A method for synthesizing nano-aluminum oxynitride (AlON) powder from a single raw material

Abstract

The application discloses a method for synthesizing AlON powder with single raw material. A composite precursor material containing Al source or AlN source and Al x O y H z source is synthesized by hydrolysis with single aluminum source, and then pure-phase AlON powder is synthesized by combining aluminum-thermal direct nitriding method or solid-phase reaction method. The Al x O y H z source of the application is a composite precursor material with coating structure based on raw material powder surface hydrolysis or pyrolysis and with nanometer size, which improves the contact area and mixing uniformity of the raw material, shortens the diffusion path of the reactants, effectively inhibits local sintering and gathering and growing of the intermediate product, and synthesizes powder with a particle size of about 50 nm, thereby significantly reducing the synthesis temperature of the powder and effectively avoiding the difficulty in controlling the proportion of two-phase or more raw material powders and the uneven mixing, which leads to uneven composition of the synthesized AlON powder. The application simplifies the synthesis process, reduces the production cost and improves the powder synthesis quality.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of ceramic powder preparation, and particularly relates to a method for synthesizing nano AlON powder from a single raw material. BACKGROUND

[0002] AlON ceramic with cubic spinel structure has excellent optical and mechanical properties, and is an ideal structural-functional integrated polycrystalline ceramic material, which can be used as a candidate material in the fields of transparent armor, mid-infrared window, radome and the like. The preparation of high-optical-quality AlON transparent ceramic material depends on the synthesis process of the powder thereof, and the powder with high purity, small particle size, good dispersity and high sintering activity is a prerequisite for optimizing the sintering process of AlON ceramic.

[0003] The synthesis of AlON powder is currently the most mature carbon reduction nitriding method (CRN), solid phase reaction method (SSR) and direct nitriding method (DN). For CRN method, the patent application with publication number CN103242043B discloses a synthesis method of aluminum oxynitride powder, taking Al2O3 and carbon powder as raw materials, adopting ball milling method to mix materials, flowing nitrogen gas is continuously filled into graphite atmosphere furnace after passing through humidifying device, graphite furnace is heated to 1850℃ at a rate of 10℃ / min and kept for 2h to synthesize aluminum oxynitride powder. The patent application with publication number CN109265177A discloses a synthesis method of AlON powder, adopting high-purity alumina grinding balls to ball mill and sieve mixed powder of alumina and aluminum nitride, and then high-temperature calcination is carried out under flowing nitrogen gas environment, high-temperature calcination temperature is 1750℃, and calcination time is 10-30min to obtain AlON transparent ceramic powder. The patent application with publication number CN108610054A discloses an AlON powder synthesis technology, which selects γ-Al2O3 powder with certain purity and carbon source as raw materials, the carbon source is loaded into the heating chamber of the fluidized bed and preheated, nitrogen gas is introduced into the reaction chamber of the fluidized bed at the same time to form a nitrogen atmosphere, the temperature in the reaction chamber of the fluidized bed is raised, and nitrogen gas is introduced from the bottom of the reaction chamber of the fluidized bed as a boiling gas, so that part of Al2O3 is reduced by the carbon source to form gaseous Al2O3 or Al, then reacts with nitrogen to form a mixed powder of AlN and Al2O3, and the temperature in the reaction chamber of the fluidized bed is continuously raised to make Al2O3 and AlN generate AlON through solid phase reaction at high temperature. The patent application with publication number CN105622104A discloses an AlON powder synthesis technology, which takes C and Al2O3 as raw materials, and the mass percentage of C and γ-Al2O3 is 4.5-6.5wt% and 93.5-95.5wt% respectively, through pre-mixed liquid preparation, slurry preparation, freeze-drying, low-temperature calcination, and high-temperature 1700-1800℃ holding for 0.5-2h reaction to synthesize AlON. For solid phase reaction method, Liu Xuejian et al. (Liu Xuejian, Li Huili, Huang Zhengren, Wang Shivi, Jiang Dongliang. Preparation of AlON powder by high-temperature solid phase reaction process [J]. Journal of Inorganic Materials, 2009, 24(06): 1159-1162) take Al2O3 and AlN as raw materials, and synthesize single-phase AlON powder when calcined at 1950℃ for 4h. For direct nitriding method of alumina, Zhou Jicheng et al. (Zhou Jicheng, Liao Zhijun, Qi Jianqi, Pang Wei, Cheng Zimo, Wu Dengxue, Lu Tiecheng. Study on synthesis of AlON powder by reaction sintering method [J]. Rare Metal Materials and Engineering, 2007(S1): 72-75) take micron-sized Al powder and nano-sized Al2O3 powder as raw materials, and synthesize pure-phase AlON powder under the condition of direct nitriding at 1800℃ for 3h.Patent application with publication number CN104446496A discloses a method for preparing AlON powder and transparent ceramics prepared therefrom. It uses aluminum powder and alumina powder as raw materials and adopts direct nitridation method to synthesize pure phase AlON powder. The synthesis conditions are keeping warm at 1750°C for 3 hours.

[0004] The AlON powders prepared by the above-mentioned carbon thermal reduction method, solid-phase reaction method and direct nitridation method of alumina generally have a synthesis temperature of up to 1750-1850°C. The high synthesis temperature increases the preparation cost of the material, and the particle size of the powder will also grow to several microns or even tens of microns, thereby reducing the sintering activity of the powder. In addition, the existing AlON powder synthesis methods all use two or more phases of raw materials, the powder ratio is difficult to control and the mixing is uneven, which easily leads to uneven chemical composition of the synthesized AlON powder and complex and difficult to control process, and has high requirements on equipment and cumbersome procedures. Summary of the Invention

[0005] In order to improve the above technical problems, the present invention provides a method for synthesizing AlON powder, comprising subjecting a single aluminum source to a hydrolysis reaction to obtain a composite precursor having a coating structure, and then calcining at a high temperature to prepare the AlON powder.

[0006] According to an embodiment of the present invention, the hydrolysis reaction is carried out in a solvent system. For example, the volume solid content of the single aluminum source in the solvent is 0.1% vol-70% vol, exemplified by 0.1% vol, 1% vol, 2% vol, 5% vol, 10% vol, 20% vol, 50% vol, and 70% vol.

[0007] According to an embodiment of the present invention, the hydrolysis reaction is carried out under stirring. For example, the stirring time is 1-200 hours, exemplified by 1 hour, 10 hours, 20 hours, 30 hours, 40 hours, 50 hours, 60 hours, 70 hours, 80 hours, 100 hours, 150 hours, and 200 hours.

[0008] In the present invention, hydrolysis starts from the surface of the raw material, so the precursor material prepared by the hydrolysis method has the characteristics of small particle size, uniform distribution, high activity, etc., which can effectively avoid grain growth and impurity introduction during the high-temperature calcination of the powder.

[0009] According to an embodiment of the present invention, the single aluminum source is elemental Al powder or an Al-containing compound (such as at least one of AlN, 27R (Al9O3N7), 21R (Al7O3N5) and 12H (Al6O3N4), etc.).

[0010] According to an embodiment of the present invention, the solvent is preferably at least one of water and alcohol.

[0011] According to an embodiment of the present invention, the purity of the single aluminum source is preferably ≥99.0%, and the particle size is 0.2-50 μm, exemplified by 0.2 μm, 1 μm, 2.4 μm, 5 μm, 10 μm, 20 μm, 30 μm, 40 μm, and 50 μm.

[0012] According to an embodiment of the present invention, the preparation method also includes a process in which after the hydrolysis reaction is completed, the reaction system is subjected to solid-liquid separation to obtain a reaction product. For example, the solid-liquid separation can be carried out by means known in the art, such as suction filtration. For example, suction filtration can be carried out as follows: a disc filter paper moistened with deionized water is placed in a Büchner funnel and placed on a suction filtration bottle, a vacuum water pump is opened to adsorb the filter paper on the Büchner funnel, and then the composite precursor solution obtained by the hydrolysis reaction is poured into the Büchner funnel, deionized water is added while vacuum filtration, and the solution is washed 1-5 times until the filtered solution is clarified (vacuum filtration and washing can remove impurities in the mobile phase and stabilize the components of the composite precursor).

[0013] According to an embodiment of the present invention, the preparation method further comprises washing the reaction product obtained by solid-liquid separation. For example, the solvent may be water.

[0014] According to an embodiment of the present invention, the preparation method further comprises drying the reaction product after washing. For example, the drying method is, for example, vacuum drying. Preferably, the drying temperature is 60 to 80°C, exemplified by 70°C; the drying time is 1-4h, exemplified by 1h, 2h, 3h, 4h. For example, the composite precursor after suction filtration and water washing can be placed in a vacuum drying oven together with a disc filter paper and dried at 70°C for 1-4h, and the composite precursor after drying is sieved through a 150-mesh sieve. Drying the disc filter paper together with the composite precursor after suction filtration and water washing can easily peel off the composite precursor from the filter paper, and can effectively avoid the composite precursor material from adhering to the disc filter paper, resulting in a reduction in mass and uneven components.

[0015] According to an embodiment of the present invention, the preparation method further comprises sieving the dried sample.

[0016] According to an embodiment of the present invention, the composite precursor is at least one of a single aluminum source coated with diaspore, a single aluminum source coated with aluminum hydroxide, or a single aluminum source coated with diaspore and aluminum hydroxide. The precursor powder with the coating structure increases the contact area and mixing uniformity between the raw materials, shortens the diffusion path, and effectively inhibits the localized sintering and convergent growth of the mesophase during high-temperature calcination.

[0017] According to an embodiment of the present application, the high-temperature calcination is performed at a temperature of 1600-1750℃, for example, 1600℃, 1650℃, 1700℃, 1720℃, 1750℃; the high-temperature calcination is performed for a holding time of 1-4h, for example, 1h, 2h, 3h, 4h; and the high-temperature calcination is performed at a heating rate of 1-20℃ / min, for example, 1℃ / min, 5℃ / min, 10℃ / min, 15℃ / min, 20℃ / min.

[0018] According to an embodiment of the present application, the high-temperature calcination is performed in an inert atmosphere. For example, the inert gas is one or a combination of nitrogen, argon and helium.

[0019] According to an embodiment of the present application, after the high-temperature calcination, the reaction system is further cooled. For example, the reaction system is cooled to a temperature of 900-1100℃ (for example, 1000℃), and then naturally cooled to room temperature; and the cooling rate is 1-10℃ / min, for example, 1℃ / min, 5℃ / min, 10℃ / min.

[0020] In one embodiment of the present application, the high-temperature calcination is performed by, for example, placing the composite precursor in a boron nitride crucible, heating the composite precursor to a temperature of 1600-1750℃ at a heating rate of 1-20℃ / min under a nitrogen atmosphere, holding the temperature for 1-4h, and then cooling the composite precursor to a temperature of 1000℃ at a cooling rate of 1-10℃ / min, and cooling the composite precursor to room temperature in the furnace.

[0021] According to an embodiment of the present application, the method for preparing the AlON powder comprises the following steps:

[0022] ① Hydrolysis reaction: stirring a single aluminum source in a solvent to obtain a composite precursor solution with a coating structure;

[0023] ② Filtration and sieving: filtering, washing and drying the composite precursor solution, and sieving to obtain the composite precursor;

[0024] ③ Calcination: high-temperature calcination of the composite precursor in an inert atmosphere to synthesize the AlON powder.

[0025] The present application also provides the AlON powder prepared by the above method.

[0026] According to an embodiment of the present application, the particle size of the AlON powder is 10-100nm, for example, 10nm, 20nm, 30nm, 40nm, 50nm, 60nm, 70nm, 80nm, 90nm, 100nm.

[0027] The present application also provides the application of the AlON powder in the fields of transparent armor, mid-infrared window, spinner, etc.

[0028] Beneficial effects of the present invention:

[0029] Aiming at the problems existing in the synthesis of AlON powder in the existing technology, especially the mixing of multiple raw materials, complex process, high equipment requirements, cumbersome operation procedures, high synthesis temperature, large particle size of synthetic powder, and low controllability. The present invention adopts a single raw material hydrolysis method to synthesize a composite precursor material with a coating structure. First, the raw materials required for the synthesis are easy to obtain and single. Second, the hydrolysis method has low equipment requirements and is simple to operate and easy to control. Finally, the composite precursor material with a coating structure can increase the direct contact area and mixing uniformity of the raw materials in the SSR or DN method, shorten the diffusion path of the reaction raw materials, effectively inhibit the local sintering and aggregation growth of the intermediate phase in the SSR or DN method, significantly reduce the AlON synthesis temperature while also inhibiting the growth of grains, so that its synthesis temperature is 50-250°C lower than the traditional AlON powder synthesis temperature. The low synthesis temperature and the composite precursor with a coating structure enable the particle size of the finally prepared AlON powder to be controlled at about 50nm, which is significantly smaller than the particle size of AlON powder prepared by the existing CRN, SSR, and DN methods, which is more than 10μm, and the submicron-level AlON powder prepared by the wet chemical method of CRN. At the same time, the introduction of a single raw material avoids the difficulty in controlling the ratio of two or more raw material powders and uneven mixing, which results in uneven chemical composition of the synthesized AlON powder. The use of a single powder raw material to synthesize AlON powder simplifies the synthesis process, reduces production costs, and improves the quality of powder synthesis.

[0030] Compared with existing technologies for synthesizing AlON powder, the hydrolysis combined with SSR or DN methods significantly reduces the synthesis temperature of AlON powder. Furthermore, the present invention shortens the synthesis time and produces a small AlON powder with a particle size of approximately 50 nm. Furthermore, the present invention uses a single aluminum source to avoid the difficulty in controlling the ratio and uneven mixing of two or more raw material powders, which can result in uneven chemical composition of the synthesized AlON powder. Furthermore, the use of a single powder raw material to synthesize AlON powder simplifies the synthesis process, reduces production costs, and improves the quality of the powder synthesis. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 (a) is the XRD spectrum of the composite precursor powder synthesized in Example 1, Figure 1 (b) is the SEM image of the composite precursor powder synthesized in Example 1.

[0032] Figure 2 This is the XRD spectrum of the AlON powder obtained by calcining in Examples 2 and 3.

[0033] Figure 3 This is the SEM image of the AlON powder obtained by calcining in Example 2.

[0034] Figure 4 TEM and EDS images of the composite precursor powder synthesized in Example 1.

[0035] Figure 5 This is the XRD spectrum of the composite precursor powder synthesized in Example 4.

[0036] Figure 6 This is the XRD spectrum of the AlON powder synthesized in Example 5. DETAILED DESCRIPTION

[0037] The technical solutions of the present invention will be described in further detail below with reference to specific embodiments. It should be understood that the following embodiments are merely illustrative and explanations of the present invention and should not be construed as limiting the scope of protection of the present invention. All technologies implemented based on the above content of the present invention are encompassed within the scope of protection that the present invention is intended to protect.

[0038] Unless otherwise specified, the raw materials and reagents used in the following examples are commercially available or can be prepared by known methods.

[0039] In the following examples of the present invention, X-ray diffraction (XRD) analysis was performed using an X-ray diffraction analyzer (Miniflex-600, Rigaku, Japan).

[0040] Scanning electron microscopy (SEM) analysis was performed using a scanning electron microscope (SU-8010, Hitachi, Japan).

[0041] Transmission electron microscopy (TEM) analysis was performed using a transmission electron microscope (TEM; FEI Tecnai G 2 F20, Hillsboro, OR, USA).

[0042] Example 1

[0043] A method for synthesizing a composite precursor powder comprises the following steps:

[0044] ① Hydrolysis reaction: Deionized water and Al powder (particle size 2.4 μm, purity 99.9%) were measured and placed in the same plastic cup at a concentration of 2% vol. The mixture was then hydrolyzed for 0 h, 10 h, 20 h, 30 h, 40 h, 50 h, 60 h, and 70 h using magnetic stirring to obtain a composite precursor solution.

[0045] ② Filtration and drying: Pour the composite precursor solution hydrolyzed in step ① into a Buchner funnel and place it on a filtration bottle. Vacuum filter and wash with water 1-5 times until the filtered solution is clear. Dry in a vacuum drying oven at 60°C for 4 hours and then pass through a 150 sieve.

[0046] Figure 1 Figure (a) shows the XRD spectra of the composite precursor powders obtained after hydrolysis for 0, 10, 20, 30, 40, 50, 60, and 70 hours in Example 1. The figure shows that the hydrolysis of elemental aluminum powder produces low-temperature alumina (diaspore and aluminum hydroxide). Due to the incomplete hydrolysis of elemental aluminum, both low-temperature alumina and elemental aluminum are present in the hydrolysis product. Therefore, AlON powder can be synthesized by direct nitridation (DN) under a nitrogen atmosphere.

[0047] Figure 1 (b) is the SEM characterization result of the composite precursor powder obtained by hydrolysis for 20 hours in Example 1. It can be seen from the figure that after the elemental aluminum powder is hydrolyzed for 20 hours, a thin layer of diaspore begins to appear on the surface.

[0048] Figure 4 These are TEM and EDS images of the composite precursor obtained after hydrolysis of elemental aluminum for 20 hours in this embodiment. It can be seen from the figure that the hydrolysis product is a composite structure of low-temperature phase alumina coating elemental aluminum.

[0049] Example 2

[0050] A method for synthesizing AlON powder

[0051] ③ Hydrolysis combined with DN method: The composite precursor powder obtained in step ② of Example 1 was hydrolyzed for 20 hours. It was placed in a boron nitride crucible and placed in a carbon tube furnace. The furnace was then slowly evacuated and filled with high-purity nitrogen to a slightly positive pressure. The carbon tube furnace was heated from room temperature to 1700°C at 10°C / min for 2 hours, then cooled to 1000°C at 10°C / min, and then cooled to room temperature with the furnace to obtain pure phase AlON powder.

[0052] The obtained product was tested by X-ray diffraction. Figure 2 As shown in the figure, it can be seen that the pure phase AlON powder is prepared in this embodiment.

[0053] Figure 3 This is a SEM image of the AlON powder obtained by calcining in Example 2. As can be seen from the figure: the particle size of the AlON powder obtained in this example is about 50nm.

[0054] Example 3

[0055] A method for synthesizing AlON powder, compared with Example 2, differs in that: reaction conditions, such as the carbothermal reaction heating rate and synthesis temperature, are changed.

[0056] ③ Hydrothermal combined with DN method: The composite precursor powder obtained in step ② of Example 1 was hydrolyzed for 20 hours. It was placed in a boron nitride crucible and placed in a carbon tube furnace. The furnace was then slowly evacuated and filled with high-purity nitrogen to a slightly positive pressure. The carbon tube furnace was heated from room temperature to 1720°C at 15°C / min for 2 hours and then cooled to 1000°C at 10°C / min. It was cooled to room temperature with the furnace to obtain pure phase AlON powder.

[0057] The obtained product was detected by X-ray diffraction to be pure AlON powder.

[0058] Example 4

[0059] A method for synthesizing a composite precursor powder, compared with Example 1, differs in that the single aluminum source used is aluminum nitride AlN powder, and includes the following steps:

[0060] A method for synthesizing a composite precursor powder comprises the following steps:

[0061] ① Hydrolysis reaction: Deionized water and AlN powder (particle size 4.1 μm, purity 99.9%) were measured and placed in the same plastic cup at a ratio of 2% vol. The mixture was hydrolyzed for 0 h, 10 h, 20 h, 30 h, 40 h, 50 h, and 60 h using magnetic stirring to obtain a composite precursor solution.

[0062] ② Filtration and drying: Pour the composite precursor solution hydrolyzed in step ① into a Buchner funnel and place it on a filtration bottle. Vacuum filter and wash with water 1-5 times until the filtered solution is clear. Dry in a vacuum drying oven at 60°C for 4 hours and then pass through a 150 sieve.

[0063] Figure 5 Figure 3 shows the XRD spectra of the composite precursor powder obtained after hydrolysis for 0, 10, 20, 30, 40, 50, and 60 hours in Example 4. The spectra show that aluminum hydroxide is first generated after AlN hydrolysis. By utilizing incomplete hydrolysis of AlN, a composite precursor of aluminum hydroxide and aluminum nitride can be obtained. Subsequently, AlON powder can be synthesized by solid-state reaction (SSR method) under a nitrogen atmosphere.

[0064] Example 5

[0065] A method for synthesizing AlON powder

[0066] ③ Hydrothermal combined with SSR method: The composite precursor powder obtained in step ② of Example 4 was hydrolyzed for 20 hours. It was placed in a boron nitride crucible and placed in a carbon tube furnace. The furnace was then slowly evacuated and filled with high-purity nitrogen to a slightly positive pressure. The carbon tube furnace was heated from room temperature to 1700°C at 20°C / min for 3 hours and then cooled to 1000°C at 10°C / min. It was cooled to room temperature with the furnace to obtain pure phase AlON powder.

[0067] like Figure 6 As shown, the obtained product was detected by X-ray diffraction to be pure phase AlON powder.

[0068] The above describes the embodiments of the present invention. However, the present invention is not limited to the above embodiments. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention shall be included in the scope of protection of the present invention.

Claims

1. A method for synthesizing AlON powder, characterized in that: The method comprises subjecting a single aluminum source to a hydrolysis reaction to obtain a composite precursor having a coating structure, and then calcining the precursor at a high temperature to obtain the AlON powder; The single aluminum source is at least one of elemental Al powder, Al9O3N7, Al7O3N5 and Al6O3N4.

2. The method according to claim 1, wherein The hydrolysis reaction is carried out in a solvent system, and the volume solid content of the single aluminum source in the solvent is 0.1% vol-70% vol; And / or, the hydrolysis reaction is carried out under stirring, and the stirring time is 1-200 hours.

3. The method according to claim 2, wherein The solvent is water.

4. The method according to any one of claims 1 to 3, further comprising a step of performing solid-liquid separation on the reaction system to obtain a reaction product after the hydrolysis reaction is completed; The method further comprises washing the reaction product obtained by solid-liquid separation, wherein the washing solvent is water; The method further comprises drying the washed reaction product.

5. The method according to any one of claims 1 to 3, wherein The composite precursor is at least one of a single aluminum source coated with diaspore, a single aluminum source coated with aluminum hydroxide, and a single aluminum source coated with diaspore and aluminum hydroxide.

6. The method according to any one of claims 1 to 3, wherein: The temperature of the high-temperature calcination is 1600-1750° C.; the holding time of the high-temperature calcination is 1-4 hours; and the heating rate of the high-temperature calcination is 1-20° C. / min.

7. The method according to any one of claims 1 to 3, wherein: The high-temperature calcination is carried out under an inert atmosphere, and the inert atmosphere is one, two or more of nitrogen, argon and helium.

8. The method according to any one of claims 1 to 3, wherein: After the high-temperature calcination is completed, the reaction system is cooled to 900-1100° C. and then naturally cooled to room temperature.

9. The method according to claim 8, wherein The cooling rate is 1-10°C / min.

10. The method according to any one of claims 1 to 3, wherein: The following steps are involved: ① Hydrolysis reaction: a single aluminum source is placed in a solvent and stirred evenly, and hydrolyzed to obtain a composite precursor solution with a coating structure; ② Filtration and sieving: Filter the composite precursor solution, wash, dry, and sieve to obtain the composite precursor; ③ Calcination: Calcine the composite precursor at high temperature in an inert atmosphere to synthesize AlON powder.

11. AlON powder prepared by the method according to any one of claims 1 to 10.

12. The AlON powder according to claim 11, wherein The particle size of the AlON powder is 10-100 nm.

13. Application of the AlON powder according to claim 11 or 12 in the fields of transparent armor, mid-infrared windows, and fairings.

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