Metastable nanostructured metallized fluoropolymer composites for energetics

Abstract

Metastable composites were prepared from a fl uoropolymer-coated nano-aluminum blended formulation entrained in an epoxy matrix. This composition produced a moldable/post-machinable composite that undergoes thermally activated metal-mediated oxidation. The simplistic, scalable design can warrant consideration for a new class of engineered metal-based fl uoropolymer pyrolant composite systems. As featured in:See S. Fluoropolymers have long served as potent oxidizers for metal-based pyrolant designs for the preparation of energetic materials. Commercial perfluoropolyethers (PFPEs), specifically known as FomblinsÒ, are wellknown to undergo accelerated thermal degradation in the presence of native metals and Lewis acids producing energetically favorable metal fluoride species. This study employs the use of PFPEs to coat nano-aluminum (n-Al) and under optimized stoichiometric formulations, harness optimized energy output. The PFPEs serve as ideal oxidizers of n-Al because they are non-volatile, viscous liquids that coat the particles thereby maximizing surface interactions. The n-Al/PFPE blended combination is required to interface with an epoxy-based matrix in order to engineer a moldable/machinable, structurally viable epoxy composite without compromising bulk thermal/mechanical properties. Computational modeling/ simulation supported by thermal experimental studies showed that the n-Al/PFPE blended epoxy composites produced an energetic material that undergoes latent thermal metal-mediated oxidation.Details of the work include the operationally simple, scalable synthetic preparation, thermal properties from DSC/TGA, and SEM/TEM of these energetic metallized nanocomposite systems. Post-burn analysis using powder XRD of this pyrolant system confirms the presence of the predominating exothermic metal-mediated oxidized AlF 3 species in addition to the production of Al 2 O 3 and Al 4 C 3 during the deflagration reaction. Details of this first epoxy-based energetic nanocomposite entrained with a thermally reactive formulation of PFPE coated n-Al particles are presented herein.

Activating Aluminum Reactivity with Fluoropolymer Coatings for Improved Energetic Composite Combustion

“…23 Similar to results shown by Kappagantula et al, 19 the liquid fluorooligomer may readily activate the PIR and promote greater overall Al reactivity. The liquid fluoro-oligomer used in this study is a class of viscous fluorinated oligomers called perfluoropolyethers (PFPEs).…”

“…Miller et al 23 used a PFPE protective coating on nanoscale Al because of its thermal stability at low temperatures (up to 316°C in an oxygen-rich environment) and potential to produce exothermic activity beyond 316°C. 23 When coated with PFPE, the Al particles were able to suspend in a structural epoxy-based matrix. Miller used differential scanning calorimetry (DSC) to study the exothermic behavior for Al−perfluoropolyether (PFPE) blends of various weight percents.…”

Design and fabrication of energetic superlattice like-PTFE/Al with superior performance and application in functional micro-initiator

“…The fuel of choice is Al because of its high relative heat. Moreover, Al and PTFE have an ultrahigh energy density of 21 kJ/cm 3 [27,29]. Second, the reaction of PTFE and Al exhibits a potential gas release because of the low boiling point of reaction product (AlF 3 ) and carbon which would react with oxygen to form oxycarbide in the atmospheric conditions, which is beneficial for the release of energy, combustion rate and many applications [30,31].…”

“…In this work, polytetrafluoroethylene (PTFE) and aluminum (Al) are chosen as oxidizer and reducing agent based on the following reasons. First, fluorine is the strongest oxidizing agent, which can be reacted with metal such as Al to form AlF 3 liberating high heat (13.31 kcal/g [26,27]). PTFE contents 76 wt% of fluorine and possesses unique properties, in particular, high chemical and thermal stability [28].…”

Chemical and Morphological Inhomogeneity of Aluminum Metal and Oxides from Soft X-ray Spectromicroscopy

“…42,43 These analytes were specifically chosen because they provided a range of particle sizes, compositions, surface chemistries, and reactivities. [44][45][46][47] For example, previous studies have shown that protecting agents including organic ligands 40,[48][49][50][51][52][53][54] and polymer [55][56][57] or metal coatings 44,58,59 enhanced reactivity properties and provided chemical control over structural attributes like particle size and monodispersity. The STXM-XAS results were consistent with earlier spectromicroscopy studies, 26,55,60 and also revealed new differences in the surface and micron-scale speciation of Al nanoparticles.…”