Reactivity Enhancement and Fabrication of Al-MoO 3 Thermite Coating Using Ball Milling for Kinetic Spraying
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Reactivity Enhancement and Fabrication of Al-MoO3 Thermite Coating Using Ball Milling for Kinetic Spraying Seungtae Lee1 • Jaeick Kim1 • Changhee Lee1
Submitted: 19 February 2020 / in revised form: 25 June 2020 Ó ASM International 2020
Abstract 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.
& Changhee Lee [email protected] 1
Kinetic Spraying Coating Laboratory, Division of Materials Science and Engineering, Hanyang University, Seoul, Republic of Korea
Keywords Al-MoO3 ball milling cold spray Goldschmidt reaction kinetic spray reactive material thermite
Introduction Reactive material, also called energetic material, can release a high amount of stored chemical energy (Ref 1). The most common reactive materials are mono-molecular compounds such as 2,4,6-trinitrotoluene (TNT) and cyclotrimethylenetrinitramine (RDX). These materials have the advantage of rapid exothermic reactions but are limited by their low energy density. Due to this drawback, thermite materials with high gravimetric and volumetric reaction enthalpies have attracted the attention of researchers. Recently, studies have focused on the various applications of thermite materials, such as in explosive additives or propellants, reactive joining (Ref 2), thermal fuses (Ref 3), and microelectromechanical systems (Ref 4). Thermite materials are heterogeneous and are mostly composed of metal–metal oxides. Most of the conventional thermite materials have been used in powder form. Representatively, Al-Fe2O3 was used for thermite welding in railways. Recently, there has been an increasing demand for bulk form of thermite material. In addition, increasing the contact area and improving the uniformity of the mixture in
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