Review
Studies on energetic compounds: Part 8 : Thermolysis of Salts of HNO3 and HClO4

https://doi.org/10.1016/S0304-3894(00)00159-XGet rights and content

Abstract

The thermolysis of various substituted ammonium salts of nitric and perchloric acids has been reviewed in the present communication. The mechanistic aspects of thermal decomposition of these salts have been discussed critically. It has been observed that the proton transfer process do play a major role during thermolysis of these salts. The plausible decomposition pathways have also been described.

Introduction

Energetic materials are the nucleus of modern warfare and one of the most intriguing classes of compounds, which can act as a source of high chemical energy. An energetic material [1], [2] is a chemical substance or mixture of substances, when raised to a sufficient high temperature, whether by direct heating, friction, impact, shock, spark or flame, suddenly undergoes very rapid chemical transformations with the evolution of large amount of heat and gases, thereby exerting high pressure on the surroundings. In other words, it may be defined as a material that can undergo very rapid self propagative decomposition to release its potential energy and produces a sudden outburst of heat and volume of gases considerably greater than the original volume of the energetic material.

Energetic material may be solid, liquid or gas and the products of explosion/ignition are gases or mixture of gases and solids. The thermal decomposition and explosivity of energetic materials, particularly in relation to their molecular structure, are of current interest. The explosive properties of any substance depend upon the presence of the following groups called explosophores:

  • 1.

    NO2 and ONO2 in both inorganic and organic substances,

  • 2.

    NN and NNN in inorganic and organic azides,

  • 3.

    NX2 (X — a halogen),

  • 4.

    NC in fulminates,

  • 5.

    OClO2 and OClO3 in inorganic and organic chlorates and perchlorates, respectively,

  • 6.

    OO and OOO in inorganic and organic peroxides and ozonides, respectively,

  • 7.

    CC in acetylene and metal acetylides,

  • 8.

    MC (metal bonded with carbon) in some organometallic compounds.

A further classification of explosives was also made on the basis of oxygen balance, “plosophoric” groups, auxoplosive groups and heat of explosion. A plosophore is a group capable of forming an explosive compound on introduction into a hydrocarbon and are divided into two classes, i.e., “primary” and “secondary”. Primary plosophores include nitrate esters, aromatic and aliphatic nitro groups and the nitramine group. The secondary plosophores comprise groups, such as azo, azide, nitroso, peroxide, ozonide, perchlorate and nitrate, etc. Groups that do not themselves produce explosive properties, but may influence them, are called auxoplosive. The hydroxyl, carboxyl, chlorine, sulfur, ether, oxygen, amine, etc., are the examples of such groups.

Section snippets

Evaluation of structure–sensitivity relationship of energetic materials

Energetic materials are mostly employed in military, space, civil and mining. Both experimental and theoretical methods are available to evaluate the energy released and related parameters of energetic materials. Much information concerning any new energetic compound can be obtained for acceptance as a standard material and also to establish a structure–sensitivity relationship. The following are some of the important parameters (i–x) helpful to evaluate the energetic materials and give

Thermolysis of salts of nitric acid

The nitrates (salts of nitric acid) demonstrate explosive properties and can act as readily available oxygen carriers. The chemistry and thermolysis of some of the nitrate salts are described below.

Thermolysis of salts of perchloric acid

All the perchlorates (salts of perchloric acid) find technological application in explosives, pyrotechnics, and propellants. Most of the perchlorates are in the form of ammonium salt, which serve as an ideal solid oxidiser than any other commercially available compounds. Some of the important perchlorates are described below.

Conclusion

The thermal decomposition of energetic compounds is a very complex process even in a simple case expressed by the stoichiometric equation:A(s)→B(s)+C(g).This process takes place in several stages, e.g., the chemical act of breaking of bonds; destruction of initial crystal lattice; formation of crystal lattice of the solid product (B), consisting of the formation of crystallisation centres and the growth of these centres; adsorption/desorption of gaseous products C; diffusion of C and heat

Acknowledgements

The financial support by DST and CSIR to (IPSK) is thankfully acknowledged. Thanks are also due to Head, Chemistry Department, for laboratory and library facilities.

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