Non-isothermal Kinetic Analysis Method

Kinetic studies have traditionally been extremely useful in characterizing several physical and chemical phenomena in organic, inorganic and metallic systems. It provides valuable qualitative, quantitative and kinetic information on phase transformations, solid state precipitation, crystallization, oxidation and decomposition. Unfortunately, no single reference comprehensively presents non-isothermal kinetic analysis method for the study of complex processes, determining the actual mechanism and kinetic parameters. This book provides a new method for non-isothermal kinetics and its application in heterogeneous solid state processes. In the backdrop of limitations in existing methods, this book presents a brief review of the widely used isothermal and non-isothermal kinetic analysis methods. 

It is evident that a non-isothermal kinetic analysis, even in the case of a simple reaction, is very labor intensive and especially prone to errors. It stands to reason that the analysis of a system of reactions is usually much more complex. A kinetic analysis on the basis of mathematical-analytical relations is usually impossible. A kinetic analysis is only practicable by an interactive procedure between numeric calculations and experimental results on the basis of common optimization methods... 

The kinetics of the CTMAB thermal decomposition has been studied by the non-parametric kinetics (NPK) method [6-8], The kinetic analysis has been performed separately for process I and process II in the appropriate a regions. The NPK method for the analysis of non-isothermal TG data is based on the usual assumption that the reaction rate can be expressed as a product of two independent functions,/ and h(T), where f(a) accounts for the kinetic model while the temperature-dependent function, h(T), is usually the Arrhenius equation h(T) = k = A exp(-Ea / RT). The reaction rates, da/dt, measured from several experiments at different heating rates, can be expressed as a three-dimensional surface determined by the temperature and the conversion degree. This is a model-free method since it yields the temperature dependence of the reaction rate without having to make any prior assumptions about the kinetic model. 

The methods used in the analysis of non-isothermal kinetic data can be classified as derivative, also referred to as differential methods, based on the use of equation... 

In thermal analysis, the reactions studied are almost invariably heterogeneous and the reaction temperature is usually being continuously increased or decreased according to some set (usually linear) program. Many methods for the analysis of the non-isothermal kinetic data have been developed and numerous papers have appeared and are still appearing on this topic. On the other hand, it is a field of considerable controversy. All controversies regarding the versatility or otherwise of non-isothermal kinetics stem from the applicability of the Arrhenius... 

Budrugeac, P. (2007). The Kissinger law and the IKP method for evaluating the non-isothermal kinetic parameters. Journal of Thermal Analysis and Calorimetry, Vol. 89, pp. 143-151 ISSN 1388-6150 (Print), 1572-894 (electronic version)... 

The book is divided into six chapters Chap. 1 is an introduction to the basic concepts of kinetics Chap. 2 describes a new, realistic and more accurate non-isothermal kinetic method Chap. 3 shows application of this method on the mechanistic determination of evolution of a nanosystem and Chap. 4 is kinetic analysis of a heterogeneous solid state process through the aforementioned method. 

Similar to studies reported by Litwinienko and co-workers discussed above, a recent report (Dunn, 2006b) demonstrated that non-isothermal (conventional) DSC, static mode P-DSC and dynamic mode P-DSC may be employed to study kinetics of the oxidation of SME. OT results obtained at ambient pressure for DSC and P = 2000kPa for P-DSC and with varying p = 1-20 °C/ min were analyzed by the Ozawa-Flynn-Wall method to calculate activation energies and rate constants. This work concluded that rates of the oxidation reaction could be calculated at any temperature based on accurate measurement of kinetic parameters from analysis of non-isothermal dynamic mode P-DSC scans. 

Budrugeac et al. [123] examined the kinetics of the non-isothermal crystallization of (GeS2)o.3(Sb2S3)o.7 by employing the methods of Friedman and of invariant kinetic parameters and demonstrated that the process can be treated as a single step. A more complex kinetic situation has been encoimtered by Thomas and Simon in re-crystallization of nickel sulfide from the a- to P-form. Their analysis yielded evidence of at least two steps involved in the overall process [124]. 

Rychly and Pavlinec have developed a method for analysing thermo-gravimetric data for multi-step processes obtained under non-isothermal conditions to provide kinetic data for each step [38]. Rychly and co-workers have applied this and other methods to a detailed study of the flame retardant effects of fillers [36]. In addition to the oxygen index, they used an ignition test based on an adapted thermal analysis method to assess flammability. 

The crystallization kinetics of amorphous materials can be investigated either isothermally or non-isothermally by using thermal analysis techniques. In the isothermal method, the sample is heated above the glass transition temperature and the heat absorbed during the crystallization process is measured as a function of time. On the other hand, in the non-isothermal method, the sample is heated at a fixed rate and then the change in enthalpy is recorded as a function of temperature. Thermal analysis techniques such as differential thermal analysis (DTA) and differential scanning calorimetry (DSC) are quite popular for kinetic analysis of crystallization processes in amorphous solids (Araujo Idalgo, 2009 Malek, 2000 Prasad Varma, 2005). 

Therefore, this chapter covers the investigation of the crystallization kinetics of amorphous materials by studying the crystallization mechanism in terms of isothermal and non-isothermal methods and describing different thermal analysis techniques used in crystallization kinetic studies and explaining the structural characterization techniques used to determine the crystallization mechanism... 

The DSC method is commonly used for the study of the cming kinetics of a UPR. The kinetic analysis of the crosslinking process initiated with MEKP was performed by means of an empirical and theoretical model based on the concept of free-radical polymerization [190]. A calculation algorithm based on the downhill simplex method and the Rimge-Kutta procedure was proposed. The non-isothermal DSC analyses allowed to obtain the concentration of the initiator and the radicals as a function of cure temperature at... 

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