| Thermal kinetic analytics play a very important role in many fields. In this thesis, we put forward the approximate formulae of temperature integral and suggested a procedure to determine the most possible kinetic model function based on the principle of thermal kinetic analysis. And various amino acids were subjected to pyrolysis and their pyrolytic mechanism and kinetics were studied. What we have done is shown below:I. Study on the approximate formulae for temperature integral1. Simpson's procedure is used to evaluate numerical integral values of and forvarious u at interval of 1 in the range of The linear dependence of on x has been established. Combining this linear dependence andintegration-by-parts, the approximate formula I was proposed, which can be put in the formThe validity of this equation has been tested with data from numerical calculating. Compared with several published approximate formulae, this new one is much superior, to all other approximations and is the most suited solution for the evaluation of kinetic parameters from linear-heating TG experiments.2. Numerical procedure is used to evaluate the linear dependence of d lnP(u)/du on 1/wand the lineardependence of (In P(u)-cln u) on u in the range of 20 < u < 60. Good linear relationships of these two dependences have been established. Also, the coefficients a, b and c of lnP(u) = a+bu + c\nu have been obtained from the slopes and the intercepts. Finally, the approximate formula II was proposed, which can be put in the form-In P(u) = 0.37771216 + 1.89467112 ln i +1.00 145007uCompared with several published approximate formulae in the similar form, the accuracy of the approximate formula II is improved observably. It is evident that the new one is valid and easily used in the field of linear-heating TG experiments data analysis.3. The concept of generalized temperature integral function was introduced. The approximate formulae I for the generalized temperature integral function was proposed for the first time by using part-integration, which can be put in the formAlso, the approximate formulae II for the generalized temperature integral function was deduced by using numerical calculation and numerical analysis.The validities and the accuracies of the formulae I and II were analyzed. Results show that both the formulae I and II were accurate, valid, and easily used for different values of m. In both the formulae, the formulae I is simpler in the style while the formulae II is more accurate.II. Determining the most possible kinetic model function by using the master plots method1. A procedure was proposed to evaluate kinetic triplet based on the formulae I and II. This procedure involves the isoconversional method and the master plot method. That is, the activation energies at various conversions were evaluated by using model-free methods and the observed independence of activation energies on the conversions is always a clear indication that the reaction under investigation proceed as a single-step reaction, then the master plots method is used to determine the most possible class of kinetic models conforms to the reaction, finally the kinetic exponent and the pre-exponent are estimated, consequently, full kinetic triplet are proposed.2. The calcination of ammonium metavanadate was investigated using simultaneous TGA-DSC techniques. Two intermediates proceed before Ammonium metavanadate produces vanadium pentoxide. Kinetic analysis of the calcination of ammonium metavanadate were carried out by using the above procedure. Results show that each steps is subjected to a single kinetic process and can be described by using the random nucleation and nuclei growth kinetic model. The kinetic triplets for each steps were obtained eventually.3. TGA technique was applied to investigate the thermal dehydration of hydrated calcium oxalate. Also, the kinetic triplets of this process were studied. The activation energies hardly varied with the conversion and the averaged value of acti...
|
PDF Full Text Request