Thermal Stability of Hydrazinium Nitroformate (HNF) Assessed by Heat Generation Rate and Heat Generation and Mass Loss

Manfred A. Bohn

Abstract: HNF, hydrazinium nitroformate, H₃NNH₂ ^+·C(NO₂)³⁻, is a water soluble salt. It has a positive oxygen balance of 13%, a much more positive enthalpy of formation than ammonium perchlorate (AP) and amuch higher heat of explosion than AP, 5579 J g⁻¹ against 1972 J g⁻¹. Additionally it has no chlorine and all the problems with hydrogen chloride formation can be avoided when used as oxidizer in rocket propellant formulations. All these advantages together could make HNF an oxidizer with better performance than AP. One inherent disadvantage may be the lesser thermal stability of HNF. Therefore an extensive investigation was performed on the thermo-chemical stability of HNF. Three sample lots of HNF have been investigated at ICT. They were provided by APP BV, The Netherlands. The thermal stability was determined by the following methods:

• autoignition temperature with 0.2 g at 5 °C min⁻¹ heat rate in a Wood’s metal bath

• vacuum stability test (VST)

• heat generation rate as function of time and temperature

• mass loss as function of time and temperature

• adiabatic self heat rate.

Lots 2 and 3 have been characterised by heat generation rate at 60 °C, 65 °C, 70 °C and 75 °C and in short by mass loss. Lot 1 was extensively used for mass loss determinations in the temperature range 50 to 80 °C. HNF shows high heat generation rates. All curves from both methods indicate self accelerating behaviour. They have been described with autocatalytic reaction kinetic models. The Arrhenius parameters have been determined for lot 1 from mass loss data and for lots 2 and 3 from heat generation data. The activation energies for the intrinsic decomposition reaction are 166, 139 and 132 kJ mol⁻¹ and for the autocatalyticreaction 159, 128 and 117 kJ mol⁻¹ in the order lots 1, 2, 3. The kinetic data are compared and discussed. Data for lifetime at different temperatures are given in terms of the times to reach preset values of mass loss and energy loss.

Keywords: autocatalytic, kinetic, HNF

Ref: JPyro, Issue 26, 2007, pp65-94
(J26_65)

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