Leaching in active protective coatings observed in-situ by nano-CT using synchrotron radiation

Geometric modelling of corrosion inhibitor pigments in active protective coatings based on SR-nano-CT images

ABSTRACTMicropore and pore evolution both severely influence pore structure and transport properties. The micropore connects isolated pores to predominate connected pore cluster while the pore evolution generates isolated pores. Therefore, investigating separate impacts of predominate and remaining pore clusters is the first step to modify the existing electrical resistivity and permeability models with consideration of the micropore and pore evolution.The main pore clusters in six porous media including sandstone and carbonate were first extracted. Then, the pore geometry, topology, electrical resistivity and permeability from the main pore cluster compared with them from all the pore clusters in the same porous medium. The calculations of pore morphological and the petrophysical properties were all based on the pore networks extracted from the porous media by maximal ball method.The predominant pore cluster mainly determined the pore geometry, electrical resistivity and permeability of the corresponded porous medium. However, the isolated pore clusters from pore evolution undermined the pore connectivity. The developments of the remaining pore clusters slightly affected the electrical resistivity and permeability while seriously impacted the porosity exponents. Therefore, the micropore could increase the pore connectivity, and then slightly increase the permeability and reduce the electrical resistivity.

A technique for the direct observation of microstructural changes in ceramics following ion- implantation is presented. Ion-implantation produces modifications to the mechanical properties of ceramic surfaces. These modifications have been investigated as a means of improving the hardness and wear of such materials. Examples of these changes will be presented for single-crystal specimens of MgO which have been implanted with Xe+ ions. The resultant microstructural changes are a function of ion fluence and are related to structural modifications at or near the surface.Transmission electron microscopy (TEM) is a powerful technique for examination of microstructure on a nanometer scale. A problem often encountered when conventional methods of specimen preparation, for TEM analysis, are used is the possibility of ion-beam induced damage. Ion-beam damage can be a serious problem especially in the preparation of MgO specimens. In the present study damage resulting from ion-milling can be entirely avoided by ion-implantation directly into an electron-transparent thin-foil specimen.

Merge pore clusters: A novel method to construct pore networks and predict permeability from 2D rock images

Image sequences recorded by high-resolution digital video cameras contain vast amount of spatial-temporal information of targeted objects. With the rapid increase of image resolution, these digital cameras can now be used to measure three-dimensional complex motion of structures with sufficient accuracy for the purpose of modal analysis or health monitoring applications. In this paper, a measurement technique based on image sequence analysis is proposed for extracting spatial-temporal responses of continuous structures. Two digital cameras are used to record two-dimensional (2D) image sequences of a three-dimensional (3D) structural vibration response. This structural vibration response is reconstructed using the two 2D image sequences through the epipolar geometry theory without the use of any pre-installed targets. The obtained displacement response provides a more direct way to quantify the modal properties of the structure. To demonstrate, a laboratory test was conducted to measure the free vibration of a cantilever steel rod. Results show that the proposed technique can obtain excellent results as compared to the analytical solution. The proposed technique provides a low-cost alternative to measure 3D vibration of low-frequency flexible structures such as bridge cables in a non-contact and non-target fashion.

Evaluating renal arterial wall by non-enhanced 2D and 3D free-breathing black-blood techniques: Initial experience

Recent developments in Internet technology, combined with the computerization of hospital radiology departments, allow the remote viewing of medical data images. Generally, however, medical images are data intensive and the transmission of such images over a network can consumer large amounts of network resources. Previous work by Liptay et al, presented an interactive, progressive program (implemented in JAVA and requiring a web browser) that allowed the transmission of multi-resolution JPEG image data using various ROI (Region of Interest) strategies in order to minimize Internet bandwidth requirements. This work handles both 2D and 3D image data, but 3D data was treated as a sequence of 2D images, where each 2D image had to be individually requested by the system. The work described in this paper replaces the representation of 3D data as a 2D JPEG image sequence with a single block of lossy 3D image data compressed using wavelets. In a similar fashion, 2D image data is wavelet compressed. Wavelet decomposition has been shown to have consistently better image quality at high compression ratios than other lossy compression methods. We use wavelet compression in a JAVA application program on the server side to construct a lossy low resolution version of the data. As well, high resolution difference sub-blocks of data are also created by the JAVA application; a difference sub-block and the corresponding low resolution lossless data. Transmitting the low resolution image and difference sub-blocks (as requested) only requires a small fraction of the network bandwidth compared to that which would otherwise be needed to transmit the entire lossless data set. The user, via a JAVA applet on the client side, is provided with a number of methods to choose a trajectory (sequence) of regions of interest in the low resolution image. Once the region(s) of interest are chosen, the sub-blocks of image data in the various trajectories are then retrieved and integrated into the low resolution display to provide lossless reconstruction in the regions of interest. Our program significantly reduces download time since extraneous information is not transmitted.

Heterogeneous functional materials for energy-conversion and –storage, such as fuel cells, electrolyzers and batteries are hierarchical, porous, electroactive materials that rely on multi-scale imaging techniques for accurate morphological characterization. These materials are building blocks for the catalyst layers, gas diffusion layers and electrodes in fuel cells, porous transport layers (PTLs) in electrolyzers and porous electrodes within batteries. Functional materials electrochemical functionality can be assessed with various in-situ and operando techniques that probe chemical state during operation, such as x-ray absorption near edge structure (XANES). Synchrotron bright x-ray sources allow for nano-scale imaging combined with XANES, which state-of-the-art lab-scale systems are still lacking. Furthermore, these bright sources allow ultra-fast imaging on sub-second and micro-second temporal resolution. Optimization of temporal, spatial and chemical dimensions is critical to answer the morphological and chemical questions of interest [1]. Transmission x-ray microscopy (TXM) and its three-dimensional analog x-ray computed tomography (CT) allows 30 nm resolution with nano-CT set-up and 1 um resolution with micro-CT beamlines. The nano-CT beamlines have precise energy resolution to enable a combination of 3D imaging and XANES. The generated imaging data sizes exceed terabytes of space and requires modeling frameworks to interpret the findings. We have developed a scale-bridging algorithm to incorporate nano-scale findings into micro-scale using direct numerical simulations and coupling algorithms via effective properties and boundary conditions. In this work we will present several examples of operando data collected on fuel cells, electrolyzers and batteries using nano and micro x-ray CT and in some instances with XANES or with sub-second radiography. Full-field x-ray imaging beamline 18-ID at National Synchrotron Light Source II has achieved 3 minutes nano-CT scan, what enables full 3D XANES scan within reasonable time-frame. Some of the questions that we attempt to answer include activity and water management of NiCu/KB electrocatalyst used in alkaline fuel cells as anode; electrocatalyst activity and its interface with the PTL within operating electrolyzers, and Li metal dendrite growth in solid polymer electrolyte batteries during cycling. Scale-bridging framework is applied to fuel cell electrodes to understand oxygen transport and reaction-diffusion processes for these multi-scale catalyst layers.

Experiments were conducted to investigate deformation-induced processes during in-situ tensile test at elevated temperature. Consequently the microstructure after creep loading was examined by 3D Electron Back Scatter Diffraction (EBSD) technique. The billets of coarse-grained copper were processed by equal-channel angular pressing (ECAP) at room temperature using a die that had an internal angle of 90° between the two parts of the channel and an outer arc of curvature of ~ 20°, where these two parts intersect. The pressing speed was 10 mm/min. To obtain an ultrafine-grained (UFG) material, the billets were subsequently pressed by route Bc by 8 ECAP passes to give the mean grain size ~ 0.7 μm. The constant strain-rate test in tension was performed at 473 K using testing GATAN stage Microtest 2000EW with EH 2000 heated grips which is configured for in-situ electron back scatter diffraction (EBSD) observations. Microstructure was examined by FEG-SEM TESCAN MIRA 3 XM equipped by EBSD detector HKL NordlysMax from OXFORD INSTRUMENT. The tensile test was interrupted by fast stress reductions after different deformation step and observation of microstructure changes was performed. Despite of a considerable interest in ECAP processing method, there are not many works documenting microstructure evolution and changes during creep testing and determining creep mechanisms of ultrafine-grained materials processed by ECAP. It was found that creep resistance of UFG pure Al and Cu is considerably improved after one ECAP pass in comparison with coarse grained material, however, further repetitive pressing leads to a noticeable deterioration in creep properties of ECAP material. Recently it was observed the coarsening of the grains in microstructure of ECAP copper during creep at elevated temperature. It was suggested that creep behaviour is controlled by storage and dynamic recovery of dislocations at high-angle boundaries. In the present work was found that ultrafine-grained microstructure is instable and significant grain growth has already occurred during heating to the testing temperature. Static recrystallization during heating led to the formation of high fraction of special boundaries Σ3 and Σ9. The tensile deformation at 473 K led to the additional grain growth and formation of new grains. Microstructure was investigated also by 3D EBSD.

Ni/8YSZ pellet was exposed to the high temperature (1073 K) redox cycle repeatedly and the micro-structural changes were observed with environmental scanning electron microscope (ESEM). It was revealed that the conditions for observing with ESEM, low gas pressure and electron beam, do not affect the mechanism of micro-structural changes, therefore it can be said that the observation of micro-structural changes under the pseudo SOFC operating condition with ESEM is reliable. However the remarkable agglomeration of Ni particles was observed only on the surface, not inside the sample.

Nowadays, mammographic examination is the gold standard technique for detecting breast cancer in asymptomatic women. However, it presents some limitations, mainly due to the superimposition of the tissues in the 2D mammograms, which may hide tumor lesions. Partially (digital breast tomosynthesis) and fully (CT dedicated to the breast) 3D breast imaging techniques have been developed in order to have a better tissues separation and to overcome such a limitation. Along with 3D breast imaging, the use of the X-ray beam phase shift, via so-called phase-contrast imaging techniques, has been shown to be a promising method in order to increase the image contrast between glandular tissue and tumor lesions. Indeed, in phase-contrast the image contrast is due to the X-ray wave phase-shift between different imaged materials, while in conventional imaging the image contrast arises from the different attenuation they introduce. Among all phase-contrast techniques, propagation based phase-contrast imaging does not need any special optical elements in the beam path, but only an X-ray beam with a certain degree of coherence and enough distance between imaged object and detector. It can be implemented either with synchrotron radiation source or with a compact X-ray tube. The 3D propagation based phase-contrast breast imaging devices are not yet employed in the routine clinical exams but they are available only at experimental level, and appropriate evaluations of image quality and dose are necessary. This is needed in order to optimize the various techniques and to understand the corresponding dose limitations. In this thesis, the dose paradigms in X-ray breast imaging are revisited and specific Monte Carlo simulation codes have been developed. A part of this work focuses on the breast dose aiming at studying the adopted breast models and the effects of the breast partial irradiation on the dose estimates, as occurs in 2D spot mammography clinical examinations as well as by adopting a narrow beam produced via synchrotron radiation. The second part of this work focuses on the image quality obtainable in 3D images of the breast by adopting propagation based phase-contrast imaging. We present the CT scanner dedicated to the breast developed within the SYRMA-CT project at Elettra synchrotron radiation facility. We evaluate its imaging performance in terms of spatial resolution, image noise properties and capability of showing breast lesions and microcalcification clusters. Finally, the CT scanner dedicated to the breast, developed at the University of Naples, which relies on compact X-ray source with a 7-μm focal spot is presented and its image performance at dose comparable to that adopted in two-view digital mammography is explored together with its capability of producing phase-contrast effects. This scanner was developed and studied in order to compare a scanner which is clinical feasible in terms of cost, setup dimension and scan time to the results obtainable via the high flux and monochromatic X-ray beam synchrotron based experimental scanner.

We report on the result of an in situ method for observing microstructural changes during hot deformation. The observation of microstructural changes of steel at 1,473 K under tensile strain is demonstrated using the reported method. The development of deformed structures and the formation of a new grain boundary, which subsequently moved with increased strain, were clearly observed. The effectiveness of this method was confirmed by the results of several examples.

The anode-supported solid oxide fuel cell (SOFC) degrades when the anode is subjected to redox cycling. The degradation has qualitatively been related to microstructural changes in the nickel-yttria stabilized zirconia anode of the tested cells. In this work, the microstructural changes were observed in situ using environmental scanning electron microscopy. In the reduced state, a dynamic rounding of the nickel particles occurred. The oxide growth upon re-oxidation depended on the oxidation kinetics. During rapid oxidation, the NiO particles divided into 2-4 particles, which grew into the surrounding voids. For slower oxidation, an external oxide layer was seen to develop around the individual particles.

The microstructure change is one of the most important research areas in the friction stir welding (FSW). However, direct observation of microstructure changes during FSW has been extremely challenging because many measurement techniques are inapplicable. Recently developed in-situ time-resolved neutron diffraction methodology, which drastically improves the temporal resolution of neutron diffraction, enables to observe the transient microstructure changes during FSW. We installed a portable FSW system in the Spectrometer for MAterials Research at Temperature and Stress (SMARTS) at Los Alamos Neutron Science Center and the FSW was made on 6.35mm-thickness 6061-T6 Al alloy plate. At the same time, the neutron beam was centered on the mid-plane of the Al plate at 8 mm from the tool center (underneath the tool shoulder) and the diffraction peak was continuously measured during welding. The peak broadening analysis has been performed using the Williamson-Hall Method. The result shows that the dislocation density of about 3.2 x 10^15 m-2 duing FSW, which is the significant increse compared to the before (4.5 x 10^14 m-2) and after (4.0 x 10^14 m-2) the FSW. The quantitatively analysis of the grain structure can provide an insight to understand the transient variation of the microstructure during FSW.

This paper attempts to summarise the microstructural changes which take place in aluminium bronzes during heat treatment. Another objective of this study was to map the potential of a certain type of aluminium bronzes for undergoing martensitic transformation. The methods, which were chosen for assessing the results of heat treatment with regard to their availability, included measurement of hardness and observation of microstructure using light and scanning electron microscopy, Additional tools for evaluation of microstructure comprised measurement of microhardness and chemical analysis by EDS. An important part of the experiment is observation of microstructural changes in the Jominy bar during the end-quench test. Upon completing experiments of this kind, one can define the heat treatment conditions necessary for obtaining optimum properties. In addition, the paper presents important findings on how to improve the corrosion resistance of aluminium bronzes by special heat treatment sequences.