Navy

Metal hydride nanoparticle energetics

Ti–B–H powders with potential uses as a powder fuel for munitions, as reactive powders for production of ceramics, or use in combustion synthesis

Materials

Hydrocarbon fuels are the substances of choice for powering all types of machines and devices due to their high-energy density, ease of storage and transfer, and their liquid state at room temperature. But for many reasons, it is worthwhile to look at other compounds as potential alternatives to hydrocarbons in all areas from machines to munitions. One such class of compounds are nanoparticles containing light elements which rival hydrocarbons in gravimetric energy content. While elemental forms of hydrogen, lithium, beryllium, boron, magnesium, titanium, and aluminum are all candidates, H, Be and B are the only ones that exceed hydrocarbons’ gravimetric energy density. Unfortunately, in their elemental forms, each of these has significant flaws. Hydrogen is difficult to transport, beryllium is acutely toxic, and boron suffers from combustion problems.

A common issue with all, as nanoparticles, is instability in the air. This has led to research in passivating the materials and trying to create a balance between the intrinsic and valuable properties of the material (energy density) and the amount of passivator applied. Such processes have relied upon on high-temperature reactions with less than ideal outcomes.

Recently, Navy researchers developed a novel metallic nano-material of titanium, boron, and hydrogen to mitigate the low volumetric energy density of hydrogen while increasing the overall energy density of the Ti-B thereby producing a reactive, high energy density material.

The process yielding Ti-B-H nanopowder is shown in the figure below.

Reaction mechanism to create Ti-B-H nanoparticles at room temperature.

This method can produce particles of a smaller size that are moisture and air stable, which will enable better burn properties. This method can be extended to other higher density transition metals, such as hafnium, tantalum, thorium, and uranium, which would produce much higher density materials, giving the munitions that carry it greater momentum while retaining the same burn or shock wave characteristics as the lighter metals currently used.

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