Differential scanning calorimetric (DSC) study was carried out at different heating rates to examine the solid state reactions in a 7150 A1-Zn-Mg alloy in water-quenched (WQ) state, naturally and artificially aged...Differential scanning calorimetric (DSC) study was carried out at different heating rates to examine the solid state reactions in a 7150 A1-Zn-Mg alloy in water-quenched (WQ) state, naturally and artificially aged tempers. The exothermic and endothermic peaks of the thermograms indicating the solid state reaction sequence were identified. The shift of peak temperatures to higher temperatures with increasing heating rates suggests that the solid state reactions are thermally activated and kinetically controlled. The artificial aging behaviour of the alloy was assessed by measuring the variations of hardness with aging time. The fraction of transformation (Y), the rate of transformation (dY/dt), the transformation functionflY), and the kinetic parameters such as activation energy (Q) and frequency factor (k0) of all the solid state reactions in the alloy were determined by analyzing the DSC data, i.e. heat flow involved with the corresponding DSC peaks. It was found that the kinetic parameters of the solid state reactions are in good agreement with the published data.展开更多
Thermodynamic analysis of the possibility of silver nanocrystalline preparation by high energy milling silver oxide was investigated. The molar Gibbs free energy function of mechanically activated samples was calculat...Thermodynamic analysis of the possibility of silver nanocrystalline preparation by high energy milling silver oxide was investigated. The molar Gibbs free energy function of mechanically activated samples was calculated from the structural defects such as amorphization, dislocation and surface energy. According to the molar Gibbs free energy function, the equilibrium temperature of mechanical reduction of silver oxide milled for 21 h was estimated at about 304 K. Consequently, at this temperature silver oxide cannot be stable and will transform to silver during the milling.展开更多
A discussion is given on the convergence of the on-line gradient methods for two-layer feedforward neural networks in general cases. The theories are applied to some usual activation functions and energy functions.
文摘Differential scanning calorimetric (DSC) study was carried out at different heating rates to examine the solid state reactions in a 7150 A1-Zn-Mg alloy in water-quenched (WQ) state, naturally and artificially aged tempers. The exothermic and endothermic peaks of the thermograms indicating the solid state reaction sequence were identified. The shift of peak temperatures to higher temperatures with increasing heating rates suggests that the solid state reactions are thermally activated and kinetically controlled. The artificial aging behaviour of the alloy was assessed by measuring the variations of hardness with aging time. The fraction of transformation (Y), the rate of transformation (dY/dt), the transformation functionflY), and the kinetic parameters such as activation energy (Q) and frequency factor (k0) of all the solid state reactions in the alloy were determined by analyzing the DSC data, i.e. heat flow involved with the corresponding DSC peaks. It was found that the kinetic parameters of the solid state reactions are in good agreement with the published data.
文摘Thermodynamic analysis of the possibility of silver nanocrystalline preparation by high energy milling silver oxide was investigated. The molar Gibbs free energy function of mechanically activated samples was calculated from the structural defects such as amorphization, dislocation and surface energy. According to the molar Gibbs free energy function, the equilibrium temperature of mechanical reduction of silver oxide milled for 21 h was estimated at about 304 K. Consequently, at this temperature silver oxide cannot be stable and will transform to silver during the milling.
基金Supported by the Natural Science Foundation of China
文摘A discussion is given on the convergence of the on-line gradient methods for two-layer feedforward neural networks in general cases. The theories are applied to some usual activation functions and energy functions.