Designer Direct Ink Write 3D‐Printed Thermites with Tunable Energy Release Rates

Abstract

Breakthroughs in additive manufacturing (AM), particularly direct ink write 3D printing, have allowed for greater control of material performance by manipulation of architecture and/or spatial composition. Herein, the range of control over the dynamic energy release rate in 3D-printed Al/CuO thermite is quantified by substituting random porous pathways present in powder beds or compacts with printed void channels to modulate the energy transport during a reaction. The thermite is produced via on-the-fly static mixing of constituent Al and CuO inks, which offers a safe way to handle these materials. By reducing the fundamental burn unit size (i.e., filament size) and introducing small amounts of engineered porosity for gas flow, it is shown that energy release rates can be increased by more than 100 times that of maximum print density strips. Unique channel structures, which display propagation velocities of over 100 m s À1 due to confinement of gas flow, are reported. Ashby plots that show the reactivity design space for 3D-printed thermites are presented as a function of the effective print/ energy density. Architecting with AM tailors an object to release its energy in a prescribed way, and this control adds much-needed versatility by allowing a single formulation to satisfy multiple applications.

Multifunctional Reactive Nanocomposites via Direct Ink Writing

“…Burn rates reported for printed reactive lines range from 10 [10] to 350 mm s −1 , [32] and can reach 100 m s −1 for thermites with controlled architecture. [8] Thus, we report velocities 2-4 times slower than the slowest extant in the literature for printed reactive materials, and we do not observe any gas production during reaction. At such slow velocities, reactions can be unsteady, producing inconsistent velocities.…”

“…

typically measured by energy release rates or material burn rates. These studies have focused predominantly on thermite [6][7][8][9][10] (metal/metal oxide) or other displacement [11] (metal fuel/organic oxidizer) reactions. Formation reactions (metal/metal or metal/metalloid) have been essentially unexplored for DIW, and their most notable use in any form of 3D printing is as small percentage additives in metal powder-bed fusion feedstocks to improve final part microstructures.

…”

“…[12] Because thermite and displacement reactions rely on oxidation as the main source of exothermic energy, they typically produce gas and undesirable oxide phases, [10] and either disintegrate the printed structure or introduce significant porosity. [6,8] As such, there has been very little focus on printing reactive materials which have any particular function beyond tailoring the reaction velocity and heat evolution.…”

Electrophoretic deposition of Al-CuOx thermite materials on patterned electrodes for microenergetic applications

“…Also, microcracks can act as gas-release vents, thus reducing the impulse of the reaction flow. The work [26] presents the results of a combustion characteristic study of Al-CuOx layers printed on a 3D printer in the form of structures with vents for a gas outlet. It has been found that the wavefront propagation velocity decreases with increasing vent size.…”

A Benchmark Study of Burning Rate of Selected Thermites through an Original Gasless Theoretical Model

“…Thermites in the form of mixed particles composed of a fuel, most commonly aluminum, and an oxidizer, such as iron, copper oxide, or molybdenum oxide [1][2][3][4][5][6][7][8][9][10], have attracted considerable attention due to their controllable versatility and high reaction enthalpies, making them good candidates for a number of applications including actuation [11,12], micropropulsion [13][14][15][16][17], heat sources for welding or joining [18,19], and, more recently, micro-initiation and environmentally clean primers [20][21][22][23]. In the last two decades, nano-sized particles have been widely studied due to their advances in reactivity, e.g., lower initiation temperature, lower initiation delay, and shortened kinetics of heat release, which was a necessary development to further improve the performances of the aforementioned applications, with the potential to dethrone other types of energetic compositions [24][25][26][27].…”