Study On YAG Ceramics By Gel-casting

Yttrium aluminum garnet（YAG）transparent ceramics have good transparency to visible light and infrared light,and have excellent mechanical properties,high thermal conductivity and easy to realize rare earth luminescence ions(Re³⁺)doping.It is a very important laser gain material,so it has been paid attention and studied.Among them,the molding process has a very important influence on the ceramic preparation process and the final optical properties.Therefore,a low-cost,simple process,and a molding method that can prepare large-scale or complex shapes is very important in the preparation of YAG transparent ceramics.In this paper,YAG ceramic slurry was prepared according to the requirements of gelcasting method.The effects of dispersant content,solid content and dispersion time on the rheological properties of YAGceramic slurry were studied.With the increase of dispersant content,the viscosity of the slurry first decreased and then increased.When the solid content waslow,the slurry didn’t have shear thinning behavior,and its settlement was high,and the slurry stability was poor.When the solid content reached 60wt.%and exceeded this value,the viscosity of slurry increased with the increase of solid content.When the solid content reached 65 wt.%,the prepared slurry had thixotropy.With the increase of ultrasonic dispersion time,the viscosity of slurry decreased.When the dispersion time was more than 60min,the variation of slurry viscosity decreased.The final slurry preparation parameters were:dispersantcontent is2.0wt.%,ultrasonic dispersion time is 60min,the solid content is 60wt.%YAGceramic slurry.In order to avoid cracking and uneven weight loss,The drying system used in this paper was that after the green body was dried at 25°C for 24h,the temperature was increased and dried at 40°C for 36h.After the analysis of TG-DSC,the degumming process was determined to heat at 500°C for 4h,the heating rate was 1°C/min,and then the calcination temperature was increased to 1200°C for 3 h at 2°C/min.XRD,SEM,mercury intrusion method and three-point bending method were used to analyze the performance of the billet.The results show that the Isobam content has no effect on the phase of the billet.When the Isobam content was 2.0 wt.%,the bending strength increased to the maximum of 23.2 MPa,the pore size distribution range was 48 nm–173 nm,and the median was 66.9 nm.The ceramic particles were arranged compactly,and the surface of the billet was smooth and uniform.The solid content had a great influence on the properties of YAG ceramic body.The results showed that the density and bending strength of YAG ceramic body increased with the increase of solid content.The linear shrinkage,porosity and pore size of YAG ceramic body decreased before and after drying.However,when the solid content continued to increase to 65 wt.%,the viscosity of the slurry increased,and it was almost solid when standing,which cannot be degassed.There were many pores in the billet,and the pore size of the billet exhibited bimodal distribution.The density of the billet was uneven,and the ceramic particles were not closely arranged,and the density and flexural strength was decreased.YAGgreen bodies with different solid content were sintered to test their density,shrinkage and microstructure.The results showed that the higher the sintering temperature was,the higher the shrinkage rate was,and the higher the density of the billet was.As the solid content increased,the shrinkage decreased and the relative density of the sintered body increased.When the solid content continued to increase to 65wt.%,the relative density of the sintered body decreased and pores appeared in the sample.When the solid content was 60wt.%and the sintering temperature was 1750°C,the relative density of the ceramic was 99.43%and the shrinkage was 19.26%.The properties of YAG green body and ceramics prepared by dry molding and gelcasting were compared.The samples prepared by dry molding showed uneven agglomeration and slight layered structure.In contrast,the sample prepared by gelcasting has uniform and smooth surface and uniform bulk density.The SEM images of the sintered samples showed thatthere were obvious pores on the surface of the dry forming billet after sintering,and the transmittance at 1064 nm was about 77.79%.The green body prepared by gelcasting method was completely dense,and there were no pores on the ceramic surface.The transmittance reached the maximum value of 81.26%at 1064 nm.In this study,the gelcasting method had obvious advantages,which played an important role in improving the optical properties of YAG transparent ceramics.Isobam gelcasting molding method will be an important molding route in YAGtransparent ceramic preparation technology.