Nanometer aluminum nitride powder with uniform particle size distribution and preparation method thereof

Abstract

The application discloses a kind of nanometer aluminum nitride powder with uniform particle size distribution and a preparation method thereof.The preparation method comprises the following steps: taking each raw material according to molar ratio: aluminum nitrate nonahydrate: aluminum alkoxide: urea=(0.7-0.9):(0.1-0.3):1, dissolving the raw materials in deionized water, stirring at room temperature until completely dissolved to obtain a homogeneous solution; solidifying the homogeneous solution to obtain a solid, vacuum drying under low temperature conditions to obtain a solid precursor; heating the solid precursor to the combustion initiation temperature in a container; at the combustion initiation temperature, the solid precursor is converted into an alumina / carbon composite precursor powder due to the redox reaction; placing the alumina / carbon composite precursor powder in a nitriding furnace, heating to the nitriding temperature under a flowing nitrogen atmosphere and holding, allowing the alumina and carbon to undergo carbothermic reduction nitriding reaction to obtain an intermediate product, and performing decarburization treatment on the intermediate product in an air atmosphere and holding to obtain nanoscale aluminum nitride powder.

Description

Technical Field

[0001] This invention relates to the field of aluminum nitride ceramics, and more specifically to a nano-aluminum nitride powder with uniform particle size distribution and its preparation method. Background Technology

[0002] In the fields of 5G communication, high-power chips, and high-end electronic devices, efficient thermal management has become crucial for device performance and reliability. Aluminum nitride (AlN) ceramics, due to their excellent thermal conductivity (320 W·m⁻¹·K⁻¹), low coefficient of thermal expansion matching that of semiconductor materials, and good insulation properties, are considered ideal high thermal conductivity substrates and packaging materials. However, the widespread application of aluminum nitride ceramics is limited by the preparation of high-quality powders. The purity, particle size, uniformity, and sintering activity of the powder directly affect the densification behavior, thermal conductivity, and mechanical properties of the final ceramic.

[0003] Currently, the industrial production of AlN powder mainly adopts the carbothermic reduction method, which has problems such as high reaction temperature (1500–1800℃), high energy consumption, poor raw material mixing uniformity, and wide product particle size distribution. Other methods, such as direct nitridation and self-propagating high-temperature synthesis, also have limitations in terms of process control, product purity, or cost.

[0004] Solution combustion synthesis is an effective method for preparing nano-oxide powders, offering advantages such as molecular-level mixing of raw materials, rapid reaction, and relatively low energy consumption. However, traditional solution combustion methods have inherent drawbacks in the solvent evaporation stage: as the solvent evaporates, different components, due to differences in solubility and surface tension, undergo stepwise crystallization and local segregation, disrupting the chemical homogeneity of the precursor. This microscale component inhomogeneity directly affects the thoroughness of subsequent nitriding reactions, leading to residual impurities or a broadened grain size distribution in the product, thereby reducing the thermal conductivity and mechanical properties of aluminum nitride ceramics.

[0005] Some studies have employed improved methods to prepare aluminum nitride powder by directly mixing aluminum salts with carbon sources. For example, Chinese patent CN117720353A attempts to achieve molecular-level mixing by co-dissolving aluminum nitrate and a water-soluble carbon source in water. However, its core drawback lies in the fact that during the subsequent evaporation and drying process, as the solvent evaporates, different components (Al...)... 3+ Due to differences in solubility and surface tension, carbon source molecules undergo stepwise crystallization and local segregation. This microscopic compositional inhomogeneity directly affects the thoroughness of subsequent nitriding reactions, leading to residual impurities or a broadened grain size distribution in the product.

[0006] Furthermore, Chinese patent CN118125391A utilizes the hydrolysis of aluminum alkoxides to form an Al-O-Al network, achieving molecular-level mixing with a carbon source. However, this method still suffers from the following inherent drawbacks:

[0007] Lack of an oxidation-fuel system: The precursor does not contain a strong oxidant and cannot utilize the self-propagating exothermic characteristics of solution combustion synthesis (SCS), resulting in the reaction relying on an external heat source for slow heating, which leads to high energy consumption and low reaction efficiency.

[0008] Hydrolysis and condensation are difficult to control: The hydrolysis and condensation reactions of aluminum alkoxides are extremely sensitive to temperature and pH. During slow hydrolysis and subsequent traditional oven drying processes that last for several hours, local over-crosslinking or agglomeration is likely to occur, which introduces new inhomogeneities at the nanoscale.

[0009] Drying segregation still exists: Traditional oven drying is essentially a liquid-phase evaporation process, and capillary forces will drag incompletely cross-linked components, resulting in a certain degree of component redistribution.

[0010] Insufficient particle size distribution control: This method only focuses on the average particle size and does not address the issue of particle size distribution broadening. For powder applications requiring high uniformity (such as tape casting), the product uniformity remains unsatisfactory. Summary of the Invention

[0011] The purpose of this invention is to provide a nano-aluminum nitride powder with uniform particle size distribution and its preparation method, so as to improve the above-mentioned problems.

[0012] This invention provides a method for preparing nano-aluminum nitride powder with uniform particle size distribution, comprising the following steps: S1. Weigh the raw materials in the following molar ratio: aluminum nitrate nonahydrate: aluminum alkoxide: urea = (0.7–0.9):(0.1–0.3):1. Dissolve the raw materials together in deionized water and stir at room temperature until completely dissolved to obtain a homogeneous solution. During the dissolution process, the aluminum alkoxide undergoes partial hydrolysis to form an Al–O–C bond network, thereby forming a molecularly homogeneous mixture with the aluminum nitrate solution. S2, the homogeneous solution is solidified to obtain a solid, and then the solid is vacuum dried at low temperature to remove all moisture and obtain a loose, sponge-like solid precursor that maintains its initial uniform distribution. S3, the solid precursor is placed in a container and heated to the combustion initiation temperature at a certain heating rate; at the combustion initiation temperature, the solid precursor is transformed into a fluffy, porous, black foam-like alumina / carbon composite precursor powder due to the redox reaction between the aluminum nitrate and the urea. S4, the alumina / carbon composite precursor powder is placed in a crucible in a nitriding furnace, and heated to the nitriding temperature under a flowing high-purity nitrogen atmosphere and kept at the temperature, so that the alumina and carbon undergo a carbothermic reduction nitriding reaction to obtain an intermediate product containing aluminum nitride and residual carbon. S5, the intermediate product is subjected to decarburization treatment and heat preservation in an air atmosphere to remove residual carbon and obtain high-purity, near-spherical, uniformly sized nano-sized aluminum nitride powder.

[0013] Preferably, in step S1, a water-soluble carbon source is added to make the molar ratio of C / Al 12–16.

[0014] Preferably, the water-soluble carbon source is glucose, and the aluminum alkoxide is one or more of aluminum isopropoxide, aluminum sec-butoxide, or aluminum ethoxide.

[0015] Preferably, in step S2, the curing process is to rapidly transform the homogeneous solution into a solid under conditions without liquid phase flow, and the vacuum drying under low temperature conditions is performed at a temperature lower than the freezing point of the solvent.

[0016] Preferably, in step S3, the heating rate is 10°C / min, and the combustion initiation temperature is 280-320°C. At the combustion initiation temperature, aluminum nitrate, as an oxidant, undergoes a redox reaction with urea, as fuel, and water-soluble carbon source, instantly releasing a large amount of gas and transforming into fluffy, porous, black foam-like alumina / carbon composite precursor powder within seconds to minutes.

[0017] Preferably, in step S4, the purity of nitrogen is 99.999%, the flow rate is 500 mL / min, the nitriding temperature is 1350–1450℃, and the holding time is 4–8 hours.

[0018] Preferably, in step S4, the decarburization treatment temperature is 680–720°C, and the holding time is 2–4 hours.

[0019] This invention also provides a nano-aluminum nitride powder with uniform particle size distribution, which is prepared by the above-described method for preparing nano-aluminum nitride powder.

[0020] Preferably, the average grain size of the nano-aluminum nitride powder is ≤50 nm, and the purity is ≥99.0%.

[0021] This invention also provides an aluminum nitride ceramic, which is prepared using nano-aluminum nitride powder with uniform particle size distribution as described above.

[0022] Compared with the prior art, the present invention has at least the following beneficial effects: 1. Enhanced chemical bonding between aluminum and carbon sources: This invention is the first to use aluminum nitrate in combination with aluminum alkoxide as a mixed aluminum source. Compared with the single aluminum nitrate system, the introduction of aluminum alkoxide establishes an Al-OC chemical bonding network; compared with the single aluminum alkoxide system, the introduction of aluminum nitrate provides the strong oxidant NO3. -This allows the combustion reaction to occur violently. The two work synergistically to achieve chemical bonding between the aluminum and carbon sources, in-situ recombination of the oxidant and fuel, and uniform mixing at the molecular / ionic level.

[0023] 2. Rapid curing and drying to lock in a uniform state: This invention utilizes a rapid curing and low-temperature vacuum drying process to completely avoid component migration caused by liquid phase shrinkage and capillary forces during solvent removal. This process transfers the molecular-level mixed state in the solution to the solid precursor, laying an ideal material foundation for subsequent combustion and nitriding reactions.

[0024] 3. High combustion reaction efficiency: This invention retains aluminum nitrate as an oxidant to ensure that the combustion synthesis reaction can occur vigorously and completely. Simultaneously, the Al–O–C network structure introduced by the aluminum alkoxide makes the combustion reaction more uniform and controllable, and the generated precursor has a higher specific surface area (>150 m²). 2 / g) and a more regular pore structure.

[0025] 4. Excellent product performance: The aluminum nitride powder finally prepared by this invention has high purity (≥99.0%), small particle size (average grain size can reach 32±5 nm), narrow particle size distribution ((D90–D10) / D50 ≤ 0.8), and regular particle morphology (near spherical). It has high specific surface area and excellent sintering activity, which is beneficial for preparing aluminum nitride ceramics with high thermal conductivity and high density.

[0026] 5. High process controllability: This invention allows for flexible control of the precursor structure and the phase, particle size, and morphology of the final powder by adjusting parameters such as the ratio of aluminum alkoxide to aluminum nitrate, the C / Al molar ratio, hydrolysis reaction conditions, combustion temperature, and nitriding temperature and time. Systematic studies have shown that the aluminum nitride powder exhibits the best overall performance when the aluminum alkoxide content is 20 mol% and the C / Al ratio is 14.

[0027] 6. The process is green and efficient: Compared with the traditional carbothermal reduction method (1500–1800℃), the nitriding temperature of this invention can be reduced by 100–200℃; compared with the conventional solution combustion method, it avoids repeated nitriding or impurity removal steps caused by component segregation. The overall process of this invention is simple, requires low equipment, has the potential for industrial production, and has significant cost advantages. Attached Figure Description

[0028] To more clearly illustrate the technical solution of the present invention, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0029] Figure 1 The images shown are SEM images and EDS elemental distribution maps of the Al2O3 / C composite precursor obtained in Example 1 of this invention; wherein, (a) is the SEM image of the Al2O3 / C composite precursor; (b) is the C elemental distribution map; (c) is the O elemental distribution map; and (d) is the Al elemental distribution map. Figure 2 This is a SEM image of the aluminum nitride powder obtained in Example 1 of the present invention; Figure 3 The XRD patterns of aluminum nitride powders prepared by different C / Al molar ratios are provided by the present invention. Detailed Implementation

[0030] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0031] Example 1 Weigh out 30.0 g (0.08 mol) of aluminum nitrate nonahydrate (Al(NO3)3·9H2O), 4.1 g (0.02 mol) of aluminum isopropoxide (Al(OC3H7)3), 6.0 g (0.1 mol) of urea (CO(NH2)2), and glucose (C6H2O). 12 25.2 g of O6·H2O (at this time, the C / Al molar ratio is 14) were dissolved together in 100 mL of deionized water and stirred at room temperature for 30 min until completely dissolved.

[0032] The above solution was subjected to rapid solidification treatment to transform the entire solution into a solid state. Subsequently, it was vacuum dried at low temperature to remove all moisture, resulting in a sponge-like solid precursor.

[0033] The solid precursor was placed in an alumina crucible and then placed in a muffle furnace. The temperature was increased to 300°C at a rate of 10°C / min to initiate a combustion reaction. The combustion reaction was completed within a few seconds. After natural cooling, a black, fluffy alumina / carbon (Al2O3 / C) composite precursor powder was obtained. After slight grinding, it was passed through a 200-mesh sieve. The SEM image and elemental distribution diagram of the Al2O3 / C composite precursor powder are shown below. Figure 1 As shown in the EDS elemental distribution diagram analysis, the Al, O, and C element distribution in the Al2O3 / C composite precursor powder of this embodiment has better uniformity, which is more than 80% higher than that of the single aluminum nitrate solution.

[0034] The sieved Al2O3 / C composite precursor powder was placed in a graphite crucible and then placed in a tube furnace. Under the protection of flowing high-purity nitrogen (99.999% purity, flow rate 500 mL / min), the temperature was increased to 1400℃ at 10°C / min and held for 6 h. After natural cooling, an intermediate product containing AlN / C was obtained. The intermediate product was placed in a muffle furnace and held at 700℃ for 3 h in air to obtain grayish-white aluminum nitride nanoparticles. The SEM image of these nanoparticles is shown below. Figure 2 As shown.

[0035] Testing revealed that the average grain size of the obtained aluminum nitride powder was approximately 32 nm. Figure 3 As shown, the XRD pattern shows no Al2O3 or AlON impurity phase peaks, the purity is ≥99.0%, and the particle size distribution is uniform.

[0036] Example 2 The same preparation process as in Example 1 was used, except that the amount of aluminum isopropoxide was adjusted: 22.5 g (0.06 mol) of aluminum nitrate nonahydrate and 8.2 g (0.04 mol) of aluminum isopropoxide, while the amounts of other raw materials remained unchanged.

[0037] The results showed that the average grain size of the obtained aluminum nitride powder was about 38 nm, the purity was ≥98.8%, and the XRD pattern showed no impurity phase peaks.

[0038] Example 3 The same preparation process as in Example 1 was used, except that the amount of glucose was adjusted: 18.0 g of glucose, at which point the molar ratio of C / Al was 10.

[0039] like Figure 3 As shown, the results indicate that weak Al2O3 diffraction peaks appear in the XRD pattern of the obtained aluminum nitride powder, indicating that the nitriding is incomplete and the average grain size is about 45 nm.

[0040] Example 4 The same preparation process as in Example 1 was used, only the amount of glucose was adjusted: 21.6 g of glucose, at which point the molar ratio of C / Al was 12.

[0041] like Figure 3 As shown, the results indicate that the obtained aluminum nitride powder has an average grain size of approximately 35 nm, a purity of ≥98.9%, and no impurity phase peaks in its XRD pattern.

[0042] Comparative Example 1 (Single aluminum nitrate + conventional evaporation drying) The same raw material ratio as in Example 1 was used (37.5 g of aluminum nitrate nonahydrate, without aluminum isopropoxide), but the drying step was changed to: the solution was placed in an oven and evaporated at 80°C to constant weight to obtain a solid precursor. Other steps were the same as in Example 1.

[0043] The results show that the uniformity of EDS element distribution in the Al2O3 / C precursor obtained in Comparative Example 1 is significantly worse than that in Example 1. A small amount of residual Al2O3 phase was detected in the final aluminum nitride powder, with an average grain size of about 80 nm and a broadened particle size distribution.

[0044] Comparative Example 2 (Single aluminum nitrate + rapid curing and drying) The same raw material ratio as Comparative Example 1 was used (without aluminum isopropoxide), but the drying steps were changed to the same rapid curing + low-temperature vacuum drying as in Example 1. The remaining steps were the same as in Example 1.

[0045] The results show that the aluminum nitride powder obtained in Comparative Example 2 has an average grain size of about 55 nm, a purity of ≥98.5%, and no obvious impurity phase peaks in its XRD pattern. However, its uniformity is still inferior to that of Example 1, indicating that the introduction of aluminum alkoxide has an irreplaceable enhancing effect on the uniformity of the precursor.

[0046] The above description is merely a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A method for preparing nano-aluminum nitride powder with uniform particle size distribution, characterized in that, Includes the following steps: S1. Weigh the raw materials in the following molar ratio: aluminum nitrate nonahydrate: aluminum alkoxide: urea = (0.7–0.9):(0.1–0.3):

1. Dissolve the raw materials together in deionized water and stir at room temperature until completely dissolved to obtain a homogeneous solution. During the dissolution process, the aluminum alkoxide undergoes partial hydrolysis to form an Al–O–C bond network, thereby forming a molecularly homogeneous mixture with the aluminum nitrate solution. S2, the homogeneous solution is solidified to obtain a solid, and then the solid is vacuum dried at low temperature to remove all moisture and obtain a loose, sponge-like solid precursor that maintains its initial uniform distribution. S3, the solid precursor is placed in a container and heated to the combustion initiation temperature at a certain heating rate; at the combustion initiation temperature, the solid precursor is transformed into a fluffy, porous, black foam-like alumina / carbon composite precursor powder due to the redox reaction between the aluminum nitrate and the urea. S4, the alumina / carbon composite precursor powder is placed in a crucible in a nitriding furnace, heated to the nitriding temperature under a flowing nitrogen atmosphere and held at that temperature, so that the alumina and carbon undergo a carbothermic reduction nitriding reaction to obtain an intermediate product containing aluminum nitride and residual carbon. S5, the intermediate product is subjected to decarburization treatment and heat preservation in an air atmosphere to remove residual carbon and obtain high-purity, near-spherical, uniformly sized nano-sized aluminum nitride powder.

2. The method for preparing uniformly sized nano-aluminum nitride powder according to claim 1, characterized in that, In step S1, a water-soluble carbon source is added to make the molar ratio of carbon source to aluminum source (C / Al) in the homogeneous solution 12–16.

3. The method for preparing uniformly sized nano-aluminum nitride powder according to claim 2, characterized in that, The water-soluble carbon source is glucose, and the aluminum alkoxide is one or more of aluminum isopropoxide, aluminum sec-butoxide, or aluminum ethoxide.

4. The method for preparing uniformly sized nano-aluminum nitride powder according to claim 1, characterized in that, In step S2, the curing process is to rapidly transform the homogeneous solution into a solid state under conditions without liquid phase flow, and the vacuum drying under the low-temperature conditions is performed at a temperature lower than the freezing point of the solvent.

5. The method for preparing uniformly sized nano-aluminum nitride powder according to claim 2, characterized in that, In step S3, the heating rate is 10°C / min, and the combustion initiation temperature is 280-320°C. At the combustion initiation temperature, aluminum nitrate, as an oxidant, reacts with urea, as fuel, and water-soluble carbon source in a redox reaction, instantly releasing a large amount of gas, and transforming into fluffy, porous, black foam-like alumina / carbon composite precursor powder within seconds to minutes.

6. The method for preparing uniformly sized nano-aluminum nitride powder according to claim 1, characterized in that, In step S4, the purity of nitrogen is 99.999%, the flow rate is 500 mL / min, the nitriding temperature is 1350–1450℃, and the holding time is 4–8 hours.

7. The method for preparing nano-aluminum nitride powder according to claim 1, characterized in that, 5. The decarburization treatment temperature is 680–720℃, and the holding time is 2–4 hours.

8. A nano-aluminum nitride powder with uniform particle size distribution, characterized in that, It was prepared using the preparation method of nano-aluminum nitride powder as described in any one of claims 1 to 7.

9. The uniformly sized aluminum nitride nanopowder according to claim 8, characterized in that, The average grain size of the nano-aluminum nitride powder is ≤50 nm, and the purity is ≥99.0%.

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