Time-resolved X-ray tomography of a fluidized bed

This paper discusses first results of bubbles moving through a fluidized bed imaged with an X-ray Tomographic Scanner. The scanner is made of 3 medical X-ray sources equipped with 30 CdWO₄ detectors each. The fluidized bed has a diameter of 23 cm and is filled with Geldart B powder. The scanner measures the attenuation in a thin slice perpendicular to the column axis at a sampling frequency of 2500 Hz.The data collected during 2 s are reconstructed using the SART algorithm with a one-step-late correction. The reconstructions show the distribution of the bubbles in the 2-dimensional cross-section. By stacking these images, a 3-dimensional view of the bubbles in the column is represented.     

Evaluation of the morphology and pore characteristics of silica refractory using X-ray computed tomography

Silica refractory has excellent high-temperature performance, but its apparent porosity is relatively high. In this work, samples obtained before and after creep testing of silica brick (1550 °C, 50 h), from used silica checker brick (existing only tridymite and amorphous) and from used dome brick (existing only cristobalite and amorphous) were investigated using a three-dimensional structure model based on X-ray computed tomography (CT). The results show that the porosity of silica brick was high but consisted mainly of interconnected pores, with a very small proportion of closed pores (smaller after long-term use). During the use of silica brick, the morphology and phase transformation caused large particles to rupture, and the mineralizer became liquid at high temperature. The broken particles and interconnected pores provided channels for the migration of the liquid in the brick at high temperature. The silica brick presented a homogeneous ceramic structure during long-term operation. Tridymite or cristobalite presented a solid frame leading to an excellent creep performance of the silica brick (the creep rate of the checker brick was ?0.16% at 1550 °C for 50 h). Results were discussed, compared with literature and a model for the transformation of the silica brick from a refractory structure to a homogeneous ceramic structure was established in this paper.     

A novel X-ray computed tomography method for fast measurement of multiphase flow

A new approach based on an improved genetic algorithm (GA) was proposed to implement the image reconstruction when using X-ray computed tomography (XCT) for the application of fast measurement of multiphase flow dynamics. Instead of directly using a traditional XCT, we pursued to develop a different discrete tomography (DT) method, aiming to achieve a high resolution in time during the measurements with only limited projection data. The proposed method assumed that the interested multiphase flow can be simplified as having distinct dense and dilute phases so that the local phase concentration can be binary-coded, e.g., 0 or 1 in a gas bubbling system. The mathematical problem under these circumstances is strongly ill-posed, and thus tackled with an optimization approach, i.e., a GA incorporated with the underlying physics as some constraints. The numerical simulations mimicking the physical measurements demonstrated the feasibility of the new approach, namely GA-XCT, especially with high robustness to the noise. Experiments were performed to simulate a transient measurement on the gas bubbles in water, with a portable X-ray tube and a 2D plane detector as the hardware and a static object rotating in between. The results further provided the validation of the GA-XCT being superior to the conventional algorithm, e.g., filtered back-projection (FBP) technique, in dealing with the tomography of multiphase system with binary local density field.     

Effects of solid loading on stereolithographic additive manufactured ZrO2 ceramic: A quantitative defect study by X-ray computed tomography

In this study, the effects of solid loading on the defects and mechanical performance of stereolithographic additive manufactured ZrO₂ ceramic were studied by X-ray computed tomography (X-CT). ZrO₂ ceramics were fabricated by stereolithographic additive manufacturing from suspensions with different solid loading. The geometrical features and distribution of the defects within the ceramic were quantitatively characterized, classified, and analyzed, the formation mechanism were discussed. The correlations between the defects and mechanical properties were also investigated, and the effects of solid loading on the performance of ZrO₂ ceramic were revealed. The authors want to give a method, X-CT, for the defect characterization among stereolithographic additive manufactured ceramic.     

Improving the interpretation of mercury porosimetry data using computerised X-ray tomography and mean-field DFT

Despite widespread use of the technique for a long time, the proper interpretation of mercury porosimetry data, particularly retraction curves, remains uncertain. In this work, the usefulness of two complementary techniques, mean-field density functional theory (MF-DFT) and micro-computerized X-ray tomography (micro-CXT), for aiding interpretation of ambiguous mercury porosimetry data has been explored. MF-DFT has been used to show that a specific, idiosyncratic form for the top of the mercury intrusion and extrusion curves is probably associated with a particular network structure where the smallest pores only form through connections between larger pores. CXT has been used to study the pore potential theory of hysteresis and entrapment directly using a model porous material with spatially varying pore wetting properties. CXT has also been used to directly study the percolation properties, and entrapment of mercury, within a macroporous pellet. Particular percolation pathways across the heart of the pellet have been directly mapped. The forms of entrapped mercury ganglia have been directly observed and related to retraction mechanisms. A combination of CXT and mercury porosimetry can be used to map spatial variation in pore neck sizes below the spatial resolution of imaging.     

Three-dimensional mathematical analysis of particle shape using X-ray tomography and spherical harmonics: Application to aggregates used in concrete

The properties of composites made by placing inclusions in a matrix are often controlled by the shape and size of the particles used. Mathematically, characterizing the shape of particles in three dimensions is not a particularly easy task, especially when the particle, for whatever reason, cannot be readily visualized. But, even when particles can be visualized, as in the case of aggregates used in concrete, three-dimensional (3-D) randomness of the particles can make mathematical characterization difficult. This paper describes a mathematical procedure using spherical harmonic functions that can completely characterize concrete aggregate particles and other particles of the same nature. The original 3-D particle images are acquired via X-ray tomography. Three main consequences of the availability of this procedure are mathematical classification of the shape of aggregates from different sources, comparison of composite performance properties to precise morphological aspects of particles, and incorporation of random particles into many-particle computational models.     

Using X-ray tomography,PALS and Raman spectroscopy for characterization of inhibitors in epoxy coatings

Model paint materials were generated by adding a range of inorganic materials into an epoxy. The inorganic materials included inhibitors (Zn₃(PO₄)₂ and SrCrO₄) and a filler (rutile TiO₂).The SrCrO₄ system was characterized using SEM, TEM, PALS and Raman spectroscopy and found to have an even distribution of inhibitor in the polymer matrix. X-ray tomography was performed on the mixed SrCrO₄/TiO₂ and Zn₃(PO₄)₂/TiO₂ systems. A new technique called data constrained modelling was combined with the tomographic technique to produce a 3D distribution of the inorganic phases within the polymer matrix.     

A 2-dimensional small-angle X-ray scattering study of the microphase-separated morphology exhibited by thermoplastic polyurethanes and its response to deformation

The morphological behaviour of poly(ether-urethane)s undergoing deformation was studied using two-dimensional small-angle X-ray scattering (2D-SAXS). The data was analysed using the Zernike-Prins and Percus-Yevick models, which fitted the data well and indicated morphologies composed of discrete, elongated hard segment (HS) microdomains. Although the formulations contained relatively large HS weight fractions, relatively low volume fractions of scattering bodies were indicated, which implied limited segmental de-mixing. Possible explanations for this were discussed.Curve-fitting the 2D-SAXS data for deformation experiments using the Zernike-Prins model, indicated that HS microdomains initially became aligned with the applied strain and subsequently fragmented. This suggested a morphological basis for the observed mechanical properties of these materials, which will be explored in more detail, in subsequent publications.     

Surface area and porosity, X-ray diffraction and chemical analyses

Texture, structure and composition of the fresh and the used EUROCAT oxide V₂O₅–WO₃/TiO₂ SCR catalysts have been investigated with aid of nitrogen adsorption/desorption at 77 K, mercury porosimetry, X-ray diffraction and chemical analyses. The BET specific surface area is around 47 and 46 m²/g for the fresh and the used catalyst, respectively. Both samples are essentially mesoporous, with pore diameters centred in the range 10–20 nm according to the data derived from the nitrogen adsorption and around 40 nm according to the mercury porosimetry. The anatase form of TiO₂ and traces of orthorhombic V₂O₅ are the only crystalline phases identified in both materials. According to the chemical analysis there are no significant differences in the contents of the main constituting elements between the fresh and the used catalyst. Selective dissolution with NH₃ aq. reveals that in the used catalyst the amount of vanadium component not susceptible to the treatment increases.     

Quantitative estimation of volume changes of granular materials during silo flow using X-ray tomography

The aim of the paper is to show the potential of the X-ray tomography to quantitatively measure volume changes in granular materials during silo flow in a rectangular model bin. The experiments were carried out with initially dense sand. The bin walls were smooth or very rough. In the first step, continuous X-ray radiographs were conducted. The results of volume changes were presented in form of 1D cross-sectional plots and 2D images. They were directly compared with corresponding experimental results obtained with a Particle Image Velocimetry (PIV) method allowing for measuring displacements on the solid surface. Measurement errors in both methods were discussed.     

Characterization of complex die-pressed Al2O3 green compact using liquid immersion,X-ray tomography,and numerical simulations

This study examined the compaction behavior of a green ceramic component with a complex shape formed by die pressing at 50 MPa using spray-dried alumina. Compared to a simple cylindrical sample, the sample with a complex shape revealed a higher degree of microstructural inhomogeneity and crack formation. Granule deformation and pore distribution at different sample locations were observed by optical microscopy after infiltrating liquid into the voids of a green compact. The refractive index of the immersion liquid should be different slightly from that of alumina for better observations. X-ray micro-computed tomography was also used to visualize the pore distribution and crack shape. Numerical simulations based on the Drucker-Prager/Cap model were performed to distinguish the stress and displacement distribution within the compact. The significant stress gradient at the crack initiation point could explain crack formation, whereas the application of a higher pressure resulted in a further increase in stress gradient.     

In situ tensile damage characterization of C/C composites through X-ray computed tomography and digital volume correlation

Carbon fiber reinforced carbon matrix (C/C) composites have been used in aerospace applications due to their excellent performance. Exploring their failure mechanisms is a subject of extensive research. Nowadays, to obtain information about changes in the failure processes, a technology known as in situ X-ray computed tomography is used. In this paper, tensile loads were applied to 3D fine-woven punctured and needle-punched C/C composites perpendicular to the punctured and needle-punched directions. In situ X-ray computed tomography was employed to observe damage development, and digital volume correlation was used to assess the laboratory X-ray computed tomographs to measure local strains. Assimilation of pores is observed in C/C composites, with cracks evolving from original micro-pores. While fine-woven punctured C/C composites present an elegant linear failure, needle-punched C/C composites present a traditional non-linear failure. This difference is due to the different structures of the preforms. Furthermore, the C/C composites are weak at the sites where they are punctured or needle-punched.     

Shape and size of microfine aggregates: X-ray microcomputed tomography vs. laser diffraction

Microfine rock aggregates, formed naturally or in a crushing process, pass a #200 ASTM sieve, so have at least two orthogonal principal dimensions less than 75 μm, the sieve opening size. In this paper, for the first time, we capture true 3-D shape and size data of several different types of microfine aggregates, using X-ray microcomputed tomography (μCT) with a voxel size of 2 μm. This information is used to generate shape analyses of various kinds. Particle size distributions are also generated from the μCT data and quantitatively compared to the results of laser diffraction, which is the leading method for measuring particle size distributions of sub-millimeter size particles. By taking into account the actual particle shape, the differences between μCT and laser diffraction can be qualitatively explained.     

Damage evolution analysis in mortar, during compressive loading using acoustic emission and X-ray tomography: Effects of the sand/cement ratio

This paper explores the use of acoustic emission (AE) and X-ray tomography to identify the mechanisms of damage and the fracture process during compressive loading on concrete specimens. Three-dimensional (3D) X-ray tomography image analysis was used to observe defects of virgin mortar specimen under different compressive loads. Cumulative AE events were used to evaluate damage process in real time according to the sand/cement ratio. This work shows that AE and X-ray tomography are complementary nondestructive methods to measure, characterise and locate damage sites in mortar. The effect of the sand proportion on damage and fracture behaviour is studied, in relation with the microstructure of the material.     

Heterogeneities and defects in powder compacts and sintered alumina bodies visualized by using the synchrotron X-ray CT

The uniaxial die compaction and sintering is an important industrial production method for metal and ceramic components. While submicron- and nano-sized powders are finding increasing use for making dense materials with finest grain sizes, the uniformity of microstructure, and then, the reliability of the products depend on the heterogeneity in powder packing structure. Here we applied the synchrotron X-ray multiscale-CT to characterize the complex domain structures, i.e., agglomerates, in powder compacts, and revealed how heterogeneous distribution of fine residual pores is formed by the differential sintering of agglomerates by using a submicron alumina powder as a model. A crack-like defect was identified as the largest defect. This defect was formed along the boundary between a plate-shaped agglomerate and its surroundings. A technique was also proposed to visualize the heterogeneous distribution of residual pores by using SEM. These characterization methods will open up new possibilities for the optimization of ceramic processing.     

Investigation of X-ray imaging of vapor-liquid contactors. 1. Studies involving stationary objects and a simple flow system

X-ray computed tomography was used to image two experimental systems containing vapor, liquid, and stainless steel. The first system consisted of a set of test objects designed to incorporate interfaces between the phases at multiple angles. The second system was a film-flow apparatus designed to operate with a film of water in the range of 0.2- thick. The amount of liquid present at selected elevations of both experimental systems was measured from the X-ray transmission data. Less than ten percent variation from expected values was measured for both the stationary objects and the film-flow apparatus. The tomography systems used included a high-energy scanner and a low-energy scanner. The size of a pixel in the reconstructed image ranged from 0.15 to . The measurement noise was identified as an important factor of the imaging system. The second article in this series will include experimental X-ray CT results for a vapor-liquid contactor and results of the analysis of images produced from simulations of X-ray CT.     

Tracking of moving interfaces in sedimentation processes using electrical impedance tomography

Sedimentation monitoring is widely used to control and optimize industrial processes. In this paper we propose a novel computational method for sedimentation monitoring using electrical impedance tomography (EIT). EIT measurements consist of electric current and voltage measurements that are made on the surface of the sedimentation tank and therefore they do not interfere with the sedimentation process. The proposed computational method is based on shape estimation and state estimation formulation of the EIT problem. The sedimentation is parameterized by the locations of the phase interfaces and conductivities of the phase layers. Three different evolution models for the state parameters are considered and the state estimates are computed using the extended Kalman filter algorithm. The performance of the method and the models are evaluated using simulated data from a six electrode EIT measurement configuration. From the results a promising performance of the method can be seen.     

X-ray absorption study of drying cement paste and mortar

X-ray absorption was used to observe water evaporation with hydration time in paste and mortar specimens, with the aim of studying the influence of water/cement (w/c) ratio, presence of aggregates, curing conditions on drying during early hydration. For the samples subjected to surface drying immediately after mixing, there exists a moisture gradient within the internal part of the specimen. However, obvious top-down drying only occurs within a small zone near the surface for early age cement pastes and mortars. The evaporation rate of water is very high in the first day after casting and is drastically reduced afterwards due to the formation of a microstructure that greatly improves specimens resistance to moisture loss. Mortars reveal a slightly lower evaporation rate since the aggregate increases the length of the transport route because of a larger tortuosity. However, the effect of sealed curing is much more important than the tortuosity effect of the aggregates.     

Investigation of Structural Changes of Alkaline-extracted Wood Using X-ray Microtomography and X-ray Diffraction: A Comparison of Microwave versus Conventional Method of Extraction

Abstract

The effect of extraction of wood components on wood anatomy and cellulose crystallinity was studied using X-ray computed microtomography (micro CT) and X-ray crystallography. Micro CT of the xylem vessels of birch wood samples was used for the quantitative determination of the wood porosity after conventional and microwave extraction. The method was also used as an indirect means for the determination of temperature generated inside the fibers. Original porosity of birch wood was 18.5 ± 1.5%, and porosity increased with both extractions. The increase in wood porosity after 10 minutes of microwave extraction was double that of wood after conventional method of extraction at 90°C for two hours (42% vs. 26%), indicating a sudden rupture of the wood structure due to the volumetric heating effect produced by the microwave heating. Comparison of porosities of the conventionally extracted samples at different temperatures for the same duration indicated that the temperature generated inside the fibers during 10 minutes of microwave extraction is around 120°C. Crystallinity of cellulose did not change after both extractions, suggesting that the extraction did not affect the strength of the fibers.