Changes In Microstructure Properties Research Articles

Prediction of Performance Degradation Due to Grain Coarsening Effects in Solid Oxide Fuel Cells

Long term degradation of solid oxide fuel cells is one of the biggest impediments to commercialization. Due to the inordinate amount of time required to properly test degradation experimentally, physics based models which can predict long term degradation can be crucial time and money saving tools. At the cell level, one of the primary modes of degradation comes from grain coarsening and the resulting changes in microstructure properties. In this study a multi-physics model of a single fuel cell is presented which aims to predict performance loss as a function of time caused by coarsening in the electrodes of an LSM/YSZ/Ni SOFC. Microstructural properties are changed as a function of time from their initial values using functional relations derived from data from experiments and phase field models. Specie and charge transport equations are solved using these parameters to predict performance changes with time which result from the aforementioned microstructural changes. The model is first calibrated such that it correctly captures the performance and impedance response of a particular button cell at a given time without any degradation. This same model is run for a duration of 750 hours with performance data being measured for the same cell including impedance measurements being taken intermittently. Performance change over time predicted by the model are compared to experimental data. It is found that the model predicts a slower degradation rate than the rate which occurs experimentally. This is deemed reasonable as other forms of degradation are not being accounted for. The model is then used to make long term predictions of cell performance loss due to grain coarsening. The resulting degradation rate is considered to be the theoretical minimum which occurs when all other modes of degradation are not present. Work is underway to include other forms of degradation in the model so that a complete and robust degradation prediction tool is available for design analysis without the need for costly long term degradation measurements.

Compromised Integrity of Central Visual Pathways in Patients With Macular Degeneration.

Macular degeneration (MD) affects the central retina and leads to gradual loss of foveal vision. Although, photoreceptors are primarily affected in MD, the retinal nerve fiber layer (RNFL) and central visual pathways may also be altered subsequent to photoreceptor degeneration. Here we investigate whether retinal damage caused by MD alters microstructural properties of visual pathways using diffusion-weighted magnetic resonance imaging. Six MD patients and six healthy control subjects participated in the study. Retinal images were obtained by spectral-domain optical coherence tomography (SD-OCT). Diffusion tensor images (DTI) and high-resolution T1-weighted structural images were collected for each subject. We used diffusion-based tensor modeling and probabilistic fiber tractography to identify the optic tract (OT) and optic radiations (OR), as well as nonvisual pathways (corticospinal tract and anterior fibers of corpus callosum). Fractional anisotropy (FA) and axial and radial diffusivity values (AD, RD) were calculated along the nonvisual and visual pathways. Measurement of RNFL thickness reveals that the temporal circumpapillary retinal nerve fiber layer was significantly thinner in eyes with macular degeneration than normal. While we did not find significant differences in diffusion properties in nonvisual pathways, patients showed significant changes in diffusion scalars (FA, RD, and AD) both in OT and OR. The results indicate that the RNFL and the white matter of the visual pathways are significantly altered in MD patients. Damage to the photoreceptors in MD leads to atrophy of the ganglion cell axons and to corresponding changes in microstructural properties of central visual pathways.

Prediction of Performance Degradation Due to Grain Coarsening Effects in Solid Oxide Fuel Cells

Long term degradation of solid oxide fuel cells (SOFCs) is one of the biggest impediments to commercialization. Physics based models which can predict long term degradation can be crucial time and money saving tools. At the cell level, one of the primary modes of degradation comes from grain coarsening and the resulting changes in microstructure properties. In this study, a multi-physics model of a single fuel cell is presented which aims to predict performance loss as a function of time and temperature caused by coarsening in the electrodes of an LSM-YSZ/YSZ/Ni-YSZ SOFC. Microstructural properties are updated as a function of time from their initial values using functional relations derived from data obtained experimentally and from phase field models. Performance change over time predicted by the model is compared to experimental data and a study is performed on the effect temperature has on the degradation rate due to coarsening.

Concurrent decrease of brain white matter tracts' thicknesses and fractional anisotropy after antenatal hypoxia‐ischemia detected with tract‐based spatial statistics analysis

To examine the extent of gray and white matter (WM) injury following global antenatal hypoxia-ischemia (H-I) and resulting in muscle hypertonia in newborns in a rabbit cerebral palsy model. Rabbit dams (n = 15) underwent uterine ischemia procedure resulting in a global fetal H-I at embryonic day 22 (embryonic 22 days gestation). Newborn's brains underwent high resolution diffusion tensor imaging on a 14 Tesla magnet ex vivo. Fractional anisotropy (FA) in brains of hypertonic (n = 9), nonhypertonic (n = 6), and sham control (n = 5) kits were compared voxel-wise using Tract-Based Spatial Statistics (TBSS) approach. Herein, we used a novel method to assess local WM tracts' thicknesses in TBSS analysis and compare between the groups. Significant (corrected P < 0.05) reduction of WM FA was found in corpus callosum splenium (91.2%), periventricular WM (83.5%), fimbria hippocampi (78.8%), cingulum (81.4%), anterior commissure (95%), internal capsule (83.2%), and optic tract (82.9%) in the hypertonic group. Significant (corrected P < 0.05) reduction in WM tracts' thicknesses was found in corpus callosum (73.3%), periventricular WM (82.5%), cingulum (73.4%), bilaterally in the hypertonic group. WM injury in newborn hypertonic kits 10 days after global fetal H-I is widespread and involves not only motor but also limbic and commissural fibers in multiple regions. WM injury in newborn hypertonic kits is manifested by changes in microstructural properties and decreased FA, as well as reduction of WM volumes, relative to nonhypertonic kits. J. Magn. Reson. Imaging 2017;45:700-709. 1 J. Magn. Reson. Imaging 2017;45:829-838.

Thermal shock behavior of W-0.5 wt% Y2O3 alloy prepared via a novel chemical method

A wet-chemical method combined with spark plasma sintering was used to prepare W-0.5 wt% Y2O3 alloy. The W-0.5 wt% Y2O3 precursor was reduced at 800 °C for 4 h under different hydrogen flow rates of 300, 400, 500, 600, and 700 ml/min. The reduced powder was analyzed by X-ray diffraction (XRD), laser particle size analyzer (LPSA), and scanning electron microscopy (SEM). An optimized process for reducing precursor was discussed. After sintering, the specimens were exposed to different laser beam irradiation energies (90, 120, 150, and 180 W) to simulate loads as expected for edge localized modes (ELMs). Top surface and cross-sectional morphology were observed by SEM, and the changes in hardness were evaluated. The changes in microstructural properties (i.e., Y2O3-particle distribution, crack propagation direction, depth of thermal shock effect, and grain size of the recrystallization region) after thermal shock were investigated.

Magnetic and Microstructural Properties of DyF3-Coated Sintered Nd–Fe–B Magnets by Electrophoretic Deposition

To meet the requirement of high coercivity of sintered Nd-Fe-B magnets in various applications of traction motors and wind power generators, substitution of Dy or Tb for Nd is essential [1, 2]. Through electrophoretic deposition (EPD), we first use the weight ratio of the DyF 3 coatings and the magnet to characterize accurately the effective content of Dy in the GBDP magnets. Here we systematically investigate the magnetic and microstructural property changes of the DyF 3 -coated sintered Nd-Fe-B magnet as a function of the effective DyF 3 content and study the mechanism of coercivity enhancement.

Study of Electrolyte pH in Production of Cu–Co–Ni Ternary Alloys and Its Effect on Microstructural and Magnetic Properties

Ternary Cu-Co-Ni alloys were electrodeposited in the mediums that have different pH levels to investigate the microstructuremagnetic relationship. The electrolyte pH was considered as high (4.2) and low (2.5) levels. For both levels, the anomalous codeposition occurred in the deposition of the alloys. The face centered cubic crystalline structure was observed in the ternary alloys grown at high and low electrolyte pH levels. In addition, a significant decrease in average grain size of the crystallites, from 60 to 21 nm, occurred when the pH was reduced from 4.2 to 2.5. A dendritic structure was detected in the surface of the alloy deposited from electrolyte with the high pH level, whereas the alloy grown at the low pH has a surface without dendritic clumps. According to magnetic analysis, an increase in the saturation magnetization, caused by the increase of Co content, was detected when the pH was reduced. The coercivity H c levels were 89 and 80 Oe for the alloys grown at high and low pH, respectively. The change of H c was attributed to the changes in microstructural properties, i.e., different average grain sizes of the crystallites and surface morphologies, occurred when the electrolyte pH changed. The anisotropic magnetoresistance (AMR) was exhibited by the alloys and the AMR ratio was enhanced from ~3% to ~3.5%-4% when the pH decreased.

Study on the stability and microstructural properties of barium sulfate nanoparticles produced by nanomilling

Barium sulfate nanoparticles were produced by nanomilling in stirred media mill using sodium salt of polyacrylic acid (PAA-Na) as a dispersant. The particles sizes of the ground product obtained in the grinding mill were determined by dynamic light scattering (DLS), Brunauer–Emmet–Teller (BET) nitrogen gas adsorption method, and transmission electron microscopy (TEM). The mean particle size calculated with various methods yielded different values due to the different characterization techniques. The stability of BaSO4 nanoparticles produced was analyzed by zeta potential measurement and Turbiscan. The stability of barium sulfate nanoparticles was high in presence of dispersant PAA-Na and higher pH values. Further, the changes in microstructural properties, caused by wet grinding and adsorption of PAA-Na on BaSO4 nanoparticles, were studied using X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and thermogravimetric analysis (TGA). The surface activation and amorphization of BaSO4 nanoparticles were observed due to increased stresses exerted on the particles during wet grinding.

Effect of Temperature on the Crystalline Form and Fat Crystal Network of Two Model Palm Oil-Based Shortenings During Storage

Fat products experienced undesirable microstructural property changes due to the temperatures during transportation and storage. In this study, the lipid composition and solid fat content (SFC) of two model palm oil-based shortenings, which are denoted as shortening A (melting point of 35.1°C) and shortening B (melting point of 51.2°C), were evaluated, and their crystallization behavior and polymorphism during storage at various temperatures (−10 °C to 30 °C) was examined by X-ray diffraction (XRD) and polarized light microscopy (PLM). The fractal dimension (D b) was calculated to qualify the change in the crystal network during storage. The aggregation of high-melting triacylglycerols (TAGs) nanostructure and the formation of the most stable β polymorph were observed in shortening at higher temperatures (≥0 °C) during storage. At the same temperature, the intensity of β crystals in the two samples increased as the storage time increased, and this trend was obvious at high temperatures (≥10 °C). In addition, the intensity of the β crystals in the two samples gradually increased as the temperature increased, and the size of the crystalline particles became larger. The crystal size in shortening A was larger than that in shortening B at high temperatures (≥10 °C). The crystal network of shortening B was denser than that of shortening A. The D b value reached a maximum at 10 °C and 30 °C for shortening A and B, respectively. These findings have important implications on the storage stability and functional properties of palm oil-based shortenings.

First Observation of Blending-Zone Morphology at Interface of Reclaimed Asphalt Binder and Virgin Bitumen

One of the challenges in designing recycled asphalt mixtures with a high amount of reclaimed asphalt pavement (RAP) is estimating the blending degree between RAP binder and added virgin bitumen. The extent of blending is crucial because asphalt concrete response is influenced by the final binder properties. This paper focuses on the evaluation of interaction and extent of blending between RAP binder and virgin bitumen by studying the microstructures of the blending zone with atomic force microscopy (AFM). AFM is used to probe the change of microstructural properties from a RAP binder and virgin bitumen to the blending zone of these two. Averaged microstructural properties have been observed in thin-film blends of RAP binder and pure bitumen. The morphology of the blending zone (spatial extent of about 50 μm) exhibits domains of a wide range of microstructure sizes (160 nm to 2.07 μm) and can be considered to be a completely blended new material that has been observed directly for the first time. The fully blended binder properties are found to be between those of the two individual binders, as could be inferred from the averaged microstructural properties derived from AFM images of the blending zone. This finding is also consistent with the results of mechanical tests by dynamic shear rheometer on the same materials. Finally, a design formula is proposed that relates the spatial dimensions of the blending zone to temperature and mixing time, which will eventually allow the results of this study to be extended from small-length scales up to the engineering level.

Architectural configuration and microstructural properties of the sacral plexus: A diffusion tensor MRI and fiber tractography study

The ability to investigate microstructural properties of the central nervous system with diffusion tensor imaging (DTI) has been shown in many studies. More recently, DTI is being applied outside the brain showing promising results, for instance, for investigating muscle tissue. In this work, we demonstrate the feasibility of diffusion tensor imaging (DTI) and fiber tractography to study the nerves of the sacral plexus in humans in vivo and to assess the architectural configuration and microstructural properties of these peripheral nerves. For this research goal we optimized the acquisition parameters of a DTI sequence and acquired data from 10 healthy adults and one 12-year patient having spina bifida and neurogenic bladder dysfunction. For the healthy volunteers, we estimated the fractional anisotropy (FA) and mean (MD), axial (AD), and radial diffusivities (RD) of the sacral plexus nerves which may serve as a baseline for future studies. We demonstrated that tractography of the sacral plexus on a 3 Tesla MR scanner is feasible, giving 3D insight in the general anatomy and organization of the nerves L4 to S3. In addition, branches to the pudendal nerve were also found in 4 volunteers. There were no significant differences in any of the estimated diffusion measures between the right and left sided nerves or between the nerves L4 to S3 on an intra-subject basis. Furthermore, clinical feasibility of DTI and tractography in a child having spina bifida and neurogenic bladder dysfunction is demonstrated. The architectural configuration of the child's sacral plexus was comparable with the healthy volunteers and no significant disrupted nerve fibers were observed. However, there are strong indications that abnormal diffusion characteristics are present at the level of the neural tube defect due to incomplete segments of the nerves that are close to the vertebrae. These findings are encouraging for using DTI as a means to investigate changes in microstructural properties of the nerves of the sacral plexus. Moreover, this new methodology may provide a new avenue to a better analysis and diagnosis of neurogenic bladder dysfunctions.

Noninvasive assessment of human jawbone using ultrasonic guided waves

The problem of detecting defects in jawbones is an important problem. Existing methods based on Xrays are invasive and constrain the achievable image quality. They also may carry known risks of cancer generation or may be limited in accurate diagnosis scope. This work is motivated by the lack of current imaging modalities to accurately predict the mechanical properties and defects in jawbone. Ultrasonic guided waves are sensitive to changes in microstructural properties and thus have been widely used for noninvasive material characterization. Using these waves may provide means for early diagnosis of marrow ischemic disorders via detecting focal osteoporotic marrow defect, chronic nonsuppurative osteomyelitis, and cavitations in the mandible (jawbone). Guided waves propagating along the mandibles may exhibit dispersion behavior that depends on material properties, geometry, and embedded cavities. In this work, we present the first study in the theoretical and experimental analysis of guided wave propagation in jawbone. Semianalytical, finite-element (SAFE) method is used to analyze dispersion behavior of guided waves propagating in human mandibles. The geometry of the cross section is obtained by segmenting the computed tomography (CT) images of the jawbone. The cross section of the mandible is divided in two regions representing the cortical and trabecular bones. Each region is modeled as a linear Hookean material. The material properties for both regions are adopted from the literature. The experimental setup for the guided waves experiment is described. The results from both numerical analysis and guided waves experiment exhibit variations in the group velocity of the first arrival signal and in the dispersion behavior of healthy and defected mandibles. These results shall provide a means to noninvasively characterize the jawbone and accurately assess the bone mechanical properties. Our study is not aimed at characterizing the bone density in human mandibles. Rather, it is aimed to assess bone mechanical properties and defects that cannot be diagnosed by X-ray or other imaging modalities. This work may pave the way to the development of inexpensive noninvasive devices to detect small defects in human mandibles.

Methodology and recent developments for using neutron diffraction to characterize the mechanical properties of rocks

Conventional deformation experiments are generally restricted to the measurement of whole sample properties, but performing such experiments in situ within a neutron beamline makes it possible to determine how this deformation is accommodated at the grain scale within the sample. By collecting neutron diffraction patterns at different applied loads, the change in lattice parameters (and from this the elastic strain) of each mineral phase present may be monitored during the experiment. Moreover, changes in microstructural properties, such as developing textures and the progress of any mineral transformations, can be monitored. We have performed axial compression experiments on large samples using the ENGIN-X beamline at ISIS to explore the potential of this approach for characterizing the mechanical properties of geological materials. Recent developments to our experimental methodologies include the ability to perform experiments at temperatures up to 800 K and confining pressures up to 200 MPa, using a newly designed pressure vessel. These methods enable us to explore phenomena such as elastic anisotropy in rocks, changes in strain partitioning during plastic yielding, and stress-induced mechanical twinning.

Ultrasonic nondestructive evaluation of microstructural changes of solid materials under plastic deformation—Part II. Experiment and simulation

Abstract The microstructure of materials introduced by rolling, drawing, heat treatment or other methods of material processing relates to the macroscopic mechanical properties of the materials, such as the strength and anisotropy. The velocity and attenuation of the ultrasonic waves propagating in the materials are known to be dependent upon such microstructural material properties. The author has proposed a theoretical modeling of an ultrasonic nondestructive method to evaluate the microstructural property changes of materials in Part I of this work. In the present paper, annealed effects on plastically deformed states of an aluminium alloy were studied using the proposed ultrasonic nondestructive evaluation method and it was found that close agreement between the simulated results and experimental data was possible.

Quantitative in situ x-ray diffraction analysis of magnetic multilayers during annealing

In situ high-angle x-ray diffraction (XRD) measurements during an annealing process and extensive low- and high-angle XRD analysis before and after annealing have been performed to study the influence of annealing on the microstructure of a Ni81Fe19/Ag multilayer film. We concentrate on a detailed description and quantification of induced changes in microstructural properties and on changes in the crystalline structure of sublayers. The observed effects obtained from the high-angle XRD, where superlattice structural refinement and standard powder diffraction methods were used, are utilized to model the changes from microscopic point of view. The low-angle XRD reflectivity measurements were analyzed using a new distorted-wave Born approximation approach which enables to get information about interlayer structure parameters such as interface roughnesses, degree of vertical correlation and lateral correlation length. The presented low-angle and high-angle analysis demonstrates general applicability of x-ray diffraction for complex and quantitative in-situ investigation of structural changes in metallic multilayers during annealing. An effect of lateral scaling for different types of roughness is discussed and a general approach is shown for the case of metallic multilayers.

EFFECTS OF EMULSIFIER AND SOY FIBER ADDITION ON SENSORY PROPERTIES OF CORN MEAL EXTRUDATE

ABSTRACTYellow dent corn meal was extruded in a twin‐screw extruder with a monoacylglycerol (MAG) and soybean fiber. A ten member descriptive analysis panel was employed to study the effects of four extrusion treatment variables on the textural properties and microstructure of extruded corn meal products. The treatment variables studied included MAG and soybean fiber contents in the feed, extruder screw speed, and feed rate. The microstructure of extruded samples was also studied to support the sensory texture evaluations. MAG addition was found to be the most significant factor affecting texture. Low levels of MAG (0.375%) and soybean fiber additions (5%) resulted in improved overall texture quality. Higher screw speeds were associated with higher cohesiveness and adhesiveness, and feed rate had the least influence. Most of these effects could be attributed to the microstructural property changes under the treatments.

Ultrasonic Nondestructive Evaluation of Microstructural Property Changes of Plastically Deformed Solid under Combined Stress States.

Ultrasonic wave velocities in a plastically deformed medium are known to depend upon its microstructural properties. Therefore, one of the authors proposed a theoretical model of an ultrasonic nondestructive method in order to evaluate plastically deformed states. We obtained good agreement between the numerical and experimental results for an aluminum alloy specimen subjected to uniaxial tension and reported the influence of annealing upon plastic anisotropy and the correlation between the Lankford's value and the shape of yield surface of the specimen. In order to verify the proposed theory we simulated using the internal state variables of an anisotropic distortional yield model longitudinal wave velocities under combined stress states and the subsequent yield surfaces, which were determined to agree well with the experimental results of the longitudinal and transverse wave velocity changes under uniaxial tension test, and then compared the simulated results with experimental results of the longitudinal wave velocity and the yield surface of the aluminum alloy tested in combinations of tension or compression and torsion.