Probing the Reaction Mechanism of Aluminum/Poly(vinylidene fluoride) Composites

Abstract

Energetic thin films with high mass loadings of nanosized components have been recently fabricated using electrospray deposition. These films are composed of aluminum nanoparticles (nAl) homogeneously dispersed in an energetic fluoropolymer binder, poly(vinylidene fluoride) (PVDF). The nascent oxide shell of the nAl has been previously shown to undergo a preignition reaction (PIR) with fluoropolymers such as polytetrafluoroethylene (PTFE). This work examines the PIR between alumina and PVDF to further explain the reaction mechanism of the Al/PVDF system. Temperature jump (T-jump) ignition experiments in air, argon, and vacuum environments showed that the nAl is fluorinated by gas phase species due to a decrease in reactivity in a vacuum. Thermogravimetric analysis coupled with differential scanning calorimetry (TGA/DSC) was used to confirm the occurrence of a PIR, and gas phase products during the PIR and fluorination of nAl were investigated with temperature jump time-of-flight mass spectrometry (T-jump TOFMS). Results show a direct correlation between the amount of alumina in the PVDF film and the relative signal intensity of hydrogen fluoride release (HF). Although the PIR between alumina and PVDF plays an important role in the Al/PVDF reaction mechanism, burn speeds of Al/PVDF films containing additional pure alumina particles showed no burn speed enhancement.

Improved Energetic-Behaviors of Spontaneously Surface-Mediated Al Particles

“…The higher pressurization rate of PVDF/Al (13.8 kPa∙μs −1 ) than that of the Al 2 O 3 passivated Al (5.8 kPa.μs −1 ) is found to be due to gaseous phases such as CO 2 and H 2 generated by the thermal decomposition of PVDF 34 . Interestingly, the pressurization rate of the mixed PVDF/Al powders was very low at 0.33 kPa.μs −1 .…”

“…On the other hand, the oxidized PVDF/Al particles show peaks at 2θ = 15.8°, 30.7°, and 32.1° indicating the formation of Al hydroxide fluoride (AlF 1.5 (OH) 1.5 ), while the additional peaks observed at 2θ = 14.8°, 25.2°, and 29.7° reveal the formation of β-phase Al fluoride (AlF 3 ) 31–33 . As reported by DeLisio et al ., the main pyrolysis product of PVDF is hydrogen fluoride at low heating rates 34 . When the PVDF is removed by increasing the temperature, because the Al-F bond (664 kJmol −1 ) is stronger than the Al-O bond (512 kJmol −1 ), Al fluoride is preferentially formed compared to Al oxide 30 .…”

Direct Deposit of Fiber Reinforced Energetic NanoComposites

“…Thus far, most studies related to nanothermites have focused on the fuel-oxidizer system itself. However, in some potential applications (e. g. the biocidal agents [7], cloud-seeding material [8]), the thermite powder were incorporated with polymer binders (epoxy, nitrocellulose, and fluoropolymer [9][10][11][12][13][14]) to form the nanothermite-polymer composites. A large content of thermite is nominally desirable since it is the dominate energy releasing source, while the polymer binder is employed to give the composite the necessary mechanical integrity.…”

Boron Carbide Based Biocide Compositions: A Study of Iodate Particle Size on Combustion and Iodine Output

“…As a replacement for metal fuels, Poret et al [13] revealed that boron carbide, B 4 C, a hard ceramic fuel, can be used as a replacement for heavy metals in time delay compositions due to its beneficial heat of formation and low thermal conductivity. Shaw et al [14] also has shown that a B 4 C/NaIO 4 system with the addition of a fluoropolymer binder, polytetrafluoroethylene (PTFE), can result in halogenated fumigants [15][16][17]. The versatility of B 4 C as a fuel has also been shown by Shaw et al [18,19] and Sabatini et al [20].…”

“…Shaw et al. also has shown that a B 4 C/NaIO 4 system with the addition of a fluoropolymer binder, polytetrafluoroethylene (PTFE), can result in halogenated fumigants . The versatility of B 4 C as a fuel has also been shown by Shaw et al.…”