Experimental observation of the heat transfer mechanisms that drive propagation in additively manufactured energetic materials

The rise of additive manufacturing has led to the development of new architectures and allowed researchers to 3D-print a variety of energetic composites with different formulations. However, reactive sintering within the composites can negatively impact overall performance of nanoenergetic or reactive materials via the loss of nanostructure. It has been previously proposed that the addition of a gas generator could reduce the impact of reactive sintering while enhancing reactivity. Iodine pentoxide (I2O5) is an extremely powerful oxidizer and a strong gas generator which has been proposed as an efficient source of molecular iodine for biocidal applications. However, fabricated Al/I2O5 nanocomposite propellants are unable to propagate. In this study, we demonstrate that the addition of small quantities of CuO enables consistent propagation. Employing high-speed pyrometry and microscopy, we estimate advective heat transfer in the system and demonstrate that the addition of CuO offers a pathway for enhanced energy-transfer by metal condensation that is not available when I2O5 is the sole oxidizer. Elimination of condensing metal vapor as a participant in energy transfer increased the reliance of the system on particle advection. Small additions of CuO yield a condensable product vapor which can effectively eliminate the reliance on heat transfer via advection, enabling consistent propagation in reactive solid materials. We conclude with a general comment that where reliable propagation is critical, such as a stable burn of a solid propellant or delivery of a biocide, small additions of an oxidizer with a condensable metal vapor could be the difference between guaranteed performance and critical failure. (C) 2020 The Combustion Institute. Published by Elsevier Inc. All rights reserved.