Microfocus X-ray CT Research Articles

Impedance Characteristics of Berea Sandstone Cores in the Process of CO<sub>2</sub> Injection Displacement with Saturated Brine

As an important means of CO<sub>2</sub> geological storage leakage monitoring, resistivity monitoring technology is of great significance to the safety and stability of CCUS project. In order to study the electrical signal response rule of the evolution of CO<sub>2</sub> saturation in the reservoir, a joint core displacement experiment system of electrochemical impedance analysis and microfocus X-ray CT was designed and constructed to simulate the process of CO<sub>2</sub> displacement of brine in Berea sandstone cores under stratigraphic temperature and pressure conditions. The electrochemical impedance characteristics of the core-fluid system are analyzed by electrochemical impedance spectroscopy. The experimental results show that at lower temperature and pressure, it is more difficult for CO<sub>2</sub> to invade the pore space occupied by the brine in situ, resulting in drastic changes in CO<sub>2</sub> plane saturation along the displacement direction. With the increase of temperature and pressure, the CO<sub>2</sub> saturation curve becomes smoother and the migration and displacement front becomes even. The Cole equivalent circuit model is used to describe the conduction mode of AC electrical signals inside the core, and the electrochemical impedance characteristic analysis focusing on the high frequency region shows that the system impedance increases with the increase of CO<sub>2</sub> saturation, and decreases with the increase of scanning frequency. In addition, the changes of impedance characteristics in the electrochemical impedance spectroscopy not only reflect the pore structure characteristics of the core, but also reveal the evolution law of CO<sub>2</sub> saturation in the porous medium. With the increase of CO<sub>2</sub> saturation, the low pore space is gradually occupied by CO<sub>2</sub>, and the residual brine connectivity of the pore space as a conductive component decreases. The decrease of the internal conductive circuit leads to the rapid increase of the impedance, which is consistent with the change of resistance and capacitance when fitting the Cole equivalent circuit model.

Compaction-induced variability in the 80/20 sand-bentonite mixture: Spatial variation in dry density at different scales in the laboratory and large-scale gas seal test

Sand-bentonite (SB) mixtures are considered as backfill materials for sealing designated sections of nuclear waste repositories. The dry density of the SB mixture is the crucial parameter for the quality control during emplacement because it strongly controls the hydraulic and mechanical properties. Backfilling of an SB mixture is often performed layer by layer by keeping track of the average dry density of each layer. The compaction is typically done in a dynamic manner leading to more compaction near the compaction surface. In this study, an SB mixture with 80% sand and 20% bentonite was compacted in the laboratory by static and dynamic procedures to a height of 10 cm and the dry density profile was characterized by destructive slicing and microfocus X-ray CT imaging. When dynamically compacted, a distinct dry density gradient was identified. The variation in the dry density identified by the slicing was as much as 0.4 g/cm3 which leads to hydraulic conductivity variation by a factor of 4.8. The SB seal emplaced in the large-scale gas seal test (GAST) for demonstrating the effective functioning of the gas permeable seals was also analyzed to identify if any variability was present at the field scale. The samples collected from the top 2 cm of each 10 cm-thick horizontal layers yielded a higher overall average by 0.06 g/cm3 than the average of the mass balance method. In conjunction with the laboratory studies, it was implied that sampling results, if only collected from the very top few centimeters of the layers, could lead to an overestimation in the global dry density. Overall, the results with different methods at different scales indicated that the dynamic compaction-induced variability within a single layer was more pronounced than the variability in the larger scales detected in the mass balance and sampling methods.

Evidence for Solution-Mediated Phase Transitions in Kidney Stones: Phase Transition Exacerbates Kidney Stone Disease

In this study, we investigated calcium oxalate (CaOx) kidney stones and showed direct evidence of the solution-mediated phase transition of calcium oxalate dihydrate (COD; the metastable phase) to calcium oxalate monohydrate (COM; the stable phase). We examined the crystal phases, crystal textures, and protein distributions within thin sections of calcium oxalate kidney stones. Observation with a polarized-light microscope showed that the outline of the mosaic texture, in which COM crystals are assembled in a mosaic pattern, roughly coincides with COD’s crystallographically stable face angles. Microfocus X-ray CT measurement captured the intermediate process of the phase transition, starting inside the COD single crystal and gradually transforming to COM crystals. In addition, the distribution of osteopontin and prothrombin fragment-1, common proteins contained in urine and visualized by multicolor fluorescence immunostaining, showed no apparent striations inside the COM single crystals with the mosaic texture, although the striation is apparent inside the COD single crystals. This is probably because the phase transition of mosaic-like COM occurred in a semiclosed system inside the COD single crystal, so the effect of periodic (day–night, seasonal, etc.) urinary protein concentration changes was small. On the other hand, striations were visible in concentrically laminated COM. This indicated that concentrically laminated COM formed in response to the changes in urinary protein concentrations. From the above, we conclude that the COD single crystals and the concentrically laminated COM seen in CaOx stones are primary structures, and the mosaic COM is a secondary structure that is a pseudomorph formed by the solution-mediated phase transition from COD single crystals.

Quantitative analysis of calcium oxalate monohydrate and dihydrate for elucidating the formation mechanism of calcium oxalate kidney stones.

We sought to identify and quantitatively analyze calcium oxalate (CaOx) kidney stones on the order of micrometers, with a focus on the quantitative identification of calcium oxalate monohydrate (COM) and dihydrate (COD). We performed Fourier transform infrared (FTIR) spectroscopy, powder X-ray diffraction (PXRD), and microfocus X-ray computed tomography measurements (microfocus X-ray CT) and compared their results. An extended analysis of the FTIR spectrum focusing on the 780 cm-1 peak made it possible to achieve a reliable analysis of the COM/COD ratio. We succeeded in the quantitative analysis of COM/COD in 50-μm2 areas by applying microscopic FTIR for thin sections of kidney stones, and by applying microfocus X-ray CT system for bulk samples. The analysis results based on the PXRD measurements with micro-sampling, the microscopic FTIR analysis of thin sections, and the microfocus X-ray CT system observation of a bulk kidney stone sample showed roughly consistent results, indicating that all three methods can be used complementarily. This quantitative analysis method evaluates the detailed CaOx composition on the preserved stone surface and provides information on the stone formation processes. This information clarifies where and which crystal phase nucleates, how the crystals grow, and how the transition from the metastable phase to the stable phase proceeds. The phase transition affects the growth rate and hardness of kidney stones and thus provides crucial clues to the kidney stone formation process.

Gaining mechanistic insight into key factors contributing to crack path transition in particle toughened carbon fibre reinforced polymer composites using 3D X-ray computed tomography

Composite materials are increasingly used to help in reducing the carbon footprint of transportation and upscaling renewable energy infrastructure that provides clean energy for future cities. However, the inherent susceptibility of carbon fibre reinforced polymers to impact damage results in knock-down in design and is linked to the micro-mechanistic response of the material to damage. In situ experimental and high-resolution imaging techniques using X-ray computed tomography (X-ray CT) have been used to gain a mechanistic understanding of the key factors controlling crack path — and hence macro-scale toughness within a composite. Multiscale Synchrotron Radiation Computed Tomography (SRCT) and lab-based micro-focus X-ray CT are used to investigate different material systems toughness response from standard Double Cantilever Beam tests. The crack transition to the weaker ply region of the composite is identified as a controlling factor across a scale of mm’s, and ‘trigger’ regions are reported on and investigated. The ‘trigger’ regions were identified as gaps in the ply adjacent to the interlayer. This work feeds directly into delamination growth predictions, a better understanding of material response, and enabling informed manufacture and design, allowing for reduced material usage, longer life and more sustainable vehicles and infrastructure.

Micro-focus X-ray CT scanning of two rare wooden objects from the wreck of the London, and its application in heritage science and conservation

Two wooden objects, a tuning peg from a stringed musical instrument and a stopper from a smoking pipe, were recovered from the 1665 CE wreck of the London and selected for wood identification. So far, they are the only recoveries of these object types from this wreck. To preserve their integrity and completeness, destructive sampling was not desirable. Instead, micro-focus computed tomography (µ-CT) scanning was carried out. The objects were scanned both pre-conservation (waterlogged/saturated) and post-conservation (PEG impregnated; freeze-dried). Although the aim was to non-destructively explore the internal structure of the objects for wood identifications, information was also gained on their manufacturing characteristics and internal condition. 1 µm voxel resolution – sufficient for positive identifications of these wood types to genus level (as is standard for wood identifications) – was achieved. This study has established that the conservation treatment used here does not obscure the microscopic anatomical features of these wood types and therefore recommends that µ-CT scanning is best undertaken after conservation, when the objects are stable.

DEVELOPMENT OF A TECHNIQUE FOR OBSERVING THE FROST HEAVING PROCESS IN SOIL USING AN INDUSTRIAL MICRO-FOCUS X-RAY CT SCANNER

This paper aims at developing a technique for observing the frost heaving process in soil nondestructively and microscopically using an industrial micro-focus X-ray CT scanner. For this purpose, a compact frost heaving apparatus that could freeze the soil in one dimension inside the X-ray CT scanner was developed. This experimental method made it possible to observe the process of ice lens formation in the soil and the shape of the ice lens in detail. In highly frost susceptible weathered volcanic ash, ice lenses like multiple cracks were observed to develop in the early stages of the experiment. When the freezing front was stagnant and the heat was balanced, thick and well-developed ice lenses could be observed. The shape of the ice lens observed in the weathered volcanic ash without gravel was relatively flat. In the terrace deposits containing gravel, ice lenses were observed to be formed from around the larger particles. Furthermore, the formed ice lenses were more uneven in shape than weathered volcanic ash. In the case of volcanic ash sand composed of coarse grains that do not have frost susceptibility, no frost heaving occurred and no ice lenses were observed. The gray levels of the frozen areas of the weathered volcanic ash and terrace deposits with frost susceptibility were found to decrease. This is thought to be because the precipitation of ice lenses in the soil pushed the soil particles apart and reduced their density relatively.

Influence of Tooth Mold Materials in Composite Resin CAD/CAM Crown Destructive Test.

A range of experimental designs have been used in destructive testing of composite resin CAD/CAM crowns. Various materials have been adopted for the abutment in such tests, including human or bovine dentin, stainless steel, PMMA, and composite resin, the selection of which is made in accordance with study objective or preference of the researcher. The purpose of this study was to determine how the material selected for the abutment material affected fracture load and maximum displacement. Destructive tests were conducted on composite resin crowns of the same design. Three types of material were used for the abutments together with 2 types of adhesive material. Images of each sample were acquired before destruction using a microfocus X-ray CT scanner to confirm the feasibility of a non-destructive test.The load required to fracture the composite CAD/CAM resin crowns depended on the abutment material used, with a decrease being observed in the order of composite resin, stainless steel, and PMMA. Maximum displacement decreased in the order of PMMA, composite resin, and stainless steel. Differences in the material used for setting (adhesive resin or polycarboxylate cement) showed no effect on fracture load. These results indicate that the load required to achieve destruction of resin CAD/CAM crowns varies according to the abutment material used.

A Morphological Analysis of the Flat-Shaped Spumellarian Radiolarian Dictyocoryne: Morpho-Functional Insights into Planktonic Mode of Life

Abstract. The three-dimensional morphology of the flat-shaped spumellarian radiolarian Dictyocoryne was analysed using a microfocus X-ray CT with a special focus on whether it was capable of a planktonic lifestyle. Two types of 3D models, the shell model, which represents a realistic 3D shell, and the wrapped model, which mimics the whole body outline without pseudopodia, were reconstructed in order to estimate volume, surface area, and centres of gravity for the shell model and buoyancy for the wrapped model. The calculated values showed that the volume of shell with respect to the total volume was negatively allometric, regardless of the differences between threshold settings. Stepwise secretions of the patagium layer may result in a comparatively lightweight shell, thereby decreasing the total density during growth but not below the density of seawater. Estimated positions for the centres of gravity and buoyancy were too close to maintain an autonomous posture while floating. Instead, the ratio between surface area and volume was greater than that in an ideal sphere. Such a broad surface area could obtain the viscous resistance necessary for sinking retardation. Spumellarian radiolarians, including Dictyocoryne, have photosynthetic symbionts located primarily in the ectoplasmic layer, which is a habitable space that can be maximised within the larger surface area. Given that radiolarians float when extending their pseudopodia, it can be hypothesised that pseudopodia may play a role in the adjustment of life posture in a hydraulically unstable shell, which can be integrated into sinking retardation, enhancement of photosynthetic activity and manoeuvrability of life posture within a unique flat-shaped morphogenesis.

Cardiac fiber tracking on super high-resolution CT images: a comparative study.

.Purpose: High-resolution cardiac imaging and fiber analysis methods are required to understand cardiac anatomy. Although refraction-contrast x-ray CT (RCT) has high soft tissue contrast, it cannot be commonly used because it requires a synchrotron system. Microfocus x-ray CT () is another commercially available imaging modality.Approach: We evaluate the usefulness of for analyzing fibers by quantitatively and objectively comparing the results with RCT. To do so, we scanned a rabbit heart by both modalities with our original protocol of prepared materials and compared their image-based analysis results, including fiber orientation estimation and fiber tracking.Results: Fiber orientations estimated by two modalities were closely resembled under the correlation coefficient of 0.63. Tracked fibers from both modalities matched well the anatomical knowledge that fiber orientations are different inside and outside of the left ventricle. However, the volume caused incorrect tracking around the boundaries caused by stitching scanning.Conclusions: Our experimental results demonstrated that scanning can be used for cardiac fiber analysis, although further investigation is required in the differences of fiber analysis results on RCT and .

X-ray computed tomography to investigate industrial cast Al-alloys

This paper describes the use of X-ray computed tomography (XCT) to inspect the internal defects of industrial Aluminum alloys die-casting, to justify the adequateness of super sealant resins in filling tiny holes, and to reduce the casting porosity of metals by the impregnation process. High-resolution 2D slice images were generated by a microfocus X-ray CT system with direct conversion Cadmium Telluride (CdTe) flat panel detector (FPD). Moreover, we were able to visualize the internal defects of the two different shapes of casting objects. The gray-value contrasts of the CT images were excellent to distinguish the resin material in the alloy samples after impregnation treatment. Furthermore, to determine the dimensions of internal defects, virtual sectioning was carried out to view the cross-section of the metal samples and dimensions of internal defects. Dual-energy X-ray computed tomography (DXCT) was used with an energy differentiation type 64-pixel linear array photon-counting line sensor for the material characterization. The impregnated resin part inside the castings defects was verified based on the effective atomic number with a 2.92% low error margin. Hence, this will be a useful qualitative and quantitative advancement to rapid and detailed non-destructive analysis within the die-casting industries in improving the quality of the impregnation process.

Linking pore network structure derived by microfocus X-ray CT to mass transport parameters in differently compacted loamy soils

Mass transport in soil occurs through the soil pore network, which is highly influenced by pore structural parameters such as pore-size distribution, porosity, pore tortuosity, and coordination number. In this study, we visualised the networks of meso- and macro-pores (typical pore radius r ≥ 10 μm) using microfocus X-ray computed tomography (MFXCT) and evaluated pore structural parameters of two loamy soils from Japan and New Zealand packed at different degrees of compaction. The effect of compaction on pore structural parameters and relationships between pore structural parameters and measured mass transport parameters were examined. Results showed a clear influence of compaction on pore structural parameters, with the MFXCT-derived mean pore radii and pore tortuosities decreasing and the mean pore coordination number increasing with increasing dry bulk density. Especially, pores with r > 80 µm became finer or were not well formed due to compaction. The MFXCT-derived pore structural parameters were not well correlated with the equivalent pore radii from measured water retention curves. However, volumetric surface areas and pore-network connectivity-tortuosity factors derived from MFXCT allowed a fair prediction of several important mass transport parameters such as saturated hydraulic conductivities, soil-gas diffusion coefficients, and soil-air permeabilities. Further studies are needed to link micro-pores with radii smaller than the X-ray CT resolution to meso- and macro-pores visualised by X-ray CT to improve the prediction of mass transport parameters in soil.

Biomimetic Riblets Inspired by Sharkskin Denticles: Digitizing, Modeling and Flow Simulation

While sharkskin surface roughness in terms of denticle morphology has been hypothesized but remains yet controversial to be capable of achieving turbulent flow control and drag reduction, sharkskin-inspired “riblets” have been reported to be an effective biomimetic design. Here we address an integrated study of biomimetic riblets inspired by sharkskin denticles by combining 3D digitizing and modeling of “fresh” denticles and computational fluid dynamic modeling of turbulent flows on a rough surface with staggered denticles and hound-tooth-patterned grooves. Realistic microstructures of denticles in five shark species of Galapagos, great white, whitetip reef, blacktip reef, and hammerhead sharks were first measured and digitized in three fold: (1) 2D imaging of lubricated sharkskin in a wet state by means of a “nano-suit” technique with a Field-Emission Scanning Electron Microscope (FE-SEM); (2) 3D structures of sharkskin denticles with a micro-focus X-ray CT; and (3) single denticles of the five shark species in a 3D manner with 3D-CAD. The denticles at mid-body location in the five species were observed to have a structure of five non-uniform-ridges (herein termed “non-uniform grooves”) with Angles Of Inclination (AOI) ranging over 20°–32°. Hydrodynamics associated with the unique five-ridge denticles were then investigated through modeling turbulent flow past a denticle-staggered skin surface. We further constructed a biomimetic riblet model inspired by the non-uniform grooves and investigated the hydrodynamic effects of height-to-spacing ratios of mid-ridge and side-ridges. Our results indicate that the morphological non-uniformity in sharkskin denticles likely plays a critical role in passively controlling local turbulent flow and point to the potential of denticle-inspired biomimetic riblets for turbulent-flow control in aquatic vehicles as well as other fluid machinery.

Development of a new loading test apparatus for microfocus X-ray CT and its application to the investigation of soil behavior surrounding driven open-section piles

In recent years, X-ray CT scanners with task-specific modifications, such as microfocus and/or a synchrotron, have been widely implemented in a variety of fields, including medical and industrial fields. Since microfocus X-ray CT systems enable the visualization of whole samples, and also yield a relatively high resolution of the region of interest in the sample, they are commonly utilized in the fields of soil mechanics and geotechnical engineering. This paper describes a novel loading test apparatus that is specifically designed for microfocus X-ray CT systems capable of performing loading tests to investigate soil behavior during the installation of driven open-section piles. The loading tests were designed to take the micro-level spatial resolution of microfocus X-ray CT systems into account. Digital image correlation (DIC) is subsequently implemented to analyze the obtained CT images, making it possible for measurements to be taken of the displacement fields in the ground following installation of the model pile. Finally, the versatility of this novel test apparatus is proof of its high potential for application in different types of loading tests.

Micro Anatomical Structure Imaging by Desktop Micro-focus X-ray CT Scanner

Micro Anatomical Structure Imaging by Desktop Micro-focus X-ray CT Scanner

X-ray CT assisted damage identification in warm forging

This study aims to identify the 3-dimensional interactions of micro-voids evolution before and after warm-forging a typical titanium alloy component by employing a micro-focus X-ray CT system so as to achieve a more accurate micro-void location and distribution as critical data input for damage prediction in warm forging. A specific forging tool was designed for warm-forging the component. Serval local regions that represented different strain levels were established as representative volume element models for the Ti-6Al-4V preform, in which, the micro-void distributions were obtained directly from the X-ray CT images. Furthermore, the micro-void evolutions of the corresponding representative volume element models were analyzed from the forged component. Thus, the damage evolution, i.e., the variation of void volume fraction, in the warm forging process was identified.

Determination of Swelling Effect in CO2-Brine Systems Using Microfocus X-ray CT

As one of the most viable technique, geological sequestration of CO2 has great potential for storing large amount of the injected CO2 into brine by dissolution. Understanding the mass transfer of CO2 into a brine sample is of great importance of CO2 sequestration. Swelling effect revealing the properties of dissolution play an important role. Other than oil swelling, it is difficult to observe directly using traditional methods due to the imperceptible extent of phase expansion in CO2-brine mixture. The combination of X-ray computed tomography and image processing techniques has made it possible to measure multiphase boundaries as well as swelling factors of CO2-brine systems at high pressures and elevated temperatures. In this work, a generalized methodology has been proposed and successfully applied. The experimental results show that both the mass transfer and the swelling factor increase with pressure. It is also found that the local contact angel significantly increases when gaseous CO2 turns into supercritical CO2.

In Situ Local Contact Angle Measurement in a CO2-Brine-Sand System Using Microfocused X-ray CT.

The wettability of porous media is of major interest in a broad range of natural and engineering applications. The wettability of a fluid on a solid surface is usually evaluated by the contact angle between them. While in situ local contact angle measurements are complicated by the topology of porous media, which can make it difficult to use traditional methods, recent advances in microfocused X-ray computed tomography (micro-CT) and image processing techniques have made it possible to measure contact angles on the scale of the pore sizes in such media. However, the effects of ionic strength, CO2 phase, and flow pattern (drainage or imbibition) on pore-scale contact angle distribution are still not clear and have not been reported in detail in previous studies. In this study, we employed a micro-CT scanner for in situ investigation of local contact angles in a CO2-brine-sand system under various conditions. The effects of ionic strength, CO2 phase, and flow pattern on the local contact-angle distribution were examined in detail. The results showed that the local contact angles vary over a wide range as a result of the interaction of surface contaminants, roughness, pore topology, and capillarity. The wettability of a porous surface could thus slowly weaken with increasing ionic strength, and the average contact angle could significantly increase when gaseous CO2 (gCO2) turns into supercritical CO2 (scCO2). Contact angle hysteresis also occurred between drainage and imbibition procedures, and the hysteresis was more significant under gCO2 condition.

Water leakage control by using vibratory roller on a dry-seeded rice field in southwestern Japan

Dry-seeded rice cultivation is an effective low-cost cultivation method in Japan, but preventing water leakage from cultivated rice fields remains a challenge. Here we assessed the efficiency of using a vibratory roller in a dry-seeded rice field for preventing water leakage. The tests were conducted at two different soil-water contents (WC: 32 and 39%) before roller compaction. We measured the acceleration response of the vibrating roller by using a micro-electro mechanical system (MEMS) accelerometer, and we determined the volume of water leakage from the field by using a rapid leakage capacity tester. We analyzed the changes in the soil structure by using a micro-focused X-ray CT scanner. We analyzed all of the resulting data to identify any correlation. We observed that water leakage from the field was sufficiently prevented when prior to roller compaction, soil moisture content was 39%. The shape of the soil pores that could efficiently prevent water leakage was flatter than that of the inefficiently compacted soil. In addition, the total porosity decreased, but the small-sized pore fraction increased. The vibration acceleration of the roller significantly increased with the decrease in the volume of water leakage. Thus, in addition to assessing the efficiency of vibratory rollers in reducing water leakage, our data suggest that it is to some extent possible to estimate the water leakage prevention effect from the acceleration response of a vibrating roller.

Permeability change and geometrical information of void spaces in Berea sandstone and Otway sandstone

To clarify the differences in permeability and three-dimensional void geometry in two sandstones, permeability change by increasing confining pressure were measured and three-dimensional geometrical information with microfocus X-ray CT were analyzed. In this research, Berea sandstone and Otway sandstone were used as a specimen, and its total porosity measured by mercury intrusion porosimetry were 17.4 and 25.0%, respectively. Pore size distribution in both sandstones was almost same as one modal manner, but Otway sandstone specimen showed slightly narrow peak of 5 μ–7 μm. Permeability change in both sandstones was decreased with increasing effective confining pressure, but the absolute value in Otway sandstone was lower by one order of magnitude than those in Berea sandstone. Three-dimensional medial axis (3MDA) method was adopted to compare pore geometry in two sandstones and tortuosity, number of connecting paths were decided. Based on this information, we evaluated the relationship between permeability and pore structures.