Low-temperature pressureless sintering preparation method of high-transparency AlON ceramic

Abstract

The invention provides a low-temperature pressureless sintering preparation method of high-transparency AlON ceramic, and belongs to the technical field of preparation of transparent ceramic. The low-temperature pressureless sintering preparation method of the high-transparency AlON ceramic, provided by the invention, comprises the following steps: S1, adding barium oxide into ethanol and AlON powder, carrying out ball milling by using a ball milling medium, and screening and calcining to obtain a mixture of the AlON powder and barium oxide; s2, the mixture is subjected to dry pressing forming to form a biscuit, then the biscuit is placed in a cold isostatic press after being subjected to vacuum pumping and sealed storage, and a compact biscuit is obtained through cold isostatic pressing forming; s3, the compact biscuit is placed in a nitrogen atmosphere sintering furnace to be sintered at the temperature of 1750 DEG C, the heat preservation time of sintering is 6-10 h, and the high-transparency AlON ceramic is obtained. The AlON transparent ceramic obtained by the method is high in transmittance, low in sintering temperature, short in sintering time and low in energy consumption.

Description

Technical Field

[0001] This invention belongs to the field of transparent ceramics preparation technology, specifically relating to a low-temperature pressureless sintering preparation method for highly transparent AlON ceramics. Background Technology

[0002] AlON transparent ceramics are advanced multifunctional ceramic materials composed of Al₂O₃-AlN solid solution, possessing a unique spinel-type cubic lattice structure. As a typical representative of inorganic transparent ceramics, AlON demonstrates irreplaceable application value in extreme environment optical windows, high-energy laser systems, and defense technology fields due to its excellent optical-mechanical-thermal synergistic properties. Currently, however, the pressureless sintering preparation process of AlON transparent ceramics, both domestically and internationally, often requires high temperatures of 1850-2000℃, and sometimes even hot isostatic pressing, to obtain highly transparent ceramics. Prolonged high temperatures can easily cause excessive grain growth and phase decomposition, reducing the material's hardness and transparency. This increases process complexity and cost, leading to a significant increase in equipment energy consumption, thus limiting the industrialization and mass production of AlON transparent ceramics.

[0003] For example, patent document CN 116768632 B (authorization announcement date: 2024.09.20) discloses a method for preparing AlON transparent ceramics by pressureless sintering. It uses ultra-low dosages of La2O3 and Y2O3 powders as sintering aids, wherein the dosage of La2O3 powder is 0.02-0.04 wt.% and the dosage of Y2O3 powder is 0.02-0.05 wt.%. The resulting AlON transparent ceramics can achieve transmittance of 76% and 82% at 400 nm and 3600 nm, respectively. However, its sintering temperature is as high as 1850-1900℃, which has the defect of extremely high sintering temperature. At the same time, its transmittance still needs to be improved.

[0004] For example, patent document CN 116789455 B (authorization announcement date: 2024.09.13) discloses a method for preparing AlON transparent ceramics by low-temperature pressureless sintering. It uses only La2O3 as a sintering aid, with a La2O3 content of 0.15-0.20 wt.%, but its sintering temperature still needs to be 1850-1900℃. It cannot solve the problem of high energy consumption caused by high sintering temperature, and the amount of sintering aid added is still relatively high.

[0005] For example, patent document CN 110272282 B discloses a low-temperature preparation method for AlON transparent ceramics, which uses MgO as a sintering aid at an addition amount of 0.4-0.8 wt.%. The sintering process involves first heating to 1600-1700℃ and holding for 1-4 hours; then heating to 1700-1800℃ and holding for 12-24 hours. The transmittance of this ceramic reaches over 80%, but it suffers from problems such as excessively long sintering time and high energy consumption. Furthermore, its transmittance still needs to be further improved.

[0006] Therefore, how to provide a low-temperature pressureless sintering preparation method for AlON transparent ceramics with low sintering temperature, short sintering time, low energy consumption, and high transmittance has become an urgent technical problem to be solved. Summary of the Invention

[0007] The present invention aims to solve the aforementioned technical problems by providing a low-temperature pressureless sintering method for preparing highly transparent AlON ceramics. The technical objective of this invention is to overcome the shortcomings of existing low-temperature pressureless sintering processes for AlON ceramics, which require high sintering temperatures or long sintering times at low temperatures, and to provide a low-temperature pressureless sintering method for preparing transparent AlON ceramics with low sintering temperature, short sintering time, low energy consumption, and high transmittance.

[0008] To achieve the above-mentioned technical objectives, the technical solution adopted by the present invention is as follows:

[0009] A method for preparing highly transparent AlON ceramics by low-temperature pressureless sintering includes the following steps:

[0010] S1. Barium oxide is added to ethanol and AlON powder, ball milled with ball milling media, dried, crushed, sieved, and calcined to obtain a mixture of AlON powder and barium oxide.

[0011] S2. The mixture obtained in step S1 is dry-pressed into a green blank, and then the green blank is taken out, vacuum-sealed and placed in a cold isostatic press for cold isostatic pressing to obtain a dense green blank.

[0012] S3. The dense green blank obtained in step S2 is placed in a nitrogen atmosphere sintering furnace and sintered at 1750-1800℃ for 6-10 hours to obtain high transparency AlON ceramic.

[0013] Furthermore, the amount of barium oxide added in step S1 is 0.05 wt.%.

[0014] Furthermore, the milling medium in step S1 is alumina milling balls with a size of 2 mm, and the milling time is 10 hours.

[0015] Furthermore, the calcination temperature is 600°C.

[0016] Furthermore, the sieve mesh size in step S1 is 200 mesh.

[0017] Furthermore, the pressure for dry pressing in step S2 is 4 MPa, and the holding time is 1 min.

[0018] Furthermore, the pressure for cold isostatic pressing in step S2 is 250 MPa, and the holding time is 15 min.

[0019] Furthermore, the sintering temperature in step S3 is 1750°C.

[0020] Furthermore, the holding time for sintering in step S3 is 8 hours.

[0021] The beneficial effects of this invention are as follows:

[0022] This invention provides a low-temperature pressureless sintering method for preparing AlON transparent ceramics with low sintering temperature, short sintering time, low energy consumption, and high transmittance. It effectively solves the shortcomings of existing low-temperature pressureless sintering processes for AlON ceramics, which require either high sintering temperatures or long sintering times at low temperatures. Using barium oxide as a sintering aid, and with an addition amount of only 0.5 wt.%, it efficiently achieves AlON transparent ceramics with a transmittance as high as 84% ​​at sintering temperatures as low as 1750℃ and sintering times of only 6-8 hours. Attached Figure Description

[0023] Figure 1 XRD diffraction pattern of the sample.

[0024] Figure 2 At 1750 degrees Celsius, the microstructure of the samples is shown in (a) the pure phase sample; (b) the sample with yttrium oxide as an additive; (c) the sample with barium oxide as an additive; and (d) the elemental distribution of the sample with barium oxide as an additive.

[0025] Figure 3 Transmittance spectrum of a sample using barium oxide as an additive. Detailed Implementation

[0026] To make the objectives, technical solutions, and advantages of this invention clearer, the invention is described in detail below with reference to embodiments. It should be noted that the following embodiments are for explanation and illustration only and are not intended to limit the invention. Non-essential improvements and adjustments made by those skilled in the art based on the above description are still within the scope of protection of this invention.

[0027] Example 1

[0028] A novel sintering aid for the low-temperature, pressureless sintering preparation of highly transparent AlON ceramics, comprising the following steps:

[0029] S1. Barium oxide (BaO) is added to ethanol and AlON powder, and ball milled using alumina balls as the ball milling medium. After drying, it is crushed, sieved, and calcined to obtain a mixture of AlON powder and barium oxide.

[0030] S2. The mixture obtained in step S1 is dry-pressed into a green blank, and then the green blank is taken out, vacuum-sealed and placed in a cold isostatic press for cold isostatic pressing to obtain a dense green blank.

[0031] S3. The dense green blank obtained in step S2 is placed in a nitrogen atmosphere sintering furnace for high-temperature sintering to obtain a highly transparent pure phase ceramic. After processing and polishing, the highly transparent AlON ceramic obtained by the novel sintering aid is obtained.

[0032] Figure 1 The image shows the XRD diffraction pattern of the sample. Figure 1 The phase composition of the undoped sample, the Y₂O₃-doped sample, and the BaO-doped sample (prepared at 1750 °C) is shown. As can be seen from the figures, they all exhibit a pure cubic AlON phase structure. Furthermore, compared to the undoped sample, the diffraction peak of the BaO-doped AlON ceramic shifts significantly to the left by 0.18° (from 37.78° to 37.6°). Considering Ba… 2+ Larger radius The leftward shift of the XRD reflection indicates that Ba 2+ It has been successfully incorporated into the AlON matrix lattice, causing lattice deformation and inducing lattice expansion.

[0033] In order to observe the microstructure of ceramics, Figure 2 Images (a) to (c) show the etched surfaces of the sintered samples. Scanning electron microscopy (SEM) images reveal that all samples sintered at 1750 °C exhibit well-defined grain boundaries, primarily consisting of polygonal grains with a relatively uniform grain size distribution. However, both undoped and doped AlON ceramics show numerous fine white spots within the grain structure; under magnification, these spots are identified as pores distributed within the grains. Figure 2 Compared to a, b Figure 2 The BaO-doped AlON ceramic shown in Figure c exhibits a dense microstructure with no intracrystalline porosity. This indicates that Ba... 2+ The incorporation of BaO effectively promoted the elimination of porosity and facilitated densification at a relatively low sintering temperature of 1750℃. Furthermore, under the same sintering conditions, the average grain size of the BaO-doped sample was significantly larger than that of the undoped and Y₂O₃-doped AlON ceramics, indicating that BaO… 2+It not only promotes densification but also acts as a grain growth promoter during sintering. This phenomenon may be due to the incorporation of barium ions leading to temporary liquid phase formation or enhancing the mass transport mechanism. According to... Figure 2 The content in section d shows the energy spectrum distribution of various elements (aluminum, oxygen, nitrogen, and barium), and demonstrates that barium ions are uniformly distributed in transparent AlON ceramics.

[0034] Figure 3 The linear transmittance of AlON ceramics sintered at 1750 °C for 8 hours and doped with 0.1% BaO by weight is shown. As shown in the figure, a high linear transmittance of approximately 84% is achieved at 850 nm. It is believed that BaO... 2+ The presence of BaO enhances transparency and densification at 1750 °C by promoting mass transport and aiding in porosity reduction. These findings demonstrate that optimized BaO concentration can effectively tune the microstructure and optical quality of AlON ceramics, enabling the use of the PLS method at relatively low temperatures while still achieving AlON ceramic materials with a transparency of up to 84%.

Claims

1. A method for preparing highly transparent AlON ceramics by low-temperature pressureless sintering, characterized in that, Includes the following steps: S1. Barium oxide is added to ethanol and AlON powder, ball milled with ball milling media, dried, crushed, sieved, and calcined to obtain a mixture of AlON powder and barium oxide. S2. The mixture obtained in step S1 is dry-pressed into a green blank, and then the green blank is taken out, vacuum-sealed and placed in a cold isostatic press for cold isostatic pressing to obtain a dense green blank. S3. The dense green blank obtained in step S2 is placed in a nitrogen atmosphere sintering furnace and sintered at 1750℃ for 6-10 hours to obtain high transparency AlON ceramic.

2. The method for preparing high-transparency AlON ceramics by low-temperature pressureless sintering according to claim 1, characterized in that, The amount of barium oxide added in step S1 is 0.05 wt.% of the AlON powder mass.

3. The method for preparing high-transparency AlON ceramics by low-temperature pressureless sintering according to claim 1, characterized in that, The ball milling media in step S1 is alumina grinding balls with a size of 2 mm, and the ball milling time is 10 hours.

4. The method for preparing high-transparency AlON ceramics by low-temperature pressureless sintering according to claim 1, characterized in that, The calcination temperature is 600℃.

5. The method for preparing high-transparency AlON ceramics by low-temperature pressureless sintering according to claim 1, characterized in that, The sieve used for sieving in step S1 has a particle size of 200 mesh.

6. The method for preparing high-transparency AlON ceramics by low-temperature pressureless sintering according to claim 1, characterized in that, The pressure for dry pressing in step S2 is 4 MPa, and the holding time is 1 min.

7. The method for preparing high-transparency AlON ceramics by low-temperature pressureless sintering according to claim 1, characterized in that, The pressure for cold isostatic pressing in step S2 is 250 MPa, and the holding time is 15 min.

8. The method for preparing high-transparency AlON ceramics by low-temperature pressureless sintering according to claim 1, characterized in that, The sintering temperature in step S3 is 1750°C.

9. The method for preparing high-transparency AlON ceramics by low-temperature pressureless sintering according to claim 8, characterized in that, The holding time for sintering in step S3 is 8 hours.

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