EVALUATION OF ELECTRIC SOLID PROPELLANT RESPONSES TO ELECTRICAL FACTORS AND ELECTRODE CONFIGURATIONS by ANDREW TIMOTHY HIATT A DISSERTATION Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy in The Department of Mechanical & Aerospace Engineering to The School of Graduate Studies of The University of Alabama in Huntsville Huntsville, Alabama 2018 In presenting this dissertation in partial fulfillment of the requirements for a doctoral degree from The University of Alabama in Huntsville, I agree that the Library of this University shall make it freely available for inspection. I further agree that permission for extensive copying for scholarly purposes may be granted by my advisor or, in his/her absence, by the Chair of the Department or the Dean of the School of Graduate Studies. It is also understood that due recognition shall be given to me and to The University of Alabama in Huntsville in any scholarly use which may be made of any material in this dissertation. Andrew Timothy Hiatt (Date) ii DISSERTATION APPROVAL FORM Submitted by Andrew Timothy Hiatt in partial fulfillment of the requirements for the degree of Doctor of Philosophy in Mechanical Engineering and accepted on behalf of the Faculty of the School of Graduate Studies by the dissertation committee. We, the undersigned members of the Graduate Faculty of The University of Alabama in Huntsville, certify that we have advised and/or supervised the candidate on the work described in this dissertation. We further certify that we have reviewed the dissertation manuscript and approve it in partial fulfillment of the requirements for the degree of Doctor of Philosophy in Mechanical Engineering. _________________________________________ Committee Chair Dr. Robert Frederick, Jr. (Date) _________________________________________ Dr. James Baird (Date) _________________________________________ Dr. Jason Cassibry (Date) _________________________________________ Dr. George Nelson (Date) _________________________________________ Dr. James Swain (Date) _________________________________________ Department Chair Dr. D. Keith Hollingsworth (Date) _________________________________________ College Dean Dr. Shankar Mahalingam (Date) _______________________________________ __ Graduate Dean Dr. David Berkowitz (Date) iii ABSTRACT The School of Graduate Studies The University of Alabama in Huntsville Degree Doctor of Philosophy College/Dept. Engineering/Mechanical & Aerospace Engineering Name of Candidate Andrew Timothy Hiatt Title Evaluation of Electric Solid Propellant Responses to Electrical Factors and Electrode Configurations Some electric solid propellants repeatedly ignite and extinguish through application and removal of electrical energy. Responses to electrical factors and electrode configurations were evaluated at atmospheric conditions using the Design of Experiment methodology for development of valid correlations. Experiment results were compared with an existing electrolytic theory describing electrochemical reactions occurring proportional to current. The high performance electrical propellant 501a formulation containing a hydroxylammonium nitrate ionic liquid and polyvinyl alcohol polymer binder was used in all experiments. External flame impingement produced charring without energetic ignition, no self-sustained burning, and extinguishment upon flame removal. Application and removal of electrical energy through stainless steel electrodes resulted in propellant ignition and extinguishment. Burning rate as a function of current density was determined using a power fitted regression equation having a current density exponent of 0.958. The nearly direct proportionality supports the electrolytic theory. The measured mass loss was 5-50 times the mass loss predicted by the electrolytic theory suggesting a significant thermochemical component exists. For experiments having equal electrode surface areas, preferential anodic burning occurred as more chemically reactive oxidative species are predicted by the electrolytic theory. For most experiments having unequal surface areas, burning occurred at the smaller electrode surface area regardless of polarity due to iv greater current density and ohmic heating predicted by the electrolytic theory. Hydroxylammonium and nitrate diffusion coefficients determined for platinum electrodes were from 3.11x10-7 to 3.62x10-7 cm2/s and 2.67x10-7 to 3.45x10-7 cm2/s, respectively. Ion mobility and drift velocity relate to diffusion coefficient thereby describing ionic transport characteristics affecting current and ultimately burning rate. The approximated electrical conductivity range for platinum electrodes was 3.8-22.0 S/m for frequencies of 0.1-10 kHz. Conductivity increased with frequency suggesting potential burning rate control through frequency modulation. Electrical response was a highly localized effect limited to the propellant/electrode interface. The electrode where burning occurred exhibited electrostatic discharge behavior as evidenced in the video, current, and voltage data suggesting the polymer breakdown voltage was achieved. Dielectric breakdown was proposed as an additional theoretical component connecting the experiment results with the electrolytic theory and augmenting the electrochemical and thermochemical processes for the overall combustion mechanism. Abstract Approval: Committee Chair _______________________________________ Dr. Robert A. Frederick, Jr. Department Chair _______________________________________ Dr. D. Keith Hollingsworth Graduate Dean _______________________________________ Dr. David Berkowitz v ACKNOWLEDGMENTS Many people have contributed to this accomplishment. I am grateful for the investments made by all those involved and for the opportunities presented. The completion of this dissertation represents the contributions, sacrifices, time, energy, finances, and resources committed by many individuals over the years. These efforts supported me in every step of the process and I would like to acknowledge the contributing individuals. I would like to thank Dr. Frederick for being my advisor from the beginning and serving as my committee chair. I greatly appreciate the opportunity he gave me through conducting research as part of the Propulsion Research Center. Dr. Frederick has provided numerous opportunities through assistantships, research guidance, academic advice, and continual support through this process. I am grateful for his encouragement and help toward achieving this goal. I would also like to thank my committee members for their unique contributions. Dr. Baird developed the electric solid propellant electrolytic theory used for comparison in this research. Dr. Cassibry provided guidance on the electric field effects related to the experiment setup and a modeling perspective of the physical process occurring. Dr. Nelson allowed use of his laboratory’s potentiostat so the electroanalysis experiments could be completed. Dr. Nelson also provided experiment guidance, potentiostat training, assisted in completing a significant portion of the electroanalysis experiments, and offered considerable help in understanding and interpreting the data and results. Dr. Swain provided guidance for the Design of Experiment methodology and helped in my understanding and interpretation of the statistical analysis data and results. I am grateful to The University of Alabama in Huntsville for funding me through many avenues such as graduate research assistantship, graduate teaching assistantships, a staff position, and through the Von Braun Propulsion Fellowship. While the funding streams seem a bit vi eclectic, I believe this to be evidence of the commitment by the university, professors, and staff toward ensuring student success. I am grateful to all those involved for continually funding me despite the financial environment. I am especially thankful for the Von Braun Propulsion Fellowship that allowed me to complete my education. I would also like to thank the Missile Defense Agency for supplying a majority of my funding through a contract with The University of Alabama in Huntsville Propulsion Research Center. This multi-year contract benefited not only me but numerous graduate students, professors, and staff. Their support extends beyond financial and includes approval of my data for public release thereby facilitating the resulting dissertation. They have also provided many of the experiment materials and guidance necessary for the successful completion of this dissertation. Specifically, I would like to thank Mr. Bill Gnacek and Mr. Joe Carden for their support and significant contributions. Additionally, I would like to thank Digital Solid State Propulsion. They provided the electric solid propellant samples used in the experimentation. They hosted orientations and hands-on experience in their laboratories. They also provided relevant technical discussions. There are a few Propulsion Research Center and Department of Mechanical and Aerospace Engineering staff members I would like to thank. Beginning with the Propulsion Research Center, I greatly appreciate Dr. David Lineberry and all the contributions he has made over the years. He has been a tremendous source of help for experiment design, setup, and analysis considerations. Mr. Tony Hall provided assistance with the testing facilities and ensuring the laboratory functions safely and properly. Mr. Anthony Edmondson facilitated the materials procurement and administrative tasks. From the Department of Mechanical and