• Journal of the Korean Chemical Society
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• v.31 no.5
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• pp.406-412
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• 1987

The electrical conductivities of ${\alpha}-Fe_2O_3$ containing 2.5 and 5.0mol% of cadmium were measured from 300 to $900^{\circ}C$ under oxygen pressures of 10$^{-7}$ to 10$^{-1}$ atmosphere. Plots of log ${\sigma}$ vs. 10$^3$/T show the extrinsic conductivity at oxygen pressure higher than $5{\times}10$^{-2}$atm. The transition points appear at about 550$^{\circ}$C and the activation energies are 1.34 eV for the intrinsic region and 0.50 eV for the extrinsic region on 5mol% Cd-doped ${\alpha}-Fe_2O_3$. The extrinsic conductivity disappears at oxygen partial pressures lower than $5{\times}10$^{-2}$ atm, and the intrinsic conductivity predominates. The electrical conductivities decrease with increasing mol% of cadmium doped. The predominant defect of ${\alpha}-Fe_2O_3$ doped with Cd is believed to be Fe${2+}$ interstitial for the intrinsic, however, oxygen vacancy predominates for the extrinsic region. The electrical conduction mechanisms are proposed and the conduction band model is suggested for the extrinsic region.

• Proceedings of the Korean Magnestics Society Conference
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• 2007.05a
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• pp.157.2-157.2
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• 2007

• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 1993.11a
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• pp.10-11
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• 1993

• Proceedings of the Materials Research Society of Korea Conference
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• 2006.05a
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• pp.33.1-33.1
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• 2006

• Electrical & Electronic Materials
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• v.5 no.2
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• pp.216-223
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• 1992

큰 보자력(iHc=19,500 Oe)과 큰에너지적[(BH)$_{max}$=32.50MGOe]을 갖는 Fe-(Ce-Didymium)-B 소결자석의 자구를 Bitter법을 개량한 Colloed SEM 법으로 관찰하였다. C축면의 자구는 소자상태에서 3-4.mu.m의 폭을 갖는 Stripe형이고 C축에 평행한 면은 미로형이다.

• Proceedings of the Korean Magnestics Society Conference
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• 2008.12a
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• pp.301.2-301.2
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• 2008

• Proceedings of the Korean Magnestics Society Conference
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• 2008.12a
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• pp.270.2-270.2
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• 2008

• Journal of Environmental Science International
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• v.9 no.6
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• pp.505-509
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• 2000

The purpose of this study was to evaluate the effects of $Ca(OH)_2$ and $CO_2$ additions on the corrosion of metal coupons(ductile iron, galvanized steel, copper and stainless steel). Corrosion rate and released metal ion concentration of ductile iron and galvanized steel decreased by adjusting alkalinity, calcium hardness and pH with $Ca(OH)_2$ & $CO_2$ additions on copper and stainless steel were less than those on ductile iron and galvanized steel. When ductile iron coupon was exposed to water treated with Ca(OH)$_2$&$CO_2$, additions, the main components of corrosion product formed on its surface were $CaCO_3$ and $Fe_2 O_3 or Fe_2 O_4$ which often reduce the corrosion rate by prohibiting oxygen transport to the metal surface.

• Journal of the Korean Ceramic Society
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• v.17 no.3
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• pp.121-128
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• 1980

In order to obtain the fundamental data for the preparation of ferroxplana $Zn_2Y(Ba_2Zn_2Fe_{12}O_{22})$, which is useful for GHz-band communication, the optimum coprecipitation condition of $Zn(NO_3)_2-6FeCl_3$ in $NH_4OH$ solution and the formation process of the hexagonal ferrite were investigated. By the hot-petroleum-drying and calcining the coprecipitated hydroxide mixture $Zn(OH)_2 +Ba(OH)_2+ 6Fe(OH)_3$, the fine and uniform powder was obtained , whose phase composition and microstructure were studied by X.R.D. and electron microscope. In results, it was found that $Zn_2Y$, BaM and $Zn_2W$ were the representative phases in calcined specimens whose activation energies of crystal growth were about 3, 8, 2.5, $5.4{\times}10^4$ J/mole , respectively. The sintered specimens would be appreciated as useful magnetic cores for the high frequency communication.

• Journal of the Korean Ceramic Society
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• v.28 no.1
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• pp.79-85
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• 1991

The effects of MnO2 on the microstructure and dielectric properties of Pb(Fe1/2Nb1/2)O3 ceramics prepared by KCl-NaCl molten salt synthesis(MSS) method have been investigated. As the amount of MnO2 increased up to 0.25wt%, the density increased and the grain size decreased, while above 0.25wt%, the density decreased with the grain growth. Dielectric constant increased with increasing the amount of MnO2, and dielectric loss decreased up to 0.25wt% and then increased. This is due to the compensation effect by the substitution of Mn4+ to Fe3+ and the appearance of the second phase.