Preparation method of MgAlON ceramic with high infrared transmittance

Abstract

The invention relates to a preparation method of MgAlON ceramic with high infrared transmittance, and belongs to the field of ceramic preparation. The invention relates to a method for preparing MgAlON ceramic with high infrared transmittance, which comprises the following steps of: ball-milling and mixing 86.2-86.6 wt.% of gamma-Al2O3, 8.6 wt.% of MgO and 4.8-5.2 wt.% of carbon black, and synthesizing pure-phase MgAlON powder with an O / N value of 9.5-12.0 by adopting a carbon thermal reduction nitridation method; caCO3 is added into the pure-phase MgAlON powder to serve as a sintering aid, MgAlON / CaCO3 mixed powder is obtained after ball milling, and a green body is prepared through dry pressing; and preparing the MgAlON ceramic with high infrared transmittance by adopting a pressureless sintering method. According to the method, the MgAlON transparent ceramic is prepared by designing the composition of the raw material powder, regulating and controlling the nitridation degree of the MgAlON powder and further adopting the powder as the raw material through a pressureless sintering method under the condition of short heat preservation time, the raw materials are easy to obtain and low in price, the prepared MgAlON powder is good in sintering performance, and the MgAlON transparent ceramic is high in infrared transmittance, good in energy-saving effect, high in efficiency, low in cost and suitable for industrial production. And the process is simple and feasible, and is suitable for industrial production.

Description

Technical Field

[0001] The invention relates to a method for preparing MgAlON ceramics with high infrared transmittance, and belongs to the field of ceramic preparation. Background Art

[0002] MgAlON ceramics not only have excellent light transmittance, wide transmission range, and good thermal stability, but also have good mechanical properties. They are a very potential structural-functional integrated ceramic window material, and are also one of the preferred transparent window materials for advanced equipment such as infrared detection windows, transparent armor, and missile fairings.

[0003] MgAlON powder is the key raw material for sintering and preparing MgAlON transparent ceramics. Its chemical composition has the characteristics of non-stoichiometric ratio. Its phase composition, chemical composition and particle size distribution characteristics directly affect the process requirements of subsequent transparent ceramic sintering preparation and the light transmittance of the prepared ceramics. Solid-phase reaction method, aluminothermic reduction nitridation method and carbon thermal reduction nitridation method are currently the main ways to synthesize MgAlON powder. Among them, the carbon thermal reduction nitridation method has the advantages of easy availability of raw materials, low price, simple process, small particle size and high purity of the synthesized MgAlON powder. It is an ideal method for batch preparation of high-purity and high sintering activity MgAlON powder, and has industrial prospects.

[0004] The carbothermal reduction nitridation method usually uses Al2O3, MgO and carbon powder as raw materials to synthesize MgAlON powder under high temperature conditions. The raw material composition and carbothermal reduction nitridation process (heating rate, synthesis temperature and holding time) jointly affect the phase composition, chemical composition and ball milling refining ability of the synthesized MgAlON powder, and then affect the sintering performance. On the other hand, at present, the sintering preparation of MgAlON transparent ceramics still has the problem of long holding time under high temperature conditions. For pressureless sintering, it is generally necessary to keep it at ≥1850℃ for ≥20h (Rare Metal Materials and Engineering. 44(1)(2015)101-104; J.Alloy.Compd.745(2018)617-623; J.Alloy.Compd.791(2019)856-863). If the method of pressureless sintering followed by hot isostatic pressing is adopted, the holding time of the pressureless sintering stage can be shortened, but hot isostatic pressing is required to prepare MgAlON transparent ceramics (Ceram. Int. 44 (2018) 4512–4515; Scr. Mater. 178 (2020) 428–432). It can be seen that the sintering performance of MgAlON powder still needs to be improved, and the holding time of pressureless sintering to prepare high infrared transmittance MgAlON transparent ceramics needs to be greatly shortened to meet the needs of industrialization and application. Summary of the invention

[0005] The purpose of the present invention is to provide a method for preparing MgAlON ceramics with high infrared transmittance by using γ-Al2O3, MgO and carbon black as raw materials, obtaining pure phase MgAlON powder with an O / N value (atomic ratio) of 9.5-12.0 by carbon thermal reduction nitridation in a nitrogen atmosphere, adding CaCO3 as a sintering aid, and adopting a pressureless sintering method under a short insulation time condition. The raw materials of this method are easily available and low in price, the process is simple and easy to operate, and the equipment requirements are not high. The synthesized pure phase MgAlON powder has good sintering performance, short pressureless sintering insulation time, high infrared transmittance of transparent ceramics, energy saving and environmental protection, high efficiency, low cost, and easy to realize industrialization.

[0006] A method for preparing MgAlON ceramics with high infrared transmittance comprises the following steps: taking 86.2-86.6wt.% γ-Al2O3, 8.6wt.% MgO and 4.8-5.2wt.% carbon black, mixing them by ball milling, and synthesizing pure phase MgAlON powder with an O / N value of 9.5-12.0 by a carbon thermal reduction nitridation method in a nitrogen atmosphere; adding 0.3wt.% CaCO3 as a sintering aid to the pure phase MgAlON powder, obtaining MgAlON / CaCO3 mixed powder by ball milling, and preparing a green body by dry pressing; and preparing the MgAlON ceramics with high infrared transmittance by a pressureless sintering method on the green body in a nitrogen atmosphere.

[0007] Preferably, the O / N value of the pure phase MgAlON powder is 11.39.

[0008] In the method of the present invention, the D of the MgAlON / CaCO3 mixed powder is 50 The particle size distribution range is 0.85-1.30μm and 0.05-8.0μm.

[0009] Preferably, the D of the MgAlON / CaCO3 mixed powder 50 The particle size is 0.87 μm and the particle size distribution range is 0.15-8.0 μm.

[0010] In the method of the present invention, the γ-Al2O3 is a nano powder with an average particle size of ≤50nm; the carbon black is a nano powder with an average particle size of ≤30nm.

[0011] In the method of the present invention, the MgO is a nano powder with an average particle size of ≤100nm, which is obtained by calcining Mg(OH)2 powder with a purity of ≥99.0% at 600-700°C for 40-80min in air.

[0012] Preferably, the mass fraction of γ-Al2O3 is 86.2wt.%, the mass fraction of MgO is 8.6wt.%, and the mass fraction of carbon black is 5.2wt.%.

[0013] Preferably, the average particle size of γ-Al2O3 is 20 nm, the average particle size of MgO is 81.4 nm, and the average particle size of carbon black is 15 nm.

[0014] In the method of the present invention, γ-Al2O3, MgO and carbon black are ball-milled and mixed, then loaded into a graphite mold, heated to 1650-1750°C in a nitrogen atmosphere, kept warm for 90-150 minutes, cooled with the furnace, and kept warm at 600-700°C in an air atmosphere for 3-5 hours to obtain pure phase MgAlON powder, wherein the heating rate is 10-30°C / min, and the cooling rate is 20-30°C / min.

[0015] Preferably, γ-Al2O3, MgO and carbon black are ball-milled and mixed, then loaded into a graphite mold, heated to 1700°C at 10°C / min in a nitrogen atmosphere and kept warm for 90 minutes, then cooled at 30°C / min, and kept warm at 640°C for 4 hours in an air atmosphere.

[0016] In the method of the present invention, the ball milling process is: using silicon nitride balls as grinding media and anhydrous ethanol as liquid phase, ball milling is performed on a planetary ball mill at 150-210 rpm for 18-30 hours.

[0017] Preferably, the ball milling process is: using silicon nitride balls as grinding media, anhydrous ethanol as liquid phase, and ball milling at 170 rpm on a planetary ball mill for 24 hours.

[0018] In the method of the present invention, the mixed powder is preformed by unidirectional pressing at 30-50 MPa, and then is cold isostatically pressed at 100-180 MPa to obtain a green body.

[0019] Preferably, the mixed powder is preformed by uniaxial pressing at 50 MPa, and then cold isostatic pressing at 120 MPa is performed to obtain a green body.

[0020] In the method of the present invention, the green body is placed in a carbon furnace, heated to 1860-1900° C. at 10-30° C. / min in a nitrogen atmosphere, and kept warm for 120-180 min, and then cooled in the furnace to obtain MgAlON transparent ceramics.

[0021] Preferably, the green body is placed in a carbon furnace, and the temperature is increased to 1880° C. at a rate of 15° C. / min in a nitrogen atmosphere and maintained at that temperature for 150 min.

[0022] Furthermore, the method also includes grinding and polishing the MgAlON transparent ceramic obtained by sintering.

[0023] The object of the present invention is to provide MgAlON transparent ceramics with high infrared transmittance prepared by the above method.

[0024] The relative density of the MgAlON transparent ceramic of the present invention is ≥99.19%, and further, the infrared transmittance is 80.0-82.4%.

[0025] The beneficial effects of the present invention are as follows: the present invention prepares pure phase MgAlON powder by designing the raw material powder composition and combining the carbon thermal reduction nitridation process, and regulates the nitridation degree of the powder to control its O / N value within 9.5-12.0. 50 The particle size is controlled at 0.85-1.30 μm, and the particle size distribution range is 0.05-8.0 μm, thereby improving the sintering performance of the MgAlON powder. Under the condition of adding 0.3wt.% CaCO3 sintering aid, the above-synthesized MgAlON powder is used to obtain a high-transmittance MgAlON ceramic with an infrared transmittance of ≥80.0% by pressureless sintering and heat preservation for a short time (120-180min). The raw materials for synthesizing pure phase MgAlON powder by this method are easy to obtain and low in price, the process is simple, and the controllability is strong. The equipment requirements for powder synthesis and transparent ceramic sintering are not high. The transparent ceramic sintering does not rely on hot isostatic pressing sintering. High-transmittance MgAlON ceramics can be obtained only by pressureless sintering, and the heat preservation time of the sintering process is short, the energy-saving effect is good, the efficiency is high, and the cost is low, which is conducive to promotion and application. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 These are the XRD diagrams of the raw material γ-Al2O3 powder and raw material MgO powder of Examples 1-4.

[0027] Figure 2 These are SEM images of the raw materials γ-Al2O3 (a), MgO (b), carbon black (c) powder and γ-Al2O3 / MgO / C mixed powder (d) of Examples 1-4.

[0028] Figure 3 This is the XRD diagram of the MgAlON powder synthesized in Example 1-4.

[0029] Figure 4 This is the SEM image of the MgAlON powder synthesized in Example 1-4.

[0030] Figure 5 This is the SEM image of the MgAlON powder after ball milling in Example 1-4.

[0031] Figure 6 This is the particle size distribution diagram of the MgAlON powder after ball milling in Examples 1-4.

[0032] Figure 7 This is the fracture morphology of the MgAlON transparent ceramic obtained in Example 1-4.

[0033] Figure 8The sample photos and transmittance curves of MgAlON transparent ceramics obtained in Examples 1-4 are shown.

[0034] Fig. 9 The XRD diagram of the MgAlON powder synthesized in Comparative Examples 1 and 2.

[0035] Fig.10 SEM images of the MgAlON powders synthesized in Comparative Examples 1 and 2.

[0036] Fig.11 The SEM images of MgAlON powders after ball milling in Comparative Examples 1 and 2 are shown.

[0037] Fig.12 This is the particle size distribution diagram of MgAlON powder after ball milling in Comparative Examples 1 and 2.

[0038] Fig.13 The sample photos and transmittance curves of MgAlON transparent ceramics obtained in Comparative Examples 1 and 2 are shown. DETAILED DESCRIPTION

[0039] The following non-limiting embodiments may enable a person skilled in the art to more fully understand the present invention, but are not intended to limit the present invention in any way.

[0040] The test methods described in the following examples are conventional methods unless otherwise specified; the reagents and materials described are commercially available unless otherwise specified.

[0041] One of the specific implementations:

[0042] A method for preparing MgAlON ceramics with high infrared transmittance comprises the following process steps:

[0043] (1) Raw material powders are weighed according to 86.2-86.6 wt.% γ-Al2O3, 8.6 wt.% MgO and 4.8-5.2 wt.% carbon black, and ball milled on a planetary ball mill at 150-210 rpm for 18-30 h using silicon nitride balls as grinding media and anhydrous ethanol as liquid phase to obtain a slurry, and after drying and granulation, a γ-Al2O3 / MgO / C mixed powder is obtained, wherein the average particle size of γ-Al2O3 is ≤50 nm, the average particle size of carbon black is ≤30 nm, and the average particle size of MgO is ≤100 nm;

[0044] (2) The γ-Al2O3 / MgO / C mixed powder is placed in a graphite mold, heated to 1650-1750°C at a rate of 10-30°C / min in a nitrogen atmosphere, kept at that temperature for 90-150min, and then cooled in the furnace to obtain MgAlON powder containing a small amount of residual carbon, with a cooling rate of 20-30°C / min;

[0045] (3) The MgAlON powder containing a small amount of residual carbon is kept at 600-700°C in an air atmosphere for 3-5 hours to obtain a pure phase MgAlON powder having an O / N value (atomic ratio) of 9.5-12.0;

[0046] (4) adding 0.3 wt.% CaCO3 as a sintering aid to the pure phase MgAlON powder, using silicon nitride balls as grinding media and anhydrous ethanol as liquid medium, ball milling for 18-30 hours at 150-210 rpm on a planetary ball mill to obtain a slurry, and after drying and granulation, obtaining a MgAlON / CaCO3 mixed powder with high sintering activity;

[0047] (5) preforming the MgAlON / CaCO3 mixed powder by uniaxial pressing at 30-50 MPa, and then cold isostatic pressing at 100-180 MPa to obtain a green body;

[0048] (6) placing the green body in a carbon furnace, heating it to 1860-1900° C. at a rate of 10-30° C. / min in a nitrogen atmosphere, and keeping the temperature for 120-180 min, and cooling the green body in the furnace to obtain MgAlON ceramics;

[0049] (7) The obtained MgAlON ceramic is ground and polished to obtain MgAlON transparent ceramic.

[0050] Example 1

[0051] 86.2wt.% γ-Al2O3 (average particle size of 20nm, purity of 99.99%), 8.6wt.% MgO (average particle size of 81.4nm, obtained by calcining Mg(OH)2 powder with a purity of 99.99% at 600°C in air atmosphere for 60min) and 5.2wt.% carbon black (average particle size of 15nm, purity of 99.0%) were weighed respectively, mixed with anhydrous ethanol, and milled at 170rpm for 24h on a planetary ball mill using silicon nitride balls as grinding media. The resulting slurry was dried and granulated to obtain γ-Al2O3 / MgO / C mixed powder. Figure 1 XRD patterns of raw materials γ-Al2O3 and MgO powders, Figure 2 These are SEM images of γ-Al2O3, MgO, carbon black powder and γ-Al2O3 / MgO / C mixed powder.

[0052] The γ-Al2O3 / MgO / C mixed powder was placed in a graphite mold, placed in an atmosphere sintering furnace, heated to 1700°C at 10°C / min in a nitrogen atmosphere for 90 minutes, and then cooled at 30°C / min to obtain MgAlON powder. The above MgAlON powder was kept at 640°C in air for 4 hours to remove the residual carbon in the powder to obtain pure phase MgAlON powder, the O / N value (atomic ratio) of the powder was 11.39, and the nitrogen content was 1.98wt.%. Figure 3 The XRD spectrum of the synthesized powder shows that the synthesized powder is pure phase MgAlON powder; Figure 4 This is the SEM image of the synthesized MgAlON powder. It can be seen that the synthesized MgAlON powder contains a large number of small-sized particles.

[0053] 0.3wt.% CaCO3 was added as a sintering aid to the synthesized MgAlON powder, and silicon nitride balls were used as grinding media and anhydrous ethanol was used as dispersion medium. The powder was ball milled at 170rpm on a planetary ball mill for 24h. The resulting slurry was dried and granulated to obtain MgAlON powder after particle refinement and mixing with the sintering aid. Figure 5 This is the SEM image of MgAlON powder after ball milling. It can be seen that the size of large particles in MgAlON powder after ball milling is significantly smaller than that before ball milling, and the powder has better dispersion. Figure 6 The particle size distribution of MgAlON powder after ball milling shows that the particle size distribution range of MgAlON powder after ball milling is 0.15~8.0μm, D 50 It is 0.87μm.

[0054] The ball-milled MgAlON powder was preformed by unidirectional pressure at 50MPa, and then cold isostatically pressed at 120MPa to obtain a green body. The green body was then placed in a graphite mold and placed in a high-temperature sintering furnace. In a nitrogen atmosphere, the temperature was raised to 1880℃ at 15℃ / min and kept for 150min. After cooling in the furnace, the sample was double-sided ground and polished to obtain MgAlON transparent ceramics. The relative density of the prepared MgAlON transparent ceramics is 99.45%, and its fracture morphology is shown in Figure 2. Figure 7 It can be seen that the density of the ceramic is relatively high and no obvious pores are found in the fracture. Figure 8 The transmittance curve diagram and sample photos of MgAlON transparent ceramics show that the prepared MgAlON ceramics have good light transmittance, with a maximum transmittance of 82.4%.

[0055] Example 2

[0056] The difference between Example 2 and Example 1 is that the holding time of the carbon thermal reduction synthesis of MgAlON powder is 120min, and the O / N value (atomic ratio) of the obtained pure phase MgAlON powder is 11.00, wherein the nitrogen content is 2.13wt.% (the XRD spectrum of the pure phase MgAlON powder is shown in Figure 3 , microscopic morphology Figure 4 ). Figure 5 and Figure 6 The morphology and particle size distribution of the MgAlON powder after ball milling are shown respectively. It can be seen that the MgAlON powder has good dispersibility, with a particle size distribution range of 0.13-7.0 μm, D 50 The relative density of the MgAlON transparent ceramics prepared by pressureless sintering is 99.43%, and the fracture morphology is shown in Figure 7 , transmittance curve and sample photos see Figure 8 It can be seen that there are no obvious pores in the fracture and the transmittance is 82.1%.

[0057] Example 3

[0058] The difference between Example 3 and Example 1 is that the holding time of the carbon thermal reduction synthesis of MgAlON powder is 150min, and the O / N value of the obtained pure phase MgAlON powder is 9.52, wherein the nitrogen content is 2.53wt.% (the XRD spectrum of the pure phase MgAlON powder is shown in Figure 3 , microscopic morphology Figure 4 ). Figure 5 and Figure 6 The morphology and particle size distribution of MgAlON powder after ball milling are shown respectively. It can be seen that the powder has good dispersion after ball milling, and the particle size distribution range is 0.13-8.0μm, D 50 The relative density of the MgAlON transparent ceramics prepared by pressureless sintering is 99.30%, and the fracture morphology is shown in Figure 7 , transmittance curve and sample photos see Figure 8 It can be seen that there are few and small pores in the fracture, and the transmittance is 80.9%.

[0059] Example 4

[0060] The difference between Example 4 and Example 1 is that the synthesis temperature of the MgAlON powder synthesized by carbothermal reduction is 1720°C, the holding time is 120 min, and the O / N value (atomic ratio) of the obtained pure phase MgAlON powder is 9.64, wherein the nitrogen content is 2.39 wt.% (the XRD spectrum of the pure phase MgAlON powder is shown in Figure 3 , microscopic morphology Figure 4 ). Figure 5 and Figure 6The morphology and particle size distribution of MgAlON powder after ball milling are shown respectively. It can be seen that the powder has good dispersion after ball milling, and the particle size distribution range is 0.07-8.0μm, D 50 The relative density of the MgAlON transparent ceramic prepared by pressureless sintering is 99.19%, and the fracture morphology is shown in Figure 7 , transmittance curve and sample photos see Figure 8 It can be seen that there are few and small pores in the fracture, and the transmittance is 81.0%.

[0061] Comparative Example 1

[0062] The difference between Comparative Example 1 and Examples 1-4 is that the MgAlON powder is synthesized at 1600°C for 120 min, and its O / N value (atomic ratio) is 14.20, and the nitrogen content is 1.64 wt.% (the XRD spectrum of pure phase MgAlON powder is shown in Fig. 9 , microscopic morphology Fig.10 ). Fig.11 and Fig.12 The morphology and particle size distribution of MgAlON powder after ball milling are shown respectively. It can be seen that the powder has good dispersion after ball milling, and the particle size distribution range is 0.1-8.0μm, D 50 The relative density of the MgAlON transparent ceramic prepared by pressureless sintering is 99.23%. The transmittance curve and sample photos are shown in Fig.13 , it can be seen that its transmittance is 76.1%.

[0063] Comparative Example 2

[0064] The difference between Comparative Example 2 and Examples 1-4 is that when synthesizing MgAlON powder, the heating rate is 5°C / min, and the mixed powder is synthesized at 1600°C for 120 min. Its O / N value (atomic ratio) is 6.77, and the nitrogen content is 2.07 wt.% (the XRD spectrum of pure phase MgAlON powder is shown in Fig. 9 , microscopic morphology Fig.10 ). Fig.11 and Fig.12 The morphology and particle size distribution of MgAlON powder after ball milling are shown respectively. It can be seen that the powder has good dispersion after ball milling, and the particle size distribution range is 0.09-8.0μm, D 50 The relative density of the MgAlON transparent ceramic prepared by pressureless sintering is 99.07%. The transmittance curve and sample photos are shown in Fig.13 , it can be seen that its transmittance is 69.9%.

Claims

1. A method for preparing MgAlON ceramics with high infrared transmittance, Features: Take 86.2-86.6wt.%γ-Al 2 O 3 , 8.6wt.% MgO and 4.8-5.2wt.% carbon black were ball-milled and mixed in a nitrogen atmosphere, and a pure phase MgAlON powder with an O / N value of 9.5-12.0 was synthesized by a carbothermal reduction nitridation method; 0.3wt.% CaCO was added to the pure phase MgAlON powder 3 As a sintering aid, MgAlON / CaCO 3 The powders are mixed and dry pressed to prepare a green body; the green body is subjected to pressureless sintering in a nitrogen atmosphere to prepare MgAlON ceramics with high infrared transmittance.

2. The method according to claim 1, Features: The MgAlON / CaCO 3 Mixed powder D 50 The particle size distribution range is 0.85-1.30μm and 0.05-8.0μm.

3. The method according to claim 1, Features: The γ-Al 2 O 3 The carbon black is a nano powder with an average particle size of ≤30nm.

4. The method according to claim 1, Features: The MgO is a nano powder with an average particle size of ≤100nm, which is made of Mg(OH) 2 The powder is calcined in air at 600-700°C for 40-80 minutes.

5. The method according to claim 1, Features: The ball-milled γ-Al 2 O 3 The mixed powder of MgO and carbon black is loaded into a graphite mold, heated to 1650-1750℃ in a nitrogen atmosphere and kept for 90-150min, then cooled with the furnace, and kept at 600-700℃ in an air atmosphere for 3-5h to obtain pure phase MgAlON powder, wherein the heating rate is 10-30℃ / min, and the cooling rate is 20-30℃ / min.

6. The method according to claim 1, Features: MgAlON / CaCO 3 The mixed powder is preformed by uniaxial pressing at 30-50 MPa, and then is cold isostatically pressed at 100-180 MPa to obtain a green body.

7. The method according to claim 1, Features: The green body is placed in a carbon furnace, heated to 1860-1900° C. at a rate of 10-30° C. / min in a nitrogen atmosphere, and kept at that temperature for 120-180 min. After cooling in the furnace, MgAlON transparent ceramics are obtained.

8. The method according to claim 1, Features: The ball milling process is as follows: using silicon nitride balls as grinding media and anhydrous ethanol as liquid phase, and ball milling at 150-210 rpm for 18-30 hours on a planetary ball mill.

9. The method according to claim 1, Features: The method comprises a post-processing step of grinding and polishing the MgAlON transparent ceramic obtained by sintering.

10. MgAlON ceramics with high infrared transmittance prepared by the method according to any one of claims 1 to 9, Features: The relative density of the MgAlON transparent ceramic is ≥99.19%, and the infrared transmittance is 80.0-82.4%.

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