Review of some peculiarities of the stability and decomposition of HNF and ADN

HNF (hydrazinium nitroformate) and ADN (ammonium dinitramide) are seen as possible replacements for the common oxidizer ammonium perchlorate (AP) in composite rocket propellants. Both HNF and ADN have the relatively great advantage to be chlorine free. But their chemical stability is much lower than the one of AP. In spite of this they are still on the list as replacement candidates. This paper intends to review and compile essential features in stability, compatibility and decomposition behaviour of the two candidates. HNF alone can be seen as relatively stable at temperatures up to 50°C. But it shows selfaccelerating decomposition behaviour. In such a case normally stabilizers help to suppress autocatalytic behaviour as it is possible with nitrate esters. This seems not a way with HNF. A look on the possible decomposition behaviour reveals that HNF seems not stabilizable. Further problems are chemical compatibility and a too high pressure exponent of the propellant formulations. ADN can be qualified as medium stable at lower temperatures similar to NC-based products. Also ADN shows self-accelerated decomposition. In contrast to HNF, it can be stabilized and a lot of possibilities exist, some stabilizers are superior. The reason for the stabilisation by stabilisers can be found in the difference in decomposition mechanisms, which will be shown. From the results presented one can conclude that ADN has a perspective to replace AP in propellants designed for selected applications. A 'universal' application as with AP-based composite rocket propellants seems at time not realistic. Special measures as coating of ADN particles may improve the situation with regard to manufacturing and compatibility, but the limited in-service temperature range will be not changed.