In the present paper, a numerical modeling was developed to simulate the growth kinetics of ferrite transformed from austenite in Fe-C-∑X （X denotes substitution elements, such as Mn, Ni, Cr etc.） steels by solving...In the present paper, a numerical modeling was developed to simulate the growth kinetics of ferrite transformed from austenite in Fe-C-∑X （X denotes substitution elements, such as Mn, Ni, Cr etc.） steels by solving the diffusion equation using finite difference method （FDM）. Coupled with the kinetic modeling, thermodynamic calculations were carried out to determine the γ/α phase equilibrium conditions using a para-equilibrium （PE） model. The dissipation of free energy for γ→α phase transformation due to the so-called solute drag effect （SDE） was taken into account in the thermodynamic modeling. With this modeling, simulations on the growth kinetics of ferrite in the steels containing austenite-stabilizing and ferrite-stabilizing elements （such as Ni, Mn and Si, Cr, respectively） were performed, which indicates that it deviates from the parabolic growth rate law after the initial stage of transformation. The results were compared with the experimental values given by Bradley and Aaronson, showing that this model has a reasonably good accuracy to predict the growth kinetics of ferrite.展开更多
CO adsorption microcalorimetry was employed in the study of γ-Al-2O-3-supported Pt, Pt-Sn and Pt-Fe catalysts. The results indicated that the initial differential heat of CO adsorption of the Pt/γ-Al-2O-3 catalyst w...CO adsorption microcalorimetry was employed in the study of γ-Al-2O-3-supported Pt, Pt-Sn and Pt-Fe catalysts. The results indicated that the initial differential heat of CO adsorption of the Pt/γ-Al-2O-3 catalyst was 125 kJ/mol. As CO coverage increased, the differential heat of adsorption decreased. At higher coverages, the differential heat of adsorption decreased significantly. 60% of the differential heat of CO adsorption on the Pt/γ-Al-2O-3 catalyst was higher than 100 kJ/mol. No significant effect on the initial differential heat was found after adding Sn and Fe to the Pt/γ-Al-2O-3 catalyst. The amount of strong CO adsorption sites decreased, while the portion of CO adsorption sites with differential heat of 60110 kJ/mol increased after increasing the Sn or Fe content. This indicates that the surface adsorption energy was changed by adding Sn or Fe to Pt/γ-Al-2O-3. The distribution of differential heat of CO adsorption on the Pt-Sn（C）/γ-Al-2O-3 catalyst was broad and homogeneous. Comparison of the dehydrogenation performance of C-4 alkanes with the number of CO adsorption sites with differential heat of 60110 kJ/mol showed a good correlation. These results indicate that the surface Pt centers with differential heats of 60110 kJ/mol for CO adsorption possess superior activity for the dehydrogenation of alkanes.展开更多
基金supported by the National Natural Sci-ence Foundation of China(50474086)the program for New Century Talents in University(NECT)the Ministry of Education,China.
文摘In the present paper, a numerical modeling was developed to simulate the growth kinetics of ferrite transformed from austenite in Fe-C-∑X （X denotes substitution elements, such as Mn, Ni, Cr etc.） steels by solving the diffusion equation using finite difference method （FDM）. Coupled with the kinetic modeling, thermodynamic calculations were carried out to determine the γ/α phase equilibrium conditions using a para-equilibrium （PE） model. The dissipation of free energy for γ→α phase transformation due to the so-called solute drag effect （SDE） was taken into account in the thermodynamic modeling. With this modeling, simulations on the growth kinetics of ferrite in the steels containing austenite-stabilizing and ferrite-stabilizing elements （such as Ni, Mn and Si, Cr, respectively） were performed, which indicates that it deviates from the parabolic growth rate law after the initial stage of transformation. The results were compared with the experimental values given by Bradley and Aaronson, showing that this model has a reasonably good accuracy to predict the growth kinetics of ferrite.
文摘CO adsorption microcalorimetry was employed in the study of γ-Al-2O-3-supported Pt, Pt-Sn and Pt-Fe catalysts. The results indicated that the initial differential heat of CO adsorption of the Pt/γ-Al-2O-3 catalyst was 125 kJ/mol. As CO coverage increased, the differential heat of adsorption decreased. At higher coverages, the differential heat of adsorption decreased significantly. 60% of the differential heat of CO adsorption on the Pt/γ-Al-2O-3 catalyst was higher than 100 kJ/mol. No significant effect on the initial differential heat was found after adding Sn and Fe to the Pt/γ-Al-2O-3 catalyst. The amount of strong CO adsorption sites decreased, while the portion of CO adsorption sites with differential heat of 60110 kJ/mol increased after increasing the Sn or Fe content. This indicates that the surface adsorption energy was changed by adding Sn or Fe to Pt/γ-Al-2O-3. The distribution of differential heat of CO adsorption on the Pt-Sn（C）/γ-Al-2O-3 catalyst was broad and homogeneous. Comparison of the dehydrogenation performance of C-4 alkanes with the number of CO adsorption sites with differential heat of 60110 kJ/mol showed a good correlation. These results indicate that the surface Pt centers with differential heats of 60110 kJ/mol for CO adsorption possess superior activity for the dehydrogenation of alkanes.
