The two-step character of the II → IV transition in ND 4NO 3

Abstract

The DTA method has been applied for the investigation of the metastable II → IV transition in ND 4NO 3. This transition which differs from the usual one in NH 4NO 3, was found to occur in two steps, with the consequent observation of a double peak in the differential temperature curve. The difference between the two steps varied between about 1.9 and 0.2°C, depending on thermal cycling and on annealing. When the number of heating—cooling cycles was raised from 1 to about 60, the energy fraction W 1/( W 1 + W 2) increased from 0.22 to 0.28, and after that remained constant. Energies W 1 and W 2 above represent the high and low temperature steps of the transition, respectively. When the number of heating—cooling cycles exceeded 47, a supercooling effect was observed in the low temperature step of the transition, but not in the high temperature step.