Removing hydrochloric acid exhaust products from high performance solid rocket propellant using aluminum-lithium alloy

Abstract

Hydrochloric acid (HCl) pollution from perchlorate based propellants is well known for both launch site contamination, as well as the possible ozone layer depletion effects. Past efforts in developing environmentally cleaner solid propellants by scavenging the chlorine ion have focused on replacing a portion of the chorine-containing oxidant (i.e., ammonium perchlorate) with an alkali metal nitrate. The alkali metal (e.g., Li or Na) in the nitrate reacts with the chlorine ion to form an alkali metal chloride (i.e., a salt instead of HCl). While this technique can potentially reduce HCl formation, it also results in reduced ideal specific impulse (ISP). Here, we show using thermochemical calculations that using aluminum-lithium (Al-Li) alloy can reduce HCl formation by more than 95% (with lithium contents ≥15 mass%) and increase the ideal ISP by ∼7s compared to neat aluminum (using 80/20 mass% Al-Li alloy). Two solid propellants were formulated using 80/20 Al-Li alloy or neat aluminum as fuel additives. The halide scavenging effect of Al-Li propellants was verified using wet bomb combustion experiments (75.5±4.8% reduction in pH, ∝ [HCl], when compared to neat aluminum). Additionally, no measurable HCl evolution was detected using differential scanning calorimetry coupled with thermogravimetric analysis, mass spectrometry, and Fourier transform infrared absorption.

Tuning the Reactivity of Perfluoropolyether-Functionalized Aluminum Nanoparticles by the Reaction Interface Fuel-Oxidizer Ratio

“…However, its application has often been restrained due to the native dense oxide layer (Al 2 O 3 ) passivating on the surface, hindering the diffusion of oxygen throughout Al particles in the combustion process [ 5 , 6 , 7 ]. Meanwhile, the combustion process of Al particles usually accompanies ignition delay, incomplete combustion, and so on [ 8 , 9 , 10 ]. Moreover, the larger the size of Al particles is, the longer the path of heat conduction will be [ 11 ].…”

A mechanism for shattering microexplosions and dispersive boiling phenomena in aluminum–lithium alloy based solid propellant

“…Details pertaining to the propellant formulation/mixing as well as characterization of the fuel additives (e.g., particle size distributions, scanning electron microscopic imaging of particles) can be found in Ref. [29]. In summary, the neat aluminum powder was equiaxed in morphology and had a mean particle size (arithmetic) of 17.1 µm.…”

“…The shattering tendency of single Al-Li particles (10 wt.% lithium) has been observed by Blackman et al [25], though there is no publication showing its usage in an energetic material formulation. Recent concurrent work [29] has shown that there are both environmental and performance benefits to using Al-Li alloy (20 wt.% lithium) as an APCP fuel additive (performance metrics that are generally considered mutually exclusive).…”

New Application of Hydroxyl Groups: Ligands for High Density Metal Organic Frameworks

“…Since HE-MOFs are an emerging class of energetic material and possess very regular channels, introducing a dinitramide ion could increase [12] the sensitivity to mechanical stimulation, perhaps owing to excess compression of functional groups onto a limited backbone. Some powerful anions (azides or perchlorates) could cause serious environmental pollution [15][16][17], which restrict the range of application. Hence, finding suitable groups for high-energy MOFs remains a challenge.…”