High-resolution X-ray computed tomography (μCT) is nowadays an established technique for material characterization. However, the technique only yields morphological information, and the composition of the object can only be retrieved based on an educated guess. On the other hand, three-dimensional highresolution X-ray fluorescence spectroscopy (μXRF) is an analytical technique that yields the chemical composition of a sample. In the past, several efforts have been made to combine both methods. Typically, they apply both techniques at different setups, and register the results [1,2]. One notable system developed earlier combines micro-CT and full-field XRF in one apparatus [3].

Dietary partitioning often accompanies the increased morphological diversity seen during adaptive radiations within aquatic systems. While such niche partitioning would be expected in older radiations, it is unclear how significant morphological divergence occurs within a shorter time period. Here we show how differential growth in key elements of the feeding mechanism can bring about pronounced functional differences among closely related species. An incredibly young adaptive radiation of three Cyprinodon species residing within hypersaline lakes in San Salvador Island, Bahamas, has recently been described. Characterized by distinct head shapes, gut content analyses revealed three discrete feeding modes in these species: basal detritivory as well as derived durophagy and lepidophagy (scale-feeding). We dissected, cleared and stained, and micro-CT scanned species to assess functionally relevant differences in craniofacial musculoskeletal elements. The widespread feeding mode previously described for cyprinodontiforms, in which the force of the bite may be secondary to the requisite dexterity needed to pick at food items, is modified within both the scale specialist and the durophagous species. While the scale specialist has greatly emphasized maxillary retraction, using it to overcome the poor mechanical advantage associated with scale-eating, the durophage has instead stabilized the maxilla. In all species the bulk of the adductor musculature is composed of AM A1. However, the combined masses of both adductor mandibulae (AM) A1 and A3 in the scale specialist were five times that of the other species, showing the importance of growth in functional divergence. The scale specialist combines plesiomorphic jaw mechanisms with both a hypertrophied AM A1 and a slightly modified maxillary anatomy (with substantial functional implications) to generate a bite that is both strong and allows a wide range of motion in the upper jaw, two attributes that normally tradeoff mechanically. Thus, a significant feeding innovation (scale-eating, rarely seen in fishes) may evolve based largely on allometric changes in ancestral structures. Alternatively, the durophage shows reduced growth with foreshortened jaws that are stabilized by an immobile maxilla. Overall, scale specialists showed the most divergent morphology, suggesting that selection for scale-biting might be stronger or act on a greater number of traits than selection for either detritivory or durophagy. The scale specialist has colonized an adaptive peak that few lineages have climbed. Thus, heterochronic changes in growth can quickly produce functionally relevant change among closely related species.

In the waste recycling industry, material separation is of key importance. In this paper, we present a new material identification method, based on dual-energy X-ray radiographic images, developed in the context of waste recycling industry. The algorithm is based on a dual energy technique and allows to estimate the effective atomic number of the sample under investigation. A projection simulator with high accuracy that allows to simulate realistic measurements of a wide range of materials is used. The resulting virtual measurements are then used in an identification tool, which achieves the identification by comparing the virtual and actual measurements. Via this procedure, an extensive range of materials and thicknesses can be analyzed and identified. Finally, an optimization scheme has been developed, which allows the selection of an ideal setting for the scanner, in order to optimize the identification process.

A novel 3D elemental and morphological analysis approach is presented combining X-ray computed tomography (μCT), X-ray fluorescence (XRF) tomography, and confocal XRF analysis in a single laboratory instrument (Herakles). Each end station of Herakles (μCT, XRF-CT, and confocal XRF) represents the state-of-the-art of currently available laboratory techniques. The integration of these techniques enables linking the (quantitative) spatial distribution of chemical elements within the investigated materials to their three-dimensional (3D) internal morphology/structure down to 1-10 μm resolution level, which has not been achieved so-far using laboratory X-ray techniques. The concept of Herakles relies strongly on its high precision (around 100 nm) air-bearing motor system that connects the different end-stations, allowing combined measurements based on the above X-ray techniques while retaining the coordinate system. In-house developed control and analysis software further ensures a smooth integration of the techniques. Case studies on a Cu test pattern, a Daphnia magna model organism and a perlite biocatalyst support material demonstrate the attainable resolution, elemental sensitivity of the instrument, and the strength of combining these three complementary methodologies.

Matthieu N. Boone, Brecht Laforce, Bert Masschaele, David Schaubroeck, Manuel Dierick, Veerle Cnudde, Bart Vekemans, Luc Van Hoorebeke & Laszlo Vincze UGCT – Radiation Physics, Dept. Physics and Astronomy, Ghent University, Belgium X-Ray Microspectroscopy & imaging – Dept. Analytical Chemistry, Ghent University, Belgium XRE bvba; Technologiepark 5; 9052 Zwijnaarde Center for Microsystems Technology (CMST), imec and Ghent University, Technologiepark 15, 9052 Ghent, Belgium UGCT – PProGRess, Dept. Geology, Ghent University, Belgium

Over the past decade, laboratory based X-ray computed micro-tomography (micro-CT) has given unique insights in the internal structure of complex reservoir rocks, improving the understanding of pore scale processes and providing crucial information for pore scale modelling. Especially in-situ imaging using X-ray optimized Hassler type cells has enabled the direct visualization of fluid distributions at the pore scale under reservoir conditions. While sub-micrometre spatial resolutions are achievable in lab-based micro- CT, the temporal resolutions are still limited to minutes or hours. This time restriction is often a bottleneck for imaging dynamic in-situ processes, thus limiting the applicability to relatively slow pore scale processes occurring in the order of hours to days, or to end points in drainage-imbibition cycles. To overcome this issue, X-ray Engineering (XRE) and Ghent University’s Centre for X- ray Tomography (UGCT) have jointly developed a gantry-based micro-CT system. This system’s X-ray tube and detector rotate continuously in a horizontal plane around the fixed sample. The setup still allows to tune the geometrical magnification, with spatial resolutions down to 5 µm. This fixed sample setup is also ideal for in-situ imaging, as the flow cells can be directly connected to high pressure flow tubing and sensor lines, without the need to allow rotational movement relative to the X-ray source and detector. An efficient hardware design with a fast flat panel detector, combined with custom X-ray transparent flow cells to increase X-ray flux and dedicated 4D software tools in acquisition, reconstruction and analysis, allows to reach temporal resolutions in the order of seconds. The possibilities of this new approach in dynamic in-situ imaging are illustrated with flow tests on a carbonate sample. We discuss the challenges in dynamic imaging and present methods to improve X-ray flux and optimize image quality by means of this experiment. Furthermore, we show that the integration of fast imaging experiments with other information from peripheral sensors or from imaging data at different resolutions can help to link behaviour at the pore scale to the effective properties at the core scale, but also facilitates the experimental workflow.

Over the past decade, the wide-spread implementation of laboratory-based X-ray micro-computed tomography (micro-CT) scanners has revolutionized both the experimental and numerical research on pore-scale transport in geological materials. The availability of these scanners has opened up the possibility to image a rock's pore space in 3D almost routinely to many researchers. While challenges do persist in this field, we treat the next frontier in laboratory-based micro-CT scanning: in-situ, time-resolved imaging of dynamic processes. Extremely fast (even sub-second) micro-CT imaging has become possible at synchrotron facilities over the last few years, however, the restricted accessibility of synchrotrons limits the amount of experiments which can be performed. The much smaller X-ray flux in laboratory-based systems bounds the time resolution which can be attained at these facilities. Nevertheless, progress is being made to improve the quality of measurements performed on the sub-minute time scale. We illustrate this by presenting cutting-edge pore scale experiments visualizing two-phase flow and solute transport in real-time with a lab-based environmental micro-CT set-up. To outline the current state of this young field and its relevance to pore-scale transport research, we critically examine its current bottlenecks and their possible solutions, both on the hardware and the software level. Further developments in laboratory-based, time-resolved imaging could prove greatly beneficial to our understanding of transport behavior in geological materials and to the improvement of pore-scale modeling by providing valuable validation. (C) 2015 Elsevier Ltd. All rights reserved.

A temperature controlled sample stage, which can both heat up, and cool down a sample while it is subjected to a μCT scan has been developed. The stage was designed to reach temperatures up to 50°C and down to −20°C and has been used in several applications with a varying degree of dynamism, going from immobilizing samples by freezing them to studying fully dynamically evolving temperature dependent processes.

X-ray CT scanning is an invaluable technique in many research domains. Different commercial scanner types are developed, tailored to different needs, yet the Centre for X-ray Tomography of the Ghent University (UGCT) develops its own in-house open modular scanners with significant experimental freedom, both for applied research in various fields as for research on tomography itself. The maturity of the technique opens up possibilities in cultural heritage, more specifically the field of wooden musical instruments. Here, we present the possibilities and opportunities of two particular scanners at UGCT: Nanowood and HECTOR. Instruments of different size and shape can be scanned either entirely either one can focus on a specific region of the instrument, resulting in qualitative and quantitative mapping of a range of features at different spatial scales. A cello, acoustic guitar, violin and bow, pipa and standard recorder are scanned using different acquisition modes, and qualitative and quantitative assessment of different features such as general structure assessment, glue line integrity, thickness distribution mapping, volume calculations, growth ring analysis are illustrated. These examples demonstrate the flexible and powerful use of lab-based CT scanners for nondestructive research of wooden musical instruments.

In this work, we present a novel laboratory-based microcomputed tomography (micro-CT) experiment designed to investigate the pore-scale drainage behavior of natural sandstone under dynamic conditions. The fluid distribution in a Bentheimer sandstone was visualized every 4 s with a 12 s measurement time, allowing the investigation of single-pore and few-pore-filling events. To our knowledge, this is the first time that such measurements were performed outside of synchrotron facilities, illustrating the growing application potential of laboratory-based micro-CT with subminute temporal resolutions for geological research at the pore scale. To illustrate how the workflow can lead to an improved understanding of drainage behavior, the experiment was analyzed using a decomposition of the pore space into individual geometrical pores. Preliminary results from this analysis suggest that the distribution of drainage event sizes follows a power law scaling, as expected from percolation theory.

The study of transport and degradation processes in porous geo-materials bears importance to a variety of real-world problems, both in underground as above ground. To fully comprehend the impact these processes have on large geological entities, it is crucial to understand what happens on the pore scale level, for example to use this understanding as input to larger scale models. Over the past decade, the availability of high quality laboratory-based X-ray micro-computed tomography (micro-CT) scanners has enabled many researchers to image and analyze a geo-material’s pore space in 3D. However, a number of important challenges in both the acquisition and the analysis of 3D pore space information persists. On the one hand, specialized imaging, analysis and modeling techniques are needed to deal with the multi-scale aspect of many geo-materials. On the other hand, understanding the dynamics of pore-scale processes requires in-situ, time-resolved imaging. We will present the progress on these two key issues at Ghent University’s Centre for X-Ray Tomography (UGCT). As an approach to tackle the multi-scale problem, we will show results from new complementary high-resolution imaging techniques (e.g. ptychographic tomography). With regard to the challenge of time-resolved imaging, we will demonstrate our advances in (fast) in-situ, lab-based micro-CT imaging of transport and degradation processes in porous geo-materials (e.g. two-phase flow, salt crystallization, reactive flow).

Recent studies have provided insight in the dynamics of pore-scale events during two-phase flow in porous media [1,2]. Specifically, during drainage, discrete filling events (so-called Haines jumps) have been shown to possess complex transient dynamics, with high local flow velocities (up to 1m/s). Furthermore, a Haines jump turns out to be a non-local process, as such a jump can have a zone of influence which extends over multiple pores. However, the importance of these transient dynamics to the resulting properties on a larger, representative scale in real three-dimensional pore spaces is still unclear. In this work, we investigate this by visualizing the evolution of the fluid distribution during drainage in a Bentheimer sandstone, without having to stop the flow between every two scans, and comparing the experimental data to a static model description of the filling sequence. Over the last few years, it has become possible to monitor the pore-scale distribution of fluid phases during multi-phase flow over time by performing 4D X-ray micro-computed tomography (micro-CT) experiments [3,4]. The time resolution of these experiments is important, as short acquisition times allow to study the fluid distribution before and after single (or few) filling events without interrupting the flow. At synchrotron beam lines, (sub-)second time resolutions are attainable, but the scarcity of synchrotron beam time limits the amount of such experiments. Laboratory-based micro-CT systems are much cheaper and therefore widely available, but most systems have a much lower time resolution, on the order of tens of minutes. Nonetheless, new developments in laboratory-based micro-CT hardware and software are opening the door to time resolutions on the order of seconds. In this work, we present experiments in which two-phase (oil-water) flow in Bentheimer sandstone is visualized using a laboratory-based micro-CT set-up at Ghent University’s Centre for X-ray Tomography. The acquisition time for a complete 360 degree scan is 12 seconds, but continuous scanning allows us to further increase time resolutions. We are therefore able to capture the evolution of the pore-scale distribution of oil during drainage, without interrupting the oil flow in between scans. We capture information on single pore-filling cascades, which we compare to a quasi-static invasion-percolation description of the filling sequence. Even though time resolutions are still insufficient to capture the transient dynamics, the experiments allow us to assess their influence on the resulting fluid configuration in the pore space. It is this configuration which largely determines the macroscopic petrophysical properties of the rock in question (e.g. relative permeability, capillary pressure curve, hysteresis properties, etc.).

Freeze-thaw cycling stresses many environments which include porous media such as soil, rock and concrete. Climate change can expose new regions and subject others to a changing freeze-thaw frequency. Therefore, understanding and predicting the effect of freeze-thaw cycles is important in environmental science, the built environment and cultural heritage preservation. In this paper, we explore the possibilities of state-of-the-art micro-CT in studying the pore scale dynamics related to freezing and thawing. The experiments show the development of a fracture network in a porous limestone when cooling to -9.7 °C, at which an exothermal temperature peak is a proxy for ice crystallization. The dynamics of the fracture network are visualized with a time frame of 80 s. Theoretical assumptions predict that crystallization in these experiments occurs in pores of 6-20.1 nm under transient conditions. Here, the crystallization-induced stress exceeds rock strength when the local crystal fraction in the pores is 4.3%. The location of fractures is strongly related to preferential water uptake paths and rock texture, which are visually identified. Laboratory, continuous X-ray micro-CT scanning opens new perspectives for the pore-scale study of ice crystallization in porous media as well as for environmental processes related to freeze-thaw fracturing.

We report on a radically new instrument integrating three different X-ray based microanalysis methodologies, being absorption computed tomography (absCT), XRF tomography (XRF-CT) and confocal XRF analysis (cXRF). Each of these techniques yields complementary three dimensional information in a basically non-destructive way. The combination of these three methodologies in the same instrument enables the user to acquire both morphological and elemental 3D information on the micro-scale with a single experimental run. The experimental sequence starts with an absCT scan, providing a visualization of the internal structures of the sample with a resolution of approximately 1 micron. The reconstructed CT images are then used as a means to select the regions of interest for detailed elemental analysis using either the XRF-CT or cXRF stage. Due to the ultra-accurate motor movements, the sample can be positioned in front of the XRF source with micrometer precision, enabling analysis of even the smallest heterogeneities discovered in the sample during the absCT measurement. Furthermore, the complementary information gathered with these techniques opens a wide range of new possibilities for integrated data analysis. Data demonstrating the precision and scientific value of the new experimental procedure are represented, including measurements on both test samples and “real life” samples.

This study presents an experimental X-ray micro-CT study of the freeze-thaw processes in limestone under controlled ambient conditions. The processes weres studied with time-lapse micro-CT and dynamic micro-CT, using the Environmental X-ray CT (EMCT) at the Centre for X-ray Tomography of the Ghent University (www.ugct.ugent.be). The EMCT is a gantry-based system on which full μCT scans were aquired in approximately 80 s. A custom made freezing cell was used for freezing experiments to -15 °C with 9 mm diameter samples. The experimental data show that the observed decay is strongly related to the local water saturation and to the rock texture, i.e. pore size distribution. The decay is expressed by the fracture development in limestone due to ice crystallization. These fractures show a dynamic response to the imposed freeze-thaw cycles. Ice wedging occurs upon the moment of ice crystallization, which is indicated by the release of latent heat. During subsequent thawing, the fractures close. The timing indicates that ice crystallization alone is sufficient to instigate fracturing. Assumptions based on the ice crystallization theory allow to calculate the theoretical pore sizes where ice crystallization occurred. This shows that in these experiments, water crystallizes in the nanometric pores, thus under transient conditions. The existence of such pores were validated with other techniques such as SEM and were linked to the rock features observed with CT. Introduction Freeze-thaw processes play an important role in the physical weathering of porous rocks in cold and humid environments (e.g. Ruedrich and Siegesmund, 2007; Matsuoka and Murton, 2008). In the built environment, freeze-thaw deterioration threatens the aesthetic properties of monuments and artwork in our cultural heritage and it can cause actual danger by affecting the structural integrety of building materials. Therefore, it is important to assess the susceptibility of building stones to prolonged freezing and freeze-thaw cycling. This is typically done by normalised freeze-thaw testing. Nevertheless, the extrapolation from laboratory tests to natural conditions is not always easy (Ingham, 2005), and therefore the historical performance is an important criterium as well as are field measurements of freeze-thaw processes (Hall, 2006; Thomachot et al., 2005; McAllister et al., 2013). To improve the interpretation of macro-scale laboratory experiments, it is important to study the processes involved on the micro-scale (Hall and André, 2003). X-ray CT lends itself as good tool to study the micro-scale effects of freeze-thaw processes. Hence, since the development of laboratory micro-CT, different studies of freeze-thaw processes have been done using micro-CT (Ruiz de Argandona et al, 1999; Dewanckele et al., 2013). As these studies focus on the resulting micro-structural effect of freezethaw decay on rocks, we focus on the real-time processes of freezing and thawing in porous, sedimentary rocks. Therefore, we perform dynamic imaging of samples under ambient freeze-thaw cycling, with a gantry-based X-ray CT system capable of acquiring full micro-CT scans in the time order of a minute. The cause for freeze-thaw decay is the stress induced by the crystallization of ice within the pore network (Scherer, 1999; Steiger, 2005), where the freezing point is depressed for capillary water according to the Kelvin equation (e.g. Ruedrich et al., 2011). The main precondition for freeze-thaw decay is that the macroscopic stress induced by ice crystallization pressure exceeds rock strength, fixed by a strengthcontrolling flaw. Hence whether or not building stones will experience freeze-thaw decay depends on their intrinsic properties and the environmental conditions to which they are subjected. In these experiments, we focus on the spatial pore size distribution of the samples, local water saturation and freezing temperature. Methods X-ray micro-CT was performed at the Centre for X-ray Tomography of the Ghent University (UGCT; www.ugct.ugent.be; Masschaele et al., 2007) using two custom-built laboratory micro-CT scanners: HECTOR (Masschaele et al., 2013) and EMCT (Dierick et al., 2014). HECTOR was used to obtain high resolution (< 10 μm) images of reference samples or subsamples from laboratory freeze-thaw experiments. Dynamic X-ray micro-CT experiments were performed with EMCT, using cylindrical samples of 9 mm diameter. The samples were water-saturated by atmospheric imbibition for 24h. Subsequently, they were subjected to ambient freeze-thaw cyling from 20°C -15 °C using a custom made freezing stage (De Schryver et al., 2015). The sampled were scanned in the middle of each freezing and thawing phase. Moreover, continuous scanning was performed for 24 minutes during the cooling phase, resulting in 14400 projections of 100 ms exposure time over 18 full-360° rotations. The X-ray tube was operated at a tube voltage of 65 kV and a power of 14.3W. The reconstructed voxel resolution was around 20 μm. Laboratory freeze-thaw cycling was performed according to the European Standard EN 12371 (2010) on 40 mm edge cubic samples with 6h of freezing at -12°C, followed by 6h of thawing while immersed in water of 20 °C. A Zeiss Axioscope with camera was used for petrographical description of uncovered 30 μm thin sections stained with Alizarine Red-S. Scanning electron microscopy (SEM) was done with a FEIT Quanta 200F on gold-coated samples. Petrophysical properties were determined according to the appropriate European Standards. The experiments were performed on different sedimentary rocks, used as building materials in Belgium. Here we focus on some results of a porous miliolid limestone from the Paris basin, which are more thoroughly discussed in De Kock et al., 2015 and some preliminary results of a sandy limestone, Lede stone, and an oolitic limestone Massangis, whos properties were discussed in De Kock et al., 2013. Results and discussion Micro-CT allows to visualize the micro-scale freeze-thaw decay of the porous samples. The freeze-thaw cycling results in the development of fractures within the sample (Figure 1). This is the result of ice wedging, a process where the ice crystals push the fracture surfaces apart. The development of the fractures is strongly related to the rocks’ fabric. More specifically, they develop within the planes of discoidal forams, which are microfossils. It was already shown by Dewanckele et al. (2013) that these act as flaws. Capillary rise experiments show that these forams acts as preferential water uptake paths. Therefore it is assumed that the water saturation is relatively high in the volume fraction of the rock around these forams during freezing, increasing the volume that can be affected by freezing. Hence, there seems to be a clear link between local saturation and freeze-thaw decay. Fig. 1. Fractures segmented (in colour) within the bulk volume (transparent) and one reference slice (opaque). Sample diameter is 9 mm. Figure 2 shows the development and growth of the fracture in size in function of the freeze-thaw cycles. During the second cycle, it can be seen that a fracture develops, which cannot be segmented due to the partial volume effect. From the 3 freeze-thaw cycle, however, the fracture is large enough to be segmented and this enables that its volume can be analysed. First of all, it can be seen that the fracture opens during freezing en closes during subsequent thawing. This is in favour of the ice crystallisation theory as discussed in the introduction. After successive freeze-thaw cycling, there is a progressive opening of the fracture, allowing to observe fracture propagation. After the 4 cycle, the fracture does not close entirely and there is residual strain. Finally, the crack size also stagnates in the last cycles, illustrating that the facture volume accommodates the ice crystallization. Fig. 2. Size of a fracture expressed as equivalent diameter in function of successive freeze-thaw cycles. During cooling a temperature exotherm, considered as a proxy for ice crystallization, was recorded at a temperature of -9.7°C. According to the Kelvin equation for freezing point depression, this corresponds to crystallisation in pores smaller than 20 nm. As it is thermodynamical more favorable to crystallize within larger pores (Everett, 1961), crystallization in these experiments occurs under transient conditions. Most likely, this is related to the probability of having a nucleation site within such a small sample (Sun and Scherer, 2010). Figure 3 consists of a SEM image showing the presence of such small pores within the tests of these forams. The susceptibility of this sample to freeze-thaw decay is thus related to a combination of larger pores as the foram’s test chambers which have a higher capillary suction velocity resulting in higher local water saturation, with nanometric pores from the test itself that provide a higher probability of nucleation sites. Fig. 3. SEM image of part of the foram’s test, with larger interparticular micrometer pores (1) and nanometric pores in the test (2). In addition, continuous scanning allows to visualise the dynamics in the sample during freezing. It can be seen that the fracturing is abrupt and coincides perfectly in time with the occurrence of the exotherm. This validates the ice crystallization theory as mechanism for freeze-thaw decay in these experiments. Preliminary results of experiments with other stones also illustrate the relation of freeze-thaw fractures with the rock’s fabric, more specifically with the fabrics that promote a high local saturation degree. Acknowledgements This work was partially supported by the Research Foundation Flanders (FWO) project G.0041.15N. H. Derluyn is supported by the FWO and Thomas De Schryver is supported by the Agency for Innovation by Science and Technology in Flanders (IWT, SBO project 120033 “TomFood”). Tim De Kock is grateful to the FWO for travel g