Keywords

Aluminum, nanoaluminum, PFA, mechanical activation

Research Abstract

Aluminum inclusions have been widely used to increase the specific impulse of solid rocket propellant. However, issues arise with the addition of aluminum in the form of agglomeration, which can cause kinetic and thermal losses (i.e., two-phase flow losses) through the nozzle, which can reduce motor performance by as much as 10%. Reduction of agglomerate size may reduce the effect of two-phase flow losses. Polytetrafluoroethylene (PTFE or TeflonTM) inclusions into aluminum via mechanical activation (MA, milling) have been shown to produce a smaller coarse agglomerate size due to microexplosion of the composite particles at the propellant surface. Perflouroalkoxy (PFA) is a chemically similar to PTFE, and has yet to be investigated in metal combustion. Additionally, nanoscale aluminum (nAl) can be synthesized in situ within PFA. Using in situnAl-PFA yields both a bottom-up and top-down approach when mechanically activated with aluminum, which may further modify the combustion properties. To support this prediction, PFA powders (with and without in situ nAl)­ were combined with aluminum via MA, systematically varying the Al/PFA mixture ratio (70/30 and 90/10 wt.% Al/PFA) and milling time (30 and 45 minutes). The resulting thermal behavior of the various milled powders was investigated via butane torch ignition and differential scanning calorimetry. The various MA Al/PFA powders appeared to burn well, comparable to equivalent MA Al/PTFE powders. However, the in situ nAl-PFA inclusions did not appear to have a significant effect on the combustion properties at these low heating rates. Future work should study these materials at higher heating rates (e.g., solid propellant, laser ignition) in order to fully see the effect of in situ nAl-PFA.

Session Track

Combustion and Propulsion

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Aug 6th, 12:00 AM

Altered Combustion Characteristics of Aluminum Fuels through Low-Level Fluoropolymer Inclusions with and without in situ Nanoaluminum.

Aluminum inclusions have been widely used to increase the specific impulse of solid rocket propellant. However, issues arise with the addition of aluminum in the form of agglomeration, which can cause kinetic and thermal losses (i.e., two-phase flow losses) through the nozzle, which can reduce motor performance by as much as 10%. Reduction of agglomerate size may reduce the effect of two-phase flow losses. Polytetrafluoroethylene (PTFE or TeflonTM) inclusions into aluminum via mechanical activation (MA, milling) have been shown to produce a smaller coarse agglomerate size due to microexplosion of the composite particles at the propellant surface. Perflouroalkoxy (PFA) is a chemically similar to PTFE, and has yet to be investigated in metal combustion. Additionally, nanoscale aluminum (nAl) can be synthesized in situ within PFA. Using in situnAl-PFA yields both a bottom-up and top-down approach when mechanically activated with aluminum, which may further modify the combustion properties. To support this prediction, PFA powders (with and without in situ nAl)­ were combined with aluminum via MA, systematically varying the Al/PFA mixture ratio (70/30 and 90/10 wt.% Al/PFA) and milling time (30 and 45 minutes). The resulting thermal behavior of the various milled powders was investigated via butane torch ignition and differential scanning calorimetry. The various MA Al/PFA powders appeared to burn well, comparable to equivalent MA Al/PTFE powders. However, the in situ nAl-PFA inclusions did not appear to have a significant effect on the combustion properties at these low heating rates. Future work should study these materials at higher heating rates (e.g., solid propellant, laser ignition) in order to fully see the effect of in situ nAl-PFA.