• Economic and Environmental Geology
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• v.37 no.3
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• pp.303-309
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• 2004

Pyrochlores were known as promising materials for the immobilization of radioactive actinide. Accordingly, we synthesized pyrochlores with Gd$_2$Ti$_2$$O_7$ and Gd$_2$Zr$_2$$O_7$compositions by sintering method, and studied its properties and phase relations in Gd-Ti-O and Gd-Zr-O system. The mixed powders were pressed into pellets under 200-400 kgf/cm$^2$ at room temperature. and then sintered at 1000-1$600^{\circ}C$ for 0.5-40 hours. The synthesized samples were analyzed and were identified with XRD and SEM/EDS analyses. The optimal synthetic conditions of pyrochlores with Gd$_2$Ti$_2$$O_7$composition were at 140$0^{\circ}C$/0.5hrs, 130$0^{\circ}C$/3hrs and 120$0^{\circ}C$/20hrs. Its chemical composition was $Gd_{2.0-2.1}$$Ti_{1.9-2.0}$$O_7$ and similar to the stoichiometric composition without any relationship in temperature and atmosphere. The optimal synthetic conditions of pyrochlores with $Gd_{2}$$Zr_{2}$$O_7$composition were at 155$0^{\circ}C$/40hrs and 1$600^{\circ}C$/30hrs. The compositions of pyrochlore synthesized from these optimal conditions were irregular with $Gd_{1.5-2.4}$$Zr_{1.7-2.4}$$O_7$. Such heterogeneity indicates that the reaction rate of pyrochlore with Gd$_2$Zr$_2$$O_7$composition is very low, and then its equilibrium state could not be attained even for 40 hours which was the longest sintering time in this research.

• Journal of the Korean Ceramic Society
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• v.38 no.11
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• pp.1046-1054
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• 2001

Effects of B$_2$O$_3$and CuO addition on the microwave dielectric properties of the PbWO$_4$-TiO$_2$ceramics were investigated in order to use this material as an LTCC material for fabrication of a multilayered RF passive components module. We found that PbWO$_4$could be used as an LTCC material because of its low sintering temperature (8$50^{\circ}C$) and fairy good microwave dielectric properties($\varepsilon$$_{r}$=21.5, Q$\times$f$_{0}$=37200 GHz and $\tau$$_{f}$ =-31 ppm/$^{\circ}C$). In order to stabilize $\tau$$_{f}$ of PbWO$_4$, TiO$_2$was added to the PbWO$_4$and the mixture was sintered at 8$50^{\circ}C$. A near zero $\tau$$_{f}$ value (+0.2 ppm/$^{\circ}C$) was obtained with 8.7 mol% TiO$_2$addition. $\varepsilon$r and Q$\times$f$_{0}$ values were 22.3 and 21400 GHz, respectively. It was believed that the decrement of Q$\times$f$_{0}$ value with TiO$_2$addition was resulted from increasing grain boundary. In order to improve Q$\times$f$_{0}$, various amounts of B$_2$O$_3$and CuO were added to the 0.913PbWO$_4$-0.087TiO$_2$mixture. The optimum amount of CuO was 0.05 wt%. At this addition, the 0.913PbWO$_4$-0.087TiO$_2$ceramic showed $\varepsilon$$_{r}$=23.5, $\tau$$_{f}$ =-2.2ppm/$^{\circ}C$, and Q$\times$f$_{0}$=32900 GHz after sintered at 8$50^{\circ}C$. In case of B$_2$O$_3$addition, the optimum amount range was 1.0~2.5 wt% at which we could obtain following results; $\varepsilon$$_{r}$=20.3~22.1, Q$\times$f$_{0}$=48700~54700 GHz, and $\tau$$_{f}$ =+2.4~+8.2ppm/$^{\circ}C$.

• Korean Journal of Materials Research
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• v.11 no.3
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• pp.178-184
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• 2001

Transparent and highly oriented KLN thin films have been grown by an rf- magnetron sputtering deposition method. A homogeneous and stable KLN target was prepared by calcine and sintering process. For KLN target, stoichiometry and composition excess with K of 30% and 60%, and Li of 15% and 30% respectively, was prepared. The targets were sintered at low temperature to prevent vaporization of K and Li. KLN thin films were fabricated by rf-magnetron sputtering method using those targets. In this experiment, using the target of composition excessed with K of 60% and Li of 30%, single phase KLN thin film was produced. KLN thin film has excellent crystallinity and highly c-axis oriented on Corning 1737 substrate. Transmittance of thin film in visible range was 90%, absorption edge is 333 nm and refractive index at 632.8 nm was 1.93.

• Korean Journal of Heritage: History & Science
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• v.47 no.3
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• pp.24-41
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• 2014

Since the celadons excavated from the Son-gok 2-ri 4th kiln site are located in the Beopcheon temple site and at close range, the similarity to the celadons excavated from the Beopcheon temple site is being raised. Thus, this study examined the correlation using a natural-scientific method. In this study, historical ceramic properties of total 19 celadons were examined and they were scientifically analyzed. First of all, according to the scientific analysis, chemical compositions of celadon clay showed a dispersed distribution at RO2 3.79-7.77mole and RO+R2O 0.33-0.49mole. When the microstructure was analyzed, most celadons excavated from the Beopcheon temple site, Wonju, which are estimated to be used in real life, had a favorable state, and some celadons from the Son-gok 2-ri 4th kiln site were found not to be glazed and sintered properly. When analyzing body crystalline phases of the celadons using the XRD method, quartz and mullite were extracted from all of the samples. And corundum was extracted from sg4 sample. Though firing temperature of each sample was different, they were mostly fired to temperatures between 1150 and $1200^{\circ}C$ and some of them experienced a low temperature of $1100^{\circ}C$ or a high temperature above $1200^{\circ}C$. Various chemical compositions and producing techniques were observed in the celadons from the Beopcheon temple site and Son-gok 2-ri 4th kiln site and it is hard to assure that the Son-gok 2-ri 4th kiln site was the production kiln site of the celadons used in the Beopcheon temple site. But according to the analysis of rare earth elements, some of the celadons from the Beopcheon temple site and Son-gok 2-ri 4th kiln site displayed a distribution pattern with certain regularity and this implies there is a possibility that the raw materials used in producing the ceramics might have come from the same origin. From the perspective of ceramic history, the celadons excavated from the Beopcheon temple site and Son-gok 2-ri 4th kiln site were produced using the same molding and sintering technique. Also, it is estimated that they were produced in the 12th or 13th century, judging from the overall shapes and patterns of the celadons.