• 한국재료학회지
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• 제23권10호
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• pp.592-598
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• 2013

Graphene oxide powders prepared by two different drying processes, freeze drying and spray drying, were studied to compare the effect of the drying method on the physical properties of graphene oxide powder. The graphene oxide dispersion was prepared from graphite by chemical delamination with the aid of sulfuric acid and permanganic acid, and the dispersion was further washed and re-dispersed in a mixed solvent of water and isopropyl alcohol. A freeze drying method can feasibly minimize damage to the sample, but it requires a long process time. In contrast, spray drying is able to remove a solvent in a relatively short time, though this process requires exposure to a high temperature for a rapid evaporation of the solvent. The powders prepared by freeze drying and spray drying were characterized and compared by Raman spectroscopy, X-ray diffraction, field-emission scanning electron microscopy, transmission electron microscopy, and by an elemental analysis. The graphene oxide powders showed similar chemical compositions; however, the morphologies of the powders differed in that the graphene oxide prepared by spray drying had a winkled morphology and a higher apparent density compared to the powder prepared by freeze drying. The graphene oxide powders were reduced at $900^{\circ}C$ in an atmosphere of $N_2$. The effect of the drying process on the properties of the reduced graphene oxide was examined by SEM, TEM and Raman spectroscopy.

• 한국분말재료학회지
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• 제25권4호
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• pp.322-326
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• 2018

The hydrogen reduction behavior of $MoO_3-CuO$ powder mixture for the synthesis of homogeneous Mo-20 wt% Cu composite powder is investigated. The reduction behavior of ball-milled powder mixture is analyzed by XRD and temperature programmed reduction method at various heating rates in Ar-10% $H_2$ atmosphere. The XRD analysis of the heat-treated powder at $300^{\circ}C$ shows Cu, $MoO_3$, and $Cu_2MoO_5$ phases. In contrast, the powder mixture heated at $400^{\circ}C$ is composed of Cu and $MoO_2$ phases. The hydrogen reduction kinetic is evaluated by the amount of peak shift with heating rates. The activation energies for the reduction, estimated by the slope of the Kissinger plot, are measured as 112.2 kJ/mol and 65.2 kJ/mol, depending on the reduction steps from CuO to Cu and from $MoO_3$ to $MoO_2$, respectively. The measured activation energy for the reduction of $MoO_3$ is explained by the effect of pre-reduced Cu particles. The powder mixture, hydrogen-reduced at $700^{\circ}C$, shows the dispersion of nano-sized Cu agglomerates on the surface of Mo powders.

• 자원리싸이클링
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• 제21권6호
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• pp.32-38
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• 2012

본 연구에서는 액상 칼슘에 의한 $ZrO_2$의 직접환원에 대하여 조사하였다. $ZrO_2$의 직접환원에 미치는 Ca과 $ZrO_2$의 몰비, 반응시간, 그리고 반응온도의 영향에 대하여 검토하였다. 실험은 5분에서 60분까지 Ar 분위기의 밀폐된 스테인리스강제의 반응기에서 실시하였다. 반응온도 1223 K, Ca과 $ZrO_2$의 몰비가 3 이상인 조건에서 대부분의 $ZrO_2$는 5분만에 Zr으로 환원되었다. 반응온도가 1337 K이고 Ca을 이론적인 양의 2배를 첨가한 경우 금속 Zr 중의 산소농도는 최저 0.66 wt%를 나타내었다. 그리고 Zr 입자의 형상은 반응온도와 반응시간에 큰 영향을 받는 것으로 나타났다.

• 한국분말재료학회지
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• 제26권5호
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• pp.410-414
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• 2019

The hydrogen reduction behavior of the $CuO-SCo_3O_4$ powder mixture for the synthesis of the homogeneous Cu-15at%Co composite powder has been investigated. The composite powder is prepared by ball milling the oxide powders, followed by a hydrogen reduction process. The reduction behavior of the ball-milled powder mixture is analyzed by X-ray diffraction (XRD) and temperature-programmed reduction at different heating rates in an Ar-10%H2 atmosphere. The scanning electron microscopy and XRD results reveal that the hydrogen-reduced powder mixture is composed of fine agglomerates of nanosized Cu and Co particles. The hydrogen reduction kinetics is studied by determining the degree of peak shift as a function of the heating rate. The activation energies for the reduction of the oxide powders estimated from the slopes of the Kissinger plots are 58.1 kJ/mol and 65.8 kJ/mol, depending on the reduction reaction: CuO to Cu and $SCo_3O_4$ to Co, respectively. The measured temperature and activation energy for the reduction of $SCo_3O_4$ are explained on the basis of the effect of pre-reduced Cu particles.

• 한국포장학회지
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• 제24권3호
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• pp.113-120
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• 2018

The one-way gas valve developed in this study was designed to prevent the breakage of packages from increased internal pressure, which is a problem in packaged Kimchi, and simultaneously reduce the outflow of the offodor release. The effect of the one-way gas valve on the headspace atmospheric compositions was investigated in the packaging system. The changes of atmospheric compositions and quality factors of Kimchi, such as $CO_2$ accumulation, pH, titratable acidity, and salinity, were measured during a 4-week storage period at $4^{\circ}C$. The Kimchi package with the one-way gas valve dramatically reduced pressure build-up in the pouch by allowing the controlled flow of gas to the atmosphere. In addition, the package design allows the possibility of controlling the gas generated from Kimchi by adjusting the viscosity of the open pressure control oil. The one-way gas valve did not affect the sensory characteristics of Kimchi products during the storage period. Furthermore, the deodorizing capability of the activated carbon contained in the one-way gas valve effectively reduced the off-odor of Kimchi products released along with carbon dioxide. The novel one-way gas valve is considered to be an active packaging system that can solve major problems of expansion and off-odor leakage in the packaging of Kimchi.

• 치위생과학회지
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• 제23권4호
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• pp.396-407
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• 2023

Background: This study investigated the awareness and utilization of maternity protection and work-family balance support policies among dental hygienists in dental hospitals and clinics. Methods: We surveyed 200 dental hygienists. Twenty-two who did not meet the inclusion criteria were excluded, leaving 178 participants for analysis. The self-administered 48-item questionnaire gathered information on demographics, workplace details, policy awareness, government knowledge, and suggestions for improvement. Results: Awareness of maternity and family support programs significantly differed with age, marital status, number of children, and clinical experience. Dental hygienists in general hospitals and university hospitals reported greater ease of utilizing these policies compared to those in dental clinics. Among the participants, 27.7% took pre- and post-maternity leave, 26.6% took parental leave, 16.9% had reduced working hours during pregnancy, 15.8% had reduced working hours during childhood,and 8.5% during family leave. To promote program uptake, participants suggested mandatory implementation across workplaces (68.4%), expanded support for substitute workers (48.6%), and increased education and promotion of government support (42.4%). Conclusion: While most dental hygienists were aware of the Maternity Protection and Work-Family Balance Assistance Policy, utilizing it proved challenging due to several factors. Organizational policies or practices may not fully implement this policy, while workplace culture could discourage its use. Unfair treatment and the lack of available substitutes further hindered access. To prevent career interruptions for dental hygienists due to pregnancy, childbirth, childcare, and family care, and to maintain career continuity, the dental community and government should establish a multifaceted social support system. This system should prioritize several key areas: strengthening policy promotion, fostering a family-friendly atmosphere, improving management and supervision of policy implementation and developing a robust support system for substitute personnel.

• 한국재료학회지
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• 제14권8호
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• pp.595-599
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• 2004

We investigated the structural, electrical and magnetic properties of Mn-doped $CuAlO_2$ delafossite ceramics ($CuAl_{1-x}Mn_{x}O_2,\;0\le\;x\;\le0.05$), synthesized by solid-state reaction method in an air atmosphere at a sintering temperature of $1150^{\circ}C$. The solubility limit of Mn ions in delafossite $CuAlO_2$ was found to be as low as about 3 $mol\%$. Positive Hall coefficient and the temperature dependence of conductivity established that non-doped $CuAlO_2$ ceramic is a variable-range hopping p-type semiconductor. It was found that the Mn-doping in $CuAlO_2$ rapidly reduced the hole concentration and conductivity, indicating compensation of free holes. The analysis of the magnetization data provided an evidence that antiferromagnetic superexchange interaction is the dominant mechanism of the exchange coupling between Mn ions in $CuAl_{1-x}Mn_{x}O$ alloy, leading to an almost paramagnetic behavior in this alloy.

• 한국토양비료학회지
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• 제46권6호
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• pp.599-605
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• 2013

The effects of water-saving irrigation on the emissions of greenhouse gases and the prokaryotic communities in rice paddy soils were investigated through a field experiment. In the Water-Saving (WS) irrigation, the water layer was kept at 2~3 cm while it was kept at 6 cm in the Continuousiy Flooding (CF) irrigation. A plot was treated with Intermittently Drainage (ID) that is drained as fine cracks on the floor were seen after transplanting. GHGs emission amounts from WS plots were reduced by 78.1% compared to that from CF plot and by 70.7% compared to that from ID plot, meaning that WS could help contribute to mitigation of the greenhouse gas accumulation in the atmosphere.

• 한국분말재료학회지
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• 제16권5호
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• pp.310-315
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• 2009

Ultra-fine TiC/Co composite powder was synthesized by the carbothermal reduction process without wet chemical processing. The starting powder was prepared by milling of titanium dioxide and cobalt oxalate powders followed by subsequent calcination to have a target composition of TiC-15 wt.%Co. The prepared oxide powder was mixed again with carbon black, and this mixture was then heat-treated under flowing argon atmosphere. The changes in the phase, mass and particle size of the mixture during heat treatment were investigated using XRD, TG-DTA and SEM. The synthesized oxide powder after heat treatment at 700$^{\circ}C$ has a mixed phase of TiO$_2$ and CoTiO$_3$ phases. This composite oxide powder was carbothermally reduced to TiC/Co composite powder by the solid carbon. The synthesized TiC/Co composite powder at 1300$^{\circ}C$ for 9 hours has particle size of under about 0.4 $\mu$m.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1997년도 하계학술대회 논문집 C
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• pp.1433-1435
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• 1997

ZnO shows the properties of wide conductivity variation, high optical transmittance, and excellent piezoelectricity. Using these properties of ZnO, the material applications were extended to sensors, SAW filters, solar cells, and display devices. This paper investigated transmittance influencing factors for thin film ZnO grown by RF magnetron sputtering. The growth rate and structural investigation were carried out in conjunction with optical transmittance characteristics of thin film ZnO. The glass substrate temperature of $175^{\circ}C$ exhibited a preferential crystallization along (002) orientation. Transmittance of ZnO film deposited at the substrate temperature of $175^{\circ}C$ showed higher than 92%. An active sputter gas was investigated with a variation of $O_2$ partial pressure from 0 to 10% in an Ar atmosphere. ZnO film grown in 100% Ar gas shows that a reduced transmittance of 82% at the short wavelengths and decreased resistivity value. As the partial pressure of $O_2$ gas increased, the optical transmittance was increased above 90% at the short wavelengths, however, resistivity was drastically increased to higher than $10^4{\Omega}$-cm.