Figure 3 DSC-determined onset temperatures and energy release values for Al/NiO MIC with different NiO ratios. The dependence of the onset temperatures on the NiO ratios of the composites is shown in Figure 3. It can be observed that increasing the NiO ratio Veliparib supplier did not significantly change the onset temperature of the exothermic peak. This indicates a narrow size distribution of Al nanoparticles in these composites and sufficient intermixing between Al nanoparticles and NiO nanowires.

All measured onset temperatures are smaller than the melting temperature of bulk Al. In the literature, it was suggested that the activation energy of the thermite reaction depends on the diffusion distance over which these metal ions FK506 clinical trial (aluminum and nickel which become available from the decomposition of NiO) need to travel before initiating the reaction [46]. To quantify the activation energy of the Al nanoparticle and NiO nanowire composites, the DSC curves of sample D was processed directly using the TA software and through the implementation of the American Society for Testing and Materials E698 method. Note that the ASTM method is often the only effective approach to analyze reactions with multiple exotherms because these peak temperatures at different heating rates are not significantly influenced by the baseline shift [47]. The ASTM E698 method generally gives an accurate assessment

of the activation energy. However, calculations Lonafarnib of the pre-exponential factor (Z) assume the nth order reaction behavior. The derived activation energies for sample D are 216.3 and 214.5 kJ/mol, respectively, from two methods. Figure 4 shows the procedure

to determine the activation energy from the DSC data when the kinetic rate was expressed as a function β(T) of the temperatures T max corresponding to the maximum heat flow. The derived activation energy agrees generally with the previously reported activation energies for Al nanoparticle-based thermite composites (such as, 248, 222, and 205 kJ/mol for the Al-Fe2O3, Al-Bi2O3, and Al-MnO3, respectively [48]). The activation energy of the Al nanoparticle and NiO nanowire MIC is close to but lower than the reported activation energy of the NiO reduction process (277 KJ/mol [49]). Taking into account the size effect on the reactivity of NiO nanowires, this ignition energy may indicate a thermal decomposition of NiO about the onset temperature of the studied MIC, which behaves similarly to the ignition of the Al-Bi2O3 MIC [50]. Meanwhile, for heterogeneous condensed phase MICs, the limiting factor affecting the ignition event can also be the solid-phase diffusion. Further investigations on the ignition mechanism of the Al/NiO MIC are expected. Figure 4 Graph used for determining the activation energy of sample D, 33 wt.% NiO, using ASTM E698 method. The XRD analysis was performed on the reaction products from sample D which was a fuel-rich MIC with Φ = 3.5.