• Journal of the Korean Ceramic Society
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• v.31 no.7
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• pp.723-730
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• 1994

Stable aqueous dispersion of magnetite colloid was obtained by allowing a fatty acid, such as nonanoic acid, decanoic acid and undecanoic acid, dissociated with NH4OH solution to adsorb on the monomolecular adsorption of oleate. To obtain a stable dispersion, added amounts of sodium oleate and nonanoic acid for magnetite 20g were more than 2.63$\times$10-2 mol and 0.04 mol respectively. In this colloid, good dispersions of magnetite which is sterically stabilized in aqueous system were achieved about pH 7.7. Water-based magnetic fluids using in this study were able to redisperse to water-based magnetic fluids by adding NH4OH solution to dried water-based magnetic fluid powders. Changing a magnetic fluid carrier such as kerosene was also attemped by adding kerosene to dried water-based magnetic fluid powders. In this study, we can obtain a kerosene-based magnetic fluids using drying process.

• Journal of the Korean Magnetics Society
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• v.15 no.1
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• pp.37-41
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• 2005

We prepared water-based magnetic fluids with the spent iron oxide catalysts which were used in the styrene monomer production process. The catalyst was composed with 70% magnetite and alkali metals. The water-based magnetic fluids were prepared by mechanical grinding with olecic acid as a surfactant and water in an attritor. The magnetization of the water-based magnetic fluids was 22 emu/g in the 10 kOe.

• Journal of the Korean Ceramic Society
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• v.31 no.3
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• pp.298-304
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• 1994

Water-based magnetic fluids were made of the synthesized ultrafine magnetite with surfactants such as sodium oleate and loeic acid. The water-based magnetic fluid was prepared under the condition that added amounts of sodium oleate and oleic acid dissolved with NH4OH were 2.64$\times$10-2 mol, 1.5~2.0$\times$10-2 mol respectively. The water-based magnetic fluid was stable and should be dispersed well dispersion in the range of pH 9.0 to pH 11.0. As the solid content increased from 0.05 g/cc to 0.4 g/cc, the viscosity of water-based magnetic fluids increased from 2.5 cP to 152 cP and their magnetization at 5 KOe linearly increased from 3.1 emu/g to 26 emu/g. The aggregated powder after drying the water-based magnetic fluid was also successfully re-dispersed in dilute NH4OH solution and in kerosene.

• Journal of the Korean Magnetics Society
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• v.3 no.3
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• pp.241-246
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• 1993

The water-based magentic fluids were successfully prepared with the synthesized ultrafine magnetite using saturated with fatty acids($C_{9}~C_{18}$) and SDBS as surfactants. The dispersion index of water-based fluids was about 85 % when the amounts of lauric acid and SDBS for the 27 g of magnetite were more than $2.66{\times}10^{-2}mol$ and 5 g($7.17{\times}10^{-2}mol$) respectively. As the solid content increased from 0.05 g/cc to 0.4 g/cc, saturated magnetization of magnetic fluids at 5 kOe increased from 2.07 emu/g to 9.31 emu/g and its viscosity increased from 1.20 cp to 3.95 cp. The stable pH region in which the magnetic fluids prepared with lauric acid and SDBS was range of 3.1 to 11.1. It was found that the water-based magnetic fluids was well dispersed as the carbon length of fatty acid increased, but the amount of scum of the magnetic fluids increased.

• Journal of the Korean Magnetics Society
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• v.4 no.2
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• pp.173-178
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• 1994

The water-based magnetic fluids were prepared with the synthesized ultra-fine magnetite, oleic acid and SDBS (sodium dodecyl benzene sulfonate) as surfactants. The dispersion of water-based magnetic fluids was about 90 % when the added amounts of oleic acid and SDBS for magnetite(27 g) were more than $2.66{\times}10^{-3}$ mol and 10 g respectively. As the solid content increased from o. 05 g/cc to 0.4 g/cc, saturation magnetization of magnetic fluids at 5 kOe increased from 1.98 emu/g to 9.63 emu/g at $Fe^{2+}/Fe^{3+}=0.5$ and from 2.7 emu/g to 14.63 emu/g at $Fe^{2+}/Fe^{3+}=1.0$, and the its viscosity increased from 1.3 cp to 4.4 cp at $Fe^{2+}/Fe^{3+}=0.5$. pH region of oleic acid and SDBS stabilized water-based mag¬netic fluids was stable was in the range of pH 3.0 to pH 11.0. Stability of Water-based magnetic fluids can be obtained by observation of magnetic memory patterns on the VCR tape.

• Journal of the Korean Magnetics Society
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• v.4 no.1
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• pp.62-68
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• 1994

Water-based magnetic fluids containing synthesized ultrafine magnetite were successfully prepared with $C_{18}$ fatty acid such as oleic acid, linoleic acid and stearic acid. Oleic acid was needed the amount of $3.0{\times}10^{-2}$ mol per 20 g magnetite to stabilize the magnetite $d\;=\;113\;\AA$ particles. From pH 8.0 to pH 11.0, stable aqueous-based fluids could be obtained. The aggregated powder after drying the water-based magnetic fluid was also successfully re-dispersed in dilute $NH_{4}OH$ solution and in kerosene. The pH levels of the magnetic fluid using oleic acid system could be predicted by the pH values obtained by calculation of therrrodynamic data.

• Proceedings of the Korean Magnestics Society Conference
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• 1992.03a
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• pp.58-59
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• 1992

• Journal of the Korean Magnetics Society
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• v.3 no.3
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• pp.234-240
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• 1993

The water-based magnetic fluids were prepared with the synthesized ultrafine magnetite, dodecanoic acid as surfactant. Characteristics of synthesized ultrafine magnetite were investigated with X-ray Diffraction Pattern, Transmission Electron Microscope, Vibrating Sample Magnetometer and BET analysis. Dispersion characteristics of water-based magnetic fluids were investigated in relation to amounts of surfactant, pH and solid content.

• Proceedings of the Korean Magnestics Society Conference
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• 2003.12a
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• pp.172-172
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• 2003

• Proceedings of the Korean Magnestics Society Conference
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• 1993.03a
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• pp.40-41
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• 1993