• 폴리머
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• 제25권1호
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• pp.78-89
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• 2001

불포화폴리에스터/폴리비닐아세테이트 semi-IPN의 경화과정 중 경화속도와 상분리 확산속도의 상호관계 속에서 형성되는 상분리 모폴로지를 광산란 및 열분석 장치를 이용하여 연구하였다. 열경화성 고분자의 경화과정 중 열가소성 고분자의 확산에 기인한 물성의 변화를 측정하였고, 상분리를 수반하는 경화과정에서의 활성화에너지의 변화를 Flynn-Wall method를 이용하여 구하였다. 반응에 의하여 나타나는 상분리현상은 경화과정 중 다양한 상분리 거동을 나타내게 되는데, 폴리비닐아세테이트가 10 wt%일 경우에는 반응도중에 상분리가 일어나지 않고 냉각 후 상온에서 nucleation & growth 거동과 유사한 형태로 상분리가 발생하였고, 11.65 wt% 이상에서는 반응도중 spinodal decomposition으로 사료되는 상분리가 발생하였다. 또한 상분리현상이 경화속도에 영향을 미친 것을 활성화에너지의 변화거동으로부터 확인하였으며, 온도변화에 따라 총산란량을 측정하였고 이로부터 확산에 의한 상분리 속도 R(${\beta}_m$)를 비교하였다.

• 대한간호학회지
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• 제33권6호
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• pp.847-855
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• 2003

Purpose: This study was done to develop a bereaved family care program by identifying characteristics of a grief healing process in a child loss. Method: The subjects were five bereaved mothers who have lost their children with cancer. Data was collected with in-depth interviews using grief phase assessment tool and grief reaction assessment tool from 1, February, 2001 to 31 August, 2002. Data was analyzed on the basis of two tools. Result: Process of grief in general was as follows: evading phase was within one week - one month, confrontation phase was 5 - 12 months, and reconciliation phase was after 9 months and still going on when the study was finished. Grief reaction in five (physical, cognitive, emotional, social, and spiritual) dimensions was stabilized when the phase moved into reconciliation phase. Influencing factors were intimacy and expectation towards child, social support, personality, prior loss experience, coping style, religion, culture, family cohesion, openness of communication, and stress events. Conclusion: These results suggest that a bereaved family care program considering characteristics of Korean culture should be developed and activated.

• 한국세라믹학회지
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• 제48권1호
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• pp.99-105
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• 2011

Lead titanate ($PbTiO_3$) powder was prepared from lead nitrate ($Pb(NO_3)_2$) and titania ($TiO_2$) by hydrothermal route. Phase formation process was investigated by observing the phases formed in various experimental conditions like different KOH concentration, reaction temperature and time. $PbTiO_3$ powder was fabricated when the KOH concentration was 0.8M or higher. An intermediate compound, $PbTi_{0.8}O_{2.6}$, was formed at first by a reaction between PbO and $TiO_2$ and changed into $PbTiO_3$ powder with a perovskite crystal structure. A $PbTiO_3$ phase was formed in a shorter time when a KOH concentration was increased from 0.8M to 8M because a driving force for a $PbTiO_3$ formation was increased due to an increase in a degree of supersaturation. And $TiO_2$ (rutile) and $3PbO{\cdot}H_2O$ were observed at room temperature in a 0.8M KOH solution and $TiO_2$(rutile) and PbO (litharge) in a 8M KOH. A $PbTiO_3$phase was also formed in a shorter time at a higher reaction temperature as a reaction temperature influenced the rates for a dissolution and a precipitation.

• 한국응용과학기술학회지
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• 제13권3호
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• pp.127-136
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• 1996

Thermograms of methylene blue(MB) in $L-{\alpha}-lecithin$ vesicle and incorporated purple membrane vesicle(InPM) systems have been studied by photochemical reaction differential scanning calorimetry at $25{\sim}55^{\circ}C$. Phase transition temperatures of lecithin vesicle, purple membrane(PM), and InPM were found to be independent of illumination of light(436nm) at $39{\sim}40^{\circ}C$, but endothermic phase transition was found in InPM vesicle. In MB-InPM system, endothermic phase transition was found on unillumination of light at $40{\sim}42^{\circ}C$, but exothermic phase transition was found on steady illumination of light at $48{\sim}52^{\circ}C$. It was estimated that the light energy absorbed from MB on vesicular surface was transferred to PM, and the transferred energy was redistributed to hydrophobic site of membrane. Therefore, the exothermic phase transition was measured at high temperature because of the increased hydrophobicity of acyl chain.

• Applied Microscopy
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• 제25권3호
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• pp.90-98
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• 1995

In the Fe-Si system, a mixture of a($Fe_{2}Si_5$) - and ${\epsilon}$(FeSi)-composition powders was sintered and heat-treated subsequently at various temperatures and time to get thermoelectric ${\beta}$-phase($FeSi_2$) compacts. The different transformational sequences depending on the heat treating temperature were found through the investigation into phase transformation and microstructural development. That is, a rapid eutectoid decomposition of ${\alpha}{\to}{\beta}+Si$ occurred together with a accompanying slow reaction between the dispersed Si formed by above decomposition and the preexisted ${\epsilon}$ phase at temperatures below $830^{\circ}C$. The unreacted Si and the micropores formed due to the density change upon the transformation coarsened as heat treating time elapsed. At temperatures above $880^{\circ}C$, however, transformation was proceeded by a peritectoid reaction of ${\alpha}+{\epsilon}{\to}{\beta}$. It took at least 200min. to achieve 90% volume fracion of transformed ${\beta}$ phase, and the growth of micro-pores was also observed in this transformational sequence with prolonged heat treating time.

• 한국세라믹학회지
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• 제48권6호
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• pp.630-635
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• 2011

Bismuth vanadate($BiVO_4$) with monoclinic phase as photocatalyst under visible light is synthesized by precipitation reaction in hot water. Properties such as crystal phase, particle morphology and visual light absorbance as well as the effects of thermal treatment for $BiVO_4$ powders are investigated. $BiVO_4$ powders with both single monoclinic phase and 0.2 ${\mu}m$ in particle size are synthesized when precipitate is stirred in water for 5 h at 95$^{\circ}C$. Well-developed monoclinic phase and light absorption property under 535 nm are observed as a result of thermal treatment for 1 h at 300$^{\circ}C$ after precipitation reaction in water for 5 h at 95$^{\circ}C$. Degradation of monoclinic crystal is found in firing above 350$^{\circ}C$, and particle growth is occurred in firing above 550$^{\circ}C$.

• 한국세라믹학회지
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• 제48권5호
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• pp.354-359
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• 2011

Silicon nitride ceramics were prepared by microwave gas phase reaction sintering. By this method higher density specimens were obtained for short time and at low temperature, compared than ones by conventional pressureless sintering, even though sintering behaviors showed same trend, the relative density of sintered body inverse-exponentially increases with sintering temperature and/or holding time. And grain size of ${\beta}$-phase of the microwave sintered body is bigger than one of the conventional pressureless sintered one. Also they showed good bending strengths and thermal shock resistances.

• 한국분말재료학회지
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• 제26권2호
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• pp.107-111
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• 2019

The activation energy to create a phase transformation or for the reaction to move to the next stage in the milling process can be calculated from the slop of the DSC plot, obtained at the various heating rates for mechanically activated Al-Ni alloy systems by using Kissinger's equation. The mechanically activated material has been called "the driven material" as it creates new phases or intermetallic compounds of AlNi in Al-Ni alloy systems. The reaction time for phase transformation by milling can be calculated using the activation energy obtained from the above mentioned method and from the real required energy. The real required energy (activation energy) could be calculated by subtracting the loss energy from the total input energy (calculated input energy from electric motor). The loss energy and real required energy divided by the reaction time are considered the "metabolic energy" and "the effective input energy", respectively. The milling time for phase transformation at other Al-Co alloy systems from the calculated data of Al-Ni systems can be predicted accordingly.

• 한국세라믹학회지
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• 제33권9호
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• pp.1045-1049
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• 1996

Pressureless-sintered polycrystalline alumina and carbon steel were joined with Ag-33.5Cu-1.5Ti (wt%) brazing alloy. SEM observation revealed that two reaction layers with different thicknesses were continuously formed between the alumina and the brazing alloy. A thick layer formed on the brazing alloy side was identified as Ti3(Cu0.93Al0.07)3O phase with diamond cubic structure. Another thin layer adjacent to the alumina was revealed as $\delta$-TiO phase of which the crystal structure was HCP with a lattice parameter of a0=0.419 nm and c0=0.284 nm. It was confirmed using XPS analysis that $\delta$-TiO was formed directly by a redox reaction of alumina with titanium ir, molten brazing alloy.

• 한국수소및신에너지학회논문집
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• 제22권4호
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• pp.424-431
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• 2011

The Sulfur-Iodine(SI) thermochemical hydrogen production process consists of three sections, which are so called the Bunsen reaction section, the $H_2SO_4$ decomposition section and the HI decomposition section. In order to identify the phase separation characteristics in the reaction conditions with the high solubility of $SO_2$, we conducted the Bunsen reaction at the low temperatures, ranging from 283 to 298K, with the $I_2/H_2O$ molar ratios of 2.5/16.0 and 3.5/16.0. The molar ratios of HI/$H_2SO_4$ products obtained from low temperature Bunsen reactions were ca. 2, indicating that there were no side reactions. The amount of reacted $SO_2$ was increased with decreasing the temperature, while the amounts of unreacted $I_2$ and $H_2O$ were decreased. In the phase separation of the products, the amount of a $H_2SO_4$ impurity in $HI_x$ phase was increased with decreasing the temperature, though the temperature has little affected on HI and $I_2$ impurities in $H_2SO_4$ phase.