• Korean Journal of Materials Research
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• v.17 no.4
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• pp.232-235
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• 2007

Indium tin oxide (ITO) films were deposited on polycarbonate CR39 substrate using DC magnetron sputtering. ITO thin films were deposited at room temperature because glass-transition temperature of CR39 substrate is $130^{circ}C$ ITO thin films are used as bottom and top electrodes and for organic thin film transparent transistor (OTFT). The electrodes electrical properties of ITO thin films and their optical transparency properties in the visible wavelength range (300-800 nm) strongly depend on the volume of oxygen percent. The optimum resistivity and transparency of ITO thin film electrode was achieved with a 75 W plasma power, 10 % volume of oxygen and a 27 nm/min deposition rate. Above 85% transparency in the visible wavelength range (300-800 nm) was measured without post annealing process, and resistivity as low as $9.83{\times}^{TM}10^{-4}{\Omega}$ cm was measured at thickness of 300 nm.

• Journal of the Korean Society of Safety
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• v.24 no.6
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• pp.20-26
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• 2009

The creep deformation behavior of AZ31 magnesium alloy was examined in the temperature range from 573 to 673K (0.62 to 0.73 Tm) under various constant stresses covering low strain rate range from $4{\times}10^{-9}\;s^{-1}$ to $2{\times}10^{-2}\;s^{-1}$. At low stress level, the stress exponent for the steady-state creep rate was ~3 and the present results were in good agreement with the prediction of Takeuchi and Argon model. At high stress level, the stress exponent was ~5 and the present results were in good agreement with the prediction of Weertman model. The transition of deformation mechanism from solute drag creep to dislocation climb creep could be explained in terms of solute-atmospherebreakaway concept.

• Bulletin of the Korean Chemical Society
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• v.18 no.7
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• pp.715-719
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• 1997

In order to study the dielectric properties of the oriental lacquer films, three different films have been prepared differing purification and curing procedures. Dielectric properties were measured in the frequency range of 1 Hz to 105 Hz at various temperatures between - 50 ℃ and 150 ℃. The DEA using 1 Hz showed that glass transition and secondary relaxation temperatures of oriental lacquer film are very time dependent. In addition, the frequency-independent negative peak between 25 ℃ and 45 ℃ was observed, which could represent the formation of crosslink by laccase enzyme during heating. On the contrary, the high temperature cured film showed a hardly noticeable negative peak at the temperature range. The relationship between thermodynamic properties and chemical structures has been discussed based on the analysis of the dielectric relaxation behavior using the Cole-Cole plot and the dielectric relaxation intensity.

• Journal of Hydrogen and New Energy
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• v.7 no.1
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• pp.71-79
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• 1996

Yttrium thin film, 580nm thick, was prepared by electron beam evaporation. Film was hydrogenated room temperature upto 40 bar hydrogen pressure, without any activation process. Hydrogen concentration was determined by a quartz-crystal microbalance(QCM) method. YH2.9 sample was made without any pulverization. Electrical resistance was measured by four-point DC method in the temperature range between room temperature and 30K for various hydrogen concentration, x=0 to 2.9 of YHx sample. Temperature dependent resistance of YH2.9 shows low temperature minimum at 105K, the metal-semiconductor transition at 260K, and a hystersis above 210K.

• Journal of Hydrogen and New Energy
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• v.3 no.2
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• pp.35-43
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• 1992

Thin Film yttrium, 500 nm thick, was prepared by electron beam evaportion on sapphire substrate. Film was hydrogenated at room temperature upto 1 bar hydorgen pressure without any activation process. Electrical resistivity was measured by four-point DC method in the temperature range between room temperature and 30 K for various hydorgen concentration x = 0 to 2.924 of $YH_x$ sample. Temperature dependent resistance of $YH_{2\;924}$ shows low temperature minmum at 105K ($36{\mu}{\Omega}cm$ deep), the metal-semiconductor transition at 260K, and a hysteresis, which are similar behavior to bulk $YH_x$(x>2) experimental results.

• Journal of the Microelectronics and Packaging Society
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• v.29 no.4
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• pp.63-69
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• 2022

Vanadium dioxide shows a unique and interesting property of metal-insulator transition, which has attracted great attention from the viewpoints of fundamental materials science and industrial applications. In this study, the effect of Mg and W addition on the metal-insulator transition of VO₂ were investigated for the bulk materials that are prepared by spark plasma sintering. The X-ray diffraction analysis of the sintered specimens revealed that the lattice parameters barely change, and the secondary phases are present. The transition temperature of MIT appears in the range of 64.2-64.6℃, regardless of the impurity element and content. On the other hand, the addition of Mg and W alters the electrical conductivity, i.e., the electrical conductivity increases by a factor of up to 2.4 or decrease by a factor of up to 57.4 depending on the impurity type and its content. The thermal conductivity showed the values of 1.8~2.5 W/m·K below the transition temperature, and the values of 1.9~2.8 W/m·K above the transition temperature. These changes in electrical and thermal conductivities can be attributed to the combination of the change in charge carrier density, the impurities as scattering centers, and the change in microstructures.

• Journal of Korean Society of Environmental Engineers
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• v.29 no.4
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• pp.444-451
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• 2007

Catalytic oxidation characteristics of benzene as a VOC was investigated using a fixed bed reactor system over transition $metals/\gamma-Al_2O_3$ catalysts. As transition metals, eight metals including copper, nickel, manganese, iron etc. were adopted. The parametric tests were conducted at the reaction temperature range of $200\sim500^{\circ}C$, benzene concentration of $1,000\sim3,000$ ppm, and space velocity range of $5,000\sim60,000\;hr^{-l}$. The property analyses such as BET, SEM, XRD and the conversions of catalytic oxidation of VOC were examined. The experimental results showed that the conversion was increased with decreasing VOC concentration and space velocity. It was also found that $Cu/\gamma-Al_2O_3$ catalyst calcinated at $500^{\circ}C$ showed the highest activity for the oxidation of benzene and 15% metal loading was the optimum impregnation level.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.21 no.10
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• pp.1694-1701
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• 1997

The residual safety assessment of steel structures, an important subject in practice, is given to much attention. Life prediction in the planning course of steel structures under fatigue loading is mainly based on fatigue design criteria resulting from S-N curves. But for any reason cracks have to be assumed due to fabrication failures or fatigue loading in service which can lead total fracture of structures. The life prediction can be carried out by means of fracture mechanics using Paris-Erdogan equation($da/dN=C {\cdot}{\Delta}K^m$). The paper presents results from charpy test to interpret transition behaviour of charpy energy($A_V$) in a wide temperature range and from constant-load-amplitude test to measure fatigue crack growth of various steels widely used in steel bridges since beginning of 20 centuries in Europe. In the normal service temperature range of steel bridges, the steel S355M shows higher maximum charpy energy($A_{Vmax}$) and lower transition temperature($T_{AVmax/2}$) than other steels considered. The C and m of Paris-Erdogan equation on the steels appear to be correlated, and to be affected by the R-ratios due to crack closure, especially at a low fatigue crack growth rate. Scanning electron microscopy analysis was carried out to interpret an influence of the crack closure effects on the correlation of C and m.

• Journal of Sensor Science and Technology
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• v.23 no.5
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• pp.337-341
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• 2014

For various additives doped-$VO_2$ critical temperature sensors using the nature of semiconductor to metal transition, the crystallinity, microstructure, and temperature vs. resistance characteristics were systematically investigated. As a starting material of $VO_2$ sensor, vanadium pentoxide ($V_2O_5$) powders were used, and CaO, SrO, $Bi_2O_3$, $TiO_2$, and PbO dopants were used, respectively. The $V_2O_5$ powders with dopants were mixed with a vehicle to form paste. This paste was silk screen-printed on $Al_2O_3$ substrates and then $V_2O_5$-based thick films were heat-treated at $500^{\circ}C$ for 2 hours in $N_2$ gas atmosphere for the reduction to $VO_2$. From X-ray diffraction analysis, $VO_2$ phases for pure $VO_2$, and CaO and SrO-doped $VO_2$ thick films were confirmed and their grain sizes were 0.57 to $0.59{\mu}m$. The on/off resistance ratio of the $VO_2$ sensor in phase transition temperature range was $5.3{\times}10^3$ and that of the 0.5 wt.% CaO-doped $VO_2$ sensor was $5.46{\times}10^3$. The presented critical temperature sensors could be commercialized for fire-protection and control systems.

• Proceedings of the Korean Magnestics Society Conference
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• 2003.06a
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• pp.90-91
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• 2003

Amorphous magnetic materials with competing magnetic interactions are the subject of current interest. Critical behaviour studies have been performed in order to understand the nature of the phase transition at the Curie point (T$\sub$c/) and type of magnetic ordering below the T$\sub$c/. In some cases there exists a temperature interval in which the magnetic system consists of ferromagnetic grains separated by the paramagnetic interlayers. Magnetic properties of nanoparticles embedded in amorphous matrix also are the subject of recent interest. While these materials exhibit excellent soft magnetic properties at room temperature, some of them have been found to be superparamagnetic in the temperature range above the T$\sub$c/ of the matrix. Thus the role of different magnetic phases in the intergrain magnetic coupling can possibly be taken apart in a sufficiently broad temperature range and investigated separately. In particular materials with competing magnetic exchange interactions show characteristics of enhanced magnetoresistance and softer magnetic properties when magnetic nanocrystals are dispersed in amorphous matrix. We expect careful magnetic measurements in the vicinity of T$\sub$c/ would throw some light on magnetic behaviour of above materials. We present here the FMR analysis of Fe$\sub$82/Mn$\sub$8-x/B$\sub$x/Zr$\sub$10/ alloy near the Curie point.