Effects of rheological properties on reactivity of energetic thin films

Magnesium (Mg) and manganese dioxide (MnO2) powders were mixed with polyvinylidene fluoride (PVDF) binder and n-methyl pyrrolidone (NMP) solvent and blade cast onto stainless steel foil. The rheological properties of these mixtures were investigated to quantify the mixing condition. Parameters including wet film thickness, equivalence ratio and solids loading were varied. Flame speed and calorific output were investigated for each of these parameters. Results show energy propagation rates increased as a function of dry film thickness, although calorific output remained relatively constant. Stoichiometrically fuel rich compositions were self-quenching, demonstrating the necessity of available oxygen for reaction propagation. A 0.45 solids-liquid mixing ratio resulted in up to an order of magnitude higher energy propagation rate for both open and confined configurations. Rheometry measurements and physical characterizations of the films reveal that the solids loadings resulting in the most stable suspensions also produced the highest energy propagation. Changing solids loading affects the density of the film, which in turn affects energy propagation. Capillary drying forces at high liquid loadings result in higher porosity leading to reduced deposition density and thickness. Very high solids loading results in films with dilatant properties and poor mixing. These results show solids loading affects mixing and energy propagation and could impact slurry cast energetic materials as in additive manufacturing processes.