• Journal of the Korean Ceramic Society
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• v.38 no.10
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• pp.881-885
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• 2001

Kinetics and mechanisms of intermediate phases formation in $Ba(Mg_{1/3}Ta_{2/3})O_3$, obtained by a solid state reaction were studied. $Ba{Ta_2}{O_6}$ and ${Ba_4}{Ta_2}{O_9}$ as intermediate products were first formed at $700^{\circ}C$. $Ba(Mg_{1/3}Ta_{2/3})O_3$ was appeared at $800^{\circ}C$. Several reactions take place on heating process. $Ba{Ta_2}{O_6}$ is found at the first stage of the reaction, and then $Ba{Ta_2}{O_6}$ or ${Ba_4}{Ta_2}{O_9}$ react with MgO to form $Ba(Mg_{1/3}Ta_{2/3})O_3$. The reaction of $Ba(Mg_{1/3}Ta_{2/3})O_3$ formation does not complete until fired at $1350^{\circ}C$ for 60 min. The kinetics of solid-state reaction between powdered reactants was controlled by diffusion mechanism, and can be explained by the Jander's model for three-dimensional diffusion.

• Journal of the Korean Society of Food Science and Nutrition
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• v.34 no.7
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• pp.942-947
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• 2005

This study was investigated to analyze the effect of extracts from the Lepista nuda, on the antioxidant activity to form a part of studies on the functional materials of L. nuda. Antioxidant activity of L. nuda extracts was evaluated by measuring the electron-donating ability (EDA), the superoxide dismutase (SOD)-like activity, and the nitrite-scavenging ability. The EDAs of water and ethanol extracts at the concentration of 1,000 ppm by the rotary heating method from L. nuda were $60.47\%$ and $60.13\%$, respectively and those of water and ethanol extracts by microwave-assisted method were $87.73\%$ and $84.84\%$, respectively. The measurements of SOD-like activity were in the range of $24.58\%\~42.03\%$ at 1,000 ppm. EDA and SOD were increased with the concentrations of extracts. The nitrite-scavenging ability at the concentration of 1,000 ppm was the highest and $29.77\%$ at pH 1.2, and was decreased with an increment of pH value. These results indicated that microwave­assisted water extract from L. nuda showed the highest activities on the EDA and nitrate-scavenging ability, while the rotary heating ethanol extract had the highest effect on the SOD-like activity.