The kinetic behaviours of the substitution reaction of rare earth-PHA with CyDTA were studied systemati- cally.The relationship between the rate constant and atomic number was discussed.The rate differentiation val- u...The kinetic behaviours of the substitution reaction of rare earth-PHA with CyDTA were studied systemati- cally.The relationship between the rate constant and atomic number was discussed.The rate differentiation val- ue R_d(R_d=lgk_(z+n)-lgk_z)was proposed to evaluate the possibility of differential kinetic analysis.The R_d value between the neighbouring lanthanide ions first increases and then decreases along with increasing atomic number, so that the middle and heavy rare earth mixture(such as Sm-Gd and Gd-Y)are ideal systems for the differential rate kinetic analysis.展开更多
The drawn copper wires have been analyzed by differential scanning calorimeter(DSC) and a new method, which uses DSC measurements to determine the Johnson-Mehl-Avrami-Kolmogorov(JMAK) exponent via introducing Arrheniu...The drawn copper wires have been analyzed by differential scanning calorimeter(DSC) and a new method, which uses DSC measurements to determine the Johnson-Mehl-Avrami-Kolmogorov(JMAK) exponent via introducing Arrhenius behavior and modifying the baseline of DSC curves, has been proposed. The results show that JMAK exponent and recrystallization activation energy of the drawn copper wires with a strain of 2.77 are about 2.39 and 125 k J/mol, respectively. The line linking the tangency points of DSC curve hypotenuse can be used as the baseline when calculating recrystallization fraction. The JMAK exponent obtained by the DSC method is in a good agreement with that obtained by microhardness measurements. Compared to traditional methods to measure the exponent, the proposed method is faster and less labor intensive.展开更多
With the natural rosin derivative （maleopimaric acid, MPA） as the raw material, imide modified vinyl poly（dimethylsiloxane） （MP-VMS） was synthesized and characterized by ^1H NMR and ^13C NMR. The curing kinetic ...With the natural rosin derivative （maleopimaric acid, MPA） as the raw material, imide modified vinyl poly（dimethylsiloxane） （MP-VMS） was synthesized and characterized by ^1H NMR and ^13C NMR. The curing kinetic parameters of MP-VMS were determined by differential scanning calorimetry （DSC） at various heating rates （5, 8, 10, 15 ℃/min） from the Kissingner, Ozawa and Crane methods. The activation energy （Ea）, pre-exponential factor （A） and reaction order （n） were respectively 18.6 kJ/mol, 71,108 and 0.902. The low-temperature and high-temperature resistance of its curing product were respectively investigated by DSC and thermogravimetric analysis. The results showed that incorporation of MPA could significantly improve the thermal stability of silicone while had no effect on the low-temperature resistance, and the Tmax （the temperature corresponding to the maximum weight loss rate） increased by 70.7 ℃.展开更多
文摘The kinetic behaviours of the substitution reaction of rare earth-PHA with CyDTA were studied systemati- cally.The relationship between the rate constant and atomic number was discussed.The rate differentiation val- ue R_d(R_d=lgk_(z+n)-lgk_z)was proposed to evaluate the possibility of differential kinetic analysis.The R_d value between the neighbouring lanthanide ions first increases and then decreases along with increasing atomic number, so that the middle and heavy rare earth mixture(such as Sm-Gd and Gd-Y)are ideal systems for the differential rate kinetic analysis.
基金Projects(51171135,51371132,51471123) supported by the National Natural Science Foundation of ChinaProjects(2012K07-08,2013KJXX-61) supported by Key Science and Technology Program of Shaanxi Province,ChinaProject(2013JC14) supported by the Education Department Foundation of Shaanxi Province,China
文摘The drawn copper wires have been analyzed by differential scanning calorimeter(DSC) and a new method, which uses DSC measurements to determine the Johnson-Mehl-Avrami-Kolmogorov(JMAK) exponent via introducing Arrhenius behavior and modifying the baseline of DSC curves, has been proposed. The results show that JMAK exponent and recrystallization activation energy of the drawn copper wires with a strain of 2.77 are about 2.39 and 125 k J/mol, respectively. The line linking the tangency points of DSC curve hypotenuse can be used as the baseline when calculating recrystallization fraction. The JMAK exponent obtained by the DSC method is in a good agreement with that obtained by microhardness measurements. Compared to traditional methods to measure the exponent, the proposed method is faster and less labor intensive.
基金supported by the National Natural Science Foundation of China(No.31200446)
文摘With the natural rosin derivative （maleopimaric acid, MPA） as the raw material, imide modified vinyl poly（dimethylsiloxane） （MP-VMS） was synthesized and characterized by ^1H NMR and ^13C NMR. The curing kinetic parameters of MP-VMS were determined by differential scanning calorimetry （DSC） at various heating rates （5, 8, 10, 15 ℃/min） from the Kissingner, Ozawa and Crane methods. The activation energy （Ea）, pre-exponential factor （A） and reaction order （n） were respectively 18.6 kJ/mol, 71,108 and 0.902. The low-temperature and high-temperature resistance of its curing product were respectively investigated by DSC and thermogravimetric analysis. The results showed that incorporation of MPA could significantly improve the thermal stability of silicone while had no effect on the low-temperature resistance, and the Tmax （the temperature corresponding to the maximum weight loss rate） increased by 70.7 ℃.
