Study On Preparation And Defect Effect Of γ-ALON Ceramic Materials

Alumina nitride（γ-AlON）with spinel structure is a new type of structural and functional integration material,which has shown a wide range of application prospects in national defense and civil demand markets.γ-AlON itself is a non-stoichiometric compound,and its structure and propert have significant component dependence and rich intrinsic defects.These intrinsic defects play an important role in the service performance of the materials.The study of the effects of these intrinsic defects will lay a solid foundation for the practical application ofγ-AlON.In particular,γ-AlON transparent ceramics are expected to become a new generation of spacecraft optical window materials to meet the requirements of harsh and complex deep space service environment.At present,most of the researches onγ-AlON materials focus on the innovation of bulk materials preparation technology and optimization of process conditions.However,the defect effects ofγ-AlON powder materials and the environmental effects of bulk transparent ceramics in deep space environment applications in the future are still lack of in-depth evaluation.According to the structural characteristics ofγ-AlON materials,the defect structures and their effects ofγ-AlON materials are systematically discussed in this paper,which provide theoretical basis and practical experience for improving the properties ofγ-AlON and expanding its application fields.The specific research content is as follows:（1）Cr³⁺dopedγ-AlON powders had been synthesized by high temperature solid state method at 1700℃and in nitrogen atmosphere.Cr³⁺:γ-AlON powders possess fluorescence properties with the emission peaks at 670 nm,693 nm,720 nm,and 750 nm.Due to the defects in the matrix,there is a group of R-lines with blue shift at 670 nm.The existence of the vacancy around Cr³⁺leads to the Cr³⁺luminescence in the weak lattice field at 720 nm and the Cr³⁺luminescence in the strong lattice field at 693 nm.The broad emission peak at750 nm is caused by defects such as nitrogen substituted oxygen vacancy or nitrogen gap.The luminescence intensity first increases and then decreases with the increase of Cr³⁺doping concentration.（2）Bi³⁺:γ-AlON powder was successfully synthesized by high temperature solid state method with NH₄Cl as sintering aid.The problem of Bi ion sublimation in the synthesis ofγ-AlON powder was solved.After 120 min of UV irradiation,the degradation efficiency of MO by 2 mol%doped Bi³⁺:γ-AlON powders was 78%,which was 2.1 times higher than that of pureγ-AlON powders（only 25%）.The kinetic characteristics of the degradation process accorded with the first-order kinetic model,and the reaction rate reached 0.0113min^-1.The improved separation efficiency and redox ability of 2 mol%doped Bi³⁺:γ-AlON photogenerated carriers enhanced the improved photocatalystic performance.（3）Submicron AlN and nano-sized Al₂O₃ were used as raw materials,polyvinyl butyraland citric acid were used as organic polymer carbon source and dispersant,Al₂O₃/AlN composite powders coated with a nano-carbon layer on the surface was obtained by thermolysis of organic polymer adsorbed on the surface of Al₂O₃/AlN composite material,and then theγ-AlON powder material was synthesized by solid-phase reaction in high-temperature nitrogen.After the optimization of particle preparation process,the large sizeγ-AlON transparent ceramics with diameter of 50 mm and thickness of 5 mm were prepared by using ternary composite sintering additives.The transmittance ofγ-AlON transparent ceramics in visible light band reached 84.9%.It laid the foundation for the further preparation of large-scaleγ-AlON transparent ceramics.（4）A simulated space environment effect experiment was carried out onγ-AlON transparent ceramic samples,including ultraviolet radiation,high-energy electron radiation,gamma-ray radiation and atomic oxygen erosion.γ-AlON transparent ceramics were resistant to high-energy electron radiation;however,γ-ray irradiation,ultraviolet radiation and atomic oxygen erosion caused the decrease of transmittance of transparent ceramics Combined with structural analysis and series of spectroscopy analysis,it was clarified that the main intrinsic defects that affect the optical properties ofγ-AlON crystals were V_Al^′′′、O_N^·and the defect clusters formed between them.The existence of these defects significantly affected the optical transparency of theγ-AlON crystal material.