Seite - 182 - in Advanced Chemical Kinetics

In order tomore fully understand the relationship between structure and the kinetics,White et al. investigated the effect ofmechanical activation (MA)on theNi/Al systemkineticsusing theKissingerapproach.TwotypesofNi/Alcompositeswereused;NicladAlparticles,aswell asNi/Al composite particles produced by high-energy ballmilling (HEBM). TheNi cladAl particleswere found tohaveanapparent activationenergyof 352 8kJ/mol,while afterMA theparticleshadmuchloweractivationenergyof117 4kJ/mol [38].Reevesetal. studiedthe thermalandimpactreactionkinetics intheNi/AlsystemforbothMAandnano-sizedreactants using theKissinger approach. For the nano-mixture, the reactantswere both ~80 nm in size and, for theMAparticles, theyunderwent15minutesofHEBM.Thenano-mixtureexhibiteda 230 21kJ/mol activationenergy,while theMAmixturewas calculated tobe117 8kJ/mol [39]. Manukyan et al. studied the Ni/Al system after MA and the effect of a coarse vs. nanolaminated nanostructure on the kinetics using the Kissinger approach. Using heating rates between 10 and 50K/min, they found that the reaction proceeds in three steps, NiAl3, Ni2Al3, and then finally NiAl. For the coarse microstructure, these peaks corresponded to 99 4, 138 13, and120 37kJ/mol,while thenanolaminatedmicrostructure corresponded to93 2.5,145 13,and146 14kJ/mol, respectively [40].This illustrated that theactivation energiesdependonthemicrostructure, evenafterMA. Kuket al. studied compressionbondedNi/Alnanofoilswith andwithout aBN lubricantusing theKissinger approach.With theBNlubricant, itwas found that the reactionproceeded in two steps,with theactivationenergiesbeing224and272kJ/mol, respectively, resulting in the forma- tionofAl3Ni2 [42].Without the lubricant, thereactionproceeded inasingle stepwithactivation energyof470kJ/mol, thisdifferencewasattributed to theoxide layerbetweenthereactants [42]. MaitiandGhoroistudiedtheNi/AlsystemusingtheFriedman,Ozawa,andKissingerapproach, yieldingactivationenergiesof437.0,448.4,and457.6kJ/mol, respectively [43]. Using theETEapproach, Shteinberg et al. andMukasyan et al. confirmed thatMAaffects the activationenergy in theNi/Al system,as shown inFigure10 [12, 19]. Initially, they studied the kinetics of theNi cladAl system (whichwas also studied in [38]),which showed twodistinct steps. The first stepwas related to themelting ofAl and subsequent cracking of theNi layer, whichhadanactivationenergyof197 29kJ/mol.ThefinalstepwasthediffusionofNi intoAl, whichwasmeasuredas523 84kJ/mol. In theMAsystem, they found that onlya single step occurred andwasmeasured to be 105 13 kJ/mol. Shuck andMukasyan further studied the effects of MA on the kinetics in the Ni/Al system using the ETE approach [20]. Using 3D reconstruction techniques, they showed that the surface area contact between the reactions is directly related to the effective activation energy,which ranged from79 to 137 kJ/mol, which corresponded to a change in the contact surface area/volume ratio between 0.0120 and 0.0032 nm 1, respectively. Thiswork is further highlighted in an above section. Finally, using theETEapproach, Filimonovet al. studied the effects ofMAon thenonstoichiometric, 3Ni/Al system [21]. They utilized a criterion based on the minimum curvature of the heating rate logarithm,whichresulted inananomalously lowmeasuredactivationenergyof9.5 2kJ/mol. Marin-Ayraletal. studiedtheNi/AlsystemunderdifferentgaspressuresusingtheBoddington- Layemethod.Theyshowedthat forpressuresof100,320,and500MPa, themeasuredactivation energieswere 47, 59, and 132 kJ/mol, respectively [68, 69]. Vadchenko et al. studied theNi/Al Advanced Chemical Kinetics182