Preparation And Sintering Properties Of Bulk Yb-doped Silica Gels

In order to prepare high doped ytterbium doped fiber preform core material,ytterbium doped silica gel was prepared by sol-gel process.The effects of silicon source type,solvent type and dosage,drying control agent and catalyst on the formability of the gel were studied.The sintering process and influencing factors of the gel were also analyzed.The effects of silicon source type,solvent type and dosage,drying control agent and catalyst on the formability of the gel were studied.The sintering process and influencing factors of the gel were also analyzed.Xerogels were prepared by water,alcohol solvent system and PC and TG solvent system respectively.The gel preparation process was optimized by taking gelation time and cracking resistance as the main indexes.The optimum ratio of raw materials is TEOS:C₂H₅OH:H₂O:DMF:HCl:NH₃=1:4:8:1:0.005:0.01,the optimum hydrolysis temperature is 60℃,and the hydrolysis time is 4h.The gel was kept at 60 C for 15d in different molds,and the best mold material was polypropylene.The gel drying system was optimized,and the temperature was slowly increased from 60℃to 100℃.The drying time was greatly shortened by microwave assisted drying.Finally,the complete block free crack silica gel was prepared.Through the thermal analysis and practical experiments,the best sintering process of xerogel was determined,and the complete bulk quartz glass was prepared.The samples were tested by SEM,XRD,FT-IR,UV Vis and BET.SEM test shows that after sintering,the surface of the sample is more smooth and flat,and the small particles aggregate and grow up.XRD test shows that the samples are amorphous before and after sintering.FT-IR test showed that the hydroxyl in the gel was basically removed after sintering.UV Vis shows that the light transmittance of the sintered quartz glass is over 86%in the range of 350-1300nm.BET test shows that after sintering,the pore diameter of the sample is greatly reduced and the densification degree is greatly improved.Yb-doped gel and transparent quartz glass with the highest 2%molar ratio of ytterbium and silicon were prepared by using Yb（NO₃）₃·5H₂O as silicon source.The influence of Yb³⁺doping on the preparation process of the samples was discussed.Yb³⁺doping will increase the drying time of the gel and lead to the change of the optimum sintering temperature of the xerogels.The ytterbium doped gels were tested by SEM,XRD,BET and DMA.SEM test showed that Yb³⁺doping did not change the morphology of xerogels.XRD showed that all the samples were amorphous.BET test showed that the optimum sintering temperature of gel was positively correlated with the pore size distribution of gel.The DMA test showed that the smaller the elastic modulus,the sample could adapt to the faster heating rate when the gel was not cracked.