• 한국환경과학회지
• /
• 제22권10호
• /
• pp.1263-1271
• /
• 2013

Graphene oxide (GO)-titania composites have emerged as an attractive heterogeneous photocatalyst that can enhance the photocatalytic activity of $TiO_2$ nanoparticles owing to their potential interaction of electronic and adsorption natures. Accordingly, $TiO_2$-GO mixtures were synthesized in this study using a simple chemical mixing process, and their heterogeneous photocatalytic activities were investigated to determine the degradation of airborne organic pollutants (benzene, ethyl benzene, and o-xylene (BEX)) under different operational conditions. The Fourier transform infrared spectroscopy results demonstrated the presence of GO for the $TiO_2$-GO composites. The average efficiencies of the $TiO_2$-GO mixtures for the decomposition of each component of BEX determined during the 3-h photocatalytic processes were 26%, 92%, and 96%, respectively, whereas the average efficiencies of the unmodified $TiO_2$ powder were 3%, 8%, and 10%, respectively. Furthermore, the degradation efficiency of the unmodified $TiO_2$ powder for all target compounds decreased during the 3-h photocatalytic processes, suggesting a potential deactivation even during such a short time period. Two operational conditions (air flow entering into the air-cleaning devices and the indoor pollution levels) were found to be important factors for the photocatalytic decomposition of BEX molecules. Taken together, these results show that a $TiO_2$-GO mixture can be applied effectively for the purification of airborne organic pollutants when the operating conditions are optimized.

• Wind and Structures
• /
• 제23권2호
• /
• pp.157-169
• /
• 2016

The structural integrity of tube bundles represents a major concern when dealing with high risk industries, such as nuclear steam generators, where the rupture of a tube or tubes will lead to the undesired mixing of the primary and secondary fluids. Flow-induced vibration is one of the major concerns that could compromise the structural integrity. The vibration is caused by fluid flow excitation. While there are several excitation mechanisms that could contribute to these vibrations, fluidelastic instability is generally regarded as the most severe. When this mechanism prevails, it could cause serious damage to tube arrays in a very short period of time. The tubes are therefore stiffened by means of supports to avoid these vibrations. To accommodate the thermal expansion of the tube, as well as to facilitate the installation of these tube bundles, clearances are allowed between the tubes and their supports. Progressive tube wear and chemical cleaning gradually increases the clearances between the tubes and their supports, which can lead to more frequent and severe tube/support impact and rubbing. These increased impacts can lead to tube damage due to fatigue and/or wear at the support locations. This paper presents simulations of a loosely supported multi-span U-bend tube subjected to turbulence and fluidelastic instability forces. The mathematical model for the loosely-supported tubes and the fluidelastic instability model is presented. The model is then utilized to simulate the nonlinear response of a U-bend tube with flat bar supports subjected to cross-flow. The effect of the support clearance as well as the support offset are investigated. Special attention is given to the tube/support interaction parameters that affect wear, such as impact and normal work rate.

• Membrane and Water Treatment
• /
• 제4권1호
• /
• pp.27-51
• /
• 2013

During cleaning steps, ultrafiltration membranes are mechanically and chemically stressed. This may result in membrane degradations and failures. In this paper, polysulfone membranes were used to evaluate membrane deteriorations by commercial detergents in static conditions. Ageing of the membrane was simulated by immersing samples in solutions containing commercial detergents with various concentrations, temperatures and times defined by experimental designs. Indeed, an innovative approach in the chemical membranes ageing researches, based on methodological tools, was used in order to achieve significant ageing experiments without using an accelerated ageing protocol. The macroscopic changes were monitored by permeability measurements and mechanical strength tests coupled with a microscopic characterization by ATR-FTIR and HRSEM. The present work details results obtained for three commercial detergents: an alkaline, an acidic and an enzymatic detergent. It was found that the detergents used in the industrial advised conditions (concentration, temperature and time of contact) were not detrimental for membrane properties (permeability and elongation at break) and so for the quality of the produced water. Over the industrial cumulated time of contact, different ageing effects can be observed and compared with the ones induced by NaOCl.

• Membrane and Water Treatment
• /
• 제8권5호
• /
• pp.449-462
• /
• 2017

Direct treatment of municipal wastewater by forward osmosis (FO) process was evaluated in terms of water flux decline, reverse salt diffusion, pollutants rejection and concentration efficiency by using synthetic seawater as the draw solution. It was found that when operating in PRO mode (active layer facing the draw solution), although the FO membrane exhibited higher osmotic water flux, more severe flux decline and reverse salt diffusion was also observed due to the more severe fouling of pollutants in the membrane support layer and accompanied fouling enhanced concentration polarization. In addition, although the water flux decline was shown to be lower for the FO mode (active layer facing the feed solution), irreversible membrane fouling was identified in both PRO and FO modes as the water flux cannot be restored to the initial value by physical flushing, highlighting the necessity of chemical cleaning in long-term operation. During the 7 cycles of filtration conducted in the experiments, the FO membrane exhibited considerably high rejection for TOC, COD, TP and $NH_4{^+}-N$ present in the wastewater. By optimizing the volume ratio of seawater draw solution/wastewater feed solution, a concentration factor of 3.1 and 3.7 was obtained for the FO and PRO modes, respectively. The results demonstrated the validity of the FO process for direct treatment of municipal wastewater by using seawater as the draw solution, while facilitating the subsequent utilization of concentrated wastewater for bioenergy production, which may have special implications for the coastline areas.

• 한국진공학회지
• /
• 제13권4호
• /
• pp.175-181
• /
• 2004

미소인장시험을 통해 304 스테인리스 스틸 판재 위에 증착된 DLC 박막의 안정성을 평가하였다. 모재의 소성 변형과 함께 코팅 층의 손상이 발생하기 시작하는데, 작은 규모의 모재 변형 시에는 인장축의 수직방향으로 박막의 균열이 발생하지만, 모재의 슬립변형이 발생하기 시작하면 인장 축과 $45^{\circ}C$의 각도를 갖는 슬립 면을 따라 필름의 박리가 발생하였다. DLC박막의 박리면적으로부터 필름의 접착력을 평가할 수 있었으며, 필름의 합성 전에 실시하는 Ar 플라즈마 스퍼터링 세척시간이 길수록 그리고 세척시 기판에 인가되는 전압이 높을수록 필름의 접착력은 향상되었다. 이러한 변화는 스테인리스 스틸 모재와 Si 접합 층간의 계면특성이 향상되면, 필름의 전체 접착력을 증진시킬 수 있음을 보여주고 있다.

• 한국진공학회:학술대회논문집
• /
• 한국진공학회 2011년도 제40회 동계학술대회 초록집
• /
• pp.505-505
• /
• 2011

The control of wettability of thin films is of great importance and its success surely brings us huge applications such as self-cleaning, antifogging and bio-passive treatments. Usually, the control is accomplished by modifying either surface energy or surface topography of films. In general, hydrophobic surface can be produced by coating low surface energy materials such as fluoropolymer or by increasing surface roughness. In contrast, to enhance the hydrophillicity of solid surfaces, high surface energy and smoothness are required. Silica (SiO2) is environmentally safe, harmless to human body and excellently inert to most chemicals. Also its chemical composition is made up of the most abundant elements on the earth's crest, which means that SiO2 is inherently economical in synthesis. Moreover, modification in chemistry of SiO2 into various inorganic-organic hybrid materials and synthesis of films are easily undertaken with the sol-gel process. The contact angle of water on a flat silica surface on which the Young's equation operates shows ~50o. This is a slightly hydrophilic surface. Many attempts have been made to enhance hydrophilicity of silica surfaces. In recent years, superhydrophilic and antireflective coatings of silica were fabricated from silica nanoparticles and polyelectrolytes via a layer-by-layer assembly and postcalcination treatment. This coating layer has a high transmittance value of 97.1% and a short water spread time to flat of <0.5 s, indicating that both antireflective and superhydrophilic functions were realized on the silica surfaces. In this study, we assessed hydrophillicity and hydrophobicity of silica coating layers that were synthesized using the sol-gel process. Systematic changes of processing parameters greatly influence their surface properties.

• 한국광물학회지
• /
• 제18권2호
• /
• pp.83-92
• /
• 2005

광물의 용해속도는 기후에 따라 지역적인 차이는 있으나, 일반적으로 화강암을 구성하는 광물중 장석류의 풍화속도가 다른 광물에 비해 비교적 빠르기 때문에 파손 정도는 장석의 안정성에 지배된다. 지구화학적 반응 모델링 결과, 강우에 의해서 화강암이 변질되는데 걸리는 시간은 다른 변수를 고려하지 않고 pH만을 고려한 pH=4.5인 산성수내에서의 변질속도와 비교할 때 일반적인 빗물(pH=5.7)보다 약 2.3배 더 빠른 것으로 계산되었다. 이러한 결과는 화강암질 석조문화재의 보존에 있어서 pH가 중요한 요소로 작용할 수 있음을 의미한다. 석조문화재의 풍화를 억제하기 위해서는 암석의 풍화특성이 우선적으로 규명되어야 하며, 가수분해, 산 반응 등의 화학적 풍화작용은 물과의 접촉에 의해 이루어지므로 물을 차단하기 위하여 발수코팅, 오일코팅 또는 건조환경을 조성하는 방안을 고려해야 할 것이다. 세척제와 생물방제를 이용할 시는 빗물이나 화강암과의 장기적 반응을 고려하여 중성화작용과 환원성 환경이 형성될 수 있는 재질의 선택이 매우 중요하다.

• 한국염색가공학회지
• /
• 제21권1호
• /
• pp.10-20
• /
• 2009

The objective of this study is to investigate the efficacy of leaf powder colorants as substitutes for traditional fresh juice extract dyeing. Three kinds of leaf powder colorants were prepared by freeze drying method with or without deep freezing as pre-treatment: one powder colorant from fresh leaf juice with deep freezing; two kinds of powder colorant from fresh leaves with and without deep freezing. Their dyeing properties and storage stabilities were studied and compared with the traditional fresh juice extract dyeing. The presence of indigo in the powder colorants was confirmed by UV/Visible absorption spectra. They showed absorption peak at 602nm which was same with indigo absorption peak. Dyeing was done at low temperature around 6$^{\circ}C$. All three powder colorants produced B colors on silk fabrics, showing similar color to the one dyed traditionally with fresh juice extract. The powder colorants from leaves gave higher color strength than the powder from leaf juice. The powder colorant prepared from leaves with deep freezing was the most stable for long term storage as its color and color strength were not changed after 360 days. So, this was used for further dyeing to study the effects of concentration and repeat dyeing on color strength and colorfastness. Fastnesses to dry cleaning and rubbing were fairly good above 4 rating. Further study is needed to improve light fastness. It was concluded that the leaf powder colorant with deep freezing could be used as a substitute for traditional juice extract dyeing at all seasons.

• 한국해양환경ㆍ에너지학회지
• /
• 제12권3호
• /
• pp.111-123
• /
• 2009

허베이스피리트호의 원유유출로부터 오염된 해안이 어떻게 변화되어 가는지를 조사하는 것을 목적으로 하여, 태안군 이원면 만대(가로림만)로부터 소원면 파도리 해변까지 11개 정점에서 현장조사를 실시한 결과, 다음과 같은 결론을 얻었다. 1년이 경과한 시점에서 관측한 결과 관측지점 10개 정점 모두에서 잔존유는 발견되지 않았으나, 구름포 해변의 경우 아직도 토양중에 잔존유가 존재하고 있는 것으로 파악되었다. 오염된 태안 해안의 조속한 복원은 100만이 넘는 자원봉사자와 지역주민의 방제노력이 이루어낸 성과라고 판단되며, 또한 파도의 반복적인 작용에 의해서 조간대에 표착한 표착유가 제거되었으리라 판단된다. 조간대에 표착해 있던 원유의 일부는 물리화학적 그리고 생물학적 풍화작용으로 분해되었고, 나머지 기름은 모래입자나 미세토립자(minerals)와 부착되어 기름과 미세토립자의 합체물(OMA)의 형태로 조간대나 조하대에 분산되었으리라 판단된다.

• 한국염색가공학회지
• /
• 제21권4호
• /
• pp.23-32
• /
• 2009

The objective of this study is to investigate the efficacy of leaf powder colorants as substitutes for traditional indigo dyeing. Leaf powder colorants were prepared by hot air($50^{\circ}C$) and room temperanrre($25^{\circ}C$) drying methods from fresh leaves. The presence of indigo in the leaf powder colorants was confirmed by UV/Visible absorption spectra. All the powder colorants showed broad absorption at 602 nm as same as synthetic indigo. Dyeing was done by reduction method with sodium hydrosulfite and sodium hydroxide. Leaf powder colorants produced blue color on silk fabrics, showing similar color to the one dyed traditionally with fresh juice extract. The powder colorants prepared at room temperature drying were more stable for long term storage than that prepared by hot air drying. Thus, the powder colorants prepared by room temperature drying was reduced and dyed in one-step process without sodium hydroxide in the dyebath for further investigate dyeing properties. K/S value of the fabric dyed without sodium hydroxide was much higher than one dyed with sodium hydroxide. Regardless of the addition of sodium hydroxide, rubbing fastness was fairly good showing above 4 rating. Fastness to dry cleaning and light of the fabrics dyed without sodium hydroxide were mote higher than that dyed in alkaline condition.