Preparation and characterization of ceramic oxide La2(Sn,Zr)2O7 by coprecipitation combined with high temperature melting

• Main Authors: Kingda Lee, 李金達
• Other Authors: Chen-Feng Kao
• Format: Others
• Language: zh-TW
• Published: 1995
• Online Access: http://ndltd.ncl.edu.tw/handle/21225164640275673122

碩士 === 國立成功大學 === 化學工程研究所 === 83 === Coprecipitation combined with high temperature melting , a brand new powder preparation technique derived from the conventional chemical coprecipitation , was applied to the synthesis of lanthanum-tin-zirconium oxide . Processes were perfomed with the corresponding metal chloride and sodium hydroxide in the ethanol solution . During the calcination of dried precipitates , molten salt NaCl acted as a solvent that effectivly enhanced the reaction and deminished the calcination temperature-at about 1083K . Then the powders were sintered at 1473K , 1573K , 1673K for 4 , 4 hours , respectively . Owing to fused salt , the calcination temperature is much lower 200K than that of conventional chemical coprecipition . It's very useful for energy saving . After X-ray and Far-IR were analyzed , lanthanum-tin-zirconium oxide is confirmed as a new compound of pyrochloer structure--La2(SnxZr1-x)2O7 . However , it seems that the position of Sn and Zr is alternative in the structure . Being sintered under nitrogen atmosphere , the sample began to crack and the disk had no La2(Sn,Zr)2O7-δ compound expected , but that was nice for sintering in Air . It was found that the specimen sintered at 1673K in air for 4 hours was diamagnetic at room temperature when x was not smaller than 0.7 . With the increasing of mole percent of zirconium the specimen was paramagnetism . The compounds are characteristics of polaron mechanism of conductivity from the variations in resistivity with temperature. This semiconductor is a charasteristic of resistance changing with electricwave frequency . Comparing " powder preparation by alkali melt route " with " coprecipitation combined with high temperature melting method " , it was proved that the latter is better .