David E. Chavez, Michael A. Hiskey, My Hang Huynh, Darren L. Naud, Steven F. Son and Bryce C. Tappan
Abstract: High-nitrogen energetic materials based on the tetrazine and tetrazole ring systems have shown unique and unpredictable combustion behavior. Unlike traditional energetic compounds, such as 2,4,6-trinitrotoluene (TNT) and hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX), which derive their energy by the oxidation of the carbon and hydrogen skeletal atoms by the oxygen carrying nitro group, high-nitrogen materials typically have large positive heats of formation as their source of energy. This difference in the energy source may partly explain why the combustion chemistries of some high-nitrogen materials are unusual.
Using the precursor 3,6-bis-(3,5-dimethylpyrazol-1-yl)-s-tetrazine (BDT), several useful energetic compounds based on the s-tetrazine system have been synthesized and studied. A number of these tetrazinebased materials have shown to exhibit burn rates with low sensitivity to pressure, namely 3,6-bis(1H-1,2,3,4-tetrazol-5-ylamino)-s-tetrazine (BTATz), 3,6-bis-nitroguanyl-1,2,4,5-tetrazine (NQ2Tz), the corresponding bis-triaminoguanidinium salt (TAG2NQ2Tz) and the N-oxides of 3,3´-azobis(6-amino-1,2,4,5-tetrazine) (DAATO3.5). A fifth compound of high nitrogen make-up, triaminoguanidinium azotetrazolate (TAGzT), is not prepared from BDT, but it also burns at exceptional rates with low pressure sensitivity.
The tetrazole-based materials, bis-(1(2)H-tetrazol-5-yl)-amine (BTA) and 5,5´-bis-1H-tetrazole (BT), are useful high-nitrogen energetic ligands for the preparation of metal complexes. While BTA, BT and their salts have been previously shown as possible energetic fuels for low-smoke pyrotechnic applications, some recent combustion experiments with the metal complexes of BT and BTA have proved to be even more noteworthy. These metal ion complexes have sufficient internal energy that they can burn under an inert atmosphere to produce the free metal, usually in the form of high-surface area foams or nano-sized particles.
This highly unusual, reductive combustion chemistry may lead to efficient and controlled production of metal nanofoams. The heat of formation (ΔHf) of 3,6-diazido-1,2,4,5-tetrazine (DiAT), a highly energetic and sensitive energetic material (most notably to friction, spark and impact), was calculated to be approximately +1100 kJ mol−1, or +92 kJ mol-atom−1, using an additive method. Depending on the heating rate, DiAT can undergo pyrolytic decomposition to produce either carbon nanospheres or carbon nitride nanopolygons. With slow heating, leaf-like or rope-like forms of carbon nitride were the predominant products. With faster heating, carbon spheres with diameters on the order of 10 to 100 nm were produced. Such nanomaterials are of interest to the scientific community for a wide number of industrial applications.
Keywords: high-nitrogen, tetrazole, tetrazine, combustion, nanomaterials, propellant, foam
Ref: JPyro, Issue 23, 2006, pp70-80
(J23_70)
© Journal of Pyrotechnics and CarnDu Ltd
