AbstractThe thermal decomposition of ammonium nitrate in a fused equimolar mixture of sodium and potassium nitrates has been studied. It is shown that the reaction is first order with respect to ammonium ions. the rate of decomposition is increased by cations of a highly polarising nature, whereas anions, such as sulphates, phosphates and fluorides, which act as bases in the system, decrease the rate of decomposition. the observations are in accord with an ionic mechanism for the decomposition of ammonium nitrate, involving the reaction of ammonia with the nitronium ion.