采用Brookfield黏度计对不同聚酯热熔胶样品进行黏度测试,根据Arrhenius方程得到样品相应的黏流活化能参数,进口样品的活化能值(56,76 k J/mol)大于国内样品(49,48 k J/mol),在低温下条件下国外进口样品的流动性好;通过在一定熔融温度...采用Brookfield黏度计对不同聚酯热熔胶样品进行黏度测试,根据Arrhenius方程得到样品相应的黏流活化能参数,进口样品的活化能值(56,76 k J/mol)大于国内样品(49,48 k J/mol),在低温下条件下国外进口样品的流动性好;通过在一定熔融温度下黏度随时间的变化,引入Avrami方程对其进行黏度随时间的变化表征,发现其lg[-ln(1-Xt)]～lg t关系图呈线性(线性度R=99%),并根据计算得到相关的降解速率常数Zt,温度越高速率常数越大;在发生高温凝胶的样品体系中,其黏度的Avrami方程发生线性偏离。展开更多
The primary crystallization of the Ti40Zr25NisCu9Bc18 amorphous alloy was studied by isochronal differential scanning calorimetry （DSC）. The activation energy was determined by the Kissinger-Akahim-Sunose method. Tr...The primary crystallization of the Ti40Zr25NisCu9Bc18 amorphous alloy was studied by isochronal differential scanning calorimetry （DSC）. The activation energy was determined by the Kissinger-Akahim-Sunose method. Trying to analyze the crystallization kinetics of the Ti40Zr25NigCu9Be18 amorphous alloy by two different methods, it was found that the crystallization kinetics did not obey the Johnson-Mehl-Avrami equation. A modified method in consideration of the impingement effect was proposed to perform kinetic analysis of the isochronal crystallization of this alloy. The kinetic parameters were then obtained by the linear fitting method based on the modified kinetic equation. The results show that the isochronal crystallization kinetics of the amorphous Ti40Zr25Ni8CugBe18 alloy is heating rate dependent, and the discrepancy between the Johnson-Mehl-Avrami method and the modified method increases with the increase of heating rate.展开更多
Classic Avrami model and its modifications have found diverse applications in describing the thermal and phase behaviors of inorganic metals and organic polymers. The direct introduction of classic Avrami equation to ...Classic Avrami model and its modifications have found diverse applications in describing the thermal and phase behaviors of inorganic metals and organic polymers. The direct introduction of classic Avrami equation to offer quantitative analyses of crystallization kinetic parameters for enantiomeric poly（lactic acid） （PLA） blends may, however, lead to contradictory conclusions. As revealed by this study, during the characterization of isothermal melt and cold crystallization for stereocomplex PLA containing equal-weight poly（L-lactic acid） and poly（D-lactic acid）, the kinetic parameters yielded by Avrami equation are not in line with the classic crystallization hypotheses or the direct morphological observations. The underlying mechanisms, to some extent, lie in the generation of stereocomplex crystals （SCs） during the cooling/heating which affects the subsequent crystallization dynamics. The huge gap between the melting enthalpies of 100% crystalline SCs （142 J/g） and homo-crystals （HCs, 93 J/g） is most likely responsible for the confusing kinetic parameters acquired from the deduction of Avrami equation, which is based on the integration of enthalpies as a function of crystallization time. This prompts for great care that the classic Avrami equation is not applicable to accurately describe the crystallization kinetics of stereocomplex PLA, given the generation of SCs prior to crystallization and the coexistence of HCs and SCs during crystallization.展开更多
文摘采用Brookfield黏度计对不同聚酯热熔胶样品进行黏度测试,根据Arrhenius方程得到样品相应的黏流活化能参数,进口样品的活化能值(56,76 k J/mol)大于国内样品(49,48 k J/mol),在低温下条件下国外进口样品的流动性好;通过在一定熔融温度下黏度随时间的变化,引入Avrami方程对其进行黏度随时间的变化表征,发现其lg[-ln(1-Xt)]～lg t关系图呈线性(线性度R=99%),并根据计算得到相关的降解速率常数Zt,温度越高速率常数越大;在发生高温凝胶的样品体系中,其黏度的Avrami方程发生线性偏离。
基金supported by the National Natural Science Foundation of China (No50601011)the National Basic Research Priorities Program of China (No2007CB607603)+1 种基金the State Key Laboratory of Solidification Processing in NWPU (NoSKLSP200905)the Program for New Century Excellent Talents in Chinese Universities (NoNCET-06-0484)
文摘The primary crystallization of the Ti40Zr25NisCu9Bc18 amorphous alloy was studied by isochronal differential scanning calorimetry （DSC）. The activation energy was determined by the Kissinger-Akahim-Sunose method. Trying to analyze the crystallization kinetics of the Ti40Zr25NigCu9Be18 amorphous alloy by two different methods, it was found that the crystallization kinetics did not obey the Johnson-Mehl-Avrami equation. A modified method in consideration of the impingement effect was proposed to perform kinetic analysis of the isochronal crystallization of this alloy. The kinetic parameters were then obtained by the linear fitting method based on the modified kinetic equation. The results show that the isochronal crystallization kinetics of the amorphous Ti40Zr25Ni8CugBe18 alloy is heating rate dependent, and the discrepancy between the Johnson-Mehl-Avrami method and the modified method increases with the increase of heating rate.
基金the financial support on this research from the Talent Training Program of Yunnan Province, China (No. 202005AC160041)the Major R&D Project of Yunnan Province of China (No. 202002AB0800020102)。
文摘采用湿法冶金从废旧LiFePO_(4)正极粉末中回收有价金属锂和铁,回收产物作为原料制备磷酸铁锂。通过优化浸出工艺参数,在丙酮酸浓度为3.0 mol/L、H_(2)O_(2)体积为2 m L、固液比为0.1 g/m L、反应温度为80℃以及反应时间为20min的条件下,Li的浸出效率达到96.56%。采用XRD、XPS、FE-SEM和EDS对浸出残渣进行表征。结果表明,浸出残渣为FePO_(4),Fe/P摩尔比为0.974。将浸出液的pH值调整到12.0,并在80℃搅拌2 h后,浸出液中的Li通过原位沉淀以Li_(3)PO_(4)形式回收,其纯度为96.5%(质量分数)。丙酮酸/H_(2)O_(2)溶液浸出Li的反应动力学数据符合Avrami模型(R^(2)>0.95)。Li浸出过程的活化能较低,表明扩散限制浸出过程中的反应速率。
基金financially supported by the National Natural Science Foundation of China(No.21604016)National Undergraduate Innovation Training Program(No.201610657004)
文摘Classic Avrami model and its modifications have found diverse applications in describing the thermal and phase behaviors of inorganic metals and organic polymers. The direct introduction of classic Avrami equation to offer quantitative analyses of crystallization kinetic parameters for enantiomeric poly（lactic acid） （PLA） blends may, however, lead to contradictory conclusions. As revealed by this study, during the characterization of isothermal melt and cold crystallization for stereocomplex PLA containing equal-weight poly（L-lactic acid） and poly（D-lactic acid）, the kinetic parameters yielded by Avrami equation are not in line with the classic crystallization hypotheses or the direct morphological observations. The underlying mechanisms, to some extent, lie in the generation of stereocomplex crystals （SCs） during the cooling/heating which affects the subsequent crystallization dynamics. The huge gap between the melting enthalpies of 100% crystalline SCs （142 J/g） and homo-crystals （HCs, 93 J/g） is most likely responsible for the confusing kinetic parameters acquired from the deduction of Avrami equation, which is based on the integration of enthalpies as a function of crystallization time. This prompts for great care that the classic Avrami equation is not applicable to accurately describe the crystallization kinetics of stereocomplex PLA, given the generation of SCs prior to crystallization and the coexistence of HCs and SCs during crystallization.
