• Korean Journal of Materials Research
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• v.21 no.1
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• pp.1-7
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• 2011

Methods of producing hydrogen include steam reforming, electrochemical decomposition of water, and the SI process. Among these methods, the Sulfur iodine process is one of the most promising processes for hydrogen production. The thermochemical sulfur-iodine (SI) process uses heat from a high-temperature-gas nuclear reactor to produce $H_2$ gas; this process is known for its production of clean energy as it does not emit $CO_2$ from water. But the SI-process takes place in an extremely corrosive environment for the materials. To endure SI environments, the materials for the SI environment will have to have strong corrosion resistance. This work studies the corrosion resistances of the Fe-Si, Ni-Ti and Ni Alloys, which are tested in SI-process environments. Among the SI-process environments, the conditions of boiling sulfuric acid and decomposed sulfuric acid are selected in this study. Before testing in boiling sulfuric acid environments, the specimens of Fe-4.5Si, Fe-6Si, Ni-4.5Si, Ni-Ti-Si-Nb and Ni-Ti-Si-Nb-B are previously given heat treatment at $1000^{\circ}C$ for 48 hrs. The reason for this heat treatment is that those specimens have a passive film on the surface. The specimens are immersed for 3~14 days in 98wt% boiling sulfuric acid. Corrosion rates are measured by using the weight change after immersion. The corrosion rates of the Fe-6Si and Ni-Ti-Si-Nb-B are found to decrease as the time passes. The corrosion rates of Fe-6si and Ni-Ti-Si-Nb-B are measured at 0.056 mm/yr and 0.16 mm/yr, respectively. Hastelloy-X, Alloy 617, Alloy 800H and Haynes 230 are tested in the decomposed sulfuric acid for one day. Alloy 800H was found to show the best corrosion resistance among the materials. The corrosion rate of Alloy 800H is measured at -0.35 mm/yr. In these results, the corrosion resistance of materials depends on the stability of the oxide film formed on the surface. After testing in boiling sulfuric acid and in decomposed sulfuric acid environments, the surfaces and compositions of specimens are analyzed by SEM and EDX.

• Journal of the Korean Ceramic Society
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• v.37 no.10
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• pp.1008-1013
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• 2000

SrTi $O_3$(001) 단결정 기판 위에 졸-겔 스핀코팅으로 $SrBi_2(Ta,Nb)_2O_9$ 박막을 도포하고 그 결정화 과정을 고온 X-선 회절분석 (HTXRD)으로 추적하면서 Pt(111)/Ti/ $SiO_2$/Si 위에 성장한 박막과 비교하였다. SrTi $O_3$(001) 단결정 기판 위에 도포된 $SrBi_2Nb_2O_{9}$ 박막은 fluorite-like phase와 같은 transient phase를 거치지 않고 곧바로 순수한 $SrBi_2Nb_2O_9$ 상으로 결정화가 시작되었으며 결정화가 시작되는 온도인 ${\sim}540^{\circ}C$부터 c축 배향성장하였다. 또한 $SrB i_2(Ta,Nb)_2O_9$ 박막은 Ta/Nb 비에 관계없이 $SrTiO_3$(001) 위에서 모두 $(00{\ell})$로 배향되었으며, 코팅 횟수가 늘어나 필름의 두께가 증가함에 따라 c축 배향성은 미세한 감소를 보였다. $SrBi_2Nb_2O_9/SrTiO_3$단면을 TEM으로 관찰한 결과 $SrBi_2Nb_2O_9$은 대체로 불규칙한 크기의 다결정체로 되어 있었으나 계면 부근에서는 [001]$_{SBN}$//[001]$_{SrTi}$ $O_3$/, [100]$_{SBN}$//[100]$_{SrTi}$ $O_3$/라는 결정학적 관계를 가지며 에피탁샬 성장했음을 알 수 있었다.있었다.

• Journal of Magnetics
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• v.18 no.4
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• pp.395-399
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• 2013

The metallic glass ribbons of $[(Fe_xCo_{1-x})_{0.75}B_{0.2}Si_{0.05}]_{96}Mo_4$ (x = 0, 0.3, 0.6, 0.9 at.%) and $[(Fe_xCo_{1-x})_{0.75}B_{0.2}Si_{0.05}]_{96}Nb_4$ (x = 0, 0.3, 0.6, 0.9 at.%) were obtained by melt spinning with 25-30 ${\mu}m$ thickness. The thermal stability, mechanical properties and magnetic properties of Fe-Co-B-Si based systems were investigated. The values of thermal stability were measured using differential scanning calorimetry (DSC), including glass transition temperature ($T_g$), crystallization temperature ($T_x$) and supercooled liquid region (${\Delta}T_x=T_x-T_g$). These amorphous ribbons were identified as fully amorphous, using X-ray diffraction (XRD). The mechanical properties of Febased samples were measured by nano-indentation. Magnetic properties of the amorphous ribbons were measured by a vibrating sample magnetometer (VSM). The amorphous ribbons of $[(Fe_xCo_{1-x})_{0.75}B_{0.2}Si_{0.05}]_{96}Mo_4$ (x = 0, 0.3, 0.6, 0.9 at.%) and $[(Fe_xCo_{1-x})_{0.75}B_{0.2}Si_{0.05}]_{96}Nb_4$ (x = 0, 0.3, 0.6, 0.9 at.%) exhibited soft magnetic properties with low coercive force ($H_c$) and high saturation magnetization (Ms).

• 연구논문집
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• s.34
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• pp.121-129
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• 2004

The influence of powder size and ball-milling time on the magnetic properties of $Fe_{73}Si_{16}B_7Nb_3Cu_1$ nanocrystalline alloy powder was investigated. Flake-shaped powders were produced by pulverizing the ribbons annealed at $550^\circC$ for 1 hour. The powders were classified and consolidated into core shapes at a pressure of 18ton/$cm^2$. The initial permeability at 100kHz of the inductor core produced using $53-75\mum$ powders showed the highest value although its consolidated density showed the lowest one. The reason for the result is due to the cracking of the particles larger than $75\mum$ during the consolidation process. The ball-milling of powders for 2-4 hours improved the consolidation density and the initial permeability of the cores. The intrinsic coercivity of the powder decreased as well, resulting from the stress relief of the powder by a short-time milling.

• Transactions on Electrical and Electronic Materials
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• v.1 no.3
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• pp.29-33
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• 2000

The crystallographic and high frequency characteristics of $Fe_{73.9}Cu_{1.0}Nb_{3.5}Si_{14.0}B_{7.6}$ soft magnetic alloys were investigated under magnetic field annealing, The crystallization fraction of annealed samples with longitudinal magnetic fields is higher than that of samples without magnetic field. When the transverse magnetic field is applied, the crystallization fraction does not increases but decreases until $500^{circ}C$. It is found that for samples, the saturation induction are all same with 1.3 T. The coercive field of as-cast samples is 1.03 A/cm, but in annealed samples it decrease from 0.56 to 0.1A/cm with increasing annealing temperature from 400 to $550^{circ}C$. The squareness of annealed samples under transverse magnetic field has a small value than that of both without field and with longitudinal field annealing. It is noted that the magnetic field annealing with transverse direction to amorphous $Fe_{73.9}Cu_{1.0}Nb_{3.5}Si_{14.0}B_{7.6}$ profoundly influenced on the Mossbauer spectra in contrast to that with longitudinal direction and without magnetic field.

• Korean Journal of Metals and Materials
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• v.48 no.1
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• pp.1-7
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• 2010

Experiments have demonstrated that the addition of a moderate amount of V to $Fe_{52}Co_{(20-x)}B_{20}Si_4Nb_4V_x$ amorphous alloy enhances the plasticity of the alloy. In particular, $Fe_{52}Co_{17.5}B_{20}Si_4Nb_4V_{2.5}$ alloy withstood a maximum of 8.3% strain prior to fracture along with a strength exceeding 4.7 GPa. Energy dispersive x-ray spectroscopy conducted on the $Fe_{52}Co_{17.5}B_{20}Si_4Nb_4V_{2.5}$ alloy exhibited evidence of compositional modulation, indicating that nm-scale phase separation had occurred at local regions. In this study, the role played by nm-scale phase separation on the plasticity was investigated in terms of structural disordering and shear localization in order to better understand the structural origin of the enhanced plasticity shown by the developed alloy.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 1998.11a
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• pp.335-338
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• 1998

Ferroelectric Sr$_2$(Nb,Ta)$_2$O$_{7}$ (SNTO) thin films were prepared by chemical solution deposition processes. SNTO thin films were spin-coated on Pt/Ti/SiO$_2$/(100)Si substrates. After multiple coating, dried thin films were heat-treated for decomposition of residual organics and crystallization. B site-rich impurity phase, i.e. [Sr(Nb,Ta)$_2$O$_{6}$], was found after annealing, where its appearance was dependent on process temperature indicating the possible reaction with substrate. Dielectric and other relevant electrical properties were measured and the results showed a little possibility in ferroelectric gate random access memory devices.s.s.

• Journal of the Institute of Electronics Engineers of Korea SD
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• v.37 no.11
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• pp.50-58
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• 2000

A Mach-Zehnder type $Ti:LiNbO_3$ optical modulator with a grooved $SiO_2$ buffer layer, was evaluated in terms of an electrode structure. The finite element method was performed to find out the optinum design parameters of electrodes. characteristic impedance ($Z_o$), MW effective index ($N_{eff}$) and attenuation constant ($a_o$)of fabricated traveling-wave electrodes were measured and compared with those obtained by the simulation expectation. For an optical modulator with 11${\mu}m$thick electrodes and a grooved $SiO_2$ buffer layer, the 3dB bandwidth based on the RF measurement results turned out to be 18GHz.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2000.07a
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• pp.94-98
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• 2000

Polycrystalline SBTN ferroelectric thin films were prepared by sol-gel method with various Nb mole ratios on Pt/ $SiO_2$/Si (100) substrates. The films were annealed at different temperatures and characterized in terms of phase and microstructure. Relatively a well saturated hysteresis pattern was obtained at x =0.2 in S $r_{0.8}$B $i_{2.3}$(T $a_{1-x}$ N $b_{x}$)$_2$ $O_{9+}$$\alpha$/ thin films. At an applied voltage of 5V, the dielectric constant ($\varepsilon$$_{r}$) and dissipation factor (tan $\delta$) of typical S $r_{0.8}$B $i_{2.3}$(T $a_{1-x}$ N $b_{x}$)$_2$ $O_{9+}$$\alpha$/ thin film (x=0.2) were about 236.2 and 0.034. Measured remanent polarization (2Pr) and coercive field (Ec) were 4.28C/c $m_2$, and 38.88kv/cm respectively. No fatigue was observed up to 6$\times$10$_{10}$ switching cycles at 5V and the normalized polarization reduced by a factor of only 4%.%. 4%.%. 4%.%.%.%.%.

• Journal of the Korean Magnetics Society
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• v.8 no.1
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• pp.13-20
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• 1998

The crystallographic and high frequency characteristics of $Fe_{73.9}Cu_{1.0}Nb_{3.5}Si_{14.0}B_{7.6}$ soft magnetic alloys were investigated under the magnetic field annealing. As-cast ribbon with which already imbedded nanocrystalline Fe-Si phase on the surface have a preferred orientation with (400) plane to surface and also with the [011] direction parallel to the ribbon length. The extra nanocrystalline Fe-Si phase appeared throughout at 45$0^{\circ}C$ in samples with or without the longitudinal magnetic field. However the formation of nanocrystalline phase does not appear on the suface layer until 50$0^{\circ}C$ annealing temperature under the transverse field. The cryststallization fraction of annealed samples with longitudinal magnetic field is higher than that of samples without magnetic field. When the transverse magnetic field is applied, the crystallization fraction does not increases but decreases until 50$0^{\circ}C$. However the crystallization of internal regions can be confirmed by X-ray diffraction measurement via tilting the sample. It was found that for all samples, the saturation induction were all same with 1.3 T. The coercive field of as-cast sample was 1.06 A/cm, but in annealed samples it decrease from 0.56 to 0.1 A/cm with increasing annealing temperature from 400 and 55$0^{\circ}C$, respectively. The squareness of annealed samples under transverse magnetic field has a small value than that of both without field and with longitudinal field annealing.