• Journal of Sensor Science and Technology
• /
• v.17 no.3
• /
• pp.178-182
• /
• 2008

Planar type micro catalytic combustible gas sensor was developed by using nano crystalline $SnO_2$ Pt thin film as micro heater was deposited by thermal evaporation method on the alumina substrate. The thickness of the Pt heater was around 160 nm. The sensor showed high reliability with prominent selectivity against various gases(Co, $C_3H_8,\;CH_4$) at low operating temperature($156^{\circ}C$). The sensor with nano crystalline $SnO_2$ showed higher sensitivity than that without nano crystalline $SnO_2$. This can be explained by more active adsorption and oxidation of hydrogen by nano crystalline $SnO_2$ particles. The present planar-type catalytic combustible hydrogen sensor with nano crystalline $SnO_2$ is a good candidate for detection of hydrogen leaks.

• Journal of the Mineralogical Society of Korea
• /
• v.20 no.3
• /
• pp.155-163
• /
• 2007

A novel route to the synthesis of tetramethoxysilane and other silicon alkoxides is described using siliceous mudstone as the raw material. The reaction of amorphous silica with triethanol-amine is enhanced by using an alkali metal hydroxide catalyst to form a range of triethanol-amnine-substituted silatrane species. These can undergo alkoxide exchange in acidic alcohols to form alkoxysilatranes, tetraalkoxysilanes, hexaalkoxydisiloxanes and higher siloxanes. Products were identified by FT-IR spectroscopy, XRD, SEM, 1H and 13C NMR spectroscopy, or gas chromatography.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
• /
• 1999.11a
• /
• pp.516-519
• /
• 1999

스위칭 전원에 사용되는 Mn-Zn 페라이트에 대항하는 고성능화의 요구에 부응하기 위해 그 중요한 요인이 되는 기수가 다른 Mn 산화물에 착목하여 그것들을 이용 제작한 Mn-Zn 페라이트의 자기특성 및 결정구조를 정밀하게 조사함과 동시에 그것들의 상관성을 검토하였다. Mn-Zn 페라이트의 소성 분위기의 변경방식은 소성개시에서 종료시까지 질소 분위기, 냉각시부터 질소분위기로 변경, 소성 개시에서 종료시까지 대기중 소성 세가지를 실험하였고, 소성 온도는 115$0^{\circ}C$, 120$0^{\circ}C$, 125$0^{\circ}C$ 130$0^{\circ}C$ 135$0^{\circ}C$ 및 140$0^{\circ}C$의 6종류의 시료를 제작하였다. 이 결과는 Mn-Zn 페라이트의 소성 분위기 및 온도 최적화는 승온 및 온도 유지 단계에서는 대기중으로, 냉각단계에서는 질소가스 분위기로 치환한 것과 소성 온도는 120$0^{\circ}C$ 이다. 이 분위기에서 Mn-Zn 페라이트를 가수를 다르게 하여 시료의 투자율 및 주파수 특성, 코아로스 주파수 의존성, 코아로스 주파수로 나눈값의 주파수 의존성, 스피넬 구조(311)의 면에서의 회절픽, 자화의 온도 의존성을 분석하였다. 이 결과는 Mn$_3$O$_4$를 출발원료로 사용한 Mn-Zn 페라이트가 투자율 및 한계 주파수 모두 뛰어난 특성을 나타내었다.

• Proceedings of the Korean Vacuum Society Conference
• /
• 2013.08a
• /
• pp.278.2-278.2
• /
• 2013

그래핀은 우수한 전기적, 기계적, 광학적 특성들로 인하여 전자소자, 센서, 에너지 재료 등으로의 응용이 가능하다고 알려진 단 원자층의 탄소나노재료이다. 특히 그래핀을 전자소자로 응용하기 위해서는 캐리어 농도, 전하 이동도, 밴드갭 등의 전기적 특성을 향상시키거나 제어하는 것이 요구되며, 에너지 소재로의 응용을 위해서는 높은 전기전도도와 함께 기능화를 통한 촉매작용을 부여하여 효율을 향상시키는 것이 요구된다. 일반적으로 화학적 도핑은 그래핀의 전기적 특성을 제어하는 효율적인 방법으로 알려져 있다. 화학적 도핑의 방법으로 질소, 수소, 산소 등 다양한 이종원소를 열처리 또는 플라즈마 처리함으로써 그래핀을 구성하는 탄소원자를 이종원자로 치환하거나 흡착시켜 기능화 처리된 그래핀을 얻는 방법들이 제시되었다. 이중 플라즈마를 이용한 도핑방법은 저온에서 처리가 가능하고, 처리시간, 공정압력, 인가전압 등 플라즈마 변수를 변경하여 도핑정도를 비교적 수월하게 제어할 수 있다는 장점을 가지고 있다. 본 연구에서는 열화학기상증착법으로 합성된 그래핀을 직류 플라즈마로 처리함으로써 효율적인질소도핑 조건을 도출하고자 하였다. 그래핀의 합성은 200 nm 두께의 니켈 박막이 증착된 몰리브덴 호일을 사용하였으며, 원료가스로는 메탄을 사용하였다. 그래핀의 질소 도핑은 평행 평판형 직류 플라즈마 장치를 이용하여 암모니아($NH_3$) 플라즈마로 처리하였으며, 플라즈마 파워와 처리시간을 변수로 최적의 도핑조건 도출 및 도핑 정도를 제어하였다. 그래핀의 질소 도핑 정도는 라만 스펙트럼의 G밴드의 위치와 반치폭(Full width at half maximum; FWHM)의 변화를 통해 확인하였다. NH3 플라즈마 처리 후 G밴드의 위치가 장파장 방향으로 이동하며, 반치폭은 감소하는 것을 통해 그래핀의 질소도핑을 확인하였다.

• 한국신재생에너지학회:학술대회논문집
• /
• 2006.06a
• /
• pp.43-46
• /
• 2006

본 연구는 페라이트의 Fe 양이온 일부를 Ni, Mn, Co등으로 치환하여 M-ferrites를 제조하여 열화학적 2단계 물 분해 반응의 특성을 비교 평가하였고, XRD, SEM, GC등의 분석으로 각 금속산화물의 특성을 확인하였다. M-ferrites는 고상법으로 제조하였다. 각각의 M-ferrites에 대한 열적환원은 1573K에서 진행하였고 물 분해 반응은 1273K에서 실시하였다. 이 반응에서 생성된 가스는 전량 포집하여 GC를 통해 분석하였다. 반응 전후의 시료에 대하여 SEM, XRD를 분석하여 GC결과와 함께 금속산화물의 산화환원반응 특성을 고찰하였다. 그 결과로서 물 분해 반응 후 M-ferrite (M=Co, Ni, Mn)의 생성을 XRD를 통하여 확인할 수 있었고, 물 분해 반응과의 비교결과 격자상수의 증대가 M-ferrite내의 산소의 환원에 영향을 미치는 것을 알 수 있었다. SEM결과에서는 4cycle의 물 분해 반응 후 Mn-ferrite의 심한 sintering 현상을 확인 할 수 있었다.

• Journal of the Korean Magnetics Society
• /
• v.10 no.3
• /
• pp.123-132
• /
• 2000

Cerium substituted YIG thin films were grown by rf magnetron sputter techniques. We investigated the effects of post-deposition heat-treatment as well as various deposition parameters such as substrate materials, substrate temperature. sputter power, and sputter gas types on the crystallinity, chemical composition, microstructure and magnetic characteristics of the films. Post-deposition heat treatment over 750 $\^{C}$ was applied to crystallize as-prepared amorphous films, and a strong tendency of particular crystallographic planes tying parallel to substrate surface was observed for the post-deposition heat-treated films on GGG substrate. The chemical composition of the films exhibited a wide range of chemical stoichiometry depending on the oxygen fraction of sputter gas, and in particular the composition of the film deposited in sputter gas with an oxygen fraction of R = 10% was Ce$\_$0.23/Y$\_$1.30/Fe$\_$3.50/O$\_$12/. With raising the temperature of post-deposition heat-treatment from 900 $\^{C}$ to 1100 $\^{C}$, the surface roughness of the film on GGG substrates increased from about 3 nm to 40 nm, but their coercive force and ferromagnetic resonance line width decreased from 0.477 kA/m to 0.369 kA/m and from 12.5 kA/m to 8.36 kA/m, respectively.

• Food Science and Preservation
• /
• v.13 no.1
• /
• pp.1-7
• /
• 2006

The effects of packaging material and method on quality of fresh-cut mushrooms (Agaricus bisporus Sing.) were investigated in terms of weight loss, surface color, phenolics, vitamin C and sensory characteristics during storage at $5^{\circ}C$. The fresh-cut mushrooms were subjected to passive, gas exchange and vacuum packaging conditions at st. Polyethylene film (PE), polypropylene film (PP), anti-fogging film (AP) and pen orated film (PF) were used for the passive packaging. The mixed gas of $5\% CO_2/\;2\%O_2$ (MA1) and $10\%CO_2/\;2\%O_2$(MA2) were applied for the gas exchange packaging. The respiration rate of sliced mushroom was 1.27 times higher than intact mushroom at $5^{\circ}C$. Gas concentrations in the passive packaging were $1-2\%\;O^2\;and\;5-16\%m$ during storage of sliced mushrooms for 14 days at $5^{\circ}C$, and levels of the gases were different by the films used The mushroom in perforated film (PF) showed the highest weight loss of $4.56\%$. Anti-fogging film (AF) was somewhat effective for prevention of the weight loss compared with other films after 14 days storage. The mushrooms in MA1 and MA2 packages showed lower delta L value than in other films. PE packaging mitigated decrease of free and bound phenolics during storage. The mushrooms in MA2 kept better quality in sensory aspect, and then in MA1, PE and PP in order during storage at $5^{\circ}C$.

• Korean Journal of Food Science and Technology
• /
• v.32 no.6
• /
• pp.1271-1277
• /
• 2000

The extracts from tomatoes, apples, carrots, mallows, watercreses+pine needles, Angelica keiskei Koiz, jujubes and lemons were selected and mixed at the ratio of 3 : 3 : 3 : 1/2 : 1/2 : 1/2 : 1/2 : 1/5 on the basis of sensory evaluation. The mixed extracts were divided into three lots and treated as follows. The first lot was heated for 15 sec at $96^{\circ}C$ without centrifugation and filtration, the second filtered through a ultramembrane filter. For the third one, the ultrafiltrate combined with autoclaved retentates on the membrane filter and the previous centrifugal precipitation. The mixed juices were stored in the glass bottles with atmosphere or in film package with nitrogen gas. And then they were stored at $4^{\circ}$ and $20^{\circ}C$. During storage the treated juices showed $pH\;4.07{\sim}4.10$, titratable acidity $66.35{\sim}84.08$, soluble solid $7{\sim}9^{\circ}Brix$, reducing sugar $5.42{\sim}6.97%$, glucose $1.96{\sim}2.30%$ and fructose $3.46{\sim}4.14%$. The ultrafiltered juices showed yellow color, different from orange color of other treatment lots. Peroxidase activity and microbial population were inhibited by thermal treatment and ultrafiltration. The browning effects of the mixed juice of fruits and vegetables during storage were caused by ascorbic acid oxidation and non-enzymatic browning reaction, which could be reduced by change and packing with nitrogen gas instead of atmosphere inside bottles.

• Geophysics and Geophysical Exploration
• /
• v.11 no.3
• /
• pp.242-249
• /
• 2008

Recently, AVO analysis has been widely used in oil exploration with seismic subsurface section as a direct indicator of the existence of the gas. In the case of the deep reservoirs like the gas reservoirs in the East-sea, it is often difficult to observe AVO responses in CMP gathers even though the bright spots are shown in the stacked section. Because the reservoir becomes more consolidated as its depth deepens, P-wave velocity does not decrease significantly when the pore fluid is replaced by the gas. Thus the difference in Poisson's ratio, which is a key factor for AVO response, between the reservoir and the layer above it does not increase significantly. In this study, we analyzed the effects of Poisson's ratio difference on AVO response with a variety of Poisson's ratios for the upper and lower layers. The results show that, as the difference in Poisson's ratio between the upper and lower layers decreases, the change in the reflection amplitude with incidence angle decreases and AVO responses become insignificant. To consider the limitation of AVO responses shown in the gas reservoir in East-sea, the velocity model was made by simulation Gorae V structure with seismic data and well logs. The results of comparing AVO responses observed from the synthetic data with theoretical AVO responses calculated by using material properties show that the amount of the change in reflection amplitude with increasing incident angle is very small when the difference in Poisson's ratio between the upper and lower layers is small. In addition, the characteristics of AVO responses were concealed by noise or amplitude distortion arisen during preprocessing. To overcome such limitations of AVO analysis of the data from deep reservoirs, we need to acquire precisely reflection amplltudes In data acquisition stage and use processing tools which preserve reflection amplitude in data processing stage.

• Applied Chemistry for Engineering
• /
• v.21 no.2
• /
• pp.217-223
• /
• 2010

In general, fiber-reinforced plastics (FRP) wastes are simply buried or burned. Landfill brings about a permanent contamination of soil due to the inability of FRP to decompose and incineration causes an issue of generating toxic gases and dusts. There have been several ways to treat the FRP wastes such as landfill, incineration, chemical recycling, material recycling and the utilization of energy from combustion. Most methods excluding material recycling are known to have critical limitations in economic, technical and environmental manners. However it is known that material recycling is most desirable among the methods handling FRP wastes. In this study, to investigate the purpose of feasibility of material recycling, various bulk molding compound (BMC) specimens were prepared with the various contents of unsaturated polyester resin binder (25, 30, 35 wt%) and the various replacement ratios of FRP wastes powder (0, 25, 50, 75, 100 wt%) substituted for filler. To evaluate the physical properties BMC specimens, various tests such as tensile strength, flexural strength, impact strength, hot water resistance and SEM imaging were conducted. As a results, mechanical strengths decreased with an increase of replacement ratio of FRP waste powder and physical properties of BMC specimens were deteriorated in the hot water resistance. The fluidity of BMC with more than 50 wt% of the replacement ratio of FRP wastes powder decreased remarkably, causing a problem in the BMC composite.