Morphological characterization of a polymeric microfiltration membrane by synchrotron radiation computed microtomography

Most commercial polymeric membranes are prepared by phase inversion. The performance of the membranes depends greatly on the morphology of the porous structure formed during the different steps of this process. Researchers in this field have found it extremely difficult to foresee how a change in the composition of the polymer solution will affect pore formation without a set of methods designed to yield detailed knowledge of the morphological structure. This paper reports the new potential associated with X-Ray synchrotron microtomography to characterize the 3D structure of a PvDF hollow fibre microfiltration membrane prepared by phase inversion. 3D morphological data obtained from the ID19 line at the ESRF are presented. The membrane actually appears as a complex three-dimensional bi-continuum of interconnected pores. Within the hollow fibre structure, different regions with various thicknesses and pore size distributions have been identified and well characterized. Transversal views show the anisotropic finger-like structure of pores, while longitudinal sections reveal a honeycomb structure which resembles the structure of highly concentrated water in oil emulsion or dispersion. This typical structure might be obtained during the phase inversion process. How the phase inversion process may result in these morphologies is finally discussed

In-situ Analysis of Laminated Composite Materials by X-ray Micro-Computed Tomography and Digital Volume Correlation

The complex mechanical behaviour of composite materials, due to internal heterogeneity and multi-layered composition impose deeper studies. This paper presents an experimental investigation technique to perform volume kinematic measurements in composite materials. The association of X-ray micro-computed tomography acquisitions and Digital Volume Correlation (DVC) technique allows the measurement of displacements and deformations in the whole volume of composite specimen. To elaborate the latter, composite fibres and epoxy resin are associated with metallic particles to create contrast during X-ray acquisition. A specific in situ loading device is presented for three-point bending tests, which enables the visualization of transverse shear effects in composite structures

Experimental study of the ageing of building stones exposed to sulfurous and nitric acid atmospheres

During the last few decades, due to remediation procedures, SO2 emissions in the atmosphere have decreased, unlike NOx. Air pollution has changed. Indeed, the aim of this research is to assess the effect of NOx and their interactions with SO2 on stones, particularly on limestones used in Champagne-Ardenne (France) during the restoration processes. Three French building limestones (Courville, Dom and Savonnières) and one reconstituted stone were exposed during 28 days to four strong acid atmospheres i.e. two H2SO3 solutions with different concentrations and two mixed atmospheres with different proportions of HNO3 and H2SO3. These tests produced an intensive acid attack on the stone, allowing the observation of short-term salt precipitation and the evolution of stone properties. Each day, one sample was removed from the acid atmosphere to measure the concentration of SO4(2-) and NO3(-) by ion-chromatography. The surface changes were assessed before and after the tests by 3D scanning and observations with electron microscopy. X-ray microtomography has been performed in the Centre for X-ray Tomography (UGCT) and the Department of Geology at Ghent University (Belgium) in order to observe the penetration of salts and the consequences in stones porosity. First observations showed that exposure to acid atmosphere, led to gypsum efflorescences. Obvious colour changes occurred in all tests. Salt crystallization entailed a change in the porous system, which was evidenced by 3D, mercury porosimetry and X-ray microtomography. Difference between weathered and fresh stone was highlighted by Ion chromatography analyses

A comparative study of X-ray tomographic microscopy on shales at different synchrotron facilities: ALS, APS and SLS.

Synchrotron radiation X-ray tomographic microscopy (SRXTM) was used to characterize the three-dimensional microstructure, geometry and distribution of different phases in two shale samples obtained from the North Sea (sample N1) and the Upper Barnett Formation in Texas (sample B1). Shale is a challenging material because of its multiphase composition, small grain size, low but significant amount of porosity, as well as strong shape- and lattice-preferred orientation. The goals of this round-robin project were to (i) characterize microstructures and porosity on the micrometer scale, (ii) compare results measured at three synchrotron facilities, and (iii) identify optimal experimental conditions of high-resolution SRXTM for fine-grained materials. SRXTM data of these shales were acquired under similar conditions at the Advanced Light Source (ALS) of Lawrence Berkeley National Laboratory, USA, the Advanced Photon Source (APS) of Argonne National Laboratory, USA, and the Swiss Light Source (SLS) of the Paul Scherrer Institut, Switzerland. The data reconstruction of all datasets was handled under the same procedures in order to compare the data quality and determine phase proportions and microstructures. With a 10× objective lens the spatial resolution is approximately 2 µm. The sharpness of phase boundaries in the reconstructed data collected from the APS and SLS was comparable and slightly more refined than in the data obtained from the ALS. Important internal features, such as pyrite (high-absorbing), and low-density features, including pores, fractures and organic matter or kerogen (low-absorbing), were adequately segmented on the same basis. The average volume fractions of low-density features for sample N1 and B1 were estimated at 6.3 (6)% and 4.5 (4)%, while those of pyrite were calculated to be 5.6 (6)% and 2.0 (3)%, respectively. The discrepancy of data quality and volume fractions were mainly due to different types of optical instruments and varying technical set-ups at the ALS, APS and SLS

Damage investigation in CFRP composites using full-field measurement techniques: combination of digital image stereo-correlation, infrared thermography and X-ray tomography

The present work is devoted to damaging process in carbon–fiber reinforced laminated composites. An original experimental approach combining three optical measurement techniques is presented. Image stereo-correlation and infrared thermography, that respectively provide the kinematic and thermal fields on the surface of the composites, are used in live recording during axis and off-axis tensile tests. Special attention is paid to simultaneously conduct these two techniques while avoiding their respective influence. On the other hand, X-ray tomography allows a post-failure analysis of the degradation patterns within the laminates volume. All these techniques are non-destructive (without contact) and offer an interesting full-field investigation of the material response. Their combination allows a coupled analysis of different demonstrations of same degradation mechanisms. For instance, thermal events and densimetric fields show a random location of damage in the early stages of testing. The influence of the material initial anisotropy on damage growth, localization and failure mode can also be clearly put in evidence through various data. In addition to such characterization, this study illustrates at the same time the capabilities of the different full-field techniques and the damage features they can best capture respectively