Prestressing Metal Fuel Particles for Enhanced Reactivity
Abstract
Key Objectives: The goal of this project is to optimize the reactivity of metal fuel particles in propellant and explosive systems. The optimization strategy is based on the metallurgical process ofprestressing, 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 andquenching treatments to optimize the stress state within aluminum (Al) particles. The prestressed Al particles were shown to exhibit greater reactivity when combined with a solid oxidizer and ignited with thermal and drop weight stimuli. A focus of this project is to design micron-scale fuel particles that will release greater energy under ignition and reaction conditions relevant to the Navy: specifically,(1) in propellant systems; and, (2) with high velocity impact loading conditions. These two scenarios were selected to unravel fundamentally different reaction mechanisms associated with prestressed particles that are a function of the ignition conditions. Theoretically, in both scenarios prestressing isexpected to produce more intense fracture of the prestressed alumina shell due to release of energy associated with internal stresses during fracture or detachment of the shell from the core leading to easy access of oxygen to the aluminum core. To address this goal, our objectives are to: (1) synthesizefuel particles with altered mechanical properties that are optimized for their elevated stress; (2) experimentally characterize prestressed particles for their physical, mechanical, chemical, and thermal properties; (3) examine the reactivity of prestressed particles in controlled environments purposefullyselected to evaluate reaction mechanisms associated with thermal and impact ignition conditions and representative of propellant and explosive applications; and, (4) develop mechanochemistry based theoretical models to link the mechanical and chemical properties of individual prestressed particlesand particle agglomerates to energy release processes that describe reaction behaviors of single particles as well as bulk powders and shed light on the role of core-shell interaction throughout ignition and oxidation.Methodology/Techniques: To accomplish our goal and objectives, a systematic and multi-phase methodology will be employed to: (1) synthesize prestressed particles and characterize their material properties; (2) quantify their energetic response in terms of varied ignition stimuli predicted to incite different reaction mechanisms; and, (3) model the deformational, thermal and mechanochemicalprocesses in a single particle, particle interactions, and a bulk powder sample under various loadings that incite new reaction mechanisms and optimize energy release.Significance:Most fuel particles are a composite structure of a metal core encapsulated by a metaloxide passivation shell. Magnesium (Mg) and aluminum (Al) particles are good examples of the core-shell structure. A problem is that the chemical energy inherent within metal particles is notfully released such that garnering more energy from micron-scale fuel particles is an objective of this study. The strategy employed here is that prestressing fuel particles will activate unique reaction mechanisms that enable greater energy release and exploring these reaction mechanisms as a function of ignition condition is a focus of this study. Our team is multidisciplinary spanningexpertise in mechanochemistry, experimental combustion, propellants, and astrophysics to provide synergy for project success. Improving fuel particle combustion is a major challenge with fundamental relevance to the Office of Naval Research and will provide enhancements to metalbased energetic systems, thus delivering fundamental insights into the phenomena surroundingignition and energy generation.
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- Feb 07, 2019
- Source ID
- N000141912082
Entities
People
- Michelle L. Pantoya
Organizations
- Office of Naval Research
- Texas Tech University System
- United States Navy