Extreme Materials @ Extreme Conditions
The Pulham Group
Research Themes
Structure and Properties of Energetic Materials
Our energetic materials research revolves around solving real-world problems present in modern explosives, propellants and pyrotechnics.
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Two main issues with energetic materials are their sensitivity and stability in a range of environment. To deal with the former, several projects are focused on multi-component crystallisation - combining two or more components to yield a new crystalline material with intermediate properties. This work is taken further by using pressure to probe both the mechanisms behind sensitivity, and the behaviour of materials during detonation. In depth crystallographic investigation of these materials attempts to predict the properties of these materials from their structural motifs.
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To tackle the stability aspect, a project is currently focusing on how materials can be altered or doped such that the negative effects of temperature cycling (routinely experienced in modern operations through extreme climates and high-altitude flight) can be mitigated or suppressed.
Hunter et al. (2015) J. Phys. Chem. C.
Hunter et al. (2013) J. Phys. Chem. C.
Molecular Materials Under Extreme Conditions
Polymorphism is a crucial research area in the pharmaceutical and energetics materials industries. Different polymorphs of the same compound may have different physical properties (such as solubilites, melting point, densities, impact sensitivity) which may affect the bioavailability, safety or processibility.
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The effect of pressure on molecular solids is currently of great interest for a variety of fundamental and technological reasons. In many cases, pressure offers a route to accessing novel compounds and polymorphs of important materials. Such pressures can also occur inadvertently in solid processing (e.g. in industry), leading to unwanted physical and chemical transformations. Understanding the effects of pressure therefore has considerable industrial importance. Pressure also allows us to study the fundamental interactions that hold all solid matter together.
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Our research in this area spans the use of high pressure (DAC, Paris-Edinburgh press) and shearDACs to explore a range of extreme conditions, combined with computational and theoretical techniques.
Fabbiani et al. (2004) CrystEngComm
Oswald et al. (2010) CrystEngComm
Energy Storage Materials
Worldwide, the largest proportion of energy consumption is in the form of heat. As this has significant economic and ecological impact, there is a strong driving force to create renewable heat and improved heat storage.
Heat storage research in the Pulham group focuses on exploiting latent heat and chemical heat storage, as this offers much larger energy densities than traditional sensible heat storage.
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Research initially began with phase-change materials (PCMs), using compounds such as salt hydrates (NaOAc.3H2O- commonly found in hand-warmers) which absorb heat upon melting, and then release heat upon freezing. With problems, such as supercooling and incongruency, projects have focused on using additives to stabilise these materials, allowing them to be used on a larger scale by Sunamp Ltd.
More recently thermochemical materials (TCMs) have become of interest, which are suitable for higher temperature or long-term applications. Often with multiple staged decomposition and re-synthesis reactions, these inorganic compounds (often salt hydrates such as MgSO4.7H2O) are more complicated that initially thought.
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The use of variable temperature X-ray powder diffraction studies for both PCMs and TCMs provides invaluable insight as to how these materials work, what phase transitions they undergo, and how to improve them.
Activating phase change material to release heat for technological applications
Lubricants & Fuels Under Extreme Conditions
Our research interests in this topic revolve around understanding the nature of long hydrocarbons under extremes of temperature, pressure and shear. This combines research into fuels and lubricants themselves, as well as a series of model compounds, aiming to understand how these materials function in their numerous applications.
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Diamond-anvil cells and high-pressure piston cylinders are employed in this project to create high-pressure environments. The nature of lubricants and fuels under these conditions are studied using a variety of in situ probes, such as X-ray and neutron diffraction at large national facilities, as well as vibrational spectroscopy. Combined, this information is valuable for optimizing biodiesel and lubricant performance under high-pressure conditions, such as in englines and between gears.
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Piston cylinder for high pressure investigations
Mechanochemistry: Mechanisms & Applications
Many solid state processes (synthesis, polymorphism and co-crystallisation) can be induced solvent free using mechanical energy, e.g. ball milling and Resonant Acoustic Mixing. By conducting transformations in this way, an entirely new area of a system's phase diagram becomes accessible as no solvent is required. This therefore leads to formation of novel products (polymorphs and co-crystals), enhanced yields and greatly enhanced rates of production. The application of mechanochemistry is therefore of considerable interest to both academic and industrial communities.
Our research aims to understand the fundamental processes that drive mechanically-induced transformations. This is important as many such transformations occur without any forewarning and can have catastrophic consequences for industrial processes! Combining variable temperature, pressure, theory and conventional mechanochemical techniques, we aim to offer an understanding and ultimately control over mechanically induced processes.
Michalchuk et al (2017) Adv. Sci
K.S. Hope et al (2015) NTREM
In situ X-ray diffraction, Resonant Acoustic Mixing
Non-Photochemical Laser-Induced Nucleation
The study of the fundamentals of crystal nucleation from liquid is an important topic in physical chemistry. One recent (1996) discovery is the apparent ability of a nanosecond laser pulse to initiate nucleation from supersaturated solution in a chosen time and volume without being absorbed by solution: non-photochemical laser-induced nucleation (NPLIN).
In collabaration with the group of Dr. Andrew J. Alexander we study the applications of NPLIN for tailoring useful properties of crystals and as a method for nucletion induction. From this we hope to discover industrial applications suited to pharmaceutical and fine chemical manufacturing as well as fundamental understanding of crystal formation.
