• Journal of Hydrogen and New Energy
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• v.18 no.2
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• pp.116-123
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• 2007

[ $La_{0.5}Ce_{0.5}Co_{1-x}Cu_xO_{3-{\alpha}}$ ](X=0, 0.1, 0.3, 0.5) perovskites were prepared by coprecipitation method at pH 7 or pH 11 and its catalytic activity of selective CO oxidation was investigated. The characteristics of these catalysts were analyzed by $N_2$ adsorption, X-ray diffraction(XRD), SEM, $O_2$-temperature programmed desorption(TPD). The pH value at a preparation step made effect on particle morphology. The smaller particle was obtained with a condition of pH 7. The better catalytic activity was observed using catalysts prepared at pH 7 than pH 11. The maximum CO conversion of 98% was observed over $La_{0.5}Ce_{0.5}Co_{0.7}Cu_{0.3}O_{3-{\alpha}}$ at $320^{\circ}C$. Below $200^{\circ}C$, the most active catalyst was $La_{0.5}Ce_{0.5}Co_{0.9}Cu_{0.1}O_{3-{\alpha}}$, of which conversion was 92% at $200^{\circ}C$. By the substitution of Cu, the evolution of ${\alpha}$-oxygen was remarkably enhanced regardless of pH value at preparation step according to $O_2$-TPD. Among the different ${\alpha}$-oxygen species, the oxygen species evolved between $400^{\circ}C$ and $500^{\circ}C$, gave the better catalytic performance for selective CO oxidation including $La_{0.5}Ce_{0.5}CoO_3$ in which Cu was absent.

• Journal of the Korean Chemical Society
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• v.19 no.2
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• pp.85-91
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• 1975

The crystal structure of piperidinothiosemicarbazide, $C_6H_{13}N_3S$, has been determined by single crystal X-ray analysis. The space group is P21/c with four molecules in the unit cell of dimensions $a=14.68{\pm}0.04,\;b=4.59{\pm}0.02,\;c=12.92{\pm}0.04{\AA}\;and\;{\beta}=109.4{\pm}0.2^{\circ}$. Three-dimensional photographic intensities were estimated visually. The structure has been solved by an interpretation of a Patterson synthesis and refined by block-diagonal least-squares methods to give a final R value of 0.14 for 378 observed independent reflections. There are two independent hydrogen bonds in the structure. One of them is of the type N-H${\ldots}$S with the length 3.28 and $3.39{\AA}$, and another is of the type N-H${\ldots}$N with the length $3.03{\AA}$. Apart from the hydrogen bonding system the molecules are held together in the crystal by van der Waals forces.

• Journal of the Korean Chemical Society
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• v.7 no.4
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• pp.283-287
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• 1963

The distribution ratio of hydrogen cupferrate in $H_2O-CHCl_3$ system was considered as a function of pH ($HClO_4$), ionic strength ($NaClO_4$), and cupferron concentration in perchloric acid media, respectively. The values were independent upon pH (1.50∼3.00 range) and ionic strength (0.1∼2.00 range), but they increased as increasing the cupferron concentration in the acidic media. At the infinite dilution, the thermodynamic distribution ratio between chloroform and aqueous phase was 120. 0. The activity coefficients of hydrogen cupferrate in chloroform solution were determined by the distribution ratio. This activity coefficient may be calculated by using the empirical equation, $-log\;f_{CHCl3}=0.1285C_{CHCl3}+{7.775C^2}_{CHCl3}$ which represents the experimental data quite well for the solution in 0.1 mole/l order of hydrogen cupferrate concentration.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.14 no.10
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• pp.808-814
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• 2001

The electrical properties and stabiltiy of Pr$_{6}$O$_{11}$ -based ZnO varistors, which are composed of ZnO-Pr$_{6}$O$_{11}$-Cr$_{2}$O$_{3}$-Er$_{2}$O$_{3}$ based ceramics, were investigated in the Er$_{2}$O$_{3}$ content range of 0.5 to 2.0 mol%. As Er$_{2}$O$_{3}$content is increased up to approximaterly 1.0mol%, the nonlinearity was decreased. Increasing Er$_{2}$O$_{3}$ content further caused the nonlinearity to increase. The varistors with 2.0 mol% Er$_{2}$O$_{3}$ exhibited a high nonlinearity, in which the nonlinear exponent is 47.41 and the leakage current is 1.82 $\mu$A. Furthermore, they showed a very excellent stability, in which the variation rates of the varistor voltage, the nonlinear exponent, and leakage current are -0.52%, -4.09%, and 152.75%, respectively, under DC accelerated aging stress, such as (0.80 V$_{1mA}$9$0^{\circ}C$/12h)+(0.85 V$_{1mA}$115$^{\circ}C$/12h)+(0.90 V$_{1mA}$12$0^{\circ}C$/12h)+(0.95 V$_{1mA}$1$25^{\circ}C$/12h)+(0.95 V$_{1mA}$1$25^{\circ}C$/12h).2h).TEX>/12h).2h).

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.8 no.4
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• pp.634-639
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• 1998

$Y_2O_3$ and $Nb_2O_5$ co-doped zirconia composites containing 10~30 vol% $Al_2O_3$ with two different particle sizes were sintered for 5 h at $1550^{\circ}C$ to evaluate low-temperature phase stability of the composite using X-ray diffractometry after heat-treatments for 1000 h at $250^{\circ}C$ in air or for 5 h at $180^{\circ}C$ in 0.3 MPa $H_2O$ vapor pressure. No tetragonal to monoclinic phase transformation during degradation, so called enhanced low-temperature phase stability, was observed for all composites. It is concluded that Nb addition to the composite for the phase stability is more effective than $Al_2O_3$ addition. The optimum combination of strength (670 MPa) and fracture toughness ($7.1{\textrm} {MPam}^{1/2}$) were obtained for the composite containing 20 vol% of $Al_2O_3$ with 2.8 $\mu$m to 0.2 $\mu$m, the flexural strength increases but the fracture toughness decreases.

• Archives of Pharmacal Research
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• v.16 no.1
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• pp.75-77
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• 1993

The cycloaddition reaction of N-phenyl-C-cinnamonitrilimine 4 to coumarin leads to the for-mation of 3-styrylbenzopyrano[4,3-c]pyrazole derivative 6, whereas 3-phenylsulfonylcoumarin 9 or 3-bromocoumain 10 or 3-cyanocoumarin 11 gives 1-styrylbenzopyrano[3,4]pyrazole derivative 7. Also, the cycloaddition of 4 to 3-acetylocoumarin 15 and 3-benzoylocumain 16 gives the corresponding dihydropyrano[3,4-c]pyrazole adducts 17 and 18 respectively. Oxidation of 17 and 18 gives 7.

• Transactions of Materials Processing
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• v.8 no.3
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• pp.259-259
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• 1999

TiC ceramic particulate-reinforced titanium matrix composites were fabricated and the resultant densification, microstructure, and static and dynamic mechanical properties were studied. Comparing Ti with TiH₂powders as host materials for TiC ceramic reinforcement by pressureless vacuum sintering, TiH₂-started composites showed better sinterability and resistance to both elastic and plastic deformation than Ti-started ones. When TiH₂and TiH₂-45 vol.%TiC samples were hot pressed, TiH₂matrices transformed to alpha prime Ti and alpha Ti phase, respectively. It is interpreted that the diffusion of an alpha stabilizer carbon from TiC into the matrix is one of the plausible reasons far such a microstructural difference. The 0.2% offset yield strengths of the hot pressed TiH₂and TiH₂-45 vol.%TiC samples were 1008 and 1446 MPa, respectively, in a static compressive mode (strain rate of 1×$10^{-3}$/s). Dynamic compressive strengths of the samples were 1600 and 2060 MPa, respectively, at a strain rate of 4×10³/s.

• Bulletin of the Korean Chemical Society
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• v.14 no.1
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• pp.101-107
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• 1993

Ab initio calculations are carried out at the 6-311G$^{**}$ level for the $C_{2v}$ interactions of Be and Li atoms with acetylene molecule. The main contribution to the deep minima on the $^3B_2\;BeC_2H_2\;and\;^2B_2 LiC_2H_2$ potential energy curves is the b_2\;(2p(3b_2)-l{\pi}_g^*(4b_2))$ interaction, the $a_1\;(2s(6a_1)-I{\pi}_u(5a_1))$ interaction playing a relatively minor role. The exo deflection of the C-H bonds is basically favored, as in the $b_2$ interaction, due to steric crowding between the metal and H atoms, but the strong in-phase orbital interaction, or mixing, of the $a_1$ symmetry hydrogen orbital with the $5a'_1,\;6a'_1,\;and\;7a'_1$ orbitals can cause a small endo deflection in the repulsive complexes. The Be complex is more stable than the Li complex due to the double occupancy of the 2s orbital in Be. The stability and structure of the $MC_2H_2$ complexes are in general determined by the occupancy of the singly occupied frontier orbitals.

• Applied Biological Chemistry
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• v.37 no.6
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• pp.447-450
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• 1994

Rate of hydrolysis ethylene phosphate, dimethylphosphate and hydroxyethylmethylphosphate in neutral water have been measured. Hydrolysis of ethylene phosphate proceeds with P-0 bond cleavage $(k_{obs}=3{\times}10^{-7}s^{-1}\;at\;100^{\circ}C,\;{\Delta}H{\neq}=24\;kcal,\;{\Delta}S{\neq}=25.5\;eu)$. In constrast, hydrolysis of dimethylphosphate proceeds with C-O bond cleavage $(k_{obs}=3{\times}10^{-7}s^{-1}\;at\;150^{\circ}C)$. The rate constant for P-O bond cleavage of dimethylphosphate is estimated at $1{\times}10^{-11}s^{-1}\;at\;150^{\circ}C,\;({\Delta}H{\neq}=36\;kcal,\;{\Delta}S{\neq}=25.5\;eu)$. A phosphodiesterase catalyzed hydrolysis of dimethylphosphate is $10^{17}$ times faster than the simple water rate. The observed rate of hydrolysis of hydroxyethylmethylphosphate is comparable to that of dimethylphosphate indicating C-O bond cleavage $(k_{obs}=6{\times}10^{-7}s^{-1}\;at\;150^{\circ}C)$.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2001.07a
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• pp.431-434
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• 2001

The mechanical and phase transformation of the cold isostatically pressed $\alpha$-SiC ceramic were investigated as a function of the sintering temperature. The result of phase analysis by XRD revealed 6H, 4H, 3C and phase transformation between 6H and 4H showed a sudden change over 200$0^{\circ}C$. However, the alongrightarrow$\beta$ reverse transformation did not occur to any sintering temperature. The relative density and the mechanical properties of $\alpha$-SiC ceramic was increased with increased sintering temperature. The flexural strength rapidly inclosed below 210$0^{\circ}C$ and showed the highest value of 410 MPa at 220$0^{\circ}C$. This reason is because crack was propagated through surface flaw. The fracture toughness showed the highest value of 3.3 MPa.m$_{1}$2/ at 220$0^{\circ}C$.