Iwan Jerjen

Sub-pixel porosity revealed by x-ray scatter dark field imaging

X-ray scatter dark field imaging based on the Talbot-Lau interferometer allows for the measurement of ultra–small angle x-ray scattering. The latter is related to the variations in the electron density in the sample at the sub- and micron-scale. Therefore, information on features of the object below the detector resolution can be revealed. In this article, it is demonstrated that scatter dark field imaging is particularly adapted to the study of a material’s porosity. An interferometer, optimized for x-ray energies around 50 keV, enables the investigation of aluminum welding with conventional laboratory x-ray tubes. The results show an unprecedented contrast between the pool and the aluminum workpiece. Our conclusions are confirmed due to micro-tomographic three-dimensional reconstructions of the same object with a microscopic resolution.

Characterizing saline uptake and salt distributions in porous limestone with neutron radiography and X-ray micro-tomography

Samples of Savonnières limestone subjected to repeated wetting–drying cycles were investigated by both neutron radiography and X-ray micro-tomography to collect information on saline uptake and salt precipitation. Capillary uptake of water, 1.4 molal sodium sulphate and 5.8 molal sodium chloride solution was visualized with neutron radiography. The liquid penetration coefficients and diffusivities were determined and are markedly lower for the salt solutions than for water, due to the higher surface tension and viscosity of salt solutions. Halite distributions were derived from neutron radiographs. Porosity analysis of X-ray tomographic datasets allowed quantifying thenardite distributions and porosity decrease due to salt crystallization.

Dark-field X-ray imaging of unsaturated water transport in porous materials

We introduce in this Letter an approach to X-ray imaging of unsaturated water transport in porous materials based upon the intrinsic X-ray scattering produced by the material microstructural heterogeneity at a length scale below the imaging system spatial resolution. The basic principle for image contrast creation consists in a reduction of such scattering by permeation of the porosity by water. The implementation of the approach is based upon X-ray dark-field imaging via Talbot-Lau interferometry. The proof-of-concept is provided by performing laboratory-scale dark-field X-ray radiography of mortar samples during a water capillary uptake experiment. The results suggest that the proposed approach to visualizing unsaturated water transport in porous materials is complementary to neutron and magnetic resonance imaging and alternative to standard X-ray imaging, the latter requiring the use of contrast agents because based upon X-ray attenuation only.

Time resolved analysis of water drainage in porous asphalt concrete using neutron radiography

Porous asphalt as a road surface layer controls aquaplaning as rain water can drain through its highly porous structure. The process of water drainage through this permeable layer is studied using neutron radiography. Time-resolved water configuration and distribution within the porous structure are reported. It is shown that radiography depicts the process of liquid water transport within the complex geometry of porous asphalt, capturing water films, filled dead end pores and water islands.

Tomography-Based Determination of Effective Transport Properties for Reacting Porous Media

Reference EPFL-ARTICLE-174709doi:10.1115/1.4004842View record in Web of Science Record created on 2012-02-02, modified on 2017-05-10

Investigation of Water Uptake in Porous Asphalt Concrete Using Neutron Radiography

Porous asphalt (PA), a highly porous hydrophobic composite material, is subjected to water uptake and the process is documented with neutron radiography (NR). While the un-aged laboratory-prepared PA specimens do not show any water uptake, we observe uptake in aged PA even though the bitumen binder is a hydrophobic material. The moisture content distribution plots derived from the NR images clearly identify regions in the aged specimens where water uptake is active. Two-dimensional degree of saturation (DoS) distribution images, which are obtained by combining micro-computer tomography and NR images, identify those pores where saturated flow is certainly active. However, to clearly distinguish between saturated and unsaturated flows in the remaining wet pores, the DoS distribution images are read together with the three-dimensional PA microstructure obtained by micro-CT. It is observed that uptake begins mainly as unsaturated film/corner flow at large well-defined pores. As this uptaken water travels further into the material, the flow transforms into a combination of saturated flow and unsaturated film/corner flow. Saturated flow is seen to be mostly active in the small pores within the mastic. From the observed succession of unsaturated and saturated flows in an aged PA specimen, it can be concluded that years of environmental and mechanical loading has resulted in the stripping of binder from the aggregate surfaces and has consequently exposed patches of hydrophilic aggregate to water, which enables the capillary uptake of water. We also simulate an absolute permeability experiment and observe that relatively less tortuous and more connected paths play an important role in determining the preferential path of the uptaken water.

Reduction of phase artifacts in differential phase contrast computed tomography

X-ray differential phase contrast computed tomography (DPC CT) with a Talbot-Lau interferometer setup allows visualizing the three-dimensional distribution of the refractive index by measuring the shifts of an interference pattern due to phase variations of the X-ray beam. Unfortunately, severe reconstruction artifacts appear in the presence of differential phase wrapping and clipping. In this paper, we propose to use the attenuation contrast, which is obtained from the same measurement, for correcting the DPC signal. Using the example of a DPC CT measurement with pronounced phase artifacts, we will discuss the efficiency of our phase artifact correction method.

Dynamic X-ray radiography for the determination of foamed bitumen bubble area distribution

Foam bitumen is highly efficient in wetting and coating the surface of mineral aggregate at lower temperature. In order to improve understanding and characterization of the bitumen foam, X-ray radiography was used to study the formation and decay of bitumen foam in 2D representation. Image segmentation analysis was used to determine the foam bubble size distribution. In addition, the main parameters influencing foam bitumen formation, water content, and temperature were also investigated. The results demonstrate the influence of the water content on morphology and expansion of foam bitumen bubbles. Adding more water in the foaming process leads to quick collapse of bubbles and intensifies coalescence of foam bitumen. Higher temperatures produces larger bubbles at early foaming stage compared to lower temperature. Moreover the morphology of bubble formation depends on the types of bitumen used. An exponential function has been implemented to represent the bubble area distribution.

PHASE SENSITIVE X‐RAY IMAGING: TOWARDS ITS INTERDISCIPLINARY APPLICATIONS

X‐ray phase imaging including phase tomography has been attracting increasing attention during the past few decades. The advantage of X‐ray phase imaging is that an extremely high sensitivity is achieved for weakly absorbing materials, such as biological soft tissues, which generate a poor contrast by conventional schemes. Especially for such living samples, where the reduction of the applied dose is of paramount interest, phase sensitive measurements schemes have an inherent potential for a significant dose reduction combined with an image quality enhancement. Several methods have been invented for x‐ray phase contrast imaging that either use an approach based on interferometry, diffraction or wave‐field propagation. Some of these techniques have a potential for commercial applications, such as in medicine, non‐destructive testing, security and inspection. The scope of this manuscript thus deals with one particular such technique that measures the diffraction caused by the specimen by means of a grating ...

TOMOGRAPHY-BASED DETERMINATION OF EFFECTIVE TRANSPORT PROPERTIES FOR REACTING POROUS MEDIA

The effective heat and mass transport properties of a porous packed bed of particlesundergoing a high-temperature solid–gas thermochemical transformation are deter-mined. The exact 3D geometry of the reacting porous media is obtained by high-resolu-tion computed tomography. Finite volume techniques are applied to solve the governingconservation equations at the pore-level scale and to determine the effective transportproperties as a function of the reaction extent, namely, the convective heat transfer coeffi-cient, permeability, Dupuit–Forchheimer coefficient, tortuosity, and residence time distri-butions. These exhibit strong dependence on the bed morphological properties (e.g.,porosity, specific surface area, particle size) and, consequently, vary with time as thereaction progresses. [DOI: 10.1115/1.4004842]Keywords: packed bed, solar energy, gasification, chemical reactors, effective proper-ties, tomography, heat transfer, mass transfer