Kinetic triplet

The FDS5 pyrolysis model is used here to qualitatively illustrate the complexity associated with material property estimation. Each condensed-phase species (i.e., virgin wood, char, ash, etc.) must be characterized in terms of its bulk density, thermal properties (thermal conductivity and specific heat capacity, both of which are usually temperature-dependent), emissivity, and in-depth radiation absorption coefficient. Similarly, each condensed-phase reaction must be quantified through specification of its kinetic triplet (preexponential factor, activation energy, reaction order), heat of reaction, and the reactant/product species. For a simple charring material with temperature-invariant thermal properties that degrades by a single-step first order reaction, this amounts to -11 parameters that must be specified (two kinetic parameters, one heat of reaction, two thermal conductivities, two specific heat capacities, two emissivities, and two in-depth radiation absorption coefficients). 

The treatment of triplet state decay kinetics of the dyes obtained in the presence of DNA with the use of the two-exponential model shows that, within the chosen range of nitroxyl radical concentrations (cr = 0-6 x 10 mol 1 in some experiments, Cr reached 2x10 mol r ), only one of the kinetic triplet components is quenched, namely, the long-lived component. The addition of the radical to the dye-DNA system does not lead to a noticeable increase in the decay kinetics of the short-lived components of the carbocyanine triplet states. 

In equation (1) and (2), A and E are the Arrhenius parameters (the preexponential factor and the activation energy, respectively), a) is the reaction model (or conversion function), R is the gas constant, T is the temperature, t is the time, and a is the extent of conversion. Henceforth, the subscript a denotes values related to a constant extent of conversion. A combination of E, Ay and J a) is sometimes called the kinetic triplet . 

It has been experimentally demonstrated [17,75,85] that the model-free equations give rise to reliable predictions, whereas substitution of the kinetic triplets, obtained from a single heating rate run, into equation (44) yields fundamentally erroneous predictions. It has also been shown that the model-free predictions are superior to the predictions based on the ASTM method (equation... 

The fundamental flaw of single heating rate methods is that they produce significantly differing kinetic triplets, most of which provide quite satisfactory description of the same dataset [85]. This occurs because of the mutually compensating correlation of E and A. Known as a compensation effect, this correlation takes the following form... 

Table 1. Kinetic triplets for the decomposition of ammonium nitrate [88]...

Asa final nsml. it b essential that a compleic kinetic triplet be determined lodiancteriae a reaction. Such a ootqplcte and unique set canmit be determined from expcrimcMs done at a ringle healing me. 

Rotaru, A. Gosa, M. (2009). Computational thermal and kinetic analysis Complete standard procedure to evaluate the kinetic triplet form non-isothermal data. Journal of Thermal Analysis and Calorimetry, Vol. 97, pp. 421 26 ISSN 1388-6150 (Print), 1572-894 (electronic version)... 

The reaction rate depends on the conversion, which can be represented by a reaction model [f(a)] which may take various mathematical forms, depending on the physical mechanism assumed in the mathematical derivations (Brown 2001). A combination of the activation energy, preexponential factor, and reaction model is sometimes called a kinetic triplet. For a process involving more than one step, the individual steps are likely to have differing kinetic triplets. For example, a two-step kinetic equation involves two kinetic triplets Ai,Ei/i(a) and A2,E2,f2 o). 

Many methods have been developed for evaluating a kinetic triplet by fitting rate equations to data obtained at a single heating rate. For example, rearranging Eq. (3.17) gives... 

Where a is the extent of decomposition, Z is a pre-exponential factor, E is the activation energy, R the universal gas constant (8.3154 Jmol K 0> and f(a) depends on the decomposition mechanisms. E, Z, and a) are commonly called the kinetic triplet [28]. There are different kinds of methods to obtain the kinetic triplet reported in the scientific literatme among which are those reported by Flynn-Wall-Ozawa [29], Friedman [30], Kissinger [21], or Coats-Redfem [31], with different proposed equations presented to solve Eq. (7.1). 

Starting with Eq. (22.6), various procedures for evaluating the kinetic triplet (E, A, f(a)) are developed. The conversion function f(a) for a solid-state reaction depends on the reaction mechanism. It is an algebraic expression that is associated with the physical... 

Schenck, C. C., Blankenship, R. E., and Parson, W. W. (1982) Radical pair decay kinetics, triplet yields and delayed fluorescnece from bacterial reaction centers, Biochim. Biophys. Acta 680,44. 

---