Exploring the Effects of Reaction Conditions on Morphology and Stability of Sonochemically Generated Ti–Al–B Fuel Powders

Abstract

Sonochemically mediated dehydrogenation of in situ generated complex metal hydrides is a promising methodology for the synthesis of mixed-metal powders for fuel applications that can be tailored toward greater energy content and other desirable characteristics. Here, we report a significant improvement in the synthesis of Ti–Al–B reactive metal powders by the elimination of parasitic impurities from the synthesis, focusing on the effects of synthetic and processing parameters on the final fuel composition, morphology, energy content, and reactivity. Reactions to produce fuel samples were carried out using both the previously reported addition of ethereal solutions of LiAlH4 and LiBH4 to a solution of TiCl4 and, importantly, the reverse, where a homogeneous solution of TiCl4 in diethyl ether was added to a homogeneous solution of LiAlH4 and LiBH4. The product powders were characterized via TGA/DSC, XPS, ICP-OES of the digestate, and oxygen bomb calorimetry of polymer-encased metal powder–fuel composites. In order to accurately measure the energy content of these materials, HTPB was used as a protective matrix for powders combusted using bomb calorimetry. The powders produced by the two methods had similar elemental compositions; however, the materials produced by “reverse addition” exhibited surprisingly different morphology and fuel properties compared to the “traditional” counterparts. The improvements in synthetic methodology lead to significant improvements in the fuel energy content, remarkable particle size monodispersity in the submicron size regime, and excellent reproducibility of the energy release observed for powder fuel-HTPB composites.