• Economic and Environmental Geology
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• v.36 no.1
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• pp.39-48
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• 2003

The removal of chromate from aqueous solution using finely ground pyrite and biotite was investigated by batch experiments and the kinetics and the mechanism of chromate reduction were discussed. The chromate reduction by pyrite was about hundred times faster than that by biotite and was also faster at pH 3 than at pH 4. When pyrite was used, more than 90% of initial chromate was reduced within four hours at pH 4 and within 40 min. at pH 3. However, more than 400 hours was taken for the reduction of 90% of initial chromate by biotite. The results indicate that the rate of chromate reduction was strongly depending on the amount of Fe(II) in the minerals and on the dissolution rate of Fe(II) from the minerals. The reduction of chromate at pH 4 resulted in the precipitation of (Cr, Fe)(OH))$_3$$_{ (s)}$, which is believed to have limited the concentrations of dissolved Cr(III) and Fe(III) to less than expected values. When biotite was used, amounts of decreased Fe(II) and reduced Cr(Ⅵ) did not show stoichiometric relationship, which implying there was not only chromate reduction by ferrous ions in the acidic solution but also heterogeneous reduction of ferric ions by the structural ferrous iron in biotite. However, the results from a series of the experiments using Pyrite showed that concentrations of the decreased Fe(II) and the reduced Cr(Ⅵ) were close to the stoichiometric ratio of 3:1. It was because the oxidation of pyrite rapidly created ferrous ions even in oxygenated solutions and the chromate reduction by the ferrous ions was significantly faster than ferrous ion oxygenation.

• Journal of the Korean Magnetics Society
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• v.13 no.1
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• pp.6-14
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• 2003

The purpose of this study is to investigate the effect of chemical reaction with a bonding glass on physical and magnetic properties of Fe-Hf-N/SiO$_2$ and Fe-Hf-N/Cr/SiO$_2$ thin films. When the Fe-Hf-N/SiO$_2$ films were reacted with the bonding glass, the soft magnetic properties of them were extremely degraded. At $600^{\circ}C$, the saturation magnetization of the reacted film decreased to 1 kG, and its coercivity increased to 27 Oe, and its effective permeability decreased to 70. It was found that the degradation of soft magnetic properties of the Fe-Hf-N/SiO$_2$ films reacted with the bonding glass were attributed to the oxidation of the Fe-Hf-N layers to HfO$_2$ and Fe$_3$O$_4$. The soft magnetic properties of the Fe-Hf-N/Cr/SiO$_2$ films reacted with the bonding glass were degraded less than those of Fe-Hf-N/SiO$_2$ films. At $600^{\circ}C$, the saturation magnetization of the reacted film decreased to 13.5 kG, and its coercivity increased to 4 Oe, and its effective permeability decreased to 700. It was found that the Cr layer suppressed the oxidation of the Fe-Hf-N layers during the chemical reaction between the Fe-Hf-N layer and bonding glass.

• Journal of the Korean Magnetics Society
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• v.16 no.1
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• pp.23-27
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• 2006

By substituting Mn or Cr for Co in inverse spinel $CoFe_2O_4,\;Mn_xCo_{1-x}Fe_2O_4\;and\;Cr_xCo_{1-x}Fe_2O_4$ and thin films were prepared by sol-gel method and their structural and magnetic properties were investigated. X-ray diffraction indicates that the cubic lattice constant increase for the Mn substitution while it hardly changes for the Cr substitution. Substitution of $Mn^{2+}$ for octahedral $Co^{2+}$ sites can explain the increase of lattice constant in $Mn_xCo_{1-x}Fe_2O_4$. On the other hand, Substitution of $Cr^{3+}$ for octahedral $Co^{2+}$ and subsequent reduction of $Fe^{3+}$ ion into $Fe^{2+}$ are expected to happen. Mossbauer spectroscopy measurements on $Cr_xCo_{1-x}Fe_2P_4$ indicate the existence of tetrahedral $Fe^{2+}$ ions that are created through reduction of tetrahedral $Fe^{3+}$ ions in order to compensate charge imbalance happened by $Cr^{3+}$ substitution for octahedral $Co^{2+}$ sites. On the other hand, no $Fe^{2+}$ ions were detected by Mossbauer spectroscopy for $Mn_xCo_{1-x}Fe_2O_4$. A migration of $Fe^{3+}$ ions from octahedral to tetrahedral sites In $Mn_xCo_{1-x}Fe_2O_4$ was detected by Mossbauer spectroscopy for x>0.47. Vibrating sample magnetometry measurements on the samples at room temperature revealed that the saturation magnetization increases by Mn and Cr substitution for certain range of x, qualitatively explainable in terms of the comparison of spin magnetic moment among the related transition-metal ions.

• Journal of Magnetics
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• v.11 no.1
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• pp.51-54
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• 2006

Variation of magnetic properties through Cr substitution for Co in inverse-spinel $CoFe_2O_4$ has been investigated by vibrating-sample magnetometry (VSM) and conversion electron $M\ddot{o}ssbauer$ spectroscopy (CEMS). $Cr_{x}Co_{1-x}Fe_2O_4$ samples were prepared as thin films by a sol-gel method. The lattice constant of the $Cr_{x}Co_{1-x}Fe_2O_4$ samples was found to remain unchanged, explainable in terms of a reduction of tetrahedral $Fe^{3+}$ ion to $Fe^{2+}$ due to substitution of $Cr^{3+}$ ion into octahedral $Co^{2+}$ site. The existence of the tetrahedral $Fe^{2+}$ ions in $Cr_{x}Co_{1-x}Fe_2O_4$ was confirmed by CEMS analysis. Room-temperature magnetic hysteresis curves for the $Cr_{x}Co_{1-x}Fe_2O_4$ films measured by VSM revealed that the saturation magnetization $M_s$ increases by Cr doping. The $M_s$ is maximized when x = 0.1 and decreases for higher x but is still bigger than that of $CoFe_2O_4$. The increase of $M_s$ can be explained partly by the reduction of the tetrahedral $Fe^{3+}$ ion to $Fe^{2+}$.

• Corrosion Science and Technology
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• v.13 no.2
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• pp.41-47
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• 2014

The isothermal corrosion tests of several types of stainless steels, Ni-based alloys, and ferritic-martensitic steels (FMS) were carried out at the temperature of 550 and $650^{\circ}C$ in SFR S-$CO_2$ environment (200 bar) for 1000 h. The weight gain was greater in the order of FMSs, stainless steels, and Ni-based alloys. For the FMSs (Fe-based with low Cr content), a thick outer Fe oxide, a middle (Fe,Cr)-rich oxide, and an inner (Cr,Fe)-rich oxide were formed. They showed significant weight gains at both 550 and $650^{\circ}C$. In the case of austenitic stainless steels (Fe-based) such as SS 316H and 316LN (18 wt.% Cr), the corrosion resistance was dependent on test temperatures except SS 310S (25 wt.% Cr). After corrosion test at $650^{\circ}C$, a large increase in weight gain was observed with the formation of outer thick Fe oxide and inner (Cr,Fe)-rich oxide. However, at $550^{\circ}C$, a thin Cr-rich oxide was mainly developed along with partially distributed small and nodular shaped Fe oxides. Meanwhile, for the Ni-based alloys (16-28 wt.% Cr), a very thin Cr-rich oxide was developed at both test temperatures. The superior corrosion resistance of high Cr or Ni-based alloys in the high temperature S-$CO_2$ environment was attributed to the formation of thin Cr-rich oxide on the surface of the materials.

• Nuclear Engineering and Technology
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• v.29 no.5
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• pp.361-367
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• 1997

The phase separation in ferrite phase of duplex stainless steel is the primary cause of thermal aging embrittlement of the LWR primary pressure boundary components. In this study the phase separation of simulated duplex stainless steel was detected by Mossbauer spectroscopy and magnetic property analysis by VSM(Vibrating Specimen Magnetometer). The simulated duplex stainless steels, Fe-Cr binary, Fe-Cr-Ni ternary, and Fe-Cr-Ni-Si quarternary allots, were aged at 370 and 40$0^{\circ}C$ up to 5,340 hours. It was observed from Mossbauer spectra analysis that internal magnetic field increases with aging time and from VSM that the specific saturation magnetization and Curie temperature increase with aging time. These result are indicative that phase separation into Fe-rich region and Cr-rich region is caused by thermal aging in the temperature range of 370~40$0^{\circ}C$ In cases of specimens containing Ni, the increase of specific saturation magnetization is much higher. This implies that Ni seems to promote Fe-Cr interdiffusion, which accelerates the phase separation into Fe-rich $\alpha$ phase and Cr-rich $\alpha$' phase.

• Journal of the Korean institute of surface engineering
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• v.34 no.1
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• pp.39-48
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• 2001

Fe-Cr-Al alloy has been studied for application in automobile muffler materials due to good corrosion and oxidation resistance. In order to develop the automobile muffler materials, corrosion behaviors of electron beam physical vapor deposition (EB-PVD) coated surface of muffler matericls of muffler materials were investigated using potentiostat. For 0.1M NaCl solution, corrosion potential and pitting potential of Fe-20Cr-10Al was higher than that of Fe-5Cr- 10Al samples. Especially, in the case of Ti and Nb coated samples, pitting potential increased remarkably compared with non-coated samples. For 0.1M $CaCl_2$ solution, Ti-coated Fe-20Cr-10Al showed remarkably improved pitting corrosion resistance in comparison with non-coated Fe-20Cr-10Al and Fe-5Cr-10Al. The number and size of pits were decreased in the case of Ti coated samples in the 0.1M NaCl and 0.1M $CaCl_2$ solution.

• Journal of the Korean Magnetics Society
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• v.3 no.4
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• pp.277-283
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• 1993

The temperature dependence of DC magnetic susceptibilities of three austenitic Fe-Cr-Ni stainless alloys were measured in the temperature range of 4.2 and 300 K. Two alloys support a general magnetic description of austen-itic stsinless steels in terms of a two-magnetic-phase (spin glass + superparamagnetic cluster) model and one alloy shows magnetic double transition phenomena. Also this study shows that incressing the Ni/Cr ratio in Fe-Cr-Ni alloys causes a increase of the DC susceptibility peak value and a decrease of the magnetic transition temperature.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2000.07a
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• pp.108-110
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• 2000

The aim of this paper is to investigate the effect of Al and Ti on microstructure of Fe-Cr-Al alloy systems for applying electrical resistance wires of electrical furnace. From the preliminary study, the amount of recovered addition elements increased in the case of both vacuum and Ar-atmosphere melting than that in the case of air-atmosphere melting. Also, optimum Cr content for good performance at high temperature was approximately 24wt% from the observation of microstucture. The precipitates of Fe-Cr, Al-Cr and Al phases were observed, adding Al and Ti. Especially, Sharp rectangular shapes of precipitates were observed with increasing amount of Ti.

• Journal of the Korean Magnetics Society
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• v.4 no.2
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• pp.135-141
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• 1994

With the variation of Cr content and $N_2$ flow ratio, the soft magnetic properties, corrosion resistance and reactivity of the sputtered nanocrystalline FeZrCrN thin flims were investigated. In case of FeZrCrN thin films, a saturation magnetization was decreased with increasing $N_2$ flow ratio. In addition, good soft magnetic properties were obtained at the flow ratio of 3% $N_2$. The $Fe_{64.9}Zr_{8.8}Cr_{5.8}N_{20.5}$ nanocrystalline thin film after annealing at $550^{\circ}C$ exhibited the saturation magnetization of 12.5kG, low coercivity of 0.4 Oe and high permeability of 2600 at 5 MHz. Films containing up to 7.5% Cr showed an enhanced corrosion resistance and reduced reactivity with the bonding glass without degradation of soft magnetic properties, although the saturation magnetization was decreased slightly with the Cr addtion.