ADN Ammonium Dinitramide

DSC and DTA measurements show melting of ADN, NH4N(N02)2, at 328 K, the onset of decomposition at 421 K, and an exothermic peak at 457 K.l l Gasification of 30% of the mass of ADN occurs helow the exothermic peak temperature, and the remaining 70% decomposes after the peak temperature. The decomposition is initiated by dissociation into ammonia and hydrogen dinitramide. The hydrogen dinitramide further decomposes to ammonium nitrate and NjO. The final decomposition products in the temperature range 400-500 K are NH3, HjO, NO, 

and HNO3, with a total heat release of approximately 240 kj moh. P These molecules react in the gas phase to form O2, H2O, and N2 as the final combustion products and the adiabatic flame temperature reaches 3640 K. The excess oxygen molecules act as an oxidizer when ADN is mixed with fuel components. 

The combustion wave structure of ADN consists of three zones the melt layer zone, the preparation zone, and the flame zone. The temperature remains relatively unchanged in the melt layer zone, then increases rapidly just above the melt layer zone to form the preparation zone, in which it rises from about 1300 to 1400 K. At some distance above the melt layer zone, the temperature increases rapidly to form the flame zone, in which the final combustion products are formed. 

Similar to the situation with nitrate esters, the two-stage gas-phase reaction resulting from the combustion of ADN occurs due to the reduction of NO to N2, which is reported to be a termolecular reaction. The heat flux transferred back from the preparation zone to the melt layer zone dominates the gasification process occurring in the melt layer zone. 

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Ammonium dinitramide (ADN) is a crystalline oxidizer with the formula NH4N(N02)2, that is, it is composed ofionicaUy bonded ammonium cations, NH4, and dinitramide anions, N(N02)2- Though ADN is crystalline and has a high oxygen content, similar to AP and KP, it has no halogen or metal atoms within its structure. ADN is used as an oxidizer in smokeless composite propellants, similar to AN and HNF. It melts at about 364 K, accompanied by the latent heat of fusion. 

In search of a high performance and eco-friendly oxidizer, extensive research has been going on in this area for more than two decades and as a result, two oxidizers ammonium dinitramide (ADN) and hydrazinium nitroformate (HNF) have emerged as strong contenders of AP in composite propellants and their important aspects are as follows. 

Ammonium dinitramide (ADN) [NH4N(N02)2] is a relatively newly discovered inorganic solid salt, mainly intended as an oxidizer for composite propellants and it is widely known at present Dinitramide salts were reported [64, 65] from USA in 1996 while Russians [66] used these salts in their various missile programs in 1971. 

Ammonium dinitramide (ADN) and hydrazinium nitroformate (HNF) are potential high performance and eco-friendly replacements for AP in composite propellants and efforts are being made all over the globe in this direction. Similarly, there is a need to study these high performance oxidizers and their salts for pyrotechnic applications. Some groups of researchers have already initiated research in this direction and several alkali dinitramide salts have been synthesized and characterized for their elemental content, solubility, thermal behavior and crystal structures. 

The research into energetic molecules which produce a large amount of gas per unit mass, led to molecular structures which have a high hydrogen to carbon ratio. Examples of these structures are hydrazinium nitroformate (HNF) and ammonium dinitramide (ADN). The majority of the development of HNF has been carried out in The Netherlands whereas the development of ADN has taken place in Russia, USA and Sweden. ADN is a dense non chlorine containing powerful oxidiser and is an interesting candidate for replacing ammonium perchlorate as an oxidiser for composite propellants. ADN is less sensitive to impact than RDX and HMX, but more sensitive to friction and electrostatic spark. 

Ammonium dinitramide [ADN, NH4(N02)2] was first synthesized in Russia in 1972 (Luk yanov) and in the U.S. in 1989 (Bottaro, SRI) [132], ADN has been considered as a propellant ingredient due to its calculated performance and lack of chlorine, but its poor density somewhat offsets these advantages (Table 4). A considerable effort has been undertaken to solve its physical problems (poor morphology, high hygroscopicity, low thermal stability) and improve its synthesis [133-138]. In 1991, the first-bench scale synthesis produced material at 4000/lb. By 1997 Bofors had patented a aqueous solution preparation which afforded ADN at 525/lb. ADN is much less thermally stable than AN, probably due to a substantially lower melting point (94°C) and light sensitivity. However, like AN, addition... 

Ammonium perchlorate and ammonium dinitramide can decompose by similar routes, but perchlorate, in particular, has several other decomposition pathways available. One decomposition route of ADN produces ammonium nitrate andN20 [138],... 

The atomistic models presented in the previous sections can also be applied to the case of ionic energetic materials. Sorescu and Thompson have illustrated this for the case of crystalline ammonium dinitramide (ADN)... 

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