• 열처리공학회지
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• 제5권2호
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• pp.103-110
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• 1992

This study is aimed to investigate the effect of various thermomechanical treatments($T_6$, $T_8$ and ITMT) on the microstructure and mechanical properties of an Al-Cu-Li-Ag-Mg-Zr alloy (Weldalite 049) which has been known to strong natural aging response, good weldablity and high strength in $T_6$ sand $T_8$ temper. This experiment was performed by means of differential scaning calorimetry, tensile test, optical and transmission electron microscopy. The tensile strength in the peak aged condition shows 620, 650 MPa in $T_6$ and $T_8$(40% cold work), respectively. Also, The tensile strength is increased with cold working in $T_8$ but decreased at 60% cold working. However, the tensile strength of the intermediate thermomechanical treated speciman(ITMT) is lower than that of $T_6$ temper about 20% but the elongation is higher than two times. It might be predicted that the ITMT is effective processing to improve the toughness of this alloy. In $T_6$, $T_8$ and ITMT, the major strengthening phase is $T_1(Al_2CuLi)$ phases. and the fine $T_1$ phase which are homogeneously precipited in matrix was observed much more in $T_8$ than $T_6$ and ITMT.

• 한국결정학회지
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• 제15권2호
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• pp.99-103
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• 2004

X-선 회절법을 이용하여 $C_{16}H_{19}O_2N_3CuCl_2\;{\cdot}\;H_2O$의 분자 및 결정구조를 해석하였다. 이 결정의 결정계는 Triclinic이고 공간군은 Pl이며, 단위포 상수는 $a=7.6202(9)\;{\AA},\;b=8.5943(7){\AA},\;c= 8.6272(6){\AA},\;\alpha=67.518(6)^{\circ},\; \beta= 68.043(8)^{\circ},\;\gamma=74.370(8)^{\circ},\;V=478.89(8)\;{\AA}^3,\;T=295K,\; Z=1,\;D_c=1.504Mgm^{-3}$이다. 회절반점들의 세기는 Enraf-Nonius CAD-4 Diffractometer로 얻었으며 graphite로. 단색화한 $MoK{\alpha}$,$(\alpha=0.7107\;\AA)$을 사용하였다. 분자구조는 Direct method로 풀었으며, $F_0>4\sigma(F_0)$인 1659개의 독립회절데이터에 대하여 최소 자승법으로 234개의 변수를 정밀화하여 최종 신뢰도 값 $R=2.47\%$를 얻었다.

• 한국재료학회지
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• 제8권12호
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• pp.1082-1089
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• 1998

$YBa_2$$Cu_3$$O_{7-y}$ (123) 초전도체에서 은 입자의 미세분산을 얻고자 말릭산을 사용한 발화합성과 고상반응법으로 123와 123-Ag 복합 초전도분말을 제조하였다. 발화합성분말을 원료로 사용할 시 마이크론 미만의 미세한 123 분말과 은 분말의 복합체를 얻을 수 있었다. 원료로 사용된 산화은($Ag_2O$) 분말은 발화합성과정 중금속 은으로 환원되었다. 원료분말에 첨가된 금속 은에 의한 반응 물질간의 확산 촉진으로 123상이 단시간내에 생성되었고 입자성장도 촉진되었다. 발화합성법으로 제조한 시편은 기계적 혼합공정으로 제조한 시편에 비해 은 입자들은 미세하게 분산시킬 수 있어서 초전도체의 임계전류밀도가 향상되었다.

• Membrane and Water Treatment
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• 제9권2호
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• pp.95-104
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• 2018

Copper pollution around the world has caused serious public health problems recently. The heavy metal adsorption on traditional membranes from wastewater is limited by material properties. Different adsorptive materials are embedded in the membrane matrix and act as the adsorbent for the heavy metal. The carbonized leaf powder has been proven as an effective adsorbent material in removing aqueous Cu(II) because of its relative high specific surface area and inherent beneficial groups such as amine, carboxyl and phosphate after carbonization process. Factors affecting the adsorption of Cu(II) include: adsorbent dosage, initial Cu(II) concentration, solution pH, temperature and duration. The kinetics data fit well with the pseudo-first order kinetics and the pseudo-second order kinetics model. The thermodynamic behavior reveals the endothermic and spontaneous nature of the adsorption. The adsorption isotherm curve fits Sips model well, and the adsorption capacity was determined at 61.77 mg/g. Based on D-R model, the adsorption was predominated by the form of physical adsorption under lower temperatures, while the increased temperature motivated the form of chemical adsorption such as ion-exchange reaction. According to the analysis towards the mechanism, the chemical adsorption process occurs mainly among amine, carbonate, phosphate and copper ions or other surface adsorption. This hypothesis is confirmed by FT-IR test and XRD spectra as well as the predicted parameters calculated based on D-R model.

• Progress in Superconductivity
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• 제13권2호
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• pp.111-116
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• 2011

Since superconducting wires have no resistance, electromagnets based on the superconducting wires produce no resistive heating with DC current as long as the current does not exceed the critical current of the wire. However, unlike resistive wires, superconducting wires exhibit AC heat loss. Embedding fine superconducting filaments inside copper matrix can reduce this AC loss to an acceptable level and opens the way to AC-capable superconducting coils. Here, we introduce an easy and accurate method to measure AC heat loss from sample superconducting coils by measuring changes in the rate of gas helium outflow from the liquid helium dewar in which the sample coil is placed. This method provides accurate information on total heat loss of a superconducting coil without any size limit, as long as the coil can fit inside the liquid helium dewar. With this method, we have evaluated AC heat loss of two superconducting solenoids, a 180-turn solid NbTi wire with 0.127 mm diameter (NbTi coil) and a 100-turn filamented wire with 1.4 mm diameter where 7 NbTi filaments were embedded in a copper matrix with copper to NbTi ratio of 6.7:1 (NbTi-Cu coil). Both coils were wound on 15 mm-diameter G-10 epoxy tubes. The AC heat losses of the NbTi and NbTi-Cu coils were evaluated as $53{\pm}4.7\;{\mu}W/A^2Hzcm^3$ and $0.67{\pm}0.16\;{\mu}W/A^2Hzcm^3$, respectively.

• 분석과학
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• 제13권3호
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• pp.297-303
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• 2000

저니토 시료 중의 미량 Cd, Cu, Pb, Ni, Zn 등의 분석을 위해 동위원소희석 질량분석법을 이용하였다. 시료는 마이크로파 혼합산(질산, 불산, 과염소산) 분해법을 이용하여 용해하였다. Ammonium pyrrolidenedithiocarbamate(APDC) 용매 추출법을 이용하여 알칼리 및 알칼리 토금속을 분리한 다음 Pb를 측정하고, 나머지 원소들은 이 용액에 $NH_4OH$ 첨가 후 원심 분리하여 Fe, Sn, Ti 등을 제거한 다음 측정하였다. 측정원소의 회수율은 다소 떨어지나 동중원소 방해를 일으키는 매질원소를 효율적으로 제거할 수 있었다. 2종의 저니토 인증표준물질 중의 미량원소 분석에 이 방법을 적용한 결과 인증값과 잘 일치하는 측정 결과를 얻을 수 있었다.

• 대한화학회지
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• 제35권2호
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• pp.128-134
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• 1991

기존 칼륨이온 선택성 전극의 메트릭스로는 대체로 PVC가 사용되어졌으나, 본 연구에서는 폴리우레탄을 사용하였고, 용매 매개체로는 2-nitropheny-n-alkylate, 감응물질로는 potassium tetraphenyl borate 및 D-18-Crown-6 등을 써서 전극막을 제조하였다. 본 폴리우레탄 메트릭스의 칼륨이온 선택성전극의 수명은 75일로서 PVC 메트릭스의 칼륨이온 선택성 전극에 비하여 한층 더 길었다. 전극전위응답(slope factor)은 직선응답범위(K$^+$ 농도 : $1{\times}10^{-1}\;{\sim}\;1{\times}10^{-4}$ M)내에서 52 mV/decade이었고, 본 전극은 방해이온들 $(NH^{4+},\;Na^{+},\;Li^{+},\;Ca^{2+},\;Mg^{2+},\;Cu^{2+}$)이 존재하는 해수 중의 칼륨이온을 B(Ph)$_4^-$ 표준용액으로 전위차 적정시 종말점을 검출하는데 성공적으로 적용되었다.

• 대한치과기공학회지
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• 제28권1호
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• pp.27-41
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• 2006

The physical property and phase transformation in a commercial dental casting high gold alloy was investigated as a function of ageing temperature and time using microvickers hardness tester, X-ray diffraction, optical and electron microscopy and EPMA analyser. 1. With increasing ageing time, the hardness of solution-treated gold alloys increased slowly at the initial stage of ageing treatment at an ageing temperature of $300{\sim}400^{\circ}C$, and it reached a maximum value of hardness at the medium stage. Finally, it decreased gradually during further ageing. The maximum value of hardness at was similar with that of the conventional materials and suitable for using as the crown & bridge. 2. During isothermal ageing at a temperature range of $300{\sim}400^{\circ}C$, three phases consisting of the Au-rich ${\alpha}_1$phase with a face-centered cubic structure, the Pt3Zn ${\alpha}_2$phase with an ordered AuCu3(L12) type(f.c.c.) and the Pt-rich ${\alpha}_3$phase with face-centered cubic structure in solution-treated gold alloys were transformed into different three phases consisting of the ${\alpha}_1$phase, the ${\alpha}_3$phase and the PtZn $\beta$phase with an ordered AuCu I(L10) type. 3. The hardening of gold alloys was attributed to the lattice strains of the matrix resulting from the transformation of the ${\alpha}_2$phase to the $\beta$phase. 4. The softening of gold alloys during over-ageing was attributed to the coarsening of the nodules consisting of the $\beta$phase and ${\alpha}_1$matrix.

• 분석과학
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• 제10권6호
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• pp.395-402
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• 1997

시료의 매질에 따른 추출법의 문제점과 사용 가능성을 조사하기 위해 환경처 발행의 폐기물공정시험방법과 EPA 3050법을 비교 연구하였다. 이를 위해 sludge와 개펄 시료에 12종의 무기 priority pollutants(Cd, Cr, Cu, Pb, Ni, Zn, As, Sb, Se, Hg, Be, Tl)를 첨가하여 분석용 시료를 조제하고 AAS, HG-AAS, 그리고 ICP/MS를 사용하여 각 추출방법에 대한 대상 원소의 회수율, 상대표준편차 및 method detection limit를 측정하었다. EPA 3050법에 따라 추출한 경우 회수율이 좋지 않은 As, Sb, Se를 제외한 평균 회수율은 93%였다. 그러나 폐기물공정시험방법의 용출시험방법으로 실험한 경우는 전반적으로 회수율이 32%로 매우 좋지 않을 뿐만 아니라 시료의 매질에 의한 영향을 심각하게 받는 것으로 조사되었다.

• 한국주조공학회지
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• 제23권1호
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• pp.30-39
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• 2003

Porous hybrid preforms were fabricated by reactive sintering using the compacts consisting of SiC particles, Fe and Al powders. Squeeze casting processing was employed to produce the composite in which the matrix phase is Al-Si7Mg. The microstructural change and wear resistance of the composites were investigated in terms of an amount of SiC particles. The wear loss was increased with increasing the contact pressure in the alloy containing SiC particles coated with Cu. The most drastic change was found to the specimen tested at 2.5 MPa of contact pressure. Concerning the alloys containing SiC particles coated with Ni-P, a drastic increase in the wear loss exhibited at 2 MPa of contact pressure in those alloys containing 4 and 8 wt. % of SiC particles coated with Ni-P. In the alloy containing 16 wt. % a proportional increase in wear loss was observed to the change of contact pressure. With respecting to the sliding velocity, the wear loss of the alloy containing SiC particles coated with Cu increased at the initial stage of wear process and then decreased. Similar result was found in the alloys containing SiC particles coated with Ni-P. On the basis of the present results obtained, it was found that wear resistance of the alloys tested was improved to show in the order of the alloy reinforced by coated SiC particles > by uncoated SiC particles > by intermetallic compound without SiC particles.