 | Philip Withers |
3D and 4D X-ray imaging of the behaviour of porous systems
X-ray imaging can provide detailed structural information in 3D non destructively across scales ranging from tens of centimetre samples to tens of nanometres spatial resolution over timescales ranging from milliseconds to many months. This, and the fact that 3D image sequences can be collected non destructively, mean that it can uniquely shine a light on a range of porous materials behaviours from transport phenomena and permeability to fuel cells, from granular flow to cementitious materials, and from our perception of foods to the collapse of energy absorbing structures.
I will start with a primer on 3D and timelapse (4D) imaging for those new to the technique looking at the basic principles, the attributes and limitations of the method and its complementarity to other characterisation methods such as mercury intrusion porosimetry.
I will then examine a number of applications covering a very wide range of length and timescales and applications. In particular I will consider transport behaviour through homogeneous and inhomogeneous media, particle transport through filter cakes, the infiltration of fibrous preforms in polymer and ceramic matrix composite manufacturing, the behaviour of granular solids, the microstructure of 3D printed concrete and the long term carbonation behaviour of low carbon cements. Through these examples I will look at the practical limitations of the method, image quantification and segmentation aspects and also cover image-based modelling and digital volume correlation. I will then conclude by looking at future developments.
Interview with Philip Withers
- What advances in imaging have most impacted our understanding of porous materials?
Of course I am biased because I am involved in collecting X-ray CT imaging data. I have found that actually being able to ‘see’ the pores in fine detail and in some cases the flow of fluids through them, the build up of particles moving that move through them or the crystallisation of materials within them is fascinating and is helping us to better understand and model the behaviour of porous systems. Furthermore, timescales can range from fractions of a second to many months.
- How do you see the role of 3D and 4D imaging evolving in the next decade?
We have seen a sharp increase in the spatial and time resolution achievable by 3D X-ray imaging methods over the last 10 years and I see no reason for this trend to plateau any time soon. Nevertheless we are currently limited to observing small (mm) volumes at micron resolutions. I think this limitation will gradually loosen increasing representativeness and the range of materials problems we can examine.
- What are the challenges in linking imaging data to performance and failure in materials?
As I mentioned we can often study small regions in great detail or large regions at low resolution. Understanding materials performance and failure often requires a wider view but the mechanisms need the microscopic view thereby presenting a challenge.
- How do you bridge the gap between high-resolution data and practical applications?
In part this can be tackled through multiscale imaging and a mixture between real time imaging at lower resolution and higher resolution destructive imaging or chemical analysis post mortem. Another important aspect is imaging both microstructurally faithful (often called image based) models and continuum modelling or representative volume element modelling that can be used to infer the overarching behaviour.
- What do you hope to learn from the broader InterPore community?
I never cease to be amazed by the variety of applications and the spread or problems that come down to needing to understand the behaviours of porous materials from biomaterials to carbon sequestration, from batteries to beer. I am really looking forwards t become acquainted with new challenges and trying to see whether X-ray imaging can shine a light on such behaviours.
About Philip Withers
Philip Withers is the first Regius Professor of Materials at the University of Manchester and a fellow of various prestigious societies in the UK and internationally. He has degrees from the University of Cambridge. He was heavily involved in the conception of the Henry Royce Institute for Advanced Materials in 2016 becoming its first Chief Scientist. It brings together the universities of Manchester, Leeds, Sheffield, Oxford, Cambridge, Cranfield, Strathclyde, Imperial College, NNL and UKAEA for the accelerated design of new materials and to better understand existing ones.
He pioneered the use of X-ray CT and electron microscopy for correlative multiscale characterisation to follow the behaviour of engineering materials in 3D over time (4D). In 2008 he set up the Henry Moseley X-ray Imaging Facility, one of the most extensive suites of X-ray Imaging facilities in the world. In 2014, the Facility was awarded the Queen’s Anniversary Prize. It is now part of the UK National Facility for Lab. X-ray CT (NXCT). He has exploited X-ray imaging to characterise the static and dynamic behaviour of a range of porous materials, from biomaterials to petrology and from solid oxide fuel cells to bread.
