Crystal Morphology in Ammonium Perchlorate Based Solid Composite Propellants

Reactive and energetic materials are used in a variety of fields and therefore must be able to perform at different operating conditions. Being able to alter and control the properties of these materials in terms of the burning rate, heat of reaction as well as the sensitivity will allow the tailoring of reactive materials to perform optimally in a variety of applications. The reaction properties, performance, and sensitivity will be influenced by both the chemical and physical characteristics of the energetic material [1]. A well-known and widely used oxidizer component in composite solid propellants is ammonium perchlorate (AP). AP composite propellant formulations using metal fuel particles and polymeric binders can contain as much as 70% AP [2]. Due to the large percentage of AP in these composites, the oxidizer’s properties including the size, shape, morphology, and defects will have a large effect on the performance of the composite. Understanding the modification of the energetic crystal morphologies and structures and the influence on the reaction properties, pathways, and mechanisms is important to the overall performance and safety of the reactive material.<br/>In this work, the preparation of microscale ammonium perchlorate crystals and under confinement of nitrocellulose is demonstrated. A focus is placed on AP concentration dependence of the crystal size and morphology as well as the different observed morphological regimes. Solutions from low AP concentration up to the solubility limit are observed in scanning and transmission electron microscopy to better understand the role of solute concentration on the final crystal physical characteristics. Additional crystals are also grown in the presence of metal nanoparticles to form a composite solid propellant.<br/><br/>[1] R. Kumar, P. F. Siril, and P. Soni, “Tuning the particle size and morphology of high energetic material nanocrystals,” Def. Technol., vol. 11, no. 4, pp. 382–389, Dec. 2015.<br/>[2] Vargeese, A. A.; Joshi, S. S.; Krishnamurthy, V. N. Role of Poly(Vinyl Alcohol) in the Crystal Growth of Ammonium Perchlorate. Cryst. Growth Des. 8, 1060– 1066, 2008.