Burning properties of redox crystals of ammonium nitrate and saccharides

Ibukun Oluwoye,Mohammednoor Altarawneh,Jeff Gore,Bogdan Z Dlugogorski

doi:10.1016/j.combustflame.2019.11.030

Ibukun Oluwoye, Mohammednoor Altarawneh + Show 2 more

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https://doi.org/10.1016/j.combustflame.2019.11.030

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Abstract

Ammonium nitrate (AN, NH4NO3) constitutes the key ingredient of monofuels and civilian-grade explosives, attracting scientific interests aimed at improving their operational and safety performance. This study investigates the combustion properties of redox crystals comprising ammonium nitrate and simple saccharides, with the infrared spectroscopy, X-ray diffraction and molecular modelling. Furthermore, the thermogravimetric measurements afford the isoconversional analysis that yields the overall activation energies of the decomposition process. In addition, the synthesised samples are subjected to elemental and sorption analyses. The results outline (i) the molecular inclusion of the solid fuels within the lattice clusters of AN, (ii) a comparable hygroscopicity behaviour, i.e., a minor increase in affinity towards the absorption of moisture, and (iii) an energetically improved decomposition (and regression) rate, relatively to pristine AN. These features manifest themselves in lower activation energies of redox crystals that enhance the deflagrating properties of these materials for possible application in aviation propellants, and minimise the environmental footprint, especially the emission of nitrogen oxide to the atmosphere, which arises because of inhomogeneities in AN-fuel mixtures commonly used in civilian explosives.

Highlights

Ammonium nitrate (AN, NH4NO3) remains an essential chemical commodity that serves many industries, including the agricultural and explosive sectors
The use of AN continually replaces other conventional oxidisers such as ammonium perchlorates (AP) due to its relatively low cost and halogen-free combustion products, some technical drawbacks have been attributed to the logistics and application of AN in propellants and explosives [7]
The major downsides of AN include (i) its low-temperature transitions and high hygroscopicity which complicate the handling and shelf-life, (ii) its low-burning rate and energetics which influence the performance, mainly as aviation propellants, and (iii) its formation of nitrogen oxides (NOx, as combustion product) which contributes to atmospheric pollution [1,8]

Summary

Introduction

Ammonium nitrate (AN, NH4NO3) remains an essential chemical commodity that serves many industries, including the agricultural and explosive sectors. Civilian and military applications deploy AN as an oxidiser in emulsion (and bulk) explosives, as well as in some propellants and pyrolants. These products are crucial to the sustenance of mining and infrastructure activities [1,2], gas generation mechanisms (e.g., in automotive inflator systems and heavy-lift launchers) [3,4], alternative-fuel engines [5,6], as well as propulsive functions of rockets, satellites and cruise missiles. The use of AN continually replaces other conventional oxidisers such as ammonium perchlorates (AP) due to its relatively low cost and halogen-free combustion products, some technical drawbacks have been attributed to the logistics and application of AN in propellants and explosives [7]. The deflagration of solid AN may produce NOx (an orange plume), propagating initially both by ionic and radical mechanisms in the condensed medium [9,10], and subsequently in the gas-phase reactions [11,12] depending on the temperature, pressure, and confinement [1]

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