Method for preparing AlN whisker at low temperature by taking halloysite as raw material and AlN whisker

Abstract

The invention belongs to the technical field of material preparation, and particularly relates to a method for preparing AlN whiskers at low temperature by taking halloysite as a raw material. The method comprises the following steps: calcining halloysite; and mixing the calcined halloysite with sodium chloride and aluminum powder to react, thereby obtaining the halloysite-aluminum composite material. According to the method, the materials are cheap and easy to obtain, the purpose of synthesizing the AlN whisker under the heating condition that the temperature is relatively lower than that of a traditional AlN whisker forming temperature is achieved, and low-cost green preparation is achieved.

Description

Technical Field

[0001] The invention belongs to the technical field of new material preparation, and in particular relates to a method for preparing AlN whiskers at low temperature by taking halloysite as a raw material. Background Art

[0002] Aluminum nitride (AlN) has attracted extensive attention in high thermal conductivity fillers and optical detectors due to its excellent chemical stability and low thermal expansion coefficient. At the same time, AlN materials also have the advantages of good resistance to plasma erosion, non-toxicity (compared with toxic BeO) and high breakdown voltage. They can efficiently dissipate the heat energy of large integrated circuits and are ideal materials for preparing a new generation of high thermal conductivity electronic substrates and indispensable ceramic substrate materials for large integrated circuits. These attractive properties have made AlN materials widely used in electronics, national defense, information, aerospace, military industry, transportation, communications and other fields. High-quality nano-AlN powder has relatively good application prospects and commercial value at present. Some companies at home and abroad, such as Accumet Materials in the United States, Kyocera in Japan, and Xiamen Ju Ceramics, have achieved industrial production. The preparation process of AlN materials still has great development potential.

[0003] At present, AlN can be synthesized by a variety of methods, and the common preparation methods include direct nitridation, chemical vapor deposition, aluminum nitride self-propagating high temperature synthesis, and traditional carbon thermal reduction nitridation. Among them, the direct nitridation method uses Al powder as raw material and directly reacts with nitrogen to synthesize AlN. In 2015, Peng et al. (Literature: Low-temperature-controlled synthesis and growth mechanism of AlN whiskers. Materials Research Innovations 19. sup2 (2015): S2-108.) used aluminum powder as raw material and prepared AlN whiskers after being kept at 1550°C for 6 hours in a nitrogen atmosphere. When the temperature was raised to 1600°C, its diameter increased from 1μm to 3μm. However, the reaction temperature of this method is high, and the heat is released violently during the nitridation process, resulting in aluminum powder agglomeration and low purity of aluminum nitride. Chemical vapor deposition is a method of forming a supersaturated vapor state in the reaction system, which then spontaneously condenses into nuclei and deposits AlN particles. In 2023, Xie et al. (Reference: Study on an eco-friendly and efficient method for growing aluminum nitride whiskers. Vacuum 210 (2023): 111809.) successfully deposited high-quality AlN nanowire materials on a sapphire substrate. However, this method requires the growth temperature of the AlN crystal film to be 1400°C, resulting in high costs for growing AlN crystals. The self-propagating high-temperature synthesis method does not require a high temperature of more than 1000°C, and the reaction time is short and the reaction is rapid, but it has high requirements for nitrogen pressure. The morphology of the synthesized whiskers by carbon thermal reduction nitridation is better, but the reaction temperature is usually 1500-1800°C. This method requires high temperature conditions and long-term heat preservation, and consumes a lot of energy.

[0004] In summary, the existing various technical means require high reaction temperatures and expensive alumina or AlN as raw materials, which are costly. If the synthesis temperature of AlN whiskers can be reduced, the synthesis cost will be greatly reduced. Therefore, it is urgent to develop a low-energy AlN preparation technology. Summary of the invention

[0005] The purpose of the present invention is to reduce the temperature required for synthesizing AlN whisker materials while reducing costs, and to provide a method for preparing AlN whiskers at low temperature using halloysite as a raw material. The method achieves the purpose of synthesizing AlN whisker materials under heating conditions that are relatively lower than the traditional AlN whisker formation temperature, can significantly reduce the energy cost of AlN processing enterprises, and is conducive to energy conservation and emission reduction; and the raw material used is halloysite, which is cheap and easy to obtain.

[0006] In order to achieve the above object, the present invention adopts the following technical solution:

[0007] In a first aspect, the present invention provides a method for preparing AlN whiskers at low temperature using halloysite as a raw material, the method comprising:

[0008] calcining the halloysite;

[0009] The calcined halloysite is mixed with sodium chloride and aluminum powder for reaction to obtain the product.

[0010] In the preferred technical scheme of the method for preparing AlN whiskers at low temperature using halloysite as raw material, the reaction is carried out under the following procedure:

[0011] Heating stage: In the first stage, the temperature rises from room temperature to 350-400°C, with a heating rate of 1-5°C / min;

[0012] In the second stage, the temperature is raised to 400-450°C, with a heating rate of 1-5°C / min;

[0013] The third stage is to heat to 600-700℃, with a heating rate of 1-5℃ / min and keep warm for 3-5h;

[0014] Cooling stage: In the first stage, the temperature drops to 250-350℃, and the cooling rate is 1-2℃ / min;

[0015] The second stage is to cool naturally to room temperature.

[0016] In the preferred technical scheme of the method for preparing AlN whiskers at low temperature using halloysite as raw material, the calcination is carried out under the following procedure:

[0017] The temperature is raised from room temperature to 400-700°C at a heating rate of 1-10°C / min, kept at this temperature for 1-3 hours, and then cooled naturally to room temperature.

[0018] In the preferred technical scheme of the method for preparing AlN whiskers at low temperature using halloysite as a raw material, the mass ratio of the calcined halloysite to sodium chloride and aluminum powder is 1:1:4.

[0019] In the preferred technical solution of the method for preparing AlN whiskers at low temperature using halloysite as a raw material, the halloysite is 7A halloysite in terms of mineralogical properties.

[0020] In the preferred technical solution of the method for preparing AlN whiskers at low temperature using halloysite as raw material, the purity of the 7-A halloysite is 95-100%.

[0021] In the preferred technical solution of the above method for preparing AlN whiskers at low temperature using halloysite as raw material, the method further includes post-processing.

[0022] In the preferred technical solution of the method for preparing AlN whiskers at low temperature using halloysite as raw material, the post-treatment at least comprises:

[0023] The obtained reaction product is acid washed.

[0024] In the preferred technical solution of the method for preparing AlN whiskers at low temperature using halloysite as raw material, the post-treatment further includes solid-liquid separation, and / or water washing, and / or drying.

[0025] In a second aspect, the present invention provides an AlN whisker, which is prepared by the above-mentioned method of preparing AlN whiskers at low temperature using halloysite as raw material, and has a size of 30-100 nm in diameter and 1-3 μm in length.

[0026] Compared with the prior art, the present invention has the following technical effects:

[0027] (1) The method provided by the present invention can reduce the synthesis temperature of AlN whiskers to about 700°C, thereby achieving the purpose of synthesizing AlN whiskers under heating conditions relatively lower than the traditional AlN whisker formation temperature, which can significantly reduce the energy cost of AlN processing enterprises and contribute to energy conservation and emission reduction;

[0028] (2) The raw material used in the present invention is halloysite, which is cheap and readily available, and can achieve high added value utilization of silicate minerals. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] The preferred embodiments of the present invention are described below in conjunction with the accompanying drawings, in which:

[0030] Figure 1 is a SEM image of the natural halloysite selected in Example 1;

[0031] Figure 2 TEM image of the natural halloysite selected in Example 1;

[0032] Figure 3 The XRD patterns of the natural halloysite and the calcined halloysite selected in 1 are implemented;

[0033] Figure 4 The XRD pattern of the AlN whisker obtained in Example 1;

[0034] Figure 5 is a SEM image of the AlN whisker obtained in Example 1;

[0035] Figure 6 TEM image of the AlN whisker obtained in Example 1;

[0036] Figure 7 This is the EDS image of the AlN whisker obtained in Example 1;

[0037] Figure 8 TEM image of the AlN whisker obtained in Example 2;

[0038] Fig. 9 TEM image of the AlN whisker obtained in Example 3;

[0039] Fig.10 TEM image of the AlN powder obtained in Comparative Example 1;

[0040] Fig.11 This is the TEM image of the AlN whisker obtained in Comparative Example 2. DETAILED DESCRIPTION

[0041] The preferred embodiments of the present application are described below with reference to the accompanying drawings. Those skilled in the art should understand that these embodiments are only used to explain the technical principles of the present application and are not intended to limit the protection scope of the present application.

[0042] The experimental methods in the following examples are conventional methods unless otherwise specified, and the materials, reagents, etc. used in the following examples are commercially available unless otherwise specified.

[0043] Based on the problems pointed out in the background technology that the preparation of AlN whiskers in the prior art requires a high reaction temperature and the use of expensive aluminum oxide or AlN as raw materials, the present application provides a method for preparing AlN whiskers at low temperature using halloysite as raw material, which provides a new idea for the preparation of green, efficient and low-cost aluminum nitride whiskers and opens up a new technical route.

[0044] Specifically, in a first aspect, the present application provides a method for preparing AlN whiskers at low temperature using halloysite as a raw material, comprising the following steps:

[0045] S1. calcining the halloysite;

[0046] S2. Mix the calcined halloysite with sodium chloride and aluminum powder to react to obtain.

[0047] In the prior art, various technical means for preparing AlN whiskers not only require the use of expensive alumina or AlN as raw materials, but also generally require a relatively high reaction temperature. In order to reduce the reaction temperature of synthesizing AlN whiskers while reducing the cost, the present invention provides a method for preparing AlN whiskers at low temperature using halloysite as a raw material. The method has a lower formation temperature than the traditional AlN whiskers, thus achieving the purpose of green, efficient and low-cost preparation.

[0048] In the present invention, halloysite is used as a raw material, and the halloysite is first calcined to remove the hydroxyl groups of the halloysite and improve the activity of the halloysite; then the calcined halloysite is uniformly mixed with sodium chloride and aluminum powder in a certain proportion and then reacted, and the sodium chloride in the mixture can have a certain degree of endothermic effect on the synthesis of AlN whiskers, thereby reducing the synthesis temperature of the AlN whisker material, thereby achieving the effect of synthesizing the AlN whisker material under heating conditions that are relatively lower than the traditional AlN whisker formation temperature.

[0049] Specifically, the principle of the method is as follows: the reaction of calcined halloysite mixed with sodium chloride and aluminum powder in proportion is an aluminothermic reduction reaction, which releases a large amount of heat during the reaction. By introducing sodium chloride, the reaction heat can be significantly absorbed to achieve the effect of stabilizing the combustion reaction; in the first stage of the reaction, the molten aluminum powder reduces the Si-O layer in the halloysite to single crystal silicon, and the liquid silicon forms single crystal silicon microspheres due to capillary force; in the second stage, after the oxygen in the halloysite is taken away, the N atom occupies the position of the O atom, thereby maintaining the original tubular structure. Due to the existence of the tubular structure before and after the reaction, it is conducive to the replacement of O in the Al-O layer in the halloysite by N, thereby reducing the temperature required for the reaction.

[0050] In some embodiments, the reaction is carried out under the following procedure:

[0051] Heating stage: In the first stage, the temperature rises from room temperature to 350-400°C, with a heating rate of 1-5°C / min;

[0052] In the second stage, the temperature is raised to 400-450°C, with a heating rate of 1-5°C / min;

[0053] The third stage is to heat to 600-700℃, with a heating rate of 1-5℃ / min and keep warm for 3-5h;

[0054] Cooling stage: In the first stage, the temperature drops to 250-350℃, and the cooling rate is 1-2℃ / min;

[0055] The second stage is to cool naturally to room temperature.

[0056] In the present invention, a staged heating method is adopted, so that the heating is uniform, the heat preservation effect is better, and the difference of the material caused by temperature change will not be caused, which can effectively improve the synthesis effect of AlN whiskers.

[0057] In a preferred embodiment, the reaction is carried out under the following procedure:

[0058] Heating stage: In the first stage, the temperature rises from room temperature to 380°C at a heating rate of 5°C / min;

[0059] In the second stage, the temperature was raised to 450°C with a heating rate of 1°C / min;

[0060] In the third stage, the temperature was raised to 700°C, the heating rate was 5°C / min, and the temperature was kept for 4h;

[0061] Cooling stage: In the first stage, the temperature is reduced to 300°C, and the cooling rate is 2°C / min;

[0062] The second stage is to cool naturally to room temperature.

[0063] In some embodiments, the reaction is carried out under a nitrogen atmosphere.

[0064] In some embodiments, the reaction is carried out in a tube furnace.

[0065] In some embodiments, the calcination is performed under the following procedure: heating from room temperature to 400-700° C. at a heating rate of 1-10° C. / min, keeping the temperature for 1-3 hours, and naturally cooling to room temperature.

[0066] In a preferred embodiment, the calcination is carried out under the following procedure: heating from room temperature to 550° C. at a heating rate of 5° C. / min, keeping the temperature for 2 hours, and naturally cooling to room temperature.

[0067] In some embodiments, the calcining is performed under an air atmosphere.

[0068] In some embodiments, the calcining is performed in a muffle furnace or a tube furnace.

[0069] In some embodiments, the mass ratio of the calcined halloysite to the sodium chloride and the aluminum powder is 1:1:4.

[0070] In some embodiments, the halloysite is 7A halloysite in mineralogy.

[0071] It should be noted that the raw material 7-hexanoite in the present invention can be natural or synthetic. In practical applications, those skilled in the art can select the corresponding raw material for use according to actual needs.

[0072] In a preferred embodiment, the 7 Å halloysite is a 7 Å halloysite having an interlayer spacing of 7.25 to 7.50 Å on the (001) crystal plane.

[0073] In some embodiments, the purity of the 7A Helloysite is 95-100%.

[0074] In some embodiments, the method further comprises post-processing.

[0075] In some embodiments, the post-processing includes at least:

[0076] The obtained reaction product is acid washed.

[0077] In the present invention, the purpose of acid washing the obtained reaction product is to remove unreacted aluminum powder and silicon dioxide.

[0078] In some embodiments, the acid washing is: washing the obtained reaction product with an acid solution.

[0079] In some embodiments, the acid solution is HCl solution and / or HF solution.

[0080] In a preferred embodiment, the acid solution is HCl solution and HF solution.

[0081] In some embodiments, the solid-to-liquid ratio of the reaction product to the HCl solution is 1 g:(5-50) ml.

[0082] In some embodiments, the solid-to-liquid ratio of the reaction product to the HF solution is 1 g: (5-50) ml.

[0083] In some embodiments, the concentration of the HCl solution is 4M.

[0084] In some embodiments, the concentration of the HF acid solution is 5 wt %.

[0085] In some embodiments, the post-treatment further includes solid-liquid separation, and / or water washing, and / or drying.

[0086] In a preferred embodiment, the method of preparing AlN whiskers at low temperature using halloysite as a raw material of the present invention comprises the following steps:

[0087] S1. calcining the halloysite;

[0088] S2, mixing the calcined halloysite with sodium chloride and aluminum powder for reaction;

[0089] S3, firstly subjecting the obtained reaction product to acid washing treatment, and then subjecting the acid washed product to solid-liquid separation, water washing, and drying to obtain.

[0090] In some embodiments, the drying is performed at a temperature of 50-60°C.

[0091] The present invention provides an AlN whisker in a second aspect. The AlN whisker is prepared by the method for preparing AlN whiskers at low temperature using halloysite as raw material provided in the first aspect. The size of the prepared AlN whisker is: whisker diameter 30-100nm, length 1-3μm.

[0092] The method for preparing AlN whiskers at low temperature using halloysite as a raw material is described in detail below through several preferred specific embodiments.

[0093] It should be noted that the halloysite used in the following examples and comparative examples is natural halloysite purchased.

[0094] Example 1

[0095] The method of preparing AlN whiskers at low temperature using halloysite as a raw material in this embodiment comprises the following steps:

[0096] S1. Natural 7-Ellipse stone with a purity of 99.5% is used as raw material, and is placed in a muffle furnace and calcined in an air atmosphere according to the following procedure:

[0097] The temperature was raised from room temperature to 550°C at a rate of 5°C / min, kept at that temperature for 2 hours, and then cooled to room temperature.

[0098] Among them, the SEM image of the natural 7A Hellite used in this embodiment is as follows: Figure 1 As shown in the TEM image Figure 2 shown.

[0099] The XRD spectra of the natural 7A halloysite and the calcined halloysite used in this example are as follows: Figure 3 shown.

[0100] S2. The calcined halloysite is mixed with sodium chloride and aluminum powder in a mass ratio of 1:1:4, ground and placed in a tube furnace, and reacted under a nitrogen atmosphere according to the following procedure:

[0101] Heating stage: In the first stage, the temperature rises from room temperature to 380°C at a heating rate of 5°C / min;

[0102] In the second stage, the temperature was raised to 450°C with a heating rate of 1°C / min;

[0103] In the third stage, the temperature was raised to 700°C, the heating rate was 5°C / min, and the temperature was kept for 4h;

[0104] Cooling stage: In the first stage, the temperature is reduced to 300°C, and the cooling rate is 2°C / min;

[0105] The second stage is to cool naturally to room temperature.

[0106] S3. Take 1 g of the obtained reaction product, place it in a beaker with 25 ml of 4 M HCl solution at 30°C and stir overnight, then add 20 ml of 5 wt% HF solution after suction filtration and let stand for 10 minutes to complete the pickling treatment; separate the solid and liquid of the pickled product, wash it with water and dry it at 50°C to obtain AlN whiskers.

[0107] The XRD pattern of the AlN whiskers obtained in this embodiment is as follows: Figure 4 As shown. Figure 4It can be seen that after thermite reduction treatment, a strong and sharp AlN whisker diffraction peak appears on the XRD curve.

[0108] The SEM image of the AlN whiskers obtained in this embodiment is as follows: Figure 5 As shown. Figure 5 It can be seen that the AlN whiskers are in a rod-like structure.

[0109] The TEM image of the AlN whiskers obtained in this example is as follows: Figure 6 As shown. Figure 6 It can be seen that a single AlN whisker is in the shape of a slender rod, and the interlaminar spacing of its nanoparticles is is the interlayer spacing of the AlN (001) crystal plane. The whisker has a diameter of 92 nm and a length of 2.58 μm.

[0110] The EDS image of the AlN whiskers obtained in this embodiment is as follows: Figure 7 shown. Figure 7 (a) is the SEM image of a single AlN whisker. Figure 7 (b) is the distribution of Al element in a single AlN whisker. Figure 7 (c) shows the distribution of N element in a single AlN whisker. Figure 7 It can be seen that the main chemical components of the whiskers are N and Al, and the N and Al elements in the aluminum nitride whiskers are evenly distributed and well combined.

[0111] The methods for preparing AlN whiskers at low temperature using halloysite as raw material in Examples 2 to 10 are the same as those in Example 1, except that the process parameters of each step are different, as shown in Table 1:

[0112] Table 1. Process parameters of each step of Example 2 to Example 10

[0113]

[0114]

[0115] The TEM images of the AlN whiskers prepared in the individual embodiments of Examples 2 to 10 were tested, wherein:

[0116] The TEM image of the AlN whisker obtained in Example 2 is as follows: Figure 8 As shown. Figure 8 It can be seen that a single AlN whisker is in the shape of a slender rod, with a diameter of 121 nm and a length of 3.77 μm.

[0117] The TEM image of the AlN whisker obtained in Example 3 is as follows: Fig. 9 As shown. Fig. 9 It can be seen that a single AlN whisker is in the shape of a slender rod, with a diameter of 48 nm and a length of 1.72 μm.

[0118] Comparative Example 1

[0119] The method for preparing AlN whiskers in this comparative example refers to that of Example 1, except that natural 10 Å halloysite with a purity of 98% is used as a raw material in S1.

[0120] The TEM image of the product obtained from this comparative example was tested, and the results are as follows Fig.10 As shown. Fig.10 It can be seen that a single AlN powder is in the shape of a hollow sphere with a diameter of 3.173 μm and a thickness of 294 nm.

[0121] The above results show that under the same process conditions, AlN whiskers cannot be produced using natural 10A helium ore with a purity of 98% as a raw material.

[0122] Comparative Example 2

[0123] The method for preparing AlN whiskers in this comparative example refers to Example 1, except that the following pretreatment is performed before calcination:

[0124] Natural 7A Helloydite with a purity of 99.5% was pre-acid-washed in a 2.5 mol / L H2SO4 solution at 90°C for 3 h, washed three times by alternating centrifugation with deionized water / ethanol solution, and dried at 80°C.

[0125] The TEM of the AlN whiskers obtained in this comparative example was tested, and the results are as follows: Fig.11 As shown. Fig.11 It can be seen that a single AlN whisker is in the shape of a slender rod, with a diameter of 110 nm and a length of 1.45 μm.

[0126] The above results show that when the raw material is pre-treated such as pre-pickling before calcination, the diameter of the obtained AlN whiskers is larger.

[0127] Comparative Example 3

[0128] The method for preparing AlN whiskers in this comparative example refers to that of Example 1, except that the natural 7A Helloydite with a raw material purity of 99.5% is not calcined.

[0129] The results show that the hydroxyl groups of halloysite cannot be removed due to the lack of calcination, which makes the activity of halloysite low and affects the synthesis of AlN whiskers.

[0130] Comparative Example 4

[0131] The method for preparing AlN whiskers in this comparative example refers to Example 1, except that the reaction in step S2 is carried out under the following procedure:

[0132] Heating stage: from room temperature to 700°C, heating rate 5°C / min, keeping temperature for 4h;

[0133] Cooling stage: In the first stage, the temperature is reduced to 300°C, and the cooling rate is 2°C / min;

[0134] The second stage is to cool naturally to room temperature.

[0135] The results show that the one-time heating rate to 700℃ results in uneven heating and poor insulation, which causes differences in the material due to temperature changes and affects the synthesis of AlN whiskers.

Claims

1. A method for preparing AlN whiskers at low temperature using halloysite as raw material, characterized in that: The method comprises: calcining the halloysite; The calcined halloysite is mixed with sodium chloride and aluminum powder for reaction to obtain the product.

2. The method according to claim 1, characterized in that The reaction is carried out under the following procedure: Heating stage: In the first stage, the temperature rises from room temperature to 350-400°C, with a heating rate of 1-5°C / min; In the second stage, the temperature is raised to 400-450°C, with a heating rate of 1-5°C / min; The third stage is to heat to 600-700℃, with a heating rate of 1-5℃ / min and keep warm for 3-5h; Cooling stage: In the first stage, the temperature drops to 250-350℃, and the cooling rate is 1-2℃ / min; The second stage is to cool naturally to room temperature.

3. The method according to claim 1 or 2, characterized in that: The calcination is carried out under the following procedure: The temperature is raised from room temperature to 400-700°C at a heating rate of 1-10°C / min, kept at this temperature for 1-3 hours, and then cooled naturally to room temperature.

4. The method according to claim 1, characterized in that The mass ratio of the calcined halloysite to the sodium chloride and the aluminum powder is 1:1:

4.

5. The method according to claim 1, characterized in that The halloysite is 7-E halloysite in terms of mineralogical properties.

6. The method according to claim 5, characterized in that The purity of the 7A Helloydite is 95-100%.

7. The method according to any one of claims 1 to 6, characterized in that: The method also includes post-processing.

8. The method according to claim 7, characterized in that The post-processing at least includes: The obtained reaction product is acid washed.

9. The method according to claim 8, characterized in that The post-treatment also includes solid-liquid separation, and / or water washing, and / or drying.

10. An AlN whisker, characterized in that: The AlN whisker is prepared by the method described in any one of claims 1 to 9, and has a whisker diameter of 30 to 100 nm and a length of 1 to 3 μm.

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