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Li H L, Min P, Feng Z, et al. Effect of forming process on microstructures and properties of aluminum oxynitride[J]. Opto-Electron Eng, 2022, 49(6): 210354. doi: 10.12086/oee.2022.210354
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Effect of forming process on microstructures and properties of aluminum oxynitride
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Abstract
AlON transparent ceramic is a new structure-function integration optical material with excellent optical, thermal, and mechanical properties, which can be widely used in missile domes, and transparent armors and other fields. The preparation of green body with high density and homogeneous microstructure is the key technical procedure for fabricating AlON transparent ceramic. However, nanopowders possess high specific surface area and are easy to form non-uniform agglomeration, resulting in poor density of formed green body. In order to improve density and homogeneity of green body, micro-spheroidization of nanopowders and dense spherical particles with a diameter greater than 10 μm and good fluidity were obtained by optimizing the spray granulation process. The effect of cold isostatic pressing pressure on density, microstructure, average pore diameter of green bodies, and optical transmittance of sintered ceramics were intensively investigated. Green bodies with relative density of 58.8% were obtained. The in-line transmittance of sintered ceramics reached 83% at 2000 nm (thickness 2 mm). AlON transparent ceramics with diameter of Φ170 mm plate and Φ110 mm dome were obtained by cold isostatic pressing and pressureless sintering. -
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References
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Overview
Aluminum Oxynitride (AlON) transparent ceramic has high transparency from the ultraviolet to mid-infrared range, excellent mechanical properties, high temperature resistance and excellent chemical stability. It’s a new structure-function integration optical material and an ideal material for photoelectric windows, missile domes, and transparent armors. The fabrication of AlON transparent ceramic mainly includes synthesis of the AlON nanopowders, forming nanopowders to green body, sintering of the green body into a dense transparent ceramic, grinding and polishing. The preparation of green body with high density and homogeneous microstructure is the key technical procedure for fabricating AlON transparent ceramic. Generally, cold isostatic pressing is used for fabricating AlON green body. However, AlON nanopowders possess high specific surface area and are easy to form non-uniform agglomeration. If the nanopowders are directly formed by cold isostatic pressing, the density of the green body will be poor, and finally resulting in poor performance of the sintered AlON ceramic. In order to solve the problem of non-uniform agglomeration of AlON nanopowders, the AlON powders can be granulation processed into uniform, dense, good fluidity spherical particles, and then dense green body can be obtained by cold isostatic pressing. Spray granulation is an effective method to realize nanopowders micro-spheroidization, but, there is no report on dealing with spray granulation of AlON nanopowders. In this paper, we aimed to improve density and homogeneity of AlON green body by spray granulation combined with cold isostatic pressing, and fabricate AlON ceramics with larger size and more complex structure. First, single phase AlON powders were prepared by solid-state reaction method and ball-milled into nanopowders with an average particle diameter of 320 nm, and narrow size distribution. Second, We optimized the spray granulation process. The effect of solid content of AlON slurries on properties of spray granulated particles were investigated. When the solid content of AlON slurry was 50 wt%, dense spherical particles with a diameter greater than 10 μm and good fluidity were obtained. Third, The effect of cold isostatic pressing pressure on density, microstructure, average pore diameter of green bodies and optical transmittance of sintered ceramics were intensively investigated. The results showed that when cold isostatic pressing pressure was increased to 200 MPa, the density of AlON green body reached to 2.17 g/cm3, the relative density increased to 58.8%, and the green body had small pore and uniform microstructure. The in-line transmittance of AlON ceramic fabricated by cold isostatic pressing and pressureless sintering reached 83% at 2000 nm for the thickness of 2 mm. Last, we have demonstrated our work on fabricating AlON transparent ceramics with a diameter of Φ170 mm plate and Φ110 mm dome. Those spray granulation, cold isostatic pressing and pressureless sintering techniques can be used to fabricate high quality, large size AlON transparent ceramics in the future.
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Li H L, Min P, Feng Z, et al. Effect of forming process on microstructures and properties of aluminum oxynitride[J]. Opto-Electron Eng, 2022, 49(6): 210354. doi: 10.12086/oee.2022.210354
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Figure 1.
Schematic diagram of spray granulation[18]
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Figure 2.
SEM, XRD and particle size distribution results of AlON powder after ball milling
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Figure 3.
SEM morphology of spraying granulated powders by different solid content slurries.
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Figure 4.
Schematic diagrams of drying atomized droplets with different solid contents
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Figure 5.
Pictures of formed green body
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Figure 6.
SEM results of AlON green body formed by different pressures. (a) 150 MPa; (b) 200 MPa; (c) 260 MPa
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Figure 7.
Pore size distribution of green body formed by different pressures
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Figure 8.
Transmittance of different forming pressures (thickness 2 mm)
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Figure 9.
AlON transparent ceramic plate (a) and dome (b) fabricated by cold isostatic pressing and pressureless sintering
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