Preparation and reactive performances of Al/Co₃O₄/CoF₂ metastable intermolecular composites

Metastable intermolecular composites (MICs) typically use Al as fuel and transition metal oxides as oxidizers, while their reactivities are hindered by the inert Al₂O₃ passivation layer on the surface of Al particles. Recently, transition metal fluorides have emerged as novel fluorine-containing oxidizers for promoting the reactivity of metal fuels through interfacial fluorination of oxide layer. In this work, nanosized CoF₂ and Co₃O₄ were prepared through pyrolysis of CoF₂·4H₂O precursor using different calcination conditions. To investigate the function of CoF₂ in reaction and the influence of CoF₂ content on reactive performances, a series of MICs composed of n-Al, Co₃O₄, and CoF₂ were prepared through ultrasonic dispersion method. Thermal analysis indicated that Al/CoF₂ composite had significantly higher specific heat release (2.30 kJ/g) than that of Al/Co₃O₄ composite (1.45 kJ/g), and CoF₂ facilitated the occurrence of exothermic reaction at a relatively lower temperature. AlF₃ was found as main reaction products of Al/CoF₂ at 650 °C, and AlF₃ sublimes at the temperature above 850 °C. Although the pressure output and flame intensity of Al/CoF₂ composite is lower than that of Al/Co₃O₄ composite, hybrid Al/Co₃O₄/CoF₂ composites with 20 %–35 % CoF₂ showed significantly enhanced energetic performances compared with sole Al/Co₃O₄, suggesting that CoF₂ can function as an effective reaction modifier.