Thomas Sammet

Comparison of Hand and Mechanically Mixed AP/HTPB Solid Composite Propellants

The Rocket Propulsion Laboratory (RPL) at the University of Central Florida has recently produced a lab-scale propellant mixing unit. This new method of mechanically mixing the propellant is proposed as a more realistic, safe, and efficient method of propellant production than the previous method of hand mixing. To test for verification of the mechanically produced propellant and as a verification of data repeatability, results from both methods were compared. A baseline HTPB/AP, non-metallized propellant was used. The burning rate curves from two mixtures of each mixing method were collected and compared. Collected data showed that both methods produced extremely similar burning rate curves and that the mechanical mixing method had a slightly higher correlation coefficient than hand mixing.

Performance of Ammonium-Perchlorate-Based Composite Propellant Containing Nanoscale Aluminum

Several composite propellant mixtures of hydroxyl-terminated polybutadiene, ammonium perchlorate, and aluminum were prepared with and without the addition of small percentages of nanoscale aluminum and tested in a strandburneratpressuresupto34.5MPa.Theeffectofmonomodalversusbimodalammoniumperchlorateparticle size, coarse aluminum particle size, nano aluminum particle size, and coarse-to-fine ratios on burning rate and manufacturability were explored. A significant conclusion of the present study is that the addition of nanoscale aluminum does not always ensure an increase in the propellant’s burning rate when produced using conventional methods. It was observed that over the range of mixtures and pressures explored, a bimodal oxidizer is required for the nanoscale aluminum to affect the burning rate, and that a monomodal oxidizer tended to nullify any influence of thenanoscalealuminum.Insomecases,theadditionofnanosizedaluminumdecreasedtheburningrate.Thelevelof burning-rateincreaseordecreasedependedonthebimodalormonomodalammoniumperchlorateparticlesizes,the coarse aluminum particle size, and the pressure range.

Performance of AP-Based Composite Propellant Containing Nanoscale Aluminum

Several HTPB/AP/Al-based composite propellant mixtures were prepared with and without the addition of small percentages of nanoscale aluminum and burned in a strand burner at pressure up to 5000 psi. The effect of monomodal versus bimodal AP particle size, course aluminum particle size, nano aluminum particle size, and course-to-fine ratios on burn rate and manufacturability were explored. A significant conclusion of the present study is that the addition of nano-sized aluminum does not necessarily increase a propellants burn rate when prepared using conventional methods. It was observed that, over the range of mixtures and pressures explored, a bimodal oxidizer is required for the nanoscale Al to affect the burning rate, and that a monomodal oxidizer tended to nullify any influence. In some cases, the addition of nano-sized aluminum actually decreased the burn rate. The level of burn rate increase or decrease depended on the bimodal or monomodal AP particle sizes, the coarse Al particle size, and the pressure range.

Assessing the Mixedness of Composite Solid Rocket Propellants Using Fluorescent Particles

A new diagnostic technique was developed for assessing the effectiveness of mixing techniques of solid composite propellants using nanoparticle additives. The diagnostic uses nanosized quantum dots in suspension or micron-sized powders that are mixed into the propellant in place of the additives. Upon exposure to an ultraviolet light source, the particles fluoresce, hence serving as tracers to assess the uniformity of the mixture and therefore the effectiveness of the mixing procedure. Collection of the image using a digital camera provides data on intensity variations in the fluorescent signal, allowing for quantitative assessment of uniformity and mixedness. Various mixtures involving hydroxyl-terminated polybutadiene binder and ammonium perchlorate oxidizer were manufactured at various levels of mixing to test the diagnostic. In addition to confirming the uniformity of the nanosized particles using the target mixing procedure, variations in mixing quality and comparisons between mechanically and hand-mixed propellants showed distinct differences correlating to the mixedness of each propellant that was supported with data from burning rate studies. The present diagnostic can therefore also be used to assess the mixedness of propellants that do not contain nanoparticle additives. Other potential applications include curing agent dispersion assessment and linking homogeneity to mixedness and mechanical properties.

New Additives for Modifying the Burn Rate of Composite Solid Propellants

The ability of nano-particle additives to tailor the burning rate of composite solid rocket propellants is being explored in the authors’ laboratories. In the present study, two different nano-particles and two separate styles of mixing in the additive were investigated. These variations were tested on a typical HTPB/AP composite rocket propellant with varying characteristics. After a baseline study was completed without additives, a Taguchi L8 matrix was designed to fully test the effect of six different mixture variables and the two different additives on the burning rate. The propellants were tested in a strand bomb at pressures ranging from approximately 34 to 136 atm, and some representative data are provided. The results thus far indicate that small levels of nano-particle additives (∼ 1 wt %) can have significant effects on the magnitude and pressure dependence of the composite propellant.

Facile nanoparticle dispersion detection in energetic composites by rare earth doped in metal oxide nanostructures

The segregation and agglomeration of nanoparticles dispersed in polymer matrices play important roles in nanocomposite performance. A method of rapid and simultaneous visualization of macroscopic and submicron particle dispersion properties is presented, based on nanoparticle luminescence induced by europium doping. The luminescence intensity of polymer composites containing Eu-doped TiO2 nanoparticle catalysts varied with the nanoparticle agglomerate size between 90 nm and 10 μm, and with concentration variations from segregation. These variations were detected by photoluminescence spectroscopy and visible-light photography, making this a facile characterization method for bulk composites without affecting the nanoparticle performance.

Aging Effects of Composite AP/HTPB Propellants Containing Nano-Sized Additives

The aging behavior of a composite propellant is a key indicator in the service life of a practical rocket motor. Advancements in the development of nano-particle additives and their burning rate enhancing characteristics give rise to examining the long-term impacts on the service life of the motor. Recent research at Texas A&M has focused on tailoring ballistic characteristics through the addition of nano-additives specifically synthesized for composite propellants. This paper focuses on an AP/HTPB propellant with a dry-powder nano-titania additive to influence ballistic characteristics and fluorescing Lumidots to assess morphological changes associated with accelerated aging. Sample sets were aged at 85 o C in ambient humidity conditions for six and twelve days, simulating four and eight years of aging, respectively. Data were correlated to a set of naturally aged samples. Acceleratedaged monomodal AP formulations with 80% solids loading and nano-additive demonstrated an approximate 7% decrease in burning rate, with accompanying morophological changes. Accelerated-aged bimodal AP forumlations with 85% solids loading and nano-additive demonstrated an approximate 12% increase in burning rates, with accompanying morphological changes.

Texas Center for Undergraduate Research in Energy and Propulsion: An NSF REU Site at Texas A&M University

Since 2010, a Research Experiences for Undergraduates (REU) site focusing on energy-, propulsion-, and combustion-related research topics has been held at Texas A&M University (TAMU). A major focus of the site has been the recruitment of undergraduate participants from schools within the state of Texas that do not have major research programs in engineering. To this end, 85% of the 10-week, summer participants have fallen within this category. Four main summer sites have been held to date, involving 40 total participants. Of these students, at least 63% of them were also from underrepresented groups within the STEM fields (female, Hispanic, Black, and Native Americans). Other aspects of the REU site include the participation of one high school teacher each year and a year-round research program that involves 2 students from TAMU as well as 2 students from one of two different partner universities representing non-Tier-One research institutions in Texas, namely the University of North Texas and the University of Texas at Brownsville. Highlights on the overall program, a summary of the research projects and mentors, and details from the last four years of the REU site are provided in this paper.