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오정강(Jung Kang Oh),서경원(Kyung Won Seo) 한국화학공학회 1999 Korean Chemical Engineering Research(HWAHAK KONGHA Vol.37 No.1
Crystalline BaTiO₃ powder of cubic phase, the mean particle size of which was 0.5 ㎛, was prepared by hydrothermal synthesis at temperature between 80 and 200 ℃ with KOH as a mineralizer. A mixed phase of anatase and amorphous was formed with 0.2 M KOH, but a stable phase of BaTiO₃ crystal powder was obtained when the concentration of KOH was 0.8 M and above. As the concentration of the mineralizer increased, the relative supersaturations of Ba (OH)^+ and Ti(OH)^(4-x)_x were enhanced. A lot of crystal powder were, therefore, formed instantaneously due to an increase in nucleation rate, and consequently, the mean particle size was reduced and the size distribution became narrower. As the reaction temperature increased, condensation reaction between Ba(OH)^+ and Ti(OH)^(4-x)_x was accelerated, which led to a decrease in hydroxide concentration, so that agglomeration of powder was abated. However, the particle size became larger due to an increase in the crystal growth rate.
오정강,서경원,Oh, Jung Kang,Seo, Kyung Won 한국공업화학회 1999 공업화학 Vol.10 No.4
In Preparing $BaTiO_3$ powder under hydrothermal conditions, effects of reaction period feedstock concentration and mixing rate on crystallinity, mean size and size distribution of particles were studied. Experimental results showed that the particle size became smaller with its narrow distribution as the reaction period and mixing rate increased, but feedstock concentration decreased in contrast with the results based on the classical nucleation-growth model. From these results, $BaTiO_3$ particles seem to be prepared hydrothermally through a multiple reaction procedure that includes dissolution, precipitation, hydrolysis-condensation, aggregation, diffusion and transformation. 수열합성법을 이용한 $BaTiO_3$ 미세분말제조시 반응시간, 출발물질농도와 교반속도 등이 입자의 결정성, 평균입경과 입도분포에 미치는 영향을 조사하였다. 실험결과 기존의 핵생성-입자성장 모델과는 상이하게도 반응시간과 교반속도가 증가할수록 또는, 출발물질의 농도가 감소할수록 입자크기는 감소하였으며, 입도분포도 좁았다. 이로부터 $BaTiO_3$ 결정입자는 수열합성시 용해, 가수분해-축합반응, 침전, 응집, 확산, 전이 등의 복합적인 반응경로를 거치는 것으로 판단되었다.
오정강,서경원 한국공업화학회 1998 응용화학 Vol.2 No.2
The effects of reaction period, concentration of feedstock and mixing rate on particle diameter and size distribution in preparation of BaTiO₃ powder under hydrothermal conditions have been studied. Experimental results showed that the particle size became smaller with its narrow distribution as the reaction period and mixing rate increased and the concentration of feedstock decreased in contrast with the results based on classical nucleation and growth models. After scrutinizing these experimental results, multiple reaction model that combins transformation and dissolution-precipitation was proposed.