Thesis (Ph. D.)--Chemistry and Biochemistry, Georgia Institute of Technology, 2007. / Committee Chair: Prof. Charles L. Liotta; Committee Member: Prof. Arthur J. Ragauskas; Committee Member: Prof. Charles A. Eckert; Committee Member: Prof. John D. Muzzy; Committee Member: Prof. Rigiberto Hernandez.

Thesis (M.S.)--Auburn University, 2006. / Abstract. Vita. Includes bibliographical references.

Thesis (M.S.)--Florida State University, 2004. / Advisor: Dr. Steven Van Sciver, Florida State University, College of Engineering, Department of Mechanical Engineering. Title and description from dissertation home page (viewed Sept. 23, 2004). Includes bibliographical references.

Thesis (M.S.)--Rochester Institute of Technology, 2009. / Typescript. Includes bibliographical references (leaves 70-73).

Les processus physiques qui régissent la pulvérisation de sprays constituent la première étape vers une compréhension globale du comportement de moteurs fusées à ergols stockables. La première partie de ces travaux détermine, au moyen de visualisations et d’analyses granulométriques, les paramètres importants contrôlant la formation de sprays par impact de jets liquides. Des injecteurs dédiés à pulvériser des ergols stockables sont ensuite conçus. L’enjeu de la seconde partie des travaux est d’étudier la combustion de l’éthanol avec le peroxyde d’hydrogène, ergols stockables considérés moins nocifs. L’utilisation de cette association bi-ergols innovante a nécessité d’analyser en détail leur compatibilité à l’allumage, ainsi que leurs performances en combustion sur la gamme de richesses 0,4 – 2,0, à l’aide de diagnostics optiques et physiques spécifiques. Les efficacités de combustion atteignent entre 87 et 98 %, les fluctuations de pression ne dépassent pas 10 %, mais les légères différences obtenues permettent de sélectionner les meilleures configurations d’injection favorisant la combustion ou sa stabilité. / The physical processes involved in spraying are the first step towards a comprehensive understanding of the behavior of rocket engines using storable propellants. The first part of this work identifies, through visualizations and particle sizing, the important parameters driving the formation of spray by impinging liquid jets. Then, injectors dedicated to spray storable green-propellants are designed. The second part of this thesis aims at studying the combustion of ethanol with hydrogen peroxide, which are regarded as green-storable propellants. But the use of this innovative bi-propellant association required a detailed analysis of their ignition compatibility, as well as their combustion performance within the range of 0,4 – 2,0 in overall equivalence ratio. Specific optical and physical diagnostics helped to achieve these goals. Combustion efficiency reached between 87 and 98 %, pressure fluctuations did not exceed 10 %, but the slight differences obtained allowed to select the best injection configurations promoting efficient combustion and stability.

The manufacturing process for solventless extruded double base propellants involves a number of rolling and reworking stages. Throughout these processes a decrease in weight average molecular weight was observed, this was attributed to denitration. Differential scanning calorimetery data indicated that the reworking stages of extruded double base propellant manufacture were crucial to the homogenisation of the propellant mixture. To determine the homogeneity of the final extruded product, a sample was analysed across its diameter. No variations in stabiliser concentration, molecular weight, or Vickers hardness were detected. An accelerated thermal ageing trial simulating up to 8 years of ageing at 25°C was carried out to evaluate the storage characteristics. Reductions in stabiliser concentration, number average molecular weight, weight average molecular weight and polydispersity compared with un-aged samples were observed. The glass transition temperature measured using differential scanning calorimetery decreased by ~3°C. The decrease was attributed to the initial denitration reducing the energy of bond rotation and shortening the polymer chains, both factors reducing the energy required for movement. Modulus values determined from dynamic mechanical analysis temperature scanning experiments, did not detect significant variation between un-aged and aged samples. Though it was considered that variations would be likely if a more extensive ageing program was completed. In order to evaluate propellant behaviour at very high and low frequencies, time temperature superposition (TTS) and creep testing were carried out. The TTS technique superpositioned data well, allowing future investigation of high frequency propellant properties. Creep testing was considered to be an appropriate approach, though the equipment available was not optimised for such testing. This thesis is concerned with understanding how propellants are manufactured from nitrocellulose, nitroglycerine and other constituents. It is also about how the propellants decompose during long periods of time in storage, and how these changes can be measured using thermal and mechanical methods. It is about how the physical, chemical and thermal properties of the propellant composition change throughout the manufacture. This is relevant as it could be used to develop more efficient manufacturing processes, allow operators to adjust processes to tailor product properties or be used to re-design manufacturing to compensate for a different starting material. The thesis also considers how and why the properties of the product change over the course of years of storage. A specific focus on whether changes in mechanical and thermal properties occur, and if so how they can be detected. / © Cranfield University

Existing instrumental techniques must be adaptable to the analysis of novel explosives if science is to keep up with the practices of terrorists and criminals. The focus of this work has been the development of analytical techniques for the analysis of two types of novel explosives: ascorbic acid-based propellants, and improvised mixtures of concentrated hydrogen peroxide/fuel. In recent years, the use of these explosives in improvised explosive devices (IEDs) has increased. It is therefore important to develop methods which permit the identification of the nature of the original explosive from post-blast residues. Ascorbic acid-based propellants are low explosives which employ an ascorbic acid fuel source with a nitrate/perchlorate oxidizer. A method which utilized ion chromatography with indirect photometric detection was optimized for the analysis of intact propellants. Post-burn and post-blast residues if these propellants were analyzed. It was determined that the ascorbic acid fuel and nitrate oxidizer could be detected in intact propellants, as well as in the post-burn and post-blast residues. Degradation products of the nitrate and perchlorate oxidizers were also detected. With a quadrupole time-of-flight mass spectrometer (QToFMS), exact mass measurements are possible. When an HPLC instrument is coupled to a QToFMS, the combination of retention time with accurate mass measurements, mass spectral fragmentation information, and isotopic abundance patterns allows for the unequivocal identification of a target analyte. An optimized HPLC-ESI-QToFMS method was applied to the analysis of ascorbic acid-based propellants. Exact mass measurements were collected for the fuel and oxidizer anions, and their degradation products. Ascorbic acid was detected in the intact samples and half of the propellants subjected to open burning; the intact fuel molecule was not detected in any of the post-blast residue. Two methods were optimized for the analysis of trace levels of hydrogen peroxide: HPLC with fluorescence detection (HPLC-FD), and HPLC with electrochemical detection (HPLC-ED). Both techniques were extremely selective for hydrogen peroxide. Both methods were applied to the analysis of post-blast debris from improvised mixtures of concentrated hydrogen peroxide/fuel; hydrogen peroxide was detected on variety of substrates. Hydrogen peroxide was detected in the post-blast residues of the improvised explosives TATP and HMTD.

<div>When combined with common fuel binders, solid hypergolic fuels can simplify the overall complexity of hybrid rocket systems, as the fuel grain can be ignited and reignited without an external power source or external fluid. In addition, with the hypergolic additive embedded in the binder, the flame zone can be placed at the surface of the grain itself, thereby providing heat to the fuel, improving fuel regression rate, and combustion stability and sustainability. Coupled with high grades of mixed oxides of nitrogen (MON), such hypergolically ignited hybrid configurations are considered a potential propulsion system for a robotic Mars Ascent Vehicle (MAV). Use of the fuel additives and a suitable choice of oxidizer allows for low temperature stability and operation of the propellants, making it an appealing candidate for a simple and storable hybrid propulsion system.</div><div>The first half of this work is dedicated to a very application based study of paraffin based hypergolic hybrids, while the second half of this work, independent from the first, focuses on how theory could help in developing future hypergolic propulsion systems.</div><div>The process undertaken to develop a paraffin based hypergolic hybrid relied heavily on experimental testing of a wide variety of additive loaded fuels with MON to optimize hybrid motor grain parameters with the goals of minimizing ignition delay, improving combustion stability, and promoting sustainment of the flame. MON 3 and MON 25 (3 wt.% or 25 wt.% nitric oxide mixed with nitrogen tetroxide) were used as oxidizers. Through an initial screening process, we selected two solid hypergolic propellants, sodium amide and potassium bis(trimethylsilyl)amide (PBTSA), as additives to promote hypergolic ignition given their low ignition delays with both grades of MON. Iterations on the grain configuration consisted in minimizing the additive loading to simplify the casting process and increase performance, without losing hypergolicity of the grain or hampering combustion sustainability. Using a 90 wt.% hypergolic additive front segment, we were able to light the grain three times using the hypergolic reaction between the additives and MON 3. Once relights achieved, we mainly focused on demonstrating sustained combustion, and determined that, once the front segment depleted, the lack of heat in the system lead the motor to shut down prior to the end of the targeted burn. This led us to add a reactive additive, sodium borohydride, in the main grain, as a way to generate heat in the motor once the front segment was depleted. With the objective of testing relevant conditions for an actual Mars Ascent Vehicle, one of our final tests was done in an altitude chamber, at a 100,000 ft targeted simulated altitude (equivalent to the atmospheric pressure on Mars), with MON 25 as the oxidizer. Using a mixture of sodium amide, PBTSA, and sodium borohydride, we were able to achieve hypergolic ignition in 425 ms (delay to reach 90% of the maximum chamber pressure) at 102,000 ft simulated altitude, for an average chamber pressure of 113 psia.</div><div>During testing we determined that an ideal solid additive should exhibit both low ignition delay with the oxidizer considered, to minimize the motor start up time, and a high heat of combustion, to maximize the energy release and therefore maximize performance. However, the lack of data and theoretical understanding of the reactivity of MONs with non hydrazine based fuels made it challenging to find such an ideal solid additive. Historically, screening processes for new fuel candidates, liquids or solids, have followed a “hit or miss” approach, in which potential fuels were selected based on common characteristics with known hypergols, which is the approach we followed during the development of the hypergolic hybrid. A more robust approach, typically used in the biology and chemistry fields, can be used to predict reactivity of chemicals using statistical analysis. A quantitative structure activity relationship (QSAR) analysis is a statistical analysis used to correlate reactivity to selected molecular descriptors, or properties. Using this approach, one can create models, determined during the QSAR analysis, to predict reactivity of fuel candidates, solely based on their properties. Combined with the recent advancements in computational chemistry and computation of properties, this simple approach has the potential to greatly simplify screening processes for new fuel candidates, as experimental data is not needed anymore. With this method, we were able to fit the logarithmic of the minimum ignition delay for 30 different amines using seven molecular descriptors (heat of formation, heat of vaporization, highest occupied molecular orbital, charge on the nitrogen, rotatable bond count, and ovality), for an R² value of 0.70. While the main motivation behind starting this theoretical work was to optimize for solid additives properties for the hypergolic hybrid configuration described previously, the potential of such model extends to a wider range of propulsion systems (reaction control systems, orbital maneuvering, etc.), and could be expanded to a wider range of oxidizers using machine learning.</div>

M.S.

Electrically controllable solid propellants are an area of interest as a viable solution to the lack of throttle-ability in solid propellant rocket motors. Existing studies have focused on propellants compositions using hydroxyl-ammonium nitrate, ammonium nitrate, or lithium perchlorate as oxidizers. Additionally, the thermochemical and electrochemical reaction mechanisms have not yet been fully defined. The research in this thesis explores the nitrate and perchlorate oxidizer families to compare their cation-anion relationships. Using these oxidizers, pseudo electrically controllable solid propellant compositions were created with the addition of multi-wall carbon nanotubes to enhance ohmic heating capabilities. These additives were selected based on theory that with a non-complexing polymer, an oxidizer melt layer is required for ions to dissociate and electrically controlled ignition to occur. Using an applied voltage, ignition delay and current draw experiments were performed to expand on prior findings that ignition delay follows oxidizer melt temperature while mobility is associated with the size of the ionic radii. Additionally, neat oxidizer pellets were electrically decomposed to determine their linear regression rate. These results help to characterize the mechanism of reaction. This advances the knowledge of oxidizers in electrically controllable applications. / Master of Science / Solid propellant rocket motors have been extensively studied and used in both space and military applications because they do not use air as the source of oxygen. Their main limitation is the lack of throttle-ability, or inability to control propellant burning. This is because solid propellants, which are generally composed of an ionic oxidizer salt, a polymer fuel, and additives, are pre-combined and stored within the rocket motor. An emerging viable solution to this limitation is electrically controllable solid propellants. With an applied voltage, the oxidizer is heated and melts, allowing ions to dissociate and current to flow between electrodes. This reaction can then be controlled by turning the power supply on and off. Cations, or ions which have a net positive charge, move to the negatively charged cathode while anions, which have a net negative charge, move to the negatively charged anode. The research in this thesis explores different cation-anion oxidizer pairings using both a propellant composition and as a pure oxidizer under an applied voltage. The results help to characterize the mechanism of reaction of each oxidizer in an electrically controllable context and determine their effectiveness in these propellant applications.