EFFECTS OF NANO-METRIC ALUMINUM POWDER ON THE PROPERTIES OF COMPOSITE SOLID PROPELLANTS

Abstract

Several industrial−and research−types of hydroxy-terminated polybutadiene (HTPB)-based composite solid propellants were experimentally analyzed. In general, they feature the same nominal composition, but different nano-metric aluminum particles (nAl) are investigated as metal fuels and contrasted to a conventional propulsion grade micrometric aluminum (5.6 µm average grain size), which are taken as reference. Strand burning rates and the associated combustion flame structures of propellants were studied. The mechanical sensitivity and microstructure surface of the formulations were compared to that of a conventional aluminized propellant already certified as steady. The results show that the common Al powders are of irregular shapes, while the tested nAl particles are of disperse and approximate "spherical shapes", and tend to pack or stick together easily into cold clots. The aluminum are insensitive for friction and impact stimuli (0%, >24.66 N · m) and all the propellant formulations containing different aluminum particles size were sensitive to impact and friction (36%, 100%) except the based propellant with common aluminum powder (32%, 96%). The nano-sized metal additives can affect the combustion behavior and change the burning rate effectively. The burning rate can be increased more than 55.0% for 5% of nAl replaced common Al powder in the formulations. The burning rate and pressure exponent values depend on the formulation of the fraction of nAl powder, and a change of part mass fraction of nAl particles may boost the burning rate higher than that of the common Al powder. Both the burning rate and the pressure exponent can be increased up to 90.0% (13 MPa), and from 0.38 to 0.54 (1−15 MPa), respectively, for 10% of nAl replaced common Al powder in the propellant formulations.