High-dispersity AlON powder and synthesis method thereof, and preparation method of AlON transparent ceramic

Abstract

The invention relates to the technical field of ceramic powder preparation, and discloses high-dispersity AlON powder and a synthesis method thereof and a preparation method of AlON transparent ceramic, and the preparation method comprises the following steps: (1) powder mixing: taking gamma-Al2O3 and a solid carbon source as raw materials, and carrying out ball-milling mixing on the raw materials, an auxiliary agent, a dispersing agent and absolute ethyl alcohol to obtain mixed slurry; (2) drying and sieving: drying, grinding and sieving the mixed slurry to obtain mixed powder; (3) charging and air pressure sintering: charging the mixed powder into a perforated boron nitride crucible, and performing air pressure sintering on the mixed powder in an air pressure sintering furnace to obtain high-dispersity AlON powder; and (4) carbon removal. The AlON powder synthesized by the synthesis method disclosed by the invention is of a nearly spherical single-crystal structure and has good high dispersity.

Description

Technical Field

[0001] The present application relates to the technical field of ceramic powder preparation, and mainly relates to highly dispersible AlON powder and a synthesis method thereof, and a preparation method of AlON transparent ceramics. Background Art

[0002] Spinel aluminum oxynitride (γ-AlON) is a metastable single-phase solid solution in the pseudo-binary AlN-Al2O3 system. Precisely controlling the oxynitride stoichiometric ratio (AlN:Al2O3 = 3:5-9:11) allows for the stable construction of a cubic (Fd-3m) crystal structure. Its unique three-dimensional network structure, composed of [AlO4N4] dodecahedrons and [AlO6] octahedra connected by common vertices, endows the material with excellent structural properties and isotropic properties. Its theoretical transmittance reaches 85% in the 0.25-6.5μm spectral range, its Vickers hardness reaches 18.7±0.8GPa, and its thermal shock threshold exceeds 850°C (water quenching method). Based on these properties, γ-AlON transparent ceramics have established three strategic application areas: fully transparent visors for high-Mach number aircraft (Ma>5); composite guidance systems for visible / infrared co-aperture transmission; 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: the solid-phase reaction method relies on high-purity submicron / nanoscale Al2O3 / AlN dual-phase raw materials, which is expensive. AlN is easily hydrated (AlN+3H2O→Al(OH)3+NH3↑), which requires the raw materials to be stored and handled under strict humidity control (RH<5%) and in an inert atmosphere, and requires a complex ball milling process. At the same time, the Al2O3 / AlN interface has a high diffusion barrier, requiring high-temperature sintering exceeding 1800°C, which easily forms micron-sized hard agglomerates. The aluminothermic reduction method, due to the low melting point of aluminum powder (660°C), easily triggers local liquid-phase sintering, resulting in a discrete particle size distribution. The oxide layer on the surface of the aluminum powder causes excess oxygen, narrowing the process window. Although the carbon thermal reduction method can significantly reduce the raw material cost by reacting Al2O3 with a carbon source in a N2 atmosphere, and can use gas-solid reaction to inhibit abnormal grain growth, and the residual carbon can be removed by secondary oxidation at 600-800°C, such as patent numbers CN113582701A and CN108329036B, the native morphology of the synthesized AlON powder is still generally agglomerated.

[0004] Currently, AlON powders synthesized domestically all face the problem of primary agglomeration, requiring high-energy or prolonged mechanical crushing before use. This process not only easily introduces impurities and contamination, but also makes the particle morphology difficult to control and results in poor uniformity, adversely affecting subsequent pressing and the final ceramic properties. While patents (such as CN115196970A) utilize a spray granulation process to synthesize nearly 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 defined AlON powders (especially near-spherical single crystals) is crucial for overcoming bottlenecks in the preparation of high-performance AlON transparent ceramics, meeting their strategic application needs, and broadening the application areas of AlON powders. Existing technologies still have significant shortcomings in this regard, and improvements and innovations are urgently needed. Summary of the Invention

[0006] In view of the above-mentioned deficiencies in the prior art, the purpose of this application is to provide a highly dispersible AlON powder and a synthesis method thereof and a preparation method of AlON transparent ceramics, aiming to solve the serious problem of powder agglomeration synthesized by the existing carbothermal reduction method.

[0007] The technical solution of this application is as follows: A method for synthesizing highly dispersible AlON powder, comprising the following steps: (1) Using γ-Al2O3 and a solid carbon source as raw materials, the raw materials, the additives and anhydrous ethanol are ball-milled to obtain a mixed slurry; (2) drying, grinding, and sieving the mixed slurry to obtain a mixed powder; (3) loading the mixed powder into a boron nitride crucible prefabricated with air holes, and performing gas pressure sintering on the mixed powder under a constant pressure static nitrogen atmosphere to obtain the highly dispersible AlON powder; (4) Carbon removal; The auxiliary agent is fluoride, and the amount of the auxiliary agent added is 0-0.5wt% of the raw material, and the amount of the auxiliary agent added is not 0.

[0008] This synthesis method is based on the gas pressure sintering-additive doping synergistic technology. The AlON powder synthesized using the synthesis method of this application has a nearly spherical primary particle morphology and high dispersibility. It does not need to be crushed during subsequent use, which simplifies the process flow and saves energy costs. It is suitable for transparent ceramics, precision grinding and refractory materials.

[0009] The method for synthesizing highly dispersible AlON powder, wherein, during the ball milling process of the raw materials, the additives and the anhydrous ethanol, a polymer dispersant is further added, and the amount of the polymer dispersant added is 0-1wt% of the raw materials; The process of mixing the raw materials, the auxiliary agent and the anhydrous ethanol by ball milling is specifically as follows: firstly dissolving the polymer dispersant in the anhydrous ethanol to obtain a solvent, and then mixing the raw materials, the auxiliary agent and the solvent by ball milling.

[0010] The incorporation of a polymer dispersant is a preferred solution of the present application, which helps to improve the dispersibility and uniformity of the powder.

[0011] The method for synthesizing highly dispersible AlON powder, wherein the gas pressure sintering process comprises the following steps: Vacuum to 10 -2 After the Pa level, high-purity nitrogen is filled to 0.15-0.5MPa and the pressure is kept constant; Under constant pressure and static nitrogen atmosphere, heat to 1500-1600℃ at a heating rate of 5-20℃ / min and keep at this temperature for 45-90min; Then increase the temperature to 1750-1800℃ at a heating rate of 5-15℃ / min and keep it at that temperature for 60-120min.

[0012] The method for synthesizing highly dispersible AlON powder, wherein the drying process is dynamic drying using a magnetic rotary heater.

[0013] The method for synthesizing highly dispersible AlON powder, wherein the mass ratio of γ-Al2O3 to solid carbon source is 94-95:5-6; The mass ratio of the anhydrous ethanol to the γ-Al2O3 is 3.5-4:1.

[0014] The method for synthesizing highly dispersible AlON powder, wherein the auxiliary agent is one or more of aluminum fluoride, calcium fluoride, magnesium fluoride, yttrium fluoride and lanthanum fluoride; The solid carbon source is one of carbon black or activated carbon; The polymer dispersant is one or more of polyvinyl pyrrolidone, polyvinyl alcohol and polyethylene glycol.

[0015] The method for synthesizing highly dispersible AlON powder comprises the following steps: during the ball milling mixing process, a polytetrafluoroethylene ball mill is used as a container, high-purity silicon nitride balls or high-purity alumina balls are used as 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.

[0016] The method for synthesizing highly dispersible AlON powder comprises the following steps: the carbon removal process is a heat treatment at a constant temperature of 600-700° C. for 3-5 hours.

[0017] During the drying process, the temperature is 80°C and the time is 3-6 hours; The sieving process is to pass through an 80-100 mesh sieve; The pores have a diameter of 0.5-1.0 mm and a density of 3 pores / cm 2 .

[0018] A highly dispersible AlON powder is synthesized using the above-mentioned method for synthesizing highly dispersible AlON powder.

[0019] A method for preparing AlON transparent ceramics, comprising the following steps: The highly dispersible AlON powder and the sintering aid are placed in a container, the sintering aid is uniformly coated on the surface of the highly dispersible AlON powder by an ultrasonic-assisted co-precipitation method, the powder is dried and sieved, hydraulically formed, and densified by cold isostatic pressing, and the AlON transparent ceramic is obtained by heat preservation at 1880-1950° C. for 12-20 hours and pressureless sintering. Among them, the sintering aid is a Y2O3-MgO-La2O3 three-phase system sintering aid, the Y2O3 addition amount is 0.05-0.25wt%; the MgO addition amount is 0.05-0.25wt%; the La2O3 addition amount is 0.05-0.15wt%; the total addition amount of the three phases does not exceed 0.35wt%, and the three phases are added in the form of nitrates.

[0020] Beneficial Effects: This application provides a method for synthesizing highly dispersible AlON powder based on the synergistic technology of gas pressure sintering and additive doping. The synthesized AlON powder particles have a nearly spherical single crystal structure and are highly dispersible. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 This is the XRD pattern of the AlON powder in Example 1 of the present application.

[0022] Figure 2 This is the particle size distribution diagram of the AlON powder in Example 1 of this application.

[0023] Figure 3 This is a scanning electron microscope comparison of AlON powder in Example 1, Comparative Example 1 and Comparative Example 2 of the present application.

[0024] Figure 4 This is a scanning electron microscope image of the AlON powder in Example 2 of this application.

[0025] Figure 5 This is a scanning electron microscope image of the AlON powder in Example 3 of this application.

[0026] Figure 6 This is a scanning electron microscope image of the AlON transparent ceramic in Example 4 of this application. DETAILED DESCRIPTION

[0027] This application provides highly dispersible AlON powder, a synthesis method thereof, and a method for preparing AlON transparent ceramics. To make the objectives, technical solutions, and effects of this application more clear and explicit, this application is further described below. It should be understood that the specific embodiments described herein are merely illustrative of this application and are not intended to limit this application.

[0028] In order to solve the problem that the powder synthesized by the existing carbon thermal reduction method has serious agglomeration, and subsequent high-energy or long-time crushing is required, which is easy to introduce core defects such as impurities, the present application provides a method for synthesizing highly dispersed AlON powder. This synthesis method is based on the gas pressure sintering-auxiliary agent doping synergistic technology. The AlON powder synthesized by the synthesis method of the present application has a nearly spherical primary particle morphology and high dispersibility. It does not need to be crushed during subsequent use, which simplifies the process flow and saves energy costs. It is suitable for transparent ceramics, precision grinding and refractory materials.

[0029] Specifically, the method for synthesizing highly dispersible AlON powder of the present application comprises the following steps: (1) Powder mixing: γ-Al2O3 and solid carbon source are used as raw materials, and the raw materials, additives, dispersants and anhydrous ethanol are ball-milled to obtain a mixed slurry.

[0030] Specifically, the solid carbon source can be carbon black or activated carbon. The carbon black can be acetylene black or tar black. To reduce the reaction temperature and effectively shorten the reaction time, this application uses high-surface-area activated carbon / carbon black and nano-sized γ-Al2O3 powder as raw materials.

[0031] 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°C). Its functions include: promoting the migration and rearrangement of aluminum source (such as Al2O3) and carbon source particles; accelerating ion diffusion; and promoting dissolution-recrystallization reactions on the surfaces of aluminum oxide (Al2O3) and aluminum nitride (AlN). This synergistic effect helps lower the temperature of the carbothermal reduction reaction and the subsequent AlON solid solution temperature, effectively improving the product crystallinity.

[0032] The polymer dispersant may be one or more of polyvinyl pyrrolidone (PVP), polyvinyl alcohol (PVA), polyethylene glycol (PEG), and the like.

[0033] Furthermore, the purity of γ-Al2O3 and solid carbon source is ≥99.99%, and the purity of additive 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 micron-level.

[0034] Furthermore, the mass ratio of γ-Al2O3 to solid carbon source is 94-95:5-6.

[0035] The amount of the additive added is 0-0.5wt% of the raw material, and the amount of the additive added is not 0. In the present application, the appropriate amount of the fluoride additive added helps to improve the crystallinity of AlON and promotes the formation of a regular, nearly spherical morphology. However, excessive additives can easily induce local liquid phase sintering and hinder the uniform growth of grains. Therefore, the amount of the additive in the present application is preferably controlled within the range of 0.05-0.5wt% to take into account both morphology control and uniformity.

[0036] The amount of polymer dispersant added is 0-1wt% of the raw materials. In order to further improve the uniformity of raw material mixing, especially to ensure sufficient dispersion of trace additives in the system, the present application preferably adds a polymer dispersant.

[0037] In the embodiment of the present application, the mass ratio of anhydrous ethanol to γ-Al2O3 is preferably 3.5-4:1.

[0038] Specifically, the ball milling mixing process is to completely dissolve the polymer dispersant in anhydrous ethanol to obtain a solvent, put the raw materials, additives and solvent into a polytetrafluoroethylene ball mill, use high-purity silicon nitride balls or high-purity alumina balls as ball milling media, and use a planetary ball mill to mix and disperse according to a ball-to-material ratio of 3-6:1. The ball milling speed is 170-250r / min and the ball milling time is 15-30h.

[0039] During this ball milling process, a polytetrafluoroethylene (PTFE) ball mill and high-purity silicon nitride / alumina balls are used in an anhydrous ethanol system to achieve uniform multiphase dispersion through planetary ball milling. The steric hindrance of the polymer dispersant and the mechanochemical effects of ball milling reduce the interfacial energy of the powders, resulting in a uniform precursor, providing a highly active, low-agglomeration raw material system for the subsequent carbothermal reduction reaction.

[0040] (2) Drying and granulation: The mixed slurry is dried, ground, and sieved to obtain a mixed powder.

[0041] Specifically, a magnetic rotary heater can be used for dynamic drying during the drying process. Through the uniform distribution characteristics of the three-dimensional thermal field, it can not only achieve rapid dehydration, but also inhibit the uneven sedimentation of powders of different densities and particle sizes due to differences in sedimentation rates, thereby ensuring uniform powder composition after drying.

[0042] Furthermore, the drying temperature may be 80° C. and the drying time may be 3-6 hours.

[0043] Specifically, after drying, the mixed powder is ground and passed through an 80-100 mesh sieve to achieve the purpose of granulation and homogenization, thereby providing highly consistent raw materials for subsequent gas pressure sintering.

[0044] (3) Furnace loading and gas pressure sintering: The mixed powder is loaded into a boron nitride crucible prefabricated with air holes, and the mixed powder is subjected to gas pressure sintering in a gas pressure sintering furnace to obtain AlON powder.

[0045] Specifically, using a boron nitride crucible prefabricated with pores as a carrier can help enhance nitrogen penetration and promote the carbothermal reduction reaction.

[0046] In the embodiment of the present application, the pore size is Φ0.5-1.0 mm, and the density is 3 pores / cm 2 This design aims to prevent the leakage and escape of powder particles through the pores due to excessively large pore diameters (>1.0 mm); to avoid the cracking of the crucible wall due to local stress concentration caused by excessively high pore density; and to ensure sufficient and uniform gas diffusion channels.

[0047] Specifically, the gas pressure sintering process is performed in a gas pressure sintering furnace in a stepped process, including the following steps: Atmosphere control: vacuum to 10 -2 After the Pa level, high-purity nitrogen is filled to 0.15-0.5MPa and the pressure in the furnace is kept constant; Gradient temperature control: Under constant pressure and static nitrogen atmosphere conditions, heat the material to 1500-1600°C at a heating rate of 5-20°C / min and hold for 45-90 minutes to promote the carbon thermal reduction reaction; then heat the material to 1750-1800°C at a heating rate of 5-15°C / min and hold for 60-120 minutes to complete the AlON crystal phase reconstruction.

[0048] In this application, the sintering process utilizes a constant-pressure, static nitrogen atmosphere. AlON powder synthesis involves a complex gas-solid reaction system. During the carbothermal reduction stage, N2 reacts as a reactant to form AlN; during the solid solution stage, Al-N dissolves into Al2O3 to form AlON. Other accompanying reactions occur, such as the formation of various Al-C gaseous intermediates from γ-Al2O3 and carbon, the eventual escape of trace amounts of added fluoride additives (such as HF) from the system as a gaseous phase, and the high-temperature gas-phase decomposition of trace amounts of AlN. Due to the presence and dynamic changes of gaseous components, the sintering atmosphere conditions (pressure, flow rate) have a decisive influence on AlON grain morphology and agglomeration behavior. The results of the subsequent examples and comparative examples clearly demonstrate that in a flowing gas atmosphere, gas flow disturbances promote heterogeneous growth of AlON grains along the gas flow direction, driving particle migration and collision, leading to the formation of hard agglomerates. In contrast, a constant-pressure, static atmosphere (this solution) provides a stable pressure and no artificial flow, providing an isotropic growth environment for the grains. AlON grains mainly grow in situ, with no significant migration or collision between grains, effectively inhibiting agglomeration.

[0049] It should be pointed out in particular that in the prior art before the date of application, there are no public reports on the use of a non-flowing constant-pressure nitrogen atmosphere or the addition of fluoride additives to synthesize AlON powder. The powder obtained by the existing synthesis process, even if it is nearly spherical and dispersed in macroscopic terms, its microstructure is still a polycrystalline agglomerate (see comparative example). The present application successfully synthesized AlON powder with highly dispersed primary particle size and nearly spherical morphology by innovatively combining a constant-pressure static nitrogen sintering atmosphere-a trace amount of fluoride additives (0.05-0.5wt%). The powder is composed of a single AlON grain (non-polycrystalline agglomerate). The synthesis method of the present application can effectively simplify the process and reduce costs: the powder itself is highly dispersed and has no hard agglomerates, and no subsequent crushing treatment is required, which can significantly simplify the process and save energy. This highly dispersed, nearly spherical single crystal particle greatly improves the powder fluidity, filling density and sintering activity, which is conducive to the preparation of high-performance transparent ceramics. This unique form further expands the application boundaries of AlON powder, showing great potential in the fields of refractory materials (improving the rheological properties and sintering properties of castables / spray coatings) and CMC (ceramic matrix composites) precision grinding and polishing (as high hardness, uniform abrasives).

[0050] (4) Decarbonization: The sintered AlON powder is placed in a decarbonization furnace and heat treated at a constant temperature of 600-700°C for 3-5 hours to remove the residual free carbon through oxidation reaction.

[0051] This application also provides a highly dispersible AlON powder, which is synthesized using the above-mentioned method for synthesizing highly dispersible AlON powder. This highly dispersible AlON powder has a single AlON phase, is composed of single AlON grains, has no obvious defects such as pores within the powder, and exhibits no agglomeration between powder particles, exhibiting high dispersibility. This technology is easy to implement, reduces the difficulty of subsequent powder crushing, and reduces crushing energy consumption and costs, making it easy to industrialize.

[0052] The present application also provides a method for preparing AlON transparent ceramics, comprising the following steps: The highly dispersible AlON powder and sintering aid of the present application are placed in a beaker, and the sintering aid is evenly coated on the surface of the highly dispersible AlON powder by an ultrasonic-assisted co-precipitation method. The obtained powder is dried and sieved, and then hydraulically formed (10-50MPa, 5-10min), then cold isostatically densified (150-200MPa, 5min), and finally pressurelessly sintered at 1880-1950℃ for 12-20h to finally obtain AlON transparent ceramics with a transmittance of 58%.

[0053] A Y2O3-MgO-La2O3 three-phase system sintering aid is added to the AlON powder after decarbonization, wherein the Y2O3 addition amount is 0.05-0.25wt%, the MgO addition amount is 0.05-0.25wt%, and the La2O3 addition amount is 0.05-0.15wt%. The total addition amount of the three phases does not exceed 0.35wt%, and is added in the form of nitrate.

[0054] The AlON transparent ceramic preparation method of the present application abandons the crushing step in order to retain the inherent advantages of the powder - high dispersibility and near-spherical morphology - to the greatest extent. The core process is to directly use the highly dispersed, near-spherical AlON powder synthesized by the aforementioned method, and through the co-precipitation method, uniformly coat the sintering aid layer on the surface of the powder and introduce ultrasonic dispersion technology to assist the coating process to ensure the uniformity of the coating layer. Thanks to the excellent dispersibility and regular morphology of the powder itself, even without crushing treatment, the powder can still achieve excellent particle stacking and sintering activity, and finally prepare high-density AlON transparent ceramics.

[0055] The present application is further described below through specific examples.

[0056] In the following scheme, the purity of the γ-Al2O3 and solid carbon source used is ≥99.99%, the purity of the auxiliary agent is ≥99.9%, the primary particle size of γ-Al2O3 is 10-30nm, the primary particle size of acetylene carbon black is 10-20nm, the primary particle size of tar carbon black is 30-40nm, the particle size of activated carbon is 1-2μm, and the particle size of fluoride is micron level.

[0057] In the following scheme, the diameter of the pores of the boron nitride crucible is Φ0.5-1.0mm, and the density of the pores is 3 / cm 2 .

[0058] Example 1: According to the experimental steps, γ-Al2O3 and acetylene black with a mass ratio of 94.4:5.6 were used as raw materials, AlF3 accounting for 0.15wt% of the raw materials was added as an auxiliary agent, PVP accounting for 0.5wt% of the raw materials was used as a polymer dispersant, a polytetrafluoroethylene jar was used as a ball mill, high-purity alumina balls were used as grinding balls, and anhydrous ethanol was used as a medium (the mass ratio of anhydrous ethanol to γ-Al2O3 was 4:1). The polymer dispersant was completely dissolved in anhydrous ethanol to obtain a solvent, and the raw materials, auxiliary agents and solvent were placed in a polytetrafluoroethylene ball mill. According to the ball-to-material ratio of 4:1, a planetary ball mill was used to mix the mixture at a speed of 200r / min for 24h. The obtained mixed slurry was placed at a constant temperature of 80℃ and dried for 4h 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 boron nitride crucible with pre-made pores and evacuated to 10 -2 After reaching the Pa level, high-purity nitrogen was filled in to 0.35 MPa to ensure that the air pressure in the gas pressure sintering furnace was constant at 0.35 MPa. Under constant pressure static nitrogen atmosphere conditions, the temperature was raised to 1550°C at a heating rate of 10°C / min, and kept warm for 45 minutes. The temperature was further raised to 1770°C at a heating rate of 10°C / min, and kept warm for 60 minutes. The sintered AlON powder was placed in a decarbonization furnace and heat treated at a constant temperature of 650°C for 4 hours. The residual free carbon was removed by oxidation reaction to synthesize the highly dispersed AlON powder of this embodiment.

[0059] Comparative Example 1: (No fluorinated additive + atmospheric pressure flowing nitrogen sintering) The raw materials are γ-Al2O3 and acetylene black with a mass ratio of 94.4:5.6, and PVP accounting for 0.5wt% of the raw materials is added as a polymer dispersant. A polytetrafluoroethylene tank is used as a ball mill, imported high-purity alumina balls are used as milling balls, and anhydrous ethanol is used as a medium (the mass ratio of anhydrous ethanol to γ-Al2O3 is 4:1). The polymer dispersant is completely dissolved in anhydrous ethanol to obtain a solvent. The raw materials and the solvent are placed together in a polytetrafluoroethylene ball mill. According to the ball-to-material ratio of 4:1, a planetary ball mill is used to mix the mixture at a speed of 200r / min for 24 hours. Using a magnetic rotary heater, the obtained slurry is placed at a constant temperature of 80℃ and dried for 4 hours, and then ground through an 80-mesh sieve to obtain a uniform mixed powder. The mixed powder is placed in a boron nitride crucible with pre-made pores and evacuated to 10 -2After reaching the Pa level, high-purity nitrogen was filled in to 0.12-0.14 MPa. In an atmosphere of flowing nitrogen at a flow rate of 0.5 L / min, the temperature was increased to 1550°C at a heating rate of 10°C / min and kept warm for 45 minutes. The temperature was further increased to 1770°C at a heating rate of 10°C / min and kept warm for 60 minutes. The sintered AlON powder was placed in a decarbonization furnace and heat treated at a constant temperature of 650°C for 4 hours to remove residual free carbon through oxidation reaction to synthesize AlON powder.

[0060] Comparative Example 2: (Fluorination additive + atmospheric pressure flowing nitrogen sintering) The raw materials are γ-Al2O3 and acetylene black with a mass ratio of 94.4:5.6, AlF3 accounting for 0.15wt% of the raw materials is added as an auxiliary agent, PVP accounting for 0.5wt% of the raw materials is used as a polymer dispersant, a polytetrafluoroethylene jar is used as a ball mill, high-purity alumina balls are used as grinding balls, and anhydrous ethanol is used as a medium (the mass ratio of anhydrous ethanol to γ-Al2O3 is 4:1). The polymer dispersant is completely dissolved in anhydrous ethanol to obtain a solvent, and the raw materials, auxiliary agents and solvent are placed in a polytetrafluoroethylene ball mill. According to the ball-to-material ratio of 4:1, a planetary ball mill is used to mix at a speed of 200r / min for 24h. The obtained mixed slurry is placed at a constant temperature of 80℃ and dried for 4h using a magnetic rotary heater, and then ground through an 80-mesh sieve to obtain a uniform mixed powder. The mixed powder is placed in a boron nitride crucible with pre-made pores and evacuated to 10 -2 After reaching the Pa level, high-purity nitrogen was filled in to 0.12-0.14 MPa. In an atmosphere of flowing nitrogen at a flow rate of 0.5 L / min, the temperature was increased to 1550°C at a heating rate of 10°C / min and kept warm for 45 minutes. The temperature was further increased to 1770°C at a heating rate of 10°C / min and kept warm for 60 minutes. The sintered AlON powder was placed in a decarbonization furnace and heat treated at a constant temperature of 650°C for 4 hours to remove residual free carbon through oxidation reaction to synthesize AlON powder.

[0061] The XRD pattern of the AlON powder of Example 1 is as follows: Figure 1 As shown, the AlON powder has a single AlON phase.

[0062] The particle size distribution of AlON powder in Example 1 is shown in FIG. Figure 2 As shown by Figure 2 It can be seen that the particle size distribution of the primary particles of AlON powder is concentrated, mainly distributed below 3.5μm (>75vol%), of which particles below 1.5μm account for more than 34vol%.

[0063] The microstructure of the AlON powders prepared in Example 1, Comparative Example 1 and Comparative Example 2 was observed, and the scanning electron microscope comparison diagrams are shown in FIG. Figure 3As shown, the left and right figures in the first row are scanning electron microscope images of Example 1, the left and right figures in the second row are scanning electron microscope images of Comparative Example 1, and the figures in the third row are scanning electron microscope images of Comparative Example 2. Figure 3 The AlON powder of Example 1 is nearly spherical and highly dispersed. Each particle is a complete single crystal, free of obvious intracrystalline defects (such as pores). The particles exhibit a discrete distribution with no agglomeration. The grain size distribution is 0.5-3.5 μm, consistent with the results of laser particle size analysis.

[0064] In comparative example 1, AlF3 was not added as an additive, and the AlON powder was synthesized in a normal pressure flowing nitrogen atmosphere. The powder had a porous skeleton structure and the grains were severely agglomerated. In comparative example 2, AlF3 was added as an additive, and the AlON powder was synthesized in a normal pressure flowing nitrogen atmosphere. The grain morphology was close to spherical, but obvious agglomeration occurred due to airflow disturbance.

[0065] Example 2: The main differences between this embodiment and the first embodiment are that the solid carbon source acetylene black is changed to activated carbon, the auxiliary agent 0.15 wt% AlF3 is changed to 0.05 wt% CaF2, and the sintering temperature is adjusted to 1800°C and kept warm for 60 min.

[0066] According to the experimental requirements, γ-Al2O3 and activated carbon were used as raw materials in a mass ratio of 94.4:5.6, CaF2 was added as an auxiliary agent accounting for 0.05wt% of the raw materials, and PVP was added as a polymer dispersant accounting for 0.5wt% of the raw materials. A polytetrafluoroethylene jar was used as the ball mill, high-purity alumina balls were used as grinding balls, and anhydrous ethanol was used as the medium (the mass ratio of anhydrous ethanol to γ-Al2O3 was 4:1). The polymer dispersant was completely dissolved in anhydrous ethanol to obtain a solvent. The raw materials, auxiliary agents, and solvent were placed in the polytetrafluoroethylene ball mill and mixed at a speed of 200r / min for 24 hours at a ball-to-material ratio of 4:1 using a planetary ball mill. The resulting mixed slurry was placed at a constant temperature of 80℃ and dried for 4 hours using a magnetic rotary heater. After that, it was ground through an 80-mesh sieve to obtain a uniform mixed powder. The mixed powder was placed in a boron nitride crucible with pre-made pores and evacuated to 10 -2 After reaching the Pa level, high-purity nitrogen is filled to 0.2MPa to ensure that the gas pressure in the furnace is constant at 0.2MPa. Under constant pressure static nitrogen atmosphere conditions, the temperature is raised to 1550℃ at a heating rate of 10℃ / min, and kept warm for 45min. The temperature is further raised to 1800℃ at a heating rate of 10℃ / min and kept warm for 60min. The sintered AlON powder is placed in a decarbonization furnace and heat-treated at a constant temperature of 650℃ for 4h to remove residual free carbon by oxidation reaction to synthesize the highly dispersed AlON powder of this embodiment.

[0067] The microstructure of the AlON powder of Example 2 is shown in FIG. Figure 4 ,Depend on Figure 4It can be seen that AlON powder with high dispersion characteristics was successfully synthesized under constant nitrogen conditions of 0.2MPa using activated carbon as the solid carbon source and CaF2 as the auxiliary agent. The powder is composed of single crystal particles with no visible defects (such as pores) in the crystals, no agglomeration of particles, and a discrete distribution; the grain size range is 7-15μm.

[0068] Example 3: The main difference between this embodiment and embodiment 1 is that the solid carbon source acetylene black is adjusted to tar carbon black, the additive is adjusted 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 kept warm for 90min.

[0069] According to the experimental requirements, γ-Al2O3 and tar black were used as raw materials in a mass ratio of 94.4:5.6, AlF3 was added as an auxiliary agent accounting for 0.35wt% of the raw materials, and PVP was added as a polymer dispersant accounting for 0.5wt% of the raw materials. A polytetrafluoroethylene jar was used as the ball mill, high-purity alumina balls were used as grinding balls, and anhydrous ethanol was used as the medium (the mass ratio of anhydrous ethanol to γ-Al2O3 was 4:1). The polymer dispersant was completely dissolved in anhydrous ethanol to obtain a solvent. The raw materials, auxiliary agents and solvent were placed in the polytetrafluoroethylene ball mill and mixed at a speed of 200r / min for 24 hours according to a ball-to-material ratio of 4:1 using a planetary ball mill. The resulting mixed slurry was placed at a constant temperature of 80℃ and dried for 4 hours using a magnetic rotary heater. After that, it was ground through an 80-mesh sieve to obtain a uniform mixed powder. The mixed powder was placed in a boron nitride crucible with pre-made pores and evacuated to 10 -2 After reaching the Pa level, high-purity nitrogen is filled to 0.5MPa to ensure that the gas pressure in the furnace is constant at 0.5MPa. Under constant pressure static nitrogen atmosphere conditions, the temperature is raised to 1550℃ at a heating rate of 10℃ / min, and kept warm for 45min. The temperature is further raised to 1800℃ at a heating rate of 10℃ / min and kept warm for 90min. The sintered AlON powder is placed in a decarbonization furnace and heat-treated at a constant temperature of 650℃ for 4h to remove residual free carbon by oxidation reaction to synthesize the highly dispersed AlON powder of this embodiment.

[0070] The microstructure of the AlON powder of Example 3 is shown in FIG. Figure 5 ,Depend on Figure 5 Using tar black as the carbon source and AlF3 as the additive, highly dispersed, near-spherical AlON powders were successfully synthesized under static nitrogen conditions at a constant pressure of 0.5 MPa. The particles exhibited a single-crystal structure, with no visible defects (such as pores) within the crystals. The particles exhibited a discrete distribution with no agglomeration, and the grain size ranged from 5 to 12 μm.

[0071] It can be seen from Examples 1, 2 and 3 that the type of solid carbon source, the type of additive, the amount of additive and the synthesis process will all affect the powder particle size and morphology. However, the AlON powders synthesized according to the synthesis method provided in this application are all composed of single AlON grains, with no obvious defects inside, and the primary particle size has high dispersibility.

[0072] Example 4 The AlON powder and sintering aid prepared in Example 1 were placed in a beaker, and the sintering aid was evenly coated on the surface of the AlON powder by ultrasonic-assisted co-precipitation. The obtained powder was dried and sieved, and then hydraulically formed (15 MPa, 5 min), then densified by cold isostatic pressing (200 MPa, 5 min), and finally pressurelessly sintered at 1920°C for 15 h to obtain AlON transparent ceramics with a transmittance of 58%.

[0073] Among them, the sintering aid is a three-phase system of Y2O3-MgO-La2O3, with the addition amount of Y2O3 being 0.10wt%, the addition amount of MgO being 0.10wt%, and the addition amount of La2O3 being 0.05wt%, all added in the form of nitrate.

[0074] As can be seen from Example 4, the AlON powder obtained in Example 1 (without crushing) was used to successfully prepare high-density AlON transparent ceramics. Figure 6 As shown in the figure, there are a small number of isolated grain boundary / near-grain boundary pores (marked) inside the ceramic. These pores can be further eliminated by optimizing the sintering process parameters (such as heating rate and holding time) to achieve higher density.

[0075] It should be understood that the application of this application is not limited to the above examples. For ordinary technicians in this field, they can make improvements or changes based on the above description, and all these improvements and changes should fall within the scope of protection of this application.

Claims

1. A method for synthesizing highly dispersible AlON powder, characterized in that: The following steps are involved: (1) Using γ-Al2O3 and a solid carbon source as raw materials, the raw materials, the additives and anhydrous ethanol are ball-milled to obtain a mixed slurry; (2) drying, grinding, and sieving the mixed slurry to obtain a mixed powder; (3) loading the mixed powder into a boron nitride crucible prefabricated with air holes, and performing gas pressure sintering on the mixed powder under a constant pressure static nitrogen atmosphere to obtain the highly dispersible AlON powder; (4) Carbon removal; The auxiliary agent is fluoride, and the amount of the auxiliary agent added is 0-0.5wt% of the raw material, and the amount of the auxiliary agent added is not 0.

2. The method for synthesizing highly dispersible AlON powder according to claim 1, wherein: During the ball milling process of the raw materials, the additives and the anhydrous ethanol, a polymer dispersant is added, wherein the amount of the polymer dispersant added is 0-1 wt % of the raw materials; The process of mixing the raw materials, the auxiliary agent and the anhydrous ethanol by ball milling is specifically as follows: firstly dissolving the polymer dispersant in the anhydrous ethanol to obtain a solvent, and then mixing the raw materials, the auxiliary agent and the solvent by ball milling.

3. The method for synthesizing highly dispersible AlON powder according to claim 1, wherein: The gas pressure sintering process comprises the following steps: Vacuum to 10 -2 After the Pa level, high-purity nitrogen is filled to 0.15-0.5MPa and the pressure is kept constant; Under constant pressure and static nitrogen atmosphere, heat to 1500-1600℃ at a heating rate of 5-20℃ / min and keep at this temperature for 45-90min; Then increase the temperature to 1750-1800℃ at a heating rate of 5-15℃ / min and keep it at that temperature for 60-120min.

4. The method for synthesizing highly dispersible AlON powder according to claim 1, wherein: The drying process is to use a magnetic rotary heater to perform dynamic drying.

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

6. The method for synthesizing highly dispersible AlON powder according to claim 2, wherein: The auxiliary agent is one or more of aluminum fluoride, calcium fluoride, magnesium fluoride, yttrium fluoride and lanthanum fluoride; The solid carbon source is one of carbon black or activated carbon; The polymer dispersant is one or more of polyvinyl pyrrolidone, polyvinyl alcohol and polyethylene glycol.

7. The method for synthesizing highly dispersible AlON powder according to claim 1, wherein: During the ball milling and mixing process, a polytetrafluoroethylene ball mill is used as a container, high-purity silicon nitride balls or high-purity alumina balls are used as 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 hours.

8. The method for synthesizing highly dispersible AlON powder according to claim 1, wherein: The decarbonization process is a heat treatment at a constant temperature of 600-700°C for 3-5h; During the drying process, the temperature is 80°C and the time is 3-6 hours; The sieving process is to pass through an 80-100 mesh sieve; The pores have a diameter of 0.5-1.0 mm and a density of 3 pores / cm 2 .

9. A highly dispersible AlON powder, characterized in that: The highly dispersible AlON powder is synthesized by the method for synthesizing the highly dispersible AlON powder according to any one of claims 1 to 8.

10. A method for preparing AlON transparent ceramics, characterized in that: The following steps are involved: The highly dispersible AlON powder according to claim 9 and a sintering aid are placed in a container, the sintering aid is uniformly coated on the surface of the highly dispersible AlON powder by an ultrasonic-assisted co-precipitation method, the powder is dried and sieved, hydraulically formed, cold isostatically densified, and pressurelessly sintered at 1880-1950° C. for 12-20 hours to prepare the AlON transparent ceramic; Among them, the sintering aid is a Y2O3-MgO-La2O3 three-phase system sintering aid, the Y2O3 addition amount is 0.05-0.25wt%; the MgO addition amount is 0.05-0.25wt%; the La2O3 addition amount is 0.05-0.15wt%; the total addition amount of the three phases does not exceed 0.35wt%, and the three phases are added in the form of nitrates.

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