• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2012.11a
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• pp.131-133
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• 2012

The photoluminescence (PT) properties of Al-doped ZnO thin films grown by the sol-gel dip-coating method have been investigated. At 12 K, nine distinct PL peaks were observed at 2.037, 2.592, 2.832, 3.027, 3.177, 3.216, 3.260, 3.303, and 3.354 eV. The deep-level emissions (2.037, 2.592, 2.832, and 3.027 eV) were attributed to native defects. The near-band-edge (NBE) emission peaks at 3.354, 3.303, 3.260, 3.216, and 3.177 eV were attributed to the emission of the neutral-donor-bound excitons (D0X), two-electron satellite (TES), free-to-neutral-acceptors (e,A0), donor-acceptor pairs (DAP), and second-order longitudinal optical (2LO) phonon replicas of the TES (TES-2LO), respectively. According to Haynes' empirical rule, we calculated the energy of a free exciton (FX) to be 3.374 eV. The thermal activation energy for D0X in the nanocrystalline ZnO thin film was found to be ~25 meV, corresponding to the thermal dissociation energy required for D0X transitions.

• Journal of the Korean Ceramic Society
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• v.45 no.11
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• pp.688-693
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• 2008

This paper presents a study on the photocatalytic reaction about the composite particles of $TiO_2$-coated phosphors under visible light irradiation. Nanocrystalline titanium dioxide layers were directly coated on the alkaline earth aluminate phosphor, $CaAl_2O_4:Eu^{2+},\;Nd^{3+}$ particles by an sol-gel processing method. The photocatalytic reaction was analyzed with the degradation of methylene blue (MB) aqueous solution under UV and visible light irradiations. $TiO_2$-coated phosphor powders showed different photocatalytic mechanism, compared with pure $TiO_2$ (P-25, Degussa). Under UV-irradiation, $TiO_2$-coated phosphor powders showed slow photocatalytic reactivity in the early stage and fast in the latter, compared with that of pure $TiO_2$. However, $TiO_2$-coated phosphor powders showed much faster photocatalytic reactivity than that of pure $TiO_2$ under visible irradiation. In addition, the characterizations of the $TiO_2$-coated phosphor powders were conducted by a X-ray diffractometer (XRD), transmission electron microscope (TEM), and energy dispersive spectroscopy (EDS).

• Korean Chemical Engineering Research
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• v.43 no.4
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• pp.503-510
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• 2005

In this research, composite alumina was prepared to add the various promoters by sol-gel method and examined its thermal stability. After sintering at $1,200^{\circ}C$, the thermal stability resulted in following order, $Si{\fallingdotseq}La$ > Ti > $Ba{\fallingdotseq}Ce$ > Y > $Zr{\fallingdotseq}Mg$, in accordance with adding the promoters. Especially in case of silica-added alumina, a phase transformation temperature to ${\alpha}$-alumina increased about $150^{\circ}C$ and after sintering at $1,200^{\circ}C$, it showed to maintain in ${\gamma}$-form and ${\delta}$-form alumina phase. Also it showed an increase of surface area from $3m^2/g$ to $71m^2/g$ compared with pure ${\alpha}$-alumina. In the case of silicaadded alumina, the characterization change of this alumina particle resulted in a delay of phase transformation because Si-O-Al bond was increased when sintered at high temperature. In case of lanthanum-added alumina, there was a sintering delay phenomenon in inter-particles as $LaAlO_3$ structure existed. The existence of lanthanum structure was confirmed by XRD and XPS analysis. It appeared on the alumina surface as $La_2O_3$ structure when it was sintered under $1,000^{\circ}C$, as the perovskite structure of $LaAlO_3$ at above $1,000^{\circ}C$ and as the magneto-plumbite structure of $LaAl_{11}O_{18}$ at above $1,300^{\circ}C$.

• Journal of Nuclear Fuel Cycle and Waste Technology(JNFCWT)
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• v.5 no.3
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• pp.171-177
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• 2007

This study suggested a new method to stabilize molten salt wastes generated from the pyre-process for the spent fuel treatment. Using conventional sol-gel process, $SiO_2-Al_2O_3-P_2O_5$ (SAP) inorganic material that is reactive to metal chlorides were prepared. In this paper, the reactivity of SAP with the metal chlorides at $650{\sim}850$, the thermal stability of reaction products and their leach-resistance under the PCT-A test method were investigated. Alkali metal chlorides were converted into metal aluminosilicate($LixAlxSi1-_xO_{2-x}$) and metal phosphate($Li_3PO_4\;and\;Cs_2AlP_3O_{10}$) While alkali earth and rare earth chlorides were changed into only metal phosphates ($Sr_5(PO_4)_3Cl\;and\;CePO_4$). The conversion rate was about $96{\sim}99%$ at a salt waste/SAP weight ratio of 0.5 and a weight loss up to $1100^{\circ}C$ measured by thermogravimetric analysis were below 1wt%. The leach rates of Cs and Sr under the PCT-A test condition were about $10^{-2}g/m^2\;day\;and\;10^{-4}g/m^2\;day$. From these results, it could be concluded that SAP can be considered as an effective stabilizer for metal chlorides and the method using SAP will give a chance to reduce the volume of salt wasteform for the final disposal through further researches.

• Journal of the Korean Ceramic Society
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• v.42 no.7 s.278
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• pp.475-482
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• 2005

Zn$_{l-x}$Co$_{x}$O (x = 0.05 - 0.20) films were grown on Coming 7059 glass by sol-gel process. A homogeneous and stable Zn$_{l-x}$Co$_{x}$O sol was prepared by dissolving zinc acetate dihydrate (Zn(CH$_{3}$COO)$_{2}$$\cdot$2H$_{2}$O), cobalt acetate tetrahydrate ((CH$_{3}$)$_{2}$$\cdot$CHOH) and aluminium chloride hexahydrate (AlCl$_{3}$ $\cdot$ 6H$_{2}$O) as solute in solution of isopropanol ((CH$_{3}$)$_{2}$$\cdot$CHOH) and monoethanolamine (MEA:H$_{2}$NCH$_{2}$CH$_{2}$OH). The films grown by spin coating method were postheated in air at 650°C for 1 h and annealed in the condition of vacuum (5 $\times$ 10$^{-6}$ Torr) at 300$^{\circ}C$ for 30 min and investigated the nature of c-axis preferred orientation and physical properties with different Co concentrations. Znl_xCOxO thin films with different Co concentrations were well oriented along the c-axis, but especially a highly c-axis oriented Zn$_{l-x}$Co$_{x}$O thin film was grown at 10 at$\%$ Co concentration. The transmittance spectra showed that Zn$_{l-x}$Co$_{x}$O thin films occur typical d-d transitions and sp-d exchange interaction became activated with increasing Co concentration. The electrical resistivity of the films at 10 at$\%$ Co had the lowest value due to the highest c-axis orientation. X-ray photoelectron spectroscopy and alternating gradient magnetometer analyses indicated that no Co metal cluster was formed, and the ferromagnetic properties appeared, respectively. The characteristics of the electrical resistivity and room temperature ferromagnetism of Zn$_{l-x}$Co$_{x}$O thin films suggested the possibility for the application to dilute magnetic semiconductors.

• The Transactions of the Korean Institute of Electrical Engineers C
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• v.55 no.12
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• pp.555-559
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• 2006

Using the $Ba_{0.5}Sr_{0.5}TiO_3$(BST) powders prepared by the Sol-Gel method, the BST thick films were fabricated on the $Al_2O_3 $substrates coated with Pt by the screen printing method. Compared with pure BST thick films, the structural and dielectric properties of the BST thick films doped with $1{\sim}10$ wt % MgO were investigated. It was observed that the Mg substitution into BST causes a shift in the cubic-tetragonal BST phase transition peak to a lower temperature. The microstructure of the BST substituted with Mg was homogeneous and dense. Mg substitution into BST had a significant effect on the grain size reduction. Dielectric constant was decreased with increasing the MgO content and temperature. In the case of BST thick films doped with 1 wt% MgO, the relative permittivity and dielectric loss were 1581 and 1.4 % at 1 MHz.

• Journal of the Korean Chemical Society
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• v.9 no.1
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• pp.16-22
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• 1965

The time-lag-effect of alkali salts on the gelation of sodium alginate-$CaSO_4{\cdot}$1/2 $H_2O$ is compared with Miyake's data, and then the formation rate of the elastics measured by the continuous method (an improved Schwedoff's method) and the change of rigidity with metallic oxides are studied as follows: (1) The gelation processes of sodium alginate and $CaSO_4{\cdot}$1/2 $H_2O$-aqueous sol are studied by measuring, continuously the increases of tensions ofsamples. (2) The time-lag-effect of $Na_3PO_4$ on the formation rate of the elastic gel is larger than that of $Na_2CO_3$, but the difference between the effects of the two alkali salts on the rate is found not so greater than predicted in Miyake's data. (3) Any regularities of the effect on the rate by metallic oxides are not observed. The increasing effects of the rates of $SiO_2$ and MgO are relatively large, and that of ZnO is relatively small. However, $Al_2O_3$, $Sb_2O_3$ and $TiO_2$show some decreasing effects. As a result it is noted that the regularities do not depend on the effect of oxide species and their amounts. (4) It is not found proportionality between the rigidity and the gelation rate. However, the increasing effect of the rigidity with the addition of metallic oxides can be observed. The rigidity increasing rate of MgO is the largest of them.

• Journal of Sensor Science and Technology
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• v.7 no.3
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• pp.188-196
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• 1998

The sensing and electrical characteristics of $WO_{3}$-based n-type semiconductor gas sensors are investigated. In normal air condition, $TiO_{2}$(4 wt. %)-doped $WO_{3}$-based sensor fabricated without any binder shows the grain boundary ( GB ) potential barrier height of 0.26 V. Sensors fabricated with alumina, PVA and silica sol binders show 0.17, 0.22 and 0.26 V of GB potential barrier height, respectively. In the ambience of 120 ppm $NO_{x}$ concentration, the GB potential barrier height of the sensor fablicated without binder is increased to 0.59 V. The sensors were fabricated with alumina, PVA, silica sol binders show 0.43, 0.66 and 0.52 V of potential barrier, respectively. Thus the variation of the potential barrier at GB is largest in the sensor fabricated with the PVA binder. This is found to be the main reason why the sensor fabricated with the PVA binder shows the best sensitivity. It is also found that the decrease of sensitivity at a temperature higher than the optimum operation temperature is due to the temperature dependence of the sensor resistance in normal air condition rather than the desorption of the adsorbed $NO_{x}$ gas particles. In the ambience of 250 ppm CO concentration, the GB potential barrier heights of the sensors fabricated without binder and with PVA binder are about 0.2 V showing negligible change compared to the case of normal air ambience. This fact indicates that these sensors are good candidates for the selective detection of $NO_{x}$ gas in the mixture of CO and $NO_{x}$ gases.

• Proceedings of the KIEE Conference
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• 2004.11a
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• pp.180-182
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• 2004

Polycrystalline $BaTiO_3/SrTiO_3$ powder was prepared by sol-gel process and the multilayered thick films were prepared on the $Al_2O_3$ substrates by screen printing method. The films were sintered at $1400^{\circ}C$ for 2 hours in the air. The structural and dielectric properties were investigated, The X-ray diffraction (XRD) patterns indicate that the BST phase and porocity were formed in the interface of $BaTiO_3/SrTiO_3$ multilayered thick films. The dielectric constant and the dielectric loss of the BT/ST/BT/ST multilayered thick films were about 247 and 0.84% at 1MHz.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2005.11a
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• pp.329-334
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• 2005

The rocket grade hydrogen peroxide has been widely used as a monopropellant in propulsion systems. Conventional decomposition of hydrogen peroxide, however, requires preheating before feeding into the reactor. In the present paper, we described an experimental study of a catalytic reactor bed that employs multiple catalysts to enhance the low temperature response in the vicinity of the reactor inlet. $K_2MnO_4$ is experimentally chose as the inlet catalyst from the candidates of silver, platinum, $La_{0.8}Sr_{0.2}CoO_3(LSC),\;and\;K_2MnO_4$. We developed new synthesis and coating method using modified alumina sol-gel method to strengthen the adhesion of $K_2MnO_4$ catalyst. from the vaporizer experiment with hydrogen peroxide at room temperature, satisfactory vaporizing performance was measured.