A method for preparing high-transparency AlON ceramics by rapid pressureless sintering with the addition of nano Y2O3

Abstract

The present invention relates to a method for rapidly pressureless sintering to prepare high-transparency AlON ceramics by adding nano-Y2O3, belonging to the field of preparation of transparent ceramic materials. A method for rapidly pressureless sintering to prepare high-transparency AlON ceramics by adding nano-Y2O3. The nano-Y2O3 powder with a high specific surface area is added as a sintering aid to the pure-phase AlON powder, and the raw materials are mixed by ball milling. The mixed powder is prepared into AlON transparent ceramics with high transparency in a wide wavelength band by pressureless sintering. Among them, the nano-Y2O3 powder with a high specific surface area is obtained by calcining yttrium acetate powder after nodular graphite in air. This method only uses a general ball milling method to achieve uniform mixing of raw materials. The sintering uses pressureless sintering technology, with easy availability of equipment and easy implementation of technology. The heat preservation time in the sintering process is short, with good energy-saving effect, high efficiency, low preparation cost, and easy industrialization.

Description

Technical Field

[0001] The present invention relates to a method for rapidly pressureless sintering high-transparency AlON ceramics by adding nano Y2O3, belonging to the field of preparation of transparent ceramic materials. Background Art

[0002] AlON transparent ceramics have the characteristics of high transmittance and wide wave-transmitting range, and at the same time also have excellent mechanical properties (high strength and high hardness). They are preferred window materials for high-temperature infrared windows, transparent armors, explosion-proof windows, etc., and have broad application prospects in both military and civilian fields.

[0003] Since pressureless sintering has low cost and unique advantages in preparing large-size and complex-shaped components, it has become the preferred method for preparing AlON transparent ceramics. In order to expel pores through sintering to obtain high density and high transmittance, adding sintering aids such as Y2O3, MgO, and La2O3 is a very commonly used and effective means. Among them, Y2O3 is widely used and has achieved good densification effects. It can be used alone as a sintering aid or in combination with other sintering aids. However, at present, there is still a problem that AlON ceramics with high transmittance (transmittance ≥ 80%) in the visible to mid-infrared bands prepared by pressureless sintering need to be kept at high temperature for a long time (≥ 7h).

[0004] In recent years, the research on preparing transparent ceramics by pressureless sintering of AlON powder mainly includes aspects such as the regulation of AlON powder particle size, the optimization of sintering aids and their doping amounts, the forming method, and the sintering process. Among them, when Y2O3 is used as a sintering aid, the research results on the phase evolution and microstructure evolution of ceramics during sintering show that at 1400 - 1600 °C during the heating process, Y2O3 will promote the decomposition of AlON, and the higher the doping amount of Y2O3, the easier it is to decompose AlON at lower temperature conditions to generate more α-Al2O3 and AlN, resulting in premature agglomeration / coarsening of particles, which has an adverse effect on the subsequent densification sintering (Y.C. Shan, et al., J. Eur. Ceram. Soc. 36 (2016) 671–678; Y.C. Shan, et al., J. Eur. Ceram. Soc. 40 (2020) 3906–3917). Thus, it can be seen that the Y2O3 sintering aid needs to be evenly distributed in the AlON powder to avoid local enrichment, thereby reducing the phenomenon of too high local Y2O3 doping amount and too low overall doping amount, reducing the decomposition amount of AlON, avoiding premature aggregation / coarsening of particles in the early stage of sintering, and further providing good microstructural conditions and sufficient sintering driving force for the subsequent densification sintering.

[0005] Patent 202111293128.8 reported a method for preparing AlON transparent ceramics by adding Y2O3 sintering aids using the chemical precipitation method. First, the water-resistant treated AlON powder was dispersed in a yttrium nitrate solution to make a slurry, and then an excessive precipitant was dropped into the slurry to precipitate Y 3+ and coat it on the surface of the AlON powder. The AlON ceramic prepared by pressureless sintering the obtained powder at 1880 °C for 12 h had a transmittance of 77% at 400 nm. Min et al. (P. Min, et al., J. Eur. Ceram. Soc. 43 (2023) 1663-1670) also used the chemical precipitation method to add Y2O3 sintering aids and compared it with AlON prepared by adding Y2O3 sintering aids through ball milling and mixing. The transmittances of the ceramics prepared by the two different Y2O3 addition methods at 400 nm were 82.2% and 76% respectively when the powders were held at 1950 °C for 10 h. These research results further illustrate that the uniform distribution of Y2O3 in the AlON powder is very important for improving the light transmittance of its ceramics. Therefore, it is necessary to seek a simpler and more feasible Y2O3 addition method to uniformly mix the Y2O3 sintering aids with the AlON powder, improve the light transmittance of its ceramics while reducing the process requirements, which is very necessary for promoting the wide application of AlON transparent ceramics. Summary of the Invention

[0006] The purpose of the present invention is to provide a method for preparing high-light-transmittance AlON ceramics by adding nano-Y2O3 and rapid pressureless sintering. Specifically, nano-Y2O3 powder with a high specific surface area is prepared by calcining yttrium acetate after ball milling. Using the nano-Y2O3 powder as a sintering aid, the AlON and Y2O3 powders are uniformly mixed by ball milling, and AlON transparent ceramics are prepared by a pressureless sintering method under a nitrogen atmosphere. On the basis of ball milling and refining the particle size of yttrium acetate, a large amount of gas is released during the calcination process of yttrium acetate to prepare nano-Y2O3 powder with a high specific surface area, and then AlON and Y2O3 are uniformly mixed by simple ball milling, effectively reducing the local enrichment of Y2O3 in the mixed powder, thereby reducing the large decomposition of AlON caused by excessive local Y2O3, controlling the content of α-Al2O3 generated by the decomposition of AlON in the sample, and thus inhibiting the agglomeration / coarsening of particles in the early stage of sintering, creating good microstructural conditions for later densification sintering. At the same time, the reduction of local enrichment of Y2O3 also increases the overall effective sintering aid content of the sample, providing a more sufficient driving force for sintering. Therefore, under the dual effects of controlling the agglomeration / coarsening degree in the early stage of sample sintering and increasing the overall effective sintering aid content, high-density and small-pore-size high-light-property AlON ceramics are prepared within a short holding time. This ceramic has a high transmittance from the visible to the mid-infrared band. This method has high efficiency, good energy-saving effect, low cost, and a simple preparation process, and is easy to realize large-scale production.

[0007] A method for preparing high-transparency AlON ceramics by rapid pressureless sintering with the addition of nano-Y2O3. The nano-Y2O3 powder with a high specific surface area is added as a sintering aid to the pure-phase AlON powder. The raw materials are mixed by ball milling, and the mixed powder is prepared into an AlON transparent ceramic with high transparency in a wide wavelength band by pressureless sintering. Among them, the nano-Y2O3 powder is obtained by calcining the ball-milled yttrium acetate powder in air.

[0008] In the above technical solution, the nano-Y2O3 powder is a pure-phase Y2O3 powder with a high specific surface area, the particle size is <60 nm, the average particle size is <35 nm, the number of particles >40 nm is <20%, and the specific surface area is 30-60 m 2 / g.

[0009] Furthermore, the nano-Y2O3 powder with a high specific surface area is prepared by the following method: The yttrium acetate Y(CH3COO)3·4H2O powder is first ball-milled and then dried. The dried yttrium acetate powder is calcined in a muffle furnace under an air atmosphere, heated to 650-750 °C at a rate of 5-30 °C / min and held for 4-8 h to obtain a pure-phase Y2O3 powder.

[0010] Even further, the yttrium acetate used is ball-milled in n-butanol with silicon nitride balls as grinding media at 150-200 rpm for 12-30 h to obtain a slurry.

[0011] In the above technical solution, the yttrium acetate powder used is Y(CH3COO)3·4H2O, with a purity ≥99.9%, and the AlON powder is pure-phase AlON, with a purity ≥99.9%.

[0012] In the above technical solution, the AlON and Y2O3 powders are first ball-milled at 170 rpm for 10-16 h, and then continue to be ball-milled at 190-230 rpm for 15-22 h. The particle size distribution range of the obtained AlON / Y2O3 mixed powder is 0.1-5.0 μm, and D 50 is 0.9-1.3 μm. Among them, the doping amount of Y2O3 is 0.2-0.5% of the mass of the AlON powder.

[0013] In the above technical solution, the heating rate of the pressureless sintering is 10-50 °C / min, the sintering temperature is 1840-1900 °C, and the holding time is 1.5-3.5 h.

[0014] A preferred technical solution of the present invention is:

[0015] A method for preparing high-transparency AlON ceramics by rapid pressureless sintering with the addition of nano-Y2O3. The method includes the following technological steps:

[0016] ① Preparation of nano-Y2O3 powder: Weigh yttrium acetate powder, first ball-mill and refine yttrium acetate, and then calcine it in air to obtain nano-Y2O3 powder with a high specific surface area;

[0017] ② Raw material mixing: Weigh AlON powder and the Y2O3 powder obtained in step ①, place the two in a ball-mill tank, use silicon nitride balls as grinding media to carry out ball-milling and mixing in absolute ethanol to obtain a slurry, and obtain the AlON / Y2O3 mixed powder after drying and granulation;

[0018] ③ Green body forming: Cold isostatically press the AlON / Y2O3 mixed powder obtained in step ② to obtain a green body;

[0019] ④ Pressureless sintering: Put the green body obtained in step ③ into a vacuum atmosphere sintering furnace and carry out pressureless sintering in nitrogen to prepare AlON ceramics.

[0020] Preferably, the cold isostatic pressing in step ③ is completed under the condition of 110 - 130 MPa.

[0021] Preferably, the method for rapidly preparing the AlON transparent ceramic includes a post-treatment step: grinding and polishing the AlON transparent ceramic obtained in step ④.

[0022] Another object of the present invention is to provide an AlON transparent ceramic prepared by the above method.

[0023] The AlON transparent ceramic obtained by the present invention has a transmittance ≥ 80% in the range of 380 - 4150 nm and HV > 17 GPa.

[0024] The beneficial effects of the present invention are as follows: In the method of the present invention, nano-Y2O3 with a high specific surface area is used as a sintering aid, and its uniform mixing with AlON powder is realized through simple ball-milling. While reducing the local enrichment of Y2O3, the overall effective doping amount of the sintering aid in the sample is increased. It not only controls the decomposition degree of AlON, thereby avoiding premature agglomeration / coarsening of particles in the early stage of sintering by reducing the content of α-Al2O3 generated by the decomposition of AlON, but also improves the driving force for densification sintering of the sample. Furthermore, high-transparency AlON transparent ceramics are rapidly prepared by a pressureless sintering method under the condition of a short holding time. The holding time of the ceramic preparation process is short, only 2.5 h (the holding time of high-transparency AlON ceramics in the existing literature needs to be ≥ 7 h). Moreover, the prepared ceramic has a wide wave-transmitting range and a high transmittance, with a transmittance reaching more than 80% in the range of 380 - 4150 nm. At the same time, it also has the characteristics of high hardness, HV > 17 GPa. This method only uses a general ball-milling method to achieve uniform mixing of raw materials, and the sintering uses a pressureless sintering technology. The equipment is easy to obtain, the technology is easy to implement, the doping amount of the sintering aid is controllable, the holding time of the sintering process is short, the energy-saving effect is good, the efficiency is high, the preparation cost is low, and it is easy to realize industrialization. Description of the Drawings

[0025] Figure 1 Performance of Y2O3 powder in Example 1 and Comparative Example 1: (a) XRD pattern; (b) SEM image of Y2O3 powder in Comparative Example 1; (c) SEM image of Y2O3 powder in Example 1.

[0026] Figure 2 TEM image of the nano Y2O3 powder prepared in Example 1.

[0027] Figure 3 SEM images and Y element EDS distribution maps of the ball-milled AlON / Y2O3 mixed powder in Example 1 and Comparative Example 1: (a) and (b) Example 1; (c) and (d) Comparative Example 1.

[0028] Figure 4 Transmittance curves and sample photos of the AlON transparent ceramics prepared in Example 1 and Comparative Example 1.

[0029] Figure 5 Fracture morphologies of the AlON transparent ceramics prepared in Example 1 and Comparative Example 1.

[0030] Figure 6 α-Al2O3 content in the samples during the heating process of the AlON transparent ceramics sintered in Example 1 and Comparative Example 1.

[0031] Figure 7 Microstructural evolution process of the samples during the heating process of the AlON transparent ceramics sintered in Example 1 and Comparative Example 1.

[0032] Figure 8 Densification process curves of the AlON transparent ceramics prepared in Example 1 and Comparative Example 1. Detailed implementation manners

[0033] The following non-limiting examples can enable those of ordinary skill in the art to more comprehensively understand the present invention, but do not limit the present invention in any way.

[0034] 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.

[0035] A method for rapidly pressureless sintering high-transparency AlON ceramics by adding nano Y2O3 includes the following process steps:

[0036] ① Preparation of nano Y2O3 powder: Weigh yttrium acetate powder, first ball-mill and refine yttrium acetate, and then calcine it in air to obtain nano Y2O3 powder with a high specific surface area.

[0037] ② Raw material mixing: Weigh the AlON powder and the Y2O3 powder obtained in step ①, place the two in a ball milling tank, use silicon nitride balls as grinding media to carry out ball milling and mixing in anhydrous ethanol to obtain a slurry, dry and granulate it to obtain the AlON / Y2O3 mixed powder.

[0038] ③ Green body forming: Cold isostatically press the AlON / Y2O3 mixed powder obtained in step ② to obtain a green body.

[0039] ④ Pressureless sintering: Put the green body obtained in step ③ into a vacuum atmosphere sintering furnace and carry out pressureless sintering in nitrogen to prepare AlON ceramics.

[0040] ⑤ Processing: Grind and polish the AlON transparent ceramic.

[0041] Step ① of the present invention is preferably carried out according to the following method: The yttrium acetate powder used in step ① is Y(CH3COO)3·4H2O with a purity of ≥99.9%, and the AlON powder is pure phase AlON with a purity of ≥99.9%; Yttrium acetate is first ball milled in n-butanol with silicon nitride balls as grinding media, ball milled at 150 - 200 rpm for 12 - 30 h to obtain a slurry, the slurry is dried and then placed in an alumina crucible, and calcined in a muffle furnace, heated to 650 - 750 °C at a rate of 5 - 30 °C / min and held for 4 - 8 h to obtain pure phase Y2O3 powder, with a particle size <60 nm, an average particle size <35 nm, the number of particles >40 nm <20%, and a specific surface area of 30 - 60 m 2 / g.

[0042] The doping amount of Y2O3 in step ② of the present invention is 0.2 - 0.5% of the mass of the AlON powder; the AlON and Y2O3 powders are first ball milled at 170 rpm for 10 - 16 h, and then continue to be ball milled at 190 - 230 rpm for 15 - 22 h. The particle size distribution range of the obtained AlON / Y2O3 mixed powder is 0.1 - 5.0 μm, and D 50 is 0.9 - 1.3 μm.

[0043] The cold isostatic pressing forming in step ③ of the present invention is completed under the condition of 110 - 130 MPa.

[0044] The heating rate in step ④ of the present invention is 10 - 50 °C / min, the sintering temperature is 1840 - 1900 °C, and the holding time is 1.5 - 3.5 h.

[0045] In step ⑤ of the present invention, both sides of the AlON transparent ceramic are ground and polished.

[0046] Example 1

[0047] Yttrium acetate with a purity of 99.99% was ball-milled in n-butanol at 170 rpm for 24 h. Then, the milled powder was placed in an alumina crucible and heated in air at a rate of 10 °C / min to 700 °C and held for 6 h to obtain pure-phase Y2O3 powder. The particle size of the powder was 8 - 60 nm, the average particle size was 30 nm, the number of particles larger than 40 nm was 18%, and the specific surface area was 35.77 m 2 / g. The phase composition and microstructure of the prepared powder are shown in the appendix Figure 1 (a), (c) and Figure 2 .

[0048] The above-mentioned Y2O3 powder and AlON powder were weighed according to the Y2O3 doping amount of 0.3 wt.%. Using silicon nitride balls as grinding media, they were first ball-milled in absolute ethanol at 170 rpm for 12 h, then the rotation speed was increased to 210 rpm, and ball-milling was continued for 18 h. The particle size distribution range of the obtained AlON / Y2O3 powder after ball-milling was 0.3 - 4.2 μm, and D 50 was 1.1 μm. The morphology and Y element distribution map are shown in the appendix Figure 3 , indicating that the Y2O3 sintering aid was uniformly distributed in the mixed powder.

[0049] The ball-milled AlON / Y2O3 mixed powder was cold isostatically pressed under 120 MPa to obtain a green body; the green body was placed in a graphite crucible and heated in a nitrogen atmosphere at a rate of 20 °C / min and held at 1880 °C for 2.5 h to obtain AlON transparent ceramics. The relative density of the prepared AlON transparent ceramics was 99.67%. Its two sides were ground and polished to a thickness of 2 mm, and the transmittance at 400 nm was measured to be 80%, and the maximum infrared transmittance was 82% (at a wavelength of 3750 nm). Figure 4 are the transmittance curve and sample photo of the prepared AlON transparent ceramics Figure 5 (a) is the fracture morphology of the prepared AlON transparent ceramics. Only a small number of small-sized pores (pore size of 340 nm) could be observed in the sample; Figure 6 is the α-Al2O3 content in the sample during the heating process, indicating that the α-Al2O3 content generated by the decomposition of AlON was low; Figure 7 is the evolution process of the microstructure of the sample during the heating process. No obvious agglomeration / coarsening phenomenon was observed in the sample; Figure 8 Its densification process curve shows that the overall densification sintering of the ceramics is good.

[0050] Comparative Example 1

[0051] In Comparative Example 1, according to the method of Example 1, the difference was that the Y2O3 sintering aid used was a pure-phase micron-sized lamellar powder with a specific surface area of 15.45 m 2 / g, as shown in Figure 1(a) and (b)). There is a phenomenon of local enrichment of Y2O3 after ball-milling and mixing of AlON and Y2O3 powders, as shown in Figure 3 (c) and (d). The relative density of the prepared AlON transparent ceramic is 99.33%, and the transmittance curve and sample photo are shown in Figure 4 . Its maximum infrared transmittance is 80%, and its transmittance at 400 nm is 67%. Figure 5 In the fracture morphology of, a relatively large number of pores with a size of up to 980 nm can be seen; as Figure 6 shown, the content of α-Al2O3 in this sample is relatively high during the heating process, resulting in local particle aggregation / coarsening ( Figure 7 ) at the early stage of sintering, and the densification process is relatively slow ( Figure 8 ).

Claims

1. A method for preparing high-transparency AlON ceramics by rapid pressureless sintering with the addition of nano Y2O3, characterized in that: The nano-Y2O3 powder with high specific surface area is added to the pure-phase AlON powder as a sintering aid, and the raw materials are mixed by ball milling. The particle size distribution range of the AlON / Y2O3 mixed powder is 0.1 - 5.0 μm, and D 50 is 0.9 - 1.3 μm. Among them, the doping amount of Y2O3 is 0.2 - 0.5% of the mass of the AlON powder. The mixed powder is prepared into an AlON transparent ceramic with high light transmittance in a wide wavelength band by a pressureless sintering method. Among them, the nano-Y2O3 powder with high specific surface area is a pure-phase Y2O3 powder, the particle size < 60 nm, the average particle size < 35 nm, the number of particles > 40 nm < 20%, and the specific surface area is 30 - 60 m 2 / g, which is specifically prepared by the following method: The yttrium acetate Y(CH3COO)3·4H2O powder is ball-milled in n-butanol with silicon nitride balls as the grinding media at 150 - 200 rpm for 12 - 30 h and then dried. The dried yttrium acetate powder is calcined in a muffle furnace under an air atmosphere, heated to 650 - 750 °C at a rate of 5 - 30 °C / min and held for 4 - 8 h to obtain a pure-phase Y2O3 powder.

2. The method according to claim 1, wherein: The AlON and Y2O3 powders are first ball-milled at 170 rpm for 10 - 16 h and then continue to be ball-milled at 190 - 230 rpm for 15 - 22 h.

3. The method according to claim 1, wherein: The heating rate of the pressureless sintering is 10 - 50 °C / min, the sintering temperature is 1840 - 1900 °C, and the holding time is 1.5 - 3.5 h.

4. The method according to claim 1, characterized in that: The method includes the following technological steps: ① Preparation of nano-Y2O3 powder: Weigh the yttrium acetate powder, first ball-mill and refine the yttrium acetate, and then calcine it in air to obtain nano-Y2O3 powder with a high specific surface area; ② Raw material mixing: Weigh the AlON powder and the Y2O3 powder obtained in step ①, place the two in a ball-milling tank, and ball-mill and mix them in absolute ethanol with silicon nitride balls as the grinding media to obtain a slurry. After drying and granulating, an AlON / Y2O3 mixed powder is obtained; ③ Green body forming: Cold isostatically press the AlON / Y2O3 mixed powder obtained in step ② to form a green body; ④ Pressureless sintering: Put the green body obtained in step ③ into a vacuum atmosphere sintering furnace and sinter it without pressure in nitrogen to prepare AlON ceramics.

5. The method according to claim 4, wherein: The cold isostatic pressing in step ③ is completed under the condition of 110 - 130 MPa.

6. The method according to claim 4, characterized in that: The method for rapidly preparing the AlON transparent ceramic at low temperature includes a post-treatment step: grinding and polishing the AlON transparent ceramic obtained in step ④.

7. An AlON transparent ceramic prepared by the method according to claim 1, characterized in that: The transmittance is ≥80% at 380 - 4150 nm, and HV > 17 GPa.

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