Thermal study of the decomposition of HTPB hybrid rocket fuel in the presence of azo-tetrazolate-based high nitrogen content high energy materials
Azo-tetrazolate salts and their derivatives have identical negatively charged conjugated nitrogen rings and two varied positively charged cations. The varied cations are guanidinium, aminoguanidinium, diaminoguanidinium, triaminoguanidinium and ammonium. Azo-tetrazolate salts and their derivatives were synthesized and fully characterized by multinuclear spectroscopy (NMR) and Fourier transform infrared spectroscopy (FTIR). Hydroxyl-terminated polybutadiene (HTPB) has been used as a fuel and/or binder for devices such as hybrid and solid rockets. Present-day work on HTPB includes studying its thermal decomposition in the presence and absence of energetic material. Varying concentrations of energetic materials were used to create samples of crosslinked HTPB, which were utilized for the analysis. Different percentages (10, 15, 20%) by mass of azo-tetrazolate-based high nitrogen materials were used. Crosslinking agent polymethylene polyphenyl isocyanate (PAPI) was added to the polybutadiene R45-M resin and was maintained at 15% by mass in all samples. Differential scanning calorimetry (DSC) and thermogravimetric analysis (TG) were performed to investigate the effect of additives. This is carried out within an atmospheric air setting at a heating rate of 5 °C/min. Plain HTPB has three exothermic peaks under air, with the first occurring at 206.82 °C, the second peak at 350 °C and the third peak beginning (onset) at 421.67 °C. Total decomposition of the mixtures is exhibited by the third exothermic peak, which ends at 600 °C. The effect of mixing these high energy compounds was determined using TG and DSC. Indications are that the resulting high energy compound/HTPB mixtures may provide a better performing fuel for future hybrid rocket formulations.
KeywordsHybrid rocket Hydroxyl-terminated polybutadiene (HTPB) Fuel regression rate Thermal decomposition Azo-tetrazolate and high energy nitrogen compounds
Support from the Arkansas Space Grant Consortium (ASGC) (NASA award NNX15AR71H) in the form of a Research Infrastructure Award and multiple years STEM awards for Dr. Yousef is gratefully acknowledged. We thank the UA Little Rock Nanotech Center for use of the Thermal Laboratory and its TG and DSC equipment. Thank you to Drs. Fumiya Watanabe, Omar Abdulrazzaq, Shawn Bourdo and Viney Saini for their assistance. Ms. Missy Hill and Ms. Laura Holland were very helpful to Dr. Yousef during her studies. This work was partially presented at the 2016 ACS National Convention (Philadelphia), 2016 UA Little Rock Research EXPO, and at the 2016 Arkansas Space Grant Consortium 2016 Annual Symposium.
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