Microwave ignition characteristics and distinction of typical nanothermites under different electromagnetic radiation

Abstract

As a commonly used agent in micro-nano satellites and other small pyrotechnics, it is crucial to understand the response of nanothermite to microwave due to the growing interest in space and the increasingly complex electromagnetic environment. Microwaves can penetrate typical energetic materials and interact with them spatially and holistically. There are two ways of microwave radiation to the samples: microwave drill (contact) and single mode resonator (non-contact). To date, all previous studies were carried out in a single environment, and only for a single thermite system. In this work, the ignition performance of three representative nanothermite systems (Al/CuO, Al/MnO2, Al/Fe3O4) under two microwave ignition devices (custom-made microwave drill and single mode resonator) was first systematically studied, which contain both magnetic and non-magnetic, as well as high and low reactivity. The results showed that the relationship between ignition delay time and power basically accorded with exponential function. The ignition delay time decreased rapidly with the increase of power and finally stabilized within a fixed range. Compare to the metal oxide, pure Al was insensitive to microwave. However, the mechanism of the two ignition processes was different. The ignition sequence of the nanothermites was the same as metal oxides, indicating that the metal oxide was the decisive factor and driver of nanothermite ignition under microwave drill. For the ignition in resonator, the nanothermite behaved like bulk metal, reflecting most of the electromagnetic energy away. The ignition sequence was consistent with the aluminum content in the composites, implying nAl was the determining factor. To further analyze the ignition mechanism, the hot wire and laser sensitivity of nanothermites were also compared.