High-transmittance AlON transparent ceramic and preparation method thereof

Abstract

The invention relates to a high-transmittance AlON transparent ceramic and a preparation method thereof, and belongs to the field of transparent ceramic materials. The invention relates to a preparation method of high-transmittance AlON transparent ceramic, AlON powder is taken as a raw material, a sintering aid is added, ball-milled mixed powder is subjected to dry-pressing molding to prepare a green body, firstly, an AlON presintered body is prepared by adopting an ultrafast high-temperature sintering method, then, the AlON transparent ceramic is prepared by adopting a pressureless sintering method, the ultrafast high-temperature sintering is carried out in a nitrogen environment, the heating rate is 80-120 DEG C / s, and the sintering time is 2-3 hours; the sintering temperature is 1800-1900 DEG C, the temperature is reduced to the room temperature after heat preservation is conducted for 2-3 min, and the cooling time is 1t; and after 0.5 min, a pre-sintered body is obtained. The method is simple in process, the whole sintering process is short in time, high in efficiency, good in energy-saving effect and low in cost, the prepared AlON transparent ceramic is high in transmittance and wide in wave transmission range of the high transmittance, meanwhile, the AlON transparent ceramic has ultrahigh hardness, and the product performance and the technological process are suitable for industrial production.

Description

TECHNICAL FIELD

[0001] The application relates to high-transmittance AlON transparent ceramics and a preparation method thereof, in particular to a method for preparing high-transmittance AlON ceramics based on ultrafast pre-sintering and belongs to the field of transparent ceramic materials. BACKGROUND

[0002] AlON transparent ceramics have excellent light transmittance and good mechanical properties, can be prepared by pressureless sintering (PS), are known as one of the most promising transparent ceramic materials in the 21st century, and can be widely used in infrared windows, transparent armors and the like.

[0003] Pores are one of the main factors causing the reduction of the transmittance of AlON transparent ceramics. Therefore, one important goal of sintering for preparing high-light-transmittance AlON ceramics is to reduce the porosity of the ceramics, that is, to improve the relative density. However, the complex phase transformation and microstructure evolution process existing in the densification process of AlON makes it difficult to sinter, and a relatively high density can be obtained only by keeping the temperature at a high temperature for a long time (7-30 h). This not only causes the excessive growth of AlON grains, with a grain size generally greater than 150 µm, leading to the reduction of mechanical properties, but also inevitably brings about problems such as high risk, high energy consumption, low efficiency and high cost.

[0004] In recent years, through technical means such as adjusting the particle size of AlON powder, optimizing the sintering aid and its dosage, optimizing the distribution of the sintering aid, improving the density of the green body and improving the sintering process, the holding time for preparing AlON transparent ceramics by pressureless sintering has been shortened, but it still needs to be kept for 2.5-6 h. By adding nano-Y2O3 as a sintering aid, the distribution uniformity of Y 3+ in AlON can weaken the particle agglomeration / coarsening phenomenon in the initial sintering stage, and further promote the densification process of AlON ceramics, so that the holding time for high-light-transmittance AlON ceramics is shortened to 2.5 h (H.R. Guo, et al., J. Eur. Ceram. Soc. 44 (2024) 6013-6023). However, due to the high sintering temperature and long holding time, the grain size of the obtained ceramics is still not small, and the average grain size is 91.6 µm. J. Eur. Ceram. Soc. 44 (2024)6013-6023). However, due to the high sintering temperature and long holding time, the grain size of the obtained ceramics is still not small, and the average grain size is 91.6 µm. 3+ has the effect of promoting the grain boundary migration of AlON, so the grain size of the obtained ceramics is still not small, and the average grain size is 91.6 µm.

[0005] Therefore, the preparation of high-light-transmittance and high-hardness AlON ceramics needs to seek new technical approaches to limit the growth of AlON grains while obtaining high density. The ultrafast high-temperature sintering (UHS) technology provides a new way to solve the contradiction between densification and grain growth. The heating rate of UHS can reach 10 3 ~10 4℃ / min, the ceramic green body can be heated to the sintering temperature in a few seconds, and a higher density can be obtained. The extremely fast heating rate of UHS can effectively limit the grain coarsening on the one hand, and also make the non-equilibrium grain boundary remain to the temperature dominated by densification (Z.H. Guo, et al., Acta Mater. 282 (2025)120471), thereby promoting the sintering densification of the ceramic. However, as a new ceramic sintering technology, the UHS equipment currently allows a holding time of not more than 3 min under high temperature conditions. It can be seen that it is difficult to prepare transparent ceramics only by UHS.

[0006] For the preparation of AlON transparent ceramics, the extremely fast heating rate of UHS makes it possible to avoid the phase transition of AlON and the adverse microstructure evolution during the heating process. Based on the UHS-prepared pre-sintered body, combined with the traditional pressureless sintering method, it is expected to further shorten the preparation time of high-transmittance AlON ceramics, thereby limiting the grain growth, and obtaining high transmittance and good mechanical properties at the same time. SUMMARY

[0007] The purpose of the present application is to provide a method for preparing high-transmittance AlON ceramics based on ultrafast pre-sintering, specifically using AlON powder as raw material, adding nano Y2O3 powder as sintering aid, and using the mixed powder to prepare a green body. The green body is first prepared into an AlON pre-sintered body by using an ultrafast high-temperature sintering technology, and then high-transmittance AlON transparent ceramics are prepared by a pressureless sintering method. The ultrafast high-temperature sintering technology has an extremely fast heating rate, and the sample can be heated to the sintering temperature within 20 s. The prepared pre-sintered body has smaller pore size, higher density and smaller grain size. Based on this, the density of the AlON ceramic is further improved in a shorter holding time through subsequent pressureless sintering, thereby enabling the preparation of high-transmittance AlON ceramics with high light transmittance in a wide wavelength range. Moreover, due to the short holding time during the preparation process, the grain growth of AlON is effectively controlled, and the prepared high-transmittance AlON ceramic also has the characteristics of small grain size and high hardness. The whole sintering process of this method is short in duration, high in efficiency, good in energy-saving effect, low in cost, and simple in operation process, and easy to realize large-scale production.

[0008] A method for preparing high-transmittance AlON transparent ceramics, using AlON powder as raw material, adding sintering aid, and dry pressing the mixed powder after ball milling to prepare a green body. First, an AlON pre-sintered body is prepared by using an ultrafast high-temperature sintering method, and then an AlON transparent ceramic is prepared by a pressureless sintering method, The ultrafast high-temperature sintering is performed in a nitrogen environment, the heating rate is 80-120 DEG C / s, the sintering temperature is 1800-1900 DEG C, the temperature is kept for 2-3 min, and then the temperature is reduced to room temperature, and the cooling time is less than 0.5 min, so as to obtain the pre-sintered body.

[0009] The ultrafast high-temperature sintering is performed in a nitrogen environment, the heating rate is 100-120 DEG C / s, the sintering temperature is 1850-1900 DEG C, the temperature is kept for 2 min, and then the temperature is reduced to room temperature, and the cooling time is less than 0.5 min, so as to obtain the pre-sintered body.

[0010] Further, the cooling time is preferably less than 10 s.

[0011] In the technical scheme, the pre-sintered body is subjected to pressureless sintering in nitrogen, the heating rate is 5-50 DEG C / min, the sintering temperature is 1850-1900 DEG C, and the holding time is 1.5-2.5 h.

[0012] In the technical scheme, the sintering aid is nano Y2O3 powder, and the average particle size is 20-60 nm.

[0013] In the technical scheme, the doping amount of the Y2O3 powder is 0.05-0.30% of the mass of the AlON powder.

[0014] In the technical scheme, the AlON and the sintering aid powder are mixed by ball milling in anhydrous ethanol with silicon nitride balls as the grinding medium, and the median particle size of the mixed powder after ball milling is 0.3-0.7 um.

[0015] In the technical scheme, the mixed powder of the AlON and the sintering aid is first dry-pressed at 10-60 MPa to form a preform, and then cold isostatic pressed at 100-150 MPa to form a green body.

[0016] In the technical scheme, further, the obtained AlON transparent ceramic is ground and polished.

[0017] Another object of the application is to provide an AlON transparent ceramic prepared by the above method.

[0018] Further, the AlON transparent ceramic has a density of 99.70%-99.71%, an average grain size of 42.02-47.06 um, a transmittance of greater than or equal to 80% in a wide wavelength range of 380-4630 nm, and a Vickers hardness of 19.57±0.23-19.79±0.21 GPa.

[0019] Furthermore, the maximum transmittance of the AlON transparent ceramic at a wavelength of 3750 nm is 84.72% to 84.77%, and the transmittance at a wavelength of 400 nm is 80.01% to 80.63%.

[0020] The beneficial effects of the present invention are as follows: the present invention adopts ultrafast high-temperature sintering technology to prepare AlON pre-calcined bodies with high density and small-sized grain characteristics in an extremely short time, and then combines it with the traditional pressureless sintering method to further improve the density of AlON ceramics through a shorter holding time, thereby obtaining high light transmittance, while limiting grain growth, so that the prepared AlON transparent ceramics have the characteristics of high hardness. The ceramic sintering process takes a short time, wherein the ultrafast high-temperature pre-sintering heating rate is extremely fast, which inhibits the phase transformation and grain growth before densification occurs, and at the same time retains the non-equilibrium grain boundaries to the high-temperature densification stage, thereby greatly promoting the densification process. After 2 to 3 minutes of holding, a high-density pre-calcined body with fine grain size is obtained. Subsequently, the traditional pressureless sintering method is used to achieve an increase in density within a shorter holding time (1.5 to 2.5 hours), thereby realizing the preparation of AlON transparent ceramics with high transmittance and high hardness. The resulting AlON transparent ceramics not only have high transmittance (84.72-84.77%) and a wide high transmittance band (≥80%) (380-4630 nm), but also have small grain size (average grain size 42.02-47.06 μm) and extremely high hardness (HV range of 19.57±0.23-19.79±0.21 GPa). The method is simple, with a short sintering process, high efficiency, excellent energy conservation, and low cost. The prepared AlON transparent ceramics not only have high transmittance, but also have a wide high transmittance range and ultra-high hardness. The product performance and process are suitable for industrial production. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 This is the SEM image of the mixed powder of AlON and Y2O3 after ball milling in Example 1.

[0021] Figure 2 Fracture morphologies of the AlON calcined bodies and transparent ceramics prepared in Example 1, Example 2, and Comparative Example 1: (a) calcined body in Example 1; (b) transparent ceramic in Example 1; (c) transparent ceramic in Example 2; (d) transparent ceramic in Comparative Example 1.

[0022] Figure 3 The grain morphology and grain size distribution of the AlON calcined bodies prepared in Example 1 and Example 2: (a) grain morphology; (b) grain size distribution.

[0023] Figure 4 These are the transmittance curves and sample photos of the AlON transparent ceramics prepared in Example 1, Example 2 and Comparative Example 1.

[0024] Figure 5 Figures of grain morphology and grain size distribution of the AlON transparent ceramic prepared for Example 1, Example 2 and Comparative Example 1: (a) figure of grain morphology of Example 1; (b) figure of grain size distribution of Example 1; (c) figure of grain morphology of Example 2; (d) figure of grain size distribution of Example 2; (e) figure of grain morphology of Comparative Example 1; (f) figure of grain size distribution of Comparative Example 1. DETAILED DESCRIPTION

[0025] The following non-limiting examples can make the ordinary skilled in the art more fully understand the present application, but in no way limit the present application.

[0026] The test methods described in the following examples are all conventional methods unless otherwise specified; the reagents and materials described in the following examples are all commercially available unless otherwise specified.

[0027] A method for preparing high-transmittance AlON ceramic based on ultrafast pre-sintering, comprising the following process steps: (1) batching: AlON powder is weighed, Y2O3 powder is weighed according to 0.05-0.30% of the mass of the AlON powder, anhydrous ethanol is added, silicon nitride balls are used as grinding media, the mixed slurry after ball milling is dried and granulated to obtain AlON and Y2O3 mixed powder, wherein the AlON powder used is pure phase, and the chemical purity is >99.9%; the sintering aid is nano Y2O3 powder, the average particle size is 20-60 nm; the doping amount of Y2O3 is 0.05-0.30% of the mass of the AlON powder.

[0028] (2) forming: the mixed powder of AlON and Y2O3 obtained in step (1) is first pre-formed under pressure of 10-60 MPa in a steel mold, and then cold isostatic pressing is performed at 100-150 MPa to obtain a green body.

[0029] (3) pre-sintering: the green body obtained in step (2) is placed in an ultrafast high-temperature sintering furnace, and pre-sintering is performed in a nitrogen atmosphere, the heating rate is 80-120 ℃ / s, the sintering temperature is 1800-1900 ℃, the temperature is kept for 2-3 min, then the temperature is lowered to room temperature, and the cooling time is <0.5 min, to obtain a pre-sintered body.

[0030] (4) pressureless sintering: the pre-sintered body obtained in step (3) is placed in a vacuum atmosphere sintering furnace, and pressureless sintering is performed in a nitrogen environment, the heating rate is 5-50 ℃ / min, the sintering temperature is 1850-1900 ℃, and the holding time is 1.5-2.5 h, to prepare an AlON transparent ceramic.

[0031] (5) the obtained AlON transparent ceramic is ground and polished on both sides.

[0032] The ultrafast high-temperature sintering furnace used in the following examples is model UHS-3000; the AlON powder has a chemical purity of >99.9%; and the Y2O3 powder has an average particle size of 30 nm.

[0033] Example 1 Pure-phase AlON powder was weighed, and nano-Y2O3 powder was weighed according to a Y2O3 doping amount of 0.15 wt.%. The AlON and Y2O3 mixed powder was ball-mixed in anhydrous ethanol with silicon nitride balls as the grinding medium. The micro-morphology of the obtained AlON and Y2O3 mixed powder is shown in FIG. 1, wherein the median particle size is 0.5 μm, and the dispersibility is good. The mixed powder of AlON and Y2O3 was first pre-formed by pressurization in a steel mold at 50 MPa, and then cold isostatic pressing was performed at 120 MPa to obtain a green body. Figure 1

[0034] The green body was placed in an ultrafast high-temperature sintering furnace, and the temperature was raised to 1850℃ at a rate of 100℃ / s under a nitrogen atmosphere. After holding for 2 min, the temperature was lowered to room temperature, and the cooling time was 9.3 s. An AlON pre-sintered body was prepared. The pre-sintered body was then placed in a vacuum atmosphere sintering furnace, and pressureless sintering was performed in a nitrogen atmosphere. The temperature was raised to 1880℃ at a rate of 50℃ / s, and the temperature was held for 2 h to prepare an AlON transparent ceramic. The obtained AlON transparent ceramic was ground and polished on both sides, and the transmittance was measured. Figure 2 (a) is the fracture morphology of the AlON pre-sintered body, and small-size pores of 190-880 nm can be observed. The relative density of the pre-sintered body is 97.43%. FIG. 2(b) is a transmittance curve of the AlON pre-sintered body, and it can be seen that the AlON pre-sintered body has good light transmittance. The maximum transmittance is 97.43% (880 nm), and the transmittance at 400 nm is 97.43%. Figure 3 It can be seen that the grain size of the AlON pre-sintered body is small, and the grains are mainly less than 8 μm, and the average grain size is 6.12 μm. Figure 4 is a transmittance curve of the AlON transparent ceramic prepared by pressureless sintering of the pre-sintered body. It can be seen that the AlON ceramic has good light transmittance, and the maximum transmittance is 84.77% (3750 nm). The transmittance at 400 nm is 80.63%, and the transmittance in the wide wavelength range of 350-4900 nm is all ≥80%. The fracture morphology of the AlON transparent ceramic prepared is shown in FIG. 3(b). Figure 2 (b), only a small amount of small-size pores (110-370 nm) can be observed, and the density test results show that the sample has a high density of 99.71%. Figure 5 (a) and 5(b) are the grain morphology and grain size distribution diagram of the AlON transparent ceramic prepared. It can be seen that the grain size is small as a whole, and the grain size is uniform. The average grain size is 47.06 μm, and the hardness is high, HV=19.57±0.23 GPa.

[0035] Example 2 ​Example 2 was prepared according to the method of Example 1, except that the holding time of pressureless sintering was 1.5 h. The transmittance curve and sample photo of the obtained AlON transparent ceramic are shown in Figure 4 The maximum transmittance thereof was 84.72% (at 3750 nm), the transmittance at 400 nm was 80.01%, and the transmittance was all ≥80% in a wide wavelength range of 380-4630 nm. The fracture morphology of the prepared AlON transparent ceramic is shown in Figure 2 (c). A small amount of small-sized pores (381 nm) could be observed, and the density test result showed that the sample had a high density of 99.70%. Figure 5 (c) and 5(d) are the grain morphology and grain size distribution diagram of the prepared AlON transparent ceramic. It can be seen that the grain size is small in whole and uniform, with an average grain size of 42.02 μm. The ceramic has a high hardness, HV=19.79±0.21 GPa.

[0036] Comparative Example 1 Comparative Example 1 was prepared according to the method of Example 1, except that the AlON transparent ceramic was not prepared by ultrafast high-temperature sintering of the AlON pre-sintered body, but was directly prepared by pressureless sintering. The transmittance curve and sample photo of the obtained AlON transparent ceramic are shown in Figure 4 The maximum transmittance thereof was 80.84% (at 3750 nm), the transmittance at 400 nm was 58.82%, and the transmittance was all ≥80% in a wide wavelength range of 2500-4400 nm. The fracture morphology of the prepared AlON transparent ceramic is shown in Figure 2 (d). A large amount of large-sized pores (450-2400 nm) could be observed, and the relative density of the sample was 99.30%. Figure 5 (e) and 5(f) are the grain morphology and grain size distribution diagram of the prepared AlON transparent ceramic. It can be seen that the grain size is small, and most of the grain sizes are less than 40 μm. The HV of the ceramic is 16.69±0.43 GPa.

Claims

1. A method for preparing high-transmittance AlON transparent ceramics, characterized in that: Using AlON powder as raw material, adding sintering aids, the mixed powder after ball milling is dry pressed to prepare the green body. First, the AlON pre-burned body is prepared by ultra-fast high-temperature sintering method, and then the AlON transparent ceramic is prepared by pressureless sintering method. Among them, ultrafast high-temperature sintering is carried out in a nitrogen environment, with a heating rate of 80~120℃ / s and a sintering temperature of 1800~1900℃. After keeping warm for 2~3 minutes, it is cooled to room temperature and the cooling time is <0.5 min to obtain a pre-burned body.

2. The method according to claim 1, wherein The obtained pre-calcined body is pressurelessly sintered in nitrogen at a heating rate of 5-50°C / min, a sintering temperature of 1850-1900°C, and a holding time of 1.5-2.5 h.

3. The method according to claim 1, wherein The sintering aid is nano Y2O3 powder with an average particle size of 20-60 nm.

4. The method according to claim 1, wherein The amount of Y2O3 powder added is 0.05-0.30% of the mass of AlON powder.

5. The method according to claim 1, wherein The AlON and sintering aid powders are ball-milled in anhydrous ethanol using silicon nitride balls as grinding media, and the median particle size of the mixed powder after ball milling is 0.3-0.7 μm.

6. The method according to claim 1, wherein The mixed powder of AlON and sintering aid is first preformed by dry pressing at 10-60 MPa, and then cold isostatically pressed at 100-150 MPa to obtain a green body.

7. The method according to claim 1, characterized in that The obtained AlON transparent ceramics are ground and polished.

8. AlON transparent ceramics obtained by the method according to any one of claims 1 to 7.

9. The AlON transparent ceramic according to claim 8, characterized in that The AlON transparent ceramic has a density of 99.70% to 99.71%, an average grain size of 42.02 to 47.06 μm, a transmittance of ≥80% in a wide wavelength range of 380 to 4630 nm, and a Vickers hardness of 19.57±0.23 to 19.79±0.21 GPa.

10. The AlON transparent ceramic according to claim 9, wherein The maximum transmittance of the AlON transparent ceramic is 84.72-84.77% at a wavelength of 3750 nm, and the transmittance at a wavelength of 400 nm is 80.01%-80.63%.

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