High-density sintered magnesium aluminate spinel transparent ceramic and preparation method thereof

Abstract

The invention relates to a high-density sintered magnesium aluminate spinel transparent ceramic and a preparation method thereof, and belongs to the technical field of transparent ceramic preparation, and the preparation method comprises the following steps: preparing MgO-Al2O3 core-shell powder through an ALD technology, doping rare earth, dispersing and modifying the powder, carrying out cold isostatic pressing molding, carrying out vacuum liquid phase sintering, carrying out hot isostatic pressing post-treatment and the like. By optimizing the raw material design, the powder preparation and the sintering process, the sintering temperature is remarkably reduced, the grain size is refined, the percentage of closed area is greatly reduced, and the infrared light transmittance is improved to 86% or above. The problems of high sintering temperature, large percentage of close area, uneven crystal grains and the like in the traditional process can be effectively solved.

Description

Technical Field

[0001] The present invention belongs to the technical field of inorganic non-metallic materials, and specifically relates to a highly densified sintered magnesium-aluminum spinel transparent ceramic and a preparation method thereof. Background Art

[0002] Due to their excellent optical, mechanical, and thermal properties, transparent magnesium-aluminum spinel ceramics have broad application prospects in infrared windows, armor protection, and laser materials. However, the preparation of magnesium-aluminum spinel transparent ceramics with high density, low porosity, and high infrared transmittance still faces many challenges.

[0003] In traditional preparation processes, a solid-phase reaction method combined with high-temperature sintering is usually used to achieve spinelization and densification. Although this method can produce ceramic materials with better performance to a certain extent, its high sintering temperature (1700-1750°C) leads to a significant increase in energy consumption. At the same time, MgO is easily volatile at high temperatures, which can easily cause component segregation and oxygen vacancy defects, affecting the optical and mechanical properties of the material. In addition, traditional powder preparation methods such as ball milling mixing methods make it difficult to ensure uniform mixing of MgO and Al2O3, resulting in incomplete spinelization reaction, and may introduce impurities or form local defects.

[0004] In recent years, researchers have attempted to reduce the sintering temperature and increase the density by introducing additives and optimizing the sintering process. For example, some studies have used additives such as LiF and MgF2 to promote liquid-phase sintering, thereby reducing the sintering temperature to around 1600°C. However, these methods often have limited control over the closed porosity, and a certain number of micropores still remain inside the material, affecting its optical transmittance. In addition, although traditional doping methods can refine the grains to a certain extent, due to the uneven distribution of doping elements, it may be difficult to effectively suppress grain boundary migration behavior, thereby affecting the uniformity of grain size.

[0005] In summary, the existing technology for preparing highly densified magnesium aluminum spinel transparent ceramics has the following main limitations: first, the sintering temperature is high, which leads to increased energy consumption and difficulty in controlling the composition; second, the powder uniformity is insufficient, resulting in low spinelization reaction efficiency; third, the closed porosity is high, affecting the optical properties of the material; and fourth, the grain size distribution is not uniform, which limits the improvement of the mechanical properties of the material. Therefore, it is urgent to develop a new preparation method that can achieve a synergistic improvement of ultra-low closed porosity and high infrared transmittance through multi-dimensional optimization of raw material design, powder preparation and sintering process. Summary of the Invention

[0006] The technical problem to be solved by the present invention is to overcome the deficiencies of the prior art and provide a method for preparing magnesium-aluminum spinel transparent ceramics with low sintering temperature, ultra-low closed porosity and high infrared transmittance.

[0007] The technical solution adopted by the present invention to solve the technical problem is: a method for preparing magnesium aluminum spinel transparent ceramics, characterized by comprising the following steps:

[0008] (1) depositing an Al2O3 layer on the surface of MgO nanoparticles by atomic layer deposition at a deposition temperature of 200°C to 300°C and a cycle number of 50 to 100 times to form a MgO-Al2O3 core-shell powder;

[0009] (2) mixing the core-shell powder in yttrium nitrate to obtain a slurry, and spray drying the slurry to form a composite precursor with a particle size of 1 μm to 5 μm;

[0010] (3) surface-modifying the composite precursor using a silane coupling agent KH-550, and then adding 0.3 wt% to 1.0 wt% of an ammonium polyacrylate dispersant, 0.2 wt% to 0.5 wt% of LiF, and 0.05 wt% to 0.1 wt% of AlF3 to obtain a ceramic slurry;

[0011] (4) After the ceramic material is loaded into the mold, a green body is obtained by cold isostatic pressing at a pressure of 200 MPa to 300 MPa for 5 to 20 minutes;

[0012] (5) The green body is pre-sintered and degreased at a heating rate of 0.5°C / min to 2°C / min to 700°C to 900°C in an air atmosphere, and kept at this temperature for 2 to 4 hours;

[0013] (6) Vacuum liquid phase sintering in a vacuum furnace at a temperature of 1400°C to 1600°C for 3 to 5 hours;

[0014] (7) Hot isostatic pressing is performed at 1550° C. to 1650° C. and 150 MPa to 200 MPa argon pressure for 1 to 3 hours, followed by post-treatment.

[0015] The present invention significantly improves the comprehensive performance of magnesium-aluminum spinel transparent ceramics through multi-dimensional process innovation: First, the atomic layer deposition technology is used to construct the MgO-Al2O3 core-shell structure, realizing molecular-level heterogeneous interface bonding, reducing the component deviation to less than 2% compared with the traditional ball milling method, and greatly improving the efficiency of the spinelization reaction. Secondly, the LiF-AlF3 composite sintering aid is introduced to form a nano-scale liquid phase film and grain boundary phase during vacuum sintering at 1400℃~1600℃, which reduces the sintering temperature by 100℃~200℃ compared with the traditional process. At the same time, the introduction of yttrium ions improves the uniformity of grain size and bending strength. Through cold isostatic gradient pressure forming technology, the closed porosity is reduced to <0.05%. Combined with hot isostatic pressing post-treatment, the infrared transmittance of the ceramic sample reaches 86% (thickness 2mm), which is close to the theoretical value of single crystal. Compared with the traditional process (sintering at 1700-1750℃), the present invention has achieved breakthroughs in energy consumption reduction, large-size green body forming and batch stability.

[0016] Preferably, in the method for preparing the above-mentioned magnesium-aluminum spinel transparent ceramic, the molar ratio of MgO to Al2O3 in step (1) is 0.8 to 1.2:1. In terms of non-stoichiometric ratio compensation, the present invention effectively suppresses the composition imbalance problem caused by Mg volatilization during high-temperature sintering by adjusting the molar ratio of MgO to Al2O3 and the effect of the surface Al2O3 shell.

[0017] Preferably, the specific process of step (1) of the preparation method of the above-mentioned magnesium aluminum spinel transparent ceramic is as follows:

[0018] a) Placing MgO nanoparticles with a particle size of 20nm to 50nm in an oxygen plasma reaction chamber and treating them at a power of 50W to 100W for 7 to 12 minutes to generate hydroxyl active groups on their surface. This enhances the adsorption capacity of the subsequent ALD reaction;

[0019] b) Placing MgO nanoparticles in a rotating fluidized bed ALD system to ensure uniform dispersion of the nanoparticles during deposition and to prevent agglomeration; setting the rotation speed to 60 rpm to 120 rpm, the deposition temperature to 200°C to 300°C (within the ALD process window for Al2O3, with a temperature fluctuation of ≤±2°C to prevent thermal decomposition of MgO), and maintaining the reaction chamber pressure at 10 -2 Torr~10 -3 Torr, using molecular pumps to achieve high vacuum environment and reduce gas phase side reactions;

[0020] c) Trimethylaluminum is evaporated at room temperature by bubbling and pulsed into the system for 0.1s to 0.3s. Trimethylaluminum reacts with the hydroxyl groups on the surface of MgO to form the intermediate Al(CH3)2-O-Mg, releasing CH4;

[0021] d) After removing unreacted trimethylaluminum and by-products by purging with N2, water vapor is introduced for 0.1s to 0.2s to oxidize the intermediate to form Al2O3 and regenerate the hydroxyl active sites;

[0022] e) removing residual H2O and CH4 by N2 purging to obtain a single aluminum oxide layer;

[0023] f) After 50 to 100 cycles, the deposition is completed and the powder is cooled to room temperature at a rate of 1.5°C / min to 2.5°C / min under N2 protection;

[0024] g) The powder was placed in anhydrous ethanol and ultrasonically treated at a frequency of 35 kHz to 45 kHz for 25 to 35 minutes to break up soft agglomerates and ensure particle dispersion; and then vacuum dried at 60° C. for 12 hours to obtain MgO-Al 2 O 3 core-shell powder.

[0025] The present invention adopts a core-shell structure precursor synthesis process based on atomic layer deposition (ALD) technology. An Al2O3 layer is coated on the surface of MgO nanoparticles to form a MgO-Al2O3 core-shell structure. By shortening the interface contact distance between MgO nanoparticles and Al2O3 layer to less than 10nm, the activation energy required for the spinelization reaction is significantly reduced. This structural design not only reduces the Mg 2+ The high defect density at the core-shell interface provides more diffusion channels during sintering, further promoting the improvement of sintering activity.

[0026] Preferably, in the above-mentioned method for preparing magnesium-aluminum spinel transparent ceramics, the volume solid content of the spray-dried slurry in step (2) is 40% to 60%, and the spray pressure is 0.3 MPa to 0.6 MPa.

[0027] Preferably, in the preparation method of the above-mentioned magnesium aluminum spinel transparent ceramic, the mass ratio of the core-shell powder to yttrium nitrate in step (2) is 100:0.05-0.15. + By adding nitrate into the core-shell powder, the grain boundary migration behavior can be effectively regulated. + The incorporation of replaces Al3+ through its larger ionic radius, causing lattice distortion, thereby pinning grain boundary migration, inhibiting abnormal grain growth, and reducing the standard deviation of grain size from 0.8μm to 0.2μm, significantly improving the mechanical properties of the material.

[0028] Preferably, in the preparation method of the above-mentioned magnesium aluminum spinel transparent ceramic, the surface modification in step (3) is to immerse the composite precursor in a KH-550 solution, treat it at 60°C to 80°C for 30 to 120 minutes (to condense the silanol groups with the hydroxyl groups on the powder surface to form Si-OM), and then wash and dry it. In the powder dispersion and molding process, the present invention uses a silane coupling agent KH-550 to modify the surface of the composite powder, and by adding a polyacrylate ammonium dispersant, efficient dispersion of the powder is achieved. The -NH2 group of KH-550 undergoes chemical adsorption with the powder surface, which increases the Zeta potential and reduces the slurry viscosity, thereby reducing the powder agglomeration phenomenon.

[0029] Preferably, in the preparation method of the above-mentioned magnesium aluminum spinel transparent ceramic, the particle size of LiF in step (3) is 100nm to 500nm, and the particle size of AlF3 is 50nm to 200nm.

[0030] The cold isostatic pressing process achieves isotropic pressing under a set pressure, ensuring uniform density distribution of the green body and reducing the number of internal cracks. Preferably, in the above-mentioned method for preparing magnesium-aluminum spinel transparent ceramics, the standard deviation of the density distribution of the green body in step (4) is less than 0.5%.

[0031] Preferably, in the preparation method of the above-mentioned magnesium aluminum spinel transparent ceramic, the heating rate of the vacuum liquid phase sintering low temperature section in step (6) is 5°C / min to 15°C / min, and the heating rate is controlled to 2°C / min after 1250°C to the target temperature.

[0032] The sintering process design is one of the core links of this invention. In the pre-sintering stage, the air atmosphere is used to heat up to the set temperature at a specific rate and then keep the temperature, completely removing the organic residue, with an organic matter removal rate of ≥99.5%. Subsequently, during the vacuum liquid phase sintering process, the LiF and AlF3 of the composite sintering aid system form a eutectic liquid phase at 700℃, filling the gaps between the particles and significantly improving the green body density. - Ions react with impurities to generate volatile gases, which carry grain boundary impurities and volatilize, thus purifying the grain boundaries. 3+ The introduction of ions effectively inhibited grain growth. Ultimately, the residual closed pores were eliminated under hot isostatic pressing conditions, reducing the closed porosity to <0.005%, further improving the material's density.

[0033] A magnesium-aluminum spinel transparent ceramic prepared by the above preparation method.

[0034] Compared with the prior art, the highly densified sintered magnesium aluminum spinel transparent ceramic and its preparation method of the present invention have the following beneficial effects: the present invention adopts ALD technology to construct MgO-Al2O3 core-shell powder, reduces the activation energy of the spinel reaction, reduces the sintering temperature, and reduces energy consumption by more than 30%; through the synergistic effect of filling the particle gaps with LiF / AlF3 eutectic liquid phase and argon hot isostatic pressing, the closed porosity is reduced to <0.005%, the standard deviation of the density distribution is <0.5%, and the infrared transmittance is ≥86%; the present invention introduces Y in the form of yttrium nitrate 3+ By pinning grain boundaries and forming solid solutions, the flexural strength, Vickers hardness, and thermal shock resistance are all improved; through non-stoichiometric compensation of the MgO / Al2O3 molar ratio, the formation of Al-rich phase caused by Mg volatilization is suppressed, and the light scattering centers are reduced; industrial adaptability is enhanced: combining ALD rotating fluidized bed with spray drying, uniform powder dispersion and large-scale production are achieved, and process costs are reduced.

[0035] The transparent ceramics prepared through the above steps not only achieve high densification and low closed-porosity, but also significantly enhance infrared transmittance and mechanical properties. These properties make transparent ceramics promising for broad application in the field of infrared windows, while also providing reliable technical support for applications in other fields, such as laser substrates and optical lenses. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 The scanning electron microscope (SEM) image of the cross section of the transparent ceramic sample prepared in the embodiment of the present invention shows the grain size distribution and the degree of densification. DETAILED DESCRIPTION

[0037] The present invention provides a highly densified sintered magnesium aluminum spinel transparent ceramic and a preparation method thereof. Figure 1 This is a scanning electron microscope (SEM) image of a cross-section of a transparent ceramic sample, showing the grain size distribution and degree of densification.

[0038] In order to better enable relevant personnel in this technical field to fully understand and implement the present invention, the specific implementation principle of the present invention is further supplemented below in combination with a specific application scenario.

[0039] First, MgO-Al2O3 core-shell structure powder was prepared by atomic layer deposition (ALD) technology. MgO nanoparticles were fixed in the reaction chamber, and the precursor pulse time, reaction chamber temperature and cycle number were controlled to ensure that the thickness of the Al2O3 shell layer was uniform and distributed within 10nm. This design shortened the MgO 2+ With Al 3+ The diffusion paths between the core and shell avoid the incomplete spinelization reaction caused by local component segregation in traditional ball milling. In addition, the high defect density at the core-shell interface provides more diffusion channels for the subsequent sintering process, thereby improving the sintering activity.

[0040] Subsequently, rare earth element Y3 was introduced into the core-shell powder. + Doping. Disperse the composite powder in deionized water, add an appropriate amount of Y(NO3)3·6H2O solution, stir thoroughly and then spray dry. + The larger ionic radius of Al3+ replaces Al3+, causing lattice distortion, thereby pinning grain boundary migration and inhibiting abnormal grain growth. Figure 1 It shows that the grain size distribution is between 0.8μm and 1.2μm, with clear grain boundaries and no pores, indicating that the doping design effectively improves the grain growth behavior.

[0041] In the powder forming process, the silane coupling agent KH-550 is used to modify the surface of the composite powder, and the pH value of the slurry is adjusted to 8-9, and polyacrylate ammonium dispersant is added to achieve efficient dispersion. The -NH2 group of KH-550 undergoes chemical adsorption with the powder surface, which increases the Zeta potential, reduces the slurry viscosity, and reduces the powder agglomeration phenomenon. The cold isostatic pressing process achieves isotropic pressing at a pressure of 250MPa (preferred condition), ensuring uniform density distribution of the green billet and reducing the number of internal cracks. Figure 1 The cross-sectional morphology in the figure shows that the grains are closely arranged, the grain boundaries are clear and there are no pores, which reflects the excellent effect of the forming process.

[0042] During the sintering stage, the material is first heated at a specific rate in an air atmosphere and then maintained at this temperature to completely remove any residual organic matter. Subsequently, a composite additive system of LiF and AlF3 is introduced during vacuum liquid-phase sintering. LiF and AlF3 form a eutectic liquid phase at around 700°C, filling the intergranular spaces and significantly increasing the density of the green body. Simultaneously, F- ions react with impurities to generate volatile gases, purifying the grain boundaries. Finally, post-treatment with hot isostatic pressing (HIP) under specific conditions eliminates residual closed pores, further increasing the material's density. The resulting grain size distribution is uniform, with clear grain boundaries and no pores.

[0043] The present invention will be described in detail below by way of examples. Unless otherwise specified, all raw materials used are commercially available.

[0044] Example 1

[0045] (1) Preparation of MgO-Al2O3 core-shell powder:

[0046] a) preparing MgO nanoparticles and trimethylaluminum (MgO and Al2O3 at a molar ratio of 1:1); placing the MgO nanoparticles with a particle size of 20 nm to 50 nm in an oxygen plasma reaction chamber and treating them at a power of 70 W for 10 minutes to generate hydroxyl active groups on their surfaces;

[0047] b) MgO nanoparticles were placed in a rotating fluidized bed ALD system with a rotation speed of 90 rpm, a deposition temperature of 250°C, and a reaction chamber pressure of 10 -2 Torr~10 -3 Torr;

[0048] c) Trimethylaluminum was evaporated at room temperature by bubbling and pulsed into the system for 0.2s. Trimethylaluminum reacted with the hydroxyl groups on the surface of MgO to form the intermediate Al(CH3)2-O-Mg, releasing CH4;

[0049] d) After removing unreacted trimethylaluminum and by-products by purging with N2, water vapor was introduced for 0.1s to oxidize the intermediate to form Al2O3 and regenerate the hydroxyl active sites;

[0050] e) removing residual H2O and CH4 by N2 purging to obtain a single aluminum oxide layer;

[0051] f) After 70 cycles, the deposition was completed and the powder was cooled to room temperature at a rate of 2.0°C / min under N2 protection to prevent the formation of other impurity phases;

[0052] g) The powder was placed in anhydrous ethanol and ultrasonically treated at a frequency of 40 kHz for 30 minutes to break up soft agglomerates and ensure particle dispersion; and then vacuum dried at 60°C for 12 hours to obtain MgO-Al2O3 core-shell powder.

[0053] (2) The core-shell powder was mixed with yttrium nitrate solution to obtain a slurry, wherein the mass ratio of the core-shell powder to yttrium nitrate was 100:0.1, and the volume solid content of the obtained slurry was 50%. The slurry was spray-dried at a spray pressure of 0.4 MPa to form a composite precursor with a particle size of 3 μm.

[0054] (3) The composite precursor was immersed in a KH-550 solution and treated at 70°C for 70 minutes. The surface was then modified by washing and drying. Then, 0.6 wt% of ammonium polyacrylate dispersant, 0.3 wt% of LiF with a particle size of 100 nm to 500 nm, and 0.08 wt% of AlF3 with a particle size of 50 nm to 200 nm were added to obtain a ceramic slurry.

[0055] (4) After the ceramic material is loaded into the mold, a cold isostatic pressing process is performed at a pressure of 250 MPa for 10 minutes to obtain a green body with a density distribution standard deviation of <0.5%.

[0056] (5) The green body was pre-sintered and degreased at a heating rate of 1°C / min to 800°C in an air atmosphere and kept at this temperature for 3 hours.

[0057] (6) Vacuum liquid phase sintering was performed under vacuum conditions. The temperature was raised to 1250°C at a heating rate of 10°C / min, and then continued to be raised to 1500°C at a heating rate of 2°C / min, and kept at this temperature for 4 hours.

[0058] (7) Hot isostatic pressing is performed at 1600°C and 180 MPa argon pressure for 2 hours, followed by post-treatment.

[0059] Example 2

[0060] (1) Preparation of MgO-Al2O3 core-shell powder:

[0061] a) preparing MgO nanoparticles and trimethylaluminum (MgO to Al2O3 at a molar ratio of 1:1); placing the MgO nanoparticles with a particle size of 20 nm to 50 nm in an oxygen plasma reaction chamber and treating them at 80 W for 9 minutes to generate hydroxyl active groups on their surfaces;

[0062] b) MgO nanoparticles were placed in a rotating fluidized bed ALD system with a rotation speed of 100 rpm, a deposition temperature of 220°C, and a reaction chamber pressure of 10 -2 Torr~10 -3 Torr;

[0063] c) Trimethylaluminum was evaporated at room temperature by bubbling and pulsed into the system for 2 seconds. Trimethylaluminum reacted with the hydroxyl groups on the surface of MgO to form the intermediate Al(CH3)2-O-Mg, releasing CH4;

[0064] d) After removing unreacted trimethylaluminum and by-products by purging with N2, water vapor was introduced for 0.2s to oxidize the intermediate to form Al2O3 and regenerate the hydroxyl active sites;

[0065] e) removing residual H2O and CH4 by N2 purging to obtain a single aluminum oxide layer;

[0066] f) After 80 cycles, the deposition was completed and the powder was cooled to room temperature at a rate of 2.0°C / min under N2 protection to prevent the formation of other impurity phases;

[0067] g) The powder was placed in anhydrous ethanol and ultrasonically treated at a frequency of 40 kHz for 30 minutes to break up soft agglomerates and ensure particle dispersion; and then vacuum dried at 60°C for 12 hours to obtain MgO-Al2O3 core-shell powder.

[0068] (2) The core-shell powder was mixed with an yttrium nitrate solution to obtain a slurry, wherein the mass ratio of the core-shell powder to the yttrium nitrate was 100:0.08, and the volume solid content of the obtained slurry was 45%. The slurry was spray-dried at a spray pressure of 0.5 MPa to form a composite precursor with a particle size of 2 μm.

[0069] (3) The composite precursor was immersed in a KH-550 solution and treated at 65°C for 100 minutes. The surface was then modified by washing and drying. Then, 0.5 wt% of ammonium polyacrylate dispersant, 0.4 wt% of LiF with a particle size of 100 nm to 500 nm, and 0.06 wt% of AlF3 with a particle size of 50 nm to 200 nm were added to obtain a ceramic slurry.

[0070] (4) After the ceramic material is loaded into the mold, a cold isostatic pressing process is performed at a pressure of 250 MPa for 10 minutes to obtain a green body with a density distribution standard deviation of <0.5%.

[0071] (5) The green body was pre-sintered and degreased at a heating rate of 1°C / min to 800°C in an air atmosphere and kept at this temperature for 3 hours.

[0072] (6) Vacuum liquid phase sintering was performed under vacuum conditions. The temperature was raised to 1250°C at a heating rate of 12°C / min, and then continued to be raised to 1580°C at a heating rate of 2°C / min, and kept at this temperature for 3.5 hours.

[0073] (7) Hot isostatic pressing is performed at 1580°C and 180 MPa argon pressure for 2 hours, followed by post-treatment.

[0074] Example 3

[0075] (1) Preparation of MgO-Al2O3 core-shell powder:

[0076] a) preparing MgO nanoparticles and trimethylaluminum (MgO and Al2O3 at a molar ratio of 1:1); placing the MgO nanoparticles with a particle size of 20 nm to 50 nm in an oxygen plasma reaction chamber and treating them at a power of 60 W for 10 minutes to generate hydroxyl active groups on their surfaces;

[0077] b) MgO nanoparticles were placed in a rotating fluidized bed ALD system with a rotation speed of 70 rpm, a deposition temperature of 280°C, and a reaction chamber pressure of 10 -2 Torr~10 -3 Torr;

[0078] c) Trimethylaluminum was evaporated at room temperature by bubbling and pulsed into the system for 0.2s. Trimethylaluminum reacted with the hydroxyl groups on the surface of MgO to form the intermediate Al(CH3)2-O-Mg, releasing CH4;

[0079] d) After removing unreacted trimethylaluminum and by-products by purging with N2, water vapor was introduced for 0.1s to oxidize the intermediate to form Al2O3 and regenerate the hydroxyl active sites;

[0080] e) removing residual H2O and CH4 by N2 purging to obtain a single aluminum oxide layer;

[0081] f) After 60 cycles, the deposition was completed and the powder was cooled to room temperature at a rate of 2.0°C / min under N2 protection to prevent the formation of other impurity phases;

[0082] g) The powder was placed in anhydrous ethanol and ultrasonically treated at a frequency of 40 kHz for 30 minutes to break up soft agglomerates and ensure particle dispersion; and then vacuum dried at 60°C for 12 hours to obtain MgO-Al2O3 core-shell powder.

[0083] (2) The core-shell powder was mixed with an yttrium nitrate solution to obtain a slurry, wherein the mass ratio of the core-shell powder to the yttrium nitrate was 100:0.12, and the volume solid content of the obtained slurry was 55%. The slurry was spray-dried at a spray pressure of 0.4 MPa to form a composite precursor with a particle size of 4 μm.

[0084] (3) The composite precursor was immersed in a KH-550 solution and treated at 75°C for 50 minutes. The surface was then modified by washing and drying. Then, 0.8 wt% of ammonium polyacrylate dispersant, 0.3 wt% of LiF with a particle size of 100 nm to 500 nm, and 0.08 wt% of AlF3 with a particle size of 50 nm to 200 nm were added to obtain a ceramic slurry.

[0085] (4) After the ceramic material is loaded into the mold, a cold isostatic pressing process is performed at a pressure of 250 MPa for 10 minutes to obtain a green body with a density distribution standard deviation of <0.5%.

[0086] (5) The green body was pre-sintered and degreased at a heating rate of 1°C / min to 800°C in an air atmosphere and kept at this temperature for 3 hours.

[0087] (6) Vacuum liquid phase sintering was performed under vacuum conditions. The temperature was raised to 1250°C at a heating rate of 8°C / min, and then continued to be raised to 1480°C at a heating rate of 2°C / min, and kept at this temperature for 4.5 hours.

[0088] (7) Hot isostatic pressing is performed at 1620°C and 160 MPa argon pressure for 2 hours, followed by post-treatment.

[0089] Example 4

[0090] (1) Preparation of MgO-Al2O3 core-shell powder:

[0091] a) preparing MgO nanoparticles and trimethylaluminum (MgO to Al2O3 at a molar ratio of 0.8:1); placing the MgO nanoparticles with a particle size of 20 nm to 50 nm in an oxygen plasma reaction chamber and treating them at a power of 50 W for 12 minutes to generate hydroxyl active groups on their surfaces;

[0092] b) MgO nanoparticles were placed in a rotating fluidized bed ALD system with a rotation speed of 60 rpm, a deposition temperature of 300 °C, and a reaction chamber pressure of 10 -2 Torr~10 -3 Torr;

[0093] c) Trimethylaluminum was evaporated at room temperature by bubbling and pulsed into the system for 0.1s. Trimethylaluminum reacted with the hydroxyl groups on the surface of MgO to form the intermediate Al(CH3)2-O-Mg, releasing CH4;

[0094] d) After removing unreacted trimethylaluminum and by-products by purging with N2, water vapor was introduced for 0.1s to oxidize the intermediate to form Al2O3 and regenerate the hydroxyl active sites;

[0095] e) removing residual H2O and CH4 by N2 purging to obtain a single aluminum oxide layer;

[0096] f) After 100 cycles, the deposition is completed and the powder is cooled to room temperature at a rate of 1.5°C / min under N2 protection to prevent the formation of other impurity phases;

[0097] g) The powder was placed in anhydrous ethanol and ultrasonicated at a frequency of 35 kHz for 35 minutes to break up soft agglomerates and ensure particle dispersion; the powder was then vacuum dried at 60°C for 12 hours to obtain MgO-Al2O3 core-shell powder.

[0098] (2) The core-shell powder was mixed with an yttrium nitrate solution to obtain a slurry, wherein the mass ratio of the core-shell powder to the yttrium nitrate was 100:0.05, and the volume solid content of the obtained slurry was 40%. The slurry was spray-dried at a spray pressure of 0.3 MPa to form a composite precursor with a particle size of 5 μm.

[0099] (3) The composite precursor was immersed in a KH-550 solution and treated at 60°C for 120 minutes. The surface was then modified by washing and drying. Then, 0.3 wt% of ammonium polyacrylate dispersant, 0.2 wt% of LiF with a particle size of 100 nm to 500 nm, and 0.05 wt% of AlF3 with a particle size of 50 nm to 200 nm were added to obtain a ceramic slurry.

[0100] (4) After the ceramic material is loaded into the mold, a cold isostatic pressing process is performed at a pressure of 200 MPa for 20 minutes to obtain a green body with a density distribution standard deviation of <0.5%.

[0101] (5) The green body was pre-sintered and degreased at a heating rate of 0.5°C / min to 700°C in an air atmosphere and kept at this temperature for 4 hours.

[0102] (6) Vacuum liquid phase sintering was performed under vacuum conditions. The temperature was raised to 1250°C at a heating rate of 5°C / min, and then continued to be raised to 1400°C at a heating rate of 2°C / min, and kept at this temperature for 5 hours.

[0103] (7) Hot isostatic pressing is performed at 1550° C. and 200 MPa argon pressure for 1-3 hours, followed by post-treatment.

[0104] Example 5

[0105] (1) Preparation of MgO-Al2O3 core-shell powder:

[0106] a) preparing MgO nanoparticles and trimethylaluminum (MgO to Al2O3 at a molar ratio of 1.2:1); placing the MgO nanoparticles with a particle size of 20 nm to 50 nm in an oxygen plasma reaction chamber and treating them at a power of 100 W for 7 minutes to generate hydroxyl active groups on their surfaces;

[0107] b) MgO nanoparticles were placed in a rotating fluidized bed ALD system with a rotation speed of 120 rpm, a deposition temperature of 200 °C, and a reaction chamber pressure of 10 -2 Torr~10 -3 Torr;

[0108] c) Trimethylaluminum was evaporated at room temperature by bubbling and pulsed into the system for 0.3s. Trimethylaluminum reacted with the hydroxyl groups on the surface of MgO to form the intermediate Al(CH3)2-O-Mg, releasing CH4;

[0109] d) After removing unreacted trimethylaluminum and by-products by purging with N2, water vapor is introduced for 0.1s to 0.2s to oxidize the intermediate to form Al2O3 and regenerate the hydroxyl active sites;

[0110] e) removing residual H2O and CH4 by N2 purging to obtain a single aluminum oxide layer;

[0111] f) After 50 cycles, the deposition is completed and the powder is cooled to room temperature at a rate of 2.5°C / min under N2 protection to prevent the formation of other impurity phases;

[0112] g) The powder was placed in anhydrous ethanol and ultrasonically treated at a frequency of 45 kHz for 25 minutes to break up soft agglomerates and ensure particle dispersion; and then vacuum dried at 60°C for 12 hours to obtain MgO-Al2O3 core-shell powder.

[0113] (2) The core-shell powder was mixed with an yttrium nitrate solution to obtain a slurry, wherein the mass ratio of the core-shell powder to the yttrium nitrate was 100:0.15, and the volume solid content of the obtained slurry was 60%. The slurry was spray-dried at a spray pressure of 0.6 MPa to form a composite precursor with a particle size of 1 μm.

[0114] (3) The composite precursor was immersed in a KH-550 solution and treated at 80°C for 30 minutes. The surface was then modified by washing and drying. Then, 1.0 wt% of ammonium polyacrylate dispersant, 0.5 wt% of LiF with a particle size of 100 nm to 500 nm, and 0.1 wt% of AlF3 with a particle size of 50 nm to 200 nm were added to obtain a ceramic slurry.

[0115] (4) After the ceramic material is loaded into the mold, a cold isostatic pressing process is performed at a pressure of 300 MPa for 5 minutes to obtain a green body with a density distribution standard deviation of <0.5%.

[0116] (5) The green body was pre-sintered and degreased at a heating rate of 2°C / min to 900°C in an air atmosphere and kept at this temperature for 2 hours.

[0117] (6) Vacuum liquid phase sintering was performed under vacuum conditions. The temperature was raised to 1250°C at a heating rate of 15°C / min, and then continued to be raised to 1600°C at a heating rate of 2°C / min, and kept at this temperature for 3 hours.

[0118] (7) Hot isostatic pressing is performed at 1650°C and 150 MPa argon pressure for 1 hour, followed by post-treatment.

[0119] The performance of the magnesium-aluminum spinel transparent ceramics prepared in the example was tested, and the test results are shown in Table 1.

[0120] Table 1 Performance test results

[0121]

[0122] Comparative Example 1

[0123] Using traditional solid phase reaction method

[0124] Powder preparation: High-purity MgO and Al2O3 powders were mixed by ball milling for 10 hours at a speed of 300 rpm and a ball-to-powder ratio of 5:1.

[0125] Molding and sintering: Cold isostatic pressing (200 MPa), pre-sintering in air atmosphere (900 ° C, 4 hours), and then sintering at 1750 ° C under vacuum conditions for 5 hours. No hot isostatic pressing treatment was performed.

[0126] Other processes and material ratios are the same as in Example 1.

[0127] Performance comparison: Sintering temperature: 1750°C (150-250°C higher than the present invention), energy consumption increased by 40%. Closed porosity: 0.3% (much higher than the present invention's <0.005%). Abnormal grain growth is obvious. Infrared transmittance: 75%.

[0128] Comparative Example 2

[0129] Co-precipitation method without rare earth doping

[0130] Powder preparation: spinel powder was prepared by co-precipitation of magnesium nitrate and aluminum nitrate, and the calcination temperature was 1450℃.

[0131] Molding and sintering: pressureless pre-sintering (1600℃, 3 hours), no LiF / AlF3 additives added, direct hot isostatic pressing (1700℃, 100MPa).

[0132] Other processes and material ratios are the same as in Example 1.

[0133] Performance comparison:

[0134] Oxygen vacancy concentration: 101 8 cm -3 , the number of light scattering centers increases. Flexural strength: 180MPa, grain boundary impurities are not purified. Closed porosity: 0.07%.

[0135] Comparative Example 3

[0136] The ALD process of Example 1 was used, but Y was not added. 3+ Sintering process: Only LiF additive (0.5 wt%) was used, and AlF3 was not introduced. Other processes and material ratios were the same as in Example 1.

[0137] Performance comparison:

[0138] Grain size distribution: standard deviation 0.5 μm, grain boundary migration is not suppressed. Closed porosity after hot isostatic pressing: 0.01%, with a large number of residual micropores. Thermal shock resistance (ΔT): 600°C (800°C for Example 1 of the present invention).

[0139] Comparative Example 4

[0140] Powder Preparation: Industrial magnesium oxide and aluminum oxide were pretreated by high-pressure carbonization and pre-sintered to synthesize spinel powder. Sintering: Sintering temperature: 1800°C (with the addition of Sm2O3 / La2O3 additives), without hot isostatic pressing. Other processes and material ratios were the same as in Example 1.

[0141] Performance comparison:

[0142] Sintering temperature: 1800°C, cost increased by 50%. Density distribution: standard deviation 1.2% (0.2% in Example 1 of the present invention), impurity phases remaining at grain boundaries. Vickers hardness: 12 GPa.

[0143] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any other manner. Any person skilled in the art may utilize the above-disclosed technical content to modify or modify the present invention into equivalent embodiments. However, any simple modifications, equivalent variations, and modifications to the above embodiments that do not depart from the technical content of the present invention and are based on the technical essence of the present invention remain within the scope of protection of the present invention.

Claims

1. A method for preparing magnesium aluminum spinel transparent ceramics, characterized in that: The following steps are involved: (1) depositing an Al2O3 layer on the surface of MgO nanoparticles by atomic layer deposition at a deposition temperature of 200°C to 300°C and a cycle number of 50 to 100 times to form a MgO-Al2O3 core-shell powder; (2) mixing the core-shell powder in an yttrium nitrate solution to obtain a slurry, and spray drying the slurry to form a composite precursor with a particle size of 1 μm to 5 μm; (3) surface-modifying the composite precursor using a silane coupling agent KH-550, and then adding 0.3 wt% to 1.0 wt% of an ammonium polyacrylate dispersant, 0.2 wt% to 0.5 wt% of LiF, and 0.05 wt% to 0.1 wt% of AlF3 to obtain a ceramic slurry; (4) After the ceramic material is loaded into the mold, a green body is obtained by cold isostatic pressing at a pressure of 200 MPa to 300 MPa for 5 to 20 minutes; (5) The green body is pre-sintered and degreased at a heating rate of 0.5°C / min to 2°C / min to 700°C to 900°C in an air atmosphere, and kept at this temperature for 2 to 4 hours; (6) Liquid phase sintering in a vacuum atmosphere at a temperature of 1400°C to 1600°C for 3 to 5 hours; (7) Hot isostatic pressing is performed at 1550° C. to 1650° C. and 150 MPa to 200 MPa argon pressure for 1 to 3 hours, followed by post-treatment.

2. The method for preparing a magnesium-aluminum spinel transparent ceramic according to claim 1, characterized in that: The molar ratio of MgO to Al2O3 in step (1) is 0.8 to 1.2:

1.

3. The method for preparing a magnesium-aluminum spinel transparent ceramic according to claim 1, characterized in that: The specific process of step (1) is: a) placing MgO nanoparticles with a particle size of 20 nm to 50 nm in an oxygen plasma reaction chamber and treating them at a power of 50 W to 100 W for 7 to 12 minutes to generate hydroxyl active groups on their surfaces; b) MgO nanoparticles were placed in a rotating fluidized bed ALD system, the rotation speed was set to 60 rpm to 120 rpm, the deposition temperature was set to 200°C to 300°C, and the reaction chamber pressure was maintained at 10 -2 Torr~10 -3 Torr; c) Trimethylaluminum is evaporated at room temperature by bubbling and pulsed into the system for 0.1s to 0.3s. Trimethylaluminum reacts with the hydroxyl groups on the surface of MgO to form the intermediate Al(CH3)2-O-Mg, releasing CH4; d) After removing unreacted trimethylaluminum and by-products by purging with N2, water vapor is introduced for 0.1s to 0.2s to oxidize the intermediate to form Al2O3 and regenerate the hydroxyl active sites; e) removing residual H2O and CH4 by N2 purging to obtain a single aluminum oxide layer; f) After 50 to 100 cycles, the deposition is completed and the powder is cooled to room temperature at a rate of 1.5°C / min to 2.5°C / min under N2 protection to prevent oxidation of the Al2O3 layer; g) The powder was placed in anhydrous ethanol and ultrasonically treated at a frequency of 35 kHz to 45 kHz for 25 to 35 minutes to break up soft agglomerates and ensure particle dispersion; and then vacuum dried at 60° C. for 12 hours to obtain MgO-Al 2 O 3 core-shell powder.

4. The method for preparing a magnesium-aluminum spinel transparent ceramic according to claim 1, characterized in that: The volume solid content of the spray-dried slurry in step (2) is 40% to 60%, and the spray pressure is 0.3 MPa to 0.6 MPa.

5. The method for preparing a magnesium-aluminum spinel transparent ceramic according to claim 1, characterized in that: The mass ratio of the core-shell powder to yttrium nitrate in step (2) is 100:0.05-0.

15.

6. The method for preparing a magnesium-aluminum spinel transparent ceramic according to claim 1, characterized in that: The surface modification in step (3) is to immerse the composite precursor in a KH-550 solution, treat it at 60° C. to 80° C. for 30 to 120 minutes, and then wash and dry it.

7. The method for preparing a magnesium-aluminum spinel transparent ceramic according to claim 1, characterized in that: The particle size of LiF described in step (3) is 100nm~500nm, and the particle size of AlF3 is 50nm~200nm.

8. The method for preparing a magnesium-aluminum spinel transparent ceramic according to claim 1, characterized in that: The standard deviation of the density distribution of the green body in step (4) is less than 0.5%.

9. The method for preparing a magnesium-aluminum spinel transparent ceramic according to claim 1, characterized in that: The heating rate of the vacuum liquid phase sintering in step (6) is 5°C / min to 15°C / min in the low temperature section, and after reaching 1250°C, the heating rate is 2°C / min.

10. A magnesium-aluminum spinel transparent ceramic prepared by the preparation method according to any one of claims 1 to 9.

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