| Summary: | 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 .
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