Methodological Principles in studying chemical reaction kinetics under conditions of programmed heating

To predict the isothermal course of a reaction from the dynamic DSC curves, the application of isothermal DSC curve transformation has been proposed. To perform such a transformation, it is sufficient only to determine the effective activation energy. To transform integral dynamic curves, a(T)), into isothermal ones, a(t), a better equation has been derived and its validity has been demonstrated on the example of two typical thermosetting ~]~tems. In addition, it hasd~een shown that the transformation of differential curves, (T), into isothermal ones -~-(a), readily allows determination of the kinetic function and rate constants. The procedure used to obtain information on the curing kinetics for thermosetting resins is characterized by simplicity and reliability and can work at E = E(a).

Section: T = ~ Exp (-E/rt) F(a ) (2)mentioning

confidence: 99%

Isothermal transformation of dynamic DSC curves for thermosetting polymers in curing kinetics analysis

Khabenko¹,

Dolmatov²

1990

“…The mathematical analysis of the description of a DTA curve has been carried out on the basis of an idealistic model [21], i.e. assuming that the temperature distribution within the sample is uniform and that the heat loss term is linear in temperature.…”

Section: Appendixmentioning

confidence: 99%

Thermal ignition behaviour of ammonium perchlorate in presence of fuel-rich compounds

Sundararajan

Jain

1983

The thermal ignition behaviour of ammonium perchlorate has been investigated in the presence of fuel-rich compounds such as tetramethylammonium perchlorate, trimethylammonium nitrate, carbon and cellulose. The ignition characteristics, as studied by differential thermal analysis, have been found to be strongly influenced by self-decomposition and other physicochemical properties of the additives. For a simple system, an analytical model proposed on the basis of the coupling of two exothermic decomposition reaction kinetics and a heat-balance equation, appears to explain to some extent the observed trend in peak ignition temperature when the composition is varied. The salient features of the analysis, as regards its application to fuel-oxidizer interactions in general, have been pointed out.The importance of thermal ignition studies on condensed fuel-oxidizer systems arises mainly because of their extensive application in the field of propellants and explosives. Of the condensed systems, the mixtures involving ammonium perchlorate (AP) are of special interest due to their wide use in solid propellants. The thermal ignition behaviour of AP is known to be modified in the presence of catalysts, impurities and additives [1]. A systematic study of the differential thermal analysis (DTA) of AP in the presence of structurally similar, fuel-rich compounds, viz. methylammonium perchlorates (MAPs), was recently carried out in our laboratory [2]. It was observed that although AP shows two exotherms due to partial and complete decomposition at around 300 ~ and 400 ~ respectively [1] in DTA, it ignites in asingle step at around its partial decomposition temperature in the presence of small amounts of mono-, di-, tri-or tetramethylammonium perchlorate. Interestingly, the critical concentration of a MAP needed to cause ignition in a single step corresponds to a unique composition of the mixture, expressed in terms of its elemental stoichiometric coefficient, ~e [3]. However, some of the features in the DTA of the mixtures of AP and tetramethylammonium perchlorate (TMAP), such as the shift of the terminal exotherm to lower temperatures as a function of concentration, were not clearly explained.

“…In the case of simple, one-stage chemical reactions, assuming a correct experiment (methodological aspects of non-isothermal experiments are presented in detail in [1]) and a proper choice of the form of the function f((x), Eq. (1) enables one to estimate kinetic parameters which, in the majority of cases, have a distinct physical meaning, using experimental dependences e(r) or a(T).…”

mentioning

confidence: 99%

Applicability of one-stage chemical reaction kinetic equation to describe non-isothermal destruction processes

Venger¹,

Fraiman²,

Yurevich³

1983

The applicability of the traditional kinetic power equation to describe the thermal destruction of solids, and in particular polymers, is discussed. It is shown that in the majority of cases the use of such an equation is reasonable, even though the true mechanism of the process under study is either obscure or so complex that it cannot be analytically described in detail. In such cases the effective rather than the true kinetic parameters are obtained and provide certain useful information on the process.The fixed conversion temperature dependence on the heating rate is analyzed with examples on the model process and the thermal degradation of an epoxy binder.In studies on the kinetics and mechanisms of thermal transformations of materials via thermal analysis methods, the well-known kinetic equation is applied:where (~ is the degree of conversion by time T at temperature T; Z and E are the Arrhenius pre-exponential factor and the activation energy; f(~) is some single-valued function of (~, whose form depends on the mechanism of the process. In the case of simple, one-stage chemical reactions, assuming a correct experiment (methodological aspects of non-isothermal experiments are presented in detail in [1]) and a proper choice of the form of the function f((x), Eq. (1) enables one to estimate kinetic parameters which, in the majority of cases, have a distinct physical meaning, using experimental dependences e(r) or a(T). If the form of the function f(a) is unknown a priori, as is often the case, then the parameters Z and E may be calculated either from the data of several experiments carried out with different heating rates (for example [2,3]), or by choosing a function f(a) for which Eq, (1) best fits the experimental function ~(r) [4]. Wide use is made of the functionwhere n is the reaction order; this describes the kinetics of homogeneous reactions and heterogeneous processes governed by a phase-boundary reaction mechanism, Eq. (2) being meaningful only for discrete values of n [5].