OPTICAL IGNITION AND COMBUSTION CHARACTERIZATION OF METAL FLUOROPOLYMER COMPOSITES
Creators: name: Uhlenhake, Kyle
Publisher: name: Purdue University Graduate School
Year: 2022
Subjects: Chemical and thermal processes in energy and combustion
Chemical thermodynamics and energetics

description: The ignition of energetic materials, and specifically solid propellants, is a complex process that must be safe, consistent, and precisely controlled. There is a wide range of applications with specific ignition requirements for solid propellants including inflation of airbags, propulsion systems (including rockets), as well as arm and fire devices. Currently, electrical or percussion pyrotechnic igniters are most the commonly used ignition systems. These systems must be carefully designed to deliver the proper amount of energy to a specified surface area of the propellant. A photon light source (i.e. flash or laser-based, ranging from UV to IR wavelengths) can potentially be used to ignite energetic materials with lower input energy and more precise spatial and temporal control, thereby improving safety and reliability by eliminating electrical systems used in pyrotechnic igniters. In addition, they could be potentially safer from stray electrical charges causing unintentional ignition. The purpose of this work is to further explore the potential of optical ignition for energetic systems and identify ideal materials that can be used for optical ignition. In order to identify optically sensitive materials, we will study ignition energies, ignition delays, flame temperatures, and other combustion characteristics for possible energetic materials. This research addresses a gap in understanding of optical ignition for energetic materials, as finding and integrating materials that are optically sensitive while still being practical can be extremely challenging. These challenges include: (1) a lack of absorptivity to optical wavelengths in the UV to low-IR range, and subsequently, a very high sensitivity to input energy at the absorptive wavelengths that makes sustained ignition difficult, (2) a need for full density materials in practical energetic systems, while optically sensitive materials are exceedingly difficult to ignite as packing density increases due to heat transfer, and (3) the lack of research regarding novel fuels/oxidizers for the specific purpose of optical ignition. Metal/fluoropolymer energetic materials have been of interest to the energetic materials community for many years. Due to fluorine’s excellent oxidizing ability, they can be used in composite materials with metal fuels to produce energetic materials for a wide variety of applications. Polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), polycarbon 13 monofluoride (PMF), and terpolymers such as tetrafluoroethylene, hexafluoropropylene, and vinylidene fluoride (THV) have already seen extensive use in applications ranging including protective coatings, strain gauges, and electronics. However, when combined with metals such as lithium, magnesium, aluminum, or titanium, they also present an opportunity for a wide variety of energetic materials. For this study, metal/fluoropolymer composites present a novel opportunity for exploring optical ignition of widely absorptive, full-density energetic materials. This work will characterize the combustion and sensitivity of metal/fluoropolymer composites to provide novel materials for optical ignition of energetics. Specifically, this work will begin with finding a suitable energetic composite that is optically sensitive. Once this material has been identified, research will be done to thoroughly characterize the optically sensitive composite by looking at additive manufacturability, flame temperatures, and ignition sensitivities from various methods and formulations. Once the material has been thoroughly characterized, it will be implemented into solid propellants to test the feasibility of the material in practical energetic systems. Finally, the lessons learned from this work will be applied to novel formulations to identify new optically sensitive energetic composites.