Russian Journal of Applied Chemistry, 2011, Vol. 84, No. 9, pp. 1516−1523.
Pleiades Publishing, Ltd., 2011.
Original Russian Text © A.I. Kazakov, O.G. Ivanova, L.S. Kurochkina, N.A. Plishkin, 2011, published in Zhurnal Prikladnoi Khimii, 2011, Vol. 84, No. 9,
OF SYSTEMS AND PROCESSES
Kinetics and Mechanism of Thermal Decomposition
of Ammonium Nitrate and Sulfate Mixtures
A. I. Kazakov, O. G. Ivanova, L. S. Kurochkina, and N. A. Plishkin
Institute for Problems of Chemical Physics, Russian Academy of Sciences,
Chernogolovka, Moscow oblast, Russia
Received October 7, 2010
Abstract—Fundamental kinetic aspects of the decomposition of mixtures and double salts of ammonium nitrate
and ammonium sulfate were studied. The effect of water and sulfuric acid additives on the thermal decomposition
rate of ammonium nitrate and sulfate mixtures was examined. The constant of proton exchange between nitric
acid and the sulfate anion in molten ammonium nitrate was estimated.
Manufacture, transportation, and storage of a nitrate
fertilizer, ammonium nitrate (AN) and complex fertilizers
based on this compound involves a certain hazard of its
explosive transformation via thermal self-ignition of
AN if the thermal mode of its fabrication or granulation
is violated or because of ﬁ res in its transportation or
storage . Explosions have most frequently occurred
in ﬁ res in warehouses or railway cars with AN.
The main cause of thermal explosions is that the
equilibrium between the heat release and heat removal
across boundaries of a system is disturbed [2–5].
Therefore, a particular attention has been given in
studies to ﬁ nding the fundamental kinetic aspects of
heat release in thermal decomposition of AN and to the
inﬂ uence exerted by various factors on its rate.
As the main way to diminish the heat release rate in
thermal decomposition of AN has been recommended
introduction of minor amounts of additives that can
, primarily carbonates and phosphates.
Introduction of calcium carbonate (CC) into AN
results in that heat absorption is observed in mixture
decomposition during a long time  because a rather
slow endothermic exchange reaction of these salts
occurs in a melt of AN with CC to give ammonium
carbonate, which, in turn, decomposes into NH
O. The rate of this endothermic process under
experimental conditions exceeds the heat release rate
in decomposition of AN, and this predetermines the
overall heat absorption in the system. The technological
processing of AN mixtures with CC is substantially
safer and is performed on an at all different level as
compared with technical-grade AN. In the technological
temperature range 170–190°C, and even at substantially
higher temperatures when heat absorption is observed
during the ﬁ rst 24 h of decomposition, any signiﬁ cant
heating of the samples under study is impossible, and
the more so their thermal self-ignition. Introduction
of ammonium phosphates into AN in amounts smaller
than 1% noticeably diminishes the heat release rate
in thermal decomposition and makes slower the self-
acceleration of the reaction because of a decrease in the
excess amount of HNO
both in model mixtures of AN
with phosphates and in an industrial sample of ammonia
saltpeter with a phosphate-sulfate additive .
At present, manufacture of a complex fertilizer, ni-
trosulfate NS 32 : 5 [AN with addition of 21% ammo-
nium sulfate (AS)] is being developed in Russia. This
poses the question of the explosion safety in production
of such a fertilizer as compared with pure AN.
The goal of our study was to obtain data on thermal
decomposition rates of mechanical mixtures of pure AN
and AS with addition of water, sulfuric acid, and double
and to compare these rates with those for pure AN.