Metal–Halocarbon Pyrolant Combustion

Abstract

Energetic materials are characterized by their ability to undergo a spontaneous highly exothermic reaction. They can be classified into high explosives (HEs), propellants, and pyrolants. High explosives upon initiation yield a detonation -that is a supersonic shock wave sustained by a chemical reaction. Propellants and pyrolants on the contrary undergo a thermally propagated reaction and yield either large amount of gaseous species, or in the case of pyrolants yield mainly condensed products. Unlike most high explosives, which are homogeneous organic compounds containing nitro-and nitramine groups, pyrolants and most propellants are heterogeneous fuel/oxidizer mixtures [1,2].The term pyrolant describes hot burning compositions that are constituted from micrometric or nanometric metal powders and crystalline and/or polymeric oxidizers.Typical pyrolants are used as illuminant (Mg/NaNO 3 ), thermite (Al/Bi 2 O 3 ), and igniter (Zr/BaCrO 4 ) compositions [3], in addition coruscative combinations such as, for example, Zn/S or Mg/P [4, 5] find use as both amateur propellants (sic) and incendiaries [6].An important group of pyrolants consists of combinations of metal powders with halocarbon compounds. The large energy content of metal-halocarbon pyrolants stems from the high enthalpy of formation of the corresponding metal-halogen bond (MÀX). Thus, chlorocarbon and especially fluorocarbon compounds are used as oxidizers. Table 15.1 lists the gravimetric and volumetric enthalpy of combustion, adiabatic flame temperature, and ignition temperature for selected energetic materials taken from the groups of high explosives, propellants, and pyrolants.Mg/Teflon/Viton (MTV) (Teflon is the proprietary brand name of DuPont Company for polytetrafluoroethylene) [7] and Zn/ZnO/hexachloroethane (HC) [8] are typical metal-halocarbon pyrolants and are used as infrared decoy flare compositions (MTV) and obscurant smoke formulations (HC). In addition metal-halocarbon

Fabrication, Characterization, and Energetic Properties of Metallized Fibers

“…When first approaching the idea of electrospinning fibers and loading them with an energetic blend of n-Al and PFPE, Teflon AF was chosen as the likely precursor polymer to enable electrospinning of the suspension in order to maximize fluorine content of the bulk composite system. Pantoya et al showed that reaction of micrometer- and nanometer-sized aluminum blended with polytetrafluoroethylene (PTFE or Teflon) is driven to proceed by extraction of fluorine from the PTFE and formation of the thermodynamically stable species AlF 3 . − This reaction is exothermic in nature and the reaction kinetics are well understood and extensively documented in the literature by numerous groups. ,− Teflon AF, a copolymer of Teflon, seemed like a logical choice for fiber fabrication because it is a solution processable, amorphous thermoplastic. However, in practice, Teflon and Teflon AF are not conducive to electrospinning because of their low dielectric constant values .…”

Nanoenergetic Composites with Fluoropolymers: Transition from Powders to Structures

“…Over the past decades, PTFE mixtures with alternate metal fuels were developed. Among them, PTFE/Al mixtures have received significant attention as a reactive material formulation [ 19 ]. Aluminum nanoparticles, on account of their higher reactivity [ 20 ], have been progressively used as metal fuels in PTFE formulations as compared to the conventional micron-Al powders.…”