Page - 181 - in Advanced Chemical Kinetics

this system.Thus it is possible to compare thedata collectedacross a largenumberof experi- mental conditions togivemorecompleteunderstandingof thisgasless reaction.Althoughthis systemhas been extensively studied for over 40 years now, a consensus has not emerged on the exact activationenergy, as canbe seen inFigure9. Thedata again illustrate the effect that differing experimental conditions play, whether in the material structure, heating rates, or otherexperimental factors. In1987,Philpotet al.didpreliminarystudieson theNi/Al systemkineticsusing theKissinger approach [35]. They showed that there is an effect of heating rate, the nickel particle size, as well as an effect of a varyingAl content, on the reactionmechanism in this system [35], this work is highlighted in more detail in an above section. Hunt et al. examined the effect of particlesizeontheapparentactivationenergyusingaCO2laser tocontrol theheatingcoupled with theDTA-basedKissinger approach.Using800nmsizeNiparticles coupledwith20μm, 4μm, 80 nm, and 40 nmAl particles, it was found that that these reactions had activation energies of: 103.5 10.5, 97.3 5, 21.2 2.5, and 17.4 2.85 kJ/mol, respectively [36]. They then increased the Ni size to 15 μm and measured with the four Al sizes, resulting in 162.5 1.4,131.2 2.6,103.6 5.2,and80.1 6.3kJ/mol, respectively [36].Thisconfirmsthat the initial reactant structure plays a significant impact on the kinetics. The size of either reactant significantly alters the effective kinetics. Kim et al. studied this reaction using nanolaminated composite micro-foils with different thickness ratios between Ni and Al at heating rates between 5 and 100K/min. For 4:1 foils, they found that the formation ofNiAl3 occurred, followedbyNi2Al3,withactivationenergiesof142and106kJ/mol, respectively [37]. Figure9. Summaryofkineticdatacollected for theNi/Al system. Kinetics of Heterogeneous Self-Propagating High-Temperature Reactions http://dx.doi.org/10.5772/intechopen.70560 181