CN114059195B - Method for preparing aluminum nitride fibers by using graphite felt - Google Patents

Method for preparing aluminum nitride fibers by using graphite felt Download PDF

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CN114059195B
CN114059195B CN202111349066.8A CN202111349066A CN114059195B CN 114059195 B CN114059195 B CN 114059195B CN 202111349066 A CN202111349066 A CN 202111349066A CN 114059195 B CN114059195 B CN 114059195B
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aluminum nitride
graphite felt
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graphite
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CN114059195A (en
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王�琦
郝旭
万诗琴
曹文斌
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University of Science and Technology Beijing USTB
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    • D06M11/00—Treating fibres, threads, yarns, fabrics or fibrous goods made from such materials, with inorganic substances or complexes thereof; Such treatment combined with mechanical treatment, e.g. mercerising
    • D06M11/58—Treating fibres, threads, yarns, fabrics or fibrous goods made from such materials, with inorganic substances or complexes thereof; Such treatment combined with mechanical treatment, e.g. mercerising with nitrogen or compounds thereof, e.g. with nitrides
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    • D06M2101/40—Fibres of carbon

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Abstract

The invention discloses a method for preparing aluminum nitride fibers by using graphite felt, belonging to the field of ceramic material synthesis. The preparation method comprises the following specific steps: dissolving a certain mass of alumina powder in deionized water or absolute ethyl alcohol to prepare uniform alumina slurry, then immersing a graphite felt in the alumina slurry, and drying in vacuum to obtain the graphite felt containing alumina inside. And placing the prepared reaction precursor in a graphite sintering furnace, and carrying out carbothermic reduction reaction in nitrogen atmosphere at the reaction temperature of 1500-1900 ℃ for 0.5-6 h, wherein 0.1-2L/min of nitrogen is introduced in the reaction process until the reaction is finished. The graphite felt with aluminum nitride fibers grown on the surface can then be obtained. Collecting the fibers, placing the fibers in a muffle furnace, preserving the heat for 1 to 5 hours at the temperature of between 600 and 750 ℃ to remove carbon, and obtaining a white cotton-like product, namely the aluminum nitride fibers. The aluminum nitride fiber prepared by the method has high purity, large length-diameter ratio, simple process method and low raw material cost, and has wide application prospect in the field of ceramic fiber reinforcement and thermal interface materials.

Description

Method for preparing aluminum nitride fibers by using graphite felt
Technical Field
The invention relates to a method for preparing aluminum nitride fibers by using graphite felt, belonging to the technical field of ceramic material preparation.
Background
Aluminum nitride is a ceramic material with excellent comprehensive performance, the thermal conductivity of the aluminum nitride is as high as 320W/mK, and meanwhile, the aluminum nitride has a series of excellent characteristics of good electrical insulation, low dielectric constant and dielectric loss, thermal expansion coefficient matched with silicon and the like, and is considered to be one of the most ideal substrate materials and electronic device packaging materials at present. The aluminum nitride fiber has the excellent characteristics of aluminum nitride materials and fiber materials, can greatly improve the mechanical property and the thermal property of the composite material when used as a reinforcing material, and can also greatly improve the thermal conductivity of the heat-conducting composite material when used as a filler. The aluminum nitride fiber has wide application prospect in the fields of electronics, metallurgy and aerospace.
The invention patent (publication No. CN98103408. X) uses microcrystalline aluminum silicate fiber with sillimanite structure and carbon black as raw materials, and heats and preserves heat in nitrogen atmosphere to obtain aluminum nitride fiber, but because the aluminum silicate in the raw materials contains SiO2Resulting in the reaction product containing SiC to reduce the purity of the aluminum nitride fiber.
The invention discloses a preparation method of cubic phase aluminum nitride fiber (publication number: CN 104211025A), anhydrous aluminum chloride and tetrabutyl ammonium azide are dissolved in xylene, then a template agent is added, the mixture is transferred to a high-temperature reaction kettle to carry out solvothermal reaction, and the cubic phase aluminum nitride fiber is obtained after centrifugation, drying and calcination. The organic precursor method has complex process and high cost, and is difficult to be widely applied.
The invention patent (publication No. CN 104213252A) uses carbon fiber, aluminum inorganic salt, ammonia water solution and the like as raw materials to prepare aluminum-containing carbon fiber gel, and then the aluminum nitride fiber is obtained by heat preservation in a flowing nitrogen atmosphere. The method has high raw material cost and complex process, and is difficult to realize industrial production.
The invention content is as follows:
the invention provides a novel method for preparing aluminum nitride fibers by utilizing graphite felts and adopting a carbothermic reduction technology, aiming at the problems of the existing aluminum nitride fibers.
A method for preparing aluminum nitride fibers comprises the following steps:
(1) Preparing materials: adding alumina powder into deionized water or alcohol, and ball-milling for a certain time to obtain uniform alumina slurry.
(2) Preparing a reaction precursor: cutting the graphite felt into a proper size, completely immersing the graphite felt in the alumina slurry obtained in the step (1), transferring the graphite felt to a vacuum drying oven, soaking the graphite felt for 1 to 4 hours at room temperature, and heating to 80 ℃ for vacuum drying for 6 to 12 hours to obtain the graphite felt containing alumina inside.
(3) Synthesizing: and (3) placing the graphite felt precursor obtained in the step (2) in a graphite crucible, transferring the graphite felt precursor to a graphite sintering furnace, continuously introducing flowing nitrogen, heating to 1500-1900 ℃, preserving the temperature until the total reaction time reaches 0.5-6 h, and ending the reaction to obtain the graphite felt with the aluminum nitride fibers growing on the surface.
(4) Carbon discharge: and (4) collecting the aluminum nitride fibers obtained by the reaction in the step (3), placing the aluminum nitride fibers in a muffle furnace, heating to 600-750 ℃, and preserving heat for 1-5 hours to remove carbon impurities contained in reaction products, wherein the finally obtained off-white cotton-like product is the aluminum nitride fibers.
Further, the alumina powder in the step (1) is alpha-Al2O3Or gamma-Al2O3The average particle size is 0.1 to 2 μm.
Further, the solid content of the alumina slurry in the step (1) is 5wt% to 30wt%.
Further, the ball milling time for preparing the alumina slurry in the step (1) is 4-12 h.
Further, the graphite felt used in the step (2) is an asphalt-based graphite felt, a polyacrylonitrile-based (PAN-based) graphite felt or a viscose-based graphite felt.
Further, when the graphite felt prepared in the step (2) reacts with the precursor, the weight ratio of the alumina to the graphite felt is as follows: 0.1 to 1.
Further, the temperature rise rate of the sintering furnace in the step (3) is 10-100 ℃/min.
Further, in the step (3), nitrogen gas is introduced into the reaction furnace at a flow rate of 0.1 to 2L/min.
The alumina powder in the step (1) is alpha-Al2O3Or gamma-Al2O3The average particle size is 0.1 to 2 μm.
The carbothermal reduction nitridation method is the most commonly used method for preparing aluminum nitride powder, and the total reaction formula is as follows:
Al2O3(s)+3C(s)+N2(g)→2AlN(s)+3CO(g) (1)
the carbothermic reduction reaction proceeds by a solid-solid diffusion reaction mechanism according to formula (1), and a gas phase reaction mechanism, i.e., al, may occur under certain conditions2O3First reduced by C to produce Al2O、Al2O2Waiting for the gaseous compounds, and subsequently reacting these with N2A nitriding reaction occurs to produce aluminum nitride. The aluminum nitride fiber is generally generated by a gas-solid mechanism (VS) on the premise of low supersaturation degree, so that the solid phase diffusion reaction is inhibited, and the key for preparing the aluminum nitride fiber is to improve the proportion of a gas phase reaction mechanism.
The invention utilizes the porous characteristic of the graphite felt to prepare Al2O3Firstly, fully contacting aluminum oxide on the surface with a graphite felt and nitrogen to generate a carbothermic reduction nitridation reaction to generate aluminum nitride crystal seeds on the surface of the graphite felt; the alumina in the graphite felt is difficult to contact with nitrogen, and only carbothermic reduction occurs to generate a large amount of Al2Aluminum-containing gas phase compounds such as O; along with the reaction, the aluminum-containing gas-phase compound overflows the surface of the graphite felt, contacts with nitrogen to carry out nitridation reaction, and grows into aluminum nitride fibers by taking the existing aluminum nitride seed crystals on the surface of the graphite felt as crystal nuclei and a VS mechanism.
The method has the advantages of simple process, high production efficiency and low production cost, can greatly improve the fiber yield, can realize the control of the fiber growth habit by changing the size of the graphite felt and the nitrogen circulation rate, and is expected to provide a high-efficiency new way for preparing the aluminum nitride fiber with controllable morphology.
The innovative thought of the method is that on the basis of preparing aluminum nitride by the traditional carbothermic reduction nitridation method, the porous carbon fiber material of graphite felt is used as a carbon source, the carbon thermal reduction reaction and nitridation reaction are controlled by utilizing the concentration difference of nitrogen inside and outside the graphite felt, the nucleation and growth processes of aluminum nitride are regulated and controlled to synthesize the aluminum nitride fiber, and finally the aluminum nitride fiber is promoted to be generated in a large amount by a VS mechanism under the condition of low supersaturation.
Compared with the prior art, the invention has the advantages that:
1. the raw materials used by the invention are cheap alumina, graphite felt, nitrogen and the like, and additives are not needed, so that the raw materials have low cost and high feasibility and are easy to realize industrial production;
2. the method soaks the graphite felt through the alumina slurry, so as to control the nucleation and growth process of the aluminum nitride, has simple process, can greatly improve the fiber yield, and can realize the control of the growth habit of the fiber by changing the size and the nitrogen flow rate of the graphite felt;
3. the aluminum nitride fiber product prepared by the method has high purity, good crystallization degree, good mechanical strength and high thermal conductivity, and has wide application prospect in the fields of fiber reinforcement and heat conduction and radiation.
Drawings
FIG. 1: macroscopic photograph of the synthetic aluminum nitride fiber of example 1;
FIG. 2 is a drawing: scanning Electron Microscope (SEM) photographs of the aluminum nitride fibers synthesized in example 1;
FIG. 3: x-ray diffraction (XRD) analysis of the synthetic aluminum nitride fibers of example 1;
FIG. 4 is a drawing: a macroscopic photograph of the synthetic aluminum nitride fiber of example 2;
FIG. 5 is a drawing: scanning Electron Microscope (SEM) photograph of the aluminum nitride fiber synthesized in example 2;
FIG. 6: x-ray diffraction (XRD) analysis of the synthetic aluminum nitride fibers of example 2;
FIG. 7: a macro photograph of the aluminum nitride fiber synthesized in comparative example 1;
FIG. 8: a macroscopic photograph of the aluminum nitride fiber synthesized in comparative example 2.
Detailed Description
Example 1
5g of alpha-Al having a particle size of 1 μm2O3Adding the mixture into 80ml of deionized water, carrying out ball milling for 12h to obtain uniform slurry containing aluminum oxide, soaking 2g of the cut polyacrylonitrile-based graphite felt into the prepared slurry, then transferring the slurry into a vacuum drying oven, soaking for 2h at room temperature, and then heating to 80 ℃ for vacuum drying for 10h. And placing the obtained graphite felt precursor in a graphite crucible, transferring the graphite felt precursor into a graphite sintering furnace, introducing circulating nitrogen into the graphite sintering furnace at an aeration rate of 1L/min, simultaneously heating to 1600 ℃ at a rate of 50 ℃/min, and preserving the temperature until the total reaction time reaches 2 hours, and then finishing the reaction. Subsequently, the cotton-like fibers grown on the surface of the graphite felt are collected and reacted in a muffle furnace at 700 ℃ for 3 hours to remove carbon.
The digital photos of the product are shown in figure 1, the SEM image is shown in figure 2, XRD analysis is shown in figure 3, and the aluminum nitride fiber prepared by the method has good crystallization degree, large yield, good fiber uniformity and high length-diameter ratio.
Example 2
8g of gamma-Al having a particle size of 0.5. Mu.m2O3Adding into 100ml of absolute ethyl alcohol, and ball-milling for 6h to obtain uniform slurry containing aluminaAnd soaking 4g of the cut asphalt-based graphite felt into the prepared slurry, transferring the slurry to a vacuum drying oven, soaking at room temperature for 2 hours, and heating to 80 ℃ for vacuum drying for 12 hours. And placing the obtained graphite felt precursor in a graphite crucible, transferring the graphite felt precursor into a graphite sintering furnace, introducing circulating nitrogen into the graphite sintering furnace at an inflation rate of 0.5L/min, simultaneously heating to 1600 ℃ at a rate of 40 ℃/min, and preserving heat until the total reaction time reaches 4h, and then finishing the reaction. Subsequently, the cotton-like fibers grown on the surface of the graphite felt are collected and reacted in a muffle furnace at 600 ℃ for 4 hours to remove carbon.
The digital photos of the product are shown in figure 4, the SEM image is shown in figure 5, the XRD analysis is shown in figure 6, and the aluminum nitride fiber prepared by the method has the advantages of good crystallization degree, large yield, good fiber uniformity and high length-diameter ratio.
Comparative example 1
The same as in example 1 except that the nitrogen aeration rate during the incubation was 0.05L/min until the end of the reaction.
A digital photograph of the product is shown in FIG. 7, and when AlN fibers were produced by this method, since nitrogen gas was not sufficiently circulated, the amount of nitrogen gas supplied during the reaction was insufficient, the yield of aluminum nitride fibers as a product was small, and the main component remained granular aluminum nitride.
Comparative example 2
The same as example 2, except that the cut graphite felt was dipped in the prepared alumina slurry without vacuum drying, and dried under normal pressure.
The photo of the product is shown in figure 8, and the aluminum nitride fiber prepared by the method has no or very little aluminum oxide in the graphite felt, the aluminum-containing gas phase ratio is too small in the reaction process, the growth driving force is insufficient, and the aluminum nitride fiber is hardly generated on the surface of the graphite felt.

Claims (7)

1. A method for preparing aluminum nitride fibers by using graphite felt is characterized by comprising the following specific steps:
(1) Preparing materials: adding alumina powder into deionized water or absolute ethyl alcohol, and performing ball milling for a certain time to obtain uniform alumina slurry, wherein the solid content of the alumina slurry is 5-30 wt%;
(2) Preparing a reaction precursor: cutting a graphite felt into a proper size, completely immersing the graphite felt in the alumina slurry obtained in the step (1), transferring the graphite felt to a vacuum drying oven, soaking the graphite felt for 1 to 4 hours at room temperature, and heating to 80 ℃ for vacuum drying for 6 to 12 hours to obtain the graphite felt containing alumina inside;
(3) Synthesis: placing the graphite felt precursor obtained in the step (2) in a graphite crucible, transferring the graphite felt precursor into a graphite sintering furnace, continuously introducing flowing nitrogen, heating to 1500-1900 ℃, preserving the temperature until the total reaction time reaches 0.5-6 h, and finishing the reaction to obtain the graphite felt with the aluminum nitride fibers growing on the surface;
(4) Carbon discharge: and (4) collecting the aluminum nitride fibers obtained by the reaction in the step (3), placing the aluminum nitride fibers in a muffle furnace, heating to 600-750 ℃, and preserving heat for 1-5 hours to remove carbon impurities contained in reaction products, wherein the finally obtained off-white cotton-like product is the aluminum nitride fibers.
2. The method for preparing aluminum nitride fiber according to claim 1, wherein the alumina powder in the step (1) is α -Al2O3Or gamma-Al2O3The average particle size is 0.1 to 2 μm.
3. The method for preparing aluminum nitride fiber according to claim 1, wherein the ball milling time for preparing the alumina slurry in the step (1) is 4 to 12 hours.
4. The method for preparing aluminum nitride fiber according to claim 1, wherein the graphite felt used in the step (2) is pitch-based graphite felt, polyacrylonitrile-based (PAN-based) graphite felt or viscose-based graphite felt.
5. The method for preparing the aluminum nitride fiber according to claim 1, wherein the weight ratio of the alumina to the graphite felt is as follows when the graphite felt prepared in the step (2) is reacted with the precursor: 0.1 to 1.
6. The method for preparing aluminum nitride fiber according to claim 1, wherein the temperature rise rate of the sintering furnace in the step (3) is 10 to 100 ℃/min.
7. The method for producing aluminum nitride fibers according to claim 1, wherein nitrogen gas is passed through the reaction furnace in the step (3) at a flow rate of 0.1 to 2L/min.
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Publication number Priority date Publication date Assignee Title
US5817274A (en) * 1995-08-11 1998-10-06 Toshiba Ceramics Co., Ltd. Method of manufacturing aluminum nitride
CN104213252B (en) * 2014-08-20 2016-03-02 中国计量学院 A kind of take carbon fiber as the method for Template preparation aluminium nitride fibres
CN106829915B (en) * 2017-03-03 2018-10-30 中国科学院合肥物质科学研究院 A kind of method of growth in situ carbon fiber in graphite felt
CN112142020B (en) * 2020-09-08 2021-12-24 北京科技大学 Method for preparing aluminum nitride fiber by carbothermic reduction

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