• Microbiology and Biotechnology Letters
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• v.20 no.1
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• pp.61-67
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• 1992

The synthesis of N-benzyloxycarbonyl-L-aspartyl-L-phenylalanine methyl ester(ZAPM), a precursor of aspartame, from N-benzyloxycarbonyl-L-aspartic acid(Z-Asp) and L-phenylalanine methyl ester hydrochloride(L-PM-HCl) was investigated in ethylacetate-MES buffer two-phase system using thermolysin. In organic two-phase system, the degree of spontaneous hydrolysis of L-PM. HCl was significantly reduced with increasing the volume ratio of organic to aqueous phase. Stability of thermolysin in organic two-phase system was found to be higher than that in MES buffer solution. More than 90% of initial enzyme activity was maintained after 10 days of incubation in case that the volume of organic phase was equal to that of buffer phase, while the half life of thermolysin was about 2 days in aqueous buffer solution. The results of partitioning of substrates and product in organic two-phase system showed that the difference in partition coefficients between substrates and product was maximum at pH 5.5. The optimal pH for 2-APM synthesis in organic two-phase system was found to be 5.5-5.8, which is consistent with the value expected from the partition experiments. As the concentration of substrates was increased the conversion yield of Z-APM was increased with concomitant reduction of L-PMqHC1 hydrolysis. In case that the concentration of L-PM-HCl and Z-Asp were 160 mM and 80 mM respectively, the conversion yield of Z-APM reached 90% after 28 hrs of reaction. The yield obtained at different volume ratio of organic phase compares well with the predicted equilibrium constant in biphasic system.

• Proceedings of the KIEE Conference
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• 2005.11a
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• pp.79-80
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• 2005

The solid precursor produced by the dehydration of the gel at $120^{\circ}C$ for 12h is not in the amorphous state as expected but in a crystalline state. X-ray diffraction peaks of nearly the same angular position as the peaks of high Tc phase were observed in the precursor. Experimental results suggest that the intermediate phase formed before the formation of the superconducting phase may be the most important fact in determining whether it is easy to form the superconducting phase or not, because the nucleation barriers of the two superconducting phase may be altered by the variation of the crystal structures of those intermediate phase.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2005.11a
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• pp.242-243
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• 2005

In this study, (La,Sr)$MnO_{3+\delta}$ powder used cathode material for SOFC was synthesized with precursor by GNP and the properties of powder, crystal phase, electric properties and deoxidization properties with precursor were investigated. The synthesis powder was prepared when oxidant/fuel mole and pH were 1 and 1, respectively and the synthesis powder was synthesized by GNP method using nitrate solution or oxide solution as precursor. Deoxidization peak of the nitrate solution was appeared lower temperature than the oxide solution, at $450^{\circ}C$. In this result, synthesis (La,Sr)$MnO_{3+\delta}$ powder using nitrate solution with Mn excess was suitable cathode material for SOFC due to had higher deoxidization properties. Also synthesis (La,Sr)$MnO_{3+\delta}$ powder according to precursor had difference electrical conductivity according to influence sintering density and crystal phase with precursor. Specially, the synthesis method and starting material had effect on deoxidization properties for SOFC.

• Progress in Superconductivity
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• v.3 no.2
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• pp.198-212
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• 2002

The effects of reacted precursors on phase evolution, microstructure, $J_{c}$ and junctional characteristic of the inter-granular contacts were investigated in Ag-sheathed T1-1223 tapes prepared using three kinds of reacted precursors, and compared to those in the tape prepared using an unreacted precursor The precursors were prepared by heat-treating a mixture of Sr-Ba-Ca-Cu-O, $Tl_2$$O_3$, PbO and $Bi_2$$O_3$ powders at $805^{\circ}C$ (precursor I ), $840^{\circ}C$ (precursor II ) and $905^{\circ}C$(precursor III) for 20 min. Tl-1223 phase content, grain size and J\ulcorner in the tapes appeared to increase in an order of precursors I, II and III Compared to tapes prepared using an unreacted precursor, the tapes prewar ed using precursors II and III revealed reduced pore and impurity densities and an enhanced texture. Also characteristic of inter -granular contacts and fraction of strong-links were improved. The improved properties are attributed to enhanced densification resulting from using the reacted precursors.s.

• Clean Technology
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• v.12 no.2
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• pp.101-106
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• 2006

HT-$LiCoO_2$ powders were synthesized from hydroxide precursors in this study. The cobalt hydroxide compounds with hydrotalcite-like(${\alpha}$-phase) and/or brucite-like(${\beta}$-phase) structures as a component of the precursor were prepared in various PH conditions using precipitation method. It was found that various phase and compositions of cobalt hydroxides could be tailor-prepared via a careful control of preparation parameters such as the concentration ratio of $[OH^-]/[CO^{2+}]$ and aging time. The hydroxides $Co(OH)_2$ and LiOH were mixed with aqueous methyl-alcohol. The precursor of a HT-$LiCoO_2$ was synthesized via subsequent processes including evaporation, drying and aging. The transformation of tailor-made ${\beta}$-phase $Co(OH)_2$ to CoOOH and formation of solid solution in the precursor were achieved during aging. These results cause HT-$LiCoO_2$ to be synthesized at low temperature($600^{\circ}C$ ) for a short time(10min).

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 1999.11a
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• pp.69-72
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• 1999

A Well oriented Bi$_2$re$_2$CaCu$_2$O$\sub$8/(Bi2212) superconductor thick films were formed successfully on a copper substrate by liquid reaction between a Cu-free precursor and Cu tape using method in which Cu-free BSCO powder mixture was printed on copper plate and heat-treated. And we examined the mechanism for the rapid formation of Bi2212 superconducting films from observing the surface microstructure with heat-treatment time. At heat-treatment temperature, the printing layer partially melt by reacting with CuO of the oxidizing copper plate, and the nonsuperconducting phases present in the melt are typically Bi-free phases and Cu-free phases. Following the partial melting, the Bi$_2$Sr$_2$CaCu$_2$O$\sub$8/ superconducting phase is formed at Bi-free phase/liquid interface by nucleation and grows. It was confirmed that the phase colony from the phase diagram of Bi$_2$O$_3$-(SrO+CaO)/2-CuO system is similar to the observed result.

• Bulletin of the Korean Chemical Society
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• v.24 no.5
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• pp.645-646
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• 2003

• Proceedings of the Korea Institute of Applied Superconductivity and Cryogenics Conference
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• 2003.02a
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• pp.105-108
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• 2003

Long length of Bi-2223 superconducting wires were fabricated by stacking, drawing process with different precursor owders and different heat-treatment histories. The precursor powders were 2 kinds of Pb content. And a part of the tapes were experienced pre-annealing process which caused tetragonal structure of Bi-2212 phase to orthorhombic structure of it was during drawing process. We confirmed the transformation of Bi-2212 phase from tetragonal structure to orthorhombic structure and reduction of second phases. We designed and made a continuous Ic measurement system for Bi-2223/Ag HTS tape. We could achieve best Ic of 65 A at the Bi-2223/Ag tape using low Pb content of precursor powder and experienced pre-annealing process.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2003.07a
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• pp.585-588
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• 2003

Bi-2223 superconducting wires were fabricated by stacking, drawing process with different precursor powders and different heat-treatment histories. The precursor powders were 2 kinds of Pb content. And a part of the tapes were experienced pre-annealing process which caused tetragonal structure of Bi-2212 phase to orthorhombic structure of it was during drawing process. We confirmed the transformation of Bi-2212 phase from tetragonal structure to orthorhombic structure and reduction of second phases. AC magnetization analysis were performed in order to investigate the fraction of Bi-2223 phase in Bi-2223/Ag HTS tape. The cross sections of 55 filaments and 61 filaments were investigated after rolled in order to understand deformation mechanism of superconducting cores. We could achieve best Ic of 70 A class at the Bi-2223/Ag tape using low Pb content of precursor powder and experienced pre-annealing process. AC magnetization analysis was useful to investigate the fraction of Bi-2223 phase in the Bi-2223/Ag tape.

• 한국초전도학회:학술대회논문집
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• v.14
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• pp.76-76
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• 2004