Urea nitrate completely sublimes in a continuously pumped vacuum at a rate dependent upon the extent of the surface area. The fraction sublimed (α) vs. time (t) curve is sigmoidal in shape with an inflection point fluctuating between 5.3 and 8.1 % weight loss in the temperature range 56 to 97°.
Decomposition of urea nitrate in an initially evacuated system gave sigmoidal pressurevs. time curves. The experimental kinetic data fit the growing nuclei model with a measured enthalpy of activation of 142±12.5 kJ/mole as compared to 115±11.3 kJ/mole obtained thermogravimetrically. This higher value ofΔH‡ is explained on the basis of two factors: 1) the inhibitory effect of the product gases and 2) self heating, whose extent increasedΔH‡ by about 12.5 kJ/mole.