• Korean Chemical Engineering Research
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• 제49권5호
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• pp.633-638
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• 2011

Mn이 치환된 헥사알루미네이트 촉매인 $LaMnAl_{11}O_{19}$, $BaMnAl_{11}O_{19}$, $SrMnAl_{11}O_{19}$을 $(NH_4)_2CO_3$ 공침법을 이용하여, $1,200^{\circ}C$ 5시간 소성을 통해 제조하였다. X-선 회절, 질소흡착을 통해 촉매의 결정구조와 비표면적을 분석한 결과, 결정 격자 내 거울면에 La이 존재하는 $LaMnAl_{11}O_{19}$이 $BaMnAl_{11}O_{19}$과 $SrMnAl_{11}O_{19}$보다 우수한 헥사알루미네이트 결정 구조를 가지는 동시에 13 $m^2/g$의 높은 비표면적을 가지고 있었다. 또한 SEM 분석을 통해 $LaMnAl_{11}O_{19}$이 특유의 판상구조가 잘 발달함을 확인하였다. 메탄 연소 활성은 다음과 같은 차례로 증가하였고: $LaMnAl_{11}O_{19}$ > $SrMnAl_{11}O_{19}$ > $BaMnAl_{11}O_{19}$. 메탄 연소 활성은 비표면적에 의존하였다. $LaMnAl_{11}O_{19}$에 60 wt%의 $CeO_2$를 첨가하고 $700^{\circ}C$의 저온에서 소성한 경우 $700^{\circ}C$의 저온에서 100% 전환율에 도달함으로써 ceria 첨가에 의한 메탄 연소 개선 효과를 확인할 수 있었으며, 이 촉매가 저온 및 중온 영역의 메탄 연소 촉매로 활용될 수 있음을 확인하였다. 그러나, 이 촉매의 경우 $1,200^{\circ}C$의 고온에서 5시간 소성한 후에는 ceria입자 크기의 증가로 인해 메탄의 연소 활성 개선 효과를 잃게됨으로 고온용 연소 촉매로서의 사용은 한계가 있음을 확인하였다.

• Bulletin of the Korean Chemical Society
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• 제32권6호
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• pp.1912-1920
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• 2011

The $SnO_2$ with a particle size of about 300 nm instead of Ni is used in this study to overcome rapid catalytic deactivation by the formation of a $NiAl_2O_4$ spinal structure on the conventional Ni/${\gamma}$-$Al_2O_3$ catalyst and simultaneously impregnated the catalyst with potassium (K). The $SnO_2-K_2O$ impregnated Zeolite Y catalyst ($SnO_2-K_2O$/ZY) exhibited significantly higher ethanol reforming reactivity that that achieved with $SnO_2$ 100 and $SnO_2$ 30 wt %/ZY catalysts. The main products from ethanol steam reforming (ESR) over the $SnO_2$-$K_2O$/ZY catalyst were $H_2$, $CO_2$, and $CH_4$, with no evidence of any CO molecule formation. The $H_2$ production and ethanol conversion were maximized at 89% and 100%, respectively, over $SnO_2$ 30 wt %-$K_2O$ 3.0 wt %/ZY at 600 $^{\circ}C$ for 1 h at a $CH_3CH_2OH:H_2O$ ratio of 1:1 and a gas hourly space velocity (GHSV) of 12,700 $h^{-1}$. No catalytic deactivation occurred for up to 73 h. This result is attributable to the easier and weaker of reduction of Sn components and acidities over $SnO_2-K_2O$/ZY catalyst, respectively, than those of Ni/${\gamma}$-$Al_2O_3$ catalysts.

• Korean Chemical Engineering Research
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• 제45권6호
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• pp.566-572
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• 2007

본 연구에서는 DME 직접 합성을 위한 혼성촉매가 두 가지 방법으로 제조되었으며, 이들의 촉매적 활성이 조사되었다. DME 합성을 위한 혼성촉매는 메탄올 합성과 메탄올 탈수반응에 촉매적 활성을 가진 성분들로 제조되었다. 메탄올 합성촉매는 Cu와 Zn이 함유된 전구물질로부터 합성되었으며, 메탄올 탈수촉매는 ${\gamma}-Al_2O_3$를 이용하였다. 두 촉매는 물리혼합법과 침전법에 의해서 혼성촉매로 제조되었다. 물리혼합법은 두 촉매를 분말상태에서 혼합하는 것이며, 침전법은 ${\gamma}-Al_2O_3$ 촉매상에 Cu-Zn 또는 Cu-Zn-Al 성분을 퇴적시키는 방법이다. 제조된 촉매의 물리적 특성을 조사하기 위하여 X선 회절법에 의한 결정구조, 질소흡착에 의한 BET 표면적, $N_2O$ 화학흡착에 의한 Cu의 표면적 그리고 주사전자현미경에 의한 표면형상 등이 조사되었다. 또한 이들 혼성촉매의 촉매적 활성은 여러 가지 반응조건을 변화시키면서 조사되었다. 이때 반응온도는 $250{\sim}290^{\circ}C$, 반응압력은 30~70 atm, $[H_2]/[CO]$ 몰비는 0.5~2.0, 그리고 공간속도는 $1,500{\sim}6,000 h^{-1}$ 촉매활성이 조사되었다. 반응성 실험 결과로부터 침전법으로 제조된 혼성촉매(CP-CZA/D)가 물리혼합법으로 제조된 혼성촉매(PM-CZ+D)보다 우수한 반응성을 나타냄을 확인할 수 있었으며, 특히 반응 온도, 압력, $[H_2]/[CO]$ 비, 공간속도가 각각 $260^{\circ}$, 50 atm, 1.0, $3,000h^{-1}$인 조건에서 침전법에 의해 제조된 촉매의 CO 전화율이 72%로 물리혼합법으로 제조된 촉매보다 약 20% 이상 높았다. $N_2O$ 화학흡착실험으로부터 Cu 표면적을 측정한 결과, PM-CZ+D 혼성촉매보다 CP-CZA/D 혼성촉매의 Cu 표면적이 더 높았다. 그러므로 침전법으로 제조된 혼성촉매상의 Cu입자가 더 잘 분산되었기 때문에 촉매의 활성이 개선된 것으로 판단된다.

• 한국표면공학회지
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• 제34권2호
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• pp.105-114
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• 2001

$Al_2$$O_3$ coatings were deposited on M2 high speed steels by the plasma enhanced chemical vapor deposition (PECVD) process, using a gas mixture of AlC1$_3$, $H_2$, $CO_2$ and Ar $Al_2$$O_3$ coatings had interference color and showed amorphous phase. $A1_2$X$A1_3$/($Ti_{0.5}$ /$Al_{0.5}$ )N double layer coatings were produced in the sequence of substrate $NH_3$ plasma pretreatment, ($Ti_{0.5}$$Al_{0.5}$)N depoition process, $Al_2$$O_3$ deposition process. $Al_2$ $O_3$/( $Ti_{0.5}$A $l_{0.5}$)N double layer coatings showed NaCl structure in ( $Ti_{0.5}$A $l_{0.5}$)N layer and amorphous phase in A1$_2$ $O_3$ layer. It was shown that $Al_2$ $O_3$ columns continuously grew onto ( $Ti_{0.5}$A $l_{0.5}$)N columns. ( $Ti_{0.5}$A $l_{0.5}$)N single coating and $Al_2$ $O_3$/( $Ti_{0.5}$A $l_{0.5}$)N double layer coating were oxidized at $700^{\circ}C$, 80$0^{\circ}C$, 90$0^{\circ}C$ for 1hr, 3hr in atmosphere. At 80$0^{\circ}C$, single layer coatings were oxidized, which were examined substrate oxide particle. But $Al_2$ $O_3$/ ( $Ti_{0.5}$A $l_{0.5}$)N double layer coatings maintained the asdeposited state. Therefore, $Al_2$ $O_3$/ ( $Ti_{0.5}$A $l_{0.5}$)N double layer coatings have moreexcellent oxidation resistance than ( $Ti_{0.5}$A $l_{0.5}$)N single layer coatings.X> 0.5/)N single layer coatings.s.

• 한국재료학회지
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• 제24권7호
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• pp.351-356
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• 2014

A spherical $Sr_4Al_{14}O_{25}:Eu^{2+}$ phosphor for use in white-light-emitting diodes was synthesized using a liquid-state reaction with two precipitation stages. For the formation of phosphor from a precursor, the calcination temperature was $1,100^{\circ}C$. The particle morphology of the phosphor was changed by controlling the processing conditions. The synthesized phosphor particles were spherical with a narrow size-distribution and had mono-dispersity. Upon excitation at 395 nm, the phosphor exhibited an emission band centered at 497 nm, corresponding to the $4f^65d{\rightarrow}4f^7$ electronic transitions of $Eu^{2+}$. The critical quenching-concentration of $Eu^{2+}$ in the synthesized $Sr_4Al_{14}O_{25}:Eu^{2+}$ phosphor was 5 mol%. A phosphor-converted LED was fabricated by the combination of the optimized spherical phosphor and a near-UV 390 nm LED chip. When this pc-LED was operated under various forward-bias currents at room temperature, the pc-LED exhibited a bright blue-green emission band, and high color-stability against changes in input power. Accordingly, the prepared spherical phosphor appears to be an excellent candidate for white LED applications.

• Korean Chemical Engineering Research
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• 제49권6호
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• pp.720-725
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• 2011

금속질산염과 염화금산을 전구체로 사용하여 다양한 금속산화물($$Al_{2}O_{3}$, ZnO, $Fe_{2}O_{3}$, $Cr_{2}O_{3}$, $MnO_{2}$, CuO, NiO, $Co_{3}O_{4}$)에 담지된 금촉매를 공침법을 이용하여 제조한 후, 일산화탄소 산화반응에서 수분첨가의 영향을 검토하였다. 이들 중 $Co_{3}O_{4}$와 ZnO에 담지된 금촉매가 일산화탄소에 대하여 높은 활성을 보여주었다. 반응가스 중에 수분이 첨가될 때 Au/$Co_{3}O_{4}$ 촉매는 활성이 약간 감소하였으나, Au/ZnO 촉매에서는 활성이 크게 증가하여 수분에 의한 일산화탄소 산화 활성은 담체의 종류에 크게 의존함을 알 수 있었다. 반응가스 중에 포함된 수분에 관계없이 반응 전과 후의 Au(5 wt%)/ZnO 촉매의 금입자 크기는 거의 변하지 않아 활성이 감소되는 이유는 금입자들의 소결에 의한 영향보다는 카보네이트와 같은 화학종에 의해 불활성화가 일어남을 알 수 있었으며, 이 화학종은 수분의 첨가에 의해 이산화탄소로 분해되어 활성이 증가한 것으로 생각된다.

• Environmental Engineering Research
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• 제11권1호
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• pp.54-61
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• 2006

An electron probe microanalysis (EPMA) investigation can provide quantitative and qualitative insight into the nature of the surface and bulk chemistry on solidified waste forms(SWF). The proportion of Pb in grain areas is below 0.3 wt. %, and the proportion near the border of the grain slightly increases to 0.98 wt. % but in the inter-particle areas farther from the grain, the concentration of Pb markedly increases. It is apparent that very little Pb diffuses into the tricalcium silicate($C_3S$) particles and most of the Pb exists as precipitates of sulfate, hydroxide, and carbonate in the cavity areas between $C_3S$ grains. Calcite additions on Pb-doped SWF are also observed to induce deeper incorporation of lead into the cement grains with EPMA line-analysis of cross-sections of cement grains. The line-analysis reveals the presence of $0.2{\sim}5$ weight % Pb over $5\;{\mu}m$ from cement grain boundaries. In the inter-particle areas, the ratio of Ca, Si, Al and S to Pb is relatively similar even at some distance from the grain border and the Pb (wt. %) ratio is reasonably constant throughout the whole inter-particles area. It is apparent that the enhanced development of C-S-H on addition of calcite can increasingly absorbs lead species within the silica matrix.

• 한국대기환경학회지
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• 제11권2호
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• pp.191-198
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• 1995

In order to evaluate the distribution and behaviour of atmospheric particulate metals in high-altitude area, we collected 22 aerosol samples using a high volume air sampler at Soback Mt. Meteorological Observation Station from Jan. to Nov. 1993 and analysed for metals (Al, Fe, Mg, Na, Ca, Mn, Co, Ni, Cu, Zn, Cd, and Pb) with ICP/AES and ICP/MS. Although sampling site is located in high-altitude and far from local sources of atmospheric pollutants, enrichments of metals are 2 times higher than those of western coastal reural area. This fact may imply that of metallic pollutants in the coastal rural site were came from further western side (e.g. China), atmospheric metals in this study area contain the signal of metropolitan cities located in the main wind direction (NNW). Sea salts are negligible in the aerosol particle population because reference elements of sea salts (Na, Mg) are all originated from soil particles. The contents of soil particles in aerosols are highest in spring and lowest in winter. Atmospheric enriched elements (Ni, Cu, Zn, Cd and Pb) are diluted with soil particles, especially during the yellow sand period. The results of factor analysis suggest possibility of interpreting their chemical significance in terms of sources (soil, pollutants) and gas-particle conversion processes (formation of ammonium sulfates, ammonium nitrates and/or their mixtures).

• Asian Journal of Atmospheric Environment
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• 제9권2호
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• pp.165-172
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• 2015

Under a very tough situation that there has been increasing concern to the air quality in underground subway spaces, this study set sights on the thorough estimation of the chemical properties and source apportionment of particulate matter (PM) collected on an underground subway platform by a cooperative approach of semi-bulk and single particle analyses. The size-resolved PMs were intensively collected on the platform of Miasageori station on the Seoul Subway Line-4, and then, they were semibulkily analyzed by a PIXE and the TOR$^{(R)}$ method, and individually analyzed by a SEM-EDX. Overwhelmingly enriched iron was a notable feature of elemental concentration of $PM_{2.5}$. Source classification of iron in $PM_{10-2.5}$ and $PM_{2.5}$ performed along with their elemental concentrations, indicates that the railway originated iron accounts for 95.71% and 66.39% of total iron in $PM_{10-2.5}$ and $PM_{2.5}$, respectively. Via a stoichiometric categorization, $Fe_2O_3$, $CaAl_2Si_2O_8$, $Al_2O_3$, and $CaCO_3$ show more than 85% abundance ratio in individual coarse particles. The result of theoretical estimation of the subway derived organic carbon ($OC_{Subway}$) suggests that $OC_{Subway}$ in $PM_1$ and $PM_{2.5-1}$ account for 75.86% and 51.88% of total organic carbon, respectively.

• 한국재료학회지
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• 제18권8호
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• pp.417-421
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• 2008

$Al_2O_3$ sol with long-term stability was prepared by mechanical milling. Thin films were evaluated and created for use as coating materials. The particle size of the manufactured sol was 98 nm when 2 wt% of nitric acid was added. This indicates that the viscosity of the sol is 12 cps and that it has long-term stability. The thickness of the thin films, which varied from 100 nm to 500 nm, could be managed by adjusting the draw rate and the amount of an organic additive. A thin film heated to $500^{\circ}C$ indicated a hydrophilic property against water and excellent permeability against a visible ray.