Time-resolved X-ray diffraction study of SHS-produced NiAl and NiAl-ZrO2 composites

New Entropic Routes for Nano‐Bands and Nano‐Particles

“…The overall reaction thus can yield products of NiAl banded (for low T") or multiple phases, e.g., NiAl, Ni2Al 3 and NiAl 3 , (for high T 0 , slow cooling and higher T c ). Other solidification products could be seen if cooled much slower or the synthesis begun with a higher initial temperature, T 0 , which normally leads to a very' high combustion temperature (T c ), full mixing and then the precipitation of equilibrium compounds during cooling, e.g., [10,12,29,[42][43][44][45][46][47]. An important point to note is that significant variations in the final product chemistry are possible depending on the initial processing conditions chosen.…”

“…Several time-resolved X-ray studies have been carried out and reported [24,26,27,29,32,46,60,61,[78][79][80][81] which indicate the occurrence of the intermediates during micropyretic synthesis of NiAl compound. The list of reactants, intermediates, and products reported in different studies at different time intervals from time-resolved X-Ray diffraction patterns are shown in Table 2 [4,26,27,29,46,60,61,80,81].…”

“…A compilation of published data [24,25,41,47,[62][63][64][65] and new data on thermal oscillations also points to the BZ hypothesis [31,40,[66][67][68][69][70][71]. Table 1 Variation in the product phases generated from the different processing techniques and initial conditions [10,27,29,[42][43][44][45][46][47]. Note the change in the observed phases with a change in the initial temperature.…”

“…The problem is illustrated by an example from NiAl alloys. A summary of reported mechanical properties [31,40,41] and phase constituents of micropyretically synthesized NiAl alloy objects is shown in the previous study [9] and Table 1 [10,27,29,[42][43][44][45][46][47]. The increase in compressive ductility and increase in toughness are not fully correlated.…”

“…A Brusselator sequence (a simple BZ sequence) is discussed below for BZ oscillations in the equimolar NiAl system. The sub-reactions shown below, especially when oscillatory (i.e., dissipative), offers a method of dispersing nano-particles and faulted regions in a manner similar to micro-particle and micro-band formation in lower temperature chemical reactions [7], We also compile evidence from the literature for the sub-reactions and BZ hypothesis from published synchrotron and fine-scale time-lapse XRD studies [24,26,27,32,46,60,61] for explosive micropyretic synthesis of NiAl and other compounds. A compilation of published data [24,25,41,47,[62][63][64][65] and new data on thermal oscillations also points to the BZ hypothesis [31,40,[66][67][68][69][70][71].…”