• Journal of the Korean Ceramic Society
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• v.31 no.12
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• pp.1545-1551
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• 1994

Various kinetic parameters of the nucleation and crystallization in anorthite glass (CaO.Al2O3.2SiO2) were calculated by nonisothermal differential thermal analysis. Base glass and glass with TiO2 were prepared by melting. In base glass, the temperature where nucleation can occur ranges from 85$0^{\circ}C$ to 9$25^{\circ}C$ and the temperature for maximum nucleation was 900$\pm$5$^{\circ}C$. In glass with TiO2, the nucleation temperature range was 800~875$^{\circ}C$ and the maximum nucleation temperature was 850$\pm$5$^{\circ}C$. Kissinger equation, Bansal equation, and modified Ozawa equation were used for calculating activation energy for crystallization, Ec. The results showed the same activation energies for both glasses with and without TiO2 in the different equations. The shape of maximum exotherm peak and Ozawa equation were used for Avrami exponent, n. The n value for each glass was 2, indicating that each glass crystallized primarily by bulk crystallization.

• Korean Journal of Food Science and Technology
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• v.14 no.1
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• pp.80-81
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• 1982

Staling rates of cooked rice from Akibare (Japonica) and Milyang 23 (Indica) stored at $21^{\circ}C$ and $72^{\circ}C$ were analyzed using the expression ${\theta}={\exp}\;(-kt^n)$, where ${\theta}$ in the fraction of uncrystallized material remaining after time t. The values for the rate constant (k) indicated that the firming process for both rices was not dependent on the variety, but was dependent on the storage temperature. The Avrami exponent (n) was found to be unity at two temperatures, suggesting that the staling of cooked rice is characterized by instantaneous nucleation followed by rod-like growth of starch crystals.

• Transactions of Materials Processing
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• v.10 no.1
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• pp.35-41
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• 2001

The high temperature deformation behavior of SCM 440 can be characterized by the hot torsion test in the temperature ranges of $900^{\circ}C$~$1100^{\circ}C$ and strain rate ranges of 0.05/sec~5/sec. The aim of this paper is to establish the quantitative equation of the volume fraction of dynamic recrystallization (DRX) as a function of processing variables, such as strain rate ($\varepsilon$), temperature (T), and strain ('$\varepsilon$). During hot deformation, the evolution of microstructure could be analyzed from work hardening rate ($\theta$). For the exact prediction of dynamic softening mechanism the critical strain ($\varepsilon_c$), the strain for maximum softening rate ($\varepsilon^*$ and Avrami' exponent (m') were quantitatively expressed by dimensionless parameter, Z/A, respectively. The transformation-effective strain-temperature curve for DRX could be composed. It was found that the calculated results were agreed with the experimental data for the steel at any deformation conditions.

• Journal of the Korean Magnetics Society
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• v.5 no.5
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• pp.511-514
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• 1995

The crystallization kinetics of $Fe_{73.5}Si_{13.5}B_{9}Cu_{1}Nb_{3}$ amorphous alloy has been investigated using differential scanning calorimetry (DSC). The crystallization process had two stages, i.e. precipitation of the $\alpha$-Fe(Si) solid solution and the tetragonal borides. The isothermal transformation data of the amorphous alloy has been fitted successfully to the generalized Johnson-Mehl-Avrami equation. The mean time exponent, n, obtained is close to 2.5. The value of n=2.5 may be interpreted as being due to a diffusion-controlled transformation process with a constant nucleation rate, one likely transformation mode for the crystallization of metallic amorphous alloys. The activation energy of the overall crystallization process deduced from the time to 50% crystallization are about 81 kcal/mole. The value is of the same order as those estimated from viscous flow.

• Journal of Powder Materials
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• v.16 no.1
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• pp.9-15
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• 2009

Amorphization and crystallization behaviors of $Ti_{50}Cu_{50}Ni_{20}Al_{10}$ powders during high-energy ball milling and subsequent heat treatment were studied. Full amorphization obtained after milling for 30 h was confirmed by X-ray diffraction and transmission electron microscope. The morphology of powders prepared using different milling times was observed by field-emission scanning electron microscope. The powders developed a fine, layered, homogeneous structure with prolonged milling. The crystallization behavior showed that the glass transition, $T_g$, onset crystallization, $T_x$, and super cooled liquid range ${\Delta}T=T_x-T_g$ were 691,771 and 80 K, respectively. The isothermal transformation kinetics was analyzed by the John-Mehn-Avrami equation. The Avrami exponent was close to 2.5, which corresponds to the transformation process with a diffusion-controlled type at nearly constant nucleation rate. The activation energy of crystallization for the alloy in the isothermal annealing process calculated using an Arrhenius plot was 345 kJ/mol.

• Korean Journal of Materials Research
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• v.26 no.1
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• pp.54-60
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• 2016

We have investigated the crystallization mechanism of the lithium disilicate ($Li_2O-2SiO_2$, LSO) glass particles with different sizes by isothermal and non-isothermal processes. The LSO glass was fabricated by rapid quenching of melt. X-ray diffraction and differential scanning calorimetry measurements were performed. Different crystallization models of Johnson-Mehl-Avrami, modified Ozawa and Arrhenius were adopted to analyze the thermal measurements. The activation energy E and the Avrami exponent n, which describe a crystallization mechanism, were obtained for three different glass particle sizes. Values of E and n for the glass particle with size under $45{\mu}m$, $75{\sim}106{\mu}m$, and $125{\sim}150{\mu}m$, were 2.28 eV, 2.21 eV, 2.19 eV, and ~1.5 for the isothermal process, respectively. Those values for the non-isothermal process were 2.4 eV, 2.3 eV, 2.2 eV, and ~1.3, for the isothermal process, respectively. The obtained values of the crystallization parameters indicate that the crystallization occurs through the decreasing nucleation rate with a diffusion controlled growth, irrespective to the particle sizes. It is also concluded that the smaller glass particles require the higher heat absorption to be crystallized.

• Korean Journal of Food Science and Technology
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• v.29 no.5
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• pp.982-986
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• 1997

Propolis extract was added to white bread(P1-1.48%, P2-0.74%, P3-0.37%), prepared in the straight-dough method, and its effects on shelf-life, antimicrobial activity, staling and sensory evaluation of white bread were investigated. In all P1, P2 samples, added propolis inhibited the growth of fungi, and the more propolis extract was added, the higher degree of inhibition of fungal growth was observed. The staling rates of white breads with P1, P2 and P3 were retarded by 22.5%, 19.2% and 6.4% respectively compared to that of control, and the Avrami exponent was similar in all samples. As a result of sensory evaluation, flavor, off-flavor, texture and overall acceptability of P2 and P3 were not significantly different from that of control.

• Journal of the Korean Society of Food Science and Nutrition
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• v.32 no.8
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• pp.1262-1269
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• 2003

In this study, enzymes were investigated as an antistaling agent for a Korean rice cake. Thermograms by a DSC demonstrated that the gelatinization-onset temperature of the Korean rice cake was at its lowest temperature of 71.1$^{\circ}C$ with the GP (glucoamylase+pullulanase) treatment, followed by $\beta$-amylase and $\alpha$-amylase. The gelatinization peak temperature of the Korean rice cake with enzyme treatment was relatively lower compared to the control. Furthermore, the Korean rice cake with GP treatment showed the lowest peak temperature. Melting enthalpy of the Korean rice cake increased with the enzyme treatment, with $\beta$-amylase, followed by $\alpha$-amylase and GP. Melting enthalpy of the Korean rice cake with GP treatment was significantly lower compared to the $\beta$- and $\alpha$-amylase treatment. Recrystallinity in the case of GP treatment was also significantly lower than control. The range of Avrami exponent (n) was 0.90 ∼ 1.20 and the time constant of retrogradation (1/k) of the Korean rice cake crystalline decreased in the following order: GP, $\beta$-, $\alpha$ -amylase and control. Textural characteristics of the Korean rice cake with enzyme treatment differed greatly from that of control. The L＊ values of all the Korean rice cakes made without $\beta$-amylase decreased and the a＊ values were significantly different at p<0.05. The GP treatment altered the b＊ value toward blue color, whereas $\beta$-and $\alpha$-amylase changed to the direction to yellow color. In sensory evaluation, the Korean rice cake with enzyme treatment showed higher evaluation compared to control.

• Journal of the East Asian Society of Dietary Life
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• v.27 no.1
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• pp.41-49
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• 2017

This study investigated the effects of teff flour on the properties of pound cakes. Five types of pound cakes were made by addition of 0% (Control), 5% (TF5), 10% (TF10), 15% (TF15), and 20% (TF20) of teff flour based on wheat flour. Specific gravity of pound cake batter showed no significant differences among samples as 0.54 (p<0.05). Baking loss was the highest in the control at 5.92% and the lowest in TF20 at 5.27%. Batter yield was the highest in TF20 at 94.73% and the lowest in control at 94.08%. Moisture content was the highest in TF20 at 23.68% and the lowest in control at 21.32%. pH showed no significant differences among samples at 7.61~7.65 (p<0.05). a-values of crumb significantly increased while L-values and b-values significantly decreased with added teff flour amounts. (p<0.05). ${\Delta}E$ values significantly increased with teff flour at 34.32~49.24 (p<0.05). Hardness was lowest in TF20 at $180.60g/cm^2$. Springiness was the lowest in TF20 at 85.37%. Cohesiveness showed no significant differences among samples (p<0.05). Chewiness was the lowest in TF20 at 172.17 g. Hardness more rapidly increased in control at $273.13{\sim}26,123.33g/cm^2$ than that of pound cakes with teff flour. Avrami exponent (n) was the highest in the control at 3.5987 and the lowest in TF20 at 1.2144. In sensory evaluation, flavor of TF20 was higher than that of the control at 4.43. Overall acceptability had a higher score in TF20 than in the control. It is considered that addition of 20% teff flour can improve the quality characteristics and retard retrogradation of pound cake.

• The Korean Journal of Food And Nutrition
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• v.17 no.3
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• pp.246-253
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• 2004

This study was carried out to examine softening stability, exponent of Avrami equation, color change, sensory characteristcs during storage when hydrocolloid was added to the sea tangle paste treated with acetic acid and heat treatment. Rate constant of solidification showed the least value of 0.05 in Avrami equation. In addition hardness of the softened sea tangle paste was not changed after two days of storage in case of carrageenan. Rate of hardness in the softened sea tangle paste formulated with carrageenan exhibited the lowest value of 0.28 kg/mm/day. Heat melting spreadability of the softened sea tangle paste showed the highest value in case of carrageenan and its fluid behavior was rheopectic. Viscosity change in the sea tangle paste formulated with carrageenan was the least during storage and its significant difference at the level of p < 0.05 was exhibited. Change of L, a and b value of softened sea tangle formulated with carrageenan during storage was significantly different at level of p<0.05. Color preference, odor, cohesiveness, softerness, process compatibility and overall acceptance of softened sea tangle were revealed to be in best when carrageenan was added. When hydrocolloid was added to the softened sea tangle paste, it showed the positive result in quality and storage stability of softened sea tangle paste. It was extremely effective on softening stability when carrageenan was added to the softened sea tangle paste.