Page - 175 - in Advanced Chemical Kinetics

conditionssimilar to those inSHSwave.Additionally,because thewiresare thin, thesample is quenchedessentiallyassoonas thepower is turnedoff.After thewire is cooled, cross-sections of thewire are collected and thewidth of the product films is measured, which allows for informationonthekineticsofphase formation.This,whendoneatmultiple temperaturesand times,givesamorecompletepictureof the reactionmechanism. Theelectrothermography techniquehasbeenwidelyused to studygas-solid reactions.This is because thewires canbeexposed toanysort of gaseous environment andalsobecauseof the equipment itself; the wires can be heated with any heating rate, mirroring those found in conventional SHS reactions. Because of this, a number of experiments were conducted in nitrogen environments. In specific, the Ta/N [94], Ti/N [95–98], Nb/N [98, 99], and Zr/N [8] systemshavebeenstudies.However, the techniquehasalsobeused tostudycarbides, includ- ing theTi/C [100],Zr/C [100],W/C[101],Nb/C[102], alongwithother systems, includingMo/ Si [103–106],W/Si [107, 108],Ni/Al [109], andNi/Ti [109]. Figure 4 shows the values of the activation energies obtained by this method in gas-solid systems. It can be seen that some reactions have limited steps relating to the gas pressure, whileothersarerelatively independent, suggesting that therearedifferentmechanismsfor the Figure4. Summaryofdataobtainedusing theelectrothermographyapproach. Kinetics of Heterogeneous Self-Propagating High-Temperature Reactions http://dx.doi.org/10.5772/intechopen.70560 175