A method for batch production of aluminum nitride whiskers

Abstract

The application discloses a method for batch preparation of aluminum nitride whiskers, and belongs to the field of inorganic non-metal material preparation. The specific steps are as follows: aluminum particles, iron powder and carbon powder are mixed uniformly according to a certain mass ratio and placed in an alumina crucible, then transferred to a graphite sintering furnace, and reacted under a nitrogen atmosphere, wherein the nitrogen flow rate is 0.1-2 L / min, the reaction temperature is 1500-1700 DEG C, and the holding time is 0.5-6 h; after the reaction is completed, white aluminum nitride whiskers with high length-diameter ratio can be obtained. The aluminum nitride whiskers prepared by the method have high purity and large length-diameter ratio. By using aluminum particles as raw materials and adding carbon powder and iron powder, the yield is significantly improved, the process method is simple, the raw material cost is low, the product can be used as a heat conduction filler and an aluminum nitride ceramic toughening material, and has a wide application prospect in the fields of aviation, environmental protection, communication and power.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of inorganic non-metallic material preparation, and particularly relates to a method for batch preparation of aluminum nitride whiskers. BACKGROUND

[0002] Aluminum nitride has an ultra-high theoretical thermal conductivity of 320 W / mK, and has excellent properties such as high resistivity, low dielectric constant, low thermal expansion coefficient and non-toxicity, and is an ideal substrate material and electronic device packaging material. The one-dimensional whisker form is a single crystal with nearly perfect crystal properties, which can reduce phonon scattering at the grain boundary and exhibit extremely high aspect ratio (5-1000), and has broad application prospects in the fields of ceramic toughening and heat-conducting fillers. However, the existing methods for preparing AlN whiskers often have problems such as low safety factor, low yield, low purity and high cost.

[0003] Invention patent CN103382113A discloses a method for preparing aluminum nitride fibers, which uses aluminum powder and aluminum oxide powder as raw materials, adopts briquetting forming method, and sintering in a nitrogen atmosphere to obtain aluminum nitride fibers. However, the raw material aluminum powder itself is flammable and has high activity, and the fine powder can easily form a flammable and explosive mixture with air, which has safety hazards and requires a relatively high equipment.

[0004] Invention patent CN102584244A discloses a method for preparing hexagonal phase aluminum nitride nanofibers by electrospinning combined with ammonia nitriding, which uses aluminum nitrate as the main raw material, first prepares nano-aluminum oxide fibers, and then mixes carbon powder to nitride into aluminum nitride fibers in an ammonia atmosphere. However, due to the large difference in density between aluminum oxide and carbon powder, uneven distribution of aluminum oxide fibers and carbon powder is prone to occur during the mixing process, and the use of ammonia gas in the nitriding process is harmful to the respiratory tract, which seriously limits its industrial application.

[0005] Invention patent CN98103408.X discloses a method for synthesizing aluminum nitride fibers, which uses microcrystalline aluminum silicate fibers with a sillimanite structure and carbon black as starting materials, and performs heating and holding treatment in a nitrogen atmosphere to finally form aluminum nitride fiber whiskers. However, since the aluminum silicate in the original material contains SiO2, the reaction product contains SiC, and the purity of the aluminum nitride fibers decreases.

[0006] Invention patent CN104211025A discloses a method for preparing cubic phase aluminum nitride fibers, which first prepares a mixed solution of anhydrous aluminum chloride, tetrabutylammonium azide and a template agent, then performs a solvothermal reaction, washes, centrifuges and dries to obtain a reaction product, then calcines in a vacuum or inert atmosphere to crack the attached template agent, and then calcines in an air atmosphere to remove organic matter, and finally obtains cubic phase aluminum nitride. However, this organic precursor method has complex process, high cost and long cycle.

[0007] It can be seen that, to further realize the large-scale preparation of aluminum nitride whiskers and expand the application range thereof, it is still necessary to further improve the existing method. SUMMARY

[0008] The present application is directed to the low yield of the existing aluminum nitride whiskers, and proposes a method for batch preparation of aluminum nitride whiskers. In the method, the generation of aluminum nitride is mainly based on direct nitriding method and carbon thermal reduction nitriding method. The total reaction formula of the direct nitriding method is:

[0009] 2Al(s)+N2(g)→2AlN(s)

[0010] The total reaction formula of the carbon thermal reduction nitriding method is:

[0011] Al2O3(s)+3C(s)+N2(g)→2AlN(s)+3CO(g)

[0012] The present application combines the direct nitriding method and the carbon thermal reduction nitriding method to prepare aluminum nitride whiskers with high purity and high aspect ratio. The keys are mainly three points: (1) large particle aluminum particles are used as raw materials, and there is generally a certain thickness of oxide layer on the surface of the aluminum particles. The addition of carbon powder can cause a carbon thermal reduction reaction with the oxide layer on the surface of the aluminum particles, thereby improving the yield of aluminum nitride; (2) while the surface oxide layer is slowly consumed, the aluminum source inside the large particle aluminum particles is slowly released in the form of vapor, and after contacting with nitrogen, aluminum nitride whiskers are generated through the gas-solid (VS) reaction mechanism; (3) iron powder is added as a catalyst to further improve the concentration of Al vapor, promote the Al-N reaction from liquid-gas reaction to gas-gas reaction, avoid the rapid nucleation of AlN liquid phase, and grow into one-dimensional morphology under low supersaturation.

[0013] Specifically, the present application provides a method for batch preparation of aluminum nitride whiskers, comprising the following steps:

[0014] (1) batching: uniformly mix aluminum particles, iron powder and carbon powder according to a certain mass ratio;

[0015] (2) synthesis: placing the above obtained mixture into an alumina crucible, and transferring the crucible into a graphite sintering furnace, then after heating from room temperature to 1500-1700℃ in a nitrogen atmosphere, keeping the temperature for 0.5-6h, and then naturally cooling, white aluminum nitride whiskers with high aspect ratio are obtained.

[0016] Further, the size of the aluminum particles in step (1) is 0.5-1mm. Too small aluminum particles will lead to too high reactivity of the raw materials, and the rapid evaporation of aluminum vapor will make the reaction rate too fast, so that it is impossible to obtain one-dimensional morphology under low supersaturation. Too large aluminum particles will lead to incomplete reaction, and there will be aluminum impurities in the product. The mass ratio of aluminum particles to iron powder is 1:1-1:2.5.

[0017] Further, the carbon powder used in step (1) is carbon black, graphite or activated carbon, and the mass ratio of the carbon powder to the aluminum particles is 1:100 to 5:100.

[0018] Further, in step (2), nitrogen gas is introduced into the reaction furnace, and the flow rate of the nitrogen gas is 0.1 to 2 L / min.

[0019] Further, in step (2), the heating rate of the atmosphere sintering furnace is 5 to 60 ℃ / min.

[0020] The application also provides the aluminum nitride whiskers prepared by the method, which have a one-dimensional morphology and a length-diameter ratio of 500:1 to 5000:1.

[0021] The application provides a method for batch preparation of aluminum nitride whiskers, which uses aluminum particles as raw materials and adds carbon powder and iron powder to improve the yield of aluminum nitride whiskers. First, the aluminum oxide on the surface of the aluminum particles is in contact with the carbon powder to generate a large amount of Al2O and other aluminum-containing gas phase compounds through carbothermic reduction, and further contact with nitrogen to generate aluminum nitride. The consumption of the oxide layer on the surface of the aluminum particles can also promote the slow evaporation of the internal aluminum into aluminum vapor, which is in contact with nitrogen to generate aluminum nitride whiskers through direct nitriding method in a gas-solid (VS) mechanism under low supersaturation. In addition, the addition of iron powder can further improve the concentration of aluminum vapor and the yield of aluminum nitride whiskers.

[0022] The application has the advantages of simple process, high production efficiency, low production cost, and high yield of whiskers, and can control the growth habit of the whiskers by changing the ratio of the carbon powder and the nitrogen flow rate, which is expected to provide a new efficient way for preparing aluminum nitride whiskers with controllable morphology.

[0023] The application uses aluminum particles as raw materials and adds iron powder and carbon powder to significantly improve the yield of aluminum nitride whiskers. Compared with the prior art, the application has the following advantages:

[0024] 1. The main raw materials used in the application are inexpensive aluminum particles, iron powder, carbon powder and nitrogen, which have low raw material cost, high feasibility and are easy to realize industrialization.

[0025] 2. The method uses aluminum particles as an aluminum source, which has a higher safety factor than explosive aluminum powder.

[0026] 3. The large particles of aluminum are used as raw materials, and the surface has a certain thickness of oxide layer. The addition of carbon powder can cause carbothermic reduction reaction with the oxide layer on the surface of the aluminum particles to improve the yield of aluminum nitride. In addition, the slow consumption of the surface oxide layer and the slow release of the aluminum source in the form of vapor from the inside of the large particle aluminum can generate aluminum nitride whiskers through a gas-solid (VS) reaction mechanism after being in contact with nitrogen.

[0027] 4. Adding iron powder as a catalyst, further increasing the concentration of aluminum vapor, promoting the Al-N reaction from liquid-gas reaction to gas-gas reaction, avoiding the rapid nucleation of AlN liquid phase, and under low supersaturation, AlN preferentially grows into one-dimensional morphology.

[0028] 5. The aluminum nitride whiskers prepared by the method have high purity and high aspect ratio, and have wide application prospects in the field of ceramic toughening and heat dissipation. BRIEF DESCRIPTION OF DRAWINGS

[0029] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the drawings needed in the embodiment description will be briefly introduced. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can be obtained by those skilled in the art without creative labor.

[0030] Figure 1 The sample macroscopic morphology of the aluminum nitride whiskers synthesized in Example 1;

[0031] Figure 2 The optical microscope photograph of the aluminum nitride whiskers synthesized in Example 1;

[0032] Figure 3 The scanning electron microscope (SEM) photograph of the aluminum nitride whiskers synthesized in Example 1;

[0033] Figure 4 The X-ray diffraction (XRD) analysis of the aluminum nitride whiskers synthesized in Example 1;

[0034] Figure 5 The sample macroscopic morphology of the aluminum nitride whiskers synthesized in Example 2;

[0035] Figure 6 The sample macroscopic morphology of the aluminum nitride whiskers synthesized in Example 3;

[0036] Figure 7 The sample macroscopic morphology of the aluminum nitride whiskers synthesized in Comparative Example 1;

[0037] Figure 8 The sample macroscopic morphology of the aluminum nitride whiskers synthesized in Comparative Example 2;

[0038] Figure 9 The sample macroscopic morphology of the aluminum nitride whiskers synthesized in Comparative Example 3. DETAILED DESCRIPTION

[0039] In order to make the technical problems, technical solutions and advantages of the present application more clear, the following will be described in detail in combination with the drawings and specific embodiments.

[0040] Example 1

[0041] 3g of 0.5mm aluminum particles, 5g of iron powder and 0.1g of activated carbon were uniformly mixed, the mixture was placed in an alumina crucible and transferred into a graphite sintering furnace, 1L / min of nitrogen was introduced, the temperature was raised to 1700℃ at a rate of 50℃ / min, and then the temperature was kept constant for 1h.

[0042] The macroscopic morphology of the sample of the synthesized aluminum nitride whiskers is shown in Figure 1 It can be seen that a large amount of white aluminum nitride whiskers with high aspect ratio were obtained on the wall of the alumina crucible.

[0043] The optical microscope photograph of the aluminum nitride whiskers is shown in Figure 2 The scanning electron microscope (SEM) photograph is shown in Figure 3 It can be seen that the aluminum nitride whiskers have obvious one-dimensional morphology, are hexagonal prisms, have smooth surface, uniform thickness and ultra-high aspect ratio, and the average aspect ratio is ≥2000:1.

[0044] The XRD pattern of the aluminum nitride whiskers is shown in Figure 4 The characteristic diffraction peak positions thereof are consistent with AlN (JCPDS No 25-1133), and the phase purity is high.

[0045] Example 2

[0046] 3g of 0.5mm aluminum particles, 7.5g of iron powder and 0.05g of carbon black were uniformly mixed, the mixture was placed in an alumina crucible and transferred into a graphite sintering furnace, 0.1L / min of nitrogen was introduced, the temperature was raised to 1600℃ at a rate of 20℃ / min, and then the temperature was kept constant for 2h.

[0047] The macroscopic morphology of the sample of the aluminum nitride whiskers synthesized in Example 2 is shown in Figure 5 It can be seen that a large amount of aluminum nitride whiskers were grown on the alumina crucible.

[0048] Example 3

[0049] 3g of 1mm aluminum particles, 3g of iron powder and 0.03g of carbon black were uniformly mixed, the mixture was placed in an alumina crucible and transferred into a graphite sintering furnace, 1L / min of nitrogen was introduced, the temperature was raised to 1650℃ at a rate of 20℃ / min, and then the temperature was kept constant for 4h.

[0050] The macroscopic morphology of the sample of the aluminum nitride whiskers synthesized in Example 3 is shown in Figure 6 It can be seen that a large amount of aluminum nitride whiskers were grown on the alumina crucible.

[0051] Comparative Example 1

[0052] It is basically the same as Example 1, except that the content of activated carbon is 0.

[0053] The product morphology in Comparative Example 1 is shown in Figure 2, and the product morphology in Comparative Example 2 is shown in Figure 3. Figure 7 As shown in Figure 2, the yield of aluminum nitride whiskers in Comparative Example 1 without adding activated carbon is significantly less than that in Example 1 with adding activated carbon.

[0054] Comparative Example 2

[0055] The same as Example 1, except that the aluminum particles are replaced by aluminum powder (average particle size ≥ 200 μm) of the same mass.

[0056] The product morphology in Comparative Example 2 is shown in Figure 3, and the product morphology in Comparative Example 3 is shown in Figure 4. Figure 8 As shown in Figure 3, the yield of aluminum nitride whiskers in Comparative Example 2 with aluminum powder as raw material is significantly less than that in Example 1 with aluminum particles as raw material.

[0057] Comparative Example 3

[0058] The same as Example 1, except that the content of iron powder is 0.

[0059] The product morphology in Comparative Example 3 is shown in Figure 4. Figure 9 As shown in Figure 4, the yield of aluminum nitride whiskers in Comparative Example 3 without adding iron powder is significantly less than that in Example 1 with adding iron powder, and large agglomerates are generated at the bottom of the crucible.

[0060] The above merely illustrates the specific embodiments of the present application, but the protection scope of the present application is not limited thereto, and any person skilled in the art can easily think of the changes or replacements within the technical range disclosed by the present application, which should be covered within the protection scope of the present application. Therefore, the protection scope of the present application should be subject to the protection scope of the claims.

Claims

1. A method for batch production of aluminum nitride whiskers, characterized by, The method comprises the following steps: (1) mixing: uniformly mixing aluminum particles, iron powder and carbon powder according to a certain mass ratio; (2) synthesizing: placing the mixture obtained above into an alumina crucible, and transferring the crucible into a graphite sintering furnace, then after heating from room temperature to 1500-1700℃ in a nitrogen atmosphere, keeping the temperature for 0.5-6h, and then naturally cooling, obtaining white aluminum nitride whiskers with high length-diameter ratio; The aluminum particle size in step (1) is 0.5-1mm, and the mass ratio of carbon powder to aluminum particle is 1:100-5:

100.

2. The method of claim 1, wherein the aluminum nitride whiskers are produced in a batch process. The mass ratio of aluminum particle to iron powder in step (1) is 1:1-1:2.

5.

3. The method of claim 1, wherein the aluminum nitride whiskers are produced in a batch process. The carbon powder used in step (1) is carbon black, graphite or activated carbon.

4. The method of claim 1, wherein the aluminum nitride whiskers are produced in a batch process. In step (2), nitrogen is introduced into the reaction furnace with a flow rate of 0.1-2L / min.

5. The method of claim 4, wherein the aluminum nitride whiskers are produced in a batch process. In step (2), the heating rate of the atmosphere sintering furnace is 5-60℃ / min.

6. Aluminum nitride whiskers prepared by the method of any one of claims 1-5.

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