Reactivity Enhancement and Fabrication of Al-MoO3 Thermite Coating Using Ball Milling for Kinetic Spraying

Thermite materials, which are a pyrotechnic composition of metal and metal oxide, can create bursts of heat and high temperature thanks to an exothermic reduction–oxidation reaction. Fabrication methods of bulk thermite materials should preserve the reactivity of the materials and ensure a sufficient mixing of components. This work investigated the use of kinetic spraying and ball milling to overcome the limitations of existing preparation methods. Aluminum–molybdenum trioxide (Al-MoO3) was selected as thermite material. Ball milling and the fractions of metal and oxide were chosen as the variables of the study. The mechanical properties and reactivity of various powders and coatings were evaluated. The milled powders and coatings were successfully fabricated without reactivity loss by properly controlling the process parameters. The bond strength of the Al-MoO3 coating was however weaker than that of a pure Al coating because the MoO3 powder interrupted the intimate bonding between the Al splats. A reactivity analysis demonstrated that ball milling improved the reactivity of both the powders and the coatings by increasing the exothermic value, decreasing the reaction onset temperature, and decreasing the activation energy required for the thermite reaction. The mechanical properties and reactivity of coatings did not vary significantly with the MoO3 fraction.