A critical examination was made on the reliability of kinetic parameters of nonisothermal thermoanalytical rate measurement by the widely applied Coats-Redfern(CR)equation.For this purpose,simulated TGA curves were ma...A critical examination was made on the reliability of kinetic parameters of nonisothermal thermoanalytical rate measurement by the widely applied Coats-Redfern(CR)equation.For this purpose,simulated TGA curves were made for reactions with different kinetic models,including chemical,diffusion(Janders)and mixed mechanism at different heating rates.The results show that,for reactions controlled kinetically by one mechanism,all solid state reaction models show linear trends by use of CR method and this method can not distinct the correct reaction model.For reactions with mixed mechanism,the CR method shows nonlinear trends and the reaction models and kinetic parameters can not be extracted from CR curves.The overall conclusion from this comparative appraisal of the characteristics of the CR approach to kinetic analysis of TGA data is that the CR approach is generally unsuitable for determination of kinetic parameters.展开更多
The most general dynamic tendencies of the energy redistribution in the high-pressure region are considered. Their influence on the possible deviations from the kinetic conceptions, which is now generally accepted, is...The most general dynamic tendencies of the energy redistribution in the high-pressure region are considered. Their influence on the possible deviations from the kinetic conceptions, which is now generally accepted, is examined. In this way, the structural elements of an organic molecule that promote internal energy mobilization in the high-pressure region and, conversely, hamper it, are defined. The first of these elements reduces both the Arrhenius parameters of the unimolecular reactions while the second leads to the opposite results. Some well-known exceptions to existing kinetic theories, which find an explanation in the framework of these proposed concepts, is considered. The proposed concept is very general as distinct from the existing dynamic studies, which investigate more particular details of the separate bond behaviors. The proposed general concept can broaden the study of chemical kinetics.展开更多
Molecular surface electrostatic potentials V_S(r) ( ESP) of seventeen nitramines have been calculated. As a criterion of the imbalance between the maximum positive,V_(S,max) and minimum negative,V_(S,min),values of mo...Molecular surface electrostatic potentials V_S(r) ( ESP) of seventeen nitramines have been calculated. As a criterion of the imbalance between the maximum positive,V_(S,max) and minimum negative,V_(S,min),values of molecular surface electrostatic potentials their sum was derived and used as a new simple characteristic for ESPs-V_(S,Σ). These V_(S,Σ) values have close relationships with the Arrhenius parameters,activation energy E_a and preexponent log A,of thermal decomposition of the nitramines studied. The correlation between the V_(S,Σ) values and heats of fusion of the nitramines studied is described. These findings suggested analyzing the physico-chemical behavior of the nitramine crystals during this decomposition; in this connection an investigation was carried out using isothermal thermogravimetry and scanning electron microscopy of thermally exposed crystals of cis-1,3,4,6-tetranitrooctahydroimidazo-[4,5-d]imidazole( sintering of its crystal surfaces),of β-1,3,5,7-tetranitro-1,3,5,7-tetrazocane( cracking of its crystals during β !δ transition) and of 2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane. The results suggest a need to study the pre-decomposition states on thermal decomposition of the nitramines' molecule's crystals.展开更多
文摘A critical examination was made on the reliability of kinetic parameters of nonisothermal thermoanalytical rate measurement by the widely applied Coats-Redfern(CR)equation.For this purpose,simulated TGA curves were made for reactions with different kinetic models,including chemical,diffusion(Janders)and mixed mechanism at different heating rates.The results show that,for reactions controlled kinetically by one mechanism,all solid state reaction models show linear trends by use of CR method and this method can not distinct the correct reaction model.For reactions with mixed mechanism,the CR method shows nonlinear trends and the reaction models and kinetic parameters can not be extracted from CR curves.The overall conclusion from this comparative appraisal of the characteristics of the CR approach to kinetic analysis of TGA data is that the CR approach is generally unsuitable for determination of kinetic parameters.
文摘The most general dynamic tendencies of the energy redistribution in the high-pressure region are considered. Their influence on the possible deviations from the kinetic conceptions, which is now generally accepted, is examined. In this way, the structural elements of an organic molecule that promote internal energy mobilization in the high-pressure region and, conversely, hamper it, are defined. The first of these elements reduces both the Arrhenius parameters of the unimolecular reactions while the second leads to the opposite results. Some well-known exceptions to existing kinetic theories, which find an explanation in the framework of these proposed concepts, is considered. The proposed concept is very general as distinct from the existing dynamic studies, which investigate more particular details of the separate bond behaviors. The proposed general concept can broaden the study of chemical kinetics.
文摘Molecular surface electrostatic potentials V_S(r) ( ESP) of seventeen nitramines have been calculated. As a criterion of the imbalance between the maximum positive,V_(S,max) and minimum negative,V_(S,min),values of molecular surface electrostatic potentials their sum was derived and used as a new simple characteristic for ESPs-V_(S,Σ). These V_(S,Σ) values have close relationships with the Arrhenius parameters,activation energy E_a and preexponent log A,of thermal decomposition of the nitramines studied. The correlation between the V_(S,Σ) values and heats of fusion of the nitramines studied is described. These findings suggested analyzing the physico-chemical behavior of the nitramine crystals during this decomposition; in this connection an investigation was carried out using isothermal thermogravimetry and scanning electron microscopy of thermally exposed crystals of cis-1,3,4,6-tetranitrooctahydroimidazo-[4,5-d]imidazole( sintering of its crystal surfaces),of β-1,3,5,7-tetranitro-1,3,5,7-tetrazocane( cracking of its crystals during β !δ transition) and of 2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane. The results suggest a need to study the pre-decomposition states on thermal decomposition of the nitramines' molecule's crystals.
