• Journal of the Korean Crystal Growth and Crystal Technology
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• v.10 no.3
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• pp.264-270
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• 2000

Quantitative analysis of iron ore sinter consisting of hematite, magnetite, calcium ferrite and slag was investigated by X-ray internal standard method. After selecting NaF and $SiO_2$as internal standard materials, the calibration curves were determined and were applied to quantitative analysis of the internal standard method. Calcium ferrite was identified as a solid solution of CaO.$2Fe_2$$O_3$with 7 wt% and 3 wt% solubility of $AI_2$$O_3$and $SiO_2$, respectively. The maximum deviation of quantitative analysis of synthetic iron ore was about $\pm$5 wt%. The contents of each mineral calculated in industrial sinter were 27~40 wt% of hematite, 20~30 wt% of magnetite, 22~33 wt% of calcium ferrite and 10~20 wt% of slag.

• Journal of Magnetics
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• v.7 no.2
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• pp.25-28
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• 2002

Slowly cooled $Cu_xFe_{3-x}O_4$ ($\chi$=0.1, 0.2) have been investigated over a temperature range from 82 to 700 K using the M$\ddot{o}$ssbauer technique. X-ray diffraction shows that these have a single-phase cubic spinel structure of lattice parameters $\alpha$=8.396 and 8.398${\AA}$, respectively. Since Cu ions prefer B (octahedral) sites to A (tetrahedral) sites, the ionic distribution is $(Fe)_A[Fe_{2-x}Cu_x]_BO_4$. M$\ddot{o}$ssbauer spectra consisted of two sets of 6-line pattern from. A site in ferric state and B site in ferrous-ferric state. Intensity ratio of B to A subspectra is 1.0 at 82 K and increases to 2.0 at 700 K with increasing temperature. After annealing the samples under vacuum at $450^circ{C}$ for a half hour, x-ray diffraction patterns have the peaks of magnetite- and hematite-phase. Lattice constants of magnetite-phase are 8.395 and 8.392 ${\AA}$ smaller than 8.396 and 8.398 ${\AA}$ before annealing, respectively. M$\ddot{o}$ssbauer spectra reveal the conventional magnetite pattern with the additional hematite pattern. Intensity ratios of B to A subspectra fur magnetite-phase become 1.9-2.0 over all temperature ranges and Cu ions are distributed over A and B sites randomly. Ratios of hematite to total intensity in M$\ddot{o}$ssbauer spectra for $\chi$= 0.1 and $\chi$= 0.2 are 10 and 21%, respectively. These hematite ratios may be due to annealing under vacuum at $450^circ{C}$, which transforms $Cu^{2+}$ ionic states into $Cu^{1+}$. Verwey temperatures far $\chi$= 0.1 and $\chi$= 0.2 are $123\pm2$ K and $128\pm2$ K.

• Korean Journal of Materials Research
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• v.22 no.11
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• pp.620-625
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• 2012

A general synthetic method to make $Fe_3O_{4-{\delta}}$ (activated magnetite) is the reduction of $Fe_3O_4$ by $H_2$ atmosphere. However, this process has an explosion risk. Therefore, we studied the process of synthesis of $Fe_3O_{4-{\delta}}$ depending on heat-treatment conditions using $FeC_2O_4{\cdot}2H_2O$ in Ar atmosphere. The thermal decomposition characteristics of $FeC_2O_4{\cdot}2H_2O$ and the ${\delta}$-value of $Fe_3O_{4-{\delta}}$ were analyzed with TG/DTA in Ar atmosphere. ${\beta}-FeC_2O_4{\cdot}2H_2O$ was synthesized by precipitation method using $FeSO_4{\cdot}7H_2O$ and $(NH_4)_2C_2O_4{\cdot}H_2O$. The concentration of the solution was 0.1 M and the equivalent ratio was 1.0. ${\beta}-FeC_2O_4{\cdot}2H_2O$ was decomposed to $H_2O$ and $FeC_2O$4 from $150^{\circ}C$ to $200^{\circ}C$. $FeC_2O4$ was decomposed to CO, $CO_2$, and $Fe_3O_4$ from $200^{\circ}C$ to $250^{\circ}C$. Single phase $Fe_3O_4$ was formed by the decomposition of ${\beta}-FeC_2O_4{\cdot}2H_2O$ in Ar atmosphere. However, $Fe_3C$, Fe and $Fe_4N$ were formed as minor phases when ${\beta}-FeC_2O_4{\cdot}2H_2O$ was decomposed in $N_2$ atmosphere. Then, $Fe_3O_4$ was reduced to $Fe_3O_{4-{\delta}}$ by decomposion of CO. The reduction of $Fe_3O_4$ to $Fe_3O_{4-{\delta}}$ progressed from $320^{\circ}C$ to $400^{\circ}C$; the reaction was exothermic. The degree of exothermal reaction was varied with heat treatment temperature, heating rate, Ar flow rate, and holding time. The ${\delta}$-value of $Fe_3O_{4-{\delta}}$ was greatly influenced by the heat treatment temperature and the heating rate. However, Ar flow rate and holding time had a minor effect on ${\delta}$-value.

• Corrosion Science and Technology
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• v.22 no.2
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• pp.90-98
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• 2023

In this study, cobalt oxide (Co₃O₄) and cobalt-doped magnetite (CoFe₂O₄) nanoparticles were synthesized by a hydrothermal method. They were then used as corrosion inhibitors for corrosion protection of AA2024-T3 aluminum alloys. These obtained nanoparticles were characterized by x-ray diffraction, field-emission scanning electron microscopy, and Zeta potential measurements. Corrosion inhibition activities of Co₃O₄ and CoFe₂O₄ nanoparticles were determined by performing electrochemical measurements for bare AA2024-T3 aluminum alloys in 0.05 M NaCl + 0.1 M Na₂SO₄ solution containing Co₃O₄ or CoFe₂O₄ nanoparticles. Corrosion protection for AA2024-T3 aluminum alloys by a water-based epoxy with or without the synthesized Co₃O₄ or CoFe₂O₄ nanoparticles was investigated by electrochemical impedance spectroscopy during immersion in 0.1 M NaCl solution. The corrosion protection of epoxy coating deposited on the AA2024-T3 surface was improved by incorporating Co₃O₄ or CoFe₂O₄ nanoparticles in the coating. The corrosion protection performance of the epoxy coating containing CoFe₂O₄ was higher than that of the epoxy coating containing Co₃O₄.

• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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• 2004.11a
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• pp.289-295
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• 2004

The relationship between friction characteristics and iron oxides at the sliding interface was investigated. Three friction materials containing iron, magnetite $(Fe_3O_4)$ or hematite $(Fe_2O_3)$ were manufactured and friction tests were performed on gray cast iron disks to evaluate the friction coefficient as a function of sliding speed $\mu-\nu$. In-situ noise spectrum analyzer was employed to compare noise propensity during friction tests. Results show that the specimens with magnetite are more sensitive to velocity than those with iron or hematite. The specimens containing magnetite and hematite generated noise with different peaks in the spectrum. The difference in the peak frequency seems attributed to the different surface aggressiveness of iron oxides and intermittent changes of real contact area at the sliding interface during sliding. Surface morphology and roughness of the counter disc after the tests are also consistent with the aggressiveness of iron oxides.

• Korean Journal of Materials Research
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• v.21 no.4
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• pp.225-231
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• 2011

The effect of ferrous/ferric molar ratio on the formation of nano-sized magnetite particles was investigated by a co-precipitation method. Ferrous sulfate and ferric sulfate were used as iron sources and sodium hydroxide was used as a precipitant. In this experiment, the variables were the ferrous/ferric molar ratio (1.0, 1.25, 2.5 and 5.0) and the equivalent ratio (0.10, 0.25, 0.50, 0.75, 1.0, 2.0 and 3.0), while the reaction temperature ($25^{\circ}C$) and reaction time (30 min.) were fixed. Argon gas was flowed during the reactions to prevent the $Fe^{2+}$ from oxidizing in the air. Single-phase magnetite was synthesized when the equivalent ratio was above 2.0 with the ferrous/ferric molar ratios. However, goethite and magnetite were synthesized when the equivalent ratio was 1.0. The crystallinity of magnetite increased as the equivalent ratio increased up to 3.0. The crystallite size (5.6 to 11.6 nm), median particle size (15.4 to 19.5 nm), and saturation magnetization (43 to 71 $emu.g^{-1}$) changed depending on the ferrous/ferric molar ratio. The highest saturation magnetization (71 $emu.g^{-1}$) was obtained when the equivalent ratio was 3.0 and the ferrous/ferric molar ratio was 2.5.

• Applied Chemistry for Engineering
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• v.2 no.4
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• pp.372-384
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• 1991

The sulfation of the domestic titaniferous magnetite ore with ammonium sulfate was investigated to find a cyclic process for the production of synthetic rutile and high purity iron oxide and to test the feasibility of ammonium sulfate being an alternative sulfation agent. The proper sulfation conditions were determined to be a temperature of $425^{\circ}C$, 2.5 hours of reaction time, the weight ratio of ammonium sulfate to titaniferous magnetite : 11, and particle size or titaniferous magnetite : -250 mesh. 90.4 % of $TiO_2$ and 85.3 % of iron were extracted from the titaniferous magnetite sulfated under these conditions by the water leaching. From the leachate $TiO_2$ of 93.8 % purity as a mixture of rutile and anatase and ${\alpha}-Fe_2O_3$ of 97.6 % purity were obtained.

• Bulletin of the Korean Chemical Society
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• v.19 no.5
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• pp.533-539
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• 1998

A magnetic film was deposited on a slide glass substrate from aqueous solutions of $FeCl_2$ and $NaNO_2$ at 363 K. XRD analysis showed that the film was polycrystalline magnetite $(Fe_{3(1-{\sigma})}O_4)$ without impurity phase. The lattice constant was 0.8390 nm. Mossbauer spectrum of the film could be deconvoluted by the following parameters: isomer shifts for tetrahedral $(T_d)$ and octahedral $(O_h)$ sites are 0.28 and 0.68 mm/s, respectively, and corresponding magnetic hyperfine fields are 490 and 458 kOe, respectively. The estimated chemical formula of the film by the peak intensity of Mossbauer spectrum was $Fe_{2.95}O_4$. Low temperature transition of the magnetite (Verwey transition) was not detected in resistivity measurement of the film. Properties of the film were discussed with those of pressed pellet and single crystal of synthetic magnetites. On the surface of the film, magnetite particles of about 0.2 μm in diameter were identified by noncontact atomic force microscopy (NAFM) and magnetic force microscopy (MFM).

• The Korean Journal of Ceramics
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• v.6 no.4
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• pp.401-404
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• 2000

Mimicking the bacterial synthesis of magnetosomes, in which the functionalized surface of a cytoplasmic (lipid) membrane is considered to be stimulating the crystal growth of magnetite, we have successfully grown magnetite films at $30^{\circ}C$ using an arachic acid monomolecular layer as a functionalized surface. The lipid monomolecular layer was spread on an aqueous solution of FeCl$_2$ which was oxidized by flowing a mixed gas, with ratio $O_2$/$N_2$=1/2000, on the surface of the lipid layer. Mossbauer and X-ray diffraction analyses revealed that the Fe$_3$O$_4$ films contain small amounts of ferric hydroxyl impurity phases of ${\alpha}$-FeOOH and ${\tau}$-FeOOH. This is because the oxygen partial pressure at the ferrite/aqueous interface changed as the film (through which the gas penetrated) increased in thickness. Methods to obtain single phase magnetite films are proposed.

• Journal of the Korean Applied Science and Technology
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• v.27 no.3
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• pp.344-352
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• 2010

Magnetite and inorganic sludge were mainly composed of $Fe_2O_4$ and $Fe_2O_3$, respectively. Initial specific surface areas of magnetite and inorganic sludge were 130 $m^2$/g and 31.7 $m^2$/g. $CO_2$ decomposition rate for inorganic sludge was increased with temperature. Maximum $CO_2$ decomposition rates were shown 89% for magnetite at $350^{\circ}C$ and 84% for inorganic sludge at $500^{\circ}C$. Specific surface area for magnetite was not varied significantly after $CO_2$ decomposition. However, specific surface area for inorganic sludge was greatly decreased from initial 130 $m^2$/g to approximately 50~60 $m^2$/g after reaction. Therefore, it was estimated that magnetite could be used for $CO_2$decomposition for a long time and inorganic sludge should be wasted after $CO_2$ decomposition reaction.