Steric stabilization of colloidal aluminium particles for advanced metalized-liquid rocket propulsion systems

The achievement of stable colloidal suspensions of reactive metal powders in liquid propellants is crucial for obtaining enhanced thrust per unit mass. Aluminium is of interest due to its availability, stability, and high combustion enthalpy (32000 J/g). In this manuscript, ultrafine spherical aluminium particles with the average size of 15 $\mu$m are produced by wet milling. Aluminium particles are effectively surface-modified with a polymeric surfactant and sterically stabilized in an organic solvent (toluene). Organically modified aluminium demonstrates a drastic change in surface properties from hydrophilic to hydrophobic, with effective transfer from the aqueous to organic phase. The stabilized particles are effectively dispersed in a liquid rocket propellant (hydrazine). The impact of aluminium particles on hydrazine combustion characteristics is evaluated by using a thermodynamic code named ICT (Institute of Chemical Technology in Germany, 2008). Aluminium particles offer an increase in the combustion temperature, oxygen balance, characteristic exhaust velocity, and specific impulse. The optimum solid loading level of aluminium in the hydrazine fuel is found to be 6 wt%.