TiO₂-Bi₂O₃ bimetallic oxide nanocomposite coatings for enhanced ignition and combustion of boron-based energetic materials

Boron is a promising high-energy-density fuel for solid propellants and pyrotechnics, but its practical application is hindered by poor ignition and incomplete combustion due to the formation of a viscous B₂O₃ passivation layer that restricts oxygen diffusion. To overcome these challenges, this study explores nanostructured TiO 2 -Bi 2 O 3 bimetallic oxide composite coatings as surface additives for boron particles. These composites harness the complementary functions of TiO 2 , which provides catalytic support and facilitates oxygen vacancy formation, and Bi 2 O 3 , which serves as a rapid oxygen donor and exothermic reaction partner to mitigate the kinetic barriers imposed by the native boron oxide layer. Structural and morphological characterization via XRD, SEM, TEM, and EDS confirm successful Bi integration into the TiO 2 lattice, resulting in altered crystallinity, increased lattice distortion, and homogeneous Ti-Bi dispersion. Optical studies show a redshift in TiO 2 absorption upon Bi 2 O 3 incorporation, indicating enhanced surface interaction and defect-state formation. Compositional validation through ICP-OES and EDS confirms the targeted Bi 2 O 3 content, ensuring consistent synthesis and deposition. Thermal reactivity evaluations, including ignition delay time (IDT), heat of combustion (HOC), thermogravimetric (TGA), derivative thermogravimetric (DTG), and differential scanning calorimetry (DSC) analyses, demonstrate significantly enhanced ignition and combustion performance for TiO 2 -Bi 2 O 3 -coated boron formulations compared to bare boron and TiO 2 -only coated boron. The optimal composition (25 wt% Bi 2 O 3 at 0.9 mol% composite loading) exhibited the 28% reduction in IDT (193.9 µs) and a 21.6% increase in HOC (16.9 MJ/kg), highlighting the synergistic effects of the bimetallic system. These findings establish TiO 2 -Bi 2 O 3 composites as efficient, tunable, and scalable surface additives that lower ignition temperatures, enhance combustion completeness, and optimize thermal energy transfer in boron-based energetic materials. This work provides a foundation for the development of next-generation metal oxide additives with multifunctional catalytic roles, opening new avenues for advancements in high-performance combustion systems.