• Journal of the Korean Magnetics Society
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• v.8 no.2
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• pp.79-85
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• 1998

The $[Ni_{80}Fe_{20}/Cu/Co/Cu]$ multilayers were grown by evaporation technique, and according to magnetic exchange coupling relation, magnetoresistance ratio and magnetization curve were studied by Co inserting $Ni_{80}Fe_{20}/Cu$ interface. Insertion of Co layer to the antiferromagnetically coupled system, i. e $t_{Cu} = 25\;{\AA}$, decrese the MR ratio contrary to previous reports. However the insertion to the ferromagneticalyl coupled $(t_{Cu} = 27\;{\AA})$ and the noncoupled $(t_{Cu} = 47\;{\AA})$ systems increase the ratio to 3.5 % and 6 % respectively. The results imply that the insertion change the magnetic exchange coupling state as well as the spin dependent scattering of conduction electrons. Besides, insertion of Co layer between Cu and $Ni_{80}Fe_{20}$ layer enhaces thermal stability to the 300 $^{\circ}C$, which indicates that insertion of Co has a role of the effective diffusion barrier.

• Transactions of Materials Processing
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• v.27 no.1
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• pp.37-47
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• 2018

In this paper, a double spot welding process, utilizing electric resistance heating dies, is suggested for the spot welding of dissimilar metal plates for drawing and concurrent spot welding. This double welding process has two heating methods for the fusion welding at the interfacial zone between steel and aluminum plates, such as heating method by thermal conduction of electric resistance by welding current induced to heating dies, and heating method by electric resistance between contacted surfaces of two plates by welding current induced to copper electrode. This double welding process has welding variables such as each current induced in heating dies and in copper electrode, outer diameters of heating dies, and edge shape of copper electrode. Experiments for current conditions in welding process should be demanded in order to get successful welding strength. It was known that the welding strength could be reached to the value demanded on industry fields under such welding conditions as heating dies of outer ring dia.12mm contacted on steel plate, as heating dies of outer ring dia. 14mm contacted on aluminum plate, and as copper electrode of dia. 6.0mm, and as 3 times continuous heating method by $1^{st}$ current of 11 kA(9cycle), $2^{nd}$ current 11 kA(60cycle), $3^{rd}$ current 7 kA(60cycle) applied in steel heating dies and copper electrodes, flat edge of copper electrode, for double spot welding process of dissimilar metal plates of steel and aluminum of 1.0 mm thickness.

• Journal of the Society of Naval Architects of Korea
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• v.39 no.3
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• pp.81-88
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• 2002

The root joint in the welding structures are apt to failure by the stress concentration which is occurred by the external force. Therefore, in the safety and reliability of structure, the complete penetration joint welding which are obtained by the groove welding with edge preparation is generally required. Nevertheless, fillet T-joint welding without edge preparation is often carried out in the fields to reduce working time and consumption of welding electrode, however, this process is likely to produce inadequate joint penetration such as root gap. In this paper, the focus of research is to investigate distribution of welding residual stresses in the plate(or flange) and web of T-joint weld, and especially in the near of root gap notch that is due to incomplete joint penetration. For the analysis, we have chosen model of T-joint weld in the cases of single and multi-pass welding with submerged arc welding and analyzed model by using finite element programs considering the heat conduction and thermal elasto-plastic theory.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.16 no.9
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• pp.807-811
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• 2003

We investigated the electrical characterisitics of T $a_2$ $O_{5}$ (tantalum pentoxide) film and Ti-O/T $a_2$ $O_{5}$ film deposited on $Al_2$ $O_3$based substrate. Ta (tantalum) electrode and $Al_2$ $O_3$ substrate was used for the purpose of simplifying the manufacturing process in IPD's (integrated passive devices). Dielectric materials (T $a_2$ $O_{5}$ and Ti-O/T $a_2$ $O_{5}$ films) deposited on Ta/Ti/A $l_2$ $O_3$ were annealed at 700 $^{\circ}C$ for 60 sec. in vacuum. The XRD results showed that as-deposited T $a_2$ $O_{5}$ film possessed amorphous structure, which was transformed to crystallines by rapid thermal heat treatment. We compared the lnJ- $E^{{\frac}{1}{2}}$, C-V, C-F of both as-deposited and annealed dielectric thin films deposited on Ta bottom electrode. From this results, we concluded that the leakage current could be reduced by introducing Ti-O buffer layer and conduction mechanisms of T $a_2$ $O_{5}$ and Ti-O/T $a_2$ $O_{5}$ could be interpreted appropriately by Schottky emission effect.

• Journal of Magnetics
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• v.12 no.3
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• pp.118-123
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• 2007

We have studied the effect of Au-Cu back layer system ${\sim}10{\AA}$ thick on the properties of a spin valve. The back layers were Cu, Au, co-sputtered $Cu_xAu_{1-x}$, laminated $[Au/Cu]_n$. and bi-layer [Au/Cu]. When Au was added to the Cu, the resistance of the spin valve abruptly increased most likely due to impurity scattering. The GMR values were not increased significantly for all the structures. In the case of co-sputtered $Cu_xAu_{1-x}$, the changes in the resistance, ${\Delta}R$, was increased at a composition of ${\sim}Au_{0.5}Cu_{0.5}$. This increase in ${\Delta}R$ is due to increase in the resistance and not from the enhanced spin-dependent scattering. The structural analyses showed that the orthorhombic $Au_{0.5}Cu_{0.5}$ was formed in the back layer instead of the face-centered tetragonal $Au_{0.5}Cu_{0.5}$ as we expected. Thermal annealing over $400^{\circ}C$ may be required to have face-centered tetragonal in the $10{\AA}$ thick ultra-thin film. In the case of a laminated or bi-layered back layer, the properties of the spin valve were improved, which may be attributed to the increase in the mean free path of conduction electrons.

• Journal of the Korean Institute of Telematics and Electronics
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• v.14 no.3
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• pp.25-31
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• 1977

Fe V spinels were prepared by sintering the well-ground stoichiometric mixtures of Fe O and V O at 1,10$0^{\circ}C$ under H -CO atmosphere. The activation energy for electrical conduction decreases with increasing amount of iron. The tendency of activation energy depending on the amount of iron contained clarifies that the electrical condction of the spinel is mainly due to electron hopping between Fe and Fe ions at B sites. In the experiment for negative resistance characteristics, the threshold voltage (Vth) for the samples is related to ambient temperature, thickness and raising rate of applied voltage. Vth decreases as temperature increases while Vth increases linearly with thickness and Vth increases linearly with the raising rate of applied voltage in semi-logarithmic scale. These results lead to a conclusion that current paths mainly formed by thermal breakdown are ascribed to the negative resistance phenomena. Applying this property, these vanadium iron spinels may be used for switching elements.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.12 no.1
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• pp.44-49
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• 1999

In this study, microstructure and electrical conductivity of {(G $d_2$ $O_3$)$_{0.75}$( $Y_2$ $O_3$)$_{0.25}$}$_{x}$ (Ce $O_2$)$_{1-x}$ (0.01$\leq$x$\leq$0.25) was investigated as a function of composition x. GYO addition(x) increased the bulk density and G $d_2$ $O_3$ was found to be monoclinic at x>0.15. From the change of the lattice parameter with the addition(x), GYO solution limit for ceria was exceeded in the range of x=0.05 to 0.09. Thermal expansion coefficient(15~17$\times$10$^{-6}$ $^{\circ}C$) of GYC samples at x=0.01 to 0.07 was higher in value than that of 8YSZ(10.8$\times$10$^{-6}$ $^{\circ}C$). The electrical conductivity of GYC samples at x=0.05 showed the maximum(0.01S/cm) in value at 1073K which was 2 times higher than that of 8YSZ. The activation energy for the electrical conduction was determined to be 0.60eV in the temperature range of 1073K.3K..3K.

• Journal of the Korean Ceramic Society
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• v.35 no.11
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• pp.1171-1181
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• 1998

$SrZr_{0.95}$$Y_{0.05}$$O_{2.975}$ powder was synthesized by ultrasonic spray pyrolysis using a solution that Sr carbonate and Zr and Y nitrates were dissolved in a citric acid solution. The processes of particle formation were in-vestigated with respect to solution properties and pyrolysis temperature. With changing the solution con-centration form 0.1M to 0.01M there was a tendency that average sizes of droplets and particles were de-creased and their size distributions were narrowed. Citrate functional groups converted the droplets into gel particles which prevented an inhomogeneous precipitation of the metal ions and facilitated the diffusion of gases during thermal decomposition. As a result the powder having spherical particles without hollow par-ticles could be prepared. Low pyrolysis temperature led to amorphous particles due to incomplete pyrolysis and made the particles difficult to maintain spherical shape due to retarded gelation of the droplets. Whereas higher pyrolysis temperature produced hollow and broken particles because the droplets un-derwent rapid gelationand decomposition. The particles obtained at two pyrolysis temperature $500^{\circ}$and $1000^{\circ}C$ consisted of a perovskite phase and a very small amount of $SrCO_3$ However after calcination at $1000^{\circ}C$ the particles contained a single perovskite phase having an average particle size of 0.63${\mu}{\textrm}{m}$ and an apparent density near to the theoretical density.

• Journal of the Korea institute for structural maintenance and inspection
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• v.22 no.6
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• pp.1-8
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• 2018

The object of this paper is to find the characteristics of fire proof materials through an analytical method and to suggest a proper approach for fire-proof design of reinforced concrete beam strengthened with fiber reinforced polymer (FRP). Heating tests for fire-proof materials were conducted and the thermal conductivities and specific heats of them were simulated through finite element analyses. In addition, a finite element analysis on the beam specimen strengthened with FRP under high temperature, which was conducted by previous researchers, was performed and the analytical result was compared with test result. And then the compatibility of the analytical approach was evaluated. Finally, the heat resistance characteristic of RC beam strengthened with FRP was analyzed by the proposed analytical method and the strength decrease of the beam due to the high temperature was evaluated. From the comparison with analytical and test result, it was found that the heat transfer from outside to inside through the fire-proof materials can be suitably simulated by using the proposed analytical approach.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.21 no.11
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• pp.968-972
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• 2008

Ni/Ti/Al multilayer system ('/'denotes the deposition sequence) was tested for low-resistance ohmic contact formation to Al-implanted p-type 4H-SiC. Ni 30 nm / Ti 50 nm / Al 300 nm layers were sequentially deposited by e-beam evaporation on the 4H-SiC samples which were implanted with Al (norminal doping concentration = $4\times10^{19}cm^{-3}$) and then annealed at $1700^{\circ}C$ for dopant activation. Rapid thermal anneal (RTA) temperature for ohmic contact formation was varied in the range of $840\sim930^{\circ}C$. Specific contact resistances were extracted from the measured current vs. voltage (I-V) data of linear- and circular transfer length method (TLM) patterns. In constrast to Ni contact, Ni/Ti/Al contact shows perfectly linear I-V characteristics, and possesses much lower contact resistance of about $2\sim3\times10^{-4}\Omega{\cdot}cm^2$ even after low-temperature RTA at $840^{\circ}C$, which is about 2 orders of magnitude smaller than that of Ni contact. Therefore, it was shown that RTA temperature for ohmic contact formation can be lowered to at least $840^{\circ}C$ without significant compromise of contact resistance. X-ray diffraction (XRD) analysis indicated the existence of intermetallic compounds of Ni and Al as well as $NiSi_{1-x}$, but characteristic peaks of $Ti_{3}SiC_2$, a probable narrow-gap interfacial alloy responsible for low-resistance Ti/Al ohmic contact formation, were not detected. Therefore, Al in-diffusion into SiC surface region is considered to be the dominant mechanism of improvement in conduction behavior of Ni/Ti/Al contact.