Thermal decomposition properties and compatibility

Authors: T Gołofit K Zyśk

Publish Date: 2015/01/31

Volume: 119, Issue: 3, Pages: 1931-1939

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Abstract

The compatibility of filler 24681012hexanitro24681012hexaazaisowurtzitane CL20 with rocket propellant binders hydroxylterminated polybutadiene HTPB butadieneacrylonitrileacrylic acid terpolymer PBAN glycidyl azide polymer GAP and poly3nitratomethyl3methyloxetane polyNIMMO has been examined The compatibility of the compounds has been tested in accordance with the STANAG 4147 standard and its modification consisting in the change of the heating rate As it arises from STANAG 4147 standard criterion CL20 is not compatible with polyNIMMO PBAN and GAP and possibly incompatible with HTPB Changes of relative position of peaks between measurements performed in hermetical pans and pans with a pinhole and with different heating rate were observed In case of polyNIMMO and HTPB changes of measurement parameters lead to estimated compatibility change The analysis of the thermal decomposition of CL20 revealed that it is a twophase process The first phase is associated with decomposition in solid phase the second phase is associated with decomposition of volatile intermediate products of CL20 decomposition Due to the complex process of decomposition of tested samples the apparent activation energy was used for the assessment of the compatibility The apparent activation energy of the initial phase of decomposition CL20 and its mixtures with binders are compatible with one another within the limits of measurement error Results of measurement of apparent activation energy do not indicate a destabilizing effect of binders on the initial phase of decomposition of CL20Binders such as hydroxylterminated polybutadiene HTPB butadieneacrylonitrileacrylic acid terpolymer PBAN glycidyl azide polymer GAP and poly3nitratomethyl3methyloxetane polyNIMMO are substances added to rocket propellants in purpose to bond solid components of propellant and to give it the appropriate mechanical properties Fast burning rocket propellants with a high specific impulse very commonly contain ammonium chlorateVII AP and aluminium Al in addition to binders in its composition 1 The main disadvantage of such propellants is the formation of signature during engine operation which allows easy detection of a flying rocket and its launch site The signature can be reduced by the elimination of Al and reduction of AP These components can be replaced with a highenergy filler such as 24681012hexanitro24681012hexaazaisowurtzitane CL20 In order to ensure the safe storage and use of rockets propellant components should be compatible with each other 2 3 4 5 6 7 8 The NATO Standardization Agency recommends determination of compatibility at heating rate of 2 K min−1 7 There are some descriptions found in the literature which concern the compatibility examinations performed at heating rate of 10 K min−1 2 8 However the best influence visibility of one substance on thermal decomposition of the other can be obtained by analysing changes of kinetic parameters of decomposition reaction 3 5 6 In accordance with the recommendations of International Confederation for Thermal Analysis and Calorimetry ICTAC full kinetic analysis should be based on the determination of the activation energy preexponential factor and reaction model 9 During the decomposition of highenergy materials and especially a multicomponent mixture many parallel and successive reactions can proceed 5 9 Determined kinetic parameters are the result of all the processes taking place during the decomposition of the sample Therefore it is difficult to determine the model of such a decomposition reaction Without assuming the reaction model it is impossible to determine the preexponential factor Recommended isoconversional methods allow estimating the activation energy without assuming any reaction model For practical reasons in this study the effect of one compound on the thermal degradation of the second compound in the mixture was analysed by changes in the activation energy Due to the complex process of decomposition of tested samples determined parameter in the later work is called the apparent activation energy aEa Uncontrolled decomposition of a highenergy mixture caused for example by the lack of compatibility may lead to the thermal explosion 10 Such an event can occur even in low degrees of conversion 11 For this reason the influence of ingredients on the changes in the apparent activation energy was analysed for the initial level of conversionThe following paper presents the study of the compatibility of CL20 with selected binders of heterogeneous rocket propellants The compatibility was determined in hermetic pans and in pans with a pinhole at two different heating rates 2 and 10 K min−1 The influence of the measurement conditions on the determined compatibility was analysed The apparent activation energy of decomposition reaction of the examined mixtures and their components was determined and compared depending on the degree of conversion The results of compatibility of the studied systems determined by comparison of peaks were compared with the results of compatibility determined by comparison of the activation energy changesεCL20 impact sensitivity about 4 J with the chemical purity of 98  and the polymorphic purity 95  was synthesized in the Department of High Energetic Materials of the Faculty of Chemistry at the Technological University of Warsaw Poland GAP and polyNIMMO with the chemical purity of 98  were synthesized in the Industrial Chemistry Research Institute Poland HTPB was synthesized at the Industrial Chemistry Research Institute Poland Mn = 2500 Mw = 4000 OH = 12 meq g−1 water content max 02  PBAN is manufactured by the Research and Development Centre of Rubber and Vinyl Plastics OBR KiTW in Oświęcim Mn 2230 Binary mixtures used in the study were obtained by grinding components in an agate mortar at the mass ratio of 11The compatibility was determined according to the method specified in STANAG 4147 7 The measurements were carried out for samples of the tested substances with a mass of 1 ± 01 mg and 11 w/w mixture with a mass of 2 ± 01 mg in pans with a pinhole at a heating rate of β = 2 K min−1 Decomposition peak minimum temperatures of CL20 T a were compared with values obtained for the mixture of CL20 with other ingredient T ab If T ab of mixture decomposition is more than 20 K lower in relation to T a CL20 then CL20 is incompatible with this other ingredient If the shift in the direction of lower temperatures is in the range of 4–20 K then CL20 is uncertainly compatible with the other ingredient and it demands further investigation CL20 is compatible with the analysed ingredient when T ab is maximum 4 K lower than CL20 decomposition temperature T a

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