Page - 178 - in Advanced Chemical Kinetics

of thereactivecompositebyusinghigh-energyballmilling(HEBM)inthesamebinarysystem, one can significantly change the measured effective activation energy [20]. There are two approaches to quantifying this effect; the first is by rigorous quantification of the already existing structures, and the second isbyuseofmore simple, so-calledmodelmicrostructures, typicallymanifested inreactivenanofoilswithperiodically fabricated layersof reactants. Shuck et al. utilized two techniques for quantitativedeterminationofHEBM-producedmate- rials [5, 157]. The first technique, X-rayNanotomography, works by passing high brilliance X-rays through the sample and collecting the transmittedX-rays. In order to convert this 2D projectionintothreedimensions, thesample isrotatedandthesamequalityofX-rays ispassed throughagainandtheprojectionsatdifferentanglesarecollected; thiscollectionof imagescan be combined, leading to a 3Dmapof the internal sample. The second technique, focused ion beam(FIB)sectioning,usesaFIBtoseriallysectiontheHEBM-producedparticles.Theseriesof imageswere first shear corrected, contrastnormalized, and thenalignedusinga least-squares method, with the reconstructions shown in Figure 6. After structure analysis, Shuck and Figure6. Reconstructed internalvolumesof thenanocomposites fordifferent time (min)ofWG: (a)10, (b) 20, (c) 30, and (d)40 (Ni is thegrayphase,andAl is thevoid-space).Adapted fromShucketal. [5]. Advanced Chemical Kinetics178