Calorimetry studies of ammonium nitrate – Effect of inhibitors, confinement, and heating rate

Abstract

Ammonium nitrate (AN) has been widely used as a fertilizer for almost a century because it is an excellent nitrogen source. However, AN related explosions continue to occur time and again, despite the fact that AN has been extensively investigated. There have been more than 70 AN-related incidents during the last century, which reemphasize the dire need for further research on AN reactive hazards. This research focuses on the alternatives to make AN safer as a fertilizer by reducing its explosivity, by studying the effect of inhibitors, confinement, and heating rate on AN thermal decomposition using the Reactive Systems Screening Tool (RSST). First, the thermal decomposition of AN in the presence of different types of additives, including sodium bicarbonate, potassium carbonate, and ammonium sulfate, was studied under two concentrations, i.e., 2.8 wt.% and 12.5 wt.%. The results show that they are good inhibitors for AN. Second, the effect of confinement was tested by observing AN decomposition under five different initial pressures, varying from ambient pressure to 187 psig. It is concluded that confinement is dangerous to AN, which should be avoid in AN storage and transportation. Lastly, the effect of heating rate was studied by heating up AN under two heating rates of 0.25 °C min−1 and 2 °C min−1. The lower the heating rate, the lower the “onset” temperature detected.