In this paper, in-situ X-ray microtomography was used to analyze liquor penetration/impregnation and delignification of wood chips during kraft pulping, allowing microstructural changes to be assessed over time. The study was conducted with sapwood of three hardwood species (alder, aspen and birch), using a reactor designed to provide liquor circulation and temperature control. Each wood sample was digested at 141 °C for four hours and, throughout this time, fifteen 3D images of the central portion of the samples were acquired. The images were segmented and used to measure lumen size, cell wall thickness and wood chip porosity. The results confirmed that vessels offered the preferred path for liquor penetration in the hardwoods. Moreover, liquor penetration from ray cells to adjacent fibers was shown to be a less efficient path for impregnation. Regarding delignification, fiber separation began first in aspen and last in alder, and the complete separation took between 1 and 1.5 h to occur in the center of the samples. The porosity of the chips increased continuously after liquor penetration, whereas cell wall thickness decreased more substantially during fiber separation, especially in aspen, but remained relatively stable afterwards. Furthermore, the position of the fibers in relation to vessels and rays did not impact the rate of delignification significantly. Overall, this work shows that in-situ tomography can be a valuable technique to move forward research on wood impregnation and on topochemistry of lignin removal during pulping.

This study introduces a novel contrast modality in neutron imaging, enabling the visualization of plastically deformed zones within ARMCO® iron. Utilizing differences in transmitted neutron intensity, we exploit variations in Bragg diffraction strength between deformed and non-deformed areas. Our findings reveal that deformed regions exhibit stronger diffraction due to extensive sub-grain divisions and angular spreading caused by plastic deformation. This contrast effect, attributed to extinction phenomena, is particularly evident in ARMCO® iron. We demonstrate the applicability of this technique through detailed 2D and 3D imaging of tensile and deep drawing samples. In tensile samples, the contrast effectively highlights regions of localized plastic deformation and Lüders band formation. For deep-drawing samples, the technique captures significant deformation patterns around the punch area and differentiates between the inner and outer surfaces of the sheet metal. The contrast modality is another step forward in fully exploiting and unraveling the rich information in transmission based neutron imaging and enables full-field characterization for samples up to tens of centimeters in size.

Deep ice cores from polar ice sheets enable reconstructions of Earth’s past climate. Ice-core records are therefore crucial for projecting future climate change, however, our ability to interpret them relies on our understanding of polycrystalline-ice microstructures and mechanics. In turn, these microstructures enable modeling of ice flow and large-scale effects of ice-sheet evolution. Since drilling began in the 1950s, the ice textures and climate proxies developed to decipher ice-core records have been analyzed in one- or two-dimensional (2D) spaces, necessitated by the analytical instruments of core-processing lines and laboratories. Here we develop a three-dimensional (3D), non-destructive approach to textural analysis that preserves the natural context of ice and complements standard methods. Our method combines lab-based absorption and diffraction contrast tomography to simultaneously visualize, measure, and spatially correlate ice grains and air bubbles from volumetric and 3D crystallographic perspectives, both lost during traditional sample preparations. We evaluate the representation of 3D versus 2D data and discuss how access to both c- and a-axis directions of grains may help constrain micromechanical models. We also built a specially designed cooling device for the laboratory X-ray system to extend observational volumes by several orders of magnitude over previous synchrotron-based measurements.

This study utilizes advanced 3D imaging techniques, combining X-ray and neutron tomography, to investigate the hydromechanical evolution of Idaho Gray sandstone during coupled triaxial permeability tests. The analysis involved correlating mechanical and hydraulic bulk measurements, porosity fields, strain fields derived from Digital Volume Correlation analysis and fluid speed fields derived from time series of neutron tomograms. This experimental approach provides an improved understanding of the relationship between the volume of active pores and bulk hydraulic conductivity on our samples. In particular, the results reveal that the confining pressure and rock porosity heterogeneity play crucial roles in global and local mechanisms, strain field evolution and fluid flow dynamics.

We present new true triaxial compression data obtained in the ductile regime on Bleurswiller sandstone. The deformed samples show a range of failure modes qualitatively similar to what was reported by earlier experimental studies performed in conventional conditions (axisymmetric compression). In particular, visual inspection and X-ray Computed Tomography imaging reveal compaction localization in all our deformed samples. The pore collapse model of Zhu et al.( 2010) 1 is extended to include the role of the intermediate principal stress and our new data for the onset of shear-enhanced compaction are in basic agreement with this extended model that includes three stress invariants. Published true triaxial data obtained in the brittle regime highlights the impact of the intermediate principal stress on the onset of dilatancy. The predictions of the conventional sliding wing crack model extended to true triaxial conditions are in poor agreement with these data. Another energetic approach pioneered by Wiebols & Cook shows a better agreement with the experimental results. Our new data and analysis will help the interpretation of inelastic deformation under polyaxial compression in various geotechnical and tectonic settings.

Darcy’s law provides a fundamental framework for understanding fluid flow through porous media. However, deviations from its linear superficial velocity-hydraulic gradient (v-i) relationship have been widely reported, at high and low flow rates. While previous studies have attributed the low flow rate deviations to factors such as fluid properties, boundary effects, and experimental artifacts, the role of material heterogeneity has received less attention. This study employs neutron imaging to investigate how rock heterogeneity influences macroscopically observed flow behavior. Volume-controlled percolation tests were conducted on Idaho Gray sandstone cores under near-single-phase conditions using heavy water (D2O) and normal water (H2O) across a wide range of flow rates. Bulk measurements (pore pressure at the sample boundaries and the controlled injection flow rate) revealed a decline in hydraulic conductivity at lower injection rates. Through a novel method for interpreting the breakthrough curves (BTC) derived from the neutron imaging data, we are able to quantify the volume of pores active in the flow during each test. The neutron radiography imaging acquired during the flow tests revealed that flow paths were strongly influenced by the rock’s heterogeneous pore structure, with higher flow rates promoting more uniform front propagation. This suggests greater pore space access at higher injection rates and implies the presence of threshold pressure gradients needed to access different parts of the pore network. The BTC analysis from neutron image shows a decrease in the volume of pores active in the flow (effective porosity) with decreasing injection rates, aligning with the observed reduction in hydraulic conductivity. By linking nonlinearity in vi-curves to variations in effective porosity, this study highlights the critical role of heterogeneity in controlling the fluid flow behavior. These findings underscore the importance of understanding the role of spatial variability in porous media when interpreting macroscopic (bulk) permeability measurements, especially when interpreting apparent deviations from Darcy’s law.

With several upcoming sample return missions, such as the Mars Sample Return Campaign, non-destructive methods will be key to maximizing their scientific output. In this study, we demonstrate that the combination of neutron and X-ray tomography provides an important tool for the characterization of such valuable samples. These methods allow quantitative analyses of internal sample features and also provide a guide for further destructive analyses with little to no sample treatment, which maintains sample integrity, including minimizing the risk of potential contamination. Here, we present and review the results from four case studies of terrestrial impactites and meteorites along with their analytical setup. Using combined X-ray and neutron tomography, a Ni-Fe silicide spherule, that is, projectile material, was located within a Libyan Desert Glass sample and the distribution of hydrous phases was pinpointed in selected impactite samples from the Chicxulub IODP-ICDP Expedition 364 drill core and the Luizi impact structure, as well as in the Miller Range 03346 Martian meteorite. Neutron and X-ray tomography give complementary three-dimensional information about the distribution of different phases within a geologic sample. We demonstrate that these two methods can be successfully used to locate meteoritic material (i.e., from the impacting object) and hydrous components in terrestrial impactites and meteorites. This can help shed light on aqueous processes in the Solar System as well as the impact cratering process. Non-destructive methods like these will be important for up-coming sample return missions to characterize the returned samples and guide further destructive analyses. Combined neutron and X-ray imaging was used to locate projectile material and hydrous phases in meteorites and terrestrial impactites Locating and identifying projectile material can shed light on the impact cratering process Combined neutron/X-ray tomography can serve as a fundamental method for the characterization of material from (future) sample return missions

The true promise of MXene as a practical supercapacitor electrode hinges on the simultaneous advancement of its three-dimensional (3D) assembly and the engineering of its nanoscopic architecture, two critical factors for facilitating mass transport and enhancing an electrode's charge-storage performance. Herein, we present a straightforward strategy to engineer robust 3D freestanding MXene (Ti3C2Tx) hydrogels with hierarchically porous structures. The tetraamminezinc(II) complex cation ([Zn(NH3)4]2+) is selected to electrostatically assemble colloidal MXene nanosheets into a 3D interconnected hydrogel framework, followed by a mild oxidative acid-etching process to create nanoholes on the MXene surface. These hierarchically porous, conductive holey-MXene frameworks facilitate 3D transport of both electrons and electrolyte ions to deliver an excellent specific capacitance of 359.2 F g-1 at 10 mV s-1 and superb capacitance retention of 79% at 5000 mV s-1, representing a 42.2% and 15.3% improvement over pristine MXene hydrogel, respectively. Even at a commercial-standard mass loading of 10.1 mg cm-2, it maintains an impressive capacitance retention of 52% at 1000 mV s-1. This rational design of an electrode by engineering nanoholes on MXene nanosheets within a 3D porous framework dictates a significant step forward toward the practical use of MXene and other 2D materials in electrochemical energy storage systems.

This article introduces a novel testing system for investigating rock hydromechanical behavior with neutron and X-ray imaging techniques. The system comprises four subsystems: an axial compression system, a confining pressure system, a fluid flow system, and a triaxial cell. In order to enable imaging with both modalities to track fluid flow and deformation in situ and 3D, the cell was designed to have sufficient transparency to X-rays and neutrons. The system's capabilities are demonstrated by showing neutron and X-ray tomography data of Idaho Gray sandstone samples during in situ coupled flow-triaxial tests. Quasi-single-phase flow analysis was enabled by directly visualizing the fluid front advance via neutron tomography by exchanging light water (H2O) and heavy water (D2O). Digital Volume Correlation (DVC) could be performed on both the X-ray and neutron tomography images to quantify the mechanical strain field evolution in the samples, which can be compared to the evolution of the fluid flow fields. In addition, the cell and a sample of Idaho Gray sandstone were imaged in a laboratory X-ray tomography machine, generating 3D reconstructed volumes with grain-scale resolution. Improvements are proposed for future experiments to obtain grain-scale resolution images during coupled flow-triaxial tests using neutron and X-ray beams simultaneously and conducting in situ experiments on laboratory tomographs.

A method for semantic segmentation of microstructure evolution from 4D imaging data is described and demonstrated. The method is based on a joint histogram describing the time history of the grayscale in each voxel of the images. After identifying and labeling clusters in the joint histogram, the labels are mapped back to the image. The results demonstrate accurate segmentation and characterization of sample evolution. The advantages of the proposed method include automatic segmentation of many time steps and the ability to track grayscale evolution over time and thereby discriminate similar evolution in different material phases. The method is demonstrated through application to 4D X-ray tomography datasets of temperature cycling in cement mortar and tensile testing of a cast iron sample. Water and air exchange in a pore inside the cement mortar is successfully segmented as a function of temperature. In the case of the deforming cast iron sample, several damage mechanisms are identified and segmented. The method is implemented in an open-source Python package called evoSegment.

This paper investigates the critical role of material thickness in freeze-dried pellets for enhancing the storage stability of encapsulated bacteria. Freeze dried material of varying thicknesses obtained from different annealing durations is quantified using Scanning Electron Microscopy (SEM) and X-ray microtomography (μCT), the material thickness is then correlated to the storage stability of the encapsulated cells. A formulation comprising of sucrose, maltodextrin, and probiotic cells is quenched in liquid nitrogen to form pellets. The pellets undergo different durations of annealing before undergoing freeze-drying. The material thickness is quantified using SEM and μCT. Storage stability in both oxygen-rich and oxygen-poor environments is evaluated by measuring CFU counts and correlated with the pellet structure. The varying annealing protocols produce a range of material thicknesses, with more extensive annealing resulting in thicker materials. Storage stability exhibits a positive correlation with material thickness, indicating improved stability with thicker materials. Non-annealed pellets exhibit structural irregularities and inconsistent storage stability, highlighting the impracticality of avoiding annealing in the freeze-drying process. Extensive annealing not only enhances the storage stability of probiotic products but also provides greater control over the freeze-drying process, ensuring homogeneous and reproducible products. This study underscores the importance of material thickness in freeze-dried pellets for optimizing storage stability for probiotic formulations, and emphasize the necessity of annealing as a critical step in freeze-drying quenched pellets to achieve desired structural and stability outcomes.

Tomographic X-ray imaging techniques offer novel opportunities for studying membranes and membrane processes in 3D on a spatial resolution not seen before. Traditional 2D imaging techniques used to characterise membranes have limitations that can be overcome by tomographic X-ray imaging. Tomographic X-ray imaging can provide information in 2D/3D or 4D (3D plus time) on membranes, membrane modules, and membrane processes on a scale ranging from micro- to nanometre. They offer the possibility to uncover many fundamental issues related to membrane science, including the detection and monitoring of macroscopic biofilm formation, scaling, and cake build-up. High-resolution nanotomographic X-ray imaging enables even microscopic characterisations such as pore size distribution or pore network analysis. This Perspective paper introduces the tomographic X-ray imaging techniques with the most potential for membrane science: microtomography, nanotomography, holotomography, and ptychotomography, and presents their applications in the literature regarding the field of membrane science. Based on these findings and our experiences opportunities, challenges, and limitations of tomographic X-ray imaging techniques are discussed. It is concluded that in the near future tomographic X-ray imaging techniques will become increasingly common analytical techniques for membrane manufacturers, scientists, and users.

Highly anisotropic cellulose nanofibrils can solidify liquid water, creating self-supporting structures by incorporating a tiny number of fibrils. These fibrillar hydrogels can contain as much as 99.99 wt% water. The structure and mechanical properties of fibrillar networks have so far not been completely understood, nor how they solidify the bulk water at such low particle concentrations. In this work, the mechanical properties of cellulose fibrillar hydrogels in the dilute regime from a wt% perspective have been studied, and an elastoplastic model describing the network structure and its mechanics is presented. A significant insight from this work is that the ability of the fibrils to solidify water is very dependent on particle stiffness and the number of contact points it can form in the network structure. The comparison between the experimental results and the theoretical model shows that the fibrillar networks in the dilute regime form via a non-stochastic process since the fibrils have the time and freedom to find contact points during network formation by translational and rotational diffusion. The formed, dilute fibrillar network deforms by sliding fibril contacts upon straining the network beyond its elastic limit. Our results also show that before macroscopic failure, the fibril contacts are restored once the load is released. The exceptional properties of this solidified water are exploited to host fluidic channels, allowing directed fluid transportation in water. Finally, the microfluidic channels formed in the hydrogels are tailored by the layer-by-layer technique to be interactive against external stimuli, a characteristic envisioned to be useful in biomedical applications.

The advent of diffraction-limited storage rings (DLSRs) has boosted the brilliance or coherent flux by one to two orders of magnitude with respect to the previous generation. One consequence of this brilliance enhancement is an increase in the flux density or number of photons per unit of area and time, which opens new possibilities for the spatiotemporal resolution of X-ray imaging techniques. This paper studies the time-resolved microscopy capabilities of such facilities by benchmarking the ForMAX beamline at the MAX IV storage ring. It is demonstrated that this enhanced flux density using a single harmonic of the source allows micrometre-resolution time-resolved imaging at 2000 tomograms per second and 1.1 MHz 2D acquisition rates using the full dynamic range of the detector system.

In this work, regenerated cellulose textile fibers, Ioncell-F, dry-wet spun with different draw ratios, have been investigated by scanning wide-angle X-ray scattering (WAXS) using a mesoscopic X-ray beam. The fibers were found to be homogeneous on the 500 nm length scale. Analysis of the azimuthal angular dependence of a crystalline Bragg spot intensity revealed a radial dependence of the degree of orientation of crystallites that was found to increase with the distance from the center of the fiber. We attribute this to radial velocity gradients during the extrusion of the spin dope and the early stage of drawing. On the other hand, the fiber crystallinity was found to be essentially homogeneous over the fiber cross section.

Strength, ductility, and failure properties of metals are tailored by plastic deformation routes. Predicting these properties requires modeling of the structural dynamics and stress evolution taking place on several length scales. Progress has been hampered by a lack of representative 3D experimental data at industrially relevant degrees of deformation. We present an X-ray imaging based 3D mapping of an aluminum polycrystal deformed to the ultimate tensile strength (32% elongation). The extensive dataset reveals significant intra-grain stress variations (36 MPa) up to at least half of the inter-grain variations (76 MPa), which are dominated by grain orientation effects. Local intra-grain stress concentrations are candidates for damage nucleation. Such data are important for models of structure-property relations and damage.

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