Synchrotron X-ray Microtomography Research Articles

Mechanistic studies of atmospheric pitting corrosion of stainless steel for ILW containers

Atmospheric pitting corrosion of stainless steel was examined with synchrotron X-ray microtomography, laboratory based tests and electrochemical measurements in order to provide a mechanistic basis for the development of corrosion prediction models. It was found that the morphology of corrosion pits was affected by the presence of residual ferrite, and some pits showed dense covers that may affect pit stability. Fluctuations in relative humidity may lead to partial or complete repassivation of pits, sometimes leading to the formation of new pits. Electrochemical measurements in artificial pits containing concentrated salt solutions show a strong dependence of the diffusion limited current density on chloride concentration.

The humerus of Eusthenopteron: a puzzling organization presaging the establishment of tetrapod limb bone marrow.

Because of its close relationship to tetrapods, Eusthenopteron is an important taxon for understanding the establishment of the tetrapod body plan. Notably, it is one of the earliest sarcopterygians in which the humerus of the pectoral fin skeleton is preserved. The microanatomical and histological organization of this humerus provides important data for understanding the evolutionary steps that built up the distinctive architecture of tetrapod limb bones. Previous histological studies showed that Eusthenopteron's long-bone organization was established through typical tetrapod ossification modalities. Based on a three-dimensional reconstruction of the inner microstructure of Eusthenopteron's humerus, obtained from propagation phase-contrast X-ray synchrotron microtomography, we are now able to show that, despite ossification mechanisms and growth patterns similar to those of tetrapods, it also retains plesiomorphic characters such as a large medullary cavity, partly resulting from the perichondral ossification around a large cartilaginous bud as in actinopterygians. It also exhibits a distinctive tubular organization of bone-marrow processes. The connection between these processes and epiphyseal structures highlights their close functional relationship, suggesting that either bone marrow played a crucial role in the long-bone elongation processes or that trabecular bone resulting from the erosion of hypertrophied cartilage created a microenvironment for haematopoietic stem cell niches.

Ptinid beetles from the Cretaceous gymnosperm-dominated forests

The diversity of ptinid beetles (Coleoptera: Ptinidae) is described from Cretaceous amber that originated from the North Atlantic and Western Tethian resiniferous forests. All studied specimens belong to the subfamily Anobiinae. Stegobium raritanensis sp. nov. is described from Raritan amber (Turonian in age) of Sayreville (New Jersey, USA), whereas Actenobius magneoculus sp. nov. is described from San Just amber (early Albian in age) of Utrillas (Teruel Province, Spain). Both species have been examined using propagation phase-contrast X-ray synchrotron microtomography. An additional specimen from Peñacerrada I amber (Moraza, Burgos Province, Spain) is described without further taxonomic placement due to poor preservation. The Spanish specimens represent the most ancient adult record of the family Ptinidae to date. Mesernobius anawrahtai from Burmese amber (late Albian–early Cenomanian in age), the only previously described Cretaceous ptinid species, is transferred to Scirtidae based on a re-examination of the holotype. Hypotheses about ecological habits of fossil ptinids are also provided.

Combining X-ray microtomography and three-dimensional digital volume correlation to track microstructure evolution during sintering of copper powder

Optimising the manufacture, and ultimately the mechanical performance, of powder-processed components requires an understanding of how the state of the material evolves during processing and in particular during the final sintering stage. Synchrotron X-ray microtomography has been employed to follow in situ the evolution of particle microstructure during sintering of copper powder. In particular, three-dimensional digital volume correlation of a time-lapse computed tomography image sequence allows accurate quantification of the three-dimensional movements of the particles and thereby local strain for the first time. Strains are quantified both at a coarse scale across the whole powder assembly and at higher magnification for a smaller local region of interest. Unsurprisingly, the rate of shrinkage is observed to decrease with sintering time in accordance with changes in the overall density. Heterogeneities in straining within the body are observed at the several particle level, often associated with anisotropic shrinkage in part associated with non-uniform movement and densification of small aggregates of particles between which significant changes in shrinkage are observed. These differences in shrinkage could be responsible for cracking on further densification.

Plant inclusions from the Cenomanian flints of Archingeay, Les Nouillers, western France

Here, we report flint nodules bearing fossil plant inclusions from the early Cenomanian of the Font-de-Benon sand quarry, between the villages of Archingeay and Les Nouillers, Charente-Maritime, western France. The broken-open surfaces of these dense siliceous rocks only partly show the whole diversity, which is established using a non-destructive, multi-scale approach based on propagation phase-contrast X-ray synchrotron microtomography. The conifer genera Brachyphyllum, Frenelopsis, Geinitzia, and Glenrosa have three-dimensional preservation, and vegetative and reproductive organs are in connection in some cases. The flint nodules formed by silicification of Cenomanian sediments, probably as a result of an intensive period of soil alteration and leaching under warm and wet climate during the Eocene. Although the time was long between the Cenomanian sedimentation and the Eocene silicification, the fossil plants show three-dimensional external morphology. These mineralizations are interpreted as fine silica microcrystallization over the cell walls and thus are examples of late silica permineralization. The association of foraminifers, echinoids, sponge spicules, and conifers suggests that the Cenomanian sediments were deposited in a coastal and open to the sea palaeoenvironment, near a conifer-dominated mangrove.

The 3D quantitative lattice and shape preferred orientation of a mylonitised metagranite from Monte Rosa (Western Alps): Combining neutron diffraction texture analysis and synchrotron X-ray microtomography

Two complementary 3D techniques, neutron diffraction and synchrotron X-ray microtomography (SXR-μCT), were used to compare the Shape and Lattice Preferred Orientations of a mylonitised metagranite from the Monte Rosa unit (Western Alps, Italy). The goal of using these techniques was to obtain two different orientation distribution functions. Although the two functions describe relatively independent characteristics of the rock fabric, nonetheless they also exhibit close relationships to macroscopic fabrics and may be complementarily used to quantify rock fabrics and microstructures, thereby highlighting 3D features that cannot be obtained with either technique, if used independently. We describe an approach that can be potentially useful in various disciplines, e.g., structural geology, rock mechanics, tectonics and geophysics, when a complete data set of preferred orientations and size distribution is needed.Micas display a strong orthorhombic symmetry between mesoscopic lineation and microscopic SPO and LPO, whereas quartz and feldspars are characterised by a monoclinic symmetry between mesoscopic lineation and LPO. These observations suggest a rheological decoupling between the weak phase mica layers and the stronger quartz + feldspar layers. This mechanical decoupling occurred during the Alpine subduction-collision, when the Monte Rosa unit was part of the Insubric Line system and accommodated large vertical strain.

Crystallization of hydrated and anhydrous salts in porous limestone resolved by synchrotron X-ray microtomography

The crystallization processes of two anhydrous salts (NaCl and Na2SO4) and one hydrated (sodium sulfate) salt in the pore space of a natural building stone, Savonnières limestone, are studied. We imaged the salt solution distribution before and after crystallization and the solid crystal distribution in between repeated crystallization cycles using synchrotron X-ray microtomography. This technique proves to be very useful to study salt crystallization processes at the pore scale. The use of simultaneous phase-and-amplitude retrieval during X-ray tomographic reconstruction allows a clear segmentation of sodium sulfate solution and hydrated sodium sulfate crystals without the need for a dopant. Salt crystals can precipitate under unconfined as well as confined conditions in the multiple pore systems of Savonnières limestone, depending on their interconnection. Salt solution and salt crystals are located in mechanically weak zones of the limestone, which can be linked to damage patterns observed in this stone after repeated salt weathering cycles. The distribution and the process of pore filling by salt crystals that are revealed here advance the understanding of salt damage in porous media and may open ways to perform remediation.

The presumed hagfish Myxineidus gononorum from the Upper Carboniferous of Montceau-les-Mines (Saône-et-Loire, France): New data obtained by means of Propagation Phase Contrast X-ray Synchrotron Microtomography

The re-examination of the presumed hagfish Myxineidus gononorum from the Carboniferous of Montceau-les-Mines by means of propagation phase contrast X-ray synchrotron microtomography confirms the presence of two series of non-mineralized denticles arranged in chevrons in the oral region. It also indicates the presence of possible traces of post-mortem mineralized soft tissues. A peculiar zone of less X ray-absorbing matter around the animal suggests the presence of an enlarged, lamprey-like oral disc. Re-interpreting Myxineidus as a lamprey would be in better agreement with the reputedly fresh-water environment of the Montceau-les-Mines Lagerstätte.

Measurement of Local Plastic Deformation in Aluminum Alloy by Means of X-ray 3D Imaging Technique

To understand the local deformation behavior is very important for improvement of deformability in aluminum alloys which possess poor deformation limit in comparison with steels. However, measurement of local deformation in the interior of metal is not sufficiently carried out. In this study, the development of local plastic strain is measured by means of X-ray 3D imaging technique, i.e. high-resolution synchrotron X-ray microtomography. The marker tracking method, which is based on 3D image processing in volumetric image, is developed for obtaining local strains in 3D. Deformation behaviour is particularly different in individual grains. It was found that grains with different orientations deform maintaining harmony by shear deformation.

Pore-scale dynamics of salt transport and distribution in drying porous media

Understanding the physics of water evaporation from saline porous media is important in many natural and engineering applications such as durability of building materials and preservation of monuments, water quality, and mineral-fluid interactions. We applied synchrotron x-ray micro-tomography to investigate the pore-scale dynamics of dissolved salt distribution in a three dimensional drying saline porous media using a cylindrical plastic column (15 mm in height and 8 mm in diameter) packed with sand particles saturated with CaI2 solution (5% concentration by mass) with a spatial and temporal resolution of 12 μm and 30 min, respectively. Every time the drying sand column was set to be imaged, two different images were recorded using distinct synchrotron x-rays energies immediately above and below the K-edge value of Iodine. Taking the difference between pixel gray values enabled us to delineate the spatial and temporal distribution of CaI2 concentration at pore scale. Results indicate that during early stages of evaporation, air preferentially invades large pores at the surface while finer pores remain saturated and connected to the wet zone at bottom via capillary-induced liquid flow acting as evaporating spots. Consequently, the salt concentration increases preferentially in finer pores where evaporation occurs. Higher salt concentration was observed close to the evaporating surface indicating a convection-driven process. The obtained salt profiles were used to evaluate the numerical solution of the convection-diffusion equation (CDE). Results show that the macro-scale CDE could capture the overall trend of the measured salt profiles but fail to produce the exact slope of the profiles. Our results shed new insight on the physics of salt transport and its complex dynamics in drying porous media and establish synchrotron x-ray tomography as an effective tool to investigate the dynamics of salt transport in porous media at high spatial and temporal resolution.

Enzymatic oxidation as a potential new route to produce polysaccharide aerogels

Specific enzymatic oxidation of terminal galactosyl-containing polysaccharides (guar galactomannan (GM), and tamarind seed galactoxyloglucan (XG)) was used to prepare hydrogels. The hydrogels were lyophilized to form novel types of polysaccharide aerogels: biobased and biodegradable, lightweight, and stiff materials. The compressive moduli of the aerogels were greatly dependent on the oxidation, polysaccharide type, freezing method, and ambient moisture. Ice crystal templated, oriented aerogels from oxidized XG (XG-OX) showed the highest compressive modulus, 359 kPa, when determined parallel to the freezing and drying direction (i.e., the vertical direction). The water vapor sorption of freeze-dried GM and XG was not significantly affected by oxidation, even though the oxidized GM (GM-OX) and XG-OX aerogels were no longer water-soluble. GM-OX and XG-OX aerogels absorbed liquid water 40 and 20 times their initial weight, respectively. Focused ion beam scanning electron microscopy showed that the inner structure of oriented aerogels from GM-OX consisted of a honeycomb architecture with a pore diameter of some tens of micrometers. On the other hand, corresponding aerogels from XG-OX seemed to contain longer capillaries oriented in the freezing direction. This observation was supported by imaging the XG-OX aerogels using high-resolution synchrotron X-ray microtomography. The enzymatic hydro- and aerogel preparation method is considered a green way to obtain novel, functional products from polysaccharides.

Experimental quantification of permeability of partially molten mantle rock

Melt percolation in mantle rocks is currently poorly constrained, especially at low melt fractions. At mid-ocean ridges, for example, geochemical and geophysical observations produce divergent estimates of how much melt is present in the mantle and how quickly it moves. Accurate estimates of permeability and grain-scale melt distribution in mantle rock are necessary to reconcile these observations. We present three-dimensional (3-D), 700 nm-resolution images of olivine–basalt aggregates, containing nominal melt fractions (ϕn) between 0.02 and 0.20. Samples were prepared from a powdered mixture of San Carlos olivine and high-alumina basalt and hot-pressed in a solid-medium piston–cylinder apparatus at 1350 °C and 1.5 GPa. Images were obtained using synchrotron X-ray microtomography (SXμT) from the Advance Photon Source at Argonne National Laboratory. Stokes flow simulations, conducted using the digital melt volume as the numerical domain, determine that the permeabilities of experimental charges range from 2×10−16 to 5×10−13 m2 for ϕn=0.02 to 0.20, respectively. The simulation results are well represented by the power-law relation between permeability (k) and melt fraction (ϕ), k=ϕnd2/C, where n=2.6±0.2, and assuming a grain size of 35 μm in the experiments, C=58−22+36. These results place important new constraints on rates of melt migration and melt extraction within partially molten regions of the mantle.

Evaluation of sintering stress from 3-D visualization of microstructure: Case study of glass films sintered by viscous flow and imaged by X-ray microtomography

The sintering stress is a driving force for morphological evolution of pores in sintering, and can be determined from knowledge of the microstructure. The sintering stress of non-equilibrium, non-uniform and non-isotropic porous glass films cast and sintered on rigid substrates was computed from synchrotron X-ray microtomography data. This method was able to show how the inhomogeneous distribution of local density at the particle scale led to a difference in local sintering stress. The anisotropic microstructure in the film was correlated to the deviatoric components of the sintering stress, which were defined by surface energy tensor. The topological evolution of pore structure was characterized by genus and Euler characteristic.

Cockroaches Probably Cleaned Up after Dinosaurs

Dinosaurs undoubtedly produced huge quantities of excrements. But who cleaned up after them? Dung beetles and flies with rapid development were rare during most of the Mesozoic. Candidates for these duties are extinct cockroaches (Blattulidae), whose temporal range is associated with herbivorous dinosaurs. An opportunity to test this hypothesis arises from coprolites to some extent extruded from an immature cockroach preserved in the amber of Lebanon, studied using synchrotron X-ray microtomography. 1.06% of their volume is filled by particles of wood with smooth edges, in which size distribution directly supports their external pre-digestion. Because fungal pre-processing can be excluded based on the presence of large particles (combined with small total amount of wood) and absence of damages on wood, the likely source of wood are herbivore feces. Smaller particles were broken down biochemically in the cockroach hind gut, which indicates that the recent lignin-decomposing termite and cockroach endosymbionts might have been transferred to the cockroach gut upon feeding on dinosaur feces.

Propagation-based phase-contrast X-ray microtomography of a cerebral protection device retrieved after carotid artery stenting

Phase-contrast synchrotron X-ray microtomography (pcSyncX) based on the highly coherent X-ray beam has previously been used to visualize the microstructures of biologic specimens, but it has never been used to evaluate embolic debris adherent on a cerebral protection device (CPD). The purpose of this study was to demonstrate the feasibility of pcSyncX for evaluating embolic debris during carotid artery stenting (CAS). Five patients (four males, age range 67-77 years) with severe carotid artery stenosis underwent CAS. The retrieved CPD was exposed to synchrotron radiation and 1000 pcSyncX projection images were obtained by rotating the CPD through 180°. An X-ray shadow of a CPD was converted into a visual image by the scintillator. After microtomographic reconstruction, the three-dimensionally reconstructed images were further segmented into the embolic debris and CPD. The total volume of emboli was calculated by summing the volume at each scanning level. The number of membrane pores covered by emboli as seen from the outer surface was counted and the percentage of covered area was calculated. Embolic debris was clearly demonstrated not only on the inner surface and within pores but also on the outer surface of the CPD. The mean total volume of embolic debris was 0.538 × 10(-6) mm(3) (range 0.225-0.965 × 10(-6) mm(3)). Most (61.5%) of the debris was located at the apical one-third of the CPD and 20.8% of the pore area was covered by debris.

Three dimensional post-mortem study of damage after compression of cast Al–Si alloys

The damage introduced by compressive deformation at room temperature and 300°C in three cast AlSi alloys with different additions of Cu and Ni is investigated by synchrotron X-ray microtomography. The same damage mechanisms are identified for all alloys independent of the heat treatment and test temperature: fracture of aluminides, fracture of eutectic Si, debonding between Si and Al-matrix, debonding between aluminides and Al-matrix and fracture of primary Si. The volume fraction of damage decreases with solution treatment time and deformation temperature due to the partial spheroidisation of rigid phases and increase in flowability of the matrix, respectively. The morphology of voids is quantified in terms of their three-dimensional aspect ratio and is correlated with their orientation to obtain information on the load carrying capability of the networks formed by Si and aluminides.

Applications of synchrotron X-ray micro-tomography on nondestructive 3D studies of diesel nozzle internal micro-structure

In diesel engines, the fuel spray breakup and atomization process have tremendous dependence on the nozzle internal geometries, then the performance, fuel consumption and emission of the engines will be affected. Based on the synchrotron X-ray micro-tomography, the three-dimensional models of the diesel nozzles were established. Then the internal geometries of the nozzle orifices, such as the diameter, the length and the inlet chamfer radius of the orifice, can be measured, making it possible to analyze the impact of different nozzle orifice processing methods. Meanwhile, the nozzle digital models were successfully applied to simulate the internal flow of high pressure fuel inside the nozzle; the effects of nozzle geometries on internal flow characteristics have been analyzed. The results show that these works are significant to the promoting of diesel nozzle processing technologies, and the revealing of high pressure fuel spray breakup mechanism.

Micro-pore development phenomenon in hydrogen pre-charged aluminum alloy studied using synchrotron X-ray micro-tomography

The paper provides an insight into the development of the micro-pore damage phenomenon during the hydrogen ingress and egress in a high strength aluminum alloy. High resolution micro tomography scans on samples subjected to combinations of cathodic hydrogen charging and de-sorption heat treatment were carried out. The quantitative analysis, spatial mapping, and probabilistic evaluation of the 3D datasets revealed that the development of micro-pore damage during hydrogen ingress–egress had a non-trivial dependence on the particle size distribution. This provides a rationale to mitigate the deleterious effects of hydrogen in aluminum alloys by controlling particle size characteristics.

Three-dimensional morphology of the Sinocyclocheilus hyalinus (Cypriniformes : Cyprinidae) horn based on synchrotron X-ray microtomography.

Sinocyclocheilus is a cave-dwelling cyprinid genus endemic to southwest China. Several species possess a conspicuous horn on their head, which has been suggested as a constructive troglomorphic trait but lacks substantial evidence. We used non-invasive, high spatial resolution synchrotron X-ray microtomography to investigate the three-dimensional (3D) morphology of the horn of Sinocyclocheilus hyalinus, one of eight such troglobiotic species. 3D renderings demonstrated the osteological components, which were comprised of a rear wall comprised of the supraoccipital bone, a remaining frontal wall with numerous fenestrae, and the bottom continuous with the parietal and epiotic. A horn cavity occurred within the horn. The fenestrae in the frontal wall were continuous in the horn cavity and showed elaborate channeling, and were, connected to the cranial cavity by soft tissue. We tentatively called this configuration the "otocornual connection" due to its anatomic and putative functional similarity to the otolateralic connection in clupeids and loricariids, which provide an indirect pathway to enhance perception of underwater sound signals. This study provides a functional morphology context for further histological and physiological investigations of such horn structures in Sinocyclocheilus cavefish, and we suggest that the horn might enhance acoustic perception to compensate for visual loss in subterranean life, which warrants future physiological examination as lab-reared S. hyalinus become available.

Characterization of crocodile teeth: Correlation of composition, microstructure, and hardness

Structure and composition of teeth of the saltwater crocodile Crocodylus porosus were characterized by several high-resolution analytical techniques. X-ray diffraction in combination with elemental analysis and infrared spectroscopy showed that the mineral phase of the teeth is a carbonated calcium-deficient nanocrystalline hydroxyapatite in all three tooth-constituting tissues: Dentin, enamel, and cementum. The fluoride content in the three tissues is very low (<0.1 wt.%) and comparable to that in human teeth. The mineral content of dentin, enamel, and cementum as determined by thermogravimetry is 71.3, 80.5, and 66.8 wt.%, respectively. Synchrotron X-ray microtomography showed the internal structure and allowed to visualize the degree of mineralization in dentin, enamel, and cementum. Virtual sections through the tooth and scanning electron micrographs showed that the enamel layer is comparably thin (100-200 μm). The crystallites in the enamel are oriented perpendicularly to the tooth surface. At the dentin-enamel-junction, the packing density of crystallites decreases, and the crystallites do not display an ordered structure as in the enamel. The microhardness was 0.60±0.05 GPa for dentin, 3.15±0.15 GPa for enamel, 0.26±0.08 GPa for cementum close to the crown, and 0.31±0.04 GPa for cementum close to the root margin. This can be explained with the different degree of mineralization of the different tissue types and is comparable with human teeth.