• 한국광물학회지
• /
• 제13권3호
• /
• pp.147-163
• /
• 2000

The mineralogy and chemical composition of reddish to brownish yellow residual soils, so called "Hwangto" have been examined according to representative host rocks. The result of the study indicates that Hwangto consists of 40-80% clay minerals and various minerals such as quartz, feldspar, hornblende, goethite, and gibbsite. Clay minerals include kaolinite, halloysite, illite, hydroxy interlayered vermiculite (HIV), mica/vermiculite interstratifield mineral and chlorite. The mineralogical constituents and contents of Hwangto were different depending on the types of host rocks. Moreover, the Jurassic granitic rocks contain relatively more kaolin minerals, whereas the Cretaceous granitic rocks contain more HIV and illite. In addition, reddish Hwangto contains relatively more kaolinite and HIV, and yellowish Hwangto contains more illite and halloysite. It is suggested that feldspars and micas of host rocks were chemically weathered into illite, halloysite, illite/vermiculite interstratified minerals, and HIV, and finally into kaolinite. Compared with their host rocks, the major chemical compositions of Hwangto tend to contain more $Al_2O_3,\;Fe_2O_3,\;H_2O$ in amount and less Ca, Mg, and Na. Hwangto contains relatively high amount of trace elements, P, S, Zr, Sr, Ba, Rb, and Ce including considerable amount of Li, V, Cr, Zn, Co, Ni, Cu, Y, Nb, La, Nd, Pb, Th in excess of 10 ppm. Relatively high amount of most trace elements were detected in the Hwangto. The major and minor chemical compositions of the Hwangto were different depending on the types of host rocks. However, their difference was in the similar range compared with the compositions of host rocks.

• 대한환경공학회지
• /
• 제28권4호
• /
• pp.368-375
• /
• 2006

순수한 아나타제 구조로 이루어진 DT51D $TiO_2$에 $CrO_x,\;FeO_x,\;MnO_x,\;LaO_x,\;CoO_x,\;NiO_x,\;CeO_x,\;CuO_x$와 같은 단일 산화물 촉매를 각각 5 wt.% 담지하여 모델반응으로 선택한 기상 TCE 제거반응을 수행하였으며, 이로부터 얻어진 결과를 바탕으로 $CrO_x/TiO_2$-based 복합 산화물 촉매상에서 TCE 산화반응을 연구함으로써 유해 중금속의 사용량을 최소화하기 위한 최적의 촉매 디자인 방법을 도출하고자 하였다. DT51D $TiO_2$에 담지된 여러 단일 금속 산화물들 중에서 기상 TCE 제거반응에 대하여 $CrO_x$가 가장 우수한 촉매활성을 보이는 것으로 나타났으며, 반응온도의 함수로 얻어진 TCE 제거반응의 활성은 $CrO_x$의 담지량에 의존하였다. 5 wt.% $CrO_x$-based 복합 산화물 촉매는 10 wt.% $CrO_x$만으로 이루어진 단일 산화물 촉매와 거의 동일한 수준의 TCE 제거반응 활성을 보였을 뿐만 아니라 이 복합 산화물 촉매들은 10 wt.% $CoO_x,\;MnO_x,\;FeO_x,\;NiO_x$ 등과 같은 단일 산화물 촉매들보다 높은 반응활성을 갖는 것으로 나타났다. 단일 산화물 촉매의 반응활성과 비교하였을 때 5 wt.% $CrO_x$-based 복합 산화물 촉매상에서 TCE 제거반응 동안에 얻어지는 반응활성의 증가 정도는 $420^{\circ}C$ 이하의 반응온도 기준으로 약 $10{\sim}80%$ 이상이었다. 따라서, CVOCs 제거반응을 위하여 널리 사용되고 있는 단일 $CrO_x/Al_2O_3$ 촉매보다는 $CrO_x$의 사용량을 최소화하면서도 우수한 반응활성을 얻을 수 있는 $CrO_x/TiO_2$-based복합 산화물 촉매가 보다 바람직하며 하나의 대안적인 촉매 디자인 방법으로 응용될 수 있을 것으로 생각된다.

• 전자공학회논문지A
• /
• 제30A권12호
• /
• pp.51-59
• /
• 1993

A 4${\times}10^{19}cm^{3}$ carbon-doped base AlGaAs/GaAs HBY was grown using carbontetracholoride(CCl$_4$) by atmospheric pressure MOCVD. Abruptness of emitter-base junction was characterized by SIMS(secondary ion mass spectorscopy) and the doping concentration of base layer was confirmed by DXRD(double crystal X-ray diffractometry). Mesa-type HBTs were fabricated using wet etching and lift-off technique. The base sheet resistance of R$_{sheet}$=550${\Omega}$/square was measured using TLM(transmission line model) method. The fabricated transistor achieved a collector-base junction breakdown voltage of BV$_{CBO}$=25V and a critical collector current density of J$_{O}$=40kA/cm$^2$ at V$_{CE}$=2V. The 50$\times$100$\mu$$^2$ emitter transistor showed a common emitter DC current gain of h$_{FE}$=30 at a collector current density of JS1CT=5kA/cm$^2$ and a base current ideality factor of ηS1EBT=1.4. The high frequency characterization of 5$\times$50$\mu$m$^2$ emitter transistor was carried out by on-wafer S-parameter measurement at 0.1~18.1GHz. Current gain cutoff frequency of f$_{T}$=27GHz and maximum oscillation frequency of f$_{max}$=16GHz were obtained from the measured Sparameter and device parameters of small-signal lumped-element equivalent network were extracted using Libra software. The fabricated HBT was proved to be useful to high speed and power spplications.

• 한국세라믹학회지
• /
• 제52권4호
• /
• pp.229-233
• /
• 2015

Currently, the majority of commercial white LEDs are phosphor converted LEDs made of a blue-emitting chip and YAG yellow phosphor dispersed in organic silicone. However, silicone in high-power devices results in long-term performance problems such as reacting with water, color transition, and shrinkage by heat. Additionally, yellow phosphor is not applicable to warm white LEDs that require a low CCT and high CRI. To solve these problems, mixing of green phosphor, red phosphor and glass, which are stable in high temperatures, is common a production method for high-power warm white LEDs. In this study, we fabricated conversion lenses with LUAG green phosphor, SCASN red phosphor and low-softening point glass for high-power warm white LEDs. Conversion lenses can be well controlled through the phosphor content and heat treatment temperature. Therefore, when the green phosphor content was increased, the CRI and luminance efficiency gradually intensified. Moreover, using high heat treatment temperatures, the fabricated conversion lenses had a high CRI and low luminance efficiency. Thus, the fabricated conversion lenses with green and red phosphor below 90 wt% and 10 wt% with a sintering temperature of $500^{\circ}C$ had the best optical properties. The measured values for the CCT, CRI and luminance efficiency were 3200 K, 80, and 85 lm/w.

• 한국수소및신에너지학회논문집
• /
• 제34권6호
• /
• pp.587-593
• /
• 2023

This research project focused on the production of hydrogen through ammonia decomposition reactions while investigating how the reactivity of this process varies when employing different catalysts. Several metal oxide supports (Al₂O₃, La₂O₃, CeO₂) were utilized as catalysts, with active metals from both the transition metal group (Co, Ni, Fe, Cr, Cu) and the noble metal group (Ru, Rh, Pd, Pt) impregnated onto these supports. Furthermore, the study examined how the reactivity evolves with changes in reaction temperature when employing the prepared catalysts. Additionally, the research delved into the distinctive activation energies associated with each of the catalysts. In this research, In the noble metal catalyst system, the order of high activity for ammonia decomposition reaction to produce hydrogen is Ru > Rh > Pt ≈ Pd. In the transition metal catalyst system, the order of high activity is Co > Ni > Fe > Cr > Cu.

• 한국세라믹학회지
• /
• 제43권6호
• /
• pp.369-375
• /
• 2006

[ $(Ba_{0.5}Sr_{0.5})_{0.99}Co_{x}Fe_{1-x}O_{3-{\delta}}$ ] [x=0.8, 0.2](BSCF) powders were synthesized by a Glycine-Nitrate Process (GNP) and the electrochemical performance of the BSCF cathode on a scandia stabilized zirconia, $[(Sc_{2}O_3)_{0.11}(ZrO_2)_{0.89}]-1Al_{2}O_3$ was investigated. In order to prevent unfavorable solid-state reactions between the cathode and zirconia electrolyte, a GDC ($Gd_{0.1}Ce_{0.9}O_{2-{delta}}$) buffer layer was applied on ScSZ. The BSCF (x = 0.8) cathode formed on GDC(Buffer)/ScSZ(Disk) showed poor electrochemical property, because the BSCF cathode layer peeled off after the heat-treatment. On the other hand, there were no delamination or peel off between the BSCF and GDC buffer layer, and the BSCF (x = 0.2) cathode exhibited fairly good electrochemical performances. It was considered that the observed phenomenon was associated with the thermal expansion mismatch between the cathode and buffer layer. The ohmic resistance of the double layer cathode was slightly lower than that of the single layer BSCF cathode due to the incorporation of platinum particle into the BSCF second layer.

• Journal of Mechanical Science and Technology
• /
• 제20권1호
• /
• pp.1-12
• /
• 2006

This work reviews the effects of catalyst formulation and exhaust gas composition on soot oxidation in CDPF (Catalytic Diesel Particulate Filter). DOC's (Diesel Oxidation Catalysts) have been loaded with Pt catalyst (Pt/$Al_{2}O_3$) for reduction of HC and CO. Recent CDPF's are coated with the Pt catalyst as well as additives like Mo, V, Ce, Co, Fe, La, Au, or Zr for the promotion of soot oxidation. Alkali (K, Na, Cs, Li) doping of metal catalyst tends to increase the activity of the catalysts in soot combustion. Effects of coexistence components are very important in the catalytic reaction of the soot. The soot oxidation rate of a few catalysts are improved by water vapor and NOx in the ambient. There are only a few reports available on the mechanism of the PM (particulate matter) oxidation on the catalysts. The mechanism of PM oxidation in the catalytic systems that meet new emission regulations of diesel engines has yet to be investigated. Future research will focus on catalysts that can not only oxidize PM at low temperature, but also reduce NOx, continuously self-cleaning diesel particulate filters, and selective catalysts for NOx reduction.

• 한국수소및신에너지학회논문집
• /
• 제18권4호
• /
• pp.406-412
• /
• 2007

An experimental study on the design of a catalytic combustor for 1.6 kW MCFC system has been performed. The roles of the catalytic combustor are to completely burn anode off-gas and to supply sufficient $CO_2$ to cathode channels. In order to avoid hot spot or fuel slippage, flow uniformity at the catalyst inlet was achieved by installing two crossing perforated plates between the catalyst and the mixing chamber with minimal pressure drop. A Pd/Ce/Ni-$Al_2O_3$ catalyst was used for complete combustion of the off-gas at GHSV=36,000.

• Nuclear Engineering and Technology
• /
• 제54권3호
• /
• pp.1024-1029
• /
• 2022

Composite scintillation screens on a base of Gd_1.2Y_1.8Ga_2.5Al_2.5O₁₂:Ce (GYAGG) scintillator have been evaluated for neutron detection. Besides the powdered scintillator, the composite includes ⁶LiF particles; both are merged with a binder and deposited onto the light-reflecting aluminum substrate. Results obtained demonstrates that screens are suitable for use with a silicon photomultiplier readout to create a prospective solution for a compact and low-cost thermal neutron sensor. Composite GYAGG/⁶LiF scintillation screen shows a pretty matched sensitivity and γ-background rejection with a widely used ZnS/⁶LiF screens however, possesses forty times faster response.

• 한국표면공학회지
• /
• 제47권4호
• /
• pp.192-197
• /
• 2014

Red-emitting nitride phosphors recently attracted considerable attention because of their high thermal stability and high color rendering index properties. For excellent phosphor of white light-emitting-diode, ternary nitride phosphor of $Sr/SmSi_5N_8:Eu^{2+}$ with different $Eu^{2+}$ ion concentration were synthesized by solid state reaction method. In this work, red-emitting nitride $Sr/SmSi_5N_8:Eu^{2+}$ phosphor was successfully synthesized by using multi-step high frequency induction heat treatment. The effects of molar ratio of component and experimental conditions on luminescence property of prepared phosphors have been investigated. The structure and luminescence properties of prepared $Sr/SmSi_5N_8:Eu^{2+}$ phosphors were investigated by XRD and photoluminescence spectroscopy. The excitation spectra of $Sr/SmSi_5N_8:Eu^{2+}$ phosphors indicated broad excitation wavelength range of 300 - 550 nm, namely from UV to visible area with distinct enhanced emission peaks. With an increase of $Eu^{2+}$ ion concentration, the peak position of emission in spectra was red-shifted from 613 to 671 nm. After via multi-step heat treatment, prepared phosphor showed excellent luminescence properties, such as high emission intensity and low thermal quenching, better than commercial phosphor of $Y_3Al_5O_{12}:Ce^{3+}$. Using $Eu_2O_3$ as a raw material for $Eu^{2+}$ dopant with nitrogen gas flowing instead of using commercial EuN chemical for $Sr/SmSi_5N_8:Eu^{2+}$ synthesis is one of characteristic of this work.