Combustion of 3D printed 90 wt% loading reinforced nanothermite

Abstract

The use of Al-based nano-energetic materials has been limited in part due to difficulties in fabrication of high-density composites. In this paper, free-standing energetic composites with loading of up to 90 wt% Al-CuO were fabricated by 3D printing. A polymer hybrid of 3 wt% hydroxy propyl methyl cellulose (HPMC), 3.5 wt% nitrocellulose (NC) and 3.5 wt% polystyrene (PS), enables fabrication of mechanically strong and highly reactive composites. The energy flux can be readily tuned through the combustion speed and flame temperature by changing equivalence ratio. The highest energy flux was found to occur under fuel rich conditions (equivalence ratio = 2.4) which also corresponds to the maximum combustion speed (25 cm/s) despite the fact that the flame temperatures was lower. The Young's modulus of free-standing burn sticks was found to be as high as ~1 GPa, which is comparable to pure polypropylene. PS polymer flakes created during the high shear direct write process is believed to be critical to the enhanced mechanical properties we observed. The burning behavior using other oxidizers corresponds closely with that observed with mixed powders but with the added strength offered in a printed structure. This study offers an attractive route for safe, reliable and scalable additive manufacturing of Al-based nano-energetic materials at high energy densities.