Chemistry-Assembly-Function Relationships of Reactive Materials for CWMD
Abstract
Modern conflicts and threats have highlighted the need for a preemptive strike, capable of neutralizing chemical and biological agent munitions, stockpiles and production facilities. Conventional warheads however are unsuitable to the task as they will result in considerable dispersion of these agents to the surrounding population. New strategies are required. Thus the ideal agent defeat weapon should possess both a thermal and catalytic defeat mechanism. The first two points listed above tend to focus attention on both the type of thermal and biocidal sources. For the thermal component, “reactives”, particularly those comprising thermite chemistry produce the highest energy release per unit volume. Furthermore since the products of combustion tend to be primarily in the condensed phase, some of the issues associated with high blast overpressures are minimized. As described above, many reactive components when operated in isolation offer superior reactivity and energy release, as well as offer biocidal products of combustion. However, these same components in many cases suffer from long term stability when exposed to air or moisture. While the use of nanoscale components is known to enhance energy release rate, a major challenge is developing field deployable formulations that are easy to manufacture, economical, offer long term stability, with enhanced performance both from the energetic and biocidal standpoints. Iodine-rich and fluorine-rich reactive material compositions have shown good efficacy for killing spores in explosive tests conducted under the DTRA CWMD Basic Research program. These results are consistent with direct studies of spore kill by the chemical species I2 and HF, although the spore-killing mechanism is unknown; synergistic effects of moisture and heat are clearly in play, but have yet to be quantified. Reactive materials must produce high thermal output and large amounts of biocidal chemical products over both short (milliseconds) and long (seconds) time scales to accomplish prompt and persistent agent defeat. Fine control of reactive material ignition and propagation behavior is needed to meet this requirement. While a few reactive material compositions have shown good efficacy in explosive tests using low density powders, the spore-killing mechanisms remain to be identified and the systems may be far from optimized. An additional consideration is that there is evidence that many reactive materials, even including nanothermites, do not undergo complete reaction, and may have energy release as much as a factor of two lower than expected. This suggests a kinetic bottleneck that should be evaluated and mitigated. This project focuses on synthesis, characterization, reactive analysis and biocidal efficacy of candidate halogen-rich energetic compositions. The materials will be designed to greatly enhance control over ignition and propagation characteristics to allow temporal control of reactions over the time scale of less than 1 ms to at least 1 s, and function at relatively high percent of theoretical maximum density (TMD), while maintaining high thermal output and high output of biocidal chemical products. We focus on both chemical and structure relations, and the work entails synthesis of individual components and assembly of these components. We employ a variety of diagnostics methods to tweeze out these relationships. This research will elucidate Chemistry-Assembly-Function relationships for reactive materials. Using a variety of state-of-art probes with reactive materials designed for control of reactive interfaces, we will characterize fundamental aspects of initiation and propagation. Independent control of initiation and propagation will allow for temporal and spatial control of thermal output and biocidal chemical products, which could be used to dramatically improve the function of reactive materials in agent defeat and other applications.
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- May 26, 2016
- Source ID
- HDTRA11510018
Entities
People
- Michael R. Zachariah
Organizations
- Defense Threat Reduction Agency
- University of Maryland