Preparation method of high-infrared-transmittance MgAlON ceramic

Abstract

This invention relates to a method for preparing high infrared transmittance MgAlON ceramics, belonging to the field of ceramic preparation. The method for preparing high infrared transmittance MgAlON ceramics involves ball milling and mixing 86.2-86.6 wt.% γ-Al₂O₃, 8.6 wt.% MgO, and 4.8-5.2 wt.% carbon black, followed by carbothermic reduction nitriding to synthesize pure-phase MgAlON powder with an O / N value of 9.5-12.0. CaCO₃ is added to the pure-phase MgAlON powder as a sintering aid, and after ball milling, a MgAlON / CaCO₃ mixed powder is obtained, which is then dry-pressed to prepare a green body. Finally, high infrared transmittance MgAlON ceramics are prepared using a pressureless sintering method. This method designs the composition of raw material powder and controls the degree of nitridation of MgAlON powder. Then, using this powder as raw material, MgAlON transparent ceramics are prepared by pressureless sintering under short holding time conditions. The raw materials are readily available and inexpensive. The MgAlON powder prepared has good sintering performance, and the MgAlON transparent ceramics have high infrared transmittance, good energy-saving effect, and high efficiency. It is not only low in cost, but also simple and easy to implement, making it suitable for industrial production.

Description

Technical Field

[0001] This invention relates to a method for preparing MgAlON ceramics with high infrared transmittance, belonging to the field of ceramic preparation. Background Technology

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

[0003] MgAlON powder, as a key raw material for the sintering preparation of transparent MgAlON ceramics, exhibits a non-stoichiometric chemical composition. Its phase composition, chemical composition, and particle size distribution directly influence the subsequent sintering process requirements and the light transmittance of the prepared ceramics. Solid-state reaction, aluminothermic reduction nitridation, and carbothermic reduction nitridation are currently the main methods for synthesizing MgAlON powder. Among these, carbothermic reduction nitridation offers advantages such as readily available and inexpensive raw materials, simple process, and the production of small-particle-size and high-purity MgAlON powder. It is an ideal method for the mass production of high-purity, high-sintering-activity MgAlON powder and has promising industrialization prospects.

[0004] Carbothermic reduction nitriding typically uses Al2O3, MgO, and carbon powder as raw materials to synthesize MgAlON powder under high temperature conditions. The composition of raw materials and the carbothermic reduction nitriding process (heating rate, synthesis temperature, and holding time) jointly affect the phase composition, chemical composition, and ball milling refinement ability of the synthesized MgAlON powder, thus affecting 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 hold at ≥1850℃ for ≥20 h (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 a method of first pressureless sintering followed by hot isostatic pressing (HIP) is adopted, the holding time in the pressureless sintering stage can be shortened. However, subsequent HIP sintering is still required to prepare transparent MgAlON ceramics (Ceram. Int. 44 (2018) 4512–4515; Scr. Mater. 178 (2020) 428–432). Therefore, the sintering performance of MgAlON powder still needs improvement, and the holding time for preparing high infrared transmittance MgAlON transparent ceramics by pressureless sintering needs to be significantly shortened to meet the requirements of industrialization and application. Summary of the Invention

[0005] The purpose of this invention is to provide a method for obtaining high-infrared-transmittance MgAlON ceramics by using γ-Al₂O₃, MgO, and carbon black as raw materials, obtaining pure-phase MgAlON powder with an O / N ratio (atomic ratio) of 9.5-12.0 through carbothermic reduction nitridation in a nitrogen atmosphere, adding CaCO₃ as a sintering aid, and employing a pressureless sintering method with a short holding time. This method uses readily available and inexpensive raw materials, is simple and easy to implement, has low equipment requirements, produces pure-phase MgAlON powder with good sintering performance, requires a short pressureless sintering holding time, produces transparent ceramics with high infrared transmittance, is energy-saving and environmentally friendly, highly efficient, low-cost, and easily industrialized.

[0006] A method for preparing high infrared transmittance MgAlON ceramics involves ball milling 86.2-86.6 wt.% γ-Al2O3, 8.6 wt.% MgO, and 4.8-5.2 wt.% carbon black together, and then synthesizing pure-phase MgAlON powder with an O / N value of 9.5-12.0 using a carbothermic reduction nitriding method under a nitrogen atmosphere. 0.3 wt.% CaCO3 is added to the pure-phase MgAlON powder as a sintering aid, and the mixture is ball milled to obtain a MgAlON / CaCO3 mixed powder, which is then dry-pressed to prepare a green body. The green body is then sintered under a nitrogen atmosphere using a pressureless sintering method to prepare high infrared transmittance MgAlON ceramics.

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

[0008] In the method described in this invention, the D of the MgAlON / CaCO3 mixed powder 50 The particle size ranges from 0.85 to 1.30 μm, with a particle size distribution range of 0.05 to 8.0 μm.

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

[0010] In the method described in this invention, the γ-Al2O3 is a nanoparticle with an average particle size ≤50 nm; the carbon black is a nanoparticle with an average particle size ≤30 nm.

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

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

[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 described in this invention, γ-Al2O3, MgO and carbon black are ball-milled and mixed, then loaded into a graphite mold. The mixture is heated to 1650-1750℃ in a nitrogen atmosphere and held for 90-150 min, then cooled in the furnace. Finally, it is held at 600-700℃ in an air atmosphere for 3-5 h to obtain pure phase MgAlON powder. The heating rate is 10-30℃ / min and the cooling rate is 20-30℃ / min.

[0015] Preferably, γ-Al2O3, MgO and carbon black are ball-milled and mixed, then loaded into a graphite mold. The mixture is heated to 1700℃ at 10℃ / min and held for 90 min in a nitrogen atmosphere, then cooled at 30℃ / min and held at 640℃ for 4 h in an air atmosphere.

[0016] In the method described in this invention, the ball milling process is as follows: using silicon nitride balls as the grinding medium and anhydrous ethanol as the liquid phase, the ball mill is performed on a planetary ball mill at 150-210 rpm for 18-30 h.

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

[0018] In the method described in this invention, the mixed powder is pre-formed under unidirectional pressure at 30-50 MPa, and then cold isostatically pressed at 100-180 MPa to obtain a blank.

[0019] Preferably, the mixed powder is pre-formed under unidirectional pressure at 50 MPa, and then cold isostatically pressed at 120 MPa to obtain the blank.

[0020] In the method described in this invention, the green body is placed in a carbon furnace and heated to 1860-1900℃ in a nitrogen atmosphere at a rate of 10-30℃ / min. The temperature is then held for 120-180 min, and the green body is cooled in the furnace to obtain MgAlON transparent ceramic.

[0021] Preferably, the billet is placed in a carbon furnace and heated to 1880°C at a rate of 15°C / min in a nitrogen atmosphere and held for 150 min.

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

[0023] The purpose of this invention is to provide a high infrared transmittance MgAlON transparent ceramic prepared by the above method.

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

[0025] The beneficial effects of this invention are as follows: This invention prepares pure-phase MgAlON powder by designing the composition of raw material powder and combining it with a carbothermal reduction nitriding process, and controls the degree of nitriding of the powder to maintain its O / N value between 9.5 and 12.0. Furthermore, the D-phase of the powder is further controlled by ball milling. 50 The particle size was controlled within the range of 0.85-1.30 μm, and the particle size distribution range was 0.05-8.0 μm, to improve the sintering performance of MgAlON powder. With the addition of 0.3 wt.% CaCO3 sintering aid, the synthesized MgAlON powder was used to prepare high-transmittance MgAlON ceramics with an infrared transmittance ≥80.0% by pressureless sintering with a short holding time (120-180 min). This method uses readily available and inexpensive raw materials for synthesizing pure-phase MgAlON powder. The process is simple, highly controllable, and requires minimal equipment for both powder synthesis and transparent ceramic sintering. Transparent ceramic sintering does not rely on hot isostatic pressing; high-transmittance MgAlON ceramics can be obtained solely through pressureless sintering. Furthermore, the short holding time during sintering results in good energy efficiency, high cost, and is conducive to widespread application. Attached Figure Description

[0026] Figure 1 The images show the XRD patterns of the raw materials γ-Al2O3 powder and MgO powder in Examples 1-4.

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

[0028] Figure 3 The images show the XRD patterns of the MgAlON powders synthesized in Examples 1-4.

[0029] Figure 4 The images show SEM images of the MgAlON powders synthesized in Examples 1-4.

[0030] Figure 5 The images show SEM images of MgAlON powder after ball milling in Examples 1-4.

[0031] Figure 6 The particle size distribution diagrams of MgAlON powder after ball milling in Examples 1-4 are shown.

[0032] Figure 7 The images show photographs and transmittance curves of the MgAlON transparent ceramics obtained in Examples 1-4.

[0033] Figure 8 The XRD patterns are of the MgAlON powders synthesized in Comparative Examples 1 and 2.

[0034] Figure 9 The image shows the SEM images of the MgAlON powders synthesized in Comparative Examples 1 and 2.

[0035] Figure 10 The images show the SEM images of MgAlON powder after ball milling in Comparative Examples 1 and 2.

[0036] Figure 11 The particle size distribution diagrams of MgAlON powder after ball milling are shown for Comparative Examples 1 and 2.

[0037] Figure 12 Photographs and transmittance curves of the MgAlON transparent ceramics obtained in Comparative Examples 1 and 2 are shown. Detailed Implementation

[0038] 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.

[0039] 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.

[0040] One of the specific implementation methods:

[0041] A method for preparing MgAlON ceramics with high infrared transmittance includes the following process steps:

[0042] (1) Weigh the raw material powder according to 86.2-86.6 wt.% γ-Al2O3, 8.6 wt.% MgO and 4.8-5.2 wt.% carbon black, use silicon nitride balls as the grinding medium and anhydrous ethanol as the liquid phase, and ball mill at 150-210 rpm for 18-30 h on a planetary ball mill to obtain a slurry. After drying and granulation, 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.

[0043] (2) The γ-Al2O3 / MgO / C mixed powder is loaded into a graphite mold, heated to 1650-1750℃ in a nitrogen atmosphere at a rate of 10-30℃ / min and held for 90-150 min, and then cooled in the furnace to obtain MgAlON powder containing a small amount of residual carbon. The cooling rate is 20-30℃ / min.

[0044] (3) MgAlON powder containing a small amount of residual carbon is kept at 600-700℃ for 3-5 h in air atmosphere to obtain pure phase MgAlON powder with an O / N value (atomic ratio) of 9.5-12.0.

[0045] (4) Add 0.3 wt.% CaCO3 as a sintering aid to pure phase MgAlON powder, use silicon nitride balls as grinding media and anhydrous ethanol as liquid phase medium, and ball mill at 150-210 rpm for 18-30 h on a planetary ball mill to obtain slurry. After drying and granulation, MgAlON / CaCO3 mixed powder with high sintering activity is obtained.

[0046] (5) The MgAlON / CaCO3 mixed powder is preformed under unidirectional pressure at 30-50 MPa and then cold isostatically pressed at 100-180 MPa to obtain the blank.

[0047] (6) Place the green body in a carbon furnace and heat it to 1860-1900℃ in a nitrogen atmosphere at a rate of 10-30℃ / min. Hold the temperature for 120-180 min and cool it in the furnace to obtain MgAlON ceramic.

[0048] (7) The obtained MgAlON ceramic is ground and polished to obtain MgAlON transparent ceramic.

[0049] Example 1

[0050] The raw material powders were weighed separately as follows: 86.2 wt.% γ-Al2O3 (average particle size 20 nm, purity 99.99%), 8.6 wt.% MgO (average particle size 81.4 nm, obtained by calcining Mg(OH)2 powder with purity 99.99% at 600℃ for 60 min in air atmosphere), and 5.2 wt.% carbon black (average particle size 15 nm, purity 99.0%). After being mixed with anhydrous ethanol, the mixture was ball-milled at 170 rpm for 24 h on a planetary ball mill using silicon nitride balls as the grinding medium. The resulting slurry was dried and granulated to obtain γ-Al2O3 / MgO / C mixed powder. Figure 1 The XRD patterns of the raw materials γ-Al2O3 and MgO powders are shown. Figure 2 SEM images of γ-Al2O3, MgO, carbon black powder, and γ-Al2O3 / MgO / C mixed powder.

[0051] The γ-Al₂O₃ / MgO / C mixed powder was placed in a graphite mold and then in an atmosphere sintering furnace. Under a nitrogen atmosphere, the temperature was increased to 1700℃ at 10℃ / min and held for 90 min, followed by a decrease at 30℃ / min to obtain MgAlON powder. The MgAlON powder was then held in air at 640℃ for 4 h to remove residual carbon, yielding pure-phase MgAlON powder with an O / N ratio (atomic ratio) of 11.39 and a nitrogen content of 1.98 wt.%. Figure 3 The XRD pattern of the synthesized powder shows that it is a pure phase MgAlON powder. Figure 4 The SEM image of the synthesized MgAlON powder shows that it contains a large number of small particles.

[0052] 0.3 wt.% CaCO3 was added as a sintering aid to the synthesized MgAlON powder. The powder was ball-milled at 170 rpm for 24 h on a planetary ball mill with silicon nitride balls as the grinding medium and anhydrous ethanol as the dispersion medium. The resulting slurry was dried and granulated to obtain MgAlON powder with finer particles and mixed with the sintering aid. Figure 5 The SEM image of the MgAlON powder after ball milling shows that the large particle size of the MgAlON powder after ball milling is significantly smaller than that before ball milling, and the powder dispersion is better. Figure 6 The particle size distribution diagram of MgAlON powder after ball milling shows that the particle size distribution range of MgAlON powder after ball milling is 0.15~8.0 μm, D 50 It is 0.87 μm.

[0053] The ball-milled MgAlON powder was first pre-formed under unidirectional pressure at 50 MPa, and then cold isostatically pressed at 120 MPa to obtain a green body. The green body was then placed in a graphite mold and sintered in a high-temperature furnace. Under a nitrogen atmosphere, the temperature was increased to 1880℃ at a rate of 15℃ / min and held for 150 min. After furnace cooling, the sample was ground and polished on both sides to obtain transparent MgAlON ceramic. The prepared transparent MgAlON ceramic had a relative density of 99.45%, indicating high density. Figure 7 The transmittance curve and sample photograph of the MgAlON transparent ceramic show that the prepared MgAlON ceramic has good light transmittance, with a maximum transmittance of 82.4%.

[0054] Example 2

[0055] The difference between Example 2 and Example 1 is that the holding time for the carbothermic reduction synthesis of MgAlON powder is 120 min, and the O / N ratio (atomic ratio) of the obtained pure phase MgAlON powder is 11.00, with a nitrogen content of 2.13 wt.% (XRD pattern of pure phase MgAlON powder can be found in...). Figure 3 Microscopic morphology Figure 4 ). Figure 5 and Figure 6 The images show the morphology and particle size distribution of the ball-milled MgAlON powder. It can be seen that the MgAlON powder has good dispersibility, with a particle size distribution range of 0.13~7.0 μm. 50 The transmittance is 0.96 μm. The relative density of the MgAlON transparent ceramic prepared by pressureless sintering is 99.43%. The transmittance curve and sample photographs are shown below. Figure 7 As can be seen, the transmittance is 82.1%.

[0056] Example 3

[0057] The difference between Example 3 and Example 1 is that the holding time for the carbothermic reduction synthesis of MgAlON powder is 150 min, and the O / N value of the obtained pure phase MgAlON powder is 9.52, with a nitrogen content of 2.53 wt.% (XRD pattern of pure phase MgAlON powder can be found in...). Figure 3 Microscopic morphology Figure 4 ). Figure 5 and Figure 6 The images show the morphology and particle size distribution of MgAlON powder after ball milling. It can be seen that the powder has good dispersibility after ball milling, with a particle size distribution range of 0.13-8.0 μm. 50 The relative density of the MgAlON transparent ceramic prepared by pressureless sintering is 99.30%. The transmittance curve and sample photographs are shown below. Figure 7 As can be seen, the transmittance is 80.9%.

[0058] Example 4

[0059] The difference between Example 4 and Example 1 is that the synthesis temperature of the carbothermic reduction synthesis of MgAlON powder was 1720℃, and the holding time was 120 min. The O / N ratio (atomic ratio) of the obtained pure phase MgAlON powder was 9.64, and the nitrogen content was 2.39 wt.% (XRD pattern of pure phase MgAlON powder can be found in...). Figure 3 Microscopic morphology Figure 4 ). Figure 5 and Figure 6 The images show the morphology and particle size distribution of MgAlON powder after ball milling. It can be seen that the powder has good dispersibility after ball milling, with a particle size distribution range of 0.07-8.0 μm. 50The relative density of the MgAlON transparent ceramic prepared by pressureless sintering is 99.19%. The transmittance curve and sample photographs are shown below. Figure 7 As can be seen, the transmittance is 81.0%.

[0060] Comparative Example 1

[0061] The difference between Comparative Example 1 and Examples 1-4 is that the MgAlON powder was synthesized at 1600℃ for 120 min, with an O / N ratio (atomic ratio) of 14.20 and a nitrogen content of 1.64 wt.% (XRD pattern of pure phase MgAlON powder can be found in...). Figure 8 Microscopic morphology Figure 9 ). Figure 10 and Figure 11 The images show the morphology and particle size distribution of MgAlON powder after ball milling. It can be seen that the powder has good dispersibility after ball milling, with a particle size distribution range of 0.1-8.0 μm. 50 The relative density of the MgAlON transparent ceramic prepared by pressureless sintering is 99.23%. The transmittance curve and sample photographs are shown below. Figure 12 It can be seen that its transmittance is 76.1%.

[0062] Comparative Example 2

[0063] The difference between Comparative Example 2 and Examples 1-4 is that the heating rate was 5℃ / min during the synthesis of MgAlON powder, and the mixed powder was synthesized by holding at 1600℃ for 120 min. Its O / N ratio (atomic ratio) was 6.77, and its nitrogen content was 2.07 wt.% (XRD pattern of pure phase MgAlON powder can be found in...). Figure 8 Microscopic morphology Figure 9 ). Figure 10 and Figure 11 The images show the morphology and particle size distribution of MgAlON powder after ball milling. It can be seen that the powder has good dispersibility after ball milling, with a particle size distribution range of 0.09-8.0 μm. 50 The transmittance is 0.71 μm. The relative density of the MgAlON transparent ceramic prepared by pressureless sintering is 99.07%. The transmittance curve and sample photographs are shown below. Figure 12 As can be seen, its transmittance is 69.9%.

Claims

1. A method for preparing MgAlON ceramics with high infrared transmittance, characterized in that: 86.2-86.6 wt.% γ-Al2O3, 8.6 wt.% MgO and 4.8-5.2 wt.% carbon black were ball-milled and mixed, and then pure-phase MgAlON powder with an O / N value of 9.5-12.0 was synthesized by carbothermic reduction nitriding in a nitrogen atmosphere. 0.3 wt.% CaCO3 was added to the pure-phase MgAlON powder as a sintering aid, and after ball milling, MgAlON / CaCO3 mixed powder was obtained. The powder was then dry-pressed to prepare a green body. The green body was then sintered under a nitrogen atmosphere using a pressureless sintering method to prepare MgAlON ceramics with high infrared transmittance.

2. The method according to claim 1, characterized in that: The D of the MgAlON / CaCO3 mixed powder 50 The particle size ranges from 0.85 to 1.30 μm, with a particle size distribution range of 0.05 to 8.0 μm.

3. The method according to claim 1, characterized in that: The γ-Al2O3 is a nanoparticle with an average particle size ≤50nm; the carbon black is a nanoparticle with an average particle size ≤30nm.

4. The method according to claim 1, characterized in that: The MgO is a nanoparticle with an average particle size ≤100nm, obtained by calcining Mg(OH)2 powder with a purity ≥99.0% in air at 600-700℃ for 40-80min.

5. The method according to claim 1, characterized in that: The ball-milled and mixed γ-Al2O3, MgO and carbon black powder was loaded into a graphite mold, heated to 1650-1750℃ in a nitrogen atmosphere and held for 90-150 min, then cooled in the furnace and held at 600-700℃ in an air atmosphere for 3-5 h to obtain pure phase MgAlON powder. The heating rate was 10-30℃ / min and the cooling rate was 20-30℃ / min.

6. The method according to claim 1, characterized in that: The MgAlON / CaCO3 mixed powder is pre-formed under unidirectional pressure at 30-50MPa, and then cold isostatically pressed at 100-180MPa to obtain the green body.

7. The method according to claim 1, characterized in that: The green body is placed in a carbon furnace and heated to 1860-1900℃ in a nitrogen atmosphere at a rate of 10-30℃ / min. It is then held for 120-180 min and cooled in the furnace to obtain MgAlON transparent ceramic.

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

9. The method according to claim 1, characterized in that: The method includes a post-processing step: grinding and polishing the sintered MgAlON transparent 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 transparent ceramic has a relative density of ≥99.19% and an infrared transmittance of 80.0-82.4%.

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