Dissolution of tungsten-tin compared to tungsten-nylon rounds.

Abstract

Several materials have been used as binders in tungsten composite materials, including nylon fibers and metals such as tin, nickel, iron and cobalt. Tungsten composite materials have been used in munitions formulations ranging from smalland medium-caliber rounds to anti-tank missiles. There is concern that the nature of these metal composites may affect the solubility, and, therefore, the possible migration of tungsten and/or other metals into ecological systems. Tungsten solubility issues were addressed in this study by determining the bullet component mass loss associated with unfired tungsten–nylon bullet components, compared to unfired tungsten–tin bullet components. Tungsten concentrations detected in solutions that had been exposed to unfired tungsten–tin bullet components ranged from 1 to 4% of the tungsten concentrations in solutions exposed to unfired tungsten– nylon bullet components. The difference in bullet component mass loss rates between tungsten–nylon and tungsten–tin rounds may be explained by the difference in the materials used as binders in the tungsten composite matrix. The nylon polymer binder is an organic polymer that provides pathways for water to permeate the interior of the bullet component. The tin binder is less porous than the nylon polymer, which decreases the potential for tungsten dissolution from the interior of the metal composite matrix. Tungsten dissolution from the tungsten composite matrix is also decreased by galvanic corrosion when a metal (tin) binder is used. The protective effect of galvanic corrosion is reduced as the metal binder dissolves from the composite matrix and exposes more tungsten to solution. Galvanic corrosion and increased surface area explain why the relative positive effect of the metal binder with regard to dissolution rate was reduced when particle sizes decreased.