• 한국초전도학회:학술대회논문집
• /
• 한국초전도학회 2004년도 High Temperature Superconductivity Vol.XIV
• /
• pp.7-7
• /
• 2004

• 분석과학
• /
• 제6권3호
• /
• pp.275-282
• /
• 1993

지르콘사 광물에서 지르코니아를 회수하기 위하여 지르콘사를 분해 반응시킨 소성산물 중의 $SiO_2$와 $ZrO_2$를 DC arc source를 이용한 직독식 분광기로 동시 분석하였다. 순수한 금속산화물을 혼합하여 합성표준시료를 만들고 완충제(흑연)와 융제($Li_2B_4O_7$)의 혼합비를 조절하면서 최적의 들뜸조건을 선정하였다. 완충제와 흑연의 비를 0.22:1로 하고 시료와의 혼합비를 40배로 하였을 때 가장 좋은 들뜸조건을 얻을 수 있었다. 분석 결과의 표준편차는 $SiO_2$는 1.3%, $ZrO_2$는 4.9%였다.

• 소성∙가공
• /
• 제15권8호
• /
• pp.615-620
• /
• 2006

The reduction behavior of $TiO_{2}$ in Al and Al/CaSi containing self-reducing $TiO_{2}$ briquettes(SRTB) was investigated. The maximum yield of Ti was expected with the slag composition of 45-55%CaO in the $CaO-Al_{2}O_{3}$ system. When $CaCO_{3}$ was used as a flux, the oxidation loss of reducing agent by $CO_{2}$ should be compensated, and therefore it leads to excessive requirement of the reducing agent. By using Al and CaSi mixture as a reducing agent of $TiO_{2}$, the reaction products both oxide and metal could be liquefied, and separated effectively with each other. As a result, the yield of Ti increases remarkably. The optimum mixing ratio of CaSi to Al is 78%CaSi-22%Al.

• 대한기계학회논문집B
• /
• 제31권11호
• /
• pp.949-956
• /
• 2007

Pool boiling critical heat flux (CHF) of nanofluids with oxide nanoparticles of $TiO_2$ or $Al_2O_3$ was experimentally investigated under atmospheric pressure. The results showed that a dispersion of oxide nanoparticles significantly enhances the CHF over that of pure water. Moreover it was found that nanoparticles were seriously deposited on the heater surface during pool boiling of nanofluids. CHF of pure water on a nanoparticle-deposited surface, which is produced during the boiling of nanofluids, was not less than that of nanofluids. The result reveals that the CHF enhancement of nanofluids is absolutely attributed to modification of the heater surface by the nanoparticle deposition. Then, the nanoparticle-deposited surface was characterized with parameters closely related to pool boiling CHF, such as surface roughness, contact angle, and capillary wicking. Finally, reason of the CHF enhancement of nanofluids is discussed based on the changes of the parameters.

• 대한기계학회논문집B
• /
• 제29권9호
• /
• pp.979-987
• /
• 2005

Numerical simulations were performed at atmospheric pressure in order to understand the effect of additives on flame speed, flame temperature, radical concentrations, $NO_x$ formation, and heat flux in freely propagating $CH_4-Air$ flames. The additives were both carbon dioxide and hydrogen chloride which had a combination of physical and chemical behavior on hydrocarbon flame. In the flame established with the same mole of methane and additive, hydrogen chloride significantly contributed toward the reduction of flame speed, flame temperature, $NO_x$ formation and heat flux by the chemical effect, whereas carbon dioxide mainly did so by the physical effect. The impact of hydrogen chloride on the decrease of the radical concentration was about $1.4\~3.0$ times as large as that of carbon dioxide. Hydrogen chloride had higher effect on the reduction of $EI_{NO}$ than carbon dioxide because of the chemical effect of hydrogen chloride. The reaction, $OH+HCl{\rightarrow}Cl+H_2O$, played an important role in the heat flux from flames added by hydrogen chloride instead of the reaction, $OH+H_2{\rightarrow}H+H_2O$ which was an important reaction in hydrocarbon flames.

• 한국세라믹학회지
• /
• 제27권1호
• /
• pp.43-47
• /
• 1990

An attempt was made to grow Y-Ba-Cu-O single crystals by skull method(cold crucible process). Grown YBa2Cu3O7-x(YBC) single crystals were obtained from the upper part of the YBC solid mixture. There were plate-like YBC single crystals aligned with solidified flux along the crystal growth direction. Single crystal size was (5$\times$2$\times$0.2㎣) and was grown to a-b plane of YBC crystal structure which can flow super currents. Optical microscope and X-ray diffraction were employed characterize these microstructure and YBC single crystals.

• 한국결정학회지
• /
• 제7권1호
• /
• pp.20-29
• /
• 1996

(Sr1-xCax)CuO2 단결정을 융제법으로 제조하고 단결정 X-선 회절법을 이용하여 그 결정구조를 밝혔다. 이 화합물의 결정축계는 사방정계(orthorhombic system)이며, 공간군은 Cmcm(63), 그리고 격자상수 a, b, c는 각각 3.4645Å, 16.1417Å, 3.8727Å이었다. (Sr1-xCax)CuO2 화합물에서 Sr대신 치환되는 Ca이온의 한계를 구조적인 관점에서 연구하였다. 이를 위해 X-선 회절(CAD4), energy dispersive X-ray fluorescence (EDAX) and electron probe micro-analysis (EPMA) 등을 사용하였다. Ca가 치환됨에 따른 Cu-O 결합길이의 변화로부터 Ca의 치환한계를 결정하였는데 그 한계치는 Xca≒0.73이었다.

• 보존과학회지
• /
• 제20권
• /
• pp.105-117
• /
• 2007

사적 제450호 사천 늑도 유적에서 출토된 구슬의 분석을 통하여 이 유적의 고대유리 문화의 특성을 확인하고 이를 경상도 지역 출토 고대유리의 특성과 비교하였다. 시료는 광학현미경과 SEM을 이용하여 미세구조를 관찰하고 비중측정을 통해 물성을 확인하였다. SEM-EDS를 이용하여 유리의 구성 요소인 융제, 안정제, 착색제의 조성을 분석하였으며, XRD를 이용하여 기타 구슬시료의 재질을 조사하였다. 조개구슬로 분류한 백색 불투명 구슬은 비정질의 규산염계 물질로 확인되었으며, 청색 계열의 유리구슬은 포타쉬유리군($SiO_2-K_2O$ group). LCA(Low-CaO, $Al_2O_3$) 계통으로 색상별로 벽색과 청록색은 LCA-A(LCA-CaO<$Al_2O_3$) 계통, 감색은 LCA-B(LCA-CaO>$Al_2O_3$) 계통으로 확인된다. 이를 경상도지역에서 출토된 고대유리와 비교하면 AD $2{\sim}3$세기 이전의 포타쉬유리와 유사한 특징을 보인다.

• E2M - 전기 전자와 첨단 소재
• /
• 제8권6호
• /
• pp.787-794
• /
• 1995

To improvement the magnetic and frequency properties of YIG(Yttrium-Iron Garnet) in microwave region, it is investigated that the effect of $Al^{3+}$ ions on magnetic and frequency characteristics of YIG, using samples of basic YIG composition( $Y_{3}$F $e_{5}$ $O_{l2}$) added with A1$_{2}$ $O_{3}$ from 0 to 2.5 [mol%]. The measurment is conducted mainly for the structural properties and magnetical properties. The structural properties is measured using SEM(Scanning Electro Microscope), EDX(Energy-dispersive X-ray spectrometer) and XRD(X-ray diffraction equipment). The magnetical properties is measured with B-H curve tracer and impedance analyzer. As a result, it is confin-ned that the effect of eddy current loss is minimized while maintaining high saturation flux density of YIG, when YIG is added with 0.5 [mol%] of A1$_{2}$ $O_{3}$.>.>.

• 대한기계학회논문집B
• /
• 제26권11호
• /
• pp.1503-1512
• /
• 2002

From the view of the environmental protection against the use of fossil fuels, a great of efforts have been exerted to find an alternative energy source. Hydrogen may become an alternative However the product species of the hydrogen flame is only $H_2O$, which emits only non-luminous radiation so the radiation from it is much smaller than that for a hydrocarbon flame. In this study, the authors designed and fabricated a laboratory scale test furnace to study thermal characteristics of hydrogen-air diffusion flame. In addition. the effects of addition of reacting as welt as non-reacting solid particles were experimentally investigated. Among the total heat flux to the wall, about 75 % was occupied by radiation while 25% by convection. When the aluminum oxide (Al$_2$O$_3$) particles were added, the radiative heat flux was reduced due to heat blockage effects. On the other hand, the total as well as the radiative heat flux was increased when the carbon particles were seeded, since the overall temperature increased. The effects of swirl and excess air ratio were also examined.