Modifying burning rate and agglomeration size in aluminized composite solid propellants using mechanically activated metals

Hatem Mohamed Belal, Purdue University

Abstract

Agglomeration reduction techniques are important field in solid propellant industry, Large agglomeration results in excessive two phase losses. Tailored composite particles has been applied to tailor aluminum particle ignition and combustion. In this research, mechanical activated aluminum magnesium powders are synthesized, tested in both laser ignition using CO2 and propellant. Prepared powders categorized into particle size that suitable for propellant application. Laser ignition tests showed that the prepared powder are more reactive than magnalium which has the same Al:Mg weight ratio. Agglomeration capturing showed that the prepared powder produce much less than neat aluminum or even similar physical mixture of aluminum and magnesium. The burning rate of propellant using the prepared powder is increased. MA Al/Mg powders as long as with comparable physical mixture are applied in propellant formulation with AP/HTPB. In order to quantify the effect of changing Mg percent. Burning rate is measured from videos captured for strand burning in windowed pressure vessel, also the agglomeration was capturing using special setup. The results showed that MA powder increase burning rate and this increase reach maximum at 50% Mg, while propellant using physical mixture of Al/Mg show constant or little decrease in burning rate. In addition, the MA powder show lower agglomeration size in comparison to neat aluminum propellant or physical mixture with the same Mg percent. The lowest agglomeration sizes were for MA50. However, equilibrium calculation showed 4 sec losses in specific impulse, so MA 70 was chosen as a compromise between low agglomeration size at the minimum loss in specific impulse. Magnalium is an alloy of aluminum and magnesium and it is known for its ease of ignition and high oxidation energy content. It has been used as a metal fuel to increase burning rates of composite modified double base (CMDB) and ammonium perchlorate (AP) composite propellants. However, the ignition temperature is larger than the comparable mechanically activated (MA) Al-Mg powder. Mechanical milling was performed on magnalium powders and modifications of structure and morphology of the alloy during milling were examined by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The prepared magnalium powder was used in a solid propellant, which showed higher burning rates than those containing as-received magnalium. Furthermore, milled magnalium showed higher agglomeration reduction than both as received magnalium as well as MA Al-Mg powders. Extend the application of mechanical alloying of aluminum to other metals with extreme difference in melting/ boiling temperature, the first is Zirconium which is a long time candidate in solid propellant community. The ease of zirconium ignition and the micro-explosive behavior shown by neat zirconium particles promote its usage in agglomeration reduction effort. the other metal is Indium, which has very low melting point compared to other metal, this may open the possibility of earlier reaction of aluminum particles at or near propellant surface resulting in less pre ignition time which reduce agglomeration tendency. MA of 90% Aluminum and 10% of Zirconium or 10% Indium using High energy ball milling, particle characterization using SEM/FIB, XRD and DSC/TGA are performed, burning rate and agglomeration size analyses of solid propellant using sieved MA-powder are done. The results showed that the both MA Al-ZR and MA Al-In ignite in laser beam which verify change in reactivity from neat aluminum with its protective alumina coating. However, burning rate results show no change in burning rate from neat aluminum, also the prepared material shows no reduction in agglomeration sizes

Degree

Ph.D.

Advisors

Ortalan, Purdue University.

Subject Area

Mechanical engineering

COinS