• Corrosion Science and Technology
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• v.3 no.3
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• pp.98-101
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• 2004

The corrosion behavior of Al-Fe coatings was studied in the wet-seal atmosphere of molten carbonate fuel cells (MCFC). Fe-8Al, Fe-16Al, Fe-25Al, Fe-36Al, and Fe-70Al (in at.%) specimens were tested in Li/K carbonate at $650^{\circ}C$ by a single cell test and an immersion test. In general, the corrosion resistance of the Al-Fe coatings was enhanced due to the formation of a protective $LiAlO_2$ layer. However, when the Al-Fe coatings didn't have sufficient content of aluminum enough for maintaining the protective layer, the corrosion resistance of the Al-Fe coatings was severely degraded by the growth of non-protective scales like $LiAlO_2$. The test results revealed that the aluminum contents in the coatings should be higher than 25 at.% in order to form and maintain the protective $LiAlO_2$ layers.

• Journal of the Korean Electrochemical Society
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• v.13 no.4
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• pp.246-250
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• 2010

In this study, nano-crystallized $Al_2O_3$ was coated on the surface of $LiFePO_4$ powders via a novel dry coating method. The influence of coated $LiFePO_4$ upon electrochemical behavior was discussed. Surface morphology characterization was achieved by transmission electron microscopy (TEM), clearly showing nano-crystallized $Al_2O_3$ on $LiFePO_4$ surfaces. Furthermore, it revealed that the $Al_2O_3$-coated $LiFePO_4$ cathode exhibited a distinct surface morphology. It was also found that the $Al_2O_3$ coating reduces capacity fading especially at high charge/discharge rates. Results from the cyclic voltammogram measurements (2.5-4.2 V) showed a significant decrease in both interfacial resistance and cathode polarization. This behavior implies that $Al_2O_3$ can prevent structural change of $LiFePO_4$ or reaction with the electrolyte on cycling. In addition, the $Al_2O_3$ coated $LiFePO_4$ compound showed highly improved area-specific impedance (ASI), an important measure of battery performance. From the correlation between these characteristics of bare and coated $LiFePO_4$, the role of $Al_2O_3$ coating played on the electrochemical performance of $LiFePO_4$ was probed.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.7 no.2
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• pp.244-252
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• 1997

The pseudo-spinel type solid solution, $LiAl_{2.5}/Fe_{2.5}O_8$ was prepared by reaction of $LiCO_3, Al_2O_3, Fe_2O_3$ mixture at 1620K, which can be used for cathode material in lithium batteries. Its structure was investigated by Rietveld profile-analysis of XRD in detail. The space group of solid solution is $P4_3$32(a=8.1293$\AA$) and the final residual index of structure refinement was about 5%. Cations $Al^{3+}, Fe^{3+}$ are located at both tetra- and octahedral-coordination and $Li^+$ ions are occupied in the octahedral 4b-, 12d-site of the inverse spinel.

• Korean Journal of Plant Resources
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• v.20 no.1
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• pp.12-21
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• 2007

Ginsengs (1,2 3 years) from the Keumsan are analysed for the inorganic compounds and compared with the their soils from the granite, phyllite and shale areas. In the soils, the granite areas show high $Al_2O_3\;and\;Na_2O$ contents while the phyllite areas have high $Fe_2O_3,\;MnO\;and\;MgO$ contents. Positive correlations are shown in the $Al_2O_3-K_2O\;and\;Fe_2O_3-MgO$ pairs while negative correlations are shown in the $SiO_2-CaO$ pair. In the ginsengs, the shale areas are high in the most of the elements, but low in the granite areas. Compared with same soils of different ages, Al, Na and Ti contents of the ginsengs are high in the all areas. The shale areas are mainly high in the upper parts while the granite areas are mainly high in the root parts. Regardless of the localities, Fe, Mn and Ca contents are high in the upper parts while Ti contents are high in the root parts with differences of several times. Relative ratios between field soils and ginsengs (field soil/ginseng) suggest that the ginsengs show high Ca contents with differences of several ten times whereas the soils have high Na, Fe, Ti and Al contents with differences of several times. Regardless of the localities, the ratios of the Al, Mn and Na are high in the 2 year relative to the 3 year. Overall ratios between field soils and ginsengs are mainly big in the 2 year area relative to the 3 year area. It suggests that contents of the 3 year ginsengs are more similar to those of their soils relative to the 2 year and the ginsengs may absorpt eligible element contents with increasing ages.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.23 no.6
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• pp.314-319
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• 2013

Fabrication of nanocomposite material for the $Fe_2O_3-Al$ system by mechanical alloying (MA) has been investigated at room temperature. It is found that ${\alpha}-Fe/Al_2O_3$ nanocomposite powders in which $Al_2O_3$ is dispersed in ${\alpha}-Fe$ matrix are obtained by mechanical alloying of $Fe_2O_3$ with Al for 5 hours. The change in magnetization and coercivity also reflects the details of the solid state reduction process of hematite by pure metal of Al during mechanical alloying. Densification of the MA powders was performed in a spark plasma sintering (SPS) machine using graphite dies at $1000^{\circ}C$ and $1100^{\circ}C$ under 60 MPa. Shrinkage change after SPS of MA'ed sample for 5 hrs was significant above $700^{\circ}C$ and gradually increased with increasing temperature up to $1100^{\circ}C$. X-ray diffraction result shows that the average grain size of ${\alpha}-Fe$ in ${\alpha}-Fe/Al_2O_3$ nanocomposite sintered at $1100^{\circ}C$ is in the range of 180 nm. It can be also seen that the coercivity (Hc) of SPS sample sintered at $1000^{\circ}C$ is still high value of 88 Oe, suggesting that the grain growth of magnetic ${\alpha}-Fe$ phase during SPS process tend to be suppressed.

• Journal of the Korean Magnetics Society
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• v.8 no.1
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• pp.27-33
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• 1998

We have investigated tunneling magnetoresistance (TMR) properties of Fe/$Al_2O_3$/Co magnetic trilayer junctions sputtered on single-crystal Si (001) substrates. $Al_2O_3$ layers with thicknesses of 50~200 $\AA$ were deposited directly on the bottom ferromagnetic layer by a reactive rf sputtering. For comparsion, we prepared Pt/$Al_2O_3$/Pt tunnel junctions whose current-voltage (I-V) characteristics measured at 300 K indicated that reactively sputtered $Al_2O_3$ is a particularly good material for thin insulating barriers and allows us to form pinhole-free tunnel barriers. The magnetic tunnel junctions exhibit changes of tunnel resistance of about 0.1% at 300 K with an applied magnetic field and it was found that most junctions with Co as a top electrode have rather good I-V and TMR characteristics compared to those with Fe as a electrode. These results were discussed in relation to interfacial on the basis of those for Pt/$Al_2O_3$/Pt.

• The Journal of Natural Sciences
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• v.7
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• pp.19-25
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• 1995

In this study, the Mossbauer effect of the $NiAl_0.8Fe_1.2O_4$ was investigated in the temperature range of 77K-1000K. The spectra were composed of two component, one is sixtet and the other doublet, at low temperature. From the temperature dependence of Mossbauer spectum, it is appeared that the magnetic properties of $NiAl_0.8Fe_1.2O_4$ varies from ferrimagnetism to paramagnetism as the increasing tempereture. And the magnetic relaxation patterns of the $NiAl_0.8Fe_1.2O_4$ were shown superparamagnetic effect.

• Journal of Powder Materials
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• v.11 no.3
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• pp.247-252
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• 2004

Recently, it has been found that mechanical alloying (MA) facilitates the nanocomposites formation of metal-metal oxide systems through solid-state reduction during ball milling. In this work, we studied the MA effect of Fe$_{3}$O$_{4}$-M (M = Al, Ti) systems, where pure metals are used as reducing agents. It is found that composite powders in which $Al_{2}$O$_{3}$ and TiO$_{2}$ are dispersed in $\alpha$-Fe matrix with nano-sized grains are obtained by mechanical alloying of Fe$_{3}$O$_{4}$ with Al and Ti for 25 and 75 hours, respectively. It is suggested that the large negative heat associated with the chemical reduction of magnetite by aluminum is responsible for the shorter MA time for composite powder formation in Fe$_{3}$O$_{4}$-Al system. X-ray diffraction results show that the reduction of magnetite by Al and Ti if a relatively simple reaction, involving one intermediate phase of FeAl$_{2}$O$_{4}$ or Fe$_{3}$Ti$_{3}$O$_{10}$. The average grain size of $\alpha$-Fe in Fe-TiO$_{2}$ composite powders is in the range of 30 nm. From magnetic measurement, we can also obtain indirect information about the details of the solid-state reduction process during MA.

• Korean Journal of Materials Research
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• v.9 no.4
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• pp.345-348
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• 1999

The properties of Fe ions in the $ CdFe_2$$O_4$ and $CdFeAlO_4$ were investigated using the Mossbauer spectroscopy, in the temperature range from 300K to 900K. The calculated Debye temperature, recoil free fraction, mean square displacement and velocity are, 476.5K, 0.835, 3.39$\times$10\ulcorner$\textrm{cm}^2$, and 1.11$\times$10\ulcorner$\textrm{cm}^2$sec$^2$for Fe ions in the $CdFe_2$$O_4$ and 369.0K, 0.741, 5.65$\times$10\ulcorner$\textrm{cm}^2$ and 1.33$\times$10\ulcorner$\textrm{cm}^2$/$sec^2$in the $CeFeAlO_4$. The difference of the properties in the two samples were explained by the variation of the Fe\ulcorner-O\ulcorner bonding length with the substituted Al ions.

• Journal of the Korean Ceramic Society
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• v.37 no.4
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• pp.354-358
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• 2000

Tetragonal (t)-ZrO2/Al2O3 composites doped with Y2O3, Nb2O5, and Fe2O3 ((Y, Nb, Fe)-TZP/Al2O3) were prepared over the range containing Fe2O3 from 0.1 to 0.5 mol% with 0.1 mol% intervals to evaluate the effect of Fe2O3 addition on chromaticity, hydrothermal stability, and mechanical property of the composites. After autoclaving for 20 h at 18$0^{\circ}C$ under 3.5 MPa water vapor pressure, no tlongrightarrowm phase transformation was observed probably due to the preferential solid solubility of Fe2O3 in Al2O3, the presence of the rigid Al2O3 particles, and the inherent phase stability of (Y, Nb)-TZP. The optimized strength and the fracture toughness of the composite were 700 MPa and 8.5 MPa.m1/2, respectively, when 0.1 mol% Fe2O3 was added. The composites have shown a gradual color change from a slightly white ivory to a pale yellowish brown with increasing the Fe2O3 concentration.