Ozawa Equation (ozawa + equation)

Distribution by Scientific Domains


Selected Abstracts


Nonisothermal and isothermal crystallization kinetics of nylon-12

JOURNAL OF APPLIED POLYMER SCIENCE, Issue 2 2008
Neil L. A. McFerran
Abstract The isothermal and nonisothermal crystallization behavior of Nylon 12 was investigated using differential scanning calorimetry (DSC). An Avrami analysis was used to study the isothermal crystallization kinetics of Nylon 12, the Avrami exponent (n) determined and its relevance to crystal growth discussed and an activation energy for the process evaluated using an Arrhenius type expression. The Lauritzen and Hoffman analysis was used to examine the spherulitic growth process of the primary crystallization stage of Nylon 12. The surface-free energy and work of chain folding were calculated using a procedure reported by Hoffmann and the work of chain folding per molecular fold (,) and chain stiffness of Nylon 12 (q) was calculated and compared to values reported for Nylons 6,6 and 11. The Jeziorny modification of the Avrami analysis, Caz and Chuah average Avrami parameter methods and Ozawa equation were used in an attempt to model the nonisothermal crystallization kinetics of Nylon 12. A combined Avrami and Ozawa treatment, described by Liu, was used to more accurately model the nonisothermal crystallization kinetics of Nylon 12. The activation energy for nonisothermal crystallization processes was determined using the Kissinger method for Nylon 12 and compared with values reported previously for Nylon 6,6 and Nylon 11. 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 [source]


Nucleation and Crystallization of a Lead Halide Phosphate Glass by Differential Thermal Analysis

JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 4 2002
Hongsheng Zhao
The nucleation and crystallization mechanisms of a lead halide phosphate glass [40P2O530PbBr230PbF2 (mol%)] were investigated by differential thermal analysis (DTA) and X-ray diffraction analysis. There were two crystalline phases in the crystallized samples: the major phase was PbP2O4, and the minor phase was PbP2O6. The average activation energy for crystallization, E, for two different particle sizes of this glass was determined to be 119 4 kJ/mol by the Kissinger method and 124 4 kJ/mol by the Augis,Bennett method. The Avrami constants were determined to be 1.6 and 2.5 for particle sizes of 203 and 1040 ,m, respectively, by the Ozawa equation, and 1.7 and 2.4 for particle sizes of 203 and 1040 ,m, respectively, by the Augis,Bennett equation. The decrease in the crystallization peak height in the DTA curve with increasing particle size suggested that the particles crystallize primarily by surface crystallization. A nucleation-rate type curve was determined by plotting either the reciprocal of the temperature corresponding to the crystallization peak maximum, 1/Tp, or the height of the crystallization peak, (,T)p, as a function of nucleation temperature, Tn. The temperature where nucleation can occur for this glass ranges from 360,450C and the maximum nucleation rate is at 420 10C. [source]


Nonisothermal melt crystallization kinetics of poly(ethylene terephthalate)/Barite nanocomposites

POLYMER COMPOSITES, Issue 9 2010
Chunhua Ge
Poly(ethylene terephthalate) (PET)/Barite nanocomposites were prepared by direct melt compounding. The nonisothermal melt crystallization kinetics of pure PET and PET/Barite nanocomposites, containing unmodified Barite and surface-modified Barite (SABarite), was investigated by differential scanning calorimetry (DSC) under different cooling rates. With the addition of barite nanoparticles, the crystallization peak became wider and shifted to higher temperature and the crystallization rate increased. Several analysis methods were used to describe the nonisothermal crystallization behavior of pure PET and its nanocomposites. The Jeziorny modification of the Avrami analysis was only valid for describing the early stage of crystallization but was not able to describe the later stage of PET crystallization. Also, the Ozawa method failed to describe the nonisothermal crystallization behavior of PET. A combined Avrami and Ozawa equation, developed by Liu, was used to more accurately model the nonisothermal crystallization kinetics of PET. The crystallization activation energies calculated by Kissinger, Takhor, and Augis-Bennett models were comparable. The results reveal that the different interfacial interactions between matrix and nanoparticles are responsible for the disparate effect on the crystallization ability of PET. POLYM. COMPOS., 31:1504,1514, 2010. 2009 Society of Plastics Engineers [source]


The turning point on plots of log , and log t of Mo's equation

POLYMER INTERNATIONAL, Issue 7 2009
Jian-bin Song
Abstract BACKGROUND: Mo's equation based on the Avrami equation and Ozawa equation has been successfully used in non-isothermal crystallization kinetics by many researchers. However, in recent years we have found that plots of log ,,log t of Mo's equation are not straight lines, but there appears a turning point at , = 7 C min,1 or so. The aim of this article is to analyze in detail the reason for the occurrence of this turning point by studying the non-isothermal crystallization of poly(vinylidene fluoride) (PVDF) using differential scanning calorimetry. RESULTS: A turning point at about 7 C min,1 appeared on plots of log ,,log t. The cooling rate where the turning point occurred showed little change with increasing relative crystallinity, but the temperature decreased. It is noted that this turning-point temperature is lower than transition temperature of regime I , II reported for PVDF. CONCLUSION: We deemed that the occurrence of turning points on plots of log ,,log t of Mo's equation can be ascribed to the different crystallization regimes based on the Hoffman nucleation theory, and presumed that the turning point corresponded to transition of regime I , II. Finally, we considered that Mo's equation should be analyzed using two beelines, instead of one beeline. Copyright 2009 Society of Chemical Industry [source]


Nonisothermal crystallization behavior of a luminescent conjugated polymer, poly(9,9-dihexylfluorene- alt -2,5-didodecyloxybenzene)

POLYMER INTERNATIONAL, Issue 2 2007
Gui-Zhong Yang
Abstract The nonisothermal crystallization kinetics of poly(9,9-dihexylfluorene- alt -2,5-didodecyloxybenzene) (PF6OC12) from the melt were investigated using differential scanning calorimetry under different cooling rates. Several analysis methods were used to describe the nonisothermal crystallization behavior of PF6OC12. It was found that the modified Avrami method by Jeziorny was only valid for describing the early stage of crystallization but was not able to describe the later stage of PF6OC12 crystallization. Also, the Ozawa method failed to describe the nonisothermal crystallization behavior of PF6OC12. However, the method developed by combining the Avrami and Ozawa equations could successfully describe the nonisothermal crystallization kinetics of PF6OC12. According to the Kissinger method, the activation energy was determined to be 114.9 kJ mol,1 for the nonisothermal melt crystallization of PF6OC12. Copyright 2006 Society of Chemical Industry [source]