cryolite (Na3AlF6) as a whisker generating agent can provide the CO or carbon vapor necessary for the synthesis of SiC at a lower temperature, thereby enabling the generation of SiC whiskers at a lower temperature; secondly, the AlF3 decomposed by cryolite at high temperature can also provide an additional aluminum source for the reaction.

[0034] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0035] At least one embodiment provides an aluminum nitride-coated silicon carbide composite ceramic whisker, which consists of a SiC whisker as the core, with AlN coated on the surface of the SiC whisker in the form of particles or a thin film. The composite ceramic whisker has a whisker length of 20–200 μm, a diameter of 0.8–2.5 μm, and an aspect ratio of 40–150.

[0036] Meanwhile, a method for preparing the aforementioned aluminum nitride-coated silicon carbide composite ceramic whiskers is also provided. The method uses alumina, silicon oxide, carbon black, and cryolite as raw materials. The slurry is mixed evenly by ball milling. The mixed slurry is then dried in a drying oven and then subjected to a carbothermal reduction reaction to obtain a mixed powder containing aluminum nitride-coated silicon carbide composite ceramic whiskers and carbon. Finally, excess carbon is removed to obtain AlN-coated SiC composite ceramic whiskers.

[0037] Specifically, the method includes the following steps:

[0038] Step (1): Add silicon dioxide, aluminum oxide, carbon black, and whisker-forming agent into a ball mill jar, use deionized water as the dispersion medium, and mix evenly by ball milling to obtain a viscous mixed slurry A; the whisker-forming agent is cryolite (Na3AlF6).

[0039] Step (2): Place the viscous mixed slurry A into a drying oven and dry it to obtain mixed powder B;

[0040] Step (3): The mixed powder B is placed in a graphite sintering furnace and synthesized by carbothermic reduction under flowing nitrogen to obtain nitrided powder C;

[0041] Step (4): Place the nitrided powder C into a high-temperature box furnace to remove excess carbon and obtain aluminum nitride coated silicon carbide composite ceramic whiskers.

[0042] in:

[0043] As an example, the alumina mentioned in step (1) is at least one of nano-sized alumina powder and submicron-sized alumina powder, wherein the alumina diameter is 20 nm to 1 nm. m, preferably 20-100 nm.

[0044] As an example, the silicon oxide mentioned in step (1) is nano-silicon oxide with a midpoint diameter of 10 nm to 1 nm. m, preferably 10 to 100 nm.

[0045] As an example, the carbon black in step (1) is an ultrafine powder with a midpoint diameter of 10 to 100 nm.

[0046] As an example, the mass ratio of silicon oxide, aluminum oxide, carbon black and whisker generating agent in step (1) is 100: (20-50): (120-160): (5-100).

[0047] As an example, the ball milling speed in step (1) is 100-250 r / min and the ball milling time is 2-8 h, preferably the ball milling speed is 100-160 r / min and the ball milling time is 2-4 h.

[0048] As an example, the drying temperature of the viscous mixed slurry A in step (2) is 70 to 100°C, preferably 70°C.

[0049] As an example, the carbothermic reduction synthesis temperature in step (3) is 1500-1600℃, the synthesis time is 2-8h, preferably 4-8h, and the heating rate from 1200℃ to the synthesis temperature is 2-8℃ / min, preferably 6℃ / min.

[0050] This invention employs a gradient heating process to decompose cryolite in stages: in the low-temperature stage (<1200℃), active fluorine ions are released, which corrode the SiO2 / Al2O3 surface to enhance the reactivity; in the medium-temperature stage (1200~1500℃), liquid O'sialon is generated to promote the axial growth of whiskers; and in the high-temperature stage (1500~1600℃), aluminum is provided through the decomposition of AlF3, which drives AlN to coat SiC whiskers in the form of particles / films, forming a "SiC core-AlN shell" heterostructure, breaking through the limitation of uniform mixing of existing solid solution whiskers.

[0051] As an example, the reaction conditions of the high-temperature box furnace in step (4) are to keep it at 600-700°C in dry air for 4-8 hours.

[0052] This invention employs a low-temperature decarbonization process (≤700℃) to avoid high-temperature oxidation damage to whiskers. Combined with a catalyst-free process throughout, it achieves compatibility with traditional ceramic powder preparation equipment, reduces raw material costs, and improves product purity.

[0053] The embodiments of the present invention will be described in detail below with reference to specific examples. However, those skilled in the art will understand that the following examples are for illustrative purposes only and should not be considered as limiting the scope of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention. Unless otherwise specified, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all commercially available conventional products.

[0054] It should be noted that:

[0055] Unless otherwise specified, all embodiments and preferred embodiments mentioned herein can be combined to form new technical solutions.

[0056] Unless otherwise specified, all the technical features and preferred features mentioned herein can be combined to form new technical solutions.

[0057] In this invention, unless otherwise specified, percentage (%) or parts refer to weight percentage or parts relative to the composition.

[0058] Unless otherwise specified, the components or preferred components involved in this invention can be combined with each other to form new technical solutions.

[0059] In this invention, unless otherwise stated, the "scope" disclosed herein may take the form of a lower limit and an upper limit, and may be one or more lower limits and one or more upper limits, respectively.

[0060] In this invention, unless otherwise stated, the various reactions or operation steps may be performed sequentially or in a particular order. Preferably, the reaction methods described herein are performed sequentially.

[0061] Unless otherwise stated, the technical and scientific terms used herein have the same meanings as those familiar to those skilled in the art. Furthermore, any methods or materials similar to or equivalent to those described herein may also be used in this invention.

[0062] Example 1

[0063] First, a certain amount of alumina (particle size 13nm), silicon dioxide (particle size 14nm), carbon black (particle size 18nm), and cryolite (whisker generating agent) were weighed out in a mass ratio of 100:20:150:5. All the powders were placed in a ball mill jar and milled at 100 r / min for 8 hours to obtain a uniformly mixed viscous slurry. Next, the slurry and milling beads were separated through a sieve. The slurry separated from the milling beads was placed in a 70℃ oven to dry, obtaining a dry mixed powder. The powder was then placed in a graphite sintering furnace, and under a flowing nitrogen atmosphere, the heating rate was controlled at 2℃ / min between 1200 and 1600℃, followed by calcination at 1600℃ for 4 hours to obtain a mixed product. The product was then placed in a box furnace and held at 600℃ for 8 hours to remove carbon, finally obtaining aluminum nitride-coated silicon carbide composite ceramic whiskers. The microstructure and images of the obtained products were observed using scanning electron microscopy, as shown in the attached figures. Figure 1 As shown, tightly wrapped AlN particles were observed on the SiC whiskers. The composite ceramic whiskers were approximately 40–50 μm long, relatively thin, with a diameter between 1 and 1.5 μm, and an aspect ratio of approximately 40.

[0064] Example 2

[0065] First, a certain amount of alumina (particle size 13nm), silicon dioxide (particle size 14nm), carbon black (particle size 18nm), and cryolite (whisker generating agent) were weighed out in a mass ratio of 100:30:150:60. All the powders were placed in a ball mill jar and milled at 250 r / min for 2 hours to obtain a uniformly mixed viscous slurry. Next, the slurry and milling beads were separated through a sieve. The slurry separated from the milling beads was placed in a 70℃ oven to dry, obtaining a dry mixed powder. The powder was then placed in a graphite sintering furnace, and under a flowing nitrogen atmosphere, the temperature was first controlled at a rate of 8℃ / min between 1200 and 1600℃, and then calcined at 1600℃ for 4 hours to obtain a mixed product. The product was then placed in a box furnace and held at 680℃ for 6 hours to remove carbon, finally obtaining aluminum nitride-coated silicon carbide composite ceramic whiskers. The microstructure and image analysis of the obtained products were observed using scanning electron microscopy, as shown in the attached figure. Figure 2As shown, tightly wrapped AlN particles were observed on the SiC whiskers, with lengths ranging from 30 to 200 μm, thicknesses ranging from 0.8 to 1.2 μm, and aspect ratios ranging from 40 to 150.

[0066] Example 3

[0067] First, a certain amount of alumina (particle size 13nm), silicon dioxide (particle size 14nm), carbon black (particle size 18nm), and cryolite (whisker generating agent) were weighed out in a mass ratio of 100:30:150:100. All the powders were placed in a ball mill jar and milled at 120 r / min for 4 hours to obtain a uniformly mixed viscous slurry. Next, the slurry and milling beads were separated through a sieve. The slurry separated from the milling beads was placed in a 70℃ oven to dry, obtaining a dry mixed powder. Then, the powder was placed in a graphite sintering furnace, and under a flowing nitrogen atmosphere, the heating rate was controlled at 6℃ / min between 1200 and 1600℃, followed by calcination at 1600℃ for 4 hours to obtain a mixed product. Finally, the product was placed in a box furnace and held at 680℃ for 6 hours to remove carbon, ultimately obtaining aluminum nitride-coated silicon carbide composite ceramic whiskers. The microstructure and image analysis of the obtained products were observed using scanning electron microscopy, X-ray diffraction, and energy dispersive spectroscopy (EDS), respectively. (See attached image.) Figure 3 (a) Figure 3 As shown in (b), tightly wrapped AlN particles were observed on the SiC whiskers. The composite ceramic whiskers were uniformly distributed and relatively densely packed. The product contained a large number of whiskers with lengths ranging from 30 to 200 μm and thicknesses from 0.5 to 2.5 μm, with aspect ratios from 40 to 150. The product contained both AlN and SiC. (See attached image) Figure 4 (a) Figure 4 As shown in (e), the core of the whisker in the energy spectrum is mainly composed of silicon and carbon, while the particles covering the surface of the whisker are mainly composed of aluminum and nitrogen, indicating that the whisker structure has SiC as the core and AlN as the shell.

[0068] Example 4

[0069] First, a certain amount of alumina (particle size 13nm), silicon dioxide (particle size 14nm), carbon black (particle size 18nm), and cryolite (whisker generating agent) were weighed out in a mass ratio of 100:50:150:100. All the powders were placed in a ball mill jar and milled at 120 r / min for 4 hours to obtain a uniformly mixed viscous slurry. Next, the slurry and milling beads were separated through a sieve. The slurry separated from the milling beads was placed in a 70℃ oven to dry, obtaining a dry mixed powder. Then, the powder was placed in a graphite sintering furnace, and under a flowing nitrogen atmosphere, the heating rate was controlled at 2℃ / min between 1200 and 1500℃, followed by calcination at 1500℃ for 8 hours to obtain a mixed product. Finally, the product was placed in a box furnace and held at 700℃ for 4 hours to remove carbon, ultimately obtaining aluminum nitride-coated silicon carbide composite ceramic whiskers. The microstructure and image analysis of the obtained products were observed using scanning electron microscopy, as shown in the attached figure. Figure 5 As shown, tightly wrapped AlN particles were observed on the SiC whiskers. The composite ceramic whiskers ranged in length from 50 to 200 μm, in thickness from 0.5 to 1.5 μm, and in aspect ratio from 40 to 150.

[0070] Comparative Example 1

[0071] First, a certain amount of alumina (particle size 13nm), silicon dioxide (particle size 14nm), and carbon black (particle size 18nm) were weighed out in a mass ratio of 100:30:150. All the powders were loaded into a ball mill jar and milled in a planetary ball mill at 120 r / min for 4 hours to obtain a uniformly mixed viscous slurry. Next, the slurry and milling beads were separated through a sieve. The slurry separated from the milling beads was placed in a 70℃ oven to dry, obtaining a dry mixed powder. The powder was then placed in a graphite sintering furnace, and under a flowing nitrogen atmosphere, the temperature was first controlled at a rate of 6℃ / min between 1200 and 1600℃, and then calcined at 1600℃ for 4 hours to obtain a mixed product. The product was then placed in a box furnace and held at 680℃ for 6 hours to remove carbon, finally obtaining a mixed powder. The microstructure and image analysis of the obtained product were observed using a scanning electron microscope, as shown in the attached figure. Figure 6 As shown, the product is mainly composed of particles, with no whiskers present.

[0072] Figure 8 These are XRD patterns of the synthesized powders from Examples 1, 2, 3, 4 and Comparative Example 1.

[0073] Comparative Example 2

[0074] First, weigh out a certain amount of alumina (particle size 13nm), silicon dioxide (particle size 14nm), carbon black (particle size 18nm), and cryolite (whisker generating agent) in a mass ratio of 100:50:150:160. Place all the powders into a ball mill jar and mill at 120 rpm for 4 hours to obtain a uniformly mixed viscous slurry. Next, separate the slurry and milling beads through a sieve. Place the slurry separated from the milling beads in a 70℃ oven to dry the moisture, obtaining a dry mixed powder. Then, place the powder in a graphite sintering furnace and, under a flowing nitrogen atmosphere, first control the heating rate between 1200 and 1600℃ at 4℃ / min, then calcine at 1600℃ for 4 hours to obtain a mixed product. Finally, place the product in a box furnace and hold at 680℃ for 6 hours to remove carbon, ultimately obtaining a mixed powder. The microstructure and image analysis of the obtained products were observed using scanning electron microscopy, as shown in the attached figure. Figure 7 As shown, the product is mainly composed of large spherical particles, with only a very small number of whiskers.

[0075] The results above show that, compared with no whisker-forming agent or excessive whisker-forming agent, adding an appropriate amount of whisker-forming agent is the only source of promoting whisker synthesis, and a suitable ratio is required. Within a suitable range, the final synthesized aluminum nitride-coated silicon carbide composite ceramic whiskers increase with the increase of the whisker-forming agent content.

[0076] The above embodiments are not intended to limit the present invention, and the present invention is not limited to the above embodiments. Any embodiment that meets the requirements of the present invention is within the protection scope of the present invention.

Claims

1. A method for preparing aluminum nitride-coated silicon carbide composite ceramic whiskers, characterized by, The method comprises the following steps: Silicon oxide, aluminum oxide, carbon black and whisker forming agent are added into a ball mill tank, and deionized water is used as a dispersion medium to uniformly mix the materials by ball milling to obtain a viscous mixed slurry A; the whisker forming agent is ice crystal; the mass ratio of the silicon oxide, aluminum oxide, carbon black and whisker forming agent is 100: (20-50): (120-160): (5-100); The viscous mixed slurry A is placed into a drying box for drying to obtain a mixed powder B; The mixed powder B is placed into a graphite sintering furnace for carbonthermal reduction synthesis under flowing nitrogen to obtain a nitrided powder C; The nitrided powder C is placed into a high-temperature box furnace to remove excess carbon to obtain an aluminum nitride-coated silicon carbide composite ceramic whisker.

2. The method of claim 1, wherein, The median diameter of the alumina is 20 nm to 1 m, the median diameter of the silica is 10 nm to 1 m, the median diameter of the carbon black is 10 to 100 nm.

3. The method of claim 1, wherein, The rotation speed of the ball milling is 100-250 r / min, and the ball milling time is 2-8 h.

4. The method of claim 1, wherein, The drying temperature of the viscous mixed slurry A is 70-100℃.

5. The method of claim 1, wherein, The carbonthermal reduction synthesis temperature is 1500-1600℃, and the synthesis time is 2-8 h; the temperature rising rate from 1200℃ to the synthesis temperature is 2-8℃ / min.

6. The method of claim 1, wherein, The reaction condition of the high-temperature box furnace is that the temperature is kept at 600-700℃ for 4-8 h in dry air.

7. An aluminum nitride-coated silicon carbide composite ceramic whisker, characterized by, The method is prepared by any one of claims 1-6.

8. The aluminum nitride coated silicon carbide composite ceramic whisker of claim 7, wherein, The composite ceramic whisker is a SiC whisker as a core, and AlN is coated on the surface of the SiC whisker in the form of particles or a film.

9. The aluminum nitride coated silicon carbide composite ceramic whisker of claim 7 or 8, wherein, The length of the composite ceramic whisker is 20-200 μm, the diameter is 0.8-2.5 μm, and the length-diameter ratio is 40-150.

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