Development and Characterization of 3D Printable Thermite Component Materials

Abstract

shown that architecture could be used to manipulate the reactivity of aluminum/ copper oxide (Al/CuO) thermites by tailoring the flow of gases and entrained particles using structure. [23] A similar behavior had previously been seen in porous-Sibased energetic materials. [21] This is an exciting result in that it enables one to tailor the energy release rate in such materials without defaulting to the conventional approach of changing the formulation.To further expand upon the previous results, we seek to develop AM formulations which can enable a wide range of architectures to be printed. With this, we can design test articles to further understand and quantify to what extent architecture can be used to control reactivity. However, the direct printing of thermite raises safety concerns since, as-mixed, the materials can lead to a rapid reaction in the event of accidental ignition. A far safer approach would be to formulate the precursor materials separately, and then to directly mix during the printing process.In this work, we formulated an Al and a CuO precursor ink separately. One factor in the choice of these precursors was to pick two systems that could be formulated with similar rheological properties, as disparate rheological properties could lead to potential issues during mixing operations. Al and CuO powder feedstock materials were formulated using micron-sized particles of the materials incorporated into an aqueous hydrogel matrix to render an extrudable prethermite "ink." The rheology of these high solids loaded prethermite inks had to be such that the inks could be extruded through a nozzle (i.e., shear thinning) as wet filaments. The formulation parameters can be seen in Table 1, and some considerations are discussed later in the text. Once formulated, the inks were loaded into a syringe and mounted on the printer. A schematic of the printing setup is shown in Figure 1. The basic components of this setup are highlighted, and include two mounts for syringes, linear extrusion motors, and a precise xyz positioning stage (Aerotech). After extrusion, parts are dried in air and the as-deposited printed filaments retain the properties possessed by the dry powder feedstock material. The formulation and printability of the individual materials are investigated; we subsequently show that the two materials can be mixed on-the-fly to render an ignitable thermite ink.Additive manufacturing (AM) has recently shown great promise as a means to tailor a wide range of material properties, both quasi-static and dynamic. An example of controlling the dynamic behavior is to tailor the chemical energy release rate in composite energetic materials such as thermiteswhich are a subset of pyrotechnics that use a metal fuel and a metal oxide as an oxidizer. Since these materials are most hazardous once finely mixed, the approach taken here is to formulate the fuel and oxidizer separately such that they can be mixed on-the-fly. Herein, the development, formulation, and characterization of two respective aqueous 3D printable in...

Progress in Additive Manufacturing of Energetic Materials: Creating the Reactive Microstructures with High Potential of Applications

“…Substrate selection can seriously affect not only RMS function but also the deposition (printing) process itself. Thus, aqueous inks based on aluminum and copper oxide were shown to interact with Al or steel substrates, while ceramics were found to be inert (Figures 15d-f) [129]. In another study, the PET-based mesoporous substrate Novele TM was considered promising due to its strong adhesion to nanothermite inks [78].…”

“…The first example of robocasted RMS was reported by Tappan et al [26], where an intermetallic Al/Ni sample was fabricated and fired. Durban and coworkers [129] robocasted Al-or CuO-based aqueous inks individually, as well as the thermite mixture. The individual inks were composed of a methylcellulose hydrogel as suggested in [127], and the optimized compositions contained 74 wt.% Al and 85 wt.% CuO.…”

3D Printing of Micro‐Architected Al/CuO‐Based Nanothermite for Enhanced Combustion Performance

“…Nanothermites, featuring well‐defined reactive materials, which are a special family of energetic materials, provide a large amount of high energy release and adiabatic flame temperature during the redox reaction process . They are regarded as one of the potential replacements for the traditional energetic materials, due to their rapid heat release and lower sensitivity . Nanothermites are a class of active metal/metal oxide mixtures, of which at least one component should be on the nanoscale .…”

“…In fluoropolymer‐based reactive inks, micro‐aluminum (μm) and nano‐aluminum (nm) as the fuel at high solids loading (up to 67 wt.%) were shown . Durban et al also discussed the development, formulation, and characterization of two aqueous 3D printable inks consisting of aluminum and copper oxide, providing a safe and simple way to mix metal fuels and metal oxides. In particular, for the promising Al/CuO thermite, Sullivan et al explored the controlled material reactivity of nanothermite using the architecture .…”

“…In particular, for the promising Al/CuO thermite, Sullivan et al explored the controlled material reactivity of nanothermite using the architecture . The authors further demonstrated the prethermite aqueous ink formulation of printable, and combustion properties . However, instability and fracture of viscoelastic inks are still the challenges in the 3D printing of nanothermites …”