Fabrication And Property Of Nd:YAG Nanopowders And Transparent Ceramics

Solid-state laser has been applied widely in many fields,such as industry,medicine,manufacturing process and military fields.So far,high-power solid-state laser has been one of the extensively developed laser in laser region.Laser material,as the core and foundation of solid-state laser,has been researched by many scientists.Compared with single crystal and glass,transparent ceramic has many comprehensive advantages,such as high thermal conductivity,high doping concentration and fabrication of large size,which is more suitable laser material for the development of high-power solid-state laser.Since A.Ikesue et al.fabricated successfully high-quality transparent Nd:YAG ceramics by solid-state reaction method and achieved laser output in 1995,polycrystalline transparent ceramics have attracted considerable attention.Generally,two methods have been applied to fabricate high-quality Nd:YAG transparent ceramics:one is solid-state reaction sintering of oxides powders,and the other is sintering of nanopowders synthesized by wet-chemical method.Among these methods,the sintering of nanopowders synthesized by co-precipitation method has unique advantages in the fabrication of transparent ceramics with large size and high optical quality.Based on above viewpoints,we studied systematically the fabrication conditions for nanopowders and transparent ceramics,who aimed to obtain high-quality Nd:YAG transparent ceramics.The main contents can be divided into the following parts.1)Nd:YAG nanopowders were synthesized by the co-precipitation method using ammonium hydrogen carbonate as the precipitant.The influence of ammonium carbonate to metal ions molar ratio?R value?on the properties of powders and ceramics was investigated.The result showed that R=3.2 powder had the best dispersity and the resultant ceramic showed the highest transmittance.However,the R=3.2 powder had lower productivity and was not suitable for the massive synthesis of nanopowders and production of ceramics with large size.Therefore,R=3.4 powder with good dispersity and high productivity was selected as the raw material for the following experiments.2)Using the R=3.4 nanopowders as the research object,the influence of calcination temperature on the properties of powders was investigated.By the analysis of FTIR,XRD,SEM,BET,XRF and green bodies densities,it was found that although higher calcination temperature can lower the sintering activity of powders,it can improve the densities of green bodies and the densification rate of ceramics.In addition,higher calcination temperature can reduce the content of sulfur impurity.Therefore,taking into comprehensive account the properties of powders,the powder calcined at 1250 ^oC for4h was chosen to fabricate transparent Nd:YAG ceramics.3)Using the R=3.4 nanopowders calcined at 1250 ^oC for 4h as the raw materials,the influence of ball milling time on the properties of powders and ceramics was studied.The result showed that ball milling can break up the sintering neck of the particles effectively.When the ball milling time reached 12h,the ceramic?1.3mm thickness?sintered at 1775 ^oC for 10h showed the best in-line transmittance of 73.6%at the wavelength of 1064nm.With further increase of ball milling time to 16h and 20h,there existed some Al₂O₃ phases,which can lower the transmittance of ceramics.4)Using the nanopowders prepared under above optimal conditions,the ceramics were fabricated by vacuum sintering method.The influence of sintering temperatures and holding times on the properties of ceramics was studied.It was found that the transmittance of ceramic?1.3mm?sintered at 1775 ^oC for 20h reached 76.0%at 1064nm.5)The ceramics were fabricated by vacuum pre-sintering coupled with HIP post-treatment.The influence of vacuum pre-sintering temperatures and annealing temperatures on the properties of ceramics was investigated.It was found that the pre-sintering temperature of 1750 ^oC is suitable for the fabrication of HIPed ceramics,and annealing led to the expansion of pores and lower the transmittance of ceramics.After being vacuum pre-sintered at 1750 ^oC for 2h and HIPed at 1750 ^oC for 3h under 200MPa of Ar atmosphere and then un-annealed,the ceramic?2mm thickness?had the best transmittance of 79.1%at 1064 nm.