Study of dynamic features of highly energetic reactions by DSC and High-Speed Temperature Scanner (HSTS)
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Study of dynamic features of highly energetic reactions by DSC and High-Speed Temperature Scanner (HSTS) M.A. Hobosyan1, Kh.G. Kirakosyan2, S.L. Kharatyan2,3, K.S. Martirosyan1*
1
University of Texas at Brownsville, Department of Physics and Astronomy, Brownsville, TX 78520, USA 2 Institute of Chemical Physics NAS RA, Yerevan, 0014, Armenia 3 Yerevan State University, Yerevan, 0025, Armenia, ABSTRACT The dynamic features of Al2O3 - polytetrafluoroethylene (PTFE) and Al - PTFE reactions in nonisothermal conditions are presented. The Differential Scanning Calorimetry (DSC) and HighSpeed Temperature Scanner (HSTS) were used to characterize the Al2O3/Al – PTFE reactions at different heating rates. The study shows that the HSTS instrument can give more information about the reaction mechanism and kinetics than the conventional DSC measurements. In this work we show that high heating rates may reveal exothermic reaction between Al2O3 and PTFE that were previously unidentified. The PTFE can potentially remove the oxide layer from aluminum in the initial period of the reaction and increase the direct contact area between oxygen and aluminum, which increases the reaction velocity and improves the energy release abilities of the system. *E-mail: [email protected] INTRODUCTION Aluminum reaction with oxygen, polymers and metal oxides exhibits high enthalpy and has been proposed to use for high-energy storage materials [1]. The size reduction of reactant powders such as aluminum from micro- to nano-size increases the reaction front propagation velocity in some systems by two to three orders of magnitude [2, 3]. The Al polytetrafluoroethylene (PTFE, TeflonTM) reaction has been widely investigated in numerous studies due to the importance of this system as an energetic additive of rocket fuels and pyrotechnics in general [4-6]. However, effective ignition of aluminum is problematic due to the oxide layer that naturally forms on the aluminum surface. The PTFE can potentially remove the oxide layer from aluminum and increase the direct contact area between oxygen and aluminum, which increases the reaction velocity and improves the energy release abilities of the system. Due to self-heating of the system, the reaction rate accelerates exponentially and can lead to explosion. In our knowledge, no investigation was made in high heating rates for the system Al PTFE, where heating rates are comparable to those in self-ignited reaction mixtures. In this work we attempt to study Al2O3 - PTFE and Al - PTFE systems at high heating rate up to 3200 °C/min. MATERIALS AND METHODS The chemicals used for this study were Aluminum (99.5 %, 100 nm, Sigma Aldrich), Polytetrafluoroethylene (PTFE, 99.99%, 1 μm, Sigma-Aldrich), Al2O3 (Spectroscopic grade, TA instruments), and Argon (99.999%, Airgas Company). The DSC-TGAQ-600 (TA Instrument) was used to test Al2O3 - PTFE reactions with linear heating range of 20-150 °C/min, with resolution of mass changes of 0.1 microgram, which gives opportunity to work with very small
amounts of mixtures. Th
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