Novel method for preparing AlON transparent ceramic with high infrared transmittance

Abstract

The invention relates to a novel method for preparing AlON transparent ceramic with high infrared transmittance, and belongs to the field of transparent ceramic preparation. The preparation method comprises the following steps: carrying out ball milling and mixing on nano gamma-Al2O3 and micron AlN powder, synthesizing AlON powder taking AlON as a main phase through a high-temperature solid-phase reaction, then adding a sintering aid CaCO3, carrying out ball milling to regulate and control the particle size of the powder, and finally preparing the pure-phase AlON transparent ceramic with high infrared transmittance by adopting a pressureless sintering method. According to the preparation method, the chemical composition is controllable, pure-phase AlON powder does not need to be obtained firstly, and the powder synthesis process is low in cost, simple and easy to implement; the synthesized powder is small in primary particle size and uniform in element distribution, and particle refinement can be easily achieved through ball milling. Therefore, the prepared ceramic is high in infrared transmittance, small in grain size and high in hardness, the ceramic sintering process has the advantages of being short in heat preservation time, high in efficiency, capable of saving energy, environmentally friendly and low in cost, and the method is suitable for industrial production.

Description

Technical Field

[0001] The present invention relates to a new method for preparing AlON transparent ceramics with high infrared transmittance, belonging to the field of transparent ceramic preparation. Background Art

[0002] AlON is an important solid solution in the Al 2 O 3 and AlN systems, and is a polycrystalline transparent ceramic material. It not only has excellent light transmittance (the transmittance can reach more than 80%), but also has the advantages of high strength, high hardness, high temperature resistance, acid and alkali corrosion resistance, etc. In addition, the cubic spinel crystal structure characteristics of AlON make its properties isotropic, and it is known as one of the most promising structure-functional integrated transparent ceramic materials in the 21st century, and can be widely used in the production of infrared detection windows, radomes and transparent armors, etc.

[0003] At present, the preparation methods of AlON transparent ceramics mainly include two categories: one is the one-step method, that is, using Al 2 O 3 and AlN as raw materials, and directly preparing AlON transparent ceramics by solid-phase reaction sintering; the other is the two-step method, that is, first synthesizing AlON powder, and then sintering to prepare AlON transparent ceramics. Since the solid-phase reaction of Al 2 O 3 and AlN and the ceramic densification sintering are carried out simultaneously in the one-step method, the mass transfer and the new phase formation process during the sintering process are relatively complex, the controllability is poor, and the transmittance of the prepared ceramics is generally not high. In contrast, the two-step method is based on sintering AlON powder to prepare ceramics, and the sintering process has stronger controllability, which is the main method for preparing high-transmittance AlON ceramics at present.

[0004] During the process of preparing AlON ceramics by the two-step method, as the raw material, the sintering performance of AlON powder is very crucial, which directly affects the process requirements of subsequent sintering to prepare ceramics and the light transmittance of the prepared ceramics. Among many methods for preparing AlON powder such as the solid-phase reaction method, the carbothermal reduction nitridation method and the aluminothermic reduction nitridation method, the solid-phase reaction method uses Al 2 O 3 and AlN powder as raw materials, and has the advantage of controllable chemical composition, which is very beneficial to controlling the composition of materials with non-stoichiometric ratio characteristics such as AlON, and thus makes the product performance controllable.

[0005] At present, in the first step of the process of preparing AlON ceramics by the two-step method, that is, the stage of synthesizing AlON powder, the goal is to obtain pure-phase AlON powder. In recent years, in order to obtain pure-phase AlON powder through solid-phase reaction, research has been carried out in aspects such as raw material selection, ratio and synthesis process. Generally, nano-Al 2 O 3Using nano-AlN powder as raw material to shorten the material transport distance and promote the formation of AlON phase. Adopting this strategy, although pure-phase AlON powder can be obtained, it is difficult to refine the particle size of the powder, and the sintering activity is not ideal either. As a result, for pressureless sintering to prepare transparent ceramics, it is necessary to keep the temperature at a high level for a long time (up to 24 h) to obtain ceramics with better light transmittance. On the other hand, due to the fact that nano-AlN powder is more prone to hydrolysis, has a higher cost, and the subsequent ceramic sintering process has demanding requirements, there are problems such as excessively high costs and difficulties in process implementation in the process of preparing high-light-transmittance AlON ceramics based on solid-phase reaction synthesis of pure-phase AlON powder. Therefore, in view of the advantage of controllable composition of AlON powder synthesized by solid-phase reaction, it is necessary to break through the original thinking and seek a new way to prepare high-light-transmittance AlON ceramics at low cost. Summary of the Invention

[0006] The present invention provides a new method for preparing AlON transparent ceramics with high infrared transmittance. The present invention uses nano-γ-Al 2 O 3 and micron AlN powder as raw materials, rapidly heats up in one step under N 2 atmosphere, obtains powder mainly composed of AlON through solid-phase reaction, adds sintering aids, and controls the particle size of the mixed powder by ball milling, and uses pressureless sintering method to prepare pure-phase AlON transparent ceramics with high infrared transmittance. The present invention uses solid-phase reaction to prepare AlON powder, which has the advantage of controllable composition, and does not aim to obtain pure-phase AlON powder in the AlON powder synthesis stage, greatly reducing the demanding requirements for the particle size of raw materials. The present invention has the advantages of easily available raw materials, low cost, simple and easy powder synthesis process, good sintering performance of the synthesized powder, short heat preservation time, high efficiency, low cost, energy conservation and environmental protection in the ceramic sintering process, and is suitable for industrial production.

[0007] A new method for preparing AlON transparent ceramics with high infrared transmittance, comprising the following steps:

[0008] Ball-mill and mix nano-γ-Al 2 O 3 and micron AlN powder to obtain γ-Al 2 O 3 / AlN mixed powder, synthesize AlON powder mainly composed of AlON through high-temperature solid-phase reaction, then add sintering aid CaCO 3 , control the particle size of the powder by ball milling to obtain AlON / CaCO 3 mixed powder, and finally use pressureless sintering method to prepare pure-phase AlON transparent ceramics with high infrared transmittance, wherein,

[0009] In the AlON powder with AlON as the main phase, the content of the AlON phase is 75-85 wt.%, and the primary particle size is ≤2.0 μm;

[0010] The AlON / CaCO obtained after ball milling 3 The mixed powder has any one of the following particle size distribution characteristics:

[0011] One is that the particle size distribution range is 0.3-10 μm, D 10 is 0.5-0.9 μm, D 50 is 1.4-1.6 μm, D 90 is 2.7-3.3 μm. Among them, the content of particles with a particle size ≤0.5 μm is 2-5 vol.%, and the content of particles with a particle size ≥4 μm is 2-5 vol.%;

[0012] The second is that the particle size distribution range is 0.2-6.0 μm, D 10 is 0.5-0.6 μm, D 50 is 1.0-1.3 μm, D 90 is 2.0-2.6 μm. Among them, the content of particles with a particle size ≤0.5 μm is 6-10 vol.%, and the content of particles with a particle size ≥4 μm is ≤1 vol.%.

[0013] In the above technical solution, the amount of the nano-γ-Al 2 O 3 is 69-73 mol%, and the amount of the micron AlN powder is 27-31 mol%.

[0014] In the above technical solution, the average particle size of the nano-γ-Al 2 O 3 is ≤50 nm, the purity is ≥99.99%, and the specific surface area is ≥100 m 2 / g.

[0015] In the above technical solution, the particle size of the micron AlN powder is ≤9 μm, the average particle size is 1-2 μm, the purity is ≥99%, and the oxygen content is ≤1 wt.%.

[0016] In the above technical solution, the γ-Al 2 O 3 / AlN mixed powder is placed in a high-temperature atmosphere reaction furnace and directly heated up to 1700-1750 °C at a micro-positive pressure N 2 atmosphere 1-10 kPa higher than the atmospheric pressure, and kept warm for 100-180 min to obtain the AlON powder with AlON as the main phase.

[0017] Furthermore, the heating rate of the one-step direct rapid heating is 40-70 °C / min.

[0018] In the above technical solution, the nano γ-Al 2 O 3 and micron AlN powder are placed in a polytetrafluoroethylene ball milling tank, with absolute ethanol as the medium and silicon nitride balls as the grinding medium, and ball milled at 160 - 240 rpm for 15 - 30 h to obtain a slurry, which is dried and granulated to obtain the γ-Al 2 O 3 / AlN mixed powder.

[0019] Further, the mass ratio of the sum of the masses of the nano γ-Al 2 O 3 and micron AlN powder to the mass of the silicon nitride balls is 1:9 - 13.

[0020] Further, the mass ratio of the sum of the masses of the nano γ-Al 2 O 3 and micron AlN powder to the mass of absolute ethanol is 1:4 - 6.

[0021] In the above technical solution, a sintering aid CaCO 3 is added to the AlON powder mainly composed of AlON obtained by solid-phase reaction, placed in a polytetrafluoroethylene ball milling tank, with absolute ethanol as the medium and silicon nitride balls as the grinding medium, and ball milled at 150 - 220 rpm for 12 - 24 h to obtain a slurry, which is dried and granulated to obtain the AlON / CaCO 3 mixed powder.

[0022] Further, the doping amount of the sintering aid CaCO 3 is 0.5 - 0.8 wt.%.

[0023] Preferably, the doping amount of the sintering aid CaCO 3 is 0.5 wt.%.

[0024] Further, the mass ratio of the sum of the masses of the AlON powder mainly composed of AlON obtained by solid-phase reaction and the sintering aid CaCO 3 to the mass of the silicon nitride balls is 1:10 - 15.

[0025] Further, the mass ratio of the sum of the masses of the powder mainly composed of AlON obtained by solid-phase reaction and the sintering aid CaCO 3 to the mass of absolute ethanol is 1:3 - 7.

[0026] In the above technical solution, the heating rate of the pressureless sintering is 10 - 30 °C / min, the sintering temperature is 1800 - 1900 °C, and the holding time is 2.5 h.

[0027] A preferred technical solution of the present invention:

[0028] A new method for preparing AlON transparent ceramics with high infrared transmittance, comprising the following steps:

[0029] ① Raw material mixing: Using nano-γ-Al 2 O 3 and micron AlN powder as raw materials, placing them in a polytetrafluoroethylene ball mill pot, using anhydrous ethanol as the medium, and silicon nitride balls as the grinding medium for ball milling to obtain a slurry, drying, granulating, and obtaining γ-Al 2 O 3 / AlN mixed powder;

[0030] ② Synthesis of AlON powder with AlON as the main phase: Placing the γ-Al 2 O 3 / AlN mixed powder obtained in step ① into a high-temperature atmosphere reaction furnace, rapidly heating to the reaction temperature in a slightly positive pressure N 2 atmosphere of 1-10 kPa higher than atmospheric pressure, and synthesizing AlON powder with AlON as the main phase through high-temperature solid-phase reaction;

[0031] ③ Controlling the powder particle size: Adding the sintering aid CaCO 3 to the AlON powder with AlON as the main phase obtained in step ②, using a polytetrafluoroethylene ball mill pot, using anhydrous ethanol as the medium, and silicon nitride balls as the grinding medium to ball mill and control the powder particle size, obtaining a slurry, drying, granulating, and obtaining AlON / CaCO 3 mixed powder;

[0032] ④ Green body forming: Cold isostatically pressing the AlON / CaCO 3 mixed powder obtained in step ③ to obtain a green body;

[0033] ⑤ Pressureless sintering: Placing the green body obtained in step ④ into a high-temperature atmosphere sintering furnace and performing pressureless sintering in an N 2 atmosphere to obtain AlON transparent ceramics.

[0034] Further, in step ④, the AlON / CaCO 3 mixed powder obtained in step ③ is preformed at 30-50 MPa first, and then cold isostatically pressed at 100-150 MPa to obtain a green body.

[0035] Further, the preparation method of the AlON transparent ceramics with high infrared transmittance further includes a post-treatment step: grinding and polishing the AlON ceramics obtained in step ⑤.

[0036] Another object of the present invention is to provide high-infrared-transmittance AlON transparent ceramics prepared by the above method.

[0037] The phase composition of the high-infrared transmittance AlON transparent ceramic described in the present invention is a pure phase of AlON, that is, only the diffraction peaks of AlON are observed in the XRD pattern.

[0038] The relative density of the high-infrared transmittance AlON transparent ceramic described in the present invention is ≥99.7%, the infrared transmittance at ~3750 nm is ≥80%, and the Vickers hardness is ≥15 GPa.

[0039] The beneficial effects of the present invention: The present invention selects nano-γ-Al 2 O 3 and micron AlN powders as raw materials, both of which are commercial products with low costs. Moreover, compared with nano-AlN, the micron AlN powder is not easily deliquescent and is easier to store. Since it is not necessary to obtain a pure phase of AlON powder in the stage of synthesizing AlON powder by solid-phase reaction, it is sufficient to achieve AlON as the main phase. Therefore, the raw material powders only need to be mixed by conventional ball milling, and the treatment process is simple. More importantly, in the stage of synthesizing AlON powder by solid-phase reaction, a one-step rapid heating technique is adopted, combined with the isolation effect of AlN, which can effectively inhibit the growth of Al 2 O 3 particles, thereby reducing the mass transfer distance for forming AlON and being beneficial to increasing the AlON content of the obtained powder. In addition, the obtained AlON powder with AlON as the main phase also has the characteristic of small primary particle size and is easy to achieve powder particle refinement by ball milling. By adding CaCO 3 as a sintering aid and regulating the particle size of the mixed powder, more AlON phases can be retained during the heating process of sintering the prepared ceramic, effectively reducing the difficulty of reforming AlON and avoiding abnormal grain growth in the early and middle stages of sintering. Therefore, an AlON ceramic with an infrared transmittance of more than 80% is prepared by rapid pressureless sintering (only holding for 2.5 h). Both the powder synthesis and ceramic sintering of the present invention have the characteristics of simple and easy processes and low costs, and are suitable for industrial production. At the same time, the present invention breaks through the thinking limitation of first synthesizing pure-phase AlON powder and also provides a new research idea for the preparation of high-infrared transmittance AlON ceramics. Description of the Drawings

[0040] Figure 1 (a) is the SEM image of the γ-Al 2 O 3 powder used in Examples 1, 2, 3 and Comparative Example 1; Figure 1 (b) is the SEM image of the AlN powder used in Examples 1, 2, 3 and Comparative Example 1; Figure 1 (c) is the SEM image of the γ-Al 2 O 3 / AlN mixed powder in Examples 1, 2, 3 and Comparative Example 1.

[0041] Figure 2 (a), (b), and (c) are SEM images of the γ-Al 2 O 3 / AlN mixed powder when heated to 1600 °C, 1700 °C, and 1800 °C (without heat preservation); Figure 2 (d), (e), and (f) are SEM images of the γ-Al 2 O 3 / AlN mixed powder when heated to 1600 °C, 1700 °C, and 1800 °C (without heat preservation).

[0042] Figure 3 are the XRD patterns of the AlON powders synthesized in Examples 1, 2, and 3.

[0043] Figure 4 are the SEM images of the AlON powders synthesized in Examples 1, 2, and 3.

[0044] Figure 5 is the SEM image of the ball-milled AlON / CaCO 3 mixed powder obtained in Example 1.

[0045] Figure 6 is the particle size distribution diagram of the ball-milled AlON / CaCO 3 mixed powder obtained in Example 1.

[0046] Figure 7 is the XRD pattern of the AlON transparent ceramic prepared in Example 1.

[0047] Figure 8 is the fracture morphology diagram of the AlON transparent ceramic prepared in Example 1.

[0048] Figure 9 are the transmittance curve diagram and sample photo of the AlON transparent ceramic prepared in Example 1.

[0049] Figure 10 is the SEM image of the ball-milled AlON / CaCO 3 mixed powder obtained in Example 2.

[0050] Figure 11 is the SEM image of the ball-milled AlON / CaCO 3 mixed powder obtained in Example 2.

[0051] Figure 12 are the transmittance curve diagram and sample photo of the AlON transparent ceramic prepared in Example 2.

[0052] Figure 13 are the transmittance curve diagram and sample photo of the AlON transparent ceramic prepared in Example 3.

[0053] Figure 14 XRD pattern of the AlON powder synthesized in Comparative Example 1

[0054] Figure 15 Microscopic morphology of the AlON powder synthesized in Comparative Example 1

[0055] Figure 16 SEM image of the ball-milled AlON powder synthesized in Comparative Example 1

[0056] Figure 17 Particle size distribution of the ball-milled AlON powder synthesized in Comparative Example 1

[0057] Figure 18 Transmittance curve and sample photo of the AlON ceramic prepared in Comparative Example 1 Detailed implementation mode

[0058] The following non-limiting examples can enable those of ordinary skill in the art to understand the present invention more comprehensively, but do not limit the present invention in any way.

[0059] In the following examples, the test methods are conventional methods unless otherwise specified; the reagents and materials can be obtained from commercial sources unless otherwise specified.

[0060] One of the specific implementation modes:

[0061] A new method for preparing AlON transparent ceramics with high infrared transmittance, comprising the following steps:

[0062] ① Raw material mixing: According to the amount of nano-γ-Al 2 O 3 being 69 - 73 mol%, and the amount of micron AlN powder being 27 - 31 mol%, weigh the raw materials, place them in a polytetrafluoroethylene ball milling tank, use anhydrous ethanol as the medium, the mass ratio of the sum of the masses of the nano-γ-Al 2 O 3 and the micron AlN powder to anhydrous ethanol is 1:4 - 6, use silicon nitride balls as grinding media, the mass ratio of the sum of the masses of the nano-γ-Al 2 O 3 and the micron AlN powder to silicon nitride balls is 1:9 - 13, ball mill at 160 - 240 rpm for 15 - 30 h to obtain a slurry, dry it, granulate it, and obtain a γ-Al 2 O 3 / AlN mixed powder, wherein, the average particle size of the nano-γ-Al 2 O 3 ≤50 nm, the purity ≥99.99%, and the specific surface area ≥100 m 2 / g; The particle size of the micron AlN powder is ≤9 μm, the average particle size is 1 - 2 μm, the purity is ≥99%, and the oxygen content is ≤1 wt.%.

[0063] ② Synthesis of AlON powder with AlON as the main phase: The γ-Al 2 O 3 / AlN mixed powder obtained in step ① is placed in a high-temperature atmosphere reaction furnace, and in a slightly positive pressure N 2 atmosphere higher than atmospheric pressure by 1 - 10 kPa, it is rapidly heated to 1700 - 1750 °C at a heating rate of 40 - 70 °C / min, held for 100 - 180 min, the heating power is turned off, and it is cooled with the furnace to obtain AlON powder with AlON as the main phase, the AlON phase content of which is 75 - 85 wt.%, and the primary particle size is ≤2.0 μm;

[0064] ③ Controlling the powder particle size: Add 0.5 - 0.8 wt.% of the sintering aid CaCO 3 to the AlON powder with AlON as the main phase obtained in step ②. Use a polytetrafluoroethylene ball milling tank, and use absolute ethanol as the medium. The mass ratio of the sum of the mass of the AlON powder with AlON as the main phase obtained by the solid-phase reaction and the sintering aid CaCO 3 to the mass of absolute ethanol is 1:3 - 7. Use silicon nitride balls as the grinding medium. The mass ratio of the sum of the mass of the AlON powder with AlON as the main phase obtained by the solid-phase reaction and the sintering aid CaCO 3 to the mass of silicon nitride balls is 1:10 - 15. Ball mill at 150 - 220 rpm for 12 - 24 h to obtain a slurry, dry it, granulate it, and obtain an AlON / CaCO 3 mixed powder, where

[0065] the AlON / CaCO 3 mixed powder obtained after ball mill control has any one of the following particle size distribution characteristics: One, the particle size distribution range is 0.3 - 10 μm, D 10 is 0.5 - 0.9 μm, D 50 is 1.4 - 1.6 μm, D 90 is 2.7 - 3.3 μm. Among them, the particle content with a particle size ≤0.5 μm is 2 - 5 vol.%, and the particle content with a particle size ≥4 μm is 2 - 5 vol.%; Two, the particle size distribution range is 0.2 - 6.0 μm, D 10 is 0.5 - 0.6 μm, D 50 is 1.0 - 1.3 μm, D 90 is 2.0 - 2.6 μm. Among them, the particle content with a particle size ≤0.5 μm is 6 - 10 vol.%, and the particle content with a particle size ≥4 μm is ≤1 vol.%;

[0066] ④ Green body forming: The AlON / CaCO 3 mixed powder obtained in step ③ is pre-formed at 30 - 50 MPa first, and then cold isostatically formed at 100 - 150 MPa to obtain a green body;

[0067] ⑤ Pressureless sintering: The green body obtained in step ④ is placed in a high-temperature atmosphere sintering furnace, and heated to 1800 - 1900 °C at a heating rate of 10 - 30 °C / min under N 2 atmosphere, held for 2.5 h, and cooled to room temperature with the furnace to obtain AlON transparent ceramic;

[0068] ⑥ Machining: The AlON ceramic obtained in step ⑤ is ground and polished.

[0069] Example 1

[0070] A new method for preparing AlON transparent ceramic with high infrared transmittance includes the following steps:

[0071] Using γ-Al 2 O 3 powder with a purity of 99.99% and an average particle size of 20 nm and AlN powder with an average particle size of 1.2 μm as raw materials. The SEM images of the two are shown in Figure 1 (a) and Figure 1 (b). Weigh the raw material powders according to 79 mol.% γ-Al 2 O 3 and 29 mol.% AlN, pour them into a polytetrafluoroethylene ball milling tank, use silicon nitride balls as grinding media, and the mass ratio of the sum of the raw material powder masses to the mass of silicon nitride balls is 1:12. Then add absolute ethanol according to the mass ratio of the sum of the raw material powder masses to absolute ethanol of 1:5. Ball mill for 24 h at 170 rpm on a planetary ball mill to obtain a slurry, dry and granulate to obtain the γ-Al 2 O 3 / AlN mixed powder, and its microscopic morphology is shown in Figure 1 (c).

[0072] Pour the γ-Al 2 O 3 / AlN mixed powder into a graphite mold and place it in an atmosphere sintering furnace. In a slightly positive pressure N 2 environment 1 - 5 kPa higher than atmospheric pressure, heat to 1600 °C, 1700 °C and 1800 °C respectively at a heating rate of 50 °C / min, Figure 2 is the SEM image of the powder under non-insulated conditions. It can be seen that when heated to 1600 °C and 1700 °C, the powder is still mainly composed of small-sized particles, but there are more larger-sized particles in the sample at 1800 °C. Under the above atmosphere and heating rate conditions, the above γ-Al 2 O 3The / AlN mixed powder is heated to 1750 °C and held for 120 min, then the power is turned off and it is cooled in the furnace to obtain the synthesized powder. The XRD pattern of the synthesized powder is shown in Figure 3 , and it can be seen that AlON is the main phase in the synthesized powder, with a content of 85 wt.%, and at the same time, it also contains a small amount of α-Al 2 O 3 and AlN. The SEM image of the synthesized powder is shown in Figure 4 , and it can be seen that the primary particle size of the powder with AlON as the main phase obtained is relatively small, about 0.5 - 1.5 μm.

[0073] Weigh 0.6 wt.% of the sintering aid CaCO 3 according to the above-mentioned AlON powder with AlON as the main phase, use a polytetrafluoroethylene ball milling tank, use silicon nitride balls as grinding media, and the mass ratio of silicon nitride balls to AlON + CaCO 3 powder is 12:1. Add anhydrous ethanol at 5 times the mass of the AlON + CaCO 3 powder, and ball mill at 170 rpm for 24 h on a planetary ball mill to obtain a slurry. After drying and granulating, the ball-milled AlON / CaCO 3 mixed powder is obtained. Figure 5 is the SEM image of the ball-milled AlON / CaCO 3 mixed powder, Figure 6 is the test result chart of its particle size distribution. It can be seen that the particle size of the powder is refined by ball milling. The particle size distribution range of the ball-milled AlON / CaCO 3 mixed powder is relatively narrow (0.34 - 7.64 μm), its D 10 = 0.74 um, D 50 = 1.57 μm, D 90 = 3.17 μm, and moreover, the content of particles with a particle size ≤ 0.5 μm in the ball-milled AlON / CaCO 3 mixed powder is 2.18 vol.%, and the content of particles with a particle size ≥ 4 μm is 3.69 vol.%.

[0074] The ball-milled AlON / CaCO 3 mixed powder is unidirectionally pressure preformed at 50 MPa and then cold isostatically pressed at 120 MPa to obtain a green body; the green body is placed in a graphite mold and then placed in an atmosphere sintering furnace. In an N 2 atmosphere, it is heated to 1880 °C at a rate of 15 °C / min and held for 150 min, and after cooling to room temperature in the furnace, the obtained ceramic is ground and polished on both sides to obtain the AlON transparent ceramic. Figure 7 is the phase composition of the prepared AlON transparent ceramic. Only the diffraction peaks of AlON are observed, indicating that a pure-phase AlON ceramic is obtained, and its relative density reaches 99.82%, atFigure 8 No obvious pores were observed in the fracture morphology shown. The transmittance curve and sample photos of the AlON ceramic are shown in Figure 9 , and it can be seen that the ceramic has good light transmittance, and the maximum transmittance reaches 81.9%. The Vickers hardness of this AlON transparent ceramic is 15.92 GPa.

[0075] Example 2

[0076] The difference between Example 2 and Example 1 is that the ball milling process of the AlON / CaCO 3 mixed powder and the particle size distribution after ball milling are different. Specifically, in Example 2, for the AlON / CaCO 3 mixed powder, the ball milling process is to ball mill at 170 rpm for 12 h first, and then ball mill at 210 rpm for 12 h. The microscopic morphology and particle size distribution of the AlON / CaCO 3 mixed powder after ball milling are as shown in Figure 10 and Figure 11 , and it can be seen that the particle size distribution range of the AlON / CaCO 3 mixed powder after ball milling is 0.24 - 5.21 μm, D 10 = 0.53 um, D 50 = 1.10 μm, D 90 = 2.43 μm, and the content of particles with a particle size ≤ 0.5 μm is 9.67 vol.%, and the content of particles with a particle size ≥ 4 μm is 0.63 vol.%. The transmittance curve and sample photos of the AlON transparent ceramic prepared in this example are shown in Figure 12 , and it can be seen that the transmittance of the ceramic is 82.3%, and the relative density is 99.84%. The Vickers hardness of this AlON transparent ceramic is 16.20 GPa.

[0077] Example 3

[0078] The difference between Example 3 and Example 2 is that the doping amount of the sintering aid CaCO 3 is 0.5 wt.%. The transmittance curve and sample photos of the ceramic prepared in this example are shown in Figure 13 , and it can be seen that the transmittance of the ceramic is 84.6%, and the relative density is 99.88%. The Vickers hardness of this ceramic is 16.12 GPa.

[0079] Comparative Example 1

[0080] The difference between Comparative Example 1 and Example 1 is that the heating rate is 10 °C / min when synthesizing the AlON powder with AlON as the main phase by solid-phase reaction. The γ-Al obtained in Comparative Example 1 2 O 3The γ-Al2O3 / AlN mixed powder is poured into a graphite mold and then placed in an atmosphere sintering furnace. In a slightly positive pressure N2 environment with a pressure 1 - 5 kPa higher than the atmospheric pressure, it is heated to 1600 °C, 1700 °C, and 1800 °C respectively at a heating rate of 10 °C / min. The SEM images of the powders obtained under non-insulation conditions are shown in 2 (d), (e), (f). It can be seen that: when the γ-Al2O3 / AlN mixed powder is heated to 1600 °C at a rate of 10 °C / min, larger-sized particles have appeared in the sample. Moreover, when the temperature reaches 1700 °C, the large-sized particles in the powder have become the main component. Especially when the temperature rises to 1800 °C, the powder is mainly composed of large-sized particles. The XRD pattern of the powder with AlON as the main phase synthesized in this comparative example is shown in Figure 2 (d), (e), (f). It can be seen that: the content of its AlON phase is 88.0 wt.%, and the primary particle size is relatively large, about 1.5 - 3 μm. The SEM image of the AlON / CaCO3 mixed powder obtained after ball milling in this comparative example is shown in 2 O 3 / AlN mixed powder. When the powder is heated to 1600 °C at a rate of 10 °C / min, larger-sized particles have appeared in the sample. Moreover, when the temperature reaches 1700 °C, the large-sized particles in the powder have become the main component. Especially when the temperature rises to 1800 °C, the powder is mainly composed of large-sized particles. The XRD pattern of the powder with AlON as the main phase synthesized in this comparative example is shown in Figure 14 , and the microscopic morphology is shown in Figure 15 . It can be seen that: the content of its AlON phase is 88.0 wt.%, and the primary particle size is relatively large, about 1.5 - 3 μm. The SEM image of the AlON / CaCO3 mixed powder obtained after ball milling in this comparative example is shown in 3 , and the particle size distribution diagram is shown in Figure 16 . It can be seen that: the AlON / CaCO3 mixed powder obtained after ball milling contains larger-sized particles, and the particle size distribution range is 0.3 - 6.0 μm, D Figure 17 3 10 50 = 0.85 μm, D 10 10 = 1.71 μm, D 50 90 = 3.20 μm. And the content of particles with a particle size ≤ 0.5 μm is 1.2 vol.%, and the content of particles with a particle size ≥ 4 μm is 3.06 vol.%. The transmittance curve and sample photo of the prepared AlON ceramic are shown in 90 Figure 18 , and the transmittance is 56.4%.​

Claims

1. A new method for preparing AlON transparent ceramics with high infrared transmittance, characterized in that: Nano-γ-Al2O3 and micron AlN powders are ball-milled to obtain γ-Al2O3 / AlN mixed powders, which are then subjected to high-temperature solid-phase reaction to synthesize AlON powders with AlON as the main phase. Then, sintering aid CaCO3 is added, and the powder particle size is adjusted by ball milling to obtain AlON / CaCO3 mixed powders. Finally, a pure-phase AlON transparent ceramic with high infrared transmittance is prepared by a pressureless sintering method, wherein: The AlON powder with AlON as the main phase has an AlON phase content of 75-85wt.%, and a primary particle size of ≤2.0μm; The AlON / CaCO3 mixed powder obtained after ball milling has any of the following particle size distribution characteristics: First, the particle size distribution range is 0.3~10μm, D 10 0.5~0.9μm, D 50 1.4~1.6μm, D 90 2.7 to 3.3 μm, of which the content of particles with a particle size of ≤0.5 μm is 2 to 5 vol.%, and the content of particles with a particle size of ≥4 μm is 2 to 5 vol.%; Second, the particle size distribution range is 0.2~6.0μm, D 10 0.5~0.6μm, D 50 1.0~1.3μm, D 90 The particle size is 2.0-2.6 μm, wherein the content of particles with a particle size of ≤0.5 μm is 6-10 vol.%, and the content of particles with a particle size of ≥4 μm is ≤1 vol.%.

2. The preparation method according to claim 1, characterized in that: The amount of the nano-γ-Al2O3 is 69-73 mol%, and the amount of the micron AlN powder is 27-31 mol%.

3. The preparation method according to claim 1, characterized in that: The average particle size of the nano-γ-Al2O3 is ≤50nm, the purity is ≥99.99%, and the specific surface area is ≥100m 2 / g; the particle size of the micron AlN powder is ≤9μm, the average particle size is 1-2μm, the purity is ≥99%, and the oxygen content is ≤1wt.%.

4. The preparation method according to claim 1, characterized in that: The γ-Al2O3 / AlN mixed powder is directly and rapidly heated to 1700-1750°C in a high-temperature atmosphere reactor in a slightly positive pressure N2 atmosphere of 1-10 kPa higher than the atmospheric pressure, and kept warm for 100-180 minutes to obtain AlON powder with AlON as the main phase, wherein the heating rate is 40-70°C / min.

5. The preparation method according to claim 1, characterized in that: The nano-γ-Al2O3 and micron AlN powders weighed according to the ratio are placed in a polytetrafluoroethylene ball mill, with anhydrous ethanol as the medium and silicon nitride balls as the grinding medium, and the ball milling is carried out at 160-240rpm for 15-30h to obtain a slurry, which is then dried and granulated to obtain a γ-Al2O3 / AlN mixed powder, wherein: The mass ratio of the sum of the mass of the nano-γ-Al2O3 and micron AlN powder to the mass of the silicon nitride ball is 1:9-13, and the mass ratio of the sum of the mass of the nano-γ-Al2O3 and micron AlN powder to the mass of anhydrous ethanol is 1:4-6.

6. The preparation method according to claim 1, characterized in that: Add sintering aid CaCO3 to AlON powder with AlON as the main phase obtained by solid phase reaction, place it in a polytetrafluoroethylene ball mill, use anhydrous ethanol as a medium and silicon nitride balls as a grinding medium, ball mill at 150-220rpm for 12-24h to obtain slurry, dry it, granulate it, and obtain AlON / CaCO3 mixed powder, wherein, The dosage of the sintering aid CaCO3 is 0.5-0.8wt.%; the mass ratio of the sum of the masses of the AlON powder with AlON as the main phase and the sintering aid CaCO3 obtained by the solid phase reaction to the silicon nitride ball is 1:10-15, and the mass ratio of the sum of the masses of the AlON powder with AlON as the main phase and the sintering aid CaCO3 obtained by the solid phase reaction to anhydrous ethanol is 1:3-7.

7. The preparation method according to claim 1, characterized in that: The heating rate of the pressureless sintering is 10-30°C / min, the sintering temperature is 1800-1900°C, and the holding time is 2.5h.

8. The preparation method according to claim 1, characterized in that: The AlON / CaCO3 mixed powder obtained after ball milling is preformed at 30-50 MPa, and then cold isostatically pressed at 100-150 MPa to obtain a green body, which is then placed in a high-temperature atmosphere sintering furnace and pressurelessly sintered in a N2 atmosphere.

9. The preparation method according to claim 1, characterized in that: The method for preparing the AlON transparent ceramic with high infrared transmittance also includes a post-processing step: grinding and polishing the obtained AlON ceramic.

10. The AlON transparent ceramic prepared by the preparation method according to any one of claims 1 to 9, characterized in that: The physical phase composition of the AlON transparent ceramic is pure phase AlON, the relative density is ≥99.7%, the infrared transmittance at 3750nm is ≥80%, and the Vickers hardness is ≥15GPa.

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