• Journal of the Korean Applied Science and Technology
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• v.17 no.2
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• pp.144-148
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• 2000

A modification of the sol-gel method to obtain phase pure superconducting oxides is described. The method starts from organic salts of yttrium, barium and copper, such as acetates, and avoids the sudden and uncontrollable decomposition of the organic fraction which occurs if nitrates are used as starting materials. The aqueous solution obtained with citric acid in an alkaline medium is concentrated under vacuum. The solid so prepared is decomposed at about $300^{\circ}C$ thus giving an oxide precursor containing well dispersed yttrium, barium and copper. Pyrolysis at 850 - $920^{\circ}C$ followed by oxygen annealing gives the superconducting orthorhombic 123 phase. The results of TGA/DTA of the precursor, as well as XRD, electrical and magnetic property measurements on the pyrolysis products are presented and discussed.

• Proceedings of the Korea Institute of Applied Superconductivity and Cryogenics Conference
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• 1999.02a
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• pp.22-25
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• 1999

A well oriented Bi-2212 superconductor thick films were fabricated by screen printing with a Cu-free Bi-Sr-Ca-Cu-O powder on a copper plate and heat-treating at 820- $880^{\circ}C$for several minute in low oxygen pressure or are. At minute in low oxygen pressure of air. At , the printing layer partially melted by reaction between the Cu-free precursor by reaction between the Cu-free$870^{\circ}C$ precursor and CuO of the oxidizing copper plate. It is believed that the solid phase is Bi : Sr : Ca : Cu = 2 : 2 : 0 : 1. It is likely that the Bi-2212 superconducting phase is formed at Bi-2212 superconducting phase is formed at Bi-free phase/liquid interface by nucleation and grows.

• Bulletin of the Korean Chemical Society
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• v.23 no.9
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• pp.1304-1323
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• 2002

Superconducting BiSrCaCu(Ni)O ceramicss have been prepared by the gel method using an aqueous solution containing a tartaric acid. The aqueous solution of metal salts was concentrated without precipitation. The precursor so prepared was homogeneou s and calcined at $825^{\circ}C$ for 24 h to produce superconducting phase. The thermal decomposition of gels, the formation of superconducting phase, and their ceramic microstructure were studied using IR, TGA, XRD, resistance measurements, and SEM. This method is highly reproducible and leads to powders with excellent homogeneity and small particle size for easy sinterability. The nickel dopant substituting for Cu gives rise to the gradual decrease of the Tc. Phase pure 2212 ceramics were obtained at 825 $^{\circ}C$ for 24 h. SEM pictures showed that liquid phase was formed when the samples were sintered temperatures higher than 825 $^{\circ}C$.

• Progress in Superconductivity
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• v.4 no.2
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• pp.162-167
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• 2003

The critical current value of Bi-2223/Ag tape can be influenced by various factors. In particular, it was known that properties of precursor powders could affect the formation of Bi -2223 and grain growth rate of the same. Since, moistures and organic matters can easily contaminate the precursor powders of Bi-2223 tapes and degrade properties of superconductors, the precursor powders should be kept in optimal conditions to minimize contamination. In this study, the effect of moisture and organic matters has been investigated. A Bi-2223/Ag tape contaminated with a large amount of moisture and organic matter has been characterized by low critical current values and bubbling. It has been found that as the quantity of moisture increases, the Bi-2223 phases are formed at lower temperature and the amount of non-superconducting phase increases.

• Korean Journal of Materials Research
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• v.4 no.4
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• pp.472-476
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• 1994

Phase transformation of PbO-precursor prepared from $Pb(NO_{3})_{2}$ by precipitation technique was observed by TG-DTA, XRD, FT-IR, and Raman spectral analysis. PbO-precursor was derived from an aqueous solution of $Pb(NO_{3})_{2}$ at $45^{\circ}C$ and pH of 9.0. The precipitate showed it to be the mixture of hydrous lead oxynitrate and lead hydroxynitrate. With increasing heat-treatment temperature ranging up to $560^{\circ}C$, the precursor changed to $3Pb(NO_{3})_{2}$ . 7Pb0, $Pb(NO_{3})_{2}$. 5Pb0 and PbO(litharge), in turn. Finally, it transformed to massicot form of PbO above $560^{\circ}C$.

• Proceedings of the Korea Institute of Applied Superconductivity and Cryogenics Conference
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• 2002.02a
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• pp.343-345
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• 2002

The influence of starting precursor powders on the phase formation and transport properties of Bi-2223/Ag tapes has been studied. The experimental results show that the average particle size of precursors as fine as 1.64 ${\mu}{\textrm}{m}$ and 1.51 ${\mu}{\textrm}{m}$ can still increase the transport properties. The J$_{c}$-B behavior is also enhanced in tapes fabricated with powders in finer particle sizes. However, at higher magnetic fields, J$_{c}$ of tape started from the powder with the finest particles drops rapidly at the direction of H//c, which is possibly attributed to the small grain sizes and weak flux pinning ability that due to the short induction period at the initial stage of phase formation as the result of fine particles in precursor powder.der.

• Journal of Microbiology and Biotechnology
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• v.4 no.3
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• pp.204-209
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• 1994

The synthesis of N-(benzyloxycarbonyl)-L-aspartyl-L-phenylalanine methylester (Z-APM), a precursor of aspartame, from N-(benzyloxycarbonyl)-L-aspartic acid (Z-Asp) and L-phenylalanine methylester hydrochlolide($L-PM\cdot HCI$) was investigated in a saturated-ethylacetate single phase system using immobilized thermolysin. Among the various supports tested, glyceryl-CPG was found to be most efficient for retaining enzyme activity. The enzyme immobilized onto glyceryl-CPG also showed the highest activity for Z-APM synthesis in saturated ethyl acetate. Z-APM conversion yield in saturated ethylacetate was half of that obtained in an ethyl acetate-buffer two-phase system under the same reaction conditions. However, as the mole ratio of $L-PM \cdot HCI$ to Z-Asp was increased to 4.0, the conversion yield reached 95 %. When continuous synthesis of Z-APM was canied out in a plug flow reactor (PFR) with 80 mM of L-PMㆍHCI and 20 mM of Z-Asp in saturated ethylacetate (pH 5.5), more than 95 % of Z-Asp was converted to Z-APM with a space velocity of 1.16 $hr^{-1} at 40^{\circ}C$. Although the operational stability in PFR was reduced rapidly, more than 80% of initial activity was maintained in CSTR even after a week of operation.

• Progress in Superconductivity and Cryogenics
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• v.9 no.1
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• pp.14-17
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• 2007

The slot-die coating & calcination process was adopted to fabricate the long YBCO precursor films on the buffered metal tape for the $2^{nd}$ generation coated conductors. To obtain the smooth and crack-free surface of long YBCO precursor films, the parameters of slot-die coating and the process variables of calcination step must be optimized simultaneously in reel-to-reel method. Among the parameter of slot-die coating process, the viscosities of the precursor solution was controlled from 60cP to 200cP to obtain the thicker films from on single coating. The slot-die gap, the injection rate of precursor solution, the moving speed of buffered metal tape etc. are controlled lot the full coverage and smooth surface of YBCO precursor films. The slot-die coated films are moved through the tube furnace with predetermined heating profiles in humid oxygen ambient The YBCO precursor films was identifed with $Y_2O_3,\;BaF_2$, and CuO phase by XRD and consisted of fine grains of about 20nm size observed by FE-SEM. The YBCO films show the critical current density over $MA/cm^2$ using the precursor films formed by the continuous slot-die coating & calcination process.

• The Korean Journal of Ceramics
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• v.4 no.3
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• pp.260-267
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• 1998

A homogeneous and stoichimetric fine powder of the ferroelectric $Pb_[0.97}La_{0.02}(Zr_{0.64}Sn_{0.25}Ti_{0.11})O_3$ (PLZST) has been prepared by the hydroxide coprecipitation method. Studies on the crystallization behavior of precursor as a function of temperature by X-ray powder diffraction and transmission electron microscopy technique were consistent with the formation of the pyrochlore phase from amorphous, initially at low temperatures around 500~$550^{\circ}C$. Further heat treatment up to $750^{\circ}C$ resulted in development of the perovskite phase with no significant pyrochlore crystallite growth. At intermediate temperatures the precursor yields a fine mixture of pyrochlore and perovskite phases. When the pyrochlore phase was heat teated in air, slight weight increase was observed in the temperature range of 300~$700^{\circ}C$, which is thought to be caused from oxygen absorption. In argon atmosphere, weight increase was not observed. On the other hand, weight loss began to occur near $700^{\circ}C$, with giving off mostly CO2 gas. This implies that the pyrochlore phase seems to be crystallorgraphycally and thermodynamically metastable. An apparent activation energy of 53.9 ㎉/mol was estimated for the pyrochlore-perovskite phase transformation.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2005.11a
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• pp.153-154
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• 2005

A high Tc superconducting with a nominal composition of $Bi_2Sr_2Ca_2Cu_3O_Y$ was prepared by the citarte method. 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. After pyrolysis at 400$^{\circ}C$ and calcination at 840$^{\circ}C$ for 4h, the (001)peak of the high Tc phase was cleary observed. Experimental results suggest that the intermediate phase formed before the formation of the superconducting phase may be the most important factro in determining whether it is easy to form the high Tc 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.