Nano Additives and Plateau Burning Rates of Ammonium-Perchlorate-Based Composite Solid Propellants

Plateau propellants exhibit burning rate curves that do not follow the typical linear relationship between burning rate and pressure when plotted on a log-log scale, and because of this deviation, their burning behavior is classified as anomalous burning. This paper contains a literature review chronicling the last half-century of research to better understand the mechanisms that govern anomalous burning and to shed light on current research into plateau and related propellants. In addition to the review, a series of experiments investigating the use of nanoscale TiO2-based additives in ammonium-perchlorate hydroxyl-terminated polybutadiene composite propellants was performed. The baseline propellant consisted of either 70 or 80% monomodal ammonium perchlorate (223 mu m) and 30 or 20% binder composed of isophorone-diisocyanate-cured hydroxyl-terminated polybutadiene with Tepanol. Propellants were tested using a strand bomb between 3.45 and 17.24 MPa (34.0-170.1 atm). Analysis of the burning rate data shows that the crystal phase and synthesis method of the TiO2 additive are influential to plateau tailoring and to the apparent effectiveness of the additive in altering the burning rate of the composite propellant. Some of the discrepancy in the literature regarding the effectiveness of TiO2 as a tailoring additive may be due to differences in how the additive was produced. Doping the TiO2 With small amounts of metallic elements (Al, Fe, or Gd) showed additional effects on the burning rate that depend on the doping material and the amount of the dopant. This work provides the first published propellant mixtures and burning rate results for composite propellants employing metal-doped nanoparticle additives.