INVESTIGATION OF THE STRUCTURE OF AN AMMONIUM-NITRATE CALCIUM NITRATE EUTECTIC MELT USING ISOTOPIC DIFFERENCE-METHODS IN NEUTRON-DIFFRACTION

A neutron diffraction study of a eutectic melt of deuterated ammonium nitrate and calcium nitrate (Ca(NO3)2 .5N(1)D4N(2)O3) is carried out at 423 K. Isotopic difference methods are applied to the nitrogen nuclei of the ammonium and nitrate ions. The results based on the first-order difference show that the local coordinations around ND4+ and NO3- are similar to that for pure molten ammonium nitrate. However, there is clear evidence from the second-order difference method that the N(1)D4+ ... N(2)O3- coordination is significantly different. In particular, the nearest-neighbour N(1)-N(2) distance is 5.5 +/- 0.2 angstrom in the mixed molten salt and 4.5 +/- 0.05 angstrom in pure molten ammonium nitrate. An explanation of this result is given in terms of the inhibiting role of the Ca2+ on the chemical-kinetics of molten ammonium nitrate.