Seite - 173 - in Advanced Chemical Kinetics

generalconclusionscanbedrawn.Additionally,becausetheexperimentalconditions, typically specifically heating rate and temperature ranges, are not the same as in traditional SHS, it is unclearwhether thedeterminedvalues canbedirectly comparedor if there is some systemic difference that isoccurring. Figure 2 illustrates the ranges of the obtained values of activation energies for a variety of gasless exothermic reactionsmeasured byDTAmethod. It can be seen that the determined valuesaredependenton theexperimental conditionsutilized, includingvariations in reactant microstructure, heating rates, among other factors. This issue is discussed in detail below. It wouldbevaluable for systematic studies tobedonewhere these factors are studied indepth across different systems. Additionally,while the activation energies reported using different DTA-based approaches does not appear to be significantly different, it is still important to understandwhythesedifferencesarepresentandwhichmethodsofanalysisaremostsuitable for these systems. 5.Combustionvelocity/temperatureanalysis Therehasbeensignificanteffortdone toaccuratelycorrelateexperimental combustionparam- eters, such as combustionwave velocity and temperature,with the kinetics parameters. Two major approaches havebeendeveloped todetermine the activation energybymeasuring the layer-by-layer combustion front combustion velocity. The first was suggested in 1977 by Merzhanovfor1Dpropagation [62].Thederivedequation takes the form: v2¼ λ�ΔHrð Þρ RT2c E k0exp � ERTc � � f ηs � � (8) where f(ηs) is the selected kinetic law. This technique is most commonly used by adding diluent to the sample. This affects the combustion velocity and temperature; the change in both of these values is measured then compared, leading to the kinetic relationship being understood. Theothermajorapproach todetermining thekineticsbasedon thevelocitywasdevelopedby Boddingtonetal. [63].Therelationship takes the form: ∂η ∂t ¼ T�T0 td�trþ ∂T∂t� αv2 � � ∂2T ∂t2 � �h i τad (9) where td and tr, are the decay and rise times, with τad being the temperature rise under adiabatic conditions. More complete derivations of these twomodels can be found in the originalarticles [62–64].Additionally,amorecompleteunderstandingof thesemodels, includ- ing their relativemerits, has been examined in a number of priorworks [65–68]. In order to properly use these techniques, relatively simple equipment is required. Typically, sets of thermocouples are used tomeasure combustion wave propagation velocities, but there are manyalternatives, suchas IRorhigh-speedcameras, tomeasure thepropagationvelocity. Kinetics of Heterogeneous Self-Propagating High-Temperature Reactions http://dx.doi.org/10.5772/intechopen.70560 173