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Microstructural Changes (microstructural + change)
Selected AbstractsMicrostructural Study of Mn and Si Co-substituted Hydroxyapatite Thin Films Produced by a Sol,Gel MethodADVANCED ENGINEERING MATERIALS, Issue 7 2009Aligül Büyükaksoy Microstructural changes in sol,gel derived hydroxyapatite thin films associated with Mn and Si co-substitution are investigated. The apatite-forming ability of fabricated thin films in simulated body fluid are found to be affected by changes in the crystallinity and formation of a more dissolvable calcium phosphate phase. [source] Effects of Zirconium Additions on the Microstructure of As-Cast and Aged AZ91 Magnesium AlloyADVANCED ENGINEERING MATERIALS, Issue 3 2009Farhoud Kabirian The effects of Zr addition on the microstructure of AZ91 alloy were investigated under as-cast and isothermally aged conditions. The microstructures contained a eutectic , -Mg17Al12 phase together with fine Al,Zr intermetallic compounds. These intermetallic compounds inhibited grain growth during the 420,°C isothermal aging of Zr-containing alloys. Microstructural changes caused by Zr additions were most probably due to the consumption of Al by Zr, and redistribution of Al during solidification of dendrites. [source] Transfer of metallic debris from the metal surface of an acetabular cup to artificial femoral heads by scraping: Comparison between alumina and cobalt,chrome headsJOURNAL OF BIOMEDICAL MATERIALS RESEARCH, Issue 1 2008Chong Bum Chang Abstract We aimed to investigate the transfer of metal to both ceramic (alumina) and metal (cobalt,chrome) heads that were scraped by a titanium alloy surface under different load conditions. The ceramic and metal heads for total hip arthroplasties were scraped by an acetabular metal shell under various loads using a creep tester. Microstructural changes in the scraped area were visualized with a scanning electron microscope, and chemical element changes were assessed using an energy dispersive X-ray spectrometry. Changes in the roughness of the scraped surface were evaluated by a three-dimensional surface profiling system. Metal transfer to the ceramic and metal heads began to be detectable at a 10 kg load, which could be exerted by one-handed force. The surface roughness values significantly increased with increasing test loads in both heads. When the contact force increased, scratching of the head surface occurred in addition to the transfer of metal. The results documented that metallic debris was transferred from the titanium alloy acetabular shell to both ceramic and metal heads by minor scraping. This study suggests that the greatest possible effort should be made to protect femoral heads, regardless of material, from contact with metallic surfaces during total hip arthroplasty. © 2007 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 2008 [source] Influence of microstructural changes on corrosion behaviour of thermally aged Ti-6Al-7Nb alloyMATERIALS AND CORROSION/WERKSTOFFE UND KORROSION, Issue 5 2004L. Thair Abstract Solution treatment and ageing (STA) is an effective strengthening method for , + , titanium alloys. This paper reports the effect of solution treatment and aging on the corrosion behaviour of Ti-6Al-7Nb alloy in a simulated body fluid (Ringer's solution). Ti-6Al-7Nb alloy is hot rolled in the , + , field and subjected to solution treatment above and below its beta transus temperature (1283 K). The solution treated specimens are water quenched (WQ), air-cooled (AC), and furnace cooled (FC) at three different rates, and subsequently aged at 823 K for 4 h. Microstructural changes were examined using optical microscopy and phases developed were analyzed using XRD. The influence of microstructure on the corrosion performance of the alloys are discussed in detail based on the Open Circuit Potential (OCP), passive current density and area of repassivation loop values obtained from the cyclic polarization study in Ringer's solution. The passive current density was low (0.5 ,A/cm2) for the specimen with duplex microstructure obtained for specimen solution treated at 1223 K, air-cooled, and aged, in comparison with that for as-rolled specimen (1.5 ,A/cm2). The corrosion aspects resulting from various heat treatments are discussed in detail. [source] Microstructural changes and material parameter developmentPROCEEDINGS IN APPLIED MATHEMATICS & MECHANICS, Issue 1 2009W. H. Müller At previous GAMM-meetings the first two authors reported on the spinodal decomposition and coarsening in lead-containing as well as lead-free solders. They derived an extended diffusion equation for the corresponding computer modelling on the basis of a multi-component theory of mixtures. Consequently, they performed numerical studies that are capable of predicting quantitatively the development of SnPb and AgCu microstructures. Knowing this development is quite important from a technological point-of-view in order to quantify the current joining capability of the solder material ("Resteigenschaften"). On the basis of these results this paper now attempts to predict the corresponding change of the materials properties, in particular of the elastic constants. This is done by means of a homogenization technique developed by the last two authors. In this paper we will briefly summarize the results related to the extended diffusion equation, present numerical simulations of the coarsening process, outline the theory underlying the homogenization and, finally, show how the material properties behave over time. Wherever possible, alternative analytical solutions for the homogenized constants are also presented (e.g., by laminate theory). (© 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] The effect of oxygen on interface microstructure evolution in CdS/CdTe solar cellsPROGRESS IN PHOTOVOLTAICS: RESEARCH & APPLICATIONS, Issue 5 2002D.S. Albin Microstructural changes at the CdS/CdTe solar cell interface where close-spaced sublimation (CSS) is used as the growth technique to deposit the p -type CdTe absorber layer are studied by systematic layer characterization at various stages during heterojunction growth. CdS layers grown by both chemical bath deposition (CBD) and CSS provide a basis for determining the effects of CdS crystallinity, grain size, and oxygen content on the subsequent CdTe layer. As-grown CBD CdS films exhibit small grains and variations in optical properties attributed to film impurities. In contrast, CSS yields CdS films with good crystallinity, larger grains, and nearly ideal optical properties. The hexagonal nature of CSS-grown CdS is seen to nucleate hexagonal CdTe during the initial stages of CdTe film growth. Cubic CdS deposited by CBD in contrast promotes cubic CdTe nucleation. Oxygen anneals in the latter case can aid hexagonal CdTe nucleation. Auger electron spectroscopy (AES) and transmission electron microscopy (TEM) of the CdS/CdTe interface show CdS-dependent differences in interdiffusion at the interface. This interdiffusion appears to be determined by the oxygen level in the CdS. When low-oxygen-containing CSS CdS films are used, sulfur diffusion is substantial, leading to significant consumption of the CdS layer. When these same films are annealed in oxygen, the consumption is reduced. Te diffusion into the CdS layer is also observed to decrease with oxygen anneals. Optical modeling shows that Te alloying with the CdS layer can greatly reduce the short-circuit current of CdS/CdTe devices. Copyright © 2002 John Wiley & Sons, Ltd. [source] A REVIEW OF CURRENT CLINICAL APPLICATIONS OF UPPER GASTROINTESTINAL ZOOM ENDOSCOPYDIGESTIVE ENDOSCOPY, Issue 2005Kenshi Yao Current clinical applications of upper gastrointestinal (GI) zoom endoscopy were reviewed. The objective of upper GI zoom endoscopy has been the diagnosis of neoplastic lesions as well as the diagnosis of minute inflammatory mucosal change. The target organ and pathology of the neoplastic lesions have been squamous cell carcinoma in the oro- and hypo-pharynx and in the esophagus; intestinal metaplasia, dysplasia, and adenocarcinoma in Barrett's esophagus; and adenocarcinoma in the stomach. For analyzing the magnified endoscopic findings, there were two different basic principles (mucosal microstructural change and subepithelial microvascular changes). Overall diagnostic accuracy for diagnosing a neoplastic lesion was above 80% throughout the upper GI tract. Although the diagnostic accuracy of the zoom endoscopy technique seems to be superior to that of the ordinary endoscopy technique alone, the continuous efforts to establish standardized guidelines and procedures are mandatory in order to lead to the routine use of upper GI zoom endoscopy in clinical practice. [source] The preservation of seismic anisotropy in the Earth's mantle during diffusion creepGEOPHYSICAL JOURNAL INTERNATIONAL, Issue 3 2009J. Wheeler SUMMARY Seismic anisotropy in the Earth, particularly in the mantle, is commonly interpreted as the result of solid-state deformation by dislocation creep that induces a lattice preferred orientation (LPO). Diffusion creep operates where stress levels are lower and/or grain sizes smaller. It is often assumed that diffusion creep induces grain rotations that eventually destroy any existing LPO. A new numerical test of this assumption shows that it is not necessarily the case: diffusion creep will create some relative grain rotations, but rotation rates decrease through time. Hence, when microstructural change due to diffusion creep dominates that due to grain growth, defined here as ,type P' behaviour (the converse being ,type O' behaviour), the model indicates that LPO will be weakened but preserved (for a variety of strain paths including both pure and simple shear). One measure of anisotropy is the proportional difference in shear wave velocities for different polarization vectors (AVs). A model olivine microstructure with equant grains and initial maximum AVs of 10.0 percent has this value reduced to 6.7 per cent when ,rotational steady state' is attained. Other models with different initial maximum AVs values exhibit final maximum AVs values more than half the initial values. If the grains are initially elongate by a factor of 2, maximum AVs is reduced just slightly, to 8.5 per cent. Thus, when grain growth plays a subordinate role to the deformation, diffusion creep weakens seismic anisotropy by a factor of less than 2 (using maximum AVs as a measure and olivine as an example). Consequently, the link between seismic anisotropy and deformation mechanism in the mantle requires reappraisal: regions with LPO may comprise material which once deformed by dislocation creep, but is now deforming by diffusion creep in a rotational steady state. [source] Influence of film thickness on the electrical and magnetic properties of Co,Fe,Al,O filmsPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 12 2007M. H. Phan Abstract Influence of film thickness (t) on the electrical and magnetic properties of Co,Fe,Al,O films has been systematically investigated via means of vibrating sample magnetometry (VSM), permeability spectra and magneto-optical Kerr effect (MOKE). It is found that the electrical resistivity (,) decreases as the film thickness increases; , = 412.5 µ,cm for the t = 600 nm sample decreases to , = 368.2 µ,cm for the t = 1200 nm sample. The coercive force, measured along the easy-axis direction, decreases as the film thickness increases. Interestingly, along the hard-axis magnetization direction, the magnetic hysteresis loop is reversed and the coercive force is negative for the t = 600 and 800 nm samples. However, this peculiar feature disappears as t reaches 1200 nm, which is probably attributed to the microstructural change with respect to changes of film thickness. At a frequency of 1GHz, the hard-axis effective permeability decreases from 1252 to 1000 as the film thickness increases from 600 to 1200 nm, respectively. The VSM and MOKE results reveal an increase in magnetic anisotropy in the near-surface region of the film. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Molecular and diffusion tensor imaging of epileptic networksEPILEPSIA, Issue 2008Aimee F. Luat Summary Several studies have shown that seizure-induced cellular and molecular changes associated with chronic epilepsy can lead to functional and structural alterations in the brain. Chronic epilepsy, when medically refractory, may be associated with an expansion of the epileptic circuitry to involve complex interactions between cortical and subcortical neuroanatomical substrates. Progress in neuroimaging has led not only to successful identification of epileptic foci for surgical resection, but also to an improved understanding of the functional and microstructural changes in long-standing epilepsy. Positron emission tomography (PET), functional magnetic resonance imaging (fMRI) and diffusion tensor imaging (DTI) are all promising tools that can assist in elucidating the underlying pathophysiology in chronic epilepsy. Studies using PET scanning have demonstrated dynamic changes associated with the evolution from acute to chronic intractable epilepsy. Among these changes are data to support the existence of secondary epileptogenesis in humans. MRI with DTI is a powerful tool which has the ability to characterize microstructural abnormalities in epileptic foci, and to demonstrate the white matter fibers and tracts participating in the epileptic network. In this review, we illustrate how PET and DTI can be applied to depict the functional and microstructural alterations associated with chronic epilepsy. [source] Neutron Reflectometry: A Tool to Investigate Diffusion Processes in Solids on the Nanometer Scale,ADVANCED ENGINEERING MATERIALS, Issue 6 2009Harald Schmidt Abstract The investigation of self-diffusion for the characterization of kinetic process in solids is one of the most fundamental tasks in materials science. We present the method of neutron reflectometry (NR), which allows the detection of extremely short diffusion lengths in the order of 1,nm and below at corresponding low self-diffusivities between 10,25 and 10,20,m2 s,1. Such a combination of values cannot be achieved by conventional methods of diffusivity determination, like the radiotracer method, secondary ion mass spectrometry, quasielastic neutron scattering, or nuclear magnetic resonance. Using our method, the extensive characterization of materials which are in a non-equilibrium state, like amorphous or nanocrystalline solids becomes possible. Due to the small experimentally accessible diffusion length microstructural changes (grain growth and crystallization) taking place simultaneously during the actual diffusion experiment can be avoided. For diffusion experiments with NR isotope multilayers are necessary, which are chemical homogeneous but isotope modulated films. We illustrate the basic aspects and potential of this technique using model systems of different classes of materials: single crystalline germanium, amorphous silicon nitride, and nanocrystalline iron. [source] Invited review: Modelling quality changes of fruits and vegetables during drying: a reviewINTERNATIONAL JOURNAL OF FOOD SCIENCE & TECHNOLOGY, Issue 9 2010Sakamon Devahastin Summary Fruits and vegetables have received much attention as these materials have been reported to contain various phytochemicals, which are claimed to exert many health benefits. When extraction of bioactive compounds cannot be performed on fresh fruits and vegetables, drying needs to be conducted to keep the materials for later use. Dried fruits and vegetables have also been regarded as alternative fat-free snacks and received more attention from the food industry during the past decade. This implies that not only nutritional changes, but also other changes including physical and microstructural changes are of importance and need to be optimised, preferably through the use of various modelling approaches. The objective of this article is to provide a brief review of some advances in modelling quality changes of fruits and vegetables during drying. These include modelling of nutritional, colour and selected physical changes. Approaches to monitoring and modelling microstructural changes are also mentioned. [source] Neuroimaging of cortical development and brain connectivity in human newborns and animal modelsJOURNAL OF ANATOMY, Issue 4 2010Gregory A. Lodygensky Abstract Significant human brain growth occurs during the third trimester, with a doubling of whole brain volume and a fourfold increase of cortical gray matter volume. This is also the time period during which cortical folding and gyrification take place. Conditions such as intrauterine growth restriction, prematurity and cerebral white matter injury have been shown to affect brain growth including specific structures such as the hippocampus, with subsequent potentially permanent functional consequences. The use of 3D magnetic resonance imaging (MRI) and dedicated postprocessing tools to measure brain tissue volumes (cerebral cortical gray matter, white matter), surface and sulcation index can elucidate phenotypes associated with early behavior development. The use of diffusion tensor imaging can further help in assessing microstructural changes within the cerebral white matter and the establishment of brain connectivity. Finally, the use of functional MRI and resting-state functional MRI connectivity allows exploration of the impact of adverse conditions on functional brain connectivity in vivo. Results from studies using these methods have for the first time illustrated the structural impact of antenatal conditions and neonatal intensive care on the functional brain deficits observed after premature birth. In order to study the pathophysiology of these adverse conditions, MRI has also been used in conjunction with histology in animal models of injury in the immature brain. Understanding the histological substrate of brain injury seen on MRI provides new insights into the immature brain, mechanisms of injury and their imaging phenotype. [source] Determination of directionally dependent structural and microstructural information using high-energy X-ray diffractionJOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 6 2008J. E. Daniels High-energy synchrotron X-ray diffraction using a monochromatic beam and large area detector offers a unique method for the study of directionally dependent sample information. The very short wavelengths and subsequent low scattering angles mean that scattering vectors at all angles approximately perpendicular to the beam direction are sampled simultaneously. Here a method is proposed and demonstrated in which the magnitude and directions of structural and microstructural changes can be determined with higher resolution than was possible with previously used techniques. The method takes advantage of parametric refinements over multiple data sets using the profile fitting package TOPAS. Examples of the technique applied to the study of strains in multiphase zirconium alloys and microstructural texture in ferroelastic/ferroelectric ceramics are given. The angular precision in lattice strain for a diffraction image with good statistics is found to be below 0.1°. [source] Influence of the remelting process on the fatigue behavior of electron beam irradiated UHMWPEJOURNAL OF BIOMEDICAL MATERIALS RESEARCH, Issue 2 2006J. A. Puértolas Abstract Electron beam irradiation at doses below 150 kGy is a widely used technique to obtain highly crosslinked ultra-high-molecular-weight polyethylene (UHMWPE). Its current use in total joint replacement components may improve wear resistance and decrease UHMWPE particle debris. However, currently used post-irradiation thermal treatments, which aim to decrease the free radicals within the material, introduce microstructural changes that affect UHMWPE mechanical properties, particularly the fatigue strength. This influence may be crucial in total knee replacements, where fatigue-related damage limits the lifespan of the prosthesis. Therefore, more studies are required to understand UHMWPE fatigue after current crosslinking protocols. This study was planned to evaluate the influence of UHMWPE remelting after irradiation on the material fatigue resistance. The remelting was achieved at 150°C for 2 h on UHMWPE previously irradiated at 50, 100, and 150 kGy. Fatigue evaluation included short-term tests under cyclic tensile stress with zero load ratio, R = 0, and 1 Hz. In addition, stress-life testing was performed using 12% yield as the criterion for failure. Near-threshold fatigue crack propagation experiments were also performed at a frequency of 5 Hz, and crack length was measured in nonthermally treated and remelted irradiated UHMWPE. Crystallinity percentage was calculated from DSC measurements. The results pointed out that irradiation positively contributed to total life analysis, but the further remelting process decreased the flaw initiation resistance. On the other hand, both processes negatively affected the fatigue resistance of notched components. From a clinical point of view, the results suggest that the material fatigue behavior should be carefully studied in new UHMWPE to avoid changes related to material processing. © 2005 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 2006 [source] Effect of Sodium Chloride, Acetic Acid, and Enzymes on Carotene Extraction in Carrots (Daucus carota L.)JOURNAL OF FOOD SCIENCE, Issue 2 2005Maria E. Jaramillo-Flores ABSTRACT: Carrot root cores were cut off longitudinally and treated with NaCl (0.6 and 1.2 M) and/or acetic acid (1.33%, 2.67%, and 4%) solutions. The extractability of the carotenes was estimated. Similarly, carrot cores were also treated with some degrading enzymes (carbohydrases, lipases, and proteases) alone or in combination to study the effect of the tissue rupture or the hydrolysis of possible complexes or interactions between carotenes and other components on the carotene extractability. The results showed that acetic acid increased the extractability of ,- and , carotenes up to 99.8% and 94.6%, respectively, at a 4% acid concentration compared with the samples without any treatment. This increase was directly proportional to the acid concentration. An increase in extractability was also observed for NaCl, although the increases were not as high as in the previous case with values of 49% and 41.4% for ,- and ,-carotenes respectively at a 0.6 M concentration. The study of microstructural changes and extractability revealed that the enzymatic treatments could have broken some carotene complexes and interactions and altered the carbohydrate matrix structure, increasing to a certain extent the extractability of carotenes. It can be concluded then that pickling with 4% acetic acid is a good method to increase the extractability of ,- and ,-carotenes. [source] Predicting and monitoring cancer treatment response with diffusion-weighted MRIJOURNAL OF MAGNETIC RESONANCE IMAGING, Issue 1 2010Harriet C. Thoeny MD Abstract An imaging biomarker that would provide for an early quantitative metric of clinical treatment response in cancer patients would provide for a paradigm shift in cancer care. Currently, nonimage based clinical outcome metrics include morphology, clinical, and laboratory parameters, however, these are obtained relatively late following treatment. Diffusion-weighted MRI (DW-MRI) holds promise for use as a cancer treatment response biomarker as it is sensitive to macromolecular and microstructural changes which can occur at the cellular level earlier than anatomical changes during therapy. Studies have shown that successful treatment of many tumor types can be detected using DW-MRI as an early increase in the apparent diffusion coefficient (ADC) values. Additionally, low pretreatment ADC values of various tumors are often predictive of better outcome. These capabilities, once validated, could provide for an important opportunity to individualize therapy thereby minimizing unnecessary systemic toxicity associated with ineffective therapies with the additional advantage of improving overall patient health care and associated costs. In this report, we provide a brief technical overview of DW-MRI acquisition protocols, quantitative image analysis approaches and review studies which have implemented DW-MRI for the purpose of early prediction of cancer treatment response. J. Magn. Reson. Imaging 2010. © 2010 Wiley-Liss, Inc. [source] Ultraviolet curing of acrylic systems: Real-time Fourier transform infrared, mechanical, and fluorescence studiesJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 23 2002Carmen Peinado Abstract The photopolymerization of acrylic-based adhesives has been studied by Fourier transform infrared and fluorescence analysis in real time. Real-time infrared spectroscopy reveals the influence of the nature of the photoinitiator on the kinetics of the reaction. Furthermore, the incident light intensity dependence of the polymerization rate shows that primary radical termination is the predominant mechanism during the initial stages of the curing of the acrylic system with bis(2,4,6-trimethylbenzoyl) phenyl phosphine oxide (TMBAPO) as a photoinitiator. The fluorescence intensity of selected probes increases during the ultraviolet curing of the adhesive, sensing microenvironmental viscosity changes. Depending on the nature of the photoinitiator, different fluorescence,conversion curves are observed. For TMBAPO, the fluorescence increases more slowly during the initial stage because of the delay in the gel effect induced by primary radical termination. Mechanical tests have been carried out to determine the shear modulus over the course of the acrylic adhesive ultraviolet curing. In an attempt to extend the applications of the fluorescence probe method, we have undertaken comparisons between the fluorescence changes and shear modulus. Similar features in both curves confirm the feasibility of the fluorescence method for providing information about microstructural changes during network formation. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 4236,4244, 2002 [source] In vivo high-resolution synchrotron radiation imaging of collagen-induced arthritis in a rodent modelJOURNAL OF SYNCHROTRON RADIATION, Issue 3 2010Chang-Hyuk Choi In vivo microstructures of the affected feet of collagen-induced arthritic (CIA) mice were examined using a high-resolution synchrotron radiation (SR) X-ray refraction technique with a polychromatic beam issued from a bending magnet. The CIA models were obtained from six-week-old DBA/1J mice that were immunized with bovine type II collagen and grouped as grades 0,3 according to a clinical scoring for the severity of arthritis. An X-ray shadow of a specimen was converted into a visual image on the surface of a CdWO4 scintillator that was magnified using a microscopic objective lens before being captured with a digital charge-coupled-device camera. Various changes in the joint microstructure, including cartilage destruction, periosteal born formation, articular bone thinning and erosion, marrow invasion by pannus progression, and widening joint space, were clearly identified at each level of arthritis severity with an equivalent pixel size of 2.7,µm. These high-resolution features of destruction in the CIA models have not previously been available from any other conventional imaging modalities except histological light microscopy. However, thickening of the synovial membrane was not resolved in composite images by the SR refraction imaging method. In conclusion, in vivo SR X-ray microscopic imaging may have potential as a diagnostic tool in small animals that does not require a histochemical preparation stage in examining microstructural changes in joints affected with arthritis. The findings from the SR images are comparable with standard histopathology findings. [source] Constrained Sintering of a Glass Ceramic Composite: II.JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 12 2009Symmetric Laminate The sintering behavior of symmetric laminates has been experimentally measured and modeled. Two cases are distinguished: (i) sintering of a viscous layer between viscous substrates and (ii) sintering of a viscous layer between elastic substrates. A simple model based on a persisting isotropic microstructure allowed computation of developing in-plane stresses. These in conjunction with a viscous Poisson's coefficient were taken to predict out-of-plane stresses and finally densification rate. This approach, however, proved unsuccessful to predict the large observed differences in densification rate between laminates constrained by either green or dense alumina substrates. The discrepancy was found to be due to widely different microstructures developing with different degrees of elastic constraint. Pore area and pore and particle orientation were determined to quantify these microstructural changes. [source] Ni,YSZ Solid Oxide Fuel Cell Anode Behavior Upon Redox Cycling Based on Electrical CharacterizationJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 11 2007Trine Klemensø Nickel (Ni),yttria-stabilized zirconia (YSZ) cermets are a prevalent material used for solid oxide fuel cells. The cermet degrades upon redox cycling. The degradation is related to microstructural changes, but knowledge of the mechanisms has been limited. Direct current conductivity measurements were performed on cermets and cermets where the Ni component was removed. Measurements were carried out before, during, and after redox cycling the cermet. The cermet conductivity degraded over time due to sintering of the nickel phase. Following oxidizing events, the conductivity of the cermets improved, whereas the conductivity of the YSZ phase decreased. An improved model of the redox degradation mechanism was established based on the measurements. [source] Correlation Between Microstructure and Creep Behavior in Liquid-Phase-Sintered ,-Silicon CarbideJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 3 2006M. Castillo-Rodríguez The influence of increasing the sintering time from 1 to 7 h on the microstructure evolution and the mechanical properties at high temperature was studied in ,-silicon carbide (,-SiC) sintered in argon atmosphere with Y2O3,Al2O3 (10% weight) as liquid phase (LPS-,-SiC). The density decreased from 98.8% to 94.9% of the theoretical value, the grain size increased from 0.64 to 1.61 ,m, and some of the grains became elongated. The compression tests were performed in argon atmosphere, between 1450°C and 1625°C and stresses between 25 and 450 MPa, with the strain rate being between 4.2 × 10,8 and 1.5 × 10,6 s,1. The stress exponent n and the activation energy Q were determined, finding values of n between 2.4±0.1 and 4.5±0.2 and Q=680±35 kJ/mol for samples sintered for 1 h, and n between 1.2±0.1 and 2.4±0.1 and Q=710±90 kJ/mol for samples sintered for 7 h. The correlation between these results and the microstructure indicates that grain-boundary sliding and the glide and climb of dislocations, both accommodated by bulk diffusion, may be two independent deformation mechanisms operating. At the temperatures of the tests, the existence of solid-state reactions between SiC and the sintering additives is responsible of the microstructural changes observed. These effects are not a consequence of the process of deformation, but rather they are because of the thermal treatment of the material during the creep. [source] Precipitation of MgO·nAl2O3 in Mg-Doped ,-Al2O3 under Electron IrradiationJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 1 2003Kenji Kaneko A number of nanoscale precipitates with random orientations were produced by electron irradiation of polycrystalline Mg-doped ,-Al2O3. The precipitation behavior and microstructural changes were observed using in situ high-resolution transmission electron microscopy. A ring pattern corresponding to a polycrystalline fcc structure was obtained from the region of these precipitates by selected-area diffraction, and they were identified as nonstoichiometric MgO·nAl2O3. It is believed that Al2O3 with MgO(ss) and/or MgO at the grain boundaries is effectively stabilized by the electron irradiation process, forming the fundamental structure of MgO·nAl2O3. The average size of the precipitates is about 10 nm. [source] Strength Degradation and Failure Mechanisms of Electron-Beam Physical-Vapor-Deposited Thermal Barrier CoatingsJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 7 2001James A. Ruud Failure mechanisms were determined for electron-beam physical-vapor-deposited thermal barrier coating (TBC) systems from the degradation of mechanical properties and microstructural changes in a furnace cycle test. Bond strength degradation for TBCs resulted from the initiation and growth of interfacial delamination defects between the yttria-stabilized zirconia topcoat and the thermally grown alumina (TGO). It is proposed that defects started from concave depressions in the bondcoat surface created by the grit-blast-cleaning process and that defect growth was driven by the reduction in compressive strain in the TGO as the alumina deformed into and displaced the bondcoat during the cooling cycles. Inclusion of yttrium in the substrate resulted in a doubling of the furnace cycle life of the TBCs because of enhanced fracture toughness of the TGO-bondcoat interface. [source] Aging Effects on the Phase Composition and Chain Mobility of Isotactic Poly(propylene)MACROMOLECULAR MATERIALS & ENGINEERING, Issue 10 2008Cristian Hedesiu Abstract Changes in phase composition and chain mobility in injection-molded isotactic poly(propylene), crystallized from the melt with slow cooling rate and subsequently quenched, associated with aging at temperature well above Tg for 150 and 1 000 h, are studied using time-domain 1H solid-state NMR and XRD. All sample exhibit physical aging when exposed to elevated temperatures, and the physical aging kinetics was observed to depend on the morphology of the homopolymer iPP and aging temperatures. The significant increase in the tensile modulus in time was observed for injection-molded iPP. The observed property changes induced by aging are attributed to microstructural changes within the semi-rigid and amorphous fractions. [source] Local electrochemical properties of laser beam-welded high-strength Al,Zn,Mg,Cu alloysMATERIALS AND CORROSION/WERKSTOFFE UND KORROSION, Issue 1 2008J. Wloka Butt welds of two high-strength Al,Zn,Mg,Cu alloys with different zinc contents were welded by a laser beam welding technique. Due to the high energy density of the laser beam, the microstructural changes are confined to very thin regions. Electrochemical properties of the weld heat-affected zones are investigated by local electrochemical measurement techniques and correlated with microhardness measurements, macroscopic corrosion behaviour and metallographic sections. It turned out that microelectrochemical techniques, especially the EC-pen is a versatile and easy to handle tool for the resolution of changes in the electrochemical properties across a weld bead. It unveils modifications, which cannot be resolved by hardness measurements. By microcell measurements, local corrosion kinetics can be estimated. [source] Influence of microstructural changes on corrosion behaviour of thermally aged Ti-6Al-7Nb alloyMATERIALS AND CORROSION/WERKSTOFFE UND KORROSION, Issue 5 2004L. Thair Abstract Solution treatment and ageing (STA) is an effective strengthening method for , + , titanium alloys. This paper reports the effect of solution treatment and aging on the corrosion behaviour of Ti-6Al-7Nb alloy in a simulated body fluid (Ringer's solution). Ti-6Al-7Nb alloy is hot rolled in the , + , field and subjected to solution treatment above and below its beta transus temperature (1283 K). The solution treated specimens are water quenched (WQ), air-cooled (AC), and furnace cooled (FC) at three different rates, and subsequently aged at 823 K for 4 h. Microstructural changes were examined using optical microscopy and phases developed were analyzed using XRD. The influence of microstructure on the corrosion performance of the alloys are discussed in detail based on the Open Circuit Potential (OCP), passive current density and area of repassivation loop values obtained from the cyclic polarization study in Ringer's solution. The passive current density was low (0.5 ,A/cm2) for the specimen with duplex microstructure obtained for specimen solution treated at 1223 K, air-cooled, and aged, in comparison with that for as-rolled specimen (1.5 ,A/cm2). The corrosion aspects resulting from various heat treatments are discussed in detail. [source] Veränderungen der mechanischen Eigenschaften von Magnesium-Druckgusslegierungen nach langzeitiger thermischer BeanspruchungMATERIALWISSENSCHAFT UND WERKSTOFFTECHNIK, Issue 2 2004D. Regener Pressure die cast magnesium alloys; long-term annealing; microstructure; mechanical properties Abstract Die thermische Belastbarkeit von Magnesium-Druckgusslegierungen ist noch nicht ausreichend untersucht. Um die Auswirkung einer thermischen Belastung auf die Gefügestabilität und damit auf das Festigkeits- und Verformungsverhalten einschätzen zu können, werden die Legierungen AZ91, AM50 und AE42 bei 150,°C und 200,°C einer 1000 h-Langzeitglühung unterworfen. Nach der Glühung werden Zugversuche, in situ-Zugversuche und Mikrohärtemessungen bei Raumtemperatur durchgeführt und die Ergebnisse anhand der mikrostrukturellen Veränderungen diskutiert. Changes of the Mechanical Properties of Pressure Die Cast Magnesium Alloys Subjected to Long-Term Thermal Exposure The thermal resistance of pressure die cast magnesium alloys is yet not investigated sufficiently. In order to assess the effect of a thermal exposure on the microstructural stability and on the strength and deformation behaviour, the alloys AZ91, AM50 and AE42 are subjected to a long-term annealing for 1000 h at 150,°C and 200,°C. After the annealing, tensile tests, in situ tensile tests and microhardness measurements are carried out and the results are discussed on the basis of the microstructural changes. [source] Thermal histories of IVA iron meteorites from transmission electron microscopy of the cloudy zone microstructureMETEORITICS & PLANETARY SCIENCE, Issue 3 2009J. I. GOLDSTEIN Thin sections for TEM analysis were produced by a focused ion beam instrument. Use of the TEM allowed us to avoid potential artifacts which may be introduced during specimen preparation for SEM analysis of high Ni particles <30 nm in size and to identify microchemical and microstructural changes due to the effects of shock induced reheating. No cloudy zone was observed in five of the eight moderately to highly shocked (>13 GPa) IVA irons that were examined in the TEM. Shock induced reheating has allowed for diffusion from 20 nm to 400 nm across kamacite/taenite boundaries, recrystallization of kamacite, and the formation, in Jamestown, of taenite grain boundaries. In the eleven IVA irons with cloudy zone microstructures, the size of the high-Ni particles in the cloudy zone increases directly with increasing bulk Ni content. Our data and the inverse correlation between cooling rate and high-Ni particle size for irons and stony-irons show that IVA cooling rates at 350-200 °C are inversely correlated with bulk Ni concentration and vary by a factor of about 15. This cooling rate variation is incompatible with cooling in a metallic core that was insulated with a silicate mantle, but is compatible with cooling in a metallic body of radius 150 ± 50 km. The widths of the tetrataenite regions next to the cloudy zone correlate directly with high-Ni particle size providing another method to measure low temperature cooling rates. [source] Microstructure,magnetic properties relationships in nanocrystalline Nd,Fe,Co,Ge,B annealed ribbonsPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 2 2006R. Gholamipour Abstract In this work, the effects of Ge addition on the microstructure and magnetic properties of some rapidly quenched Nd13.5Fe(74.9,z )Co5.5Gez B6 alloys with z = 0.0, 0.18, 0.36, 0.54, 0.72 and 0.9 prepared by a rapid solidification method were studied. For the first time, detailed microstructural study of nanometer size grain boundaries enriched with very small amount of Ge as well as Nd was carried out using 3 Dimensional Atom Probe (3DAP) technique. The magnitudes of Br and (BH )max were seen to increase for the samples substituted with up to 0.36 at% Ge in spite of the fact that Ge is a non-magnetic atom. This was related to the observed change of Co concenteration in matrix phase. However, the magnetic properties deteriorated for the samples with Ge addition beyond 0.36 at%. The observed magnetic properties are discussed in relation with the observed microstructural changes monitored by 3DAP and TEM techniques. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] | |||||||||||||||||||||||||||||||||||||