• 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.

• ETRI Journal
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• v.35 no.1
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• pp.100-108
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• 2013

In this paper, a feature extraction (FE) method is proposed that is comparable to the traditional FE methods used in automatic speech recognition systems. Unlike the conventional spectral-based FE methods, the proposed method evaluates the similarities between an embedded speech signal and a set of predefined speech attractor models in the reconstructed phase space (RPS) domain. In the first step, a set of Gaussian mixture models is trained to represent the speech attractors in the RPS. Next, for a new input speech frame, a posterior-probability-based feature vector is evaluated, which represents the similarity between the embedded frame and the learned speech attractors. We conduct experiments for a speech recognition task utilizing a toolkit based on hidden Markov models, over FARSDAT, a well-known Persian speech corpus. Through the proposed FE method, we gain 3.11% absolute phoneme error rate improvement in comparison to the baseline system, which exploits the mel-frequency cepstral coefficient FE method.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.30 no.5 s.248
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• pp.505-511
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• 2006

In the present paper, approximate plastic limit load solutions fur pipe bends under combined internal pressure and bending are obtained from detailed three-dimensional (3-D) FE limit analyses based on elastic-perfectly plastic materials with the small geometry change option. The present FE results show that existing limit load solutions for pipe bends are lower bounds but can be very different from the present FE results in some cases, particularly for bending. Accordingly closed-form approximations are proposed for pipe bends under combined pressure and in-plane bending based on the present FE results. The proposed limit load solutions would be a basis of defective pipe bends and be useful to estimate non-linear fracture mechanics parameters based on the reference stress approach.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2006.05a
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• pp.401-402
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• 2006

In the present paper, approximate plastic limit load solutions for pipe bends under combined internal pressure and bending are obtained from detailed three-dimensional (3-D) FE limit analyses based on elastic-perfectly plastic materials with the small geometry change option. The present FE results show that existing limit load solutions for pipe bends are lower bounds but can be very different from the present FE results in some cases, particularly for bending. Accordingly closed-form approximations are proposed for pipe bends under combined pressure and in-plane bending based on the present FE results. The proposed limit load solutions would be a basis of defective pipe bends and be useful to estimate non-linear fracture mechanics parameters based on the reference stress approach.

• Journal of the Korean Magnetics Society
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• v.5 no.1
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• pp.38-41
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• 1995

The effects of Nb and Cu additives as will as substitutional Co into $Nd_{4}Fe_{85.5}B_{10.5}$ melt-spun alloy were studied aiming for finding a $\alpha$-Fe based Nd-Fe-B composite alloys with high energy product. The addition of Nb and Cu to $Nd_{4}Fe_{85.5}B_{10.5}$ decreased the average grain size and increased the coercivity up to 207kA/m(2.6kOe), Further-more, the substitution of Co for Fe in $Nd_{4}Fe_{82}B_{10}Nb_{3}Cu_{1}$ alloy resulted in the decrease of the average grain size (<20nm) and improved the hard magnetic properties. The remanence, coercivity and energy product of optimally annealed $Nd_{4}Fe_{74}Co_{8}B_{10}Nb_{3}Cu_{1}$ alloy were 1.345, 219kA/m(2.75kOe) and $95.5kJ/m^{3}$(12MGOe), respectively.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.28 no.1
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• pp.44-50
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• 2018

The improved high-performance Fe-based perovskite-type oxides ($La_{0.7}Sr_{0.3}M_xFe_{1-x}O_3$, M = Cu, Cr, Ni) were synthesized by a citrate method and characterized by SEM, EDS, XRD and NMR spectroscopy analyses. The characterization analyses revealed that the stoichiometric amounts of lattice oxygen were existed in all of perovskite samples except for a nickel-doped perovskite. Fe-based perovskites exhibited a surprising result for ortho-para $H_2$ spin conversion reaction, indicating two orders of magnitude higher conversions and conversion rates than commercial $Fe_2O_3$. It was considered that this conversion difference might be attributed to the presence of oxygen vacancies in Fe-based perovskites prepared in this study.

• Clean Technology
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• v.19 no.3
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• pp.233-242
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• 2013

The influences of Ca and Fe based oxides as dechlorination sorbents on the product distribution, boiling point distribution of liquid product, concentration of Cl of the products from the pyrolysis of PVC containing combustible wastes were investigated. With Fe based oxides as the sorbents, the yield of liquid product remarkably decreased whereas the decrease of the boiling point distribution of the liquid product was not noticeable. This phenomenon indicated that Fe based oxides worked as catalysts with weak catalytic activity. With Ca based oxides as the sorbents, the yield of liquid product did not decrease and the boiling point distribution of liquid product did not change significantly, but the dechlorination performance of these was much better than that with Fe based oxides.

• Journal of the Korean Magnetics Society
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• v.4 no.2
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• pp.173-178
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• 1994

The water-based magnetic fluids were prepared with the synthesized ultra-fine magnetite, oleic acid and SDBS (sodium dodecyl benzene sulfonate) as surfactants. The dispersion of water-based magnetic fluids was about 90 % when the added amounts of oleic acid and SDBS for magnetite(27 g) were more than $2.66{\times}10^{-3}$ mol and 10 g respectively. As the solid content increased from o. 05 g/cc to 0.4 g/cc, saturation magnetization of magnetic fluids at 5 kOe increased from 1.98 emu/g to 9.63 emu/g at $Fe^{2+}/Fe^{3+}=0.5$ and from 2.7 emu/g to 14.63 emu/g at $Fe^{2+}/Fe^{3+}=1.0$, and the its viscosity increased from 1.3 cp to 4.4 cp at $Fe^{2+}/Fe^{3+}=0.5$. pH region of oleic acid and SDBS stabilized water-based mag¬netic fluids was stable was in the range of pH 3.0 to pH 11.0. Stability of Water-based magnetic fluids can be obtained by observation of magnetic memory patterns on the VCR tape.

• Journal of the Korea institute for structural maintenance and inspection
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• v.24 no.6
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• pp.67-76
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• 2020

This paper reports an experimental study to evaluate the flexural behavior of concrete beams reinforced using Fe based shape memory alloy (Fe-SMA) bars. For the experiment, a concrete beam of 200mm×300mm×2,200mm was produced, and a 4% pre-strained Fe-SMA bar was used as a tensile reinforcement. As experimental variables, type of tensile reinforcement (SD400, Fe-SMA), reinforcement ratio (0.2, 0.39, 0.59, 0.78), activation of Fe-SMA (activation, non-activation), and joint method of Fe-SMA bar (Continuous, welding, coupler) were considered. The electric resistance heating method was used to activate the Fe-SMA bar, and a current of 5A/㎟ was supplied until the specimen reached 160℃. After the upward displacement of the specimen due to the camber effect was stabilized, a three-point flexural loading experiment was performed using an actuator of 2,000 kN capacity. As a result of the experiment, it was found that the upward displacement occurred due to the camber effect as the Fe-SMA bar was activated. The specimen that activated the Fe-SMA bar had an initial crack at a higher load than the specimen that did not activate it. However, as with general prestressed concrete, the effect of the prestress by Fe-SMA activation on the ultimate state of the beam was insignificant.

• Journal of the Korean Society for Heat Treatment
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• v.15 no.2
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• pp.76-81
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• 2002

The melt-spun amorphous $Fe_{77-X}P_{13}C_4B_4Al_2Mo_X$(x=4~10) and $Fe_{82-X}P_XC_4B_4Al_2Mo_8$(x=9~15) alloys were found to exhibit a large supercooled liquid region(${\Delta}T_x$) exceeding 40 K before crystallization. The largest ${\Delta}T_x$ for the glassy alloys containing Mo reaches as large as 65 K for the $Fe_{69}P_{13}C_4B_4Al_2Mo_8$ alloy. The corrosion behavior of the amorphous $Fe_{77-X}P_{13}C_4B_4Al_2Mo_X$(x=4~15) and $Fe_(82-X)P_XC_4B_4Al_2Mo_8$ (x=9~17) alloys were examined by electrochemical measurements in 9M $H_2SO_4$ solution at 303 K. The addition of Mo(or P) for replacing some portion of Fe is effective in improving the corrosion resistance of the investigated Fe-based glassy alloys. They are spontaneously passivated and have a wide passive region with low passive current density.