Quantification of fluids injection in a glass-bead matrix using X-ray microtomography

Several daily activities involve the accumulation or percolation of fluids through porous media. X-ray microtomography is a non-invasive technique capable of providing images of the internal microstructure of materials showing the different phases of fluid distribution present in the sample directly or at the pore-scale. This methodology was used to qualitatively and quantitatively assess samples consisting with glass beads of standard size, which contained fluid filling a porous region. Three samples were prepared with 0.6 mm or 0.8 mm diameter glass beads inserted into a glass tube with an inner diameter of 6.7 mm and 1.0 mm wall thickness. The fluids injected were dopant salt–water solution, industrial oil and commercial oil. The samples were scanned using a Skyscan-1172 microtomographic system. All phases present in the sample were differentiated. The values of injected fluids were determined through 2D and 3D analyses. Two types of solutions were used, one doped with KI, and the other with BaCl₂·2H₂O. The percentage of KI used allowed the individualization of the solution and, therefore, the direct quantification of this phase through 2D and 3D images.     

Rock porosity quantification by dual-energy X-ray computed microtomography

Porous media investigation by X-ray microtomography allows obtaining valuable quantitative and qualitative information, while preserving sample integrity. Modern X-ray nanotomography or Synchrotron radiation systems may distinguish structures sized only hundreds of nanometers. However, pores sized less than a few microns (microporosity) may be undetectable due to the system’s spatial resolution and noise in microfocus sources, compromising the quality of the measurement. In this study a dual-energy methodology was developed to generate density-based images from two scans made at two different voltages (80 kV and 130 KV) with a microfocus bench-top microtomography system. The images obtained were quantized in 256 gray levels, where the lowest value (zero) corresponded to voids and the highest value (255) corresponded to the densest regions mapped. From density images and single energy images, porosity was evaluated and compared. Results indicate that density images present better results than single energy images when both are compared with porosity obtained by the helium injection method. In addition, images acquired in dual-energy show good agreement with the sample’s real density values.     

A 1800 K furnace designed for in situ synchrotron microtomography

A radiation furnace that covers the temperature range from room temperature up to 1800 K has been designed and constructed for in situ synchrotron microtomography. The furnace operates under a vacuum or under any inert gas atmosphere. The two 1000 W halogen heating lamps are water‐ and air‐cooled. The samples are located at the focus of these lamp reflectors on a rotary feedthrough that is connected to a driving rotation stage below the furnace. The X‐ray beam penetrates the furnace through two X‐ray‐transparent vacuum‐sealed windows. Further windows can be used for temperature control, sample changing and gas inflow and outflow.     

Accuracy evaluation of an X-ray microtomography system

Microstructural parameter evaluation of reservoir rocks is of great importance to petroleum production companies. In this connection, X-ray computed microtomography (μ-CT) has proven to be a quite useful method for the assessment of rocks, as it provides important microstructural parameters, such as porosity, permeability, pore size distribution and porous phase of the sample. X-ray computed microtomography is a non-destructive technique that enables the reuse of samples already measured and also yields 2-D cross-sectional images of the sample as well as volume rendering. This technique offers an additional advantage, as it does not require sample preparation, of reducing the measurement time, which is approximately one to three hours, depending on the spatial resolution used. Although this technique is extensively used, accuracy verification of measurements is hard to obtain because the existing calibrated samples (phantoms) have large volumes and are assessed in medical CT scanners with millimeter spatial resolution. Accordingly, this study aims to determine the accuracy of an X-ray computed microtomography system using a Skyscan 1172 X-ray microtomograph. To accomplish this investigation, it was used a nylon thread set with known appropriate diameter inserted into a glass tube. The results for porosity size and phase distribution by X-ray microtomography were very close to the geometrically calculated values. The geometrically calculated porosity and the porosity determined by the methodology using the μ-CT was 33.4 ± 3.4% and 31.0 ± 0.3%, respectively. The outcome of this investigation was excellent. It was also observed a small variability in the results along all 401 sections of the analyzed image. Minimum and maximum porosity values between the cross sections were 30.9% and 31.1%, respectively. A 3-D image representing the actual structure of the sample was also rendered from the 2-D images.     

同步辐射X射线相衬显微CT在古生物学中的应用

X射线无损成像技术在古生物化石标本研究领域中应用十分广泛.近几年来,随着技术的不断革新,同步辐射X射线相衬显微断层成像技术(SRX-PC-μCT)也被引入到这一领域.由于同步辐射光源产生的硬X射线具有高亮度、高准直性和高空间相干性等优点,可以实现化石标本高分辨率（亚微米级）的无损三维显微成像,给古生物学的发展带来了新的机遇.文章简要回顾了用于古生物化石标本无损成像技术的发展历程,并在此基础上综述了同步辐射X射线断层显微成像技术在古生物学领域的应用现状和前景.     

Nano particle fluidisation in model 2-D and 3-D beds using high speed X-ray imaging and microtomography

Nanoparticles and nanocomposites have become a major focus of interest in science and technology due to exceptional properties they provide. However, handling and processing of ultra-fine powders is very challenging because they are extremely cohesive. Fluidization is one of techniques available to process powders. It has become increasingly important to understand how these nanoparticles can be handled and processed to benefit from their favourable properties. A high spatial (down to 400 nm) and temporal resolution (down to 1 ms) X-ray imaging apparatus has been designed to study nanoparticles in fluidized beds under different gas flow velocities. The mean volume distribution of the nanoparticle agglomerates was determined with X-ray microtomography. The X-ray microtomography technique provides valuable in situ, non-destructive structural information on the morphological changes that take place during fluidisation of powder samples.     

Accuracy improvement in digital holographic microtomography by multiple numerical reconstructions

In this paper, we describe a method to improve the accuracy in digital holographic microtomography (DHMT) for measurement of thick samples. Two key factors impairing the accuracy, the deficiency of depth of focus and the rotational error, are considered and addressed simultaneously. The hologram is propagated to a series of distances by multiple numerical reconstructions so as to extend the depth of focus. The correction of the rotational error, implemented by numerical refocusing and image realigning, is merged into the computational process. The method is validated by tomographic results of a four-core optical fiber and a large mode optical crystal fiber. A sample as thick as 258 μm is accurately reconstructed and the quantitative three-dimensional distribution of refractive index is demonstrated.     

The investigation of cold sintering mechanism of iron powder compact

Abstract

In this paper the mechanism of cold sintering of iron powder compacts has been investigated. In the wide range of pressure between 4…5 and 12…12, 5 GPa, a considerable changes of properties, such as electrical resistivity, thermo-electric force, coercive force, changes in X-ray diffraction structures as well as changes of thermal properities (obtained by DTA analysis), have been determined.     

Investigation of final-stage sintering of various microsize structures prepared by micro powder injection molding

Micro powder injection molding (μPIM) has been developed as a potential technique for mass production of microcomponents in microsystems due to its shaping complexity at low cost, in which sintering is a crucial step to dictate the final properties of the microcomponents. In this paper, final-stage sintering behavior of 316L stainless steel microsize structures prepared by μPIM, φ100 μm and φ60 μm, respectively, was studied. The effect of size reduction in the regime of micrometers on the density of various microsize structures was investigated. Sintering kinetics of the microsize structures of φ100 μm and φ60 μm were studied based on particle level sintering models. It is found that the microsize structures of φ60 μm had higher density than the microsize structures of φ100 μm given the same sintering condition. The results indicate that size reduction in the regime of micrometers facilitated densification of microsize structures. The grain growth mechanism of microsize structures varied with size. Whereas the grain growth of the microsize structures of φ100 μm is governed by surface-diffusion-controlled pore drag, the grain growth of the microsize structures of φ60 μm is controlled by boundary diffusion. During densification, the microsize structures, φ100 μm and φ60 μm, are both controlled by lattice diffusion. The corresponding activation energies are reported in the paper.     

Reaction laser sintering of Ni–Al powder alloys

Laser reactive sintering, i.e., laser-induced self-propagating reaction sintering synthesis was carried out on Ni–Al powder alloys. The exothermic behaviors for the alloys with different Al content were characterized by sintering temperature curves produced from reactive heat. The phases transformed from the sintered alloys were identified by X-ray diffraction. Properties and microstructure of the sintered alloys were studied.     

Sintering behaviour and microstructures of nanostructured ZnO–ZnS core–shell powder by spark plasma sintering

Densification of nanostructured ZnO–ZnS core–shell powder was carried out by spark plasma sintering to produce a bulk ZnO–ZnS composite. By adjusting the sintering temperature, we could fabricate a bulk ZnO–ZnS composite without destroying the original core–shell structure of the powder. X-ray diffraction and transmission electron microscopy were used to characterize the microstructural properties of the core–shell powder and its sintering behaviour. During spark plasma sintering, phase transition from a sphalerite to a wurtzite structure was observed in the ZnS shell and the crystallographic orientation of the ZnS shell was affected by the ZnO core.     

Characterization of the nanopore structures of PAN-based carbon fiber precursors by small angle X-ray scattering

The nanopore structures in precursors are crucial to the performance of PAN-based carbon fibers. Four carbon-fiber precursors are prepared. They are bath-fed filaments (A), water-washing filaments (B), hot-stretching filaments (C) and drying-densification filaments (D). Synchrotron radiation small angle X-ray scattering is used to probe and compare the nanopore structures of the four fibers. The nanopore size, discrete volume distribution, nanopore orientation degree along the fiber axis and the porosity are obtained. The results demonstrate that the nanopores are mainly formed in the water-washing stage. During the processes of the subsequent production technologies, the slenderness ratio of nanopores and their orientation degree along the fiber axis increase further and simultaneously, the porosity decreases. These results are helpful for improving the performance of the final carbon fibers.     

Characterization of enamel caries lesions in rat molars using synchrotron X‐ray microtomography

Dental caries is a ubiquitous infectious disease with a nearly 100% lifetime prevalence. Rodent caries models are widely used to investigate the etiology, progression and potential prevention or treatment of the disease. To explore the suitability of these models for deeper investigations of intact surface zones during enamel caries, the structures of early‐stage carious lesions in rats were characterized and compared with previous reports on white spot enamel lesions in humans. Synchrotron X‐ray microcomputed tomography non‐destructively mapped demineralization in carious rat molar specimens across a range of caries severity, identifying 52 lesions across the 30 teeth imaged. Of these lesions, 13 were shown to have intact surface zones. Depth profiles of fractional mineral density were qualitatively similar to lesions in human teeth. However, the thickness of the surface zone in the rat model ranges from 10 to 58 µm, and is therefore significantly thinner than in human enamel. These results indicate that a fraction of lesions in rat caries possess an intact surface zone and are qualitatively similar to human lesions at the micrometer scale. This suggests that rat caries models may be a suitable analog through which to investigate the structure of surface zone enamel and its role during dental caries.     

A deformation rig for synchrotron microtomography studies of geomaterials under conditions down to 10 km depth in the Earth

A hard X‐ray transparent triaxial deformation apparatus, called HADES, has been developed by Sanchez Technologies and installed on the microtomography beamline ID19 at the European Radiation Synchrotron Facility (ESRF). This rig can be used for time‐lapse microtomography studies of the deformation of porous solids (rocks, ceramics, metallic foams) at conditions of confining pressure to 100 MPa, axial stress to 200 MPa, temperature to 250°C, and controlled aqueous fluid flow. It is transparent to high‐energy X‐rays above 60 keV and can be used for in situ studies of coupled processes that involve deformation and chemical reactions. The rig can be installed at synchrotron radiation sources able to deliver a high‐flux polychromatic beam in the hard X‐ray range to acquire tomographic data sets with a voxel size in the range 0.7–6.5 µm in less than two minutes.     

Quantification of microporosity in fruit by MRI at various magnetic fields: comparison with X-ray microtomography

Microstructure determines the mechanical and transport properties of fruit tissues. One important characteristic of the microstructure is the relative volume fraction of gas-filled intercellular spaces, i.e., the tissue microporosity. Quantification of this microporosity is fundamental for investigating the relationship between gas transfer and various disorders in fruit.     

Preparation of PMMA grafted aluminum powder by surface-initiated in situ polymerization

Poly(methyl methacrylate) (PMMA) grafted aluminum powder was successfully prepared by surface-initiated in situ polymerization. The process was divided into two steps: adsorption of initiator and polymerization of monomer. It was found that the driving force of adsorption between initiator and aluminum was due to electrostatic force, not chemical bonding, and the percentage of adsorption (PA) and adsorption efficiency (AE) would reach as high as 31.2% and 52.0%, respectively. As for the process of in situ polymerization, the conversion of monomer (C), percentage of grafting (PG) and grafting efficiency (GE) were investigated by evolved hydrogen detection. It was shown that the PG and GE obtained were consistent with those calculated through TGA analysis.     

SANS investigation on evolution of pore morphology for varying sintering time in porous ceria

Precipitates of ceria were synthesized by homogeneous precipitation method using cerium nitrate and hexamethylenetetramine at 80°C. The precipitates were ground to fine particles of average size ∼0.7 μm. Circular disks with 10 mm diameter, 2 and 3 mm thickness were prepared from the green compacts by sintering at 1300° C for three different sintering times. Evolution of the pore structures in these specimens with sintering time was investigated by small-angle neutron scattering (SANS). The results show that the peak of the pore size distribution shifts towards the larger size with increasing sintering time although the extent of porosity decreases. This indicates that finer pores are eliminated from the system at a faster rate than the coarser ones as sintering proceeds and some of the finer pores coalesce to form bigger ones.     

Ultra-low temperature sintering of Cu@Ag core-shell nanoparticle paste by ultrasonic in air for high-temperature power device packaging

Sintering of low-cost Cu nanoparticles (NPs) for interconnection of chips to substrate at low temperature and in atmosphere conditions is difficult because they are prone to oxidation, but dramatically required in semiconductor industry. In the present work, we successfully synthesized Cu@Ag NPs paste, and they were successfully applied for joining Cu/Cu@Ag NPs paste/Cu firstly in air by the ultrasonic-assisted sintering (UAS) at a temperature of as low as 160 °C. Their sintered microstructures featuring with dense and crystallized cells are completely different from the traditional thermo-compression sintering (TCS). The optimized shear strength of the joints reached to 54.27 MPa, exhibiting one order of magnitude higher than TCS at the same temperature (180 °C) under the UAS. This ultra-low sintering temperature and high performance of the sintered joints were ascribed to ultrasonic effects. The ultrasonic vibrations have distinct effects on the metallurgical reactions of the joints, resulting in the contact and growth of Cu core and the stripping and connection of Ag shell, which contributes to the high shear strength. Thus, the UAS of Cu@Ag NPs paste has a great potential to be applied for high-temperature power device packaging.     

Fabrication and adhesion performance of gold conductive patterns on silicon substrate by laser sintering

Laser sintering of gold-microparticle ink was examined in this study. Laser-sintered gold conductive patterns were characterized by using scanning electron microscope (SEM), energy-dispersive spectrometer (EDS), cross-cut tape test and destructive bond wire pull tests. The effects of laser power on microstructure and adhesion of gold conductive patterns were investigated. It was found that the microstructure of gold conductive patterns became denser with increase of laser power. The gold conductive patterns treated with laser power of 2 W showed poor adhesiveness of 2B in accordance with ASTM D3359-08. The adhesion level of gold conductive patterns increased to 5B by elevating laser power to 8 W. The adhesion mechanism of gold conductive patterns on silicon substrate was discussed and wire bonding test was also performed on gold conductive patterns. Wire breakage took place at the practical pull strength of around 5 gf.