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Mukasyan [20] further studied these effectson thekinetics in theNi–Alsystemusing theETE
approach.Theyshowed,byuseof theabove3Dreconstructiontechniques, that it ispossible to
control theactivationenergybymodificationof thecontact surfaceareabetweenthereactants.
Effectively, they lowered the effective activation energy from 79 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; this relationship is shown in Figure 7. Additionally, it was
suggested that, for SHS systems, the apparent activation energy is affected primarily by the
contributions between the diffusion and intrinsic reaction activation energies. Additionally,
theyofferedanexplanationfortherelationship,relatingtothedifferenceincontributionbetween
thediffusive activation energies (volume, grain-boundary, and surface) in conjunctionwith the
intrinsic activation energy. This suggests that the measured and reported activation energies
presented in literature are effective, or apparent, activation energies that dependhighly on the
structureandexperimentalconditions.
9.Modificationof thereactionmechanismdependingonthe
experimental conditions
Inaveryearlystudyonthe reactionmechanisms,Philpot etal. examined theeffectofvarying
factorsonthereactionrate [35]. Inonestudy, theysystematicallyvariedthealuminumconcen-
tration, the heating rate, and thenickel particle size. Briefly, they showed that, dependingon
the applied heating rate, twodifferentmechanisms could be initiated. The first, when using
slowerheatingrates,wasrelatedto themeltingof thealuminummetal, followedbyspreading
over thenickelparticles.For their studies, theysawtwodefinitepeaksrelating to thereaction.
Figure7. Dependenceof effectiveactivationenergyof the reactionasa functionspecific contact surfaceareabetweenNi
andAlphases.Adapted fromShuckandMukasyan [20].
Kinetics of Heterogeneous Self-Propagating High-Temperature Reactions
http://dx.doi.org/10.5772/intechopen.70560 179
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Advanced Chemical Kinetics
- Title
- Advanced Chemical Kinetics
- Author
- Muhammad Akhyar Farrukh
- Editor
- InTech
- Location
- Rijeka
- Date
- 2018
- Language
- English
- License
- CC BY 4.0
- ISBN
- 978-953-51-3816-7
- Size
- 18.0 x 26.0 cm
- Pages
- 226
- Keywords
- Engineering and Technology, Chemistry, Physical Chemistry, Chemical Kinetics
- Categories
- Naturwissenschaften Chemie