A method for preparing yttrium aluminum garnet powder at low temperature and low pressure

Abstract

The present application provides a method for preparing yttrium aluminum garnet powder at low temperature and low pressure, which relates to the field of materials. The method comprises: mixing YOCl, AlCl3•6H2O, water and ethanol to obtain a mixture, then adding hydrochloric acid to adjust the pH of the system to a strong acid, and then heating the reaction under normal pressure; after the reaction is completed, adding an aqueous solution of ammonium bicarbonate to obtain a gel precipitate; drying and grinding the gel precipitate to obtain a precursor; and calcining the precursor to obtain yttrium aluminum garnet powder. The present application uses yttrium oxychloride as a yttrium source to replace traditional yttrium oxide, combined with aluminum chloride hexahydrate as an aluminum source, to reduce the activation energy of the hydrothermal reaction. The introduction of hydrochloric acid can effectively promote the dissociation of YOCl and enhance the Y 3+ The dissolution of ions promotes the reaction. Ethanol is added to prevent the formation of impurity phases. These measures significantly reduce the reaction conditions required, enabling the preparation of high-purity yttrium aluminum garnet powder under mild conditions.

Description

Technical Field

[0001] The present application relates to the field of materials, and in particular to a method for preparing yttrium aluminum garnet powder at low temperature and low pressure. Background Art

[0002] Yttrium aluminum garnet (Y3Al5O 12 The purity of YAG (Yttrium-Ylluminated Ag) powder is a key factor in determining its functional properties and engineering application performance. High-purity YAG (phase purity >99%) can significantly improve the material's mechanical strength and high-temperature phase stability, thereby meeting the stringent intrinsic performance requirements of laser crystals, fluorescent matrices, and advanced thermal barrier coatings. However, the presence of trace impurities (such as YAP and YAM) can introduce lattice defects and interface scattering centers, leading to reduced phonon transmission efficiency, increased thermal expansion mismatch, and the risk of phase transitions in high-temperature environments, severely limiting the material's service life and reliability. In addition, impurity elements (such as Fe and Si) may cause fluorescence quenching or optical scattering, further limiting its application in optoelectronics. Therefore, developing efficient and high-purity YAG synthesis methods to suppress impurity formation and achieve atomic-scale component uniformity has become a key research direction to break through the bottleneck of material performance. Currently, the main preparation methods include solid-phase reaction, sol-gel method, co-precipitation method, hydrothermal method, etc.

[0003] Solid-phase reaction powders have poor sintering properties, making it difficult to produce large, highly transparent YAG ceramics. This is because solid-phase reactions require higher synthesis temperatures, resulting in larger powder particles, more severe agglomeration, and uneven product composition and structure. Furthermore, solid-phase methods typically require longer mixing times, which can lead to severe powder contamination and compromise microstructural uniformity. This makes achieving high density during green body sintering challenging, compromising the translucency of the YAG ceramic. The high cost and operational complexity of the sol-gel method increase the complexity of the process. The resulting product exhibits relatively low crystallinity because the precursor forms hard agglomerates of powder particles during heat treatment, resulting in poor dispersion and suboptimal sintering activity. The co-precipitation method involves a complex precipitation process requiring control of multiple factors, including the amount of precipitant added, precipitation temperature, and precipitation time. Failure to do so can easily lead to incomplete precipitation or impure products. Co-precipitation products are prone to agglomeration due to the strong interactions between particles during precipitation, which can affect product performance. The precipitation method is more expensive: a large amount of precipitant and solvent is required, and the precipitation process takes a long time, so the cost is higher.

[0004] The traditional hydrothermal method has many advantages in the field of YAG synthesis, but it faces multiple challenges: (1) High pressure dependence: the reaction needs to maintain a pressure of >10 MPa to ensure the supercritical state of the solvent, resulting in high equipment costs and complex maintenance; (2) Reaction efficiency limitations: Al2O3 is not suitable for high temperature (>220 °C) 3+ It is easy to hydrolyze to form AlOOH impurity phase, and the reaction time needs to be extended to 12~24 h to improve the conversion rate, which increases energy consumption. Summary of the Invention

[0005] The purpose of this application is to provide a method for preparing yttrium aluminum garnet powder at low temperature and low pressure to solve the above problems.

[0006] To achieve the above objectives, this application adopts the following technical solutions:

[0007] A method for preparing yttrium aluminum garnet powder at low temperature and low pressure, comprising:

[0008] YOCl, AlCl3•6H2O, water and ethanol are mixed to obtain a mixture, and then hydrochloric acid is added to adjust the pH of the system to a strongly acidic state, followed by heating and reacting under normal pressure. After the reaction is completed, an aqueous ammonium bicarbonate solution is added to obtain a gel-like precipitate.

[0009] drying and grinding the gel-like precipitate to obtain a precursor;

[0010] The precursor is calcined to obtain the yttrium aluminum garnet powder.

[0011] Preferably, the YOCl and the AlCl 3 • 6H 2 O are used in a stoichiometric ratio of n(Y):n(Al)=3:5.

[0012] Preferably, the volume ratio of the water to the ethanol is 1:0.8-1.2.

[0013] Preferably, the liquid-to-solid ratio of the mixture is 6.0-6.5 ml / g.

[0014] Preferably, the strongly acidic pH is -0.04 to 0.5.

[0015] Preferably, the aqueous ammonium bicarbonate solution is added until the pH of the system is 6-9.

[0016] Preferably, the reaction temperature is 185-195° C. and the reaction time is 6.5-7.5 h.

[0017] Preferably, the reaction is carried out under stirring at a stirring rate of 400-600 r / min.

[0018] Preferably, the calcination temperature is 1000-1200° C. and the calcination time is 2-3 hours.

[0019] Preferably, the YOCl is prepared by calcining YCl3•6H2O.

[0020] Compared with the prior art, the advantages of this application include:

[0021] The method for preparing yttrium aluminum garnet powder at low temperature and low pressure provided in this application uses yttrium oxychloride (YOCl) as the yttrium source instead of traditional yttrium oxide (Y2O3), combined with aluminum chloride hexahydrate (AlCl3•6H2O) as the aluminum source to reduce the activation energy of the hydrothermal reaction. Experimental studies have shown that when HCl is not introduced, undissociated YOCl solid residues exist in the reaction system, while the introduction of hydrochloric acid can effectively promote the dissociation of YOCl. HCl can enhance the YOCl reaction by lowering the pH value of the solution. 3+ The dissolution of ions promotes the reaction. Therefore, through these means, the reaction conditions can be significantly reduced, and the material preparation under mild conditions can be achieved. The reason for adding ethanol is to prevent the formation of impurity phases. The mechanism is: ethanol molecules react with [Al(OH)6] through a coordination competition mechanism. 3- The hydroxyl complex can effectively inhibit the formation of boehmite (γ-AlOOH) intermediate phase with the participation of OH⁻ groups. 3+ With Al 3+ Ions tend to deposit preferentially on the surface of their respective nuclei through the spontaneous nucleation process and undergo grain growth, making Y 3+ or Al 3+ The addition of ethanol will hinder the migration speed of ions, thereby reducing the Y 3+ 、Al 3+ The ability to gather together alone makes Y 3+ and Al 3+ Co-precipitation is carried out according to the stoichiometric ratio of the target high-purity product. The addition of organic solvent will reduce the oxygen bond force of the original water system and reduce the generation of agglomeration.

[0022] Based on the above reasons, the method for preparing yttrium aluminum garnet powder at low temperature and low pressure provided in this application not only reduces equipment costs but also eliminates harmful solvent pollution in the entire process, meets the requirements of green chemistry, and the purity of the obtained YAG powder reaches more than 99%. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following is a brief introduction to the drawings required for use in the embodiments. It should be understood that the following drawings only show certain embodiments of the present application and therefore should not be regarded as limiting the scope of the present application.

[0024] Figure 1A schematic diagram of the process flow of the method for preparing yttrium aluminum garnet powder at low temperature and low pressure provided in this application;

[0025] Figure 2 The XRD spectra of the powders obtained in Examples and Comparative Examples are shown in FIG. DETAILED DESCRIPTION

[0026] In order to better illustrate the technical solution provided by this application, before the embodiments, an overall description of the technical solution is first given, as follows:

[0027] A method for preparing yttrium aluminum garnet powder at low temperature and low pressure, comprising:

[0028] YOCl, AlCl3•6H2O, water and ethanol are mixed to obtain a mixture, and then hydrochloric acid is added to adjust the pH of the system to a strongly acidic state, followed by heating and reacting under normal pressure. After the reaction is completed, an aqueous ammonium bicarbonate solution is added to obtain a gel-like precipitate.

[0029] drying and grinding the gel-like precipitate to obtain a precursor;

[0030] The precursor is calcined to obtain the yttrium aluminum garnet powder.

[0031] In an optional embodiment, the YOCl and the AlCl 3 • 6H 2 O are used in a stoichiometric ratio of n(Y):n(Al)=3:5.

[0032] Since the target product is high-purity yttrium aluminum garnet powder, the raw materials need to be measured strictly according to the above-mentioned stoichiometric ratio.

[0033] In an optional embodiment, the volume ratio of the water to the ethanol is 1:0.8-1.2.

[0034] When the volume ratio of ethanol to water deviated from the range of 1:1±0.2, impurities were detected in the product.

[0035] Optionally, the volume ratio of the water to the ethanol can be 1:0.8, 1:0.9, 1:1, 1:1.1, 1:1.2 or any value between 1:0.8 and 1.2.

[0036] In an optional embodiment, the liquid-to-solid ratio of the mixture is 6.0-6.5 ml / g.

[0037] Optionally, the liquid-to-solid ratio of the mixture can be 6.0 ml / g, 6.1 ml / g, 6.2 ml / g, 6.3 ml / g, 6.4 ml / g, 6.5 ml / g or any value between 6.0 and 6.5 ml / g.

[0038] In an optional embodiment, the strongly acidic pH is -0.04 to 0.5.

[0039] Optionally, the strongly acidic pH may be -0.04, 0, 0.1, 0.5, or any value between -0.04 and 0.5.

[0040] Hydrochloric acid generally uses concentrated hydrochloric acid with a concentration greater than or equal to 35wt% to achieve the above-mentioned strong acidic environment.

[0041] In an optional embodiment, the aqueous ammonium bicarbonate solution is added until the pH of the system is 6-9.

[0042] Optionally, the aqueous ammonium bicarbonate solution is added until the pH of the system reaches 6, 7, 8, 9 or any value between 6 and 9.

[0043] In an optional embodiment, the reaction temperature is 185-195° C. and the reaction time is 6.5-7.5 h.

[0044] Optionally, the reaction temperature can be 185°C, 190°C, 195°C or any value between 185-195°C, and the reaction time can be 6.5h, 7h, 7.5h or any value between 6.5-7.5h.

[0045] In an optional embodiment, the reaction is carried out under stirring at a stirring rate of 400-600 r / min.

[0046] Optionally, the stirring rate may be 400 r / min, 500 r / min, 600 r / min or any value between 400-600 r / min.

[0047] In an optional embodiment, the calcination temperature is 1000-1200° C. and the calcination time is 2-3 hours.

[0048] High-purity products can be obtained by calcining at relatively low temperatures and in a short time.

[0049] Optionally, the calcination temperature may be 1000° C., 1100° C., 1200° C. or any value between 1000-1200° C., and the calcination time may be 2 h, 2.5 h, 3 h or any value between 2-3 h.

[0050] In an optional embodiment, the YOCl is prepared by calcining YCl3•6H2O.

[0051] The embodiments of the present application will be described in detail below in conjunction with specific examples, but it will be understood by those skilled in the art that the following examples are merely illustrative of the present application and should not be considered as limiting the scope of the present application. In the examples, if specific conditions are not specified, the conditions are carried out according to conventional conditions or manufacturer recommendations. The reagents or instruments used are not specified by the manufacturer and are conventional products that can be purchased commercially.

[0052] Example 1

[0053] like Figure 1 As shown, this embodiment provides a method for preparing yttrium aluminum garnet powder at low temperature and low pressure, comprising the following steps:

[0054] YOCl and AlCl₃•6H₂O were precisely weighed and mixed according to the stoichiometric ratio of n(Y):n(Al) = 3:5. The mixture was placed in a polytetrafluoroethylene-lined container. A mixture of deionized water and anhydrous ethanol (volume ratio 1:1) was added, resulting in a liquid-to-solid ratio of 6.2 ml / g. Hydrochloric acid (36 wt%) was then added to adjust the pH of the system to a range of -0.04–0.5 to prepare the reactants for the hydrothermal reaction. The polytetrafluoroethylene container containing the reactants was placed in a high-temperature, high-pressure reactor. The reaction temperature was set at 190°C and the reaction was maintained at this temperature for 7 h. The magnetic stirring rate in the reactor was maintained at 500 rpm. After the reaction was completed, the hydrothermal product was cooled to room temperature and 2 mol / L ammonium bicarbonate was added dropwise to adjust the pH to 7.5 to form a gel. The product was then dried in a drying oven and ground to obtain a precursor powder. The precursor was calcined in a muffle furnace at 1000°C for 2 h to obtain YAG powder. The product was analyzed by X-ray diffraction. Figure 2 The diffraction peaks of the calcined powder closely matched those of a YAG standard card, and no significant impurities (such as YAM or YAP) were detected. Compositional analysis revealed a YAG purity of 99.7%, demonstrating that this method can achieve high-purity YAG synthesis.

[0055] Example 2

[0056] This embodiment provides a method for preparing yttrium aluminum garnet powder at low temperature and low pressure, comprising the following steps:

[0057] YOCl and AlCl₃·6H₂O were precisely weighed and mixed according to a stoichiometric ratio of n(Y):n(Al) = 3:5. The mixture was placed in a polytetrafluoroethylene-lined container. A mixture of deionized water and anhydrous ethanol (volume ratio 1:1) was added, resulting in a liquid-to-solid ratio of 6.2 ml / g. Hydrochloric acid (36 wt%) was then added to adjust the pH of the system to a range of -0.04–0.5 to prepare the reactants for the hydrothermal reaction. The polytetrafluoroethylene container containing the reactants was placed in a high-temperature, high-pressure reactor. The reaction temperature was set at 188°C and the reaction was maintained at this temperature for 7 h. The magnetic stirring rate in the reactor was maintained at 500 rpm. After the reaction was completed, the hydrothermal product was cooled to room temperature and 2 mol / L ammonium bicarbonate was added dropwise to adjust the pH to 7.5 to form a gel. The product was then dried in a drying oven and ground to obtain a precursor powder. The precursor was calcined in a muffle furnace at 1000°C for 2 h to obtain YAG powder. The product was analyzed by X-ray diffraction. Figure 2 The diffraction peaks of the calcined powder were highly consistent with those of a YAG standard card, and no obvious impurities (such as YAM or YAP) were detected, which was basically consistent with the XRD pattern of Example 1. Composition analysis showed that the YAG purity reached 99.1%.

[0058] Example 3

[0059] This embodiment provides a method for preparing yttrium aluminum garnet powder at low temperature and low pressure, comprising the following steps:

[0060] YOCl and AlCl₃•6H₂O were precisely weighed according to the stoichiometric ratio of n(Y):n(Al) = 3:5. The mixture was placed in a polytetrafluoroethylene-lined container. A mixture of deionized water and anhydrous ethanol (volume ratio 1:1) was added, resulting in a liquid-to-solid ratio of 6.2 ml / g. Concentrated hydrochloric acid (36 wt%) was then added to adjust the pH of the system to a range of -0.04–0.5 to prepare the reactants for the hydrothermal reaction. The polytetrafluoroethylene container containing the reactants was placed in a high-temperature, high-pressure reactor. The reaction temperature was set at 192°C and the reaction was maintained at this temperature for 7 h. The magnetic stirring rate in the reactor was maintained at 500 rpm. After the reaction was completed, the hydrothermal product was cooled to room temperature and 2 mol / L ammonium bicarbonate was added dropwise to adjust the pH to 7.5 to form a gel. The product was then dried in a drying oven and ground to obtain a precursor powder. The precursor was calcined in a muffle furnace at 1000°C for 2 h to obtain YAG powder. The product was analyzed by X-ray diffraction. Figure 2 The diffraction peaks of the calcined powder were highly consistent with those of a YAG standard card, and no obvious impurities (such as YAM or YAP) were detected, which was basically consistent with the XRD pattern of Example 1. Composition analysis showed that the YAG purity reached 99.4%.

[0061] Example 4

[0062] This embodiment provides a method for preparing yttrium aluminum garnet powder at low temperature and low pressure, comprising the following steps:

[0063] YOCl and AlCl₃·6H₂O were precisely weighed and mixed according to a stoichiometric ratio of n(Y):n(Al) = 3:5. The mixture was placed in a polytetrafluoroethylene-lined container. A mixed solvent of deionized water and anhydrous ethanol (volume ratio 1:1.2) was added, resulting in a liquid-to-solid ratio of 6.2 ml / g. Concentrated hydrochloric acid (36 wt%) was then added to adjust the pH of the system to a range of -0.04–0.5 to prepare the reactants for the hydrothermal reaction. The polytetrafluoroethylene container containing the reactants was placed in a high-temperature, high-pressure reactor. The reaction temperature was set at 190°C and the reaction was maintained at this temperature for 7 h. The magnetic stirring rate in the reactor was maintained at 500 rpm. After the reaction was completed, the hydrothermal product was cooled to room temperature and 2 mol / L ammonium bicarbonate was added dropwise to adjust the pH to 7.5 to form a gel. The product was then dried in a drying oven and ground to obtain a precursor powder. The precursor was calcined in a muffle furnace at 1000°C for 2 h to obtain YAG powder. The product was analyzed by X-ray diffraction. Figure 2 The diffraction peaks of the calcined powder were highly consistent with those of a YAG standard card, and no obvious impurities (such as YAM or YAP) were detected, which was basically consistent with the XRD pattern of Example 1. Composition analysis showed that the YAG purity reached 99.3%.

[0064] Example 5

[0065] This embodiment provides a method for preparing yttrium aluminum garnet powder at low temperature and low pressure, comprising the following steps:

[0066] YOCl and AlCl₃•6H₂O were precisely weighed and mixed according to a stoichiometric ratio of n(Y):n(Al) = 3:5. The mixture was placed in a polytetrafluoroethylene-lined container. A mixed solvent of deionized water and anhydrous ethanol (volume ratio 1:0.8) was added, resulting in a liquid-to-solid ratio of 6.2 ml / g. Concentrated hydrochloric acid (36 wt%) was then added to adjust the pH of the system to a range of -0.04–0.5 to prepare the reactants for the hydrothermal reaction. The polytetrafluoroethylene container containing the reactants was placed in a high-temperature, high-pressure reactor. The reaction temperature was set at 190°C and the reaction was maintained at this temperature for 7 h. The magnetic stirring rate in the reactor was maintained at 500 rpm. After the reaction was completed, the hydrothermal product was cooled to room temperature and 2 mol / L ammonium bicarbonate was added dropwise to adjust the pH to 7.5 to form a gel. The product was then dried in a drying oven and ground to obtain a precursor powder. The precursor was calcined in a muffle furnace at 1000°C for 2 h to obtain YAG powder. The product was analyzed by X-ray diffraction. Figure 2The diffraction peaks of the calcined powder were highly consistent with those of a YAG standard card, and no obvious impurities (such as YAM or YAP) were detected, which was basically consistent with the XRD pattern of Example 1. Composition analysis showed that the YAG purity reached 99.1%.

[0067] In Examples 2 to 5, the YAG powder still contained impurities (YAM / YAP), but the phase purity met the basic requirement for high purity (purity > 97%). The optimized process of Example 1 is the optimal process and provides a scalable synthesis path for the industrial production of YAG powder (yield > 99%).

[0068] Comparative Example 1

[0069] YOCl and AlCl₃·6H₂O were precisely weighed according to the stoichiometric ratio of n(Y):n(Al) = 3:5. The mixture was placed in a polytetrafluoroethylene-lined container. A mixture of deionized water and anhydrous ethanol (volume ratio 1:1) was added, resulting in a liquid-to-solid ratio of 6.2 ml / g. Hydrochloric acid (36 wt%) was then added to adjust the pH of the system to a range of -0.04–0.5 to prepare the reactants for the hydrothermal reaction. The polytetrafluoroethylene container containing the reactants was placed in a high-temperature, high-pressure reactor. The reaction temperature was set at 190°C and the reaction was maintained at this temperature for 6 h. The magnetic stirring rate in the reactor was maintained at 500 rpm. After the reaction was completed, the hydrothermal product was cooled to room temperature and 2 mol / L ammonium bicarbonate was added dropwise to adjust the pH to 7.5 to form a gel. The product was then dried in a drying oven and ground to obtain a precursor powder. The precursor was calcined in a muffle furnace at 1000°C for 2 h to obtain YAG powder. The product was analyzed by X-ray diffraction. Figure 2 The main diffraction peaks of the calcined powder closely match those of a YAG standard card, with YAP and YAM impurities also detected. Compositional analysis revealed a YAG purity of 96.6%, with YAP accounting for 1.9% and YAM for 1.5%.

[0070] In this comparative example, shortening the reaction time to 6 h resulted in a significant decrease in phase purity, and the shorter constant temperature time was not sufficient to achieve complete reaction.

[0071] Comparative Example 2

[0072] YOCl and AlCl₃•6H₂O reagents were accurately weighed according to the stoichiometric ratio of n(Y):n(Al) = 3:5, mixed, and placed in a polytetrafluoroethylene-lined container. A mixture of deionized water and anhydrous ethanol (volume ratio 1:1) was added, resulting in a liquid-to-solid ratio of 6.2 ml / g. Hydrochloric acid (36 wt%) was then added to adjust the pH of the system to a range of -0.04–0.5 to prepare the reactants for the hydrothermal reaction. The polytetrafluoroethylene container containing the reactants was placed in a high-temperature, high-pressure reactor. The reaction temperature was set at 190°C and the reaction was maintained at this temperature for 8 h. The magnetic stirring rate in the reactor was maintained at 500 rpm. After the reaction was completed, the hydrothermal product was cooled to room temperature and 2 mol / L ammonium bicarbonate was added dropwise to adjust the pH to 7.5 to form a gel. The product was then dried in a drying oven and ground to obtain a precursor powder. The precursor was calcined in a muffle furnace at 1000°C for 2 h to obtain YAG powder. The product was analyzed by X-ray diffraction. Figure 2 The main diffraction peaks of the calcined powder closely match those of a YAG standard card, with some YAM and YAP impurities also detected. Compositional analysis revealed a YAG purity of 91.2%, with YAM accounting for 5.3% and YAP for 3.5%.

[0073] In this comparative example, the increase of the reaction time to 8 h resulted in a significant decrease in phase purity. The longer the constant temperature time, the more impurities in the reaction system, which may be due to the initiation of side reactions.

[0074] Comparative Example 3

[0075] According to the stoichiometric ratio of n(Y):n(Al) = 3:5, YOCl and AlCl3•6H2O reagents were accurately weighed, mixed, and placed in a polytetrafluoroethylene liner. No anhydrous ethanol solution was added, and the liquid-to-solid ratio was 6.2 ml / g. Hydrochloric acid (36 wt%) was then introduced to adjust the pH of the system to a range of -0.04 to 0.5 to prepare the reactants for the hydrothermal reaction. The polytetrafluoroethylene container containing the reactants was placed in a high-temperature, high-pressure reactor. The reaction temperature was set to 190°C and the reaction was maintained at this temperature for 7 hours. The magnetic stirring rate in the reactor was maintained at 500 r / min during the reaction. After the reaction was completed, the hydrothermal product was cooled to room temperature and 2 mol / L ammonium bicarbonate was added dropwise to adjust the pH of the system to 7.5 to form a gel. The product was then placed in a drying oven for drying and grinding to obtain a precursor powder. The precursor was calcined in a muffle furnace at 1000°C for 2 hours to obtain YAG powder. The product was analyzed by X-ray diffraction, and the results are as follows: Figure 2As shown in Figure 2, the calcined powder contained a high level of impurities, including some YAG phase, as well as YAM, YAP, and Al2O3 miscellaneous phases. Composition analysis revealed that the YAG phase accounted for 90.5%, YAM for 4.1%, and YAP for 5.4%.

[0076] In this comparative example, no ethanol was added, which resulted in the formation of an impurity phase.

[0077] Comparative Example 4

[0078] YOCl and AlCl₃•6H₂O reagents were accurately weighed according to the stoichiometric ratio of n(Y):n(Al) = 3:5, mixed, and placed in a polytetrafluoroethylene-lined container. A mixed solvent of deionized water and anhydrous ethanol (volume ratio 2:1) was added, resulting in a liquid-to-solid ratio of 6.2 ml / g. Hydrochloric acid (36 wt%) was then added to adjust the pH of the system to a range of -0.04–0.5 to prepare the reactants for the hydrothermal reaction. The polytetrafluoroethylene container containing the reactants was placed in a high-temperature, high-pressure reactor. The reaction temperature was set at 190°C and the reaction was maintained at this temperature for 7 h. The magnetic stirring rate in the reactor was maintained at 500 rpm. After the reaction was completed, the hydrothermal product was cooled to room temperature and 2 mol / L ammonium bicarbonate was added dropwise to adjust the pH to 7.5 to form a gel. The product was then dried in a drying oven and ground to obtain a precursor powder. The precursor was calcined in a muffle furnace at 1000°C for 2 h to obtain YAG powder. The product was analyzed by X-ray diffraction. Figure 2 The main diffraction peaks of the calcined powder closely match those of a YAG standard card, with some YAM and YAP impurities also detected. Compositional analysis revealed a YAG purity of 89.5%, with YAM accounting for 7.7% and YAP for 2.8%.

[0079] The amount of ethanol used in this comparative example is too low, which also leads to the generation of impurity phase.

[0080] Comparative Example 5

[0081] YOCl and AlCl₃·6H₂O reagents were accurately weighed according to the stoichiometric ratio of n(Y):n(Al) = 3:5, mixed, and placed in a polytetrafluoroethylene-lined container. A mixed solvent of deionized water and anhydrous ethanol (volume ratio 1:2) was added, resulting in a liquid-to-solid ratio of 6.2 ml / g. Hydrochloric acid (36 wt%) was then added to adjust the pH of the system to a range of -0.04–0.5 to prepare the reactants for the hydrothermal reaction. The polytetrafluoroethylene container containing the reactants was placed in a high-temperature, high-pressure reactor. The reaction temperature was set at 190°C and the reaction was maintained at this temperature for 7 h. The magnetic stirring rate in the reactor was maintained at 500 rpm. After the reaction was completed, the hydrothermal product was cooled to room temperature and 2 mol / L ammonium bicarbonate was added dropwise to adjust the pH to 7.5 to form a gel. The product was then dried in a drying oven and ground to obtain a precursor powder. The precursor was calcined in a muffle furnace at 1000°C for 2 h to obtain YAG powder. The product was analyzed by X-ray diffraction. Figure 2 The main diffraction peaks of the calcined powder closely match those of a YAG standard card, with some YAM and YAP impurities also detected. Compositional analysis reveals that the YAG phase accounts for 92.6%, YAM for 2.9%, and YAP for 4.5%.

[0082] The amount of ethanol used in this comparative example is too high, which also leads to the generation of impurity phase.

[0083] It should be noted that experiments have shown that other alcohol compounds, such as isopropanol, cannot be used to replace ethanol. In the isopropanol system, the metal aluminum / yttrium particles need to undergo high-temperature reflux (85°C) and undergo hydrolysis and condensation reactions with isopropanol to form an isopropoxide precursor. This process is limited by the low diffusion rate caused by the large molecular weight of isopropanol, and the subsequent introduction of a precipitant (NH4HCO3) to regulate the gelation process has defects such as a long process and poor controllability of the intermediate phase. In addition, the low boiling point of ethanol (78.4°C) is more conducive to the complete removal of solvent molecules in the early stages of calcination than isopropanol (82.6°C). Residual isopropanol will generate organic carbon fragments, affecting the densification and sintering properties of YAG ceramics.

[0084] Comparative Example 6

[0085] YOCl and AlCl₃•6H₂O were precisely weighed according to the stoichiometric ratio of n(Y):n(Al) = 3:4.5. The mixture was placed in a polytetrafluoroethylene-lined container. A mixture of deionized water and anhydrous ethanol (volume ratio 1:1) was added, resulting in a liquid-to-solid ratio of 6.2 ml / g. Hydrochloric acid (36 wt%) was then added to adjust the pH of the system to a range of -0.04–0.5 to prepare the reactants for the hydrothermal reaction. The polytetrafluoroethylene container containing the reactants was placed in a high-temperature, high-pressure reactor. The reaction temperature was set at 190°C and the reaction was maintained at this temperature for 7 h. The magnetic stirring rate in the reactor was maintained at 500 rpm. After the reaction was completed, the hydrothermal product was cooled to room temperature and 2 mol / L ammonium bicarbonate was added dropwise to adjust the pH to 7.5 to form a gel. The product was then dried in a drying oven and ground to obtain a precursor powder. The precursor was calcined in a muffle furnace at 1000°C for 2 h to obtain YAG powder. The product was analyzed by X-ray diffraction. Figure 2 As shown in Figure 2, the calcined powder contained a high level of impurities, including some YAG phase, as well as YAM, YAP, and Y2O3 impurities. The increased aluminum content resulted in the formation of aluminum trioxide impurities by reacting with atmospheric oxygen. Compositional analysis revealed that the YAG phase accounted for 77.4%, YAM 8.4%, YAP 4%, and Y2O3 10.2%.

[0086] Comparative Example 7

[0087] YOCl and AlCl₃•6H₂O were precisely weighed according to the stoichiometric ratio of n(Y):n(Al) = 3:6. The mixture was placed in a polytetrafluoroethylene-lined container. A mixture of deionized water and anhydrous ethanol (volume ratio 1:1) was added, resulting in a liquid-to-solid ratio of 6.2 ml / g. Hydrochloric acid (36 wt%) was then added to adjust the pH of the system to a range of -0.04–0.5 to prepare the reactants for the hydrothermal reaction. The polytetrafluoroethylene container containing the reactants was placed in a high-temperature, high-pressure reactor. The reaction temperature was set at 190°C and the reaction was maintained at this temperature for 7 h. The magnetic stirring rate in the reactor was maintained at 500 rpm. After the reaction was completed, the hydrothermal product was cooled to room temperature and 2 mol / L ammonium bicarbonate was added dropwise to adjust the pH to 7.5 to form a gel. The product was then dried in a drying oven and ground to obtain a precursor powder. The precursor was calcined in a muffle furnace at 1000°C for 2 h to obtain YAG powder. The product was analyzed by X-ray diffraction. Figure 2As shown in Figure 2, the calcined powder contains a high level of impurities, including some YAG phase, as well as YAM, YAP, and Al2O3 miscellaneous phases. The increased aluminum content causes the excess aluminum to react with atmospheric oxygen to form an aluminum oxide miscellaneous phase. Compositional analysis reveals that the YAG phase accounts for 68.6%, YAM for 10.6%, YAP for 7.4%, and Al2O3 for 13.4%.

[0088] In Comparative Examples 6 and 7, the ratio of the raw materials YOCl and AlCl3•6H2O is not appropriate, which also leads to the formation of impurity phases.

[0089] Comparative Example 8

[0090] YOCl and AlCl₃•6H₂O reagents were accurately weighed according to the stoichiometric ratio of n(Y):n(Al) = 3:5, mixed, and placed in a polytetrafluoroethylene-lined container. A mixture of deionized water and anhydrous ethanol (volume ratio 1:1) was added, resulting in a liquid-to-solid ratio of 6.2 ml / g. Hydrochloric acid (36 wt%) was then added to adjust the pH of the system to a range of -0.04–0.5 to prepare the reactants for the hydrothermal reaction. The polytetrafluoroethylene container containing the reactants was placed in a high-temperature, high-pressure reactor. The reaction temperature was set at 200°C and the reaction was maintained at this temperature for 7 h. The magnetic stirring rate in the reactor was maintained at 500 rpm. After the reaction was completed, the hydrothermal product was cooled to room temperature and 2 mol / L ammonium bicarbonate was added dropwise to adjust the pH to 7.5 to form a gel. The product was then dried in a drying oven and ground to obtain a precursor powder. The precursor was calcined in a muffle furnace at 1000°C for 2 h to obtain YAG powder. The product was analyzed by X-ray diffraction. Figure 2 The main diffraction peaks of the calcined powder closely match those of a YAG standard card, with some YAM and YAP impurities also detected. Compositional analysis reveals that the YAG phase accounts for 94.5%, YAM for 3.6%, and YAP for 1.9%.

[0091] In this comparative example, the hydrothermal reaction temperature was too high, which also led to the generation of impurity phases.

[0092] Comparative Example 9

[0093] YOCl and AlCl₃•6H₂O were precisely weighed according to the stoichiometric ratio of n(Y):n(Al) = 3:5. The mixture was placed in a polytetrafluoroethylene-lined container. A mixture of deionized water and anhydrous ethanol (volume ratio 1:1) was added, resulting in a liquid-to-solid ratio of 6.2 ml / g. Hydrochloric acid (36 wt%) was then added to adjust the pH of the system to a range of -0.04–0.5 to prepare the reactants for the hydrothermal reaction. The polytetrafluoroethylene container containing the reactants was placed in a high-temperature, high-pressure reactor. The reaction temperature was set at 180°C and the reaction was maintained at this temperature for 7 h. The magnetic stirring rate in the reactor was maintained at 500 rpm. After the reaction was completed, the hydrothermal product was cooled to room temperature and 2 mol / L ammonium bicarbonate was added dropwise to adjust the pH to 7.5 to form a gel. The product was then dried in a drying oven and ground to obtain a precursor powder. The precursor was calcined in a muffle furnace at 1000°C for 2 h to obtain YAG powder. The product was analyzed by X-ray diffraction. Figure 2 The main diffraction peaks of the calcined powder closely match those of a YAG standard card, with some YAM and YAP impurities also detected. Compositional analysis reveals that the YAG phase accounts for 94.3%, YAM for 3.3%, and YAP for 2.4%.

[0094] In this comparative example, the hydrothermal reaction temperature was too low, which also led to the generation of impurity phases.

[0095] The method provided in this application has the following advantages:

[0096] 1. A novel raw material system and pretreatment process: The new method utilizes yttrium oxychloride (YOCl) as the yttrium source, replacing traditional yttrium oxide (Y2O3), combined with aluminum chloride hexahydrate (AlCl3•6H2O) as the aluminum source to lower the activation energy of the hydrothermal reaction. This innovative raw material system avoids the low oxide diffusion rate and harsh hydrothermal conditions associated with traditional solid-phase methods, and eliminates the need for costly organic precursors.

[0097] 2. Mild hydrothermal reaction conditions achieve uniform complexation of aluminum and yttrium ions under low pressure. The alcohol-water mixed solvent system effectively suppresses side reactions, and the addition of HCl adjusts the solution pH, promoting uniform formation of the precursor gel and providing a highly active precursor for subsequent low-temperature calcination.

[0098] 3. Low-temperature calcination and crystal phase control technology: The precursor can be converted into pure YAG by a short calcination at 1000-1200°C, significantly reducing energy consumption compared to traditional solid-phase methods (above 1400°C). By controlling the calcination temperature and holding time, abnormal grain growth is suppressed, resulting in low-agglomeration YAG powder.

[0099] 4. Green and environmentally friendly with good adaptability to industrialization; the entire process adopts hydrothermal method combined with low-temperature calcination to avoid the high energy consumption of high-temperature solid-phase reaction and the pollution problem of organic solvents in sol-gel method, which meets the requirements of green chemistry and sustainable development.

[0100] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit them. Although the present application has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some or all of the technical features therein. These modifications or replacements do not deviate the essence of the corresponding technical solutions from the scope of the technical solutions of the embodiments of the present application.

Claims

1. A method for preparing yttrium aluminum garnet powder at low temperature and low pressure, characterized in that: include: YOCl, AlCl3•6H2O, water, and ethanol are mixed to obtain a mixture, and hydrochloric acid is added to adjust the pH of the system to -0.04-0.5, followed by heating under normal pressure; after the reaction, an aqueous ammonium bicarbonate solution is added until the pH of the system is 6-9 to obtain a gel-like precipitate; the reaction temperature is 185-195° C., and the reaction time is 6.5-7.5 hours; the reaction is carried out under stirring at a stirring rate of 400-600 r / min; the YOCl is prepared by calcining YCl3•6H2O; drying and grinding the gel-like precipitate to obtain a precursor; calcining the precursor at 1000-1200° C. to obtain the yttrium aluminum garnet powder; The amounts of the YOCl and the AlCl3•6H2O are measured according to a stoichiometric ratio of n(Y):n(Al)=3:5; The volume ratio of the water to the ethanol is 1:0.8-1.2; The liquid-to-solid ratio of the mixture is 6.0-6.5 ml / g.

2. The method for preparing yttrium aluminum garnet powder at low temperature and low pressure according to claim 1, characterized in that: The calcination time is 2-3 hours.

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