Method for preparing MgAlON ceramic with high infrared transmittance by utilizing pressureless sintering of coarse powder

Abstract

The invention relates to a method for preparing MgAlON ceramic with high infrared transmittance by utilizing coarse powder pressureless sintering, and belongs to the field of ceramic preparation. A method for preparing MgAlON ceramic with high infrared transmittance by utilizing pressureless sintering of coarse powder comprises the steps that pure-phase MgAlON powder and a sintering aid are subjected to ball-milling mixing, drying and granulation to obtain mixed powder of MgAlON and the sintering aid, the mixed powder is formed and subjected to pressureless sintering in the nitrogen atmosphere to obtain the MgAlON ceramic, the atomic ratio of Mg to Al to O to N in the pure-phase MgAlON powder is 1: (10-20): (15-25): (2-4), and the atomic ratio of Mg to Al to O to N in the sintering aid is 1: (10-20): (15-25): (2-4). The D50 of the mixed powder of the MgAlON and the sintering aid is 1.1-2.0 [mu] m, and the particle size distribution range is 0.2-10 [mu] m. According to the method, the difficulty of a ball-milling process is small, the risk that impurities are introduced due to particle refinement can be effectively reduced, sintering equipment is easy to obtain, the heat preservation time in the pressureless sintering process is short, the obtained ceramic is high in infrared transmittance, good in energy-saving effect, high in efficiency, low in cost and suitable for preparation of large-size and complex-shape sample pieces, and industrialization is easy to achieve.

Description

TECHNICAL FIELD

[0001] The application relates to a method for preparing high-infrared-transmittance MgAlON ceramic by coarse-powder pressureless sintering, and belongs to the field of ceramic preparation. BACKGROUND

[0002] MgAlON is a spinel-type quaternary disordered solid solution, has good thermal stability and mass quality, has excellent light transmittance in a wide wave band, has good mechanical properties, is suitable for being used as an infrared detection window of high-speed running equipment, transparent armor, and is one of main candidate materials for safety protection of special infrared monitoring equipment, and has wide application prospects.

[0003] MgAlON has the characteristics of non-stoichiometric composition, has two atoms at anion and cation sites, and thus has a wide variation range of composition. Correspondingly, the optical and mechanical properties of MgAlON are strongly dependent on the chemical composition. Sintering of MgAlON powder to prepare ceramic is a main way to obtain MgAlON transparent ceramic. At present, the preparation methods of MgAlON transparent ceramic mainly include two types: one is pressureless sintering; and the other is to prepare a pre-sintered body by pressureless sintering first, and then to perform hot isostatic pressing sintering to further improve the density of the ceramic, so as to realize preparation of MgAlON transparent ceramic. In order to obtain good light transmittance, the method of “pressureless sintering combined with hot isostatic pressing” is widely used. However, from the aspects of equipment and use cost, pressureless sintering has more advantages in preparation of large-size and special-shaped components, and thus is a more potential method for preparation of MgAlON transparent ceramic.

[0004] In recent years, new research progress has been made in preparation of MgAlON transparent ceramic by pressureless sintering. However, the sintering ability of MgAlON powder is poor, which leads to problems of high-temperature long-time holding (holding for 20-24 h at 1850 DEG C or above) in preparation of transparent ceramic, and problems of high energy consumption, low efficiency, high cost and the like limit the wide application of the material. On the basis of composition optimization design, Mg 0.058 Al 1.708 O 2.182 N 0.292 powder is used to control the particle size distribution, so that the medium particle size (D 50The particle size distribution of MgAlON was 0.9 µm, exhibiting a bimodal distribution. Combined with CaCO3 as a sintering aid, MgAlON ceramics with high transmittance were obtained (Study on Solid-State Reaction Synthesis of MgAlON Powder and its Pressureless Sintering Process for Transparent Ceramics [D], Huang CJ, Dalian Maritime University, 2024; Huang CJ, et al., MTLA 41 (2025) 102425). Therefore, the chemical composition of MgAlON is fundamental to its optical and mechanical properties as a transparent ceramic and forms the basis for research on its preparation process. Based on a reasonable chemical composition design, research on the control of MgAlON powder particle size distribution, sintering aids, and sintering processes is an effective way to achieve rapid sintering preparation of high-transmittance MgAlON ceramics. Summary of the Invention

[0005] This invention provides a method for preparing high infrared transmittance MgAlON ceramics using pressureless sintering of coarse powder, specifically using pure phase Mg1Al 10~20 O 15~25 N 2~4 (Preferred Mg1Al) 15.8 O 20.9 N 2.5 MgAlON and CaCO3 powders are mixed and sintering aids (preferably CaCO3) are added. The particle size distribution of the mixed powder is controlled by wet ball milling to obtain coarse powder with a wide particle size distribution range and a large median particle size. Then, MgAlON transparent ceramics are prepared using pressureless sintering technology. This method has the advantages of easy ball milling process, which can effectively reduce the risk of impurities introduced by particle refinement, readily available sintering equipment, short holding time in the pressureless sintering process, and high infrared transmittance of the prepared ceramics. It has good energy-saving effect, high efficiency, low cost, and is suitable for the preparation of large-size and complex-shaped samples, and is easy to industrialize.

[0006] A method for preparing high infrared transmittance MgAlON ceramics using pressureless sintering of coarse powder includes the following steps: ball milling and mixing pure phase MgAlON powder and a sintering aid, drying, granulating to obtain a mixed powder of MgAlON and sintering aid, molding, and performing pressureless sintering in a nitrogen atmosphere to obtain MgAlON ceramics. The atomic ratio of Mg, Al, O, and N in the pure phase MgAlON powder is 1:10~20:15~25:2~4; The D of the mixed powder of MgAlON and sintering aid 50 The particle size ranges from 1.1 to 2.0 μm, with a particle size distribution range of 0.2 to 10 μm.

[0007] Preferably, the atomic ratio of Mg, Al, O, and N in the pure phase MgAlON powder is 1:15.8:20.9:2.5.

[0008] Preferably, the D50 of the mixed powder of MgAlON and sintering aid is 1.5 μm, and the particle size distribution range is 0.2-10 μm. 50 Preferably, the D50 of the mixed powder of MgAlON and sintering aid is 1.5 μm, and the particle size distribution range is 0.2-10 μm.

[0009] In the method, the content of the powder with a size of ≤0.5 μm in the mixed powder of MgAlON and sintering aid is 10-25 wt.%, and the content of the powder with a size of ≥5 μm is 2-8 wt.%.

[0010] Preferably, the content of the powder with a size of ≤0.5 μm in the mixed powder of MgAlON and sintering aid is 10.4 wt.%, and the content of the powder with a size of ≥5 μm is 6.7 wt.%.

[0011] In the method, the purity of the pure-phase MgAlON powder is ≥99.9%, and there is no second phase.

[0012] In the method, the content of the sintering aid is 0.4%-0.7% of the mass of the pure-phase MgAlON powder.

[0013] Preferably, the sintering aid is CaCO3, the purity is ≥99.99%, and the average particle size is ≤20 μm.

[0014] Further preferably, the sintering aid is CaCO3, and the content is 0.5 wt.%.

[0015] In the method, the pure-phase MgAlON powder and the sintering aid are ball milled in anhydrous ethanol at 200-230 rpm for 6-12 h with silicon nitride balls as the grinding medium.

[0016] In the method, the mixed powder of MgAlON and sintering aid is first pre-formed at 30-50 MPa, and then cold isostatic pressed at 120-180 MPa to obtain a green body; or the mixed powder of MgAlON and sintering aid is directly cold isostatic pressed at 120-180 MPa to obtain a green body.

[0017] Preferably, the mixed powder of MgAlON and sintering aid is unidirectionally pre-formed at 50 MPa, and then cold isostatic pressed at 120 MPa to obtain a green body.

[0018] In the method, the green body obtained after forming is heated to 1850-1880 ℃ at a rate of 10-50 ℃ / min in a carbon furnace, and then cooled in the furnace for 2-5 h to obtain a MgAlON ceramic.

[0019] Preferably, the green body obtained after forming is heated to 1880 ℃ at a rate of 15 ℃ / min in a carbon furnace, and then cooled in the furnace for 2.5 h.

[0020] In the method, the obtained MgAlON ceramic is ground and polished to obtain the MgAlON transparent ceramic.

[0021] Another object of the present application is to provide the high-infrared-transmittance MgAlON transparent ceramic prepared by the above method.

[0022] Further, the relative density of the MgAlON ceramic is 99.4% to 99.8%, the infrared transmittance is 80% to 87%, and the hardness is 15 to 18 GPa.

[0023] Further preferably, the MgAlON transparent ceramic prepared by adding 0.5 wt.% CaCO3 and sintering at 1880℃ for 2.5 h has a relative density of 99.62%, an infrared transmittance of 86.6%, and a hardness of 17.22±0.17 GPa.

[0024] The present application has the following advantages: based on the MgAlON powder with an atomic ratio of Mg, Al, O and N being 1:10-20:15-25:2-4, after adding a sintering aid (preferably CaCO3), the D 50 The mixed powder of MgAlON and sintering aid with large particle size and wide particle size distribution range, thereby increasing the coordination number between particles, creates good particle contact conditions for densification sintering. The powder ball milling process requires weak, reduces the risk of introducing impurities and reducing light transmittance, and the obtained mixed powder has good densification sintering effect, and the high-infrared-transmittance MgAlON ceramic obtained by pressureless sintering has short holding time and high ceramic transmittance. The D 50 The ceramic prepared by adding 0.5 wt.% CaCO3 to the mixed powder of MgAlON and CaCO3 with a particle size of 1.5 μm and a particle size distribution range of 0.2-10 μm and sintering at 1850-1880℃ for 2.5-4.0 h has a transmittance higher than 80%. The MgAlON powder used in the method has good densification sintering performance, the process is simple, the equipment is easy to obtain, the cost is low, the efficiency is high, the energy-saving effect is good, and the high-density high-transmittance MgAlON ceramic is prepared by pressureless sintering in a short holding time, which is easy to popularize and apply. BRIEF DESCRIPTION OF DRAWINGS

[0025] Figure 1 The XRD pattern of the MgAlON powder.

[0026] Figure 2 The particle size distribution graph (a) and SEM graph (b) of the ball-milled MgAlON and CaCO3 powder.

[0027] Figure 3The image shows the transmittance curve and sample photograph of the MgAlON transparent ceramic prepared in Example 1.

[0028] Figure 4 The image shows the SEM image of the fracture morphology of the MgAlON transparent ceramic prepared in Example 1.

[0029] Figure 5 The image shows the transmittance curve and sample photograph of the MgAlON transparent ceramic prepared in Example 2.

[0030] Figure 6 The image shows the SEM image of the fracture morphology of the MgAlON transparent ceramic prepared in Example 2.

[0031] Figure 7 The image shows the transmittance curve and sample photograph of the MgAlON transparent ceramic prepared in Example 3.

[0032] Figure 8 The image shows the SEM image of the fracture morphology of the MgAlON transparent ceramic prepared in Example 3.

[0033] Figure 9 The image shows the transmittance curve and sample photograph of the MgAlON transparent ceramic prepared in Example 4.

[0034] Figure 10 The image shows the SEM image of the fracture morphology of the MgAlON transparent ceramic prepared in Example 4. Detailed Implementation

[0035] The following non-limiting embodiments are intended to enable those skilled in the art to more fully understand the invention, but do not limit the invention in any way.

[0036] Unless otherwise specified, the experimental methods described in the following examples are conventional methods; the reagents and materials described are commercially available unless otherwise specified.

[0037] One of the specific implementation methods: A method for preparing high infrared transmittance MgAlON ceramics by pressureless sintering of coarse powder includes the following steps: (1) Preparation of materials: Weigh pure phase MgAlON powder and sintering aid separately, use silicon nitride balls as grinding media, ball mill in anhydrous ethanol to obtain slurry, dry and granulate to obtain mixed powder of MgAlON and sintering aid; (2) Molding: Place the MgAlON and sintering aid mixed powder in a steel mold, pre-form it by unidirectional pressure, and then cold isostatically press it to obtain a blank; or, place the MgAlON and CaCO3 mixed powder in a cold isostatic pressing mold and directly cold isostatically press it to obtain a blank. (3) Sintering: the green body is placed in a graphite mold, and MgAlON ceramic is prepared by pressureless sintering in a carbon furnace under a nitrogen atmosphere; (4) The obtained MgAlON ceramic is ground and polished to obtain MgAlON transparent ceramic.

[0038] The step (1) is preferably performed according to the following method: the atomic ratio of Mg, Al, O and N in the pure-phase MgAlON powder used in the step (1) is 1:10-20:15-25:2-4; the doping amount of the sintering aid is 0.4%-0.7% of the mass of the pure-phase MgAlON powder; the D 50 of the mixed MgAlON and sintering aid powder is 1.1-2.0 µm, and the particle size distribution range is 0.2-10 µm; during ball milling, silicon nitride balls are used as grinding media, and ball milling is performed in anhydrous ethanol at 200-230 rpm for 6-12 h.

[0039] In the step (2), the mixed MgAlON and sintering aid powder is first pre-formed at 30-50 MPa, and then cold isostatic pressing is performed at 120-180 MPa to obtain a green body; or the mixed MgAlON and sintering aid powder is directly cold isostatic pressed at 120-180 MPa to obtain a green body.

[0040] In the step (3), the green body obtained after forming is heated to 1850-1880 ℃ at a rate of 10-50 ℃ / min in a carbon furnace, and then the temperature is maintained for 2-5 h, and the furnace is cooled to obtain MgAlON transparent ceramic.

[0041] Example 1 A method for preparing high-infrared-transmittance MgAlON ceramic by using coarse powder pressureless sintering, comprising the following steps: (1) Preparation of materials: pure-phase MgAlON powder with a chemical composition of Mg1Al 15.8 O 20.9 N 2.5 is weighed (XRD pattern is shown in Figure 1 ), CaCO3 is weighed at 0.5% of the mass of the pure-phase MgAlON powder, anhydrous ethanol is added, silicon nitride balls are used as grinding media, and planetary ball milling is performed at 210 rpm for 10 h to obtain a slurry, which is dried and granulated to obtain mixed MgAlON and CaCO3 powder. The D 50 of the obtained mixed MgAlON and CaCO3 powder is 1.5 µm, and the particle size distribution range is 0.2-10 µm, wherein the content of powder with a particle size of ≤0.5 µm is 10.4 wt.%, and the content of powder with a particle size of ≥5 µm is 6.7 wt.%, as can be seen from the SEM image Figure 2 ), which is consistent with the particle size distribution range measured by particle size distribution.

[0042] (2) Molding: 1.3 g of MgAlON and CaCO3 mixed powder was weighed and pre-molded at 50 MPa in a steel mold with a diameter of 13 mm, and then cold isostatic pressed at 120 MPa to obtain a green body.

[0043] (3) Sintering: the green body was placed in a graphite mold and then subjected to pressureless sintering in a high-temperature atmosphere sintering furnace, and was heated to 1880°C at a rate of 15°C / min in a nitrogen atmosphere and kept for 2.5 h, and then cooled in the furnace to obtain MgAlON ceramic.

[0044] (4) After the MgAlON ceramic was ground and polished on both sides, MgAlON transparent ceramic was obtained, and the transmittance curve and sample photos are shown in Figure 3 It can be seen that the maximum infrared transmittance of the prepared MgAlON transparent ceramic is 86.6%; and the fracture morphology is shown in Figure 4 It can be seen that there are no obvious pores in the fracture, and the relative density measured by the drainage method is 99.62%, which is the main reason for the good light transmittance of the ceramic. At the same time, the hardness of the transparent ceramic is high, HV=17.22±0.17 GPa.

[0045] Example 2 The difference between Example 2 and Example 1 is that the CaCO3 content in step (1) is 0.7 wt.%. The transmittance curve and sample photos of the MgAlON transparent ceramic prepared in this example are shown in Figure 5 , and the fracture morphology is shown in Figure 6 It can be seen that the obtained ceramic has good light transmittance, and the maximum transmittance is 80.8%, and there are no obvious pores in the fracture, and the relative density is 99.51%. At the same time, the hardness of the transparent ceramic is high, HV=16.74±0.10 GPa.

[0046] Example 3 The difference between Example 3 and Example 1 is that the pressureless sintering temperature in step (3) is 1850°C. The relative density of the MgAlON transparent ceramic prepared in this example is 99.53%, and the transmittance curve and sample photos are shown in Figure 7 , and the fracture morphology is shown in Figure 8 It can be seen that the fracture of the obtained ceramic has no obvious pores and has good light transmittance, and the maximum transmittance is 81.16%. At the same time, the hardness of the transparent ceramic is high, HV=15.62±0.13 GPa.

[0047] Example 4 The difference between Example 4 and Example 1 is that the holding time of pressureless sintering in step (3) is 4.0 h. The transmittance curve and sample photos of the MgAlON transparent ceramic prepared in this example are shown in Figure 9 , and the fracture morphology is shown in Figure 10It can be seen that the ceramic has good light transmittance, the maximum transmittance is 82.67%, no obvious pores are found in the fracture, and the relative density is 99.6%. At the same time, the transparent ceramic has high hardness, HV=17.15±0.16 GPa.

Claims

1. A method for preparing high infrared transmittance MgAlON ceramics using pressureless sintering of coarse powder, characterized in that: Pure-phase MgAlON powder and sintering aid were ball-milled, dried, and granulated to obtain a mixed powder of MgAlON and sintering aid. This powder was then shaped and pressureless sintered in a nitrogen atmosphere to obtain MgAlON ceramic. The atomic ratio of Mg, Al, O, and N in the pure phase MgAlON powder is 1:10~20:15~25:2~4; The D of the mixed powder of MgAlON and sintering aid 50 The particle size ranges from 1.1 to 2.0 μm, with a particle size distribution range of 0.2 to 10 μm.

2. The preparation method according to claim 1, characterized in that: The atomic ratio of Mg, Al, O, and N in the pure phase MgAlON powder is 1:15.8:20.9:2.

5.

3. The preparation method according to claim 1, characterized in that: The content of ≤0.5 µm powder in the MgAlON and sintering aid mixed powder is 10~25 wt.%, and the content of ≥5 µm powder is 2~8 wt.%.

4. The preparation method according to claim 1, characterized in that: The sintering aid is added at a rate of 0.4% to 0.7% of the mass of the pure phase MgAlON powder.

5. The preparation method according to claim 1 or 4, characterized in that: The sintering aid is CaCO3 with a purity ≥99.99% and an average particle size ≤20 µm.

6. The preparation method according to claim 1, characterized in that: Pure-phase MgAlON powder and sintering aids were ball-milled in anhydrous ethanol at 200-230 rpm for 6-12 h using silicon nitride balls as the milling medium.

7. The preparation method according to claim 1, characterized in that: The MgAlON and sintering aid mixture powder is first pre-formed at 30~50 MPa, and then cold isostatically pressed at 120~180 MPa to obtain a green body; or, the MgAlON and sintering aid mixture powder is directly cold isostatically pressed at 120~180 MPa to obtain a green body.

8. The preparation method according to claim 1, characterized in that: The green body obtained after molding is heated to 1850-1880℃ in a carbon furnace at a rate of 10-50℃ / min and held for 2-5 hours. It is then cooled in the furnace to obtain MgAlON ceramic.

9. The preparation method according to claim 1, characterized in that: The method includes a post-processing step: grinding and polishing the obtained MgAlON ceramic to obtain transparent MgAlON ceramic.

10. The high infrared transmittance MgAlON ceramic prepared by the method according to any one of claims 1 to 9, characterized in that: The MgAlON ceramic has a relative density of 99.4%~99.8%, an infrared transmittance of 80%~87%, and a hardness of 15~18 GPa.

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