Project Refinement #3

My research will focus on the synthesis and evaluation of various quantities of 5,5'-hydrazinebistetrazole (HBT) in paraffin-based hybrid rocket fuels. A similar compound gaunidinium azotetrazolate (GAT) has been shown to increase the burn rate performance of HTPB hybrid rocket fuels. Neither GAT nor HBT have been tested in liquefying paraffin fuels. HBT has been selected over GAT, hydrazinium 5-aminotetrazolate (HAT), and other tetrazoles due to its advantages in synthesis and performance. HBT has a higher density, nitrogen content, heat of formation, detonation pressure, and detonation velocity than GAT.  HBT is a comparable energetic material in performance to the high explosives RDX and HMX. However, HBT is far less sensitive to all forms of shock compared to these explosives. When ignited in powder or pellet form, HBT burns rapidly. HAT is even less sensitive than than HBT and has a higher performance including heat of formation and detonation velocity than HBT, RDX, HMX, and CL-20.

The synthesis of HBT is also simpler and less expensive than GAT. Cost is the main reason for HBT's selection over HAT for initial testing. For HBT's production, 5-amino-1H-tetrazole (5-AT), sodium hydroxide, potassium permanganate, hydrochloric acid, and magnesium powder are required. 5-AT is also required for the synthesis of HAT. To synthesize HAT, 5-AT must be reacted with hydrazine in an solution of tetrahydrofuran (THF) or with hydrazine hydrate. A 1M solution of hydrazine in THF is about $150.00 per liter and hydrazine hydrate is about $100.00 per kilogram. Because of a limited budget, I have tentatively eliminated the initial consideration of HAT.

5-AT is oxidized by potassium permanganate in sodium hydroxide solution to yield sodium azotetrazolate (Na2ZT). Na2ZT provides the azotetrazolate cation for producing both HBT and GAT. When Na2ZT is allowed to react for several hours with magnesium powder and is subsequently treated with hydrochloric acid, HBT is precipitated on cooling. This procedure is completely reasonable in the lab. I estimate than an average of 100g of HBT will be used for each trial. Assuming 30 trials, roughly 3Kg of HBT will need to be produced. Bulk synthesis techniques will be required to produce this volume and will be further studied. A complete list of lab equipment will need to be formulated.

The oxidizer used during firing will be held constant. Optimally, I would like to use >80% hydrogen peroxide over a catalyst bed. The exothermic decomposition of hydrogen peroxide will cause auto-ignition of the fuel, eliminating the need for costly ignition systems and fire sequence programming. Also, the use of hydrogen peroxide has been shown to increase the burn rate of hybrid rocket fuels. Hydrogen peroxide can be obtained at 85% concentrations for $8.27 per kilogram. At optimal O/F ratios of about 6 and 250g of propellant, the cost for a test comes to $12.40.

Since the ultimate goal is to improve the performance of hybrid rocket motors, the project will stay flexible. If the time exists for further testing, HAT will be synthesized, tested, and compared to HBT. Metallized fuels with HBT or HAT could also be characterized. Another direction could be the variation of the polymer chain length in the paraffin fuel to test its effect on propellant mechanical properties and performance with HBT or HAT.  This, however, may have to be left for future research.

My research will now focus on the physical aspects of hybrid rocket motor design and testing. I will first determine what parameters of the motor need to be varied and what characteristics need to be measured in order to characterize the fuel mixes with varying HBT loading. I will also focus on the design of small-scale hybrid rocket motors for testing. Later, instrumentation and equipment will be detailed and located for collecting data.