Reaction Behaviors of Al-ZnO System Ignited by High-Temperature Al Melt

In this work, a constant heat source, high-temperature Al melt, was used to fast ignite thermite reactions between Al and ZnO nanoparticles (ZnO_np). The effect of initial temperatures (T_i) on reaction behavior was emphasized to reveal underlying mechanisms. The results indicate that there were two reaction modes dependent on T_i, i.e., boundary diffusion and thermal explosion. Specifically, when T_i = 900 °C, the diffusion-assisted nucleation mechanism enabled small amounts of Al₂O₃ nanodispersions to form on Al powder surfaces. As T_i increased up to 1100 °C and above, self-sustaining combustion remarkably promoted the diffusion fluxes of Al and [O], resulting in almost instantaneous nucleation of Al₂O₃ throughout the whole region. Moreover, although in situ Al₂O₃ particles tend to sinter together under higher T_i, their limited growth could be attributed to evaporation and oxidization of the reduced [Zn] that consumed excess reaction enthalpy. Al₂O₃ particles uniformly dispersed in the aluminum matrix have been obtained by remelting and diluting the master alloy reacted at 1100 °C.