• Journal of Powder Materials
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• v.20 no.3
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• pp.210-214
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• 2013

This manuscript reports on compared color evolution about phase transformation of ${\alpha}-FeOOH@SiO_2$ and ${\beta}-FeOOH@SiO_2$ pigments. Prepared ${\alpha}$-FeOOH and ${\beta}$-FeOOH were coated with silica for enhancing thermal properties and coloration of both samples. To study phase and color of ${\alpha}$-FeOOH and ${\beta}$-FeOOH, we prepared nano sized iron oxide hydroxide pigments which were coated with $SiO_2$ using tetraethylorthosilicate and cetyltrimethyl-ammonium bromide as a surface modifier. The silica-coated both samples were calcined at high temperatures (300, 700 and $1000^{\circ}C$) and characterized by scanning electron microscopy, CIE $L^*a^*b^*$ color parameter measurements, transmission electron microscopy and UV-vis spectroscopy. The yellow ${\alpha}$-FeOOH and ${\beta}$-FeOOH was transformed to ${\alpha}-Fe_2O_3$ with red, brown at 300, $700^{\circ}C$, respectively.

• Proceedings of the KSME Conference
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• 2004.11a
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• pp.1162-1165
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• 2004

Size and crystalline phase changes of $Fe_{2}O_{3}$ nanoparticles formed in a $H_{2}/O_{2}$ flame have been investigated. At flame temperatures below $1350^{\circ}C$, the mean particle size increased monotonously with the distance from the burner edge; but in high-temperature flames above $1650^{\circ}C$, it suddenly decreased from 20 nm to ${\sim}3$ nm with the distance from the burner edge. The results of X-ray diffraction and HRTEM showed that this sudden reduction of the size of nanoparticles was accompanied by a partial phase transformation from ${\gamma}$-$Fe_{2}O_{3}$ into ${\alpha}$-$Fe_{2}O_{3}$. We suggest the structural instability due to ${\gamma}-$ to ${\alpha}-phase$ transformation as a mechanism for a rapid fragmentation of 20 nm particles into 3 nm ones.

• Journal of the Korean institute of surface engineering
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• v.33 no.5
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• pp.365-372
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• 2000

Pure $Fe_3$Al alloys with three different compositions of Fe-21.8%Al, Fe-24.1%Al and Fe-27.2%Al were prepared by vacuum induction melting followed by homogenization and hot forging. The long-time oxidation behavior of the prepared alloys was studied at 1073, 1273 and 1473k in air. The oxidation resistance greatly increased with an increase in Al contents. Thin and uniform oxide scales were always formed on Fe-27.2%Al, while thick and fragile oxide scales were formed on Fe-(21.8, 24.1%)Al. Internal oxidation was observed in Fe-(21.8, 24.1%)Al, when oxidized above 1273K. The major oxidation product of all the oxidized alloys was always $\alpha$-$Al_2$$O_3$.

• Journal of the Korean Ceramic Society
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• v.13 no.1
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• pp.25-29
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• 1976

The properties vary with quality of ferric-oxide that is major material of ferrites. In this point of view, a manufacturing method of pure and homogeneous fine ferric oxide is very important. The characters of this study are as follows: 1) Ferric oxide was made from waste pickling liquor of steel. 2) The crude ferric-oxide that is made by roasting the pickling liquor was dissolved in 20% HCI solution and then produced ferric chloride is purified by ethyl ether extraction. 3) The methanol solution of purified ferric chloride was sprayed into the refractory tube with compressed air and propane gas and then ignited leading to the ferric-oxide powder. 4) The produced oxide powder was introduced to the scrubber type vessel throught cooling system in order to collect the powder. 5) Crystalline phase of the powder was identified by X-ray diffraction and particle size, crystalline shape of the powder were investigated by settling method and electron microscope and the effects of concentration of ferric chloride in methanol on grain size were discussed. Results were obtained as fellows: 1) Total impurity in the ferric oxide produced from waste pickling liquor was 3.7%. 2) The solubilityof crude ferric oxide that was made from waste pickling liquor in HCI solution increased with the HCI concentration and reached to saturation range at 15% HCI concentration. 3) Extraction of FeCl3 increased with HCI concentration which is solvent. 4) Alpha ferric oxide obtained was very fine crystalline particles, the mean crystalline grain increased with the concentration of ferric chloride, and mean grain size distributed from 3.5$\mu$(at 0.5mole/l) to 0.5$\mu$(at 0.05mole/l).

• Corrosion Science and Technology
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• v.6 no.3
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• pp.128-132
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• 2007

For a quantitative inspection on the performance of weathering steel bridges, we have investigated the relationship between the corrosion rate and the composition of the rust layers formed on weathering steel bridges located in various environments in Japan and applied a protective ability index (PAI) to the bridges. The corrosion rates were clearly classified by the PAI, ${\alpha}/{\gamma}*$ and sub index of $({\beta}+s)/{\gamma}*$, where $\alpha$, \gamma*, $\beta$ and s are the mass ratio of crystalline $\alpha-FeOOH$, the total of $\gamma$-FeOOH+ $\beta$-FeOOH + the spinel-type iron oxide (mainly $Fe_3O_4$), $\beta-FeOOH$ and spinel-type iron oxide, analyzed by powder X-ray diffraction, respectively. In the case of ${\alpha}/{\gamma}$*>1, the rust layer works protective enough to reduce the corrosion rate less than 0.01 mm/y. The sub index $({\beta}+s)/{\gamma}*$<0.5 or >0.5 classifies the corrosion rate of the non-protective rust layers, therefore the former state of the rust layer terms inactive and the latter terms active. The quantitative inspection of a weathering steel bridge requires a performance-inspection (PI) and periodical deteriorationinspections (DI). The PI can be completed by checking of the PAI, ${\alpha}/{\gamma}*$. The DI on the weathering steel bridges where deicing salt is sprinkled can be performed by checking the PAI, $({\beta}+s)/{\gamma}*$.

• Bulletin of the Korean Chemical Society
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• v.35 no.5
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• pp.1379-1384
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• 2014

${\alpha}-Fe_2O_3$ spherical particles having an average diameter of ca. 420 nm and ${\alpha}-Fe_2O_3$ fine particles (< 10 ${\mu}m$ particle size) were prepared to examine as catalysts for CO oxidation. Kinetic studies on the catalytic reactions were performed in a flow reactor using an on-line gas chromatography system operated at 1 atm. The apparent activation energies and the partial orders with respect to CO and $O_2$ were determined from the rates of CO disappearance in the reaction stage showing a constant catalytic activity. In the temperature range of $150-275^{\circ}C$, the apparent activation energies were calculated to be 13.7 kcal/mol on the ${\alpha}-Fe_2O_3$ spherical submicron clusters and 15.0 kcal/mol on the ${\alpha}-Fe_2O_3$ fine powder. The Pco and $Po_2$ dependencies of rate were investigated at various partial pressures of CO and $O_2$ at $250^{\circ}C$. Zero-order kinetics were observed for $O_2$ on both the catalysts, but the reaction order for CO was observed as first-order on the ${\alpha}-Fe_2O_3$ fine powder and 0.75-order on the ${\alpha}-Fe_2O_3$ spherical submicron clusters. The catalytic processes including the inhibition process by $CO_2$ on the ${\alpha}-Fe_2O_3$ spherical submicron powder are discussed according to the kinetic results. The catalysts were characterized using XRD (X-ray powder diffraction), FE-SEM (field emission-scanning electron microscopy), HR-TEM (high resolution-transmission electron microscopy), and $N_2$ sorption measurements.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.19 no.4
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• pp.202-207
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• 2009

Nanocomposite formation of metal-metal oxide systems by mechanical alloying (MA) has been investigated at room temperature. The systems we chose are the $Fe_3O_4$-M (M = AI, Ti), where pure metals are used as reducing agent. It is found that $Fe/Al_2O_3$ and $Fe/TiO_2$ nanocomposite powders in which $Al_2O_3$ and $TiO_2$ are dispersed in ${\alpha}$-Fe matrix with nano-sized grains are obtained by MA of $Fe_3O_4$ with Al and Ti for 25 and 75 hours, respectively. It is suggested that the shorter MA time for the nanocomposite formation in $Fe/Al_2O_3$ is due to a large negative heat associated with the chemical reduction of magnetite by aluminum. X-ray diffraction results show that the average grain size of ${\alpha}$-Fe in $Fe/TiO_2$ nanocomposite powders is in the range of 30 nm. The change in magnetic properties also reflects the details of the solid-state reduction of magnetite by pure metals during MA.

• Korean Journal of Materials Research
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• v.16 no.11
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• pp.687-691
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• 2006

Synthesis of Iron oxides by air oxidation of $FeSO_4$ solutions in the presence of NaOH, Diethylenetriamine (DETA), Butylamine (BA) and influence of ultrasonic wave were investigated by XRD, SEM and particle size analyzer. As the DETA addition increased to 0.05 mol, $Fe_3O_4$ was formed with goethite($\alpha$- FeOOH) and $Fe_3O_4$ single phase was formed above 0.18mol of DETA. As the BA addition increased, the XRD peak intensity of (020) face of lepidocrocite($\gamma$-FeOOH) was developed until the formation of $Fe_3O_4$ and reduced the size of the iron oxide particles formed. Ultrasonic wave reduced the size of the iron oxide particles but gave little effects on the iron oxide particles synthesized by amine.

• Journal of Magnetics
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• v.22 no.1
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• pp.100-103
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• 2017

We studied the microstructure and magnetic properties of Fe nanosized powder synthesized by the pulsed wire evaporation method. The x-ray diffraction spectrum confirmed that this powder had a pure ${\alpha}$-Fe phase. Scanning electron microscope and transmission electron microscope measurements indicated that the prepared powder had uniform spherical shape with core-shell structure. The mean powder size was about 35 nm and the thickness of the surface passivation layer was about 5 nm. Energy dispersive X-ray spectroscopy measurement indicated that the surface passivation layer was iron oxide. Magnetic field dependent magnetization measurement at room temperature showed that the maximum magnetization of the prepared powder was 177.1 emu/g at 1 T.

• Particle and aerosol research
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• v.9 no.4
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• pp.209-219
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• 2013

We have used the modified diffusion flame burner to synthesize silica coated iron oxide nanoparticles having enhanced superparamagnetic property. Silica-encapsulated iron oxide particles were directly observed using a high resolution transmission electron microscope. From the energy dispersive X-ray spectroscopy (EDS) and zeta potential measurements, the iron oxide particles were found to be completely covered by a silica coating layer. X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD) measurements revealed that the iron oxide core consists of ${\gamma}-Fe_2O_3$ rather than ${\alpha}-Fe_2O_3$. Our magnetization measurements support this conclusion. Biocompatibility test of the silica-coated iron oxide nanoparticles is also conducted using the protein adsorption onto the coated particle.