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제이철염 용액으로부터 α - Fe2O3 의 직접 합성 ( α - Fe2O3 입자 생성에 미치는 반응 온도와 구연산의 영향 )
변태봉 ( T . B . Byeon ) 대한금속재료학회 ( 구 대한금속학회 ) 1996 대한금속·재료학회지 Vol.34 No.8
We have synthesized α-Fe2O3 particles directly from ferric salt solution by hydrothermal reaction. The effect of citric acid concentration and hydrothermal reaction temperature on the formation of α-Fe2O3 particles, formation process of α-Fe2O3 particles were investigated. Also, we proposed a formation model of needle-like α-Fe2O3 particles in this reaction system. The length and aspect ratio of α-Fe2O3, particles were decreased gradually with increasing of citric acid concentration. The crystallization of needle-like α-Fe2O3 particles was inhibited beyond citric acid concentration of 1.5 × 10(-4) mol. We can synthesized α-Fe2O3 particles with the most superior acicularity at 140℃. Aspect ratio of α-Fe2O3 particles was decreased with increasing reaction temperature. α-Fe2O3 particles formed above 220℃ exhibited sphere-like particles. The crystallization to α-Fe2O3 particles from ferric salt was accomplished at 140℃ in 10 minutes. Citric acid was adsorbed with the form of citrate anion(R-COO(-)) on the ferric hydroxide and exerted important role on the formation to the needle-like α-Fe2O3, particles in this reaction system.
변태봉,이재영,김대영,손진군,권순주,Byeon, T.B.,Lee, J.Y.,Kim, D.Y.,Shon, J.G.,Kwon, S.J. 한국세라믹학회 1991 한국세라믹학회지 Vol.28 No.2
$\gamma$-FeOOH suitable for magnetic recording media was synthesized using waste acid which is the by-product of the iron works factory. Effects of concentration of the acid and alkali and reaction temperature on the particle properties of $\gamma$-FeOOH and magnetic properties of $\gamma$-$Fe_2O_3$ were studied. $\gamma$-FeOOH single phase was formed below 1M of acid concentration with 1M of alkali concentration and at 0.4M of acid concentration with 4M of alkali concentration. While the width of acicular particle was increased, the length of acicular particle was decreased with diluting acid concentration. The magnetic properties of the $\gamma$-$Fe_2O_3$ improved with increasing acid concentration. $\gamma$-FeOOH single phase was formed in the temperature range of 30 to $80^{\circ}C$. The length of the particle was decreased with increasing temperature. $\gamma$-Fe2O3 produced from dehydration of $\gamma$-FeOOH showed bad magnetic properties due to the presence of many pores in the particle. But with successive reduction and oxidation of $\gamma$-$Fe_2O_3$ produced from dehydration of $\gamma$-FeOOH, $\gamma$-$Fe_2O_3$ showed good magnetic properties.
코발트 훼라이트 에피탁시얼 산화철의 생성과 자기특성(Ⅰ)
변태봉(T. B. Byeon),김대영(D. Y. Kim),이재영(J. Y. Lee),손진군(J. G. Shon) 한국자기학회 1992 韓國磁氣學會誌 Vol.2 No.1
To improve the coercivity of γ-Fe₂O₃ particles. We have made cobalt ferrite epitaxial γ-Fe₂O₃ particles by crystallizing cobalt ferrite on the surface of γ-Fe₂O₃ particles. The coercivity of Co_xFe_(3-x)O₄ which is conform to coating layer showed the most superior characteristic when the value of x was 1. On the formation of cobalt epitaxial γ-Fe₂O₃ particles, controlling reaction atmosphere as oxidation atmosphere after non-oxidation atmosphere was the optimum condition to prepare cobalt epitaxial γ-Fe₂O₃ particles with superior magnetic properties. Epitaxial growth of cobalt ferrite on the surface of γ-Fe₂O₃ particles was accomplished at 90℃ for 30 minutes.
이재영(J. Y. Lee),변태봉(T. B. Byeon),김대영(D. Y. Kim),이현(H. Lee),한기현(K. H. Han),손진군(J. G. Sohn) 한국자기학회 1993 韓國磁氣學會誌 Vol.3 No.2
This paper presents a study on the effects of silica coating in the production of γ-Fe₂O₃ powders suitable for magnetic recording media. Emphasis has been put on investigating the relationship between the powder characteristics and the effects of silica coating in the heat-treatment stage of γ-Fe₂O₃ production. After we prepared non-coated γ-Fe₂O₃ and silica coated γ-Fe₂O₃ with coating water glass on the surface of goethite and heattreatment process, we compared and investigated powder characteristics. As silica coated layer played a role of preventing the powders from overreduction to metal iron and rapid oxidation, silica coated γ-Fe₂O₃ showed superior magnetization value due to inhibiting the adulteration of α-Fe₂O₃ into the final product. When silica coated layer acted as a sintering restrainer, silica coated γ-Fe₂O₃ showed high coercivity and specific surface area due to good acicularity.
코발트 페라이트 에피탁시얼 γ-Fe2O3 의 합성 및 자기특성
이재영,변태봉,김대영,손진군 대한금속재료학회(대한금속학회) 1992 대한금속·재료학회지 Vol.30 No.4
Acicular γ-Fe₂O₃ particles were heated at 90℃ in alkaline solution containing Co^(+2) and Fe^(+2). The coercivity of resultant product increased from 0.2 to 0.25, Co^(+2)/Fe^(+2) molar ratio, and gradually decreased above 0.25. When cobalt content is increased, the coercivity of resultant product increased linearly. The increase of coercivity was attributed to the crystalline magnetic anisotropy of the cobalt ferrite which is conform to coating layer. The coercivity increased with the increasing seed content. The stability of temperature and the change on standing was largely influenced by the composition of coating layer and showed the most superior properties in the range of the Co^(+2)/Fe^(+2) molar ratio of 0.36∼0.5.
이재영,손진군,변태봉,김대영,권순주 대한금속재료학회(대한금속학회) 1992 대한금속·재료학회지 Vol.30 No.8
The influence of initial pH on the formation of iron oxyhydroxide has been investigated. As the initial pH of reactant solution increased, β-FeOOH(pH=4.5), mixture of β-FeOOH and α-FeOOH(4 5$lt;pH$lt;5.5), mixture of α-FeOOH and Fe₃O₄(6.4$lt;pH$lt;12), Fe₃O₄(pH=12), α-FeOOH(pH$gt;13) were formed in order. At the end of reaction, the product was strongly acidic(pH$lt;3) when the initial pH was lower than 13. When the initial pH was higher than 13, the product was strongly basic(pH$gt;12). In order to synthesize only iron oxyhydroxide, we propose either precipitation after the oxidation of dissolved ion is completed perpectly or oxidation simultaneously with the precipitation. Oxidation of oxygen promotes not only the oxidation of ferrous ion but also dissolution and precipitation in the range of strong basicity.
수열반응에 의한 침상형 α-Fe2O3 제조 : 입자형상에 미치는 pH 영향 The Effect of pH on the Particle morphology
이재영,이현,손진군,한기현,변태봉,김대영 대한금속재료학회(대한금속학회) 1993 대한금속·재료학회지 Vol.31 No.5
Hematite particles were obtained by hydrothermal reaction from ferric hydroxide in the presence of citric acid which is acted as crystal growth controller. Citric acid was adsorbed with citrate anion on the ferric hydroxide. Adsorbed citrate anion influenced crystallization temperature and morphology of α-Fe₂O₃in the solid reaction. Adsorbed citrate anion inhibited crystallization of α-Fe₂O₃from ferric hydroxide at pH 9.0-10.5 and induced to needle-like α-Fe₂O₃particles at pH 10.75-11.75 in the hydrothermal reaction.