Abstract
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 Å in the mixed molten salt and 4·5 ± 0·05 Å in pure molten ammonium nitrate. An explanation of this result is given in terms of the inhibiting role of Ca2+ on the chemical kinetics of molten ammonium nitrate.

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