On the mechanism of the thermal transformations in solid ammonium nitrate

The thermal transformations which take place in solid ammonium nitrate have been studied with the following techniques: differential thermal analysis, measurement of d.c. electrical conductance, optical microscopy, X-ray diffraction and nuclear magnetic resonance. It has been found that in dry ammonium nitrate, transformations between forms V, IV, II and I only take place and that the transformations appear to be of the order-disorder type. The transformations IV ⇌ III only take place in the presence of moisture and the mechanism appears to be one of dissolution and recrystallization.