Page - 174 - in Advanced Chemical Kinetics

Because of the relative simplicity inusing these techniques, theyhave foundwidespreaduse withinSHSreactions.These layervelocityapproacheshavebeenused todescribe thekinetics in theNi/Al system[69, 70], inboridesystems, includingNb/B [71–73],Ta/B [71],Zr/B [71, 74, 75], Hf/B [71], Ti/B [76],Mo/B [77], alongwith other binary systems such as Ti/C [78], Ti/Si [79, 80], thermites [81–89]andmorecomplex ternarysystems [78, 90–93]. The results obtained arepresented inFigure 3. It canbe seen that there are awidevarietyof systemsanalyzed. Itworthnoting that thesedatawereobtainedthroughdirectanalysisof the combustion parameters, which were obtained at extremely high temperatures and rapid heating rates, which are difficult to accomplish by other kinetics methods. However, it is important to remember that the quasi-homogeneous approximation is utilized for this layer- by-layer combustion front combustionvelocity basedmethod,which shouldbe appliedwith caution [68].Finally,because thismethodcanbeeasilyused forany typeof system,acompar- isonbetweenthermiteandnon-thermite typereactionscanbeanalyzed.ComparingFigure3a andb, it is obvious that the activation energies for thermites is significantly lower thannon- thermite type reactions. This is interestingand is likely related to the specific reactionmecha- nismthatoccurs in thermites, compared tonon-thermites. 6.Electrothermography Electrothermography is a technique that utilizes metal wires in either a gaseous or clad environment [8]. Thewire is resistively heated rapidly to the desired temperature, with the electricpowerbeingadjusted to compensate for theheat releasedue to the chemical reaction. Theobtaineddataallowsforextractionof therateofheatgenerationduringthereactionunder Figure 3. Summaryof data collectedusing layer velocity analysis approached for (a) binary elemental and (b) thermite systems. Advanced Chemical Kinetics174