• Bulletin of the Korean Chemical Society
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• 제26권5호
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• pp.786-790
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• 2005

A new ternary strontium germanium nitride, ${\beta}-Sr_2GeN_2$, was obtained as single crystal from constituent elements in molten Na. It crystallizes in space group Cmca (No. 64) with a = 5.441(1) $\AA$, b = 11.377(2) $\AA$, c = 12.229(2) $\AA$, and Z = 8. Its crystal structure is closely related to that of polymorphic companion, ${\alpha}-Sr_2GeN_2$, both of which contain isolated bent anions of ${GeN_2}^{4-}$.

• Bulletin of the Korean Chemical Society
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• 제25권4호
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• pp.460-465
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• 2004

Hydrofluoric acid has been used as a novel stripping agent for molybdenum(VI) after its extraction with Cyanex 301. In the extraction step, the effects of parameters such as type and initial concentration of acid, type of diluent, extractant concentration, metal concentration and temperature have been studied. In the stripping step, the effects of various stripping agents on stripping efficiency have been investigated. Hydrofluoric acid has been chosen as an effective stripping agent, and the effects of concentration of hydrofluoric acid, stripping time, volume of hydrofluoric acid and the number of stages of stripping have been studied. Molybdenum(VI) has been effectively separated from a large number of elements in binary mixtures, with a very high tolerance limit. Finally, the optimized method has been extended for the analysis of Mo(VI) in spent molybdenum catalysts.

• Bulletin of the Korean Chemical Society
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• 제32권5호
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• pp.1519-1526
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• 2011

A previous study (Lee, C. W. J. Phys. B 2010, 43, 175002) that isolated the overlapping resonances in the photoionization spectra using multichannel quantum defect theory (MQDT) in systems involving a single open channel was extended to manage many open channels when the closed channels are degenerate. The theory was applied to the dipole allowed J = 1$^{\circ}$ spectra from the ground state with excitation energies lying between the lowest ionization thresholds for rare gas atoms, Ar, Kr, and Xe, and also for group IV elements, Ge, Sn and Pb.

• 대한기계학회논문집B
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• 제22권5호
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• pp.563-572
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• 1998

An experimental study of hot filament chemical vapor deposition(HFCVD) has been carried out for the fabrication of diamond thin film. Of particular interest is the measurement of deposition uniformity on large substrates. Experimental apparatus including a vacuum chamber, heating elements, etc. has been designed and manufactured. Deposition profiles for different pretreatment powders and different flow rates have been measured in conjunction with the measurement of substrate temperature distribution on a large substrate surface. As the flow rate increases, deposition rate increases, however, the crystallinity becomes worse. Higher growth rate has been found on the region closer to the center location where substrate temperature is higher. The crystallinity has been improved as gas flow rate decreases. The growth rate and morphology of deposition were identified by SEM and the existence of diamond phase was proved by Raman spectroscopy.

• 자원환경지질
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• 제23권1호
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• pp.11-23
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• 1990

Pyrophyllite, kaolinite, and alunite deposits distributing in Southwestern parts of Cheonnam are classified into three types of minerals assemblages by the results of X-ray diffraction analysis etc. The first mineral assemblages contains pyrophyllite, kaolinite, dickite, quartz, diaspore and/or corundum, the second one contains alunite inseads of corundum, and the third one contains alunite without pyrophyllite and diaspore. It is can be considered that the depoSits which consist mainly of pyrophyllite are formed higher temperature than the other deposits. Judging form the chemical analyses the chemical compositions of hydrothermal solutions acting to the deposits seem to be relatively simple. But the hydrothermal solutions which generated Dogcheon, Jugjcon, Ogmaesan, and Seongsan mine contain rather somewhat higher $K_2O$. The values of the Trace Elements and REE analysis of the host rocks of deposits suggest that the host rocks are these deposits are the last products of magmatic differentiation.

• 한국응용과학기술학회지
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• 제19권4호
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• pp.327-334
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• 2002

Transesterfication of vegetable oils and methanol with alkaline catalyst was carried out to produce biodiesel fuel by continuous process. The process consists of two static mixers, one tubular reactor and two coolers and gave $96{\sim}99$% of methyl ester yield from soybean oil and rapeseed oil. Experimental variables were the molar ratios of methanol to vegetable oil, alkaline catalyst contents, flow rates, mixer element number. The optimum ranges of operating variables were as follows; reaction temperature of $70^{\circ}C$, l:6 of molar ratio of methanol to oil, O.4%(w/w) sodium hydroxide based on oil, static mixer elements number of 24 and 4 min. residence time.

• Bulletin of the Korean Chemical Society
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• 제29권1호
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• pp.159-164
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• 2008

Two kinds of CNT/TiO2 composite photocatalysts were synthesized with multi-walled carbon nanotubes (MWCNTs) and titanium(IV) n-butoxide (TNB) by a MCPBA oxidation method. Since MWCNTs had charge transfer and semiconducting, the CNT/TiO2 composite shows a good photo-degradation activity. The XRD patterns reveal that only anatase phase can be identified for MCT composite, but the HMCT composite synthesized with HCl treatment was observed the mixed phase of anatase and rutile. The EDX spectra were shown the presence as major elements of Ti with strong peaks. From the SEM results, the sample MCT and HMCT synthesized by the thermal decomposition with TNB show a homogenous sample with only individual MWCNTs covered with TiO2 without any jam-like aggregates between CNTs and TiO2. From the photocatalytic results, we could be suggested that the excellent activity of the CNT/TiO2 composites for organic dye and UV irradiation time could be attributed to combination effects between TiO2 and MWCNTs with plausible photodegradation mechanism.

• International Journal of Concrete Structures and Materials
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• 제3권2호
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• pp.97-101
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• 2009

It has been known that acid-resistant concretes on the liquid glass basis have high porosity (up to 18${\sim}$20%), low strength and insufficient water resistance. Therefore they can not be used as materials for load-bearing structural elements. Significant increasing of silicate matrix strength and density was carried out by incorporation of special liquid organic alkali-soluble silicate additives, which block of superficial pores and reduces concrete shrinkage deformation. It was demonstrated that introduction of tetrafurfuryloxisilane additive sharply increases strength, durability and shock resistance of silicate polymer concrete in aggressive media. This effect is attributable to hardening of contacts between silicate binder gel globes and modification of alkaline component owing to "inoculation" of the furan radical. The optimal concrete composition with the increased strength, chemical resistance in the aggressive environments, density and crack resistance was obtained.

• 대한전자공학회논문지
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• 제18권1호
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• pp.35-40
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• 1981

분무법(spray method), 화학증착법(chemical vapor deposition method) 및 진공도착법 등을 사용하여 SRO2, SROr-ZnO 및 ZnO 박막가스 검지소자를 제조하였다. 제된된 소자들은 CO 및 SO2 등 유독가스를 포함한 여러 가지 가스에 대해 민감한 반응을 나타내었다. 박막가스 검지소자가 각종 가스와 접촉할 때 생기는 전기시도도의 변화는 이들 가스의 표면흡착에 의한 캐리어밀도의 변화에 기인하는 것으로 사료된다. 아울러 제조된 청막소자의 전기부도도는 소자 주위에 유지되는 기력에 따라 크게 달라짐을 알 수 있었다.

• 대한화학회지
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• 제22권6호
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• pp.357-364
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• 1978

Spherical harmonics의 전개방법에 의하여 쌍극자모멘트의 행렬요소를 계산하는 방법을 사용하여 $NH_3$, HF, CO, HCHO, HCN, PO, $PO^-\;및\;H_2O$분자의 쌍극자모멘트를 계산하였다. 이 방법에 의하여 계산한 쌍극자모멘트의 값이 다른 방법의 값보다 실험치에 가까웠다.