Preparation method of high-performance AlON transparent ceramic based on vacancy effect and matrix purification

Abstract

The invention relates to a high-performance AlON transparent ceramic preparation method based on a vacancy effect and matrix purification. According to the invention, a Y2O3-La2O3-MgO ternary composite sintering aid is adopted to construct a densification promotion system, and alpha-Al2O3 nano powder is innovatively introduced. Through a key process of setting a heat preservation platform for 5-10 hours at 1750 DEG C, Al2O3 solid solution generated by an external source and in-situ is promoted, non-stoichiometric AlON rich in cation vacancies is formed, and the ion migration rate and the sintering activity are remarkably enhanced by utilizing a vacancy effect; meanwhile, the alpha-Al2O3 nano powder effectively eliminates an optical scattering source through the purification effect of consuming residual AlN and residual carbon. Finally, through the synergistic effect of vacancy and purification, the high-density and high-light-transmittance AlON transparent ceramic is prepared through one-step pressureless sintering in the nitrogen atmosphere, hot isostatic pressing aftertreatment is not needed, and key technical support is provided for large-scale application.

Description

Technical Field

[0001] This invention belongs to the field of transparent ceramic preparation technology, specifically relating to a method for preparing high-performance AlON transparent ceramics based on vacancy effect and matrix purification. Technical Background

[0002] AlON transparent ceramics, due to their unique cubic isotropic structure, have excellent optical transmittance in the ultraviolet to near-infrared bands. They also possess high strength, high hardness, excellent wear resistance, and chemical stability, making them a core material for modern defense equipment. They have shown great application potential in key fields such as aerospace and national defense, and are a key basic material for achieving lightweight and high-performance defense equipment.

[0003] Due to the strong covalent bonds inherent in AlON transparent ceramics, conventional sintering methods often fail to achieve the desired densification, easily leading to residual porosity and affecting optical properties. Furthermore, sintering densification requires stringent high-temperature, long-duration conditions, resulting in high energy consumption and potentially causing grain coarsening, which deteriorates mechanical properties. To address this issue, suitable sintering aids are typically added to eliminate light scattering sources such as internal pores, thereby improving transmittance and uniformity. Currently, mainstream sintering aids include Y₂O₃, La₂O₃, MgO, and SiO₂, which can be added individually or in combination. Different combinations of sintering aids exhibit different effects due to the synergistic effect of their mechanisms of action, achieving better densification even in larger volume materials.

[0004] The application of these sintering aids has improved the sintering densification effect of AlON transparent ceramics to some extent, increasing optical transmittance and mechanical properties, but limitations still exist. The visible light transmittance of the prepared AlON transparent ceramics is still insufficient to meet the application requirements of high-end fields such as transparent armor and precision optical components (visible light transmittance > 80%), and further porosity elimination and transmittance improvement are required through hot isostatic pressing (HIP) post-treatment. However, HIP equipment requires huge investment and significantly increases manufacturing costs.

[0005] Furthermore, the high light transmittance required for AlON transparent ceramics places stringent demands on the purity of the raw material powder. Trace amounts of residual carbon and other impurities not only hinder the sintering and densification process but may also lead to devitrification of the ceramic matrix. Currently, due to the insufficient stability of batch powder preparation technology, different batches of powder often exhibit performance differences, specifically incomplete reactions and the presence of residual AlN phases. This results in uneven microstructure composition of the powder, i.e., an uneven N / O atomic ratio within the powder. These powder defects easily lead to poor microstructure uniformity in the final ceramic sample, significantly limiting its optical properties.

[0006] The aforementioned problems have hindered the engineering application of AlON transparent ceramics. Therefore, it is crucial to develop a simple, low-cost, and more effective densification sintering method to simultaneously improve and optimize the optical and mechanical properties of the material. Summary of the Invention

[0007] The purpose of this invention is to solve the problems existing in the prior art and to provide a method for preparing high-performance AlON transparent ceramics based on vacancy effect and matrix purification.

[0008] The technical solution of this invention is: a method for preparing high-performance AlON transparent ceramics based on vacancy effect and matrix purification, specifically including the following steps:

[0009] A method for preparing high-performance AlON transparent ceramics based on vacancy effect and matrix purification, characterized in that the preparation method includes the following steps:

[0010] (1) AlON powder, ternary composite sintering aid and α-Al2O3 nanoparticles are mixed and ball-milled to make the powder particle size ≤0.7μm; wherein the ternary composite sintering aid includes Y2O3, La2O3 and MgO;

[0011] (2) The obtained slurry is placed in a forced-air drying oven for constant temperature drying. Then the dried block is ground and crushed and passed through a 100-200 mesh sieve to obtain AlON transparent ceramic mixed powder.

[0012] (3) The AlON transparent ceramic mixed powder is filled into the powder pressing mold, pre-pressed, and then subjected to cold isostatic pressing treatment to further press and shape to obtain a green body with high density and uniform density.

[0013] (4) The obtained green body is placed in a BN crucible and embedded with AlON powder. It is then sintered under nitrogen atmosphere at 1850-1950℃ for 10-30h without pressure to obtain AlON transparent ceramic sintered green body. It is then subjected to double-sided grinding and polishing to obtain high-performance AlON transparent ceramic.

[0014] Preferably, the total amount of the ternary composite sintering aid added is 0.1 to 0.5% of the AlON powder amount.

[0015] Preferably, the amount of α-Al2O3 nanoparticles added is 5-30% of the amount of AlON powder used, and can be flexibly adjusted according to the intrinsic nitrogen content of different batches of AlON powder.

[0016] Preferably, the mass percentages of Y2O3, La2O3, and MgO in the ternary composite sintering aid are (0.05-0.12%), (0.01-0.06%), and (0.1-0.25%) of the AlON powder, respectively. Preferably, the powder described in step (1) is placed in a ball mill jar, and grinding balls and anhydrous ethanol are added. The mixture is then ball-milled at a speed of 180-380 rpm for 18-28 hours.

[0017] Preferably, the particle size of Y2O3, La2O3 and MgO in step (1) is all <100nm; the particle size of α-Al2O3 nanopowder in step (1) is all ≤200nm.

[0018] Preferably, the AlON powder mentioned in step (1) is prepared by aluminothermic reduction nitriding, carbothermic reduction nitriding or solid-state reaction, and its purity is not less than 99.5%.

[0019] Preferably, the solid content of the slurry during planetary ball milling in step (1) is 40% to 70%.

[0020] Preferably, the grinding balls in step (1) are made of high-purity alumina with a purity of ≥99.99%; the planetary ball milling process in step (1) is carried out using a vertical planetary ball mill with a ball-to-material ratio of 4:1 to 5:1.

[0021] Preferably, the constant temperature drying in step (2) is 60-90°C and the time is 20-30 hours.

[0022] Preferably, the molding method described in step (3) is to first use a powder pressing mold to pre-press the molding under a pressure of 10 to 50 MPa, and then further press it under a pressure of 180 to 260 MPa using cold isostatic pressing.

[0023] Preferably, the heating rate of the sintering process in step (4) is set to 5-10℃ / min. After sintering, the temperature is reduced to 1200℃ at 3-5℃ / min, and then cooled to room temperature with the furnace to obtain AlON transparent ceramic sintered green body.

[0024] This invention employs a Y2O3-La2O3-MgO ternary composite sintering aid to construct a multi-mechanism synergistic densification promoting system: liquid-phase assisted mass transfer reduces the atomic diffusion activation energy; Mg 2+It hinders AlON grain boundary migration and inhibits abnormal grain growth. Based on the composite sintering aid, an appropriate amount of α-Al2O3 nanoparticles (particle size 200nm) are further introduced, and key sintering process optimization is performed—a long-term heat preservation platform of 1750℃ for 5 to 10 hours is set during ceramic sintering. Through a series of physicochemical reactions, multiple enhancement effects are achieved: (1) During the heat preservation process, Al2O3 generated by AlON decomposition and external α-Al2O3 nanoparticles are dissolved together to regenerate non-stoichiometric AlON, which is equivalent to a reduction in the N / O ratio, based on Al (64+x) / 3V (8-x) / 3O 32-x N x The lattice model introduces a suitable amount of cation vacancies. These vacancies, as fast diffusion channels, significantly enhance the ion migration rate during sintering, thereby improving the intrinsic sintering activity and densification driving force of the powder. (2) The added α-Al2O3 nanoparticles have a purifying effect: on the one hand, they react with the residual trace AlN in the raw materials to generate new AlON, reducing the harmful second phase; on the other hand, at the corresponding temperature, they effectively remove residual carbon in the powder through carbothermic reduction nitridation reaction, and react to generate AlON. These generated AlON are homogenized during the subsequent heat preservation process. The above process helps to avoid other side reactions in the subsequent high-temperature sintering, obtain a purer matrix, and thus promote better sintering densification.

[0025] By adding a suitable proportion of alumina nanoparticles to a composite sintering aid composed of these three sintering aids, the composition of the powder is optimized and controlled. This achieves a synergistic effect between the composite sintering aid and the α-Al₂O₃ nanoparticles, enabling one-step pressureless sintering for high densification. The resulting relative density can reach ≥99.5%, and the visible light transmittance is >78%, without the need for post-hot isostatic pressing. This synergistic enhancement mechanism provides a new approach for the preparation of high-performance AlON transparent ceramics. It simplifies the process, reduces production costs, and significantly improves the optical and mechanical properties of the material, meeting the requirements for the preparation of large-size, high-optical-quality transparent ceramics.

[0026] The beneficial effects of this invention are as follows:

[0027] 1. Significantly improved optical performance: Through the synergistic effect of liquid-phase mass transfer of composite sintering aids and cation vacancies introduced by α-Al2O3, residual pores are effectively eliminated, making the ceramic transmittance >78% in the visible light band (such as 600nm wavelength), without the need for hot isostatic pressing post-treatment.

[0028] 2. Efficient and simplified sintering process: By constructing a multi-element synergistic densification system, one-step pressureless sintering under conventional nitrogen atmosphere was successfully achieved, significantly shortening the process flow and laying the foundation for large-scale production;

[0029] 3. Significantly reduced costs: The selected ternary composite sintering aids are added in very small amounts (0.1-0.4%), and the raw material costs are low. At the same time, by eliminating the high-energy-consuming and high-equipment-investment process of hot isostatic pressing, the overall manufacturing cost is effectively controlled.

[0030] 4. Technical universality: The α-Al2O3 addition strategy proposed in this invention can be flexibly adjusted according to the intrinsic nitrogen content of different batches of AlON powder, effectively compatible with raw material powders prepared by various processes such as aluminothermic method and carbothermic method, showing excellent process adaptability and stability, and is suitable for the preparation of large-size, high-quality transparent ceramics. Attached Figure Description

[0031] Figure 1 Macroscopic photographs and transmittance curves of AlON transparent ceramics prepared in Example 1;

[0032] Figure 2 Macroscopic photographs and transmittance curves of AlON transparent ceramics prepared in Example 2;

[0033] Figure 3 Macroscopic photographs and transmittance curves of AlON transparent ceramics prepared for Comparative Example 1;

[0034] Figure 4 Macroscopic photographs and transmittance curves of AlON transparent ceramics prepared for Comparative Example 2. Detailed Implementation

[0035] The following embodiments further illustrate the content of the present invention in detail, but should not be construed as limiting the scope of protection of the present invention. Modifications and substitutions made to the methods, steps, or conditions of the present invention without departing from the core essence of the present invention are all within the scope of protection of the present invention.

[0036] 100g of aluminothermic reduction nitridation AlON powder, 0.1g of Y2O3, 0.02g of La2O3, 0.2g of MgO (all high-purity powders with a particle size <100nm) and 11g of α-Al2O3 nanoparticles (particle size <200nm) were weighed and added to a ball mill jar. At the same time, 100g of anhydrous ethanol and 500g of alumina grinding balls were added as grinding media. The mixture was ball-milled at 360rpm for 24h using a vertical planetary ball mill. The average particle size of the powder after grinding was 0.62μm.

[0037] After ball milling the mixture, the resulting slurry was poured into a container and placed in a forced-air drying oven, where it was dried at a constant temperature of 80°C for 24 hours. The dried lumps were then ground and crushed using an agate mortar and pestle, and passed through a 100-mesh sieve to obtain a transparent ceramic mixed powder.

[0038] The transparent ceramic mixed powder is then filled into a powder pressing mold and pressed into shape under a pressure of 20 MPa. The pre-formed green body is then subjected to cold isostatic pressing under a pressure of 200 MPa to further press and shape it, thereby obtaining a green body with high density and uniform density.

[0039] The obtained ceramic green body was then placed in a BN crucible, embedded with AlON powder, and placed in a high-temperature atmosphere sintering furnace for pressureless sintering under a nitrogen atmosphere. The sintering temperature was 1880℃, the sintering time was 25 h, the heating rate was 8℃ / min, and the cooling rate was 5℃ / min. Finally, the obtained AlON transparent ceramic green body was double-sided ground and polished to obtain high-performance AlON transparent ceramic. Figure 1 The transmittance curve and macroscopic photograph were measured for a 4mm sample. The linear transmittance at a wavelength of 600nm is 78%.

[0040] Example 2

[0041] 100g of solid-phase reaction AlON powder, 0.1g of Y2O3, 0.02g of La2O3, 0.1g of MgO (all high-purity powders with a particle size <100nm) and 28g of α-Al2O3 nanoparticles (particle size <200nm) were weighed and added to a ball mill jar. At the same time, 100g of anhydrous ethanol and 500g of alumina grinding balls were added as grinding media. The mixture was ball-milled at 360rpm for 24h using a vertical planetary ball mill. The average particle size of the powder after grinding was 0.57μm.

[0042] After ball milling the mixture, the resulting slurry was poured into a container and placed in a forced-air drying oven, where it was dried at a constant temperature of 80°C for 24 hours. The dried lumps were then ground and crushed using an agate mortar and pestle, and passed through a 100-mesh sieve to obtain a transparent ceramic mixed powder.

[0043] The transparent ceramic mixed powder is then filled into a powder pressing mold and pressed into shape under a pressure of 20 MPa. The pre-formed green body is then subjected to cold isostatic pressing under a pressure of 200 MPa to further press and shape it, thereby obtaining a green body with high density and uniform density.

[0044] The obtained ceramic green body was then placed in a BN crucible, embedded with AlON powder, and placed in a high-temperature atmosphere sintering furnace for pressureless sintering under a nitrogen atmosphere. The sintering temperature was 1880℃, the sintering time was 25 h, the heating rate was 8℃ / min, and the cooling rate was 5℃ / min. Finally, the obtained AlON transparent ceramic green body was double-sided ground and polished to obtain high-performance AlON transparent ceramic. Figure 2 The transmittance curve and macroscopic photograph were measured for a 4mm sample. The linear transmittance at a wavelength of 600nm is 78.6%.

[0045] Comparative Example 1

[0046] The difference from Example 1 is that the AlON powder used was prepared by a solid-state reaction method, and α-Al₂O₃ nanoparticles were not added to the formula; otherwise, it was the same as Example 1. Macroscopic photographs of the obtained ceramic samples and the transmittance curve of a 4mm sample are shown below. Figure 3 As shown, the linear transmittance at a wavelength of 600 nm is 38.8%.

[0047] Comparative Example 2

[0048] The difference from Example 1 is that the AlON powder used was prepared by a solid-state reaction method, and only 11g of α-Al₂O₃ nanoparticles were added to the formula, without any other sintering aids; otherwise, it was the same as Example 1. Macroscopic photographs of the obtained ceramic samples and the transmittance curve of a 4mm sample are shown below. Figure 4 As shown, the linear transmittance at a wavelength of 600 nm is 37.8%.

[0049] In summary, the comparison between Examples 1 and 2 and Comparative Examples 1 and 2 fully demonstrates that the synergistic effect of the Y2O3-La2O3-MgO ternary composite sintering aid and α-Al2O3 nanoparticles is indispensable for achieving high optical quality AlON ceramics. Comparative Example 1 (without α-Al2O3 nanoparticles) lacks the enhanced diffusion of cation vacancies and matrix purification effect, resulting in insufficient ceramic densification and low transmittance. Comparative Example 2 (with only α-Al2O3 nanoparticles) also fails to achieve effective densification due to the lack of liquid-phase mass transfer and grain boundary migration inhibition provided by the composite sintering aid, and its transmittance falls far short of application requirements. These results, from the opposite perspective, verify the necessity and superiority of the technical solution proposed in this invention.

[0050] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing high-performance AlON transparent ceramic based on the space effect and substrate purification, characterized in that: (1) AlON powder, ternary composite sintering aid and α-Al2O3 nano-powder are mixed and ball-milled to make the particle size of the powder ≤0.7 μm; the ternary composite sintering aid comprises Y2O3, La2O3 and MgO; (2) the obtained slurry is placed in a blast drying oven for constant temperature drying, and then the dried block is ground and crushed and passed through a 100-200 mesh screen to obtain AlON transparent ceramic mixed powder; (3) the AlON transparent ceramic mixed powder is filled into a powder pressing mold for pre-pressing forming, and then cold isostatic pressing is performed for further pressing forming to obtain a green body with high density and uniform density; (4) the obtained green body is placed in a BN crucible and embedded with AlON powder, and then subjected to pressureless sintering at 1850-1950 ℃ for 10-30 h under a nitrogen atmosphere to obtain an AlON transparent ceramic sintered body, which is subjected to double-sided grinding and polishing to obtain high-performance AlON transparent ceramic. The total addition amount of the ternary composite sintering aid is 0.1-0.5% of the amount of AlON powder; and the addition amount of the α-Al2O3 nano-powder is 5-30% of the amount of AlON powder. The mass of Y2O3, La2O3 and MgO in the ternary composite sintering aid is (0.05-0.12%), (0.01-0.06%) and (0.1-0.25%) of the amount of AlON powder, respectively. In step (1), the powder is placed in a ball mill tank, grinding balls and anhydrous ethanol are added, and planetary ball milling is performed at a speed of 180-380 rpm for 18-28 h. In step (1), the particle size of Y2O3, La2O3 and MgO is all <100 nm; and the particle size of the α-Al2O3 nano-powder in step (1) is ≤200 nm. In step (1), the AlON powder is prepared by aluminum thermal reduction nitridation, carbon thermal reduction nitridation or solid phase reaction, and has a purity of not less than 99.5%. In step (1), the solid content of the slurry during planetary ball milling is 40%-70%. In step (1), the material of the grinding balls is high-purity alumina with a purity of ≥99.99%; and the planetary ball milling process in step (1) is performed by using a vertical planetary ball mill, and the ball-to-material ratio is 4:1-5:

1. In step (2), the temperature of the constant temperature drying is 60-90 ℃, and the time is 20-30 h. In step (3), the forming method is pre-pressing forming under a pressure of 10-50 MPa by using a powder pressing mold, followed by cold isostatic pressing for further pressing forming under a pressure of 180-260 MPa. ​ ​ ​ ​ 2. The method according to claim 1, wherein the method is characterized by: ​ 3. The method of claim 1, wherein the method further comprises: ​ ​ 4. The method of claim 1, wherein the method further comprises: ​ ​ 5. The method for preparing high-performance AlON transparent ceramics based on the space effect and matrix purification according to claim 1, characterized in that: ​ 6. The method for preparing high-performance AlON transparent ceramics based on the space effect and matrix purification according to claim 1, characterized in that: ​ 7. The method according to claim 3, wherein the method is characterized by ​ 8. The high-performance AlON transparent ceramic based on the space effect and matrix purification according to claim 3, characterized in that: ​ 9. The high-performance AlON transparent ceramic based on the space effect and matrix purification according to claim 3, characterized in that: ​ 10. The method for preparing high-performance AlON transparent ceramics based on the space effect and matrix purification according to claim 1, characterized in that: ​

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