Thermal Decomposition Kinetics Studies of HTPB/Al/AP Solid Propellants Formulated With Iron Oxide Burning Rate Catalyst in Nano and Micro Scale

Thermal Decomposition Kinetics Studies of HTPB/Al/AP Solid Propellants Formulated With Iron Oxide Burning Rate Catalyst in Nano and Micro Scale

Luis Eduardo Nunes Almeida (Avibras Indústria Aeroespacial S.A., Brazil), Aureomar F. Martins (Avibras Indústria Aeroespacial S.A., Brazil), Susane R. Gomes (Aeronautics Institute of Technology, Brazil) and Flavio A. L. Cunha (Avibras Indústria Aeroespacial S.A., Brazil)
Copyright: © 2018 |Pages: 23
DOI: 10.4018/978-1-5225-2903-3.ch010
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Abstract

The thermal decomposition kinetics of ammonium perchlorate (AP)/hydroxyl-terminated-polybutadiene (HTPB) samples, with Iron Oxide catalyst at nano and micro scale were studied by thermal analysis techniques at different heating rates in dynamic nitrogen atmosphere. The exothermic reaction kinetics was studied by differential scanning calorimetry (DSC) in isothermal conditions. The Arrhenius kinetic parameters were obtained by Flynn-Wall and Ozawa Kissinger and Starink methods. The propellant samples thermal decomposition was studied simultaneously by TG-DTA. For this purpose, solid propellant grains containing nano and micro scale iron oxide were formulated. The effect of catalysts on the propellant burning rate and the propellant initiation sensitivity were also evaluated by friction and impact. The effect of the catalyst in the propellant binder reaction was evaluated by viscosity and mechanical properties. SEM/EDS technique was used to evaluate the iron oxide morphology. Three bench firing tests were performed with rockets motor in order to know the ballistics parameters.
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Introduction

Composite solid propellant is considered a heterogeneous mixture in which solid particles are embedded in a polymeric matrix (binder) (Kubota, 2007). There are many kinds of polymers used in binder composition and the most commonly used polymer is hydroxyl polybutadiene, which acts as a binder for the solid particles and also as a fuel during the propellant combustion. The solid particles of propellant are composed of an oxidizer, usually ammonium perchlorate (AP), and a metallic fuel, usually aluminum powder that is used to increase the temperature of the combustion products (Prajakta, Krishnamurthy, & Satyawati, 2006), (Ma & Li, 2006), (Li & Cheng, 2007), (Sciamareli, Takahashi, & Teixeira, 2002). In addition to the basic components, other ingredients like plasticizers, bonding agents and combustion catalysts are added in the propellant formulation. The function of the combustion catalysts is to increase the propellant burning rate (Prajakta, Krishnamurthy, & Satyawati, 2006), (Kubota, 2007), (Li & Cheng, 2007). The main catalysts used as accelerators for the thermal decomposition of AP based propellants were the transition metal oxides, as ferric oxide (III) (Fe2O3), cobalt oxide (III) (Co2O3), manganese oxide (MnO2), chromium oxide (III) (Cr2O3) and copper chromite (II) (CuCr2O4) (Ma & Li, 2006). The characteristics of the metal oxides catalysts, such as particle size, surface area and defects in the crystalline structure may affect the burning behavior of ammonium perchlorate based propellants (Engen & Johannessen, 1990). Different mechanisms have been suggested to explain the thermal decomposition, but no model is completely satisfactory (Kishore, Verneker, & Sunitha, 1980), (Cavalheira, Gadiot, & Klerk, 1995). (Pekel, Pinardag, & Türkan, 1990) studied the effect of two iron oxides with different specific surface area on the burning rate of composite propellant. They observed that the burning rate increases proportionally with the specific surface area of the catalyst. The same conclusion was reached by Burnside (1975) and Engen and Johannessen (1990), on evaluating the effect of the specific surface area and particle size of different types of iron oxide on the composite propellants burning rate (Burnside, 1975) (Engen & Johannessen, 1990). The burning rate of propellant can be represented by analytical expression that defines burning rate as function of pressure at given temperature. The analytical expression most frequently used to describe the burning rate of composite propellants is the Saint Robert’s and Vieille burning rate law.r = aPcnwhere:

  • r = propellant burning rate

  • a = coefficient of pressure or rate of burning constant

  • Pc = chamber pressure

  • n = pressure exponent

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