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The influence of crystal defects on the initiation of crystalline nitramine explosives PhD


Project Description

It is well understood that internal defects within crystalline explosives can promote the formation of ‘hot-spots’ under shock loading, thereby sensitising them to impact. Conversely, defect-free crystalline explosives are much less sensitive to initiation. The threshold quantity of different types of defect, and their influence on initiation is much less well understood. This PhD opportunity will investigate non-destructive analysis to characterise crystalline defect, and relate these to initiation by explosively-generated shock waves.

It is generally understood that internal defects within crystalline explosives can promote the formation of ‘hot-spots’ under shock initiation, and that this is a mechanism for sensitisation to impact. Prior studies have often focused on the preparation of compositions that contain nitramines such as RDX, in which the microstructure of the explosive content is varied by different methods of recrystallisation. However, these studies have mostly used powdered RDX within an inert binder composition, and the particle-composite mesostructure of such materials can also provide several different hot-spot impact-sensitisation mechanisms.

This project proposes to attempt to study the influence of defects in large single crystals, thus removing the influence of the particle-composite nature of previous studies. There are envisaged three aspects to the work:

a) The growth of large HMX crystals with microstructural defects, with focus on generating these defects reproducibly. Another group in the Centre for Defence Chemistry has ongoing research interest in this type of work, and there is scope for collaboration by the student with that group;

b) The non-destructive examination and characterisation of the induced defects, either in-house or in collaboration with the Diamond Light Source;

c) The experimental measurement of shock initiation in the resulting specimens, and comparison with literature studies of pure HMX crystals.

It is suggested that an explosively-generated shock would be required, to produce the high pressures (~10 GPa) required to initiate this type of target and is beyond the capability of the single-stage gun at Shrivenham. The experimental method (requiring development) would be of the gap test type, with particular attention paid to the control of the curvature of the wave emanating from the attenuator.

Funding Notes

Sponsored by AWE, EPSRC and Cranfield University, this studentship will provide a bursary of up to £17,000 (tax free) plus fees* for 4 years.

NOTE: If a student is in receipt of government funding for their degree course the advert must state that they will not eligible to apply for a Postgraduate Doctoral Loan.

Applicants should have a first or second class UK honours degree or equivalent in a related discipline. This project would suit an applicant with a strong physics or materials science background.

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