• Journal of the Korean Ceramic Society
• /
• v.39 no.1
• /
• pp.26-32
• /
• 2002

The effects of $Nd_2O_3$ addition to $Q{\cdot}f_{0}(GHz)$ ceramics with ${\varepsilon}_r$ of 126, $Q{\cdot}f_{0}(GHz)$ of 2240 and of $68\;ppm/^{\circ}C$ on their microwave properties were investigated. For the addition of 5 wt% $Nd_2O_3$, the dielectric constant (${\varepsilon}_r$) showed maximum value of 131, then decreased with the further addition of $Nd_2O_3$. $Q{\cdot}f_{0}(GHz)$ value was still increased to 3533 with 9 wt% $Nd_2O_3$ addition, it is influenced by densification of grain boundary. With more addition of $Nd_2O_3$ up to 18 wt%, the abnormal grain growth have influence on the decreasing of $Q{\cdot}f_{0}(GHz)$ value. But with the further addition of $Nd_2O_3$ over 25 wt%, the $Q{\cdot}f_{0}(GHz)$ value was again increased by the effect of the second phase ($Nd_2Ti_2O_7$) forming. The temperature coefficient of resonant frequency (${\tau}_f$) was decreased from $+\;68\;ppm/^{\circ}C$ with the addition of $Nd_2O_3$, reached $0\;ppm/^{\circ}C$ at 12 wt% addition, and became negative with the further addition of $Nd_2O_3$. The optimum microwave dielectric properties were obtained for $0.3CaTiO_3-0.7(Li_{1/2}Nd_{1/2})TiO_3$ with 9 wt% $Nd_2O_3$ sintered at $1425^{\circ}C$ for 3 hrs. The dielectric constant (${\varepsilon}_r$), the $Q{\cdot}f_{0}(GHz)$ value, and the temperature coefficient of resonant frequency (${\tau}_f$) were 108, 3533, and $+\;6\;ppm/^{\circ}C$, respectively.

• Journal of the Korean Ceramic Society
• /
• v.39 no.12
• /
• pp.1190-1196
• /
• 2002

Microwave dielectric properties and multilayer characteristics $(1-x)BiNbO_4-xCaNb_2O_6$ (0${\le}$x${\le}$1.0) ceramics were investigated as a function of $CaNb_2O_6$ content. In the composition range of 0.25${\le}$x${\le}$0.75, the mixture phases of $BiNbO_4$ with stibotantalate structure and $CaNb_2O_6$ with columbite structure were detected and secondary phase or phase transition were not detected. Dielectric constant (K) of $(1-x)BiNbO_4-xCaNb_2O_6$ ceramics was largely dependent on the existing phase and could be estimated by the dielectric mixing rule calculated from maxwell equation. Typically, dielectric constant (K) of 26, quality factor (Qf) of 4300 GHz and Temperature Coefficient of resonant Frequency (TCF) of -18 ppm/${\circ}C$ were obtained for $0.5BiNbO_4-0.5CaNb_2O_6$ specimens with 0.8 wt% $CuV_2O_6$ sintered at 1000${\circ}C$ for 3h. The deviation of X-Y shrinkage and camber value of the multilayers obtained from $0.5BiNbO_4-0.5CaNb_2O_6$ green sheet sintered at 850∼950${\circ}C$ for 20 min. were smaller than those of $BiNbO_4$ multilayers.

• Horticultural Science & Technology
• /
• v.30 no.5
• /
• pp.484-492
• /
• 2012

The present study aimed to investigate the effect of static magnetic field (SMF) on the growth and physiological characteristics of common indoor plant species. Five foliage plant species, Spathiphyllum spp., Ardisia pusilla DC., Syngonium podophyllum, Peperomia pereskiifolia, and Pilea cadierei were potted into plastic pot equipped with round type anisotropic sintered NdFeB permanent magnet inside the pot. The surface magnetic flux density of each magnet was 3,500 G. After 6 months of growth period, the biomass accumulations of Spathiphyllum, A. pusilla, and P. cadierei under SMF were statistically higher than those of controls. Tissue water content also increased under the influence of SMF in most species. The photosynthetic rate of Spathiphyllum under SMF significantly increased but other species showed no significant difference compared with control. Although there was no significant increase in the photosynthetic rates of A. pusilla, and P. cadierei, they showed remarkable increase in total fresh weight under SMF. This suggests that the demand of assimilates for normal metabolism could be decreased under magnetic influence and thereby biomass accumulation could be more favored. But this is not always true for all plant species because P. pereskiifolia in this experiment, showed no changes in both photosynthetic rate and biomass accumulation. Leaf nitrogen and chlorophyll contents were enhanced significantly in most plant species under influence of SMF. Chlorophyll a/b ratio also increased by SMF. Although there might be a limitation depending on plant species, these results suggest that long-term exposure to SMF might allow plant to have an enhanced acclimation capacity against environmental fluctuations and optimal application of SMF could increase the practical use of indoor plants such as an attempt to improve indoor air quality.

• Journal of the Korean Ceramic Society
• /
• v.41 no.8
• /
• pp.599-604
• /
• 2004

The LTCCs (Low-Temperature Co-fired Ceramics) are very important for electronic industry to build smaller RF modules and to fulfill the necessity for miniaturization of devices in wireless communication industry. The dielectric materials with sintering temperature $T_{sint}$＜90$0^{\circ}C$ are required. In this study, BaO-N $d_2$ $O_3$-Ti $O_2$ (BNT ： 20∼40 wt％) for ceramic materials and L $a_2$ $O_3$- $B_2$ $O_3$-Ti $O_2$ (LBT ： 80∼60 wt％) for crystallizable glasses were used. The glass/ceramic composites were investigated for sintering behavior, phase evaluation, densities, interface reaction and microwave dielectric properties. It was found that the addition LBT glass frist significantly lowered the sintering temperature to below 90$0^{\circ}C$ and the densification with increasing addition LBT glass frist developed rapidly which was meant to be namely 90％ of relative density. The sintered bodies ekhibited applicable dielectric properties, namely 15 for $\varepsilon$$_{r}$,, 10000 GHz for Q＊ $f_{0}$. The results suggest that the composites have good potential as a new candidate for LTCC materials.

• Applied Chemistry for Engineering
• /
• v.5 no.5
• /
• pp.862-870
• /
• 1994

$Pb(NO_3)_2$, $Mg(NO_3)_2$ and $NbCl_5$ were used as starting materials and made into solutions. For $Pb(Mg_{1/3}Nb_{2/3})O_3$ composition, each solution measured was mixed and heated to $70^{\circ}C$ to resolved $PbCl_2$ precipitated at lower temperature coprecipitates were formed by adding oxine and ammonia gas under pH ranging 8 to 10, and the prepared coprecipitates were filtered and washed by distilled water. The $Pb(Mg_{1/3}Nb_{2/3})O_3$ powders were synthesized by calcination of coprecipitates at the temperature range of $700^{\circ}C$ to $1000^{\circ}C$, for 5hr. The average particle size of the synthesized powders showing spherical shape was $0.3{{\mu}m}$. The powders were formed to make pellets under pressure of $2000Kg/cm^2$, and the formed pellets were sintered at the temperature range of 1100 to $1200^{\circ}C$, for 5hr. The speciman sintered at $1200^{\circ}C$ showed theoretical density of 97.4%, dielectric constatnt of 17000 at 1kHz, and dielectric loss of 0.02% at 1kHz

• Journal of the Korean Applied Science and Technology
• /
• v.35 no.3
• /
• pp.757-767
• /
• 2018

In the propane dehydrogenation reaction proceeding at high temperature, the main cause of deactivation of the catalyst is coke deposition and sintering. In order to investigate the catalysts for reducing such inactivation, we have investigated the applicability of $MgAl_2O_4$ as a carrier for the catalytic dehydrogenation reaction. $MgAl_2O_4$ was prepared by Alcohthermal method at calcination temperature of 800, 900, $1000^{\circ}C$, and $Pt-Sn/MgAl_2O_4$ catalyst was prepared by supporting Pt and Sn by co-impregnation method. The reaction temperature was conducted at a high temperature of 650, $600^{\circ}C$ to confirm the thermal stability. As a result of the reaction experiment, it was confirmed that the conversion rate and yield of propane dehydrogenation reaction test were higher than that of the carrier-applied catalyst having a carrier calcination temperature of 900 and $1000^{\circ}C$, when the carrier-applied catalyst having a calcination temperature of $800^{\circ}C$ was used, It was found that the yield was higher than that of $Pt-Sn/{\theta}-Al_2O_3$ at $650^{\circ}C$. TGA, BET, XRD, CO-chemisorption, and SEM-EDS analyzes were performed for characterization. $MgAl_2O_4-800^{\circ}C$ was correlated with the relationship between good yield, Pt dispersion and low deactivation rate.

• Journal of Korean Society of Environmental Engineers
• /
• v.30 no.1
• /
• pp.54-60
• /
• 2008

Deactivation of SCR catalyst applied in Orimusion fuel power plant was investigated to develope the technique for the regeneration of deactivated SCR catalyst and optimize the operation of SCR facility. The characterization study of the catalysts was carried out using XRD, ICP-AES, SEM and EDS. The NO$_X$ removal activity and SO$_2$ oxidation activity of the catalysts were measured. The NO$_X$ conversion of the deactivated catalyst was 5$\sim$10% lower than that of the fresh catalyst and the value of SO$_2$conversion to SO$_3$ over the deactivated catalyst was about 0.59% higher than that of the fresh catalyst. Vanadium(V), Magnesium(Mg) and Sulfur(S) were largely accumulated in the deactivated catalyst. The accumulation of Vanadium(V) and Sulfur(S) is due to the components of the Orimulsion fuel and the accumulation of Magnesium(Mg) is due to MgO that is injected in the boiler to prevent the oxidation of SO$_2$ to SO$_3$. The diffraction line of the TiO$_2$ of the deactivated catalyst was identified as the crystalline peaks of anatase as the fresh catalyst.

• Journal of the Korean Ceramic Society
• /
• v.40 no.6
• /
• pp.594-600
• /
• 2003

L $a_{0.7}$S $r_{0.3}$G $a_{0.6}$F $e_{0.4}$ $O_{3-}$$\delta$/ perovskite-type mixed conducting membranes, which could permeate oxygen selectively, have been fabricated and the microstructural features developed by varying the sintering conditions have been analyzed. The effects of surface modification and the membrane thickness on oxygen permeability have been evaluated under He/air environment. With increasing a grain boundary fraction, the overall oxygen permeability decreased. The syngas (CO+ $H_2$) has been produced by partial oxidation reaction of methane with the oxygen permeated through the membrane. Methane conversion and syngas yield have been evaluated as functions of the compositional ratio of feed gas and reaction temperature. In long-term duration test for 600 h, under C $H_4$+He/air environment, L $a_{0.7}$S $r_{0.3}$G $a_{0.6}$F $e_{0.4}$ $O_{3-}$$\delta$/ membrane showed a highly stable performance.

• Clean Technology
• /
• v.20 no.3
• /
• pp.212-217
• /
• 2014

In order to regenerate the sulfidated desulfurization sorbent, oxygen is used as the oxidant agent on the regeneration process. The small amount of oxygen un-reacted in regeneration process is flowed into direct sulfur recovery process. However, the reactivity for $SO_2$ reduction can be deteriorated with the un-reacted oxygen by various reasons. In this study, the deactivation effects of un-reacted oxygen contained in the off-gas of regeneration process flowed into direct sulfur recovery process of hot gas desulfurization system were investigated. Sn-Zr based catalysts were used as the catalyst for $SO_2$ reduction. The contents of $SO_2$ and $O_2$ contained in the regenerator off-gas used as the reactants were fixed to 5.0 vol% and 4.0 vol%, respectively. The catalytic activity tests with a Sn-Zr based catalyst were for $SO_2$ reduction performed at $300-450^{\circ}C$ and 1-20 atm. The un-reacted oxygen oxidized the elemental sulfur produced by $SO_2$ catalytic reduction and the conversion of $SO_2$ was reduced due to the production of $SO_2$. However, the temperature for the oxidation of elemental sulfur increased with increasing pressure in the catalytic reactor. Therefore, it was concluded that the decrease of reactivity at high pressure is occurred by catalytic deactivation, which is the re-oxidation of lattice oxygen vacancy in Sn-Zr based catalyst with the un-reacted oxygen on the catalysis by redox mechanism. Meanwhile the un-reacted oxygen oxidized CO supplied as the reducing agent and the temperature in the catalyst packed bed also increased due to the combustion of CO. It was concluded that the rapidly increasing temperature in the packed bed can induce the catalytic deactivation such as the sintering of active components.

• Journal of Sensor Science and Technology
• /
• v.1 no.1
• /
• pp.59-66
• /
• 1992

To develop the highly sensitive TLD radiation sensors, $BaSO_{4}$ : Eu-PTFE TLDs are fabricated by polymerizing the PTFE(polytetrafluoroethylene) with $BaSO_{4}$ : Eu TL phosphors. The $BaSO_{4}$ : Eu TL phosphors having the highest sensitivity of $X/{\gamma}$-rays are obtained by sintering at $1000^{\circ}C$ in $N_{2}$ atmosphere a mixture of $BaSO_{4}$ powder with 1mol% Eu($Eu_{2}O_{3}$), 6mol% $NH_{4}Cl$ and 5mol% $(NH_{4})_{2}SO_{4}$ which were co-precipitated in dilute sulfuric acid and then dried. The activation energy, frequency factor and kinetic order of $BaSO_{4}$ : Eu TL phosphor are 1.17eV, $3.6{\times}10^{11}/sec$ and 1.25, respectively. And the spectral peak of $BaSO_{4}$ : Eu is about 425nm. The optimum TL Phosphor content and thickness of the $BaSO_{4}$ : Eu-PTFE TLD are 40wt% and $105.7mg/cm^{2}$. The optimum polymerization temperature and time for fabrication of $BaSO_{4}$ : Eu-PTFE TLDs are $380^{\circ}C$ and 2 hours in air, respectively. The linear dose range to ${\gamma}$ rays is 0.01-20Gy and fading rate is about 10%/60hours.