• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 1998.06a
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• pp.367-370
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• 1998

In this paper, based on the research of high temperature YBCO superconductor, using the Yb instead of Y, with the YbBCO superconductor powder which was combined by means of conventional solid reaction, textured directional crystal was prepared by MCP method and the character was analyzed. Mixing the starting elements and calcining at 890$^{\circ}C$, 900$^{\circ}C$, 910$^{\circ}C$, single phase YbBCO, Yb$_2$BaCuO$\sub$5/ and BaCuO$\sub$2/ were certified. And from the powder which was calcined at 900$^{\circ}C$ the, sample which became texture-growth by MCP method was well oriented. The result of DTA measurement, the fusing point of YbBCO superconductor and it\`s critical current was measured to be 979$^{\circ}C$, 87K respectively. The critical current density was obtained at the value of 700A/$\textrm{cm}^2$(77K. 0H) calculated by Bean's Model using the measured hysteresis curve of VSM.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.34 no.11A
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• pp.904-908
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• 2009

The PZT(lead, zirconium, titanium) based ceramics which, are reported to be ferroelectric materials have their important applications in the areas of surface acoustic waves (SAW), filters, infrared detectors, actuators, ferroelectric random acess memory, speakers, electronic switches etc. Moreover, these PZT materials possess the large electromechanical coupling factor, large spontaneous polarization, low dielectric loss and low internal stress etc. Hence, keeping in view the unique properties of PZT piezoelectric ceramics we also tried to synthesize indigenously the small sized PZT ceramic powder in the laboratory by using the modified sol-gel approach. In this paper, Propyl alcohol based sol-gel method was used for preparation of PZT piezoelectric ceramic. The powder obtained by this sol-gel process was calcined and sintering to reach a pyrochlore-free crystal phase. The characterization of synthesized material was carried out by the XRD analysis and the surface morphology was determined by high resolution scanning electron microscopy.

• Journal of the Korean Ceramic Society
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• v.35 no.8
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• pp.843-849
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• 1998

Fine powders of Mn-Zn ferrite were prepared by the alcoholic dehydration method and densification beha-vior of synthesized powder was investigated. The concentration and pH of solution for optimal precipitation was 0.4M and 2.5 respectively. The spinel single phase metastable state was formed by thermal decom-position of precipitate and then spinel phase was disintegrated into hematite and spinel {{{{ { { ZnFe}_{2 }O }_{4 } }} at 600$^{\circ}C$ With increase of temperature reaction of solid solution between hematite and spinel was proceeded and resulted in the spinel single phase (Mn, Zn Fe){{{{ { {Fe }_{2 }O }_{4 } }} On account of high reactivity of uncalcined powders densification started at 200$^{\circ}C$ lower and completed at 50$^{\circ}C$ lower in comparison with calcined powders.

• Journal of the Korean Ceramic Society
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• v.33 no.7
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• pp.743-754
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• 1996

In this study (Ba1-xPbx)TiO3 was synthesized by modified oxalate process in order to prevent vaporization of PbO through low temperature synthesis climinate Cl ion reproducibly substitute Pb for by and uniformly distribute ion (Ba1-xPbx)TiO3 was synthesized by coprecipitation of lead acetate barium acetate and ammonium titanyl oxalate have been used as starting materials. The substitution of Pb for Ba was reproducibly possible synthetic temperature of perovskite structure becomes lowed as the Pb concentration increases and fine partic-les (specific surface are :7.2 cm2/g) were obtained, BaTiO3 powders calcined at 90$0^{\circ}C$ for 3 hours were cubic from in XRD analysis and as Pb content was increases evident split of tetragonal peaks could be observed The optimum conditions to synthesize (Ba,Pb)TiO3 powder are the followings ; synthesis temperature (5$^{\circ}C$)

• Journal of Powder Materials
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• v.10 no.4
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• pp.255-261
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• 2003

Ultrafine TaC-5%Co composite powders were synthesized by spray conversion process using tantalum oxalate solution and cobalt nitrate hexahydrate(Co($(NO_3)_2$ . 6$H_2O$). The phase of Ta-Co oxide powders had amorphous structures after calcination below 50$0^{\circ}C$ and changed $Ta_2O_5$, $TaO_2$ and $CoTa_2O_6$ phase by heating above $600^{\circ}C$. The calcined Ta-Co oxide powders were spherical agglomerates consisted of ultrafine primary particles <50 nm in size. By carbothermal reaction, the TaC phase began to form from 90$0^{\circ}C$. The complete formation of TaC could be achieved at 105$0^{\circ}C$ for 6 hours. The observed size of TaC-Co composite powders by TEM was smaller than 200 nm.

• Journal of the Korean Ceramic Society
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• v.16 no.3
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• pp.155-163
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• 1979

This study was to explore the characteristics of 6 mole% CaO stabilized $ZrO_2$ prepared by wet chemical methods. The results of the experiments were as follows: 1. The powder calcined at 1000$^{\circ}$-110$0^{\circ}C$ was partly agglomerated. The morphology of agglomerate was spherical of 0.5-1$\mu{m}$ in size for Hot Petroleum Drying Method, chain-like of 1-2$\mu{m}$ for Freeze Drying Method, and irreqular of 2-3$\mu{m}$ for Coprecipitation Method. 2. Optimum calcining conditions for powder prepared by wet chemical methods were found: 110$0^{\circ}C$, 2h in air for Hot Petroleum Drying Method and Freeze Drying Method, and 100$0^{\circ}C$, 2h in air for Coprecipitation Method. 3. When specimen was calcined at 1000$^{\circ}$-110$0^{\circ}C$ in air for 2h and then sintered at 1$600^{\circ}C$ in air for 4h, the specimens prepared by wet chemical methods showed a high sintered density (94% of theoretical density) and a low open porosity (<0.8%); however, the sintered density of the specimen prepared by Oxide Wet Mixing Method was 90%. 4. The amount of cubic phase of sintered body prepared by wet chemical methods was observed to be higher than the one prepared by Oxide Wet Mixing Method. 5. It was found that Hot petroleum Drying Method, Freeze Drying Method and Coprecipitation Method were nearly the same in respect of the results of stabilization grade and sintered density of CaO-stabilized $ZrO_2$.

• Journal of the Korean Ceramic Society
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• v.34 no.3
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• pp.289-295
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• 1997

Effect of ceramic processing was investigated on the microstructure and electronic properties of low loss Mn-Zn ferrite. Addition of CaO and SiO2 to calcined powder rather than to raw materials mixtured resulted in finer-grained microstructure. Higher oxygen pressure during sintering caused microstructural inhomogeneity and the increase in power loss and disaccommodation factor. Relatively low power loss was found for sintering up to 130$0^{\circ}C$ from powders calcined at high temperature and milled shortly. It was caused by slow densification rate and normal grain growth up to 130$0^{\circ}C$. Calcination at low temperature and prolonged milling enhanced den-sification, which gave a fine grained microstructure and low powder loss at sintering temperture below 120$0^{\circ}C$. Sintering temperature above 125$0^{\circ}C$, however, showed abnormal grain growth.

• Korean Journal of Materials Research
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• v.20 no.7
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• pp.364-369
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• 2010

A $SrAl_2O_4:Eu^{2+},Dy^{3+}$ phosphor powder with stuffed tridymite structure was synthesized by glycine-nitrate combustion method. The luminescence, formation process and microstructure of the phosphor powder were investigated by means of X-ray diffraction (XRD), scanning electron microscopy (SEM) and photoluminescence spectroscopy (PL). The XRD patterns show that the as-synthesized $SrAl_2O_4:Eu^{2+},Dy^{3+}$ phosphor was an amorphous phase. However, a crystalline $SrAl_2O_4 $ phase was formed by calcining at $1200^{\circ}C$ for 4h. From the SEM analysis, also, it was found that the as-synthesized $SrAl_2O_4:Eu^{2+},Dy^{3+}$ phosphor was in irregular porous particles of about 50 ${\mu}m$, while the calcined phosphor was aggregated in spherical particles with radius of about 0.5 ${\mu}m$. The emission spectrum of as-synthesized $SrAl_2O_4:Eu^{2+},Dy^{3+}$ phosphor did not appear, due to the amorphous phase. However, the emission spectrum of the calcined phosphor was observed at 520 nm (2.384eV); it showed green emission peaking, in the range of 450~650 nm. The excitation spectrum of the $SrAl_2O_4:Eu^{2+},Dy^{3+}$ phosphor exhibits a maximum peak intensity at 360 nm (3.44eV) in the range of 250~480 nm. After the removal of the pulse Xe-lamp excitation (360 nm), also, the decay time for the emission spectrum was very slow, which shows the excellent longphosphorescent property of the phosphor, although the decay time decreased exponentially.

• Journal of the Korean Recycled Construction Resources Institute
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• v.5 no.3
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• pp.63-69
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• 2010

This study investigates the chemical resistance of the recycled aggregate concrete containing calcined ground slag, fly ash, and diatom powder. The recycled aggregate which had the density of $2.48g/cm^3$, the absorption of 4.25%, and standard gradation was used and the concrete specimens were submerged in solutions of $Na_2SO_4$ and $CaCl_2$ at 10% concentration for 6 months. As the submersion result, pore volume of over $0.02{\mu}m$ diameter was formed less in the concrete specimens containing calcined ground slag, fly ash, and diatom powder than in the concrete without the pozzolanic materials and the result shows the effectiveness of the pozzolanic materials for the increase of chemical resistance of the recycled aggregate concrete.

• Korean Journal of Materials Research
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• v.20 no.10
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• pp.508-512
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• 2010

The optimum route to fabricate nano-sized Fe-50 wt% Co and hydrogen-reduction behavior of calcined Fe-/Conitrate was investigated. The powder mixture of metal oxides was prepared by solution mixing and calcination of Fe-/Co-nitrate. A DTA-TG and microstructural analysis revealed that the nitrates mixture by the calcination at $300^{\circ}C$ for 2 h was changed to Fe-oxide/$Co_3O_4$ composite powders with an average particle size of 100 nm. The reduction behavior of the calcined powders was analyzed by DTA-TG in a hydrogen atmosphere. The composite powders of Fe-oxide and Co3O4 changed to a Fe-Co phase with an average particle size of 40 nm in the temperature range of $260-420^{\circ}C$. In the TG analysis, a two-step reduction process relating to the presence of Fe3O4 and a CoO phase as the intermediate phase was observed. The hydrogen-reduction kinetics of the Fe-oxide/Co3O4 composite powders was evaluated by the amount of peak shift with heating rates in TG. The activation energies for the reduction, estimated by the slope of the Kissinger plot, were 96 kJ/mol in the peak temperature range of $231-297^{\circ}C$ and 83 kJ/mol of $290-390^{\circ}C$, respectively. The reported activation energy of 70.4-94.4 kJ/mol for the reduction of Fe- and Co-oxides is in reasonable agreement with the measured value in this study.