Metal atoms trapped in cryogenic matrices as potential rocket fuels

Abstract

Metal atom dispersions in cryogenic matrices are potential high-energy density rocket fuels. Using the 7sp extractable to rate a fuel, we have examined the potential of a family of in fuels, in combination with liquid oxygen or liquid fluorine oxidizers. The fuels studied were composed of a dispersion of light metal atoms in a molecular hydrogen matrix. The 7sp was calculated using a thermodynamic code designed for rocket combustion. The code requires accurate values for the enthalpy of formation of the fuel (A///(fuel)). For any particular total metal mole fraction (i.e., loading) the metal in matrix fuel will contain a distribution of metalbearing species. Each will have its own characteristic A//y. The weighted sum of these yields A/f/(fuel). Consequently, accurate calculation of A///(fuel) requires that this population, the relative concentrations of free metal atoms, dimers, and metal bearing clusters, be accurately described. A statistical model was devised to predict this distribution. Using it, the enthalpy of formation of the fuel was computed. We find that several members of the family studied have, in combination with either liquid oxygen or fluorine, an 7sp potential significantly greater than that which characterizes the best currently available fuel/oxidized combination. In general, for all the family members studied, the maximum 7sp is extracted when the metal atom concentration is maximized, and under these circumstances the oxidizer reacts exclusively with the metal inclusions while the matrix behaves as the system's working fluid. Finally these predictions, based on our statistical model of the distribution of metal bearing species, were compared with predictions based on models in which 1) only metal atoms and dimers are present in the matrix, or 2) only selectively positioned metal atoms are included in the matrix.