Highly Dispersible AlON Powder and its Synthesis Method and Preparation Method of AlON Transparent Ceramics

Abstract

This application relates to the field of ceramic powder preparation technology, and discloses highly dispersible AlON powder and its synthesis method and AlON transparent ceramic preparation method, including the following steps: (1) Powder mixing: Using γ-Al2O3 and solid carbon source as raw materials, the raw materials, additives, dispersants and anhydrous ethanol are ball-milled and mixed to obtain a mixed slurry. (2) Drying and sieving: The mixed slurry is dried, ground and sieved to obtain mixed powder. (3) Furnace loading and gas pressure sintering: The mixed powder is loaded into a perforated boron nitride crucible and sintered in a gas pressure sintering furnace to obtain highly dispersible AlON powder; (4) Decarbonization. The AlON powder synthesized by the synthesis method of this application has a near-spherical single crystal structure and has good high dispersibility.

Description

Technical Field

[0001] This application relates to the field of ceramic powder preparation technology, mainly to highly dispersible AlON powder and its synthesis method and the preparation method of AlON transparent ceramics. Background Technology

[0002] Spinel-type aluminum oxynitride (γ-AlON), as a metastable single-phase solid solution in the AlN-Al2O3 pseudo-binary system, can achieve stable cubic crystal structure (Fd-3m) by precisely controlling the stoichiometric ratio of oxynitride (AlN:Al2O3=3:5-9:11). Its unique three-dimensional network structure, with [AlO4N4] dodecahedrons and [AlO6] octahedrons sharing common vertices, endows the material with excellent structural properties and isotropic characteristics. The theoretical transmittance can reach 85% in the 0.25-6.5μm spectral range, with a Vickers hardness of 18.7±0.8GPa and a thermal shock threshold exceeding 850℃ (water quenching method). Based on these properties, γ-AlON transparent ceramics have established three major strategic application directions: fully transparent radomes for high Mach number aircraft (Ma>5); visible / infrared co-aperture transmission composite guidance systems; and gradient composite armor systems.

[0003] The preparation of high-performance γ-AlON transparent ceramics is highly dependent on obtaining AlON powder with high purity, narrow particle size distribution, regular morphology, and low agglomeration. However, existing mainstream powder synthesis technologies all have significant limitations: solid-state reaction methods rely on high-purity submicron / nano-scale Al2O3 / AlN biphase raw materials, which are costly. AlN is easily hydrated (AlN+3H2O→Al(OH)3+NH3↑), which means that the raw materials must be stored and handled under strict humidity control (RH<5%) and inert atmosphere, and complex ball milling processes are required. At the same time, the Al2O3 / AlN interface has a high diffusion barrier, requiring high-temperature sintering above 1800℃, which easily leads to the formation of micron-scale hard agglomerates. The aluminothermic reduction method is prone to local liquid phase sintering due to the low melting point of aluminum powder (660℃), resulting in a dispersed particle size distribution, and the oxide layer on the surface of the aluminum powder causes excess oxygen, resulting in a narrow process window. Although the carbothermal reduction method can significantly reduce raw material costs by reacting Al2O3 with carbon sources in an N2 atmosphere and can use gas-solid reaction to suppress abnormal grain growth, and residual carbon can be removed by secondary oxidation at 600-800℃, as in patents CN113582701A and CN108329036B, the original morphology of the synthesized AlON powder is still generally agglomerated.

[0004] Currently, domestically synthesized AlON powders all face the problem of primary agglomeration, requiring high-energy or prolonged mechanical crushing before use. This process not only easily introduces impurities and contaminants, but also makes it difficult to control the particle morphology after crushing, resulting in poor uniformity and negatively impacting subsequent pressing and molding processes and the final ceramic properties. Although some patents (such as patent CN115196970A) employ spray granulation to synthesize near-spherical AlON powders, the resulting powders are actually agglomerates of polycrystalline AlON, not truly monodisperse single-crystal particles.

[0005] Therefore, developing a new process for synthesizing high-purity, low-agglomeration, and regularly morphologically regular (especially near-spherical single-crystal particles) AlON powder is crucial for overcoming the bottleneck in the preparation of high-performance AlON transparent ceramics, meeting their strategic application needs, and broadening the application fields of AlON powder. Existing technologies still have significant shortcomings in this regard and urgently require improvement and innovation. Summary of the Invention

[0006] In view of the shortcomings of the prior art, the purpose of this application is to provide highly dispersible AlON powder and its synthesis method and AlON transparent ceramic preparation method, aiming to solve the problem of severe agglomeration of powder synthesized by the existing carbothermal reduction method.

[0007] The technical solution of this application is as follows:

[0008] A method for synthesizing highly dispersible AlON powder, comprising the following steps:

[0009] (1) Using γ-Al2O3 and solid carbon source as raw materials, the raw materials, additives and anhydrous ethanol are ball-milled and mixed to obtain a mixed slurry;

[0010] (2) The mixed slurry is dried, ground, and sieved to obtain a mixed powder;

[0011] (3) The mixed powder is loaded into a boron nitride crucible with pre-made pores, and the mixed powder is subjected to gas pressure sintering under constant pressure static nitrogen atmosphere to obtain the highly dispersible AlON powder.

[0012] (4) Decarbonization;

[0013] The additive is a fluoride, and the amount of the additive is 0-0.5 wt% of the raw material, and the amount of the additive is not 0.

[0014] This synthesis method is based on gas pressure sintering-additive doping synergistic technology. The AlON powder synthesized using the method of this application has a near-spherical primary particle morphology and high dispersibility. It does not require further crushing during subsequent use, which simplifies the process and saves energy costs. It is suitable for the fields of transparent ceramics, precision grinding and refractory materials.

[0015] The method for synthesizing highly dispersible AlON powder, wherein during the ball milling and mixing of raw materials, additives, and anhydrous ethanol, a polymeric dispersant is also incorporated, with the amount of the polymeric dispersant being 0-1 wt% of the raw materials;

[0016] The process of ball milling and mixing the raw materials, additives and anhydrous ethanol specifically involves first dissolving the polymeric dispersant in the anhydrous ethanol to obtain a solvent, and then ball milling and mixing the raw materials, the additives and the solvent.

[0017] Incorporating a polymeric dispersant is the preferred solution in this application, as it helps to improve the dispersibility and uniformity of the powder.

[0018] The method for synthesizing highly dispersible AlON powder, wherein the gas pressure sintering process includes the following steps:

[0019] Vacuum up to 10 -2 After reaching the Pa level, high-purity nitrogen is introduced to a pressure of 0.15-0.5 MPa, and then the pressure is kept constant.

[0020] Under constant pressure and static nitrogen atmosphere, the temperature is increased to 1500-1600℃ at a heating rate of 5-20℃ / min and held for 45-90min.

[0021] Then raise the temperature to 1750-1800℃ at a rate of 5-15℃ / min and hold for 60-120 minutes.

[0022] The method for synthesizing highly dispersible AlON powder, wherein the drying process is performed dynamically using a magnetic rotary heater.

[0023] The method for synthesizing highly dispersible AlON powder, wherein the mass ratio of γ-Al2O3 to solid carbon source is 94-95:5-6;

[0024] The mass ratio of anhydrous ethanol to γ-Al2O3 is 3.5-4:1.

[0025] The method for synthesizing highly dispersible AlON powder, wherein the additive is one or more of aluminum fluoride, calcium fluoride, magnesium fluoride, yttrium fluoride and lanthanum fluoride;

[0026] The solid carbon source is either carbon black or activated carbon.

[0027] The polymeric dispersant is one or more of polyvinylpyrrolidone, polyvinyl alcohol, and polyethylene glycol.

[0028] The method for synthesizing highly dispersible AlON powder, wherein during the ball milling process, a polytetrafluoroethylene ball mill jar is used as the container, high-purity silicon nitride balls or high-purity alumina balls are used as the ball milling medium, the ball-to-material ratio is 3-6:1, the ball milling speed is 170-250 r / min, and the ball milling time is 15-30 h.

[0029] The method for synthesizing highly dispersible AlON powder, wherein the decarbonization process involves constant temperature heat treatment at 600-700℃ for 3-5 hours.

[0030] During the drying process, the temperature is 80℃ and the time is 3-6 hours;

[0031] The sieving process involves passing the material through an 80-100 mesh sieve.

[0032] The pores have a diameter of Φ0.5-1.0mm and a density of 3 pores / cm³. 2 .

[0033] A highly dispersible AlON powder, wherein it is synthesized using the method described above for synthesizing highly dispersible AlON powder.

[0034] A method for preparing AlON transparent ceramic, comprising the following steps:

[0035] The highly dispersible AlON powder and sintering aid are placed in a container, and the sintering aid is uniformly coated on the surface of the highly dispersible AlON powder by ultrasonic-assisted co-precipitation. The powder is then dried, sieved, hydraulically formed, and cold isostatically densified. After being sintered at 1880-1950℃ for 12-20 hours without pressure, the AlON transparent ceramic is obtained.

[0036] The sintering aid is a three-phase system sintering aid of Y2O3-MgO-La2O3, with the amount of Y2O3 added being 0.05-0.25wt%, the amount of MgO added being 0.05-0.25wt%, the amount of La2O3 added being 0.05-0.15wt%, and the total amount of the three phases added not exceeding 0.35wt%. The three phases are added in the form of nitrates.

[0037] Beneficial effects: This application provides a method for synthesizing highly dispersible AlON powder based on gas pressure sintering-additive doping synergistic technology. The synthesized AlON powder particles have a near-spherical single-crystal structure and exhibit high dispersibility. Attached Figure Description

[0038] Figure 1 This is the XRD pattern of AlON powder in Example 1 of this application.

[0039] Figure 2 This is a particle size distribution diagram of AlON powder in Example 1 of this application.

[0040] Figure 3 These are scanning electron microscope (SEM) comparison images of AlON powder in Example 1, Comparative Example 1, and Comparative Example 2 of this application.

[0041] Figure 4 This is a scanning electron microscope image of AlON powder in Example 2 of this application.

[0042] Figure 5 This is a scanning electron microscope image of AlON powder in Example 3 of this application.

[0043] Figure 6 This is a scanning electron microscope image of the AlON transparent ceramic in Embodiment 4 of this application. Detailed Implementation

[0044] This application provides highly dispersible AlON powder, its synthesis method, and a method for preparing AlON transparent ceramics. To make the objectives, technical solutions, and effects of this application clearer and more explicit, the following provides a more detailed description. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this application.

[0045] To address the core defects of existing carbothermic reduction methods, such as severe powder agglomeration requiring high-energy or prolonged crushing and the introduction of impurities, this application provides a method for synthesizing highly dispersible AlON powder. This method is based on a gas pressure sintering-additive doping synergistic technology. The AlON powder synthesized using this method has a near-spherical primary particle morphology and high dispersibility. It eliminates the need for further crushing during subsequent use, simplifying the process, saving energy costs, and making it suitable for transparent ceramics, precision grinding, and refractory materials.

[0046] Specifically, the method for synthesizing highly dispersible AlON powder according to this application includes the following steps:

[0047] (1) Powder mixing: Using γ-Al2O3 and solid carbon source as raw materials, the raw materials, additives, dispersants and anhydrous ethanol are ball-milled and mixed to obtain a mixed slurry.

[0048] Specifically, the solid carbon source can be either carbon black or activated carbon. The carbon black can be acetylene black or tar black, etc. To lower the reaction temperature and effectively shorten the reaction time, this application uses activated carbon / carbon black with a high specific surface area and nano-sized γ-Al₂O₃ powder as raw materials.

[0049] The additive is a fluoride, specifically one or more of aluminum fluoride (AlF3), calcium fluoride (CaF2), magnesium fluoride (MgF2), yttrium fluoride (YF3), and lanthanum fluoride (LaF3). This fluoride additive forms a liquid phase at relatively low temperatures (1000-1400℃), and its functions include: promoting the migration and rearrangement of aluminum source (such as Al2O3) and carbon source particles; accelerating the ion diffusion process; and promoting the dissolution-recrystallization reaction on the surfaces of alumina (Al2O3) and aluminum nitride (AlN). These synergistic effects help lower the carbothermic reduction reaction temperature and the subsequent AlON solid solution temperature, and effectively improve the crystallinity of the product.

[0050] The polymeric dispersant can be one or more of polyvinylpyrrolidone (PVP), polyvinyl alcohol (PVA), and polyethylene glycol (PEG).

[0051] Furthermore, the purity of γ-Al2O3 and solid carbon source is ≥99.99%, and the purity of additives is ≥99.9%. Among them, the primary particle size of γ-Al2O3 is 10-30nm, the primary particle size of acetylene black is 10-20nm, the primary particle size of tar black is 30-40nm, the particle size of activated carbon is 1-2μm, and the particle size of fluoride is in the micrometer range.

[0052] Furthermore, the mass ratio of γ-Al2O3 to the solid carbon source is 94-95:5-6.

[0053] The additive is incorporated at a rate of 0-0.5 wt% of the raw material, and the amount of additive is not zero. In this application, the appropriate amount of the fluoride additive helps to improve the crystallinity of AlON and promotes its formation of a regular near-spherical morphology. However, excessive additive can easily induce local liquid phase sintering, hindering the uniform growth of grains. Therefore, the additive dosage in this application is preferably controlled within the range of 0.05-0.5 wt% to balance morphology control and uniformity.

[0054] The amount of polymeric dispersant incorporated is 0-1 wt% of the raw materials. To further improve the uniformity of the raw material mixing, and especially to ensure the full dispersion of trace additives in the system, this application preferably adds a polymeric dispersant.

[0055] In the embodiments of this application, the preferred mass ratio of anhydrous ethanol to γ-Al2O3 is 3.5-4:1.

[0056] Specifically, the ball milling process involves completely dissolving the polymeric dispersant in anhydrous ethanol to obtain a solvent, then placing the raw materials, additives, and solvent together into a polytetrafluoroethylene ball mill jar. High-purity silicon nitride balls or high-purity alumina balls are used as the milling media, and the mixture is stirred and dispersed using a planetary ball mill at a ball-to-material ratio of 3-6:1. The ball milling speed is 170-250 r / min, and the milling time is 15-30 h.

[0057] In this ball milling process, a polytetrafluoroethylene (PTFE) ball mill jar and high-purity silicon nitride / alumina ball media are used to achieve multiphase uniform dispersion in an anhydrous ethanol system via planetary ball milling. Through the synergistic effect of the steric hindrance of the polymeric dispersant and the mechanochemical effect of ball milling, the interfacial energy of the powder is reduced, resulting in a uniform precursor that provides a highly active, low-agglomeration raw material system for the subsequent carbothermic reduction reaction.

[0058] (2) Drying and granulation: The mixed slurry is dried, ground and sieved to obtain mixed powder.

[0059] Specifically, a magnetic rotary heater can be used for dynamic drying during the drying process. Through the uniform distribution of the three-dimensional thermal field, it can not only achieve rapid dehydration, but also suppress uneven sedimentation caused by the difference in sedimentation rate of powders with different densities and particle sizes, thus ensuring that the powder composition is uniform after drying.

[0060] Furthermore, the drying temperature can be 80℃, and the time can be 3-6 hours.

[0061] Specifically, after drying, the mixed powder is ground and passed through an 80-100 mesh sieve to achieve granulation and homogenization, providing highly consistent raw materials for subsequent gas pressure sintering.

[0062] (3) Loading and pressure sintering: The mixed powder is loaded into a boron nitride crucible with pre-made pores and pressure sintered in a pressure sintering furnace to obtain AlON powder.

[0063] Specifically, using a pre-fabricated boron nitride crucible with pores as a carrier can enhance nitrogen permeation and promote the carbothermic reduction reaction.

[0064] In the embodiments of this application, the pore diameter is Φ0.5-1.0mm, and the density is 3 pores / cm³. 2 This design aims to prevent powder particles from leaking out through the pores due to excessively large pore size (>1.0 mm); to avoid the crucible wall from cracking due to localized stress concentration caused by excessively high pore density; and to ensure sufficient and uniform gas diffusion channels.

[0065] Specifically, the gas pressure sintering process, performed in a gas pressure sintering furnace, includes the following steps:

[0066] Atmosphere control: Evacuate to 10 -2 After reaching the Pa level, high-purity nitrogen is introduced to a pressure of 0.15-0.5 MPa, and the pressure inside the furnace is kept constant.

[0067] Gradient temperature control: Under constant pressure and static nitrogen atmosphere, the temperature is increased to 1500-1600℃ at a heating rate of 5-20℃ / min and held for 45-90min to promote the carbothermic reduction reaction; then the temperature is increased to 1750-1800℃ at a heating rate of 5-15℃ / min and held for 60-120min to complete the AlON crystal phase reconstruction.

[0068] In this application, the sintering process employs a constant-pressure static nitrogen atmosphere. AlON powder synthesis involves a complex gas-solid reaction system. In the carbothermic reduction stage, N2 participates as a reactant to generate AlN; in the solution stage, Al-N dissolves into Al2O3 to form AlON; simultaneously, other accompanying reactions occur, such as γ-Al2O3 reacting with C to generate various Al-C gaseous intermediates, trace amounts of added fluoride additives ultimately escaping the system in gaseous form (e.g., HF), and the high-temperature gaseous decomposition of trace amounts of AlN. Due to the presence and dynamic changes of the gaseous components, the state of the sintering atmosphere (pressure, flow rate) has a decisive influence on the AlON grain morphology and agglomeration behavior. Subsequent examples and comparative results clearly show that in a gas-flowing atmosphere, airflow disturbances promote non-uniform growth of AlON grains along the airflow direction and drive particle migration and collision, leading to hard agglomeration. In contrast, a constant-pressure static atmosphere (in this application) provides an isotropic growth environment for the grains due to stable pressure and the absence of artificial flow. AlON grains mainly grow in situ, with no significant migration or collision between grains, effectively suppressing agglomeration.

[0069] It should be specifically noted that, prior to the application date, there are no publicly reported methods for synthesizing AlON powder using a non-flowing, constant-pressure nitrogen atmosphere or by adding fluoride additives. Powders obtained using existing synthesis processes, even if macroscopically nearly spherical and dispersed, still exhibit a polycrystalline aggregate microstructure (see comparative examples). This application innovatively combines a constant-pressure static nitrogen sintering atmosphere with trace amounts of fluoride additives (0.05-0.5 wt%) to successfully synthesize AlON powder with highly dispersed primary particle size and nearly spherical morphology. This powder consists of single AlON crystal grains (not polycrystalline aggregates). The synthesis method of this application effectively simplifies the process and reduces costs: the powder itself is highly dispersed and free of hard agglomerates, eliminating the need for subsequent crushing, significantly simplifying the process and saving energy. These highly dispersed, nearly spherical single-crystal particles greatly improve powder flowability, filling density, and sintering activity, facilitating the preparation of high-performance transparent ceramics. This unique form further expands the application boundaries of AlON powder, showing great potential in fields such as refractory materials (improving the rheology and sintering properties of castables / spray coatings) and CMC (ceramic matrix composites) precision grinding and polishing (as high-hardness, uniform abrasive particles).

[0070] (4) Decarbonization: The sintered AlON powder is placed in a decarbonization furnace and heat-treated at a constant temperature of 600-700℃ for 3-5 hours to remove residual free carbon through oxidation reaction.

[0071] This application also provides a highly dispersible AlON powder, which is synthesized using the aforementioned method for synthesizing highly dispersible AlON powder. This highly dispersible AlON powder has a single AlON phase, is composed of single AlON crystal grains, has no obvious pores or other defects, and exhibits high dispersibility without particle agglomeration. This technology is easy to implement, reduces the difficulty of subsequent powder crushing, decreases crushing energy consumption and costs, and is easily applicable to industrialization.

[0072] This application also provides a method for preparing AlON transparent ceramics, comprising the following steps:

[0073] The highly dispersible AlON powder and sintering aid of this application were placed in a beaker. The sintering aid was uniformly coated on the surface of the highly dispersible AlON powder by ultrasonic-assisted co-precipitation. After drying and sieving, the powder was first hydraulically formed (10-50 MPa, 5-10 min), then cold isostatically densified (150-200 MPa, 5 min), and finally sintered without pressure at 1880-1950℃ for 12-20 h to obtain AlON transparent ceramic with a transmittance of 58%.

[0074] A three-phase sintering aid consisting of Y2O3-MgO-La2O3 is added to the decarbonized AlON powder. The amount of Y2O3 added is 0.05-0.25wt%, the amount of MgO added is 0.05-0.25wt%, the amount of La2O3 added is 0.05-0.15wt%, and the total amount of the three phases added does not exceed 0.35wt%. The additive is added in the form of nitrates.

[0075] The method for preparing AlON transparent ceramics in this application eliminates the crushing step to maximize the preservation of the inherent advantages of the powder—high dispersibility and near-spherical morphology. The core process involves directly using highly dispersed, near-spherical AlON powder synthesized by the aforementioned method. A sintering aid layer is uniformly coated onto the powder surface via co-precipitation, and ultrasonic dispersion technology is introduced to assist the coating process, ensuring the uniformity of the coating layer. Thanks to the excellent dispersibility and regular morphology of the powder itself, even without crushing, the powder can still achieve excellent particle stacking and sintering activity, ultimately producing high-density AlON transparent ceramics.

[0076] The following specific embodiments further illustrate the solution of this application.

[0077] In the following schemes, the purity of γ-Al2O3 and solid carbon source used is ≥99.99%, the purity of additives is ≥99.9%, the primary particle size of γ-Al2O3 is 10-30nm, the primary particle size of acetylene black is 10-20nm, the primary particle size of tar black is 30-40nm, the particle size of activated carbon is 1-2μm, and the particle size of fluoride is in the micrometer range.

[0078] In the following scheme, the pore size of the boron nitride crucible is Φ0.5-1.0mm, and the pore density is 3 pores / cm³. 2 .

[0079] Example 1:

[0080] Following the experimental procedure, γ-Al₂O₃ and acetylene black (mass ratio 94.4:5.6) were used as raw materials, with 0.15 wt% AlF₃ as an additive and 0.5 wt% PVP as a polymeric dispersant. A polytetrafluoroethylene (PTFE) jar was used as the ball milling jar, high-purity alumina balls as the grinding balls, and anhydrous ethanol (mass ratio of anhydrous ethanol to γ-Al₂O₃ 4:1) as the medium. The polymeric dispersant was completely dissolved in anhydrous ethanol to obtain a solvent. The raw materials, additives, and solvent were then placed together in the PTFE ball milling jar and mixed at a ball-to-material ratio of 4:1 using a planetary ball mill at 200 r / min for 24 h. The resulting slurry was dried at 80℃ for 4 h using a magnetic rotary heater, and then ground through an 80-mesh sieve to obtain a uniform mixed powder. The mixed powder was placed in a pre-porous boron nitride crucible and evacuated to 10 °C. -2 After Pa level, high-purity nitrogen gas is introduced to 0.35 MPa to ensure that the gas pressure in the gas pressure sintering furnace is constant at 0.35 MPa. Under constant pressure static nitrogen atmosphere, the temperature is increased to 1550℃ at a heating rate of 10℃ / min and held for 45 min. Then, the temperature is increased to 1770℃ at a heating rate of 10℃ / min and held for 60 min. The sintered AlON powder is then placed in a decarburization furnace and heat-treated at 650℃ for 4 h to remove residual free carbon through oxidation reaction, thus synthesizing the highly dispersible AlON powder of this embodiment.

[0081] Comparative Example 1: (Fluoride-free additives + atmospheric pressure flowing nitrogen sintering)

[0082] Using γ-Al₂O₃ and acetylene black in a mass ratio of 94.4:5.6 as raw materials, and externally adding 0.5 wt% PVP as a polymeric dispersant, a polytetrafluoroethylene (PTFE) jar was used as the ball mill jar, imported high-purity alumina balls were used as grinding balls, and anhydrous ethanol (anhydrous ethanol to γ-Al₂O₃ mass ratio of 4:1) was used as the medium. The polymeric dispersant was completely dissolved in anhydrous ethanol to obtain a solvent. The raw materials and solvent were then placed together in the PTFE ball mill jar and mixed for 24 hours at 200 rpm using a planetary ball mill at a ball-to-material ratio of 4:1. The resulting slurry was dried at 80℃ for 4 hours using a magnetic rotary heater, and then ground through an 80-mesh sieve to obtain a uniformly mixed powder. The mixed powder was placed in a pre-formed porous boron nitride crucible and evacuated to 100°C. -2 After Pa level, high-purity nitrogen is introduced to 0.12-0.14 MPa. Under the atmosphere of flowing nitrogen at a flow rate of 0.5 L / min, the temperature is increased to 1550℃ at a heating rate of 10℃ / min and held for 45 min. Then, the temperature is increased to 1770℃ at a heating rate of 10℃ / min and held for 60 min. The sintered AlON powder is then placed in a decarburization furnace and heat-treated at a constant temperature of 650℃ for 4 h to remove residual free carbon through oxidation reaction, thus synthesizing AlON powder.

[0083] Comparative Example 2: (Fluorizing additive + sintering with nitrogen at atmospheric pressure)

[0084] Using γ-Al₂O₃ and acetylene black in a mass ratio of 94.4:5.6 as raw materials, 0.15 wt% AlF₃ as an additive and 0.5 wt% PVP as a polymeric dispersant were added. A polytetrafluoroethylene (PTFE) jar was used as the ball milling jar, high-purity alumina balls were used as the grinding balls, and anhydrous ethanol (anhydrous ethanol to γ-Al₂O₃ mass ratio of 4:1) was used as the medium. The polymeric dispersant was completely dissolved in anhydrous ethanol to obtain a solvent. The raw materials, additives, and solvent were placed together in the PTFE ball milling jar and mixed at a ball-to-material ratio of 4:1 using a planetary ball mill at 200 r / min for 24 h. The resulting slurry was dried at 80℃ for 4 h using a magnetic rotary heater, and then ground through an 80-mesh sieve to obtain a uniform mixed powder. The mixed powder was placed in a pre-porous boron nitride crucible and evacuated to 10 °C. -2 After Pa level, high-purity nitrogen is introduced to 0.12-0.14 MPa. Under the atmosphere of flowing nitrogen at a flow rate of 0.5 L / min, the temperature is increased to 1550℃ at a heating rate of 10℃ / min and held for 45 min. Then, the temperature is increased to 1770℃ at a heating rate of 10℃ / min and held for 60 min. The sintered AlON powder is then placed in a decarburization furnace and heat-treated at a constant temperature of 650℃ for 4 h to remove residual free carbon through oxidation reaction, thus synthesizing AlON powder.

[0085] The XRD pattern of AlON powder in Example 1 is shown below. Figure 1 As shown, the AlON powder has a single AlON phase.

[0086] The particle size distribution diagram of AlON powder in Example 1 is shown below. Figure 2 As shown, by Figure 2 It can be seen that the particle size distribution of AlON powder is concentrated, mainly distributed below 3.5μm (>75 vol%), of which particles below 1.5μm account for more than 34 vol.

[0087] The microstructure of the AlON powders prepared in Example 1, Comparative Example 1, and Comparative Example 2 was observed, and their scanning electron microscope (SEM) comparison images are shown below. Figure 3 As shown, the left and right images in the first row are scanning electron microscope (SEM) images of Example 1; the left and right images in the second row are SEM images of Comparative Example 1; and the images in the third row are SEM images of Comparative Example 2. Figure 3 As can be seen, the AlON powder in Example 1 is nearly spherical and highly dispersed. Each particle is a complete single crystal with no obvious intracrystalline defects (such as pores); there is no agglomeration between particles, and they are discretely distributed; the grain size distribution is 0.5-3.5 μm, which is consistent with the results of laser particle size analysis.

[0088] In Comparative Example 1, AlON powder synthesized without AlF3 as an additive under a normal pressure flowing nitrogen atmosphere exhibited a porous framework structure with severe grain agglomeration. In Comparative Example 2, AlON powder synthesized with AlF3 as an additive under a normal pressure flowing nitrogen atmosphere had a grain morphology that was close to spherical, but significant agglomeration occurred due to airflow disturbance.

[0089] Example 2:

[0090] The main difference between this embodiment and Embodiment 1 is that the solid carbon source acetylene black is changed to activated carbon, the additive 0.15wt% AlF3 is changed to 0.05wt% CaF2, and the sintering temperature is adjusted to 1800℃ and held for 60 minutes.

[0091] According to experimental requirements, γ-Al₂O₃ and activated carbon (mass ratio 94.4:5.6) were used as raw materials, with 0.05 wt% CaF₂ as an auxiliary agent and 0.5 wt% PVP as a polymeric dispersant. A polytetrafluoroethylene (PTFE) jar was used as the ball milling jar, high-purity alumina balls as the grinding balls, and anhydrous ethanol (mass ratio of anhydrous ethanol to γ-Al₂O₃ 4:1) as the medium. The polymeric dispersant was completely dissolved in anhydrous ethanol to obtain a solvent. The raw materials, auxiliary agent, and solvent were placed together in the PTFE ball milling jar and mixed at a ball-to-material ratio of 4:1 using a planetary ball mill at 200 r / min for 24 h. The resulting slurry was dried at 80℃ for 4 h using a magnetic rotary heater, and then ground through an 80-mesh sieve to obtain a uniform mixed powder. The mixed powder was placed in a pre-porous boron nitride crucible and evacuated to 10 °C. -2 After Pa level, high-purity nitrogen gas is introduced to 0.2 MPa to ensure that the gas pressure inside the furnace is constant at 0.2 MPa. Under constant pressure static nitrogen atmosphere, the temperature is increased to 1550℃ at a heating rate of 10℃ / min and held for 45 min. Then, the temperature is increased to 1800℃ at a heating rate of 10℃ / min and held for 60 min. The sintered AlON powder is then placed in a decarburization furnace and heat-treated at 650℃ for 4 h to remove residual free carbon through oxidation reaction, thus synthesizing the highly dispersible AlON powder of this embodiment.

[0092] The microstructure of AlON powder in Example 2 is shown below. Figure 4 ,Depend on Figure 4 It can be seen that AlON powder with high dispersion characteristics was successfully synthesized under constant nitrogen conditions of 0.2 MPa using activated carbon as solid carbon source and CaF2 as auxiliary agent. The powder is composed of single crystal particles with no visible defects (such as pores) in the crystals and no agglomeration of particles, and is discretely distributed; the grain size ranges from 7 to 15 μm.

[0093] Example 3:

[0094] The main difference between this embodiment and Embodiment 1 is that the solid carbon source acetylene black is changed to tar black, the additive is changed from 0.15wt% AlF3 to 0.35wt% AlF3, the nitrogen pressure is adjusted to 0.5MPa, and the sintering temperature is adjusted to 1800℃ and held for 90min.

[0095] According to experimental requirements, γ-Al₂O₃ and carbon black (mass ratio 94.4:5.6) were used as raw materials, with 0.35 wt% AlF₃ as an auxiliary agent and 0.5 wt% PVP as a polymeric dispersant. A polytetrafluoroethylene (PTFE) jar was used as the ball milling jar, high-purity alumina balls as grinding balls, and anhydrous ethanol (mass ratio of anhydrous ethanol to γ-Al₂O₃ 4:1) as the medium. The polymeric dispersant was completely dissolved in anhydrous ethanol to obtain a solvent. The raw materials, auxiliary agent, and solvent were placed together in the PTFE ball milling jar and mixed at a ball-to-material ratio of 4:1 using a planetary ball mill at 200 r / min for 24 h. The resulting slurry was dried at 80℃ for 4 h using a magnetic rotary heater, and then ground through an 80-mesh sieve to obtain a uniform mixed powder. The mixed powder was placed in a pre-porous boron nitride crucible and evacuated to 10 °C. -2 After Pa level, high-purity nitrogen gas is introduced to 0.5 MPa to ensure that the gas pressure inside the furnace is constant at 0.5 MPa. Under constant pressure static nitrogen atmosphere, the temperature is increased to 1550℃ at a heating rate of 10℃ / min and held for 45 min. Then, the temperature is increased to 1800℃ at a heating rate of 10℃ / min and held for 90 min. The sintered AlON powder is then placed in a decarburization furnace and heat-treated at 650℃ for 4 h to remove residual free carbon through oxidation reaction, thus synthesizing the highly dispersible AlON powder of this embodiment.

[0096] The microstructure of AlON powder in Example 3 is shown below. Figure 5 ,Depend on Figure 5 It can be seen that highly dispersed near-spherical AlON powder was successfully synthesized under constant pressure static nitrogen conditions of 0.5 MPa using carbon black as the carbon source and AlF3 as the auxiliary agent. The particles have a single crystal structure with no visible defects (such as pores) within the crystals; the particles do not agglomerate and are distributed in a discrete state; the grain size is distributed in the range of 5-12 μm.

[0097] As can be seen from Examples 1, 2 and 3, the type of solid carbon source, the type of additive, the amount of additive, and the synthesis process all affect the particle size and morphology of the powder. However, the AlON powder synthesized according to the synthesis method provided in this application consists of a single AlON crystal, with no obvious defects inside, and the primary particle size has high dispersibility.

[0098] Example 4

[0099] The AlON powder and sintering aid prepared in Example 1 were placed in a beaker. The sintering aid was uniformly coated on the surface of the AlON powder by ultrasonic-assisted co-precipitation. After drying and sieving, the powder was first hydraulically formed (15 MPa, 5 min), then cold isostatically densified (200 MPa, 5 min), and finally sintered without pressure at 1920℃ for 15 h to obtain AlON transparent ceramic with a transmittance of 58%.

[0100] The sintering aid is a three-phase system of Y2O3-MgO-La2O3, with Y2O3 added at 0.10 wt%, MgO added at 0.10 wt%, and La2O3 added at 0.05 wt%, in the form of nitrates.

[0101] As shown in Example 4, high-density transparent AlON ceramics were successfully prepared using the AlON powder (without crushing treatment) obtained in Example 1. Figure 6 As shown, a small number of isolated grain boundary / near-grain boundary pores (marked areas) exist inside the ceramic. These pores can be further eliminated by optimizing sintering process parameters (such as heating rate and holding time) to achieve higher density.

[0102] It should be understood that the application of this application is not limited to the examples above. Those skilled in the art can make improvements or modifications based on the above description, and all such improvements and modifications should fall within the protection scope of this application.

Claims

1. A method for synthesizing highly dispersible AlON powder, characterized in that, Includes the following steps: (1) Using γ-Al2O3 and solid carbon source as raw materials, the raw materials, additives and anhydrous ethanol are ball-milled and mixed to obtain a mixed slurry; (2) The mixed slurry is dried, ground, and sieved to obtain a mixed powder; (3) The mixed powder is loaded into a boron nitride crucible with pre-made pores, and the mixed powder is subjected to gas pressure sintering under constant pressure static nitrogen atmosphere to obtain the highly dispersible AlON powder. (4) Carbon removal; The additive is a fluoride, and the amount of the additive is 0-0.5 wt% of the raw material, and the amount of the additive is not 0.

2. The method for synthesizing highly dispersible AlON powder according to claim 1, characterized in that, During the ball milling process of mixing the raw materials, additives, and anhydrous ethanol, a polymeric dispersant is also incorporated, wherein the amount of the polymeric dispersant is 0-1 wt% of the raw materials. The process of ball milling and mixing the raw materials, additives and anhydrous ethanol specifically involves first dissolving the polymeric dispersant in the anhydrous ethanol to obtain a solvent, and then ball milling and mixing the raw materials, the additives and the solvent.

3. The method for synthesizing highly dispersible AlON powder according to claim 1, characterized in that, The gas pressure sintering process includes the following steps: Vacuum up to 10 -2 After reaching the Pa level, high-purity nitrogen is introduced to a pressure of 0.15-0.5 MPa, and then the pressure is kept constant. Under constant pressure and static nitrogen atmosphere, the temperature is increased to 1500-1600℃ at a heating rate of 5-20℃ / min and held for 45-90min. Then raise the temperature to 1750-1800℃ at a rate of 5-15℃ / min and hold for 60-120 minutes.

4. The method for synthesizing highly dispersible AlON powder according to claim 1, characterized in that, The drying process is a dynamic drying process using a magnetic rotary heater.

5. The method for synthesizing highly dispersible AlON powder according to claim 1, characterized in that, The mass ratio of γ-Al2O3 to solid carbon source is 94-95:5-6; The mass ratio of anhydrous ethanol to γ-Al2O3 is 3.5-4:1; The amount of the additive is 0.05-0.5 wt% of the raw material.

6. The method for synthesizing highly dispersible AlON powder according to claim 2, characterized in that, The additive is one or more of aluminum fluoride, calcium fluoride, magnesium fluoride, yttrium fluoride, and lanthanum fluoride; The solid carbon source is either carbon black or activated carbon. The polymeric dispersant is one or more of polyvinylpyrrolidone, polyvinyl alcohol, and polyethylene glycol.

7. The method for synthesizing highly dispersible AlON powder according to claim 1, characterized in that, During the ball milling process, a polytetrafluoroethylene ball mill jar is used as the container, and high-purity silicon nitride balls or high-purity alumina balls are used as the ball milling media. The ball-to-material ratio is 3-6:1, the ball milling speed is 170-250 r / min, and the ball milling time is 15-30 h.

8. The method for synthesizing highly dispersible AlON powder according to claim 1, characterized in that, The carbon removal process involves constant temperature heat treatment at 600-700℃ for 3-5 hours. During the drying process, the temperature is 80℃ and the time is 3-6 hours; The sieving process involves passing the material through an 80-100 mesh sieve. The pores have a diameter of Φ0.5-1.0mm and a density of 3 pores / cm³. 2 .

9. A highly dispersible AlON powder, characterized in that, It was synthesized using the method for synthesizing highly dispersible AlON powder as described in any one of claims 1-8.

10. A method for preparing AlON transparent ceramic, characterized in that, Includes the following steps: The highly dispersible AlON powder as described in claim 9 and the sintering aid are placed in a container, and the sintering aid is uniformly coated on the surface of the highly dispersible AlON powder by ultrasonic-assisted co-precipitation. The powder is then dried, sieved, hydraulically formed, cold isostatically densified, and pressurelessly sintered at 1880-1950℃ for 12-20h to obtain the transparent AlON ceramic. The sintering aid is a three-phase system sintering aid of Y2O3-MgO-La2O3, with the amount of Y2O3 added being 0.05-0.25wt%, the amount of MgO added being 0.05-0.25wt%, the amount of La2O3 added being 0.05-0.15wt%, and the total amount of the three phases added not exceeding 0.35wt%. The three phases are added in the form of nitrates.

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