Abstract
Energetic materials (explosives, propellants and pyrotechnics; EMs) encompass a
broad range of materials. These materials are used across a wide spectrum of
applications, including civil and defence. For example, HMX, RDX and TNT are
well-known EMs with defence applications. Silver fulminate is instead used in
household Christmas crackers, and ammonium nitrate is used for numerous
industrial applications. Common to all EMs is their propensity to rapidly release
energy upon external perturbation. The amount and type of energy that is required
to initiate an EM can vary across orders of magnitude. Some materials (e.g., triacetone triperoxide, TATP) initiate with < 1 J of impact energy, while others (e.g.,
triaminotrinitrobenzene, TATB) cannot be initiated without > 100 J of impact
energy. Understanding which materials can be handled safely is therefore of critical
importance for maintaining the safe use of EMs across all sectors.
Current trends in EM research include a drive to develop new materials with
decreased sensitivities. While it is relatively straightforward to selectively modify
some properties (e.g., environmental impact), very little is understood about what
constitutes a sensitive material. At present, a new EM must be synthesized and its
sensitivity tested. However, with no a priori knowledge of the potential sensitivity
of a novel EM, synthesis is accompanied by substantial hazard, as well as time and
financial costs. It is therefore pressing to develop a fundamental understanding of
what dictates a sensitive material, and hence develop a mechanism to predict these
properties. A particularly promising model to explore impact sensitivity of EMs is
based on vibrational up-pumping, i.e., the up-conversion of vibrational energy. This
thesis explores the application of this model to a set of azide, organic molecular and
polymorphic materials.
Azide-based EMs share the common N
À
3 explosophore. The electronic structure
of this anion was followed as a function of its normal modes of vibration. It was
found that excitation of the bending mode is sufficient to induce a thermal electronic
excitation of the molecule and spontaneous decomposition. This is valid both in the
gas and solid states. It is therefore suggested that this vibrational mode is largely
responsible for decomposition of the azide materials. Based on calculations of the
vii
Energetic materials (explosives, propellants and pyrotechnics; EMs) encompass a
broad range of materials. These materials are used across a wide spectrum of
applications, including civil and defence. For example, HMX, RDX and TNT are
well-known EMs with defence applications. Silver fulminate is instead used in
household Christmas crackers, and ammonium nitrate is used for numerous
industrial applications. Common to all EMs is their propensity to rapidly release
energy upon external perturbation. The amount and type of energy that is required
to initiate an EM can vary across orders of magnitude. Some materials (e.g., triacetone triperoxide, TATP) initiate with < 1 J of impact energy, while others (e.g.,
triaminotrinitrobenzene, TATB) cannot be initiated without > 100 J of impact
energy. Understanding which materials can be handled safely is therefore of critical
importance for maintaining the safe use of EMs across all sectors.
Current trends in EM research include a drive to develop new materials with
decreased sensitivities. While it is relatively straightforward to selectively modify
some properties (e.g., environmental impact), very little is understood about what
constitutes a sensitive material. At present, a new EM must be synthesized and its
sensitivity tested. However, with no a priori knowledge of the potential sensitivity
of a novel EM, synthesis is accompanied by substantial hazard, as well as time and
financial costs. It is therefore pressing to develop a fundamental understanding of
what dictates a sensitive material, and hence develop a mechanism to predict these
properties. A particularly promising model to explore impact sensitivity of EMs is
based on vibrational up-pumping, i.e., the up-conversion of vibrational energy. This
thesis explores the application of this model to a set of azide, organic molecular and
polymorphic materials.
Azide-based EMs share the common N
À
3 explosophore. The electronic structure
of this anion was followed as a function of its normal modes of vibration. It was
found that excitation of the bending mode is sufficient to induce a thermal electronic
excitation of the molecule and spontaneous decomposition. This is valid both in the
gas and solid states. It is therefore suggested that this vibrational mode is largely
responsible for decomposition of the azide materials. Based on calculations of the
vii