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초임계수 결정화법에서 원료 농도비 및 반응시간이 바륨 헥사펙라이트 제조 특성에 미치는 영향

Influence of Stoichiometry and Reaction Time in the Barium Hexaferrite Synthesis by Supercritical Water Crystallization Method

서순용 노승욱¹ 박상도^1† 박소진

Soon-Yong Seo Seung-Wook Rho¹ Sang-Do Park^1† So-Jin Park

충남대학교 화학공학과 ¹한국에너지기술연구소 에너지환경연구부

Department of Chemical Engineering, Chungnam National University, Korea ¹Energy and Environment Research Department, Korea Institute of Energy Research, Korea

sdopark@sun330.kier.re.kr

HWAHAK KONGHAK, February 2000, 38(1), 75-79(5), NONE

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Abstract

고밀도 자기기록 매체로 사용되는 바륨 헥사페라이트의 초임계수 결정화 제조 공정에서 입자 특성에 영향을 미치는 Fe/Ba 농도비와 반응시간에 대한 영향을 회분식 반응기를 이용하여 고찰하였다. 반응물로는 Fe(NO₃)₃·9H₂Odhk Ba(NO₃)₂ 그리고 KOH를 사용하였으며, 반응기로는 35㎤ 회분식 반응기를, 가열 매체로는 molten salt bath를 이용하였으며, 생성된 입자의 상(phase)과 형상은 XRD 및 SEM을 사용하여 관찰하였다. 초임계수 결정화법으로 BaO·6Fe₂O₃를 생성하는 경우, BaO·6Fe₂O₃의 생성반응은 비양론적 화학반응 경로를 따르는 것이 확인되었으며, 바륨 헥사페라이트의 적정 생성 농도비는 2≤Fe/Ba≤7의 범위였다. 반응시간 측면에서는 5분 이내의 빠른 시간 내에 일정한 크기의 결정이 갖추어지며, 반응시간이 증가하여도 더 이상의 결정 성장이 일어나지 않음을 확인할 수 있었다. 이는 초임계수 조건에서의 빠른 가수분해, 화학결합 및 탈수반응에 기인되는 것으로 매우 짧은 반응시간으로도 BaO·6Fe₂O₃를 생성할 수 있음이 규명됨으로써, 본 초임계수 결정화 공정 개발에 연속 공정의 도입이 충분히 가능하다는 것을 알 수 있었다.

Barium hexaferrite, which have been used as the magnetic material for high density recording media, could be prepared from aqueous suspensions containing ferric nitrate, barium nitrate and potassium hydroxide by supercritical water crystallization method. In this process, the effect of the Fe/Ba and the reaction time on the size, morphology and phase of product were investigated with batch reactor of 35㎤ heated in molten salt bath. The morphology and the phase of the fine particle produced were observed by a scanning electron microscope(SEM) and X-ray diffraction (XRD). In this experiments, we could identify that BaO·6Fe₂O₃ is produced through the path of nonstochiometric reaction and the optimum molar ratio of Fe/Ba is from 2 to 7. The crystallinity of BaO·6Fe₂O₃ obtained at a short reaction time(<5 min)was very good and then the growth of particles were not observed in spite of the reaction time increase. These are due to the rapid hydrolysis, fast chemical bonding and dyhydration reaction under supercritical water condition. Also it is thought that supercritical water crystallization process could be developed as a continuous process as the fact that barium hexaferrite could be successfully synthesized at a very shot reaction time under supercritical water condition is identified.

Keywords

Barium Hexaferrite Supercritical Water Cystallization

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