• Korean Journal of Materials Research
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• v.8 no.6
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• pp.545-550
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• 1998

Phase reactions at W /6H- SiC interfaces during heat treatments were investigated by X- Ray diffractometer and transmission electron microscopy. No detectable reactions were found after annealing at up to 900$0^{\circ}C$ whereas formation of $W_5Si_3$ and $W_2C$$0^{\circ}C$ This result is consistent with a previous report that the reactions between 3C-SiC and W occurs at llOOoe, and suggests that $W_5Si_3$ and $W_2C$ are the stable phases in this temperature range.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.14 no.5
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• pp.362-369
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• 2001

The electrical properties of varistors consisting of Zn-Pr-Co-Cr-Er oxides were investigated in the Er$_2$O$_3$content range of 0.0 to 2.0 mol%. the varistors without Er$_2$O$_3$ exhibited a relatively low nonlinearity, which was 14.24 in the nonlinear exponent and 21.47 $\mu$A in the leakage current. However, the varistors with Er$_2$O$_3$ sintered at 1335$^{\circ}C$ for 1h exhibited very high nonlinear exponent of 70, in particular, reaching a maximum value of 78.05 in 2.0 mol% Er$_2$O$_3$, and those sintered at 1335$^{\circ}C$ for 2h exhibited the nonlinear exponent close to 50, in particular, reaching a maximum value of52.76 in 0.5 mol% Er$_2$O$_3$. The others except for 0.5 mol% Er$_2$O$_3$-added varistors exhibited very high instability resulting in a thermal runaway within a short time, even a weak DC stress. Increasing soaking time decreased the nonlinearity, but increased the stability. The varistors containing 0.5mol% Er$_2$O$_3$ sintered for 2h exhibited excellent stability, in which the variation rate of the varistor voltage and nonlinear exponent was -1.70% and -7.15%, respectively, under more severe DC 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$_{1mA}$/15$0^{\circ}C$/12h).TEX>/12h).

• Bulletin of the Korean Chemical Society
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• v.18 no.8
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• pp.791-793
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• 1997

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.17 no.3
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• pp.278-282
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• 2004

The Hydrogenated amorphous carbon(a-C:H) thin films are deposited on silicon with a close field unbalanced magnetron(CFUBM) sputtering systems. The experimental data are obtained on the depositon rate and physical properties of a-C:H films using DC bias voltage and Ar/C$_2$H$_2$ pressure. The depostion rate and the surface roughness decrease with DC bias voltage, but the hardness of the thin films increases with DC bias voltage. And the position of G-peak moves to lower wavenumber indicating an increase in diamond-like carbon characteristics with the lower Ar/C$_2$H$_2$ pressure.

• Microbiology and Biotechnology Letters
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• v.2 no.3
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• pp.133-140
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• 1974

1) Two xylanase (designed as A and B) of Myriococcus albomyces were purified from an extract of wheat koji culture. Puriscation steps included first ammonium sulfate fractionation followed successively by SE-Sephadex column chromatgraphy. DEAE-Sephadex column chromatography and gel filtration on Sephadex G-100 repectively. 2) The optimum pH and pH stability for crude xylanse were found to be pH 5.0 and pH 4.0-7.0 respectively. 3) The optimium temperature was found to he 5$0^{\circ}C$ and for the thermal statbility of xylanase, the enryme incubated at $65^{\circ}C$ for 60min did not affect their stability. 4) The purised xylanase A and B were considered as liquefying xylanase and saccharogenic xylauase repectively. 5) The Bylanase A was most active at pH 4.0 and range of pH 3.0-8.0 at 3$0^{\circ}C$ for six hrs. The B was most active at pH 5.0 showing stability range of pH 4.0 to 8.5 at 3$0^{\circ}C$ for 6 hrs. incubation respectively. The Optimum temperature of xylanase A and B were found to be 7$0^{\circ}C$ and $65^{\circ}C$ for 60min repectively.

• Journal of the Institute of Electronics Engineers of Korea SD
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• v.46 no.6
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• pp.1-5
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• 2009

Analytical expressions for breakdown voltage and specific on-resistance of 6H-SiC PN diodes have been derived successfully by extracting an effective ionization coefficient from ionization coefficients for electron and hole in 6H-SiC. The breakdown voltages induced from our analytical model are compared with experimental results. The variation of specific on-resistance as a function of doping concentration is also compared with the one reported previously. Good fits with experimental results are found for the breakdown voltage within 10% in error for the doping concentration in the range of $10^{15}{\sim}10^{18}cm^{-3}$. The analytic results show good agreement with the numerical data for the specific on-resistance in the region of $5{\times}10^{15}{\sim}10^{16}cm^{-3}$.

• Journal of the Korean Society of Food Science and Nutrition
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• v.35 no.2
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• pp.212-218
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• 2006

Changes of paralytic shellfish poison (PSP) contents, toxicity and toxin composition with pH and storing periods at different temperature in toxic blue mussel, Mytilus edulis, were tested by using fluorometric HPLC method. Toxicity at pH 3 was the highest as 14.1 MU/g $(100\%)$ and showed 12.9 MU/g $(92.1\%)$ at pH 5, 9.0 MU/g $(63.8\%)$ at pH 7, 3.6 MU/g $(25.5\%)$ at pH 9 and 0.8 MU/g $(5.7\%)$ at pH 10 which suggested PSP was unstable at alkaline conditions. The decrease in toxicity during storage days was depend on pH and temperature. The toxicity markedly decreased until during the first S day storage $(19.9\~65.3\%)$ at all pH (3, 5, 7, 9) and temperature (30, 5, $-20^{\circ}C$), but, slightly decreased after then till to 30 days. C group toxin (C1 and C2) was the major components and other toxins such as GTX 1,2,3,4, STX and dcSTX were detected. Among the 8 toxins, GTX1,4, dcSTX and STX were firstly decreased according to the decreasing the toxicity at all processing conditions. The toxicity in blue mussel (14.1 MU/g) were able to remove by heating over 10 minutes at pH higher than 7.

• Bulletin of the Korean Chemical Society
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• v.24 no.3
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• pp.369-376
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• 2003

Coulson (ZINDO), Mulliken $(MP2/6-31G^*)$ and Natural $(MP2/6-31G^*)$ population analyses of several large molecules were performed by the Fragment Reassociation (FR) method. The agreement between the conventional ZINDO (or conventional MP2) and FR-ZINDO (or FR-MP2) charges of these molecules was excellent. The standard deviations of the FR-ZINDO net atomic charges from the conventional ZINDO net atomic charges were 0.0008 for $C_{10}H_{22}$ (32 atoms), 0.0012 for $NH_2-C_{16}O_2H_{28}-COOH$ (53 atoms), 0.0014 for $NH_3^+-C_{16}O_2H_{28}-COOH$ (54 atoms), 0.0017 for $NH_2-C_{16}O_2H_{28}-COO^-$ (52 atoms), 0.0019 for $NH_3^+-C_{16}O_2H_{28}-COO^-$ (53 atoms), 0.0024 for a conjugated model $(O=CH-(CH=CH)_{15}-C=O-(CH=CH)_{12}-CH=CH_2)$, 118 atoms), 0.0038 for aglycoristocetin $(C_{60}N_7O_{19}H_{52}^+$, 138 atoms), 0.0023 for a polypropylene model complexed with a zirconocene catalyst $(C_{68}H-{121}Zr^+$, 190 atoms) and 0.0013 for magainin $(C_{112}N_{29}O_{28}SH_{177}$, 347 atoms), respectively. The standard deviations of the FR-MP2 Mulliken (or Natural) partial atomic charges from the conventional ones were 0.0016 (or 0.0016) for $C_{10}H_{22}$, 0.0019 (or 0.0018) for $NH_2-C_{16}O_2H_{28}-COOH$ and 0.0033 (or 0.0023) for $NH_3^+-C_{16}O_2H_{28}-COO^-$, respectively. These errors were attributed to the shape of molecules, the choice of fragments and the degree of ionic characters of molecules as well as the choice of methods. The CPU time of aglycoristocetin, conjugated model, polypropylene model complexed with zirconocene and magainin computed by the FR-ZINDO method was respectively 2, 4, 6 and 21 times faster than that by the normal ZINDO method. The CPU time of $NH_2-C_{16}O_2H_{28}-COOH\;and\;NH_3^+-C_{16}O_2H_{28}-COO^-$ computed by the FR-MP2 method was, respectively, 6 and 20 times faster than that by the normal MP2 method. The largest molecule calculated by the FR-ZINDO method was B-DNA (766 atoms). These results will enable us to compute atomic charges of huge molecules near future.

• Korean Journal of Materials Research
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• v.13 no.4
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• pp.246-250
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• 2003

Calcium phosphate was prepared by chemical reaction formula using Oyster shells and $H_3$$PO_4$solutions. After added to 0.1 M∼0.9$ M H_3$$PO_4$ solution for oyster shell, prepared powders were investigated for heating properties and formation phase with heat treatment temperatures. As the results of XRD analysis of heated powders at $500^{\circ}C$∼$1200^{\circ}C$,$ CaCO_3$ phases were observed at the temperature of below 900 TEX>$^{\circ}C$ and in the condition of 0.1 M∼0.9 M $H_3$$PO_4$ solutions. However, $CaCO_3$, $CaPO_3$(OH) and $Ca_3$($PO_4$)$_2$ phases were appeared at the temperature range between $500∼900^{\circ}C$ and in the solution of 0.7 M to 0.9 M $H_3$$PO_4$. $Ca_{ 5}$($PO_4$)$_3$(OH) and CaO phases due to the decarbonation of oyster shells($CaCO_3$) were appeared at above $1000^{\circ}C$ and in the solution of below 0.5 M $H_3$X$PO_4$. However in the case of above 0.7 M $H_3$$H_4$ solutions, $Ca_{5}$ ($PO_4$)$_3$(OH) was decomposed into $Ca_3$($PO_4$)$_2$ at more higher 100$0^{\circ}C$. Thus $Ca_3$(X$Ca_4$)$_2$ phases were appeared at higher than 100$0^{\circ}C$.

• Journal of Sensor Science and Technology
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• v.18 no.1
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• pp.54-62
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• 2009

${Co_3}{O_4}$ and ${Co_3}{O_4}$-based thick films with additives such as ${Co_3}{O_4}-{Fe_2}{O_3}$(5 wt.%), ${Co_3}{O_4}-{SnO_2}$ (5 wt.%), ${Co_3}{O_4}-{WO_3}$(5 wt.%) and ${Co_3}{O_4}$-ZnO(5 wt.%) were fabricated by screen printing method on alumina substrates. Their structural properties were examined by XRD and SEM. The sensitivities to iso-${C_4}H_{10}$, $CH_4$, CO, $NH_3$ and NO gases were investigated with the thick films heat treated at $400^{\circ}C$, $500^{\circ}C$ and $600^{\circ}C$. From the gas sensing properties of the films, the films showed p-type semiconductor behaviors. ${Co_3}{O_4}-{SnO_2}$(5 wt.%) thick film heat treated at $600^{\circ}C$ showed higher sensitivity to i-${C_4}H_{10}$ and CO gases than other thick-films. ${Co_3}{O_4}-{SnO_2}$(5 wt.%) thick film heat treated at $600^{\circ}C$ showed the sensitivity of 170 % to 3000 ppm iso-${C_4}H_{10}$ gas and 100 % to 100 ppm CO gas at the working temperature of $250^{\circ}C$. The response time to i-${C_4}H_{10}$ and CO gases showed rise time of about 10 seconds and fall time of about $3{\sim}4$ minutes. The selectivity to i-${C_4}H_{10}$ and CO gases was enhanced in the ${Co_3}{O_4}-{SnO_2}$(5 wt.%) thick film.