• 한국산학기술학회논문지
• /
• 제18권4호
• /
• pp.584-591
• /
• 2017

수중에서 중금속은 흡착제에 의한 표면흡착과 금속수산화물로의 침전/제거반응이 동시에 일어나기 때문에 이들 각각에 의한 중금속 제거기작은 명확하게 구분되어 설명되지 못한다. 본 연구에서는 중금속 제거기작을 보다 명확하게 이해하기 위해 $850^{\circ}C$로 소성된 황토를 이용하여 다양한 pH 조건에서 Cu, Pb, Zn, Cd, 그리고 Cr 수용액 각각을 대상으로 회분식실험을 수행하였다. 실험결과 Cr을 제외한 중금속 농도는 반응초기에(<5분) 급격하게 감소되어 초기농도 대비 약 90%가 제거되었다. 한편, pH는 대상 금속 수용액에 따라 정도의 차이를 보이긴 하나 전체적으로 반응시간에 따라 지속적으로 증가되어 7.0-9.0까지 증가되었다. 반응시간에 따라 증가되는 pH 값과 높은 pH 조건에서 상대적으로 높은 중금속 제거율은 금속수산화물의 침전과 관련 있어 보인다. 흡착제(상용활성탄, 비소성황토, 소성황토)별 반응시간에 따른 pH 변화에 대한 비교실험결과, pH 증가현상은 소성황토에서만 두드러지게 나타나 소성과정에서 황토의 물성특성이 변화되었던 것으로 생각된다. 따라서 소성황토에 의한 중금속 제거는 흡착제에 의한 단순흡착뿐 아니라, 높은 pH 조건에서 금속수산화물을 형성함으로써 흡착질 표면에 침전 제어 될 수 있음을 보여준다.

• 한국대기환경학회지
• /
• 제26권5호
• /
• pp.543-553
• /
• 2010

Almost five million citizens a day are using subways as a means of traffic communication in the Seoul metropolitan. As the subway system is typically a closed environment, indoor air pollution problems frequently occurs and passengers complain of mal-health impact. Especially $PM_{10}$ is well known as one of the major pollutants in subway indoor environments. The purpose of this study was to compare the indoor air quality in terms of $PM_{10}$ and to quantitatively compare its source contributions in a Seoul subway platform before and after installing platform screen doors (PSD). $PM_{10}$ samples were collected on the J station platform of Subway Line 7 in Seoul metropolitan area from Jun. 12, 2008 to Jan. 12, 2009. The samples collected on membrane filters using $PM_{10}$ mini-volume portable samplers were then analyzed for trace metals and soluble ions. A total of 18 chemical species (Ba, Mn, Cr, Cd, Si, Fe, Ni, Al, Cu, Pb, Ti, $Na^+$, $NH_4^+$, $K^+$, $Mg^{2+}$, $Ca^{2+}$, $Cl^-$, and ${SO_4}^{2-}$) were analyzed by using an ICP-AES and an IC after performing proper pre-treatments of each sample filter. Based on the chemical information, positive matrix factorization (PMF) model was applied to identify the source of particulate matters. $PM_{10}$ for the station was characterized by three sources such as ferrous related source, soil and road dust related source, and fine secondary aerosol source. After installing PSD, the average $PM_{10}$ concentration was decreased by 20.5% during the study periods. Especially the contribution of the ferrous related source emitted during train service in a tunnel route was decreased from 59.1% to 43.8% since both platform and tunnel areas were completely blocked by screen doors. However, the contribution of the fine secondary aerosol source emitted from various outside combustion activities was increased from 14.8% to 29.9% presumably due to ill-managed ventilation system and confined platform space.

• 한국분말야금학회:학술대회논문집
• /
• 한국분말야금학회 2001년도 추계학술강연 및 발표대회
• /
• pp.7-7
• /
• 2001

The increasing interest in light weight materials coupled to the need for cost -effective processing have combined to create a significant opportunity for aluminum P/M. particularly in the automotive industry in order to reduce fuel emissions and improve fuel economy at affordable prices. Additional potential markets for Al PIM parts include hand tools. Where moving parts against gravity represents a challenge; and office machinery, where reciprocating forces are important. Aluminum PIM adds light weight, high compressibility. low sintering temperatures. easy machinability and good corrosion resistance to all advantages of conventional iron bm;ed P/rv1. Current commercial alloys are pre-mixed of either the AI-Si-Mg or AL-Cu-Mg-Si type and contain 1.5% ethylene bis-stearamide as an internal lubricant. The powder is compacted in closed dies at pressure of 200-500Mpa and sintered in nitrogen at temperatures between $580~630^{\circ}C$ in continuous muffle furnace. For some applications no further processing is required. although most applications require one or more secondary operations such as sizing and finishing. These sccondary operations improve the dimension. properties or appearance of the finished part. Aluminum is often considered difficult to sinter because of the presence of a stable surface oxide film. Removal of the oxide in iron and copper based is usually achieved through the use of reducing atmospheres. such as hydrogen or dissociated ammonia. In aluminum. this occurs in the solid st,lte through the partial reduction of the aluminum by magncsium to form spinel. This exposcs the underlying metal and facilitates sintering. It has recently been shown that < 0.2% Mg is all that is required. It is noteworthy that most aluminum pre-mixes contain at least 0.5% Mg. The sintering of aluminum alloys can be further enhanced by selective microalloying. Just 100ppm pf tin chnnges the liquid phase sintering kinetics of the 2xxx alloys to produce a tensile strength of 375Mpa. an increilse of nearly 20% over the unmodified alloy. The ductility is unnffected. A similar but different effect occurs by the addition of 100 ppm of Pb to 7xxx alloys. The lend changes the wetting characteristics of the sintering liquid which serves to increase the tensile strength to 440 Mpa. a 40% increase over unmodified aIloys. Current research is predominantly aimed at the development of metal matrix composites. which have a high specific modulus. good wear resistance and a tailorable coefficient of thermal expnnsion. By controlling particle clustering and by engineering the ceramic/matrix interface in order to enhance sintering. very attractive properties can be achicved in the ns-sintered state. I\t an ils-sintered density ilpproaching 99%. these new experimental alloys hnve a modulus of 130 Gpa and an ultimate tensile strength of 212 Mpa in the T4 temper. In contest. unreinforcecl aluminum has a modulus of just 70 Gpa.

• 한국대기환경학회지
• /
• 제22권5호
• /
• pp.590-603
• /
• 2006

Size-and time-resolved aerosol samples were collected using an eight-stage Davis rotating unit for monitoring (DRUM) sampler from 23 March to 29 April 2001 at Gosan, Jeju Island, Korea, which is one of the super sites of Asia-Pacific Regional Aerosol Characterization Experiment(ACE-Asia). These samples were analyzed using synchrotron X-ray fluorescence for 3-hr average concentrations of 19 elements including Al, Si, S, Cl, K, Ca, Ti, V, Cr, Mn, Fe, Ni, Cu, Zn, As, Se, Br, Rb, and Pb. The size-resolved data sets were then analyzed using the positive matrix factorization(PMF) technique to identify possible sources and estimate their contributions to particulate matter mass. PMF analysis uses the uncertainty of the measured data to provide an optimal weighting. Twelve sources were resolved in eight size ranges($0.09{\sim}12{\mu}m$) and included continental soil, local soil, sea salt, biomass/biofuel burning, coal combustion, oil combustion, municipal incineration, nonferrous metal source, ferrous metal source, gasoline vehicle, diesel vehicle, and volcanic emission. The PMF result of size-resolved source contributions showed that natural sources represented by local soil, sea salt, continental soil, and volcanic emission contributed about 79% to the predicted primary particulate matter(PM) mass in the coarse size range ($1.15{\sim}12{\mu}m$) while anthropogenic sources such as coal combustion and biomass/biofuel burning contributed about 58% in the fine size range($0.56{\sim}2.5{\mu}m$). The diesel vehicle source contributed mostly in ultra-fine size range($0.09{\sim}0.56{\mu}m$) and was responsible for about 56% of the primary PM mass.

• 대한화학회지
• /
• 제25권6호
• /
• pp.343-350
• /
• 1981

P-Aminobenzaldehyde cyclohexylthiosemicarbazone의 결정 및 분자구조를 Computer controlled four circle diffractometer에 의한 X-선 회절방법으로 해명하였다. 결정은 공간군 C2/c의 단사형계에 속하며 단위세포 상수는 a = 12.488(2), b = 12.276(4), c = 19.997(6)${\AA}$, ${\beta}=103.55(3)^{\circ}$이고 z = 8이다. 구조는 중원자법과 Fourier 방법으로 규명하였으며 full-matrix 최소자승법으로 정밀화하였다. 최종 R값은 2712개의 회절반점에 대하여 0.058이었다. 분자는 N(2)-N(3)결합에대하여 C(8)-S는 trans, C(8)-N(1)은 cis형으로 놓여 있으며 N(1)과 N(3) 원자들이 분자내 수소결합을 만들고 있다. 의자모양의 cyclohexane 고리는 benzene 고리와 $40.7^{\circ}$의 면각을 이루고 있다. 결정내의 분자들은 수소 결합들로 모여져 있는데 $N(2)-H{\ldots}S$ 수소결합이 분자들을 이합체 꼴을 만들며 이들 분자들을 $N-H{\ldots}N$ 수소결합들이 이어주고 있다.

• 한국대기환경학회지
• /
• 제25권2호
• /
• pp.108-121
• /
• 2009

The suspended particulate matters have been collected on membrane filters and glass fiber filters by an 8-stage cascade impactor for 2 years (Sep. 2005${\sim}$Sep. 2007) in Kyung Hee University-Global Campus located on the border of Yongin and Suwon. The 20 chemical species (Al, Mn, Si, Fe, Cu, Pb, Cr, Ni, V, Cd, Ba, $Na^+$, ${NH_4}^+$, $K^+$, $Mg^{2+}$, $Ca^{2+}$, $Cl^-$, ${NO_3}^-$, and ${SO_4}^{2-}$) were analyzed by an ICP-AES and an IC after performing proper pre-treatments of each sample filter. Based on these chemical information, the PMF receptor model was applied to identify the source of ambient size-by-size particulate matters. The receptor modeling is the one of the statistical methods to achieve resonable air pollution management strategies. A total of 10 sources was identified in 9 size-ranges such as long-range transport, secondary aerosol, $NH_{4}NO_{3}$ related source, coal combustion, sea-salt, soil, oil combustion, auto emission, incineration, and biomass burning. Especially, the secondary aerosol source assorted in fine and coarse modes was intensively studied.

• Advances in materials Research
• /
• 제5권1호
• /
• pp.55-66
• /
• 2016

This paper describes a study on the effects of $Mg_2Si_{(p)}$ addition on the microstructure, porosity, and mechanical properties namely hardness and tensile properties of AA332 composite. Each composite respectively contains 5, 10, 15, and 20 wt% reinforcement particles developed by a stir-casting. The molten composite was stirred at 600 rpm and melted at $900^{\circ}C{\pm}5^{\circ}C$. The $Mg_2Si$ particles were wrapped in an aluminum foil to keep them from burning when melting. The findings revealed that the microstructure of $Mg_2Si_{(p)}/AA332$ consists of ${\alpha}$-Al, binary eutectic ($Al+Mg_2Si$), $Mg_2Si$ particles, and intermetallic compound. The intermetallic compound was identified as Fe-rich and Cu-rich, formed as polygonal or blocky, Chinese script, needle-like, and polyhendrons or "skeleton like". The porosity of $Mg_2Si_{(p)}/AA332$ composite increased from 8-10% and the density decreased from 9-12% from as-cast. Mechanical properties such as hardness increased for over 42% from as-cast and the highest UTS, elongation, and maximum Q.I were achieved in the sample of 10% $Mg_2Si$. The study concludes that combined with AA332, the amount of 10 wt% of$Mg_2Si$ is a suitable reinforcement quantity with the combination ofAA332.

• 한국결정학회지
• /
• 제5권2호
• /
• pp.78-84
• /
• 1994

N-[1-(benzotriazol-1-yl)butyl]-P-nitroaniline ( BBN, C6H7N502) 의 분자 및 결정구조를 반-선 회절 법Abstract으로 연구하였다. 이 결정은 단사정계이고 공간군은 P21/n이다. 단위세포 길이는 a=17.542(2)A, b= 10.755(3)A, c=8.891(1)A 이며 a=b=r=90˚,b=104.58(1)˚,Z=4 이다.구조해석에 사용한 X-선은 CuKa선(λ:1.5418A )을 사용하였다. 분자구조는 직접법으로 풀었으며 최소자승법으로 정밀화하였 다. 최종 신뢰도 R값은 255개 파라메터, F≥4o(F)인 2248개의 회절반점에 대하여 R= 0.0411 이었다. 분자간 결합은 1개의 수소결합인 N(11)-Hll(Nll)‥‥N(3)로 결합되어 있으며, N(11)‥‥N(3)=3.136(2).1, N(11)-Hl 1 (Nl 1) ‥‥N(3) =164.1(15)˚이다.

• 마이크로전자및패키징학회지
• /
• 제25권2호
• /
• pp.1-8
• /
• 2018

In the soldering industry, a variety of lead-free solders have been developed as a part of restricting lead in electronic packaging. Sn-Ag-Cu (SAC) lead-free solder is regarded as one of the most superior candidates, owing to its low melting point and high solderability as well as the mechanical property. On the other hand, the mechanical property of SAC solder is directly influenced by intermetallic compounds (IMCs) in the solder joint. Although IMCs in SAC solder play an important role in bonding solder joints and impart strength to the surrounding solder matrix, a large amount of IMCs may cause poor strength, due to their brittle nature. In other words, the mechanical properties of SAC solder are of some concern because of the formation of large and brittle IMCs. As the IMCs grow, they may cause poor device performance, resulting in the failure of the electronic device. Therefore, new solder technologies which can control the IMC growth are necessary to address these issues satisfactorily. There are an advanced nanotechnology for microstructural refinement that lead to improve mechanical properties of solder alloys with nanoparticle additions, which are defined as nano-reinforced solders. These nano-reinforced solders increase the mechanical strength of the solder due to the dispersion hardening as well as solderability of the solder. This paper introduces the nano-reinforced solders, including its principles, types, and various properties.

• Journal of Microbiology and Biotechnology
• /
• 제24권5호
• /
• pp.675-682
• /
• 2014

Approximately 50% of people in the world experience abdominal flatulence after the intake of foods containing galactosides such as lactose or soybean oligosaccharides. The galactoside hydrolyzing enzymes of ${\alpha}$- and ${\beta}$-galactosidases have been shown to reduce the levels of galactosides in both the food matrix and the human gastrointestinal tract. This study aimed to optimize the production of ${\alpha}$- and ${\beta}$-galactosidases of Bifidobacterium longum subsp. longum RD47 with a basal medium containing whey and corn steep liquor. The activities of both enzymes were determined after culturing at $37^{\circ}C$ at pH 6.0 for 30 h. The optimal production of ${\alpha}$- and ${\beta}$-galactosidases was obtained with soybean oligosaccharides as a carbon source and proteose peptone no. 3 as a nitrogen source. The optimum pH for both ${\alpha}$- and ${\beta}$-galactosidases was 6.0. The optimum temperatures were $35^{\circ}C$ for ${\alpha}$-galactosidase and $37^{\circ}C$ for ${\beta}$-galactosidase. They showed temperature stability up to $37^{\circ}C$. At a 1 mM concentration of metal ions, $CuSO_4$ inhibited the activities of ${\alpha}$- and ${\beta}$-galactosidases by 35% and 50%, respectively. On the basis of the results obtained in this study, B. longum RD47 may be used for the production of ${\alpha}$- and ${\beta}$-galactosidases, which may reduce the levels of flatulence factors.