6.1 General Conclusions
183
and HNB changes between the overtone and two-layered approach, as shown in
Fig. 6.1. Noting that TATP is experimentally more sensitive than HNB [6, 7] it can
be suggested that the two-layered approach is more successful. The two-layered
approach also performs better for the ordering of β-HMX with respect to the FOX-7
systems. ABT is consistently predicted to be less sensitive than HNB. However, the
nature of the experimentally reported sensitivity for ABT [8] is not known and may
therefore represent the limiting impact energy. In this case, the ordering of ABT
would not be anomalous.
In summary, the work in this thesis has demonstrated that a vibrational up-pumping
model, based solely on ab initio input, can predict the relative sensitivity of EMs
across a range of materials and explosophores. Within the direct vibrational uppumping model (based on a target frequency) used for the azide materials, a combination of both literature models was required to obtain a successful prediction of
impact sensitivity, hence unifying the literature discrepancy. Description of the more
complex organic EMs required development of a variety of new models within the
framework of an indirect up-pumping mechanism. Of these models, the newly developed temperature-dependent two-layered approach appears to be the most successful.
This model comprises aspects of both up-pumping models previously described in
the literature and successfully unifies them into a highly successful approach. This
two layered model proved capable of successfully ordering the impact sensitivity of
a range of materials, as well as of polymorphic systems.
6.2 Future Directions
The individual challenges associated with further development of the up-pumping
model presented in this thesis are presented in each chapter. In these closing remarks,
it is instead worth considering some of the ‘real-world’ applications and new research
directions to which this thesis may lead.
There is currently considerable effort being devoted to the development of new
EMs. While the aim is always to develop EMs with enhanced performance, it is no
longer sufficient to consider performance in isolation. New constraints are now in
place, with particular emphasis on the development of insensitive munitions (IMs).
The development of IMs, however, is particularly challenging as there remains no
fundamental insight into what physical or chemical parameters define sensitivity.
Thus, current methods in EM research require (often lengthy) synthesis of new EMs
and experimental testing of their sensitivity properties. However, without a priori
insight into the physical properties of a new EM, its synthesis is not only a financial
risk, but is accompanied by potentially serious risks to health and safety.
Modern quantum chemical methods are able to correctly predict molecular and
crystalline structure, vibrational and thermodynamic properties, interaction energies,
amongst a plethora of other properties. Typically, these calculations run over the
period of days to weeks, can be run in parallel, and are comparatively cheap as
an alternative to experiment. Thus, if a method were known that was capable of
183
and HNB changes between the overtone and two-layered approach, as shown in
Fig. 6.1. Noting that TATP is experimentally more sensitive than HNB [6, 7] it can
be suggested that the two-layered approach is more successful. The two-layered
approach also performs better for the ordering of β-HMX with respect to the FOX-7
systems. ABT is consistently predicted to be less sensitive than HNB. However, the
nature of the experimentally reported sensitivity for ABT [8] is not known and may
therefore represent the limiting impact energy. In this case, the ordering of ABT
would not be anomalous.
In summary, the work in this thesis has demonstrated that a vibrational up-pumping
model, based solely on ab initio input, can predict the relative sensitivity of EMs
across a range of materials and explosophores. Within the direct vibrational uppumping model (based on a target frequency) used for the azide materials, a combination of both literature models was required to obtain a successful prediction of
impact sensitivity, hence unifying the literature discrepancy. Description of the more
complex organic EMs required development of a variety of new models within the
framework of an indirect up-pumping mechanism. Of these models, the newly developed temperature-dependent two-layered approach appears to be the most successful.
This model comprises aspects of both up-pumping models previously described in
the literature and successfully unifies them into a highly successful approach. This
two layered model proved capable of successfully ordering the impact sensitivity of
a range of materials, as well as of polymorphic systems.
6.2 Future Directions
The individual challenges associated with further development of the up-pumping
model presented in this thesis are presented in each chapter. In these closing remarks,
it is instead worth considering some of the ‘real-world’ applications and new research
directions to which this thesis may lead.
There is currently considerable effort being devoted to the development of new
EMs. While the aim is always to develop EMs with enhanced performance, it is no
longer sufficient to consider performance in isolation. New constraints are now in
place, with particular emphasis on the development of insensitive munitions (IMs).
The development of IMs, however, is particularly challenging as there remains no
fundamental insight into what physical or chemical parameters define sensitivity.
Thus, current methods in EM research require (often lengthy) synthesis of new EMs
and experimental testing of their sensitivity properties. However, without a priori
insight into the physical properties of a new EM, its synthesis is not only a financial
risk, but is accompanied by potentially serious risks to health and safety.
Modern quantum chemical methods are able to correctly predict molecular and
crystalline structure, vibrational and thermodynamic properties, interaction energies,
amongst a plethora of other properties. Typically, these calculations run over the
period of days to weeks, can be run in parallel, and are comparatively cheap as
an alternative to experiment. Thus, if a method were known that was capable of