Experimental Investigations of Fracture Process in Concrete by Means of X‐ray Micro‐computed Tomography

The paper describes investigation results on fracture in notched concrete beams under quasi‐static three‐point bending by the X‐ray micro‐computed tomography. The two‐dimensional (2D) and three‐dimensional image procedures were used. Attention was paid to width, length, height and shape of cracks along beam depth. In addition, the displacements on the surface of concrete beams during the deformation process were measured with the 2D digital image correlation technique in order to detect strain localisation before a discrete crack occurred. The 2D fracture patterns in beams were numerically simulated with the finite‐element method using an isotropic damage constitutive model enhanced by a characteristic length of micro‐structure. Concrete was modelled as a random heterogeneous four‐phase material composed of aggregate, cement matrix, interfacial transitional zones and air voids. The advantages of the X‐ray micro‐computed tomography were outlined.     

Nano‐Sized CT Contrast Agents

Computed tomography (CT) is one of the most widely used clinical imaging modalities. In order to increase the sensitivity of CT, small iodinated compounds are used as injectable contrast agents. However, the iodinated contrast agents are excreted through the kidney and have short circulation times. This rapid renal clearance not only restricts in vivo applications that require long circulation times but also sometimes induces serious adverse effects related to the excretion pathway. In addition, the X‐ray attenuation of iodine is not efficient for clinical CT that uses high‐energy X‐ray. Due to these limitations, nano‐sized iodinated CT contrast agents have been developed that can increase the circulation time and decrease the adverse effects. In addition to iodine, nanoparticles based on heavy atoms such as gold, lanthanides, and tantalum are used as more efficient CT contrast agents. In this review, we summarize the recent progresses made in nano‐sized CT contrast agents.     

Shedding Light on Metal‐Based Nanoparticles in Zebrafish by Computed Tomography with Micrometer Resolution

Metal‐based nanoparticles are clinically used for diagnostic and therapeutic applications. After parenteral administration, they will distribute throughout different organs. Quantification of their distribution within tissues in the 3D space, however, remains a challenge owing to the small particle diameter. In this study, synchrotron radiation‐based hard X‐ray tomography (SRμCT) in absorption and phase contrast modes is evaluated for the localization of superparamagnetic iron oxide nanoparticles (SPIONs) in soft tissues based on their electron density and X‐ray attenuation. Biodistribution of SPIONs is studied using zebrafish embryos as a vertebrate screening model. This label‐free approach gives rise to an isotropic, 3D, direct space visualization of the entire 2.5 mm‐long animal with a spatial resolution of around 2 µm. High resolution image stacks are available on a dedicated internet page ( http://zebrafish.pharma-te.ch ). X‐ray tomography is combined with physico‐chemical characterization and cellular uptake studies to confirm the safety and effectiveness of protective SPION coatings. It is demonstrated that SRμCT provides unprecedented insights into the zebrafish embryo anatomy and tissue distribution of label‐free metal oxide nanoparticles.     

In‐Situ Synchrotron X‐Ray Microtomography Studies of Microstructure and Damage Evolution in Engineering Materials

In materials science X‐ray microtomography has evolved as an increasingly utilized technique for characterizing the 3D microstructure of materials. The fundamentals of X‐ray microtomography experimental methods and the reconstruction and data evaluation processes are briefly described. A review of in‐situ synchrotron X‐ray microtomography studies in literature is given. Examples of recent work include in‐situ microtomography investiagtions of metallic foams, in‐situ studies of the sintering of copper particles, and in‐situ investigations of creep damage evolution in composites. Future perspectives of in‐situ X‐ray microtomography studies in materials science are outlined.     

Application of Synchrotron Radiation Techniques for Model Validation of Advanced Structural Materials

Synchrotron radiation techniques represent powerful tools to characterize materials down to the nanometer level. This paper presents a survey of the state‐of‐the‐art synchrotron‐based techniques which are particularly well‐suited for investigating materials properties. Complementary X‐ray absorption techniques such as extended X‐ray absorption fine structure (EXAFS), X‐ray magnetic circular dichroism (XMCD), photoemission electron microscopy (PEEM) are used to address the individual local atomic structure and magnetic moments in Fe–Cr model systems. The formation of atomic clusters/precipitates in such systems is also investigated by means of scanning transmission X‐ray microscopy (STXM). Such advanced analytical techniques can not only offer valuable structural and magnetic information on such systems, they can also serve for validating computational calculations performed at different time and length scales which can help improve materials lifetime predictions.     

In Situ Probing of the Particle‐Mediated Mechanism of WO3‐Networked Structures Grown inside Confined Mesoporous Channels

Nanocasting, using ordered mesoporous silica or carbon as a hard template, has enormous potential for preparing novel mesoporous materials with new structures and compositions. Although a variety of mesoporous materials have been synthesized in recent years, the growth mechanism of nanostructures in a confined space, such as mesoporous channels, is not well understood, which hampers the controlled synthesis and further application of mesoporous materials. Here, the nucleation and growth of WO₃‐networked mesostructures within an ordered mesoporous matrix, using an in situ transmission electron microscopy heating technique and in situ synchrotron small‐angle X‐ray scattering spectroscopy, are probed. It is found that the formation of WO₃ mesostructures involves a particle‐mediated transformation and coalescence mechanism. The liquid‐like particle‐mediated aggregation and mesoscale transformation process can occur in ≈10 nm confined mesoporous channels, which is completely unexpected. The detailed mechanistic study will be of great help for experimental design and to exploit a variety of mesoporous materials for diverse applications, such as catalysis, absorption, separation, energy storage, biomedicine, and nanooptics.     

Well‐Defined Cobalt Catalyst with N‐Doped Carbon Layers Enwrapping: The Correlation between Surface Atomic Structure and Electrocatalytic Property

Admittedly, the surface atomic structure of heterogenous catalysts toward the electrochemical oxygen reduction reaction (ORR) are accepted as the important features that can tune catalytic activity and even catalytic pathway. Herein, a surface engineering strategy to controllably synthesize a carbon‐layer‐wrapped cobalt‐catalyst from 2D cobalt‐based metal–organic frameworks is elaborately demonstrated. Combined with synchrotron radiation X‐ray photoelectron spectroscopy, the soft X‐ray absorption near‐edge structure results confirmed that rich covalent interfacial Co? N? C bonds are efficiently formed between cobalt nanoparticles and wrapped carbon‐layers during the polydopamine‐assisted pyrolysis process. The X‐ray absorption fine structure and corresponding extended X‐ray absorption fine structure spectra further reveal that the wrapped cobalt with Co–N coordinations shows distinct surface distortion and atomic environmental change of Co‐based active sites. In contrast to the control sample without coating layers, the 800 °C‐annealed cobalt catalyst with N‐doped carbon layers enwrapping achieves significantly enhanced ORR activity with onset and half‐wave potentials of 0.923 and 0.816 V (vs reversible hydrogen electrode), highlighting the important correlation between surface atomic structure and catalytic property.     

On the Application of X‐ray Microtomography in the Field of Materials Science

The principle of the tomography technique and the different possible set‐ups, which can be used to obtain medium‐(10 μm) and high‐(1 μm) resolution, three‐dimensional, non‐destructive images, are shown in this paper. Illustrations are made of the applications of the technique in the field of materials science. Examples are given for medium‐resolution images of metallic foams and model metal matrix composites that are reinforced with spherical particles. High‐resolution examples are shown for aluminium alloys. For low‐absorbent materials we show that the phase contrast obtained using synchrotron radiation can provide a valuable solution. The quantitative use of these images, coupled with in‐situ tensile tests or used for the simple analysis of the initial microstructure of several structural materials, is also described.     

Flexible,Printable Soft‐X‐Ray Detectors Based on All‐Inorganic Perovskite Quantum Dots

Metal halide perovskites represent a family of the most promising materials for fascinating photovoltaic and photodetector applications due to their unique optoelectronic properties and much needed simple and low‐cost fabrication process. The high atomic number (Z) of their constituents and significantly higher carrier mobility also make perovskite semiconductors suitable for the detection of ionizing radiation. By taking advantage of that, the direct detection of soft‐X‐ray‐induced photocurrent is demonstrated in both rigid and flexible detectors based on all‐inorganic halide perovskite quantum dots (QDs) synthesized via a solution process. Utilizing a synchrotron soft‐X‐ray beamline, high sensitivities of up to 1450 µC Gy_air^?1 cm^?2 are achieved under an X‐ray dose rate of 0.0172 mGy_air s^?1 with only 0.1 V bias voltage, which is about 70‐fold more sensitive than conventional α‐Se devices. Furthermore, the perovskite film is printed homogeneously on various substrates by the inexpensive inkjet printing method to demonstrate large‐scale fabrication of arrays of multichannel detectors. These results suggest that the perovskite QDs are ideal candidates for the detection of soft X‐rays and for large‐area flat or flexible panels with tremendous application potential in multidimensional and different architectures imaging technologies.     

基于SR-CT技术的泡沫铝力学性能

基于同步辐射计算机断层技术（简称SR-CT技术）,对泡沫铝材料试件进行三维无损重建,获取泡沫铝材料试件的内部体结构。在此基础上,建立泡沫铝试件的三维仿真模型,并对该模型进行模拟计算,以研究泡沫铝材料在压缩过程中的变形情况、米塞斯应力分布情况及其弹塑性区域的分布。研究结果表明,基于同步辐射计算机断层技术重建结果建立的三维...     

Breaking the Depth Dependence by Nanotechnology‐Enhanced X‐Ray‐Excited Deep Cancer Theranostics

The advancements in nanotechnology have created multifunctional nanomaterials aimed at enhancing diagnostic accuracy and treatment efficacy for cancer. However, the ability to target deep‐seated tumors remains one of the most critical challenges for certain nanomedicine applications. To this end, X‐ray‐excited theranostic techniques provide a means of overcoming the limits of light penetration and tissue attenuation. Herein, a comprehensive overview of the recent advances in nanotechnology‐enhanced X‐ray‐excited imaging and therapeutic methodologies is presented, with an emphasis on the design of multifunctional nanomaterials for contrast‐enhanced computed tomography (CT) imaging, X‐ray‐excited optical luminescence (XEOL) imaging, and X‐ray‐excited multimodal synchronous/synergistic therapy. The latter is based on the concurrent use of radiotherapy with chemotherapy, gas therapy, photodynamic therapy, or immunotherapy. Moreover, the featured biomedical applications of X‐ray‐excited deep theranostics are discussed to highlight the advantages of X‐ray in high‐sensitivity detection and efficient elimination of malignant tumors. Finally, key issues and technical challenges associated with this deep theranostic technology are identified, with the intention of advancing its translation into the clinic.     

Synthesis of BSA‐Coated BiOI@Bi2S3 Semiconductor Heterojunction Nanoparticles and Their Applications for Radio/Photodynamic/Photothermal Synergistic Therapy of Tumor

Developing an effective theranostic nanoplatform remains a great challenge for cancer diagnosis and treatment. Here, BiOI@Bi₂S₃@BSA (bovine serum albumin) semiconductor heterojunction nanoparticles (SHNPs) for triple‐combination radio/photodynamic/photothermal cancer therapy and multimodal computed tomography/photoacoustic (CT/PA) bioimaging are reported. On the one hand, SHNPs possess strong X‐ray attenuation capability since they contain high‐Z elements, and thus they are anticipated to be a very competent candidate as radio‐sensitizing materials for radiotherapy enhancement. On the other hand, as a semiconductor, the as‐prepared SHNPs offer an extra approach for reactive oxygen species generation based on electron–hole pair under the irradiation of X‐ray through the photodynamic therapy process. This X‐ray excited photodynamic therapy obviously has better penetration depth in bio‐tissue. What's more, the SHNPs also possess well photothermal conversion efficiency for photothermal therapy, because Bi₂S₃ is a thin band semiconductor with strong near‐infrared absorption that can cause local overheat. In vivo tumor ablation studies show that synergistic radio/photodynamic/photothermal therapy achieves more significant therapeutic effect than any single treatment. In addition, with the strong X‐ray attenuation and high near‐infrared absorption, the as‐obtained SHNPs can also be applied as a multimodal contrast agent in CT/PA imaging.     

Anti‐Biofouling Polymer‐Decorated Lutetium‐Based Nanoparticulate Contrast Agents for In Vivo High‐Resolution Trimodal Imaging

Nanomaterials have gained considerable attention and interest in the development of novel and high‐resolution contrast agents for medical diagnosis and prognosis in clinic. A classical urea‐based homogeneous precipitation route that combines the merits of in situ thermal decomposition and surface modification is introduced to construct polyethylene glycol molecule (PEG)‐decorated hybrid lutetium oxide nanoparticles (PEG–UCNPs). By utilizing the admirable optical and magnetic properties of the yielded PEG–UCNPs, in vivo up‐conversion luminescence and T₁‐enhanced magnetic resonance imaging of small animals are conducted, revealing obvious signals after subcutaneous and intravenous injection, respectively. Due to the strong X‐ray absorption and high atomic number of lanthanide elements, X‐ray computed‐tomography imaging based on PEG–UCNPs is then designed and carried out, achieving excellent imaging outcome in animal experiments. This is the first example of the usage of hybrid lutetium oxide nanoparticles as effective nanoprobes. Furthermore, biodistribution, clearance route, as well as long‐term toxicity are investigated in detail after intravenous injection in a murine model, indicating the overall safety of PEG–UCNPs. Compared with previous lanthanide fluorides, our nanoprobes exhibit more advantages, such as facile construction process and nearly total excretion from the animal body within a month. Taken together, these results promise the use of PEG–UCNPs as a safe and efficient nanoparticulate contrast agent for potential application in multimodal imaging.     

DVC‐based image subtraction to detect microcracking in lightweight concrete

This paper presents an image subtraction technique based on digital volume correlation to detect and extract the complex network of microcracks that progressively developed in a lightweight concrete sample submitted in situ to uniaxial compression and imaged by X‐ray computed tomography. From local digital volume correlation measurements, performed only on positions with sufficient image contrast, the mechanical transformation is estimated at all voxels within the whole sample using an adjusted interpolation procedure that computes an affine approximation of the local transformation. The deformed image (containing cracks) is thus transformed back to the same frame as the reference image (without cracks) to compute the difference between both images, taking into account possible brightness and contrast adjustments. The resulting subtracted image reveals the path of cracks, which is clearly visible without the underlying heterogeneous microstructure of the concrete. The detection accuracy is here estimated to one tenth of a voxel, allowing early‐age cracks to be detected while they would barely have been noticed on the X‐ray computed tomography images. Segmentation of the crack network is also made much easier. To overcome a low signal‐to‐noise ratio for the tiniest cracks, a Hessian‐based filter is used to extract the complex crack network. The cracks can be directly located in the microstructure segmented in the reference image and compared for all loading steps to characterise their initiation and propagation.     

A Review of X-Ray Imaging at the BAMline (BESSY II)

The hard X-ray beamline BAMline at BESSY II (Berlin, Germany) has now been in service for 20 years. Several improvements have been implemented in this time, and this review provides an overview of the imaging methods available at the BAMline. Besides classic full-field synchrotron X-ray computed tomography (SXCT), also absorption edge CT, synchrotron X-ray refraction radiography (SXRR), and synchrotron X-ray refraction tomography (SXRCT) are used for imaging. Moreover, virtually any of those techniques are currently coupled in situ or operando with ancillary equipment such as load rigs, furnaces, or potentiostats. Each of the available techniques is explained and both the current and the potential usage are described with corresponding examples. The potential use is manifold, the examples cover organic materials, composite materials, energy-related materials, biological samples, and materials related to additive manufacturing. The article includes published examples as well as some unpublished applications.     

Magneto‐Plasmonic Au‐Fe Alloy Nanoparticles Designed for Multimodal SERS‐MRI‐CT Imaging

Diagnostic approaches based on multimodal imaging are needed for accurate selection of the therapeutic regimens in several diseases, although the dose of administered contrast drugs must be reduced to minimize side effects. Therefore, large efforts are deployed in the development of multimodal contrast agents (MCAs) that permit the complementary visualization of the same diseased area with different sensitivity and different spatial resolution by applying multiple diagnostic techniques. Ideally, MCAs should also allow imaging of diseased tissues with high spatial resolution during surgical interventions. Here a new system based on multifunctional Au‐Fe alloy nanoparticles designed to satisfy the main requirements of an ideal MCA is reported and their biocompatibility and imaging capability are described. The MCAs show easy and versatile surface conjugation with thiolated molecules, magnetic resonance imaging (MRI) and computed X‐ray tomography (CT) signals for anatomical and physiological information (i.e., diagnostic and prognostic imaging), large Raman signals amplified by surface enhanced Raman scattering (SERS) for high sensitivity and high resolution intrasurgical imaging, biocompatibility, exploitability for in vivo use and capability of selective accumulation in tumors by enhanced permeability and retention effect. Taken together, these results show that Au‐Fe nanoalloys are excellent candidates as multimodal MRI‐CT‐SERS imaging agents.     

Dynamic contact strain measurement by time‐resolved stroboscopic energy dispersive synchrotron X‐ray diffraction

Recent developments of synchrotron X‐ray sources and dedicated high‐energy beamlines are now enabling strain measurements from large volumes of industrially relevant metallic materials. Such capability is allowing the validation of novel and alternative nondestructive experimental methods of strain measurement or computational models of complex deformation processes. This study describes the first dynamic contact strain measurement of a ball bearing using stroboscopic energy dispersive X‐ray diffraction. The experiment probed the dynamic contact strain in the outer raceway of a test bearing. The inner raceway of the bearing was attached to a shaft rotating at 150 revolutions per minute, and the outer raceway, where the measurements were made, was fixed in a stationary bearing housing. A triggering system was used to synchronise the data acquisition of the energy dispersive X‐ray diffraction detector with the bearing rotation. Specifically, diffraction data were acquired, stroboscopically, from the material volume within the raceway, in a known location, when the ball was positioned directly below it. A total of 20 s of accumulated diffraction signal was recorded, acquiring 2 ms of data per revolution, providing diffraction patterns of sufficient quality for the dynamic contact strain to be measured. Macromechanical stress field was calculated from the micromechanical strains measured from five lattice planes. This allowed a comparison of the experimentally measured stress field and that of finite element simulations. Good agreement was observed between the finite element results and experimental measurements indicating the applicability of this novel dynamic strain measurement technique for tribological systems.     

3D Nanoprinted Plastic Kinoform X‐Ray Optics

High‐performance focusing of X‐rays requires the realization of very challenging 3D geometries with nanoscale features, sub‐millimeter‐scale apertures, and high aspect ratios. A particularly difficult structure is the profile of an ideal zone plate called a kinoform, which is manufactured in nonideal approximated patterns, nonetheless requires complicated multistep fabrication processes. Here, 3D fabrication of high‐performance kinoforms with unprecedented aspect ratios out of low‐loss plastics using femtosecond two‐photon 3D nanoprinting is presented. A thorough characterization of the 3D‐printed kinoforms using direct soft X‐ray imaging and ptychography demonstrates superior performance with an efficiency reaching up to 20%. An extended concept is proposed for on‐chip integration of various X‐ray optics toward high‐fidelity control of X‐ray wavefronts and ultimate efficiencies even for harder X‐rays. Initial results establish new, advanced focusing optics for both synchrotron and laboratory sources for a large variety of X‐ray techniques and applications ranging from materials science to medicine.     

3D Crack‐tip Microscopy: Illuminating Micro‐Scale Effects on Crack‐Tip Behavior

Traditionally the driving force for crack growth is described in terms of global parameters which, for continua, nevertheless reflect the local conditions at the crack‐tip. Mimicking nature, materials microstructures are now being designed at the microscale, or even the nanoscale, employing interfaces and heterogeneities to shield the propagating crack for improved resistance to sub‐critical crack growth. In such cases global approaches simply will not do. Information is needed about intrinsic damage occurring ahead, and extrinsic shielding mechanisms behind, the crack. Here, high resolution X‐ray imaging and diffraction modes analogous to those in 2D electron microscopy are combined to form a 3D “crack‐tip microscope”. In this way one can quantify the effect of microstructural scale events on the crack‐tip environment. The technique is applied to study overload phenomena under fatigue, to characterize the bridging ligaments under stress corrosion cracking and fiber bridging during fatigue of a metal matrix composite. Besides identifying shielding mechanisms, it provides three methods for calculating the effective stress intensity at the crack tip; namely from the near tip stress field, from crack face tractions and from crack opening displacements. The wider opportunities opened up by this approach to study self‐healing, transformation toughening and other microstructural toughening mechanisms are also discussed.     

Fatigue behaviors of laser hybrid welded AA7020 due to defects via synchrotron X‐ray microtomography

Defect or shrinkage is known to have a detrimental effect on the fatigue resistance of casting lightweight alloys and additively manufactured or 3D printed materials. However, very few works focus on the damage mechanism of fusion welded Al alloys due to gas pores or metallurgical defects. This paper performs an investigation on the effect of porosity on the damage evolution of laser hybrid welded 7020‐T651 alloys. The critical pore size comparable with average weld grain was assumed in terms of the population and dimension of micropores. To characterize the coupling effect between gas pores and cracks, an in situ fatigue testing rig was developed to well work at the synchrotron radiation tomography system. Combining synchrotron X‐ray microtomography and fatigue resistance testing, the pore size and location were correlated with the crack initiation and crack growth path but relatively less on the long crack propagation rate. Furthermore, the interaction between the porosity and stress concentration was elucidated by using finite element simulations, which shows that the gas pore appears to be a preferred cracking site especially near the surface.