Energetic materials (EMs) are a class of self-reactive materials that store substantial chemical energy and can rapidly release it upon external stimulations. Metastable intermolecular composites (MICs), typified by nano-thermites, are a class of EMs that comprise high-energy fuels and oxidizers that can undergo highly exothermic redox reactions. Owing to advantages of high energy densities, fast reaction speeds, and good self-sustainability even at the microscale, MICs have attracted considerable interests over past three decades and are regarded as promising materials for a variety of military, aerospace, and civilian applications.

Considering that the essence of redox reaction in MIC is the transfer of high electronegative atoms (mainly oxygen and fluorine) from a high-potential donor (i.e. oxidizer) to a low potential acceptor (i.e. fuel) across the interface between the two, the reaction characteristics of MICs are highly dependent on the thermochemical properties of reactants and their interfacial structures. Typical MICs employ high-energy metals or metalloids, such as Al, Mg, B, and Si, as fuels owing to their high heat of oxidation and fluorination. However, the particles of these fuels are universally covered by oxide passivation layers on the surface, and the surface oxide layers will grow thicker with the progress of the oxidation, which increases the reaction barrier and leads to incomplete reactions. This problem can be alleviated by introducing fluorine-containing oxidizers or additives into energetic composites because fluorination products such as fluorides and oxyfluorides are generally looser and more volatile than the corresponding oxides. Previous research on fluorine-containing oxidizers mainly focused on fluoropolymers and small organic fluorides. However, inorganic metal fluorides have long been ignored even though they are also capable of same function from the perspective of thermodynamics. Considering nanosized metal fluorides may have some unique but unknown properties in energetic composites, they are worthy of more in-depth and comprehensive investigations.

The works presented in this thesis mainly aims to explore the reactive performances and reaction mechanisms of metal fluorides and fluoride derivatives in aluminum-based energetic composites. There are totally ten chapters. Chapter 1 provides a general introduction to energetic materials, metastable intermolecular composites, fluorine-containing oxidizers, and synthetic methods of metal fluorides. Chapter 2 analyses the theoretical heat of reaction in element/oxide and element/fluoride systems from the perspective of thermochemistry, which provides a theoretical guideline on the composition design. Chapter 3 concerns the methodologies of characterization instruments, testing platforms, and relevant other experimental techniques which are frequently utilized in subsequent chapters. In Chapter 4, nanosized NiF₂ and NiO are synthesized through pyrolysis of NiF₂·4H₂O precursor, and the comparison studies between Al/NiF₂ and Al/NiO are conducted in order to investigate the difference between oxide and fluoride. In Chapter 5, I develop synthesis methods of nanosized CoF₂ and Co₃O₄ from CoF₂·4H₂O precursor, and a series of Al/CoF₂/Co₃O₄ composites with various formulations are prepared and tested systematically. In Chapter 6, I synthesize porous CoF₂ through NH₄CoF₃ precursor and investigate the influence of CoF₂ on KClO₄ and Al/KClO₄ composites. Chapter 7 demonstrates the fabrication method of vertically aligned Co(OH)F@Al nano-array on substrate and presents an in-depth investigation on its reaction mechanism. In Chapter 8, the fabrication method of Co(OH)F@Al nano-array is further developed, and the relationship between morphology and heat release is investigated. Chapter 9 presents some preliminary results of some other metal fluoride derivatives which are potential fluorine-containing oxidizers. In the end, Chapter 10 briefly summarizes the main findings throughout the thesis and draws the overall conclusion.