Page - 177 - in Advanced Chemical Kinetics

dynamicswith nanosecond time resolution. The currentDTEMperformance shows a spatial resolution less than10nmfor single-shot imaging,using15nselectronpulses.The solid-state reactions inNiAl reactivemultilayer films, themartensitic transformations innanocrystalline Ti, andthecatalyticgrowthofSinanowireswerestudiedbyDTEM[156]. Theaboveuniquediagnostics,which areused todeterminephase and structural transforma- tions in situ, are incredibly valuable. Used alone, they provide information on the reaction progress andmechanism; however, there are two significant paths that would make these techniquesmorevaluable.Whencoupledwith currentmethods fordeterminationofkinetics, the understanding of the reactionmechanisms in all systemswill be improved. Furthermore, thereisnocurrentwaytoextractkineticparametersfromsometechniques(TRXRD,DTEM,etc.); itwouldbevaluabletodevelopreliableapproachesforthesetechniques. 8.Structure-kinetics relationshipofSHSsystems Therehavebeenanumberofstudiesshownthat indicatedthat thestructureofmaterialsplays arole in thekinetics;multiplegroupsusingawidevarietyof techniquesandapproacheshave confirmed this conclusion. For example, itwas shown that by changing the internal structure Figure 5. Dynamic single-shotdiffractionwith 15-ns time resolutionof regionsbefore, during, andafter the exothermic mixingreaction fronthaspassed.The times indicatedat rightare in relation to thereaction front, setat t=0s.Thecrystal structure clearly changes from separate fcc Al/Ni andNi/V layers to an intermetallic B2 structure NiAl phase within 300nsafter thearrivalof thehot reaction front; a.u., arbitraryunits.Adapted fromKimetal. [11]. Kinetics of Heterogeneous Self-Propagating High-Temperature Reactions http://dx.doi.org/10.5772/intechopen.70560 177