Synthesis and Characterization of Metal Fuels for Enhanced Reactivity
Abstract
Key Objectives: The goal of this project is to modify surface energy of metal particles and examine their energy release mechanisms in thermal and mechanical impact environments. One strategy for modifying surface energy is based on the metallurgical process of p re-stressing, defined as the intentional creation of permanent stresses in a structure for the purpose of improving its performance. We established the feasibility of this approach and designed annealing and quenching treatments to increase the strain and stress w ithin an aluminum (Al) particle. One hypothesis is that annealing and quenching induces formation of a polarized surface layer which changes surface energy and controls the electron transport at the interface which, in turn, affects reactive energy release rates. A second hypothesis is that stress-altering may produce more intense/complete fracture of the alumina shell under impact loading co nditions, leading to easy access of oxygen to the aluminum core and more complete combustion. Surface modified fuel particles using methods such as dry coating and chemical processing will also be examined to control surface energy properties. Propellant burning and ballistic environments were selected to unravel fundamentally different ignition and reaction mechanisms associated with increa sed surface energy. In propellants, metal fuel particles react mainly through thermal ignition in a dispersed medium. Surface cataly tic reactions are important at the interface of the metal oxide and propellant that are a strong function of surface energy and disp ersion. In ballistics, mechanical impact imparts dramatically different dynamics to the particle for ignition, and modified surface energy may better couple energy output to a target. To address our goal, the objectives are to: synthesize metal fuel particles wit h varied surface energy and characterize their surface properties; experimentally and theoretically examine their fundamental single particle combustion mechanisms; their reactivity in propellant formulations; their reactivity in high velocity impact ignition envi ronments; and, analyze ignition and reaction mechanisms distinct for thermal versus impact conditions and particle surface energy. M ethodology/Techniques: To accomplish our goal and objectives, tasks include: synthesize surface modified particles and characterize their properties; design and perform experiments coupled with density functional theory (DFT) calculations to quantify their energe tic response and analyze reaction mechanisms in terms of single particles, propellant reactions, and impact ignition. Significance: Two problems with metal fuel combustion are firstly, reactions are relatively slow (ms) compared to detonation events (s) so parti cles struggle to contribute to the energy release at early timescales. Secondly, while fuel particles have a high energy density, in complete combustion often plagues reactions and limits the potential chemical energy available. For example, under impact loading co nditions, the chemical energy released from Al combustion is only about 15% of the total energy available. Instead, metal particles t altering surface energy will activate unique reaction mechanisms that enable greater energy release rates and more complete combus gy such that the mechanisms promoting greater reactivity are complex. Our team is multidisciplinary spanning expertise in experiment al combustion and DFT calculations of physical and chemical surface properties including thermodynamic quantities. Improving fuel pa rticle combustion is a major challenge with fundam ts to metal-based energetic systems by deliverin
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- Nov 16, 2021
- Source ID
- N000142212006
Entities
People
- Michelle L. Pantoya
Organizations
- Office of Naval Research
- Texas Tech University System
- United States Navy