Edinburgh Research Explorer

Prof Colin Pulham

Personal Chair in High-Pressure

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Willingness to take PhD students: Yes

Continuous crystallisation of energetic materials
(as part of DTC associated with EPSRC Centre for Innovative Manufacturing in Continuous Manufacturing and Crystallisation).
This project will explore how the concept of continuous crystallisation can be applied to energetic materials, i.e. explosives and propellants. Challenges within the field of energetic materials include the reproducible preparation of polycrystalline material with close control of polymorph, particle size, crystal morphology, and levels and types of crystal defect. Each of these properties affects the performance of the energetic material, e.g. burning rate, sensitivity to shock, impact, electrostatic discharge.

Education/Academic qualification

Doctor of Philosophy (PhD), University of Oxford
Bachelor of Arts, University of Oxford

Current Research Interests

Research is focused on the study of the effects of pressure on molecular compounds such as pharmaceuticals, energetic materials (explosives, propellants), fuels, and lubricants in order to identify structural changes when these materials are compressed.  A parallel strand of research involves co-crystallisation of energetic materials with other compounds in order to produce safer compositions that are less sensitive to accidental initiation.  An ongoing industrial collaboration is the development of a compact thermal store that will replace domestic boilers, hot water tanks and air conditioning units.  This research exploits phase-change materials, which absorb heat on dissolution or melting and release heat on crystallisation or freezing.   

Administrative Roles

Director of Teaching in the School of Chemistry.

Deputy Head of School

Associate Director (Strategy and Outreach) in the Centre for Science at Extreme Conditions

STFC Advisory Panel for Public Engagement

My research in a nutshell

The responses of pharmaceutical compounds and energetic materials (explosives, propellants, pyrotechnics, and gas generators) to high pressure are of great interest. This is especially true for explosives, which experience extremes of both pressure and temperature under detonation and deflagration conditions. Within the pharmaceutical industry the phenomenon of polymorphism in the crystallisation of compounds is also of crucial importance since two polymorphs of the same drug compound may have different physical properties, e.g. solubilities, melting points, colour, and may have dramatically different properties that affect processibility. The conditions under which polymorphs interconvert is also of crucial importance, particularly when drugs undergo processes such as milling, grinding, and tabletting. Drug regulatory authorities are increasingly demanding more and more information about drug products before granting licenses for distribution. Intellectual property can also become an issue for the pharmaceutical companies who develop and market new drug products, where challenges to patents have been made on the basis of the discovery of a new polymorph.

The aim of our research programme into pharmaceutical compounds is to use pressure as a systematic method that allows for more rapid identification and characterisation of polymorphs and solvates. This is of great benefit to the pharmaceutical industry and enhances our understanding of the factors that are responsible for the packing arrangements of drug molecules in the solid state. On occasions it is possible to recover new, high-pressure forms back to ambient pressure – this recovered material can then be used to seed solutions at ambient pressure (e.g. in a continuous flow crystalliser), allowing the production of bulk amounts of the new form. 

A parallel research programme is studying the effects of pressure on selected energetic materials, e.g. explosives such as RDX and HMX, and propellants such as ammonium perchlorate, in order to identify structural changes when these materials are compressed. This information is crucial for the modelling of the performance and properties of these materials, and for the design of energetic materials that are less sensitive to accidental detonation.  Again, there are opportunities for the discovery of new forms of these materials that may have enhanced properties, e.g. reduced sensitivity to initiation or higher density.   Another strategy that is being employed is the co-crystallisation of energetic materials with other compounds in order to produce less sensitive compositions. A key aspect of this work is the correlation of crystal structure with properties such as sensitivity and performance – with a particular focus on the influence of intermolecular interactions on the transfer of energy and hence sensitivity to shock and impact. 

An ongoing industrial collaboration is the development of a compact thermal store which will replace domestic boilers, hot water tanks and air conditioning units.  A key technology component of the store is the use of Phase Change Materials (PCMs).  Such chemical compounds can include inorganic salts, (e.g. sodium sulfate and its hydrates) or organic materials (e.g. beeswax) that absorb heat and undergo a phase transition, e.g. dissolution or melting.  On cooling, the reverse phase transition occurs, e.g. crystallisation or freezing, and heat is  released. Whilst PCMs have an acceptable level of energy density to support development of a compact heat store, they traditionally suffer from poor power density and degradation in performance over time.  The project involves the evaluation of the performance characteristics of existing materials including accelerated lifetime testing and the investigation of nucleation and crystal growth processes associated with PCMs

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