Dissertation: X-rays reveal the secrets of materials to support industry and nuclear waste safety (Yliharju)
Doctoral Researcher Janne Yliharju studied whether three-dimensional dual-energy X-ray imaging can be used to monitor water movement in bentonite clay. In addition, Yliharju evaluated the performance of a previously developed X-ray-based method for measuring water content at temperatures above room temperature. He also investigated the durability of filters developed at the Department of Chemistry of the University of Jyväskylä.
New information on the moisture behavior of materials
Dual-energy X-ray imaging proved capable of producing material-specific information on changes in the mass distributions of water and bentonite, providing added value compared to conventional X-ray imaging.
- Furthermore, the previously developed X-ray-based method for measuring water content produced reliable observations also at elevated temperatures, which helps in understanding the properties of bentonite. This improves our understanding of how bentonite behaves under conditions where temperatures vary, for example in the final disposal of nuclear waste, explains Doctoral Researcher Janne Yliharju from the University of Jyväskylä.
The results provide support for critical decisions in society
Bentonite is a key material in the final disposal of nuclear waste, where bentonite is used to isolate the waste from the environment. The doctoral dissertation provides information on the behaviour of bentonite as moisture and temperature change.
- The results can be utilised in assessing the long-term safety of disposal, either through modelling or direct experimental observations, says Yliharju.
The filters, developed at the Department of Chemistry, were found to be structurally durable, supporting their suitability for industrial applications where a short-lived prototype is not sufficient. The application of the filters is the recovery of critical raw materials, for example from industrial wastewater.
- This is an example of how X-ray imaging can support solutions to today’s critical challenges, such as resource sufficiency, says Yliharju.
Dual-energy X-ray imaging has great potential
Although dual-energy X-ray imaging can in principle be applied to almost any material and situation, its accuracy is affected by many practical factors. This study improves the understanding of the performance of this method through a concrete example.
- Monitoring water content, as well as deformations and density changes of dry matter, is important in industry. The properties of many materials—such as bentonite and wood-based products—depend strongly on their moisture content. Understanding these dependencies is important when designing systems in which their moisture content may vary, specifies Yliharju.
The dissertation was carried out in the research Group of the Multiscale Materials Characterization from the Department of Physics at the University of Jyväskylä, where researchers examine the structure of a wide range of materials across different length scales with a particular focus on X‑ray and neutron-based techniques.
M.Sc. Janne Yliharju defends their doctoral dissertation "4D X-ray Tomographic Methods for Industrial Applications - Water Transport in Bentonite and Characterisation of 3D-printed Filters” on Friday 17.4.2026 at 12:00 in auditorium YAA303 at Ylistönrinne. Opponent is Professor Florian Fusseis (RWTH Aachen University) and Custos is Associate Professor Paavo Penttilä (University of Jyväskylä). The language of the event is English.
The dissertation is available online: https://jyx.jyu.fi/jyx/Record/jyx_123456789_109585?sid=264857196
