Researchers from the University of Houston, US, led by Karen Martirosyan have shown recently that a mixture of aluminium and bismuth trioxide (Al/Bi2O3) generated the highest pressure pulse among common thermite reactions. The combination may be used as a nanoenergetic gas generator (NGG) and has the potential of being used in next generation of weapons and explosives.

A possible explanation for the high pressure rise during the combustion of the Al/Bi2O3 system is that the combustion product (bismuth) boils at a temperature of 1560 degC, which is lower than the maximum reaction temperature (2000 degC). This causes bismuth evaporation and increases the pressure of the released gas.

The combination of NGG and MEMS (micro-electro-mechanical systems) technology may enable a reduction in the size and mass of weapons. For practical NGG applications it is important to develop a large scale process to produce nanocrystalline bismuth trioxide particles.

In a recent study, which was published in the journal Nanotechnology, the authors used a modified solution combustion synthesis approach to fabricate highly crystalline Bi2O3 nanoparticles. The process may be scaled up for continuous large-scale production of bismuth trioxide nanoparticles.

The researchers tested the reactivity of the synthesized bismuth trioxide with aluminium nanoparticles. A peak pressure of around 12 MPa and an estimated energy release of 20 MJ/kg were generated using as-synthesized Bi2O3 nanoparticles mixed with aluminium particles (100 nm) for 9 h. The maximum detonation front velocity for that mixture was around 2500 m/s.

Currently, the team is investigating novel NGG materials that generate high (pressure x volume) PV-values and rapidly release a vigorous amount of gaseous products.

About the author
The work was performed at the University of Houston, US, and supported by the US Air Force Research Laboratory under agreement number FA8650-07-2-5061. Karen Martirosyan is a Research Assistant Professor in the Department of Chemical and Biomolecular Engineering with a joint appointment in the Department of Electrical and Computer Engineering. Leizheng Wang is a PhD candidate and Arol Vicent is an undergraduate student studying chemical engineering. Both are based at the University of Houston. Dan Luss is a Cullen professor in the Department of Chemical and Biomolecular Engineering at the University of Houston.