• Electrical & Electronic Materials
• /
• 제8권5호
• /
• pp.594-600
• /
• 1995

Dielectric properties at microwave frequencies of ($Zr_{0.65}$, $Sn_{0.35}$) $Ti_{1.04}$ $O_{4.04}$ ceramics with additives, NiO as an agent to improve dielectric properties and $B_{2}$ $O_{3}$ as a firing agent were investigated. When 0.5 - 1.5 wt% of NiO is add, the grain growth is inhibited and the shape of the grain is uniformed, Dielectric constant(Fr) and bulk density are increased with raising amount of NiO at sintering temperature of 1330 - 1360.deg. C, but the temperature coefficient of resonant frquency(.epsilon.$_{r}$) decreased gradually as the NiO content increased. The value of Qx $f_{o}$ was increased as the amount of NiO was increased in the range of 0.5 to 1.0 wt% and the Qx $f_{o}$, was decreased slightly with raising sintering temperature. With NiO of 1.0 wt% and at sintering temperature of 1360.deg. C, this ceramics was found to have excellent microwave properties of .epsilon.$_{r}$=37.8, Qx $f_{o}$ = 48.600 and .tau.$_{f}$ = 7 ppm/.deg. C.C.. C.. C.C.. C.. C.

• Bulletin of the Korean Chemical Society
• /
• 제26권1호
• /
• pp.91-96
• /
• 2005

O-(3-[$^{18}$F]Fluoropropyl)-L-tyrosine (L-[$^{18}$F]FPT) was synthesized by nucleophilic radiofluorination followed by acidic hydrolysis of protective groups and evaluated with 9 L tumor bearing rat. L-[$^{18}$F]FPT is an homologue of O-(2-[$^{18}$F]fluoroethyl)-L-tyrosine (L-[$^{18}$F]FET) which recently is studied as a tracer for tumor imaging using positron emission tomography (PET). [$^{18}$F]FPT was directly prepared from the precursor of O-(3-ptoluenesulfonyloxypropyl)- N-(tert-butoxycarbonyl)-L-tyrosine methyl ester. FPT-PET image was obtained at 60 min in 9 L tumor bearing rats. The radiochemical yield of [$^{18}$F]FPT was 0-45% (decay corrected) and the radiochemical purity was more than 95% after HPLC purification. The total time elapsed for the synthesis of [$^{18}$F]FPT was 100 min from EOB (End-of-bombardment). A comparison of uptake studies between [$^{18}$F]FPT and [$^{18}$F]FET was performed. In biodistribution, [$^{18}$F]FPT showed similar pattern with [$^{18}$F]FET in various tissues, but [$^{18}$F]FPT showed low uptake in brain. Furthermore, [$^{18}$F]FPT showed higher tumor-to-brain ratio than [$^{18}$F]FET. In conclusion, [$^{18}$F]FPT seems to be more useful amino acid tracer than [$^{18}$F]FET for brain tumors imaging with PET.

• Journal of the Korean Society of Propulsion Engineers
• /
• 제9권4호
• /
• pp.31-38
• /
• 2005

In this paper, the combustion characteristics of a hybrid propulsion system were studied with various L/D(length vs diameter) ratio of the single po.1 type solid fuel. Experiments were performed for 2 cases with the fixed grain port diameter and fuel length respectively. For the first case, results show that there are no large variations for regression rates as the L/D ratio changes. And as the L/D ratio increases, the O/F ratio decreases and thrust, characteristic velocity tends to increase. For the second case, there is no large change for O/F ratio, thrust and characteristic velocity as L/D ratio changes. On the other hand, as the L/D ratio decreases, only the regression rate tends to increase. Experimentally, exponent n in $\dot{r}=a{G_0}^n$ was found about 0.5 and then the O/F ratio was shown nearly constant. In the experiment, PE and gas oxygen were used as a fuel and an oxidizer.

• Korean Journal of Materials Research
• /
• 제21권12호
• /
• pp.644-649
• /
• 2011

[ $A_{3-2x/3}Al_{1-z}In_{z}O_4F:Eu_x^{3+}$ ](A = Ca, Sr, Ba, x = -0.15, z = 0, 0.1) oxyfluoride phosphors were simply prepared by the solid-state method at $1050^{\circ}C$ in air. The phosphors had the bright red photoluminescence (PL) spectra of an $A_{3-2x/3}Al_{1-z}In_{z}O_4F$ for $Eu^{3+}$ activator. X-ray diffraction (XRD) patterns of the obtained red phosphors were exhibited for indexing peak positions and calculating unit-cell parameters. Dynamic excitation and emission spectra of $Eu^{3+}$ activated red oxyfluoride phosphors were clearly monitored. Red and blue shifts gradually occurred in the emission spectra of $Eu^{3+}$ activated $A_3AlO_4F$ oxyfluoride phosphors when $Sr^{2+}$ by $Ca^{2+}$ and $Ba^{2+}$ ions were substituted, respectively. The concentration quenching as a function of $Eu^{3+}$ contents in $A_{3-2x/3}AlO_4F:Eu^{3+}$ (A = Ca, Sr, Ba) was measured. The interesting behaviors of defect-induced $A_{3-2x/3}Al_{1-z}In_{z}O_{4-{\alpha}}F_{1-{\delta}}$ phosphors with $Eu^{3+}$ activator are discussed based on PL spectra and CIE coordinates. Substituting $In^{3+}$ into the $Al^{3+}$ position in the $A_{3-2x/3}AlO_4F:Eu^{3+}$ oxyfluorides resulted in the relative intensity of the red emitted phosphors noticeably increasing by seven times.

• Journal of the Korean Magnetics Society
• /
• 제7권5호
• /
• pp.243-248
• /
• 1997

The effect of $O_2$ partial pressure on microstructure and soft magnetic properties of as-deposited Fe-Hf-O thin film alloys, which are produced by rf magnetron sputtering method in $Ar+O_2$ mixed gas atmosphere, are investigated. Saturation magnetization ($4{\pi}M_s$) of Fe-Hf-O film were decreased with increasing $O_2$ partial pressure, the best soft magnetic properties exhibit at $O_2$ partial pressure of 10%. With further increase of $O_2$ partial pressure, soft magnetic properties decreased continuously. The $Fe_{82}Hf_{3.4}O_{14.6}$ film with $P_{O2}=10%$ exhibits good soft magnetic properties with $4{\pi}M_s=17.7kG$, $H_c=0.7Oe$ and ${\mu}_ {eff}$ (1~100 MHz)=2,500, respectively. The addition of O is effective in grain refinement. In case of $P_{O2}=15%$, it is observed that $Fe_3O_4$ compound is formed and high frequency soft magnetic properties are decrease. The electrical resistvity($\rho$) of Fe-Hf-O film is increased with increasing $O_2$ partial pressure. Electrical resistivity of $Fe_{82}Hf_{3.4}O_{14.6}$ film was 5 times higher than that of the film without oxygen. Thus, it is considered that the good magnetic properties of $Fe_{82}Hf_{3.4}O_{14.6}$ film results from decreasing the $\alpha$-Fe grain size by precipitates (Hf and O), high electrical resistivity.

• Korean Journal of Materials Research
• /
• 제22권8호
• /
• pp.439-444
• /
• 2012

To compare the photocatalytic performances of titania for purification of waste water according to applied voltages and doping, $TiO_2$ films were prepared in a 1.0 M $H_2SO_4$ solution containing $NH_4F$ at different anodic voltages. Chemical bonding states of F-N-codoped $TiO_2$ were analyzed using surface X-ray photoelectron spectroscopy (XPS). The photocatalytic activity of the co-doped $TiO_2$ films was analyzed by the degradation of aniline blue solution. Nanotubes were formed with thicknesses of 200-300 nm for the films anodized at 30 V, but porous morphology was generated with pores of 1-2 ${\mu}m$ for the $TiO_2$ anodized at 180 V. The phenomenon of spark discharge was initiated at about 98 V due to the breakdown of the oxide films in both solutions. XPS analysis revealed the spectra of F1s at 684.3 eV and N1s at 399.8 eV for the $TiO_2$ anodized in the $H_2SO_4-NH_4F$ solution at 180 V, suggesting the incorporation of F and N species during anodization. Dye removal rates for the pure $TiO_2$ anodized at 30 V and 180 V were found to be 14.0% and 38.9%, respectively, in the photocatalytic degradation test of the aniline blue solution for 200 min irradiation; the rates for the F-N-codoped $TiO_2$ anodized at 30 V and 180 V were found to be 21.2% and 65.6%, respectively. From the results of diffuse reflectance absorption spectroscopy (DRS), it was found that the absorption edge of the F-N-codoped $TiO_2$ films shifted toward the visible light region up to 412 nm, indicating that the photocatalytic activity of $TiO_2$ is improved by appropriate doping of F and N by the addition of $NH_4F$.

• Journal of the Korean Ceramic Society
• /
• 제16권3호
• /
• pp.135-141
• /
• 1979

This study seeks to find optimum conditions for the heating schedule of the Diopside-Devitrite system, to find the amounts and the kinds of nucleus which effect the crystal growth and forming nucleus. Generally, crystallization in the glass depends on the number of nucleus growing in the internal system and the rate of crystal growth. In order to obtain homogeneous polystalline phae, Diopside as MgO source and $ZrO_2$.$P_2O_5$, $TiO_2$, NaF, $CaF_2$ as nucleating agents were added to the $Na_2O$.CaO.$6SiO_2$ glass. The results obtained were Summarized as follows. 1) Optimum Batch Composition of base glass is 76.82 wt.% $SiO_2$, 5.84 wt.% CaO, 4.54 wt.% MgO and 9.80 wt.% $Na_2O$. 2) Best heating schedule.140$0^{\circ}C$(Melting)coolinglongrightarrow95$0^{\circ}C$reheatinglongrightarrow$1100^{\circ}C$coolinglongrightarrowRoom Temp. 3) The optimum amounts of $ZrO_2$.$P_2O_5$, $TiO_2$ and $CaF_2$ are 3wt.% and that of NaF is 4 wt.% as a nucleating agents.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
• /
• 제19권1호
• /
• pp.29-34
• /
• 2006

The effects of $B_2O_3$ addition on the low-temperature sintering behavior and microwave dielectric properties of $(Zn_{0.8}Mg_{0.2})TiO_3$ ceramic system were investigated. Highly dense samples were obtained at the sintering temperatures below $900^{\circ}C$. The $Q{\times}f_o$ values were determined by the microstructures and sintering shrinkages which are affected by the amount of $B_2O_3$ and sintering temperature. Temperature coefficient of resonance frequency($T_f$) changes to a positive value with increasing the amount of $B_2O_3$ due to the increased amount of rutile phase which is one of the reaction products between $(Zn_{0.8}Mg_{0.2})TiO_3$ and $B_2O_3$. For $6.19 moi.{\%}B_2O_3$-added $(Zn_{0.8}Mg_{0.2})TiO_3$ system, it exhibits ${\epsilon}_r$ = 23.5, $Q{\times}f_o$ = 53,000 GHz, and $T_f$ = 0 ppm/$^{\circ}C$ when sintered at $900^{\circ}C$ for 5 h.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
• /
• 제13권12호
• /
• pp.1017-1024
• /
• 2000

Effect of the microwave dielectric properties and the microstructure on a mole fraction(x=0.1~0.9) of (1-x)Mg$_2$SiO$_4$-xZnAl$_2$O$_4$ ceramics was investigated. When (1-x)Mg$_2$SiO$_4$-xZnAl$_2$O$_4$(x=0.1~0.9) ceramics were sintered at 130$0^{\circ}C$, 135$0^{\circ}C$ and 140$0^{\circ}C$ for 2hr, the microwave dielectric properties were obtained $\varepsilon$r=6.8~8.3, Q.f$_{0}$=36000~77600. On the other hand, the temperature coefficients of resonant frequency($\tau$$_{f}$) were obtained in the properties of -62ppm/$^{\circ}C$ to -49ppm/$^{\circ}C$. In order to adjust the temperature coefficient of resonant frequency($\tau$$_{f}$), CaTiO$_3$was added in (1-x)Mg$_2$SiO$_4$-xZnAl$_2$O$_4$ceramics. 0.7Mg$_2$SiO$_4$-0.2ZnAl$_2$O$_4$-0.1CaTiO$_3$ceramics sintered at 135$0^{\circ}C$ for 2hr showed the excellent microwave dielectric properties of $\varepsilon$r=7.7, Q.f$_{0}$=32000, and $\tau$$_{f}$=-7.9 ppm/$^{\circ}C$.EX>.>.EX>.

• Journal of the Chungcheong Mathematical Society
• /
• 제1권1호
• /
• pp.55-64
• /
• 1988

We introduce the concept of a w-Lindel$\ddot{o}$f space which is a more general concept than that of a Lindel$\ddot{o}$f spaces. We obtain some characterization about H-closed sapces and w-Lindel$\ddot{o}$f spaces. Also, we investigate their invariance properties.