Thermal stability of habit modified ammonium nitrate: Insights from isoconversional kinetic analysis

Compared to the conventional ammonium perchlorate based solid propellants, burning of ammonium nitrate (AN) based propellants produce environmentally innocuous combustion gases. However, the near room temperature phase transition limits the application of AN as a propellant ingredient. A method to produce phase modified ammonium nitrate (PMAN) was reported by means of habit modification route using potassium ferrocyanide. In the present study, the thermal stability and moisture absorption characteristics of PMAN were evaluated to understand the viability of its application in the environmentally benign propellant systems. The energy of activation of decomposition reaction of AN, PMAN and an admixture of AN-potassium ferrocyanide trihydrate were computed by Friedman's differential and Vyazovkin's non-linear integral isoconversional methods and used to ascertain their thermal stability. The moisture absorption characteristics were determined at 53 and 62% RH and the cyclic DSC analysis, combination of non-isothermal and isothermal, was used to trace the phase behaviour of the PMAN. The study indicates that PMAN and AN has comparable properties suggesting similar processing and handling conditions.

► Phase and habit modified ammonium nitrate (PMAN) is synthesized.
► PMAN has similar moisture absorption characteristics of AN at 53% and 62% RH.
► AN and PMAN have nearly similar energy of activation of decomposition.
► The stability sequence varies in the order AN > PMAN > admixture of AN-habit modifier.
► No influence of pH, since pH of AN-potassium ferrocyanide solution remains at 4.3 ± 0.1.