Tuning the reactivity and energy release efficiency in aluminum alloy thermite by eutectic silicon

Abstract

The unstable energy release efficiency hinders the application of Al/CuO metastable intermixed composites (MICs) in pyrotechnic applications to some extent. To overcome this issue, systematic experiments of Aluminum-Silicon (Al-Si) alloy-thermites with different Si content (12 wt% and 20 wt%) have been investigated in the context of regulating the energy release process. Optical diagnosis methods were applied synchronously to measure the flame propagation velocity and temperature field variation. Scanning electron microscopy and differential scanning calorimetry were used to observe the morphology and analyze the thermal process. Results indicated that the introduction of silicon significantly stabilized the combustion process of Al-Si/CuO due to the fewer gas-phase products and slower reaction rate of Si with CuO, while the flame temperature changed little. Excess silicon wafer blocks observed by SEM on Al-20Si led to an enhanced transport of oxygen and fuel. This explained the abnormal reactivity of hypereutectic alloy. The total heat releases of Al-20Si and Al-12Si were respectively enhanced by 110.2% and 93.1% in comparison with that of Al under DSC tests. Infrared temperature measurement of the Mg/Teflon/Viton (MTV) column revealed that Al-12Si and Al-20Si alloy thermites ignited MTV column 569.06 and 540.48 ms faster than Al/CuO, respectively, as the energy output mainly existed in the form of high-temperature residues. These improvements are attributed to the synergistic effect of the reactivity of silicon and aluminum, as well as the phase change during reaction which provides a controllable energy release process of alloy thermite and a better ignition performance. These findings are expected to facilitate the development of the nature of Al alloys and are especially promising for the thermite technology driven by reliable energy release rates.