scholarly journals Protective Alumina Scale Growth at 900 °C for a Ni- and Cr-Free Co-Base Model Alloy with γ/γ’-Microstructure: Synergistic Effects by Combining Shot-Peening and Halogenation

Author(s):  
S. P. Hagen ◽  
K. Beck ◽  
D. Kubacka ◽  
H.-E. Zschau ◽  
M. C. Galetz ◽  
...  

AbstractThe oxidation resistance of novel γ/γ’-strengthened Co-base superalloys is clearly outmatched by their Ni-base counterparts within the high-temperature regime. Therefore, surface modification strategies to foster protective alumina growth seem auspicious. This study elucidates the impact of fluorination and shot-peening on protective alumina formation at 900 °C for a quaternary Co-base model alloy (Co-Al-W-Ta system) which is well known for an exceptionally low inherent oxidation resistance. Time-resolved isothermal gravimetric analysis (TGA) in synthetic air, detailed electron microscopic analysis, and X-ray diffraction (XRD) were used. For polished samples, no pronounced enhancement of oxidation resistance could be obtained by halogenation. However, in case of shot-peened samples (halogen-free), an increased tendency for alumina formation is found compared to polished surfaces. The very early stages of oxidation were identified to be especially crucial with respect to sustainable protective scale growth. Most noteworthy is the observation of a strong synergistic effect derived by a combination of halogenation and shot-peening, leading to significantly increased oxidation resistance.

2012 ◽  
Vol 302 (1) ◽  
pp. H167-H179 ◽  
Author(s):  
Kyriakos N. Papanicolaou ◽  
Gladys A. Ngoh ◽  
Erinne R. Dabkowski ◽  
Kelly A. O'Connell ◽  
Rogerio F. Ribeiro ◽  
...  

Molecular studies examining the impact of mitochondrial morphology on the mammalian heart have previously focused on dynamin related protein-1 (Drp-1) and mitofusin-2 (Mfn-2), while the role of the other mitofusin isoform, Mfn-1, has remained largely unexplored. In the present study, we report the generation and initial characterization of cardiomyocyte-specific Mfn-1 knockout (Mfn-1 KO) mice. Using electron microscopic analysis, we detect a greater prevalence of small, spherical mitochondria in Mfn-1 KO hearts, indicating that the absence of Mfn-1 causes a profound shift in the mitochondrial fusion/fission balance. Nevertheless, Mfn-1 KO mice exhibit normal left-ventricular function, and isolated Mfn-1 KO heart mitochondria display a normal respiratory repertoire. Mfn-1 KO myocytes are protected from mitochondrial depolarization and exhibit improved viability when challenged with reactive oxygen species (ROS) in the form of hydrogen peroxide (H2O2). Furthermore, in vitro studies detect a blunted response of KO mitochondria to undergo peroxide-induced mitochondrial permeability transition pore opening. These data suggest that Mfn-1 deletion confers protection against ROS-induced mitochondrial dysfunction. Collectively, we suggest that mitochondrial fragmentation in myocytes is not sufficient to induce heart dysfunction or trigger cardiomyocyte death. Additionally, our data suggest that endogenous levels of Mfn-1 can attenuate myocyte viability in the face of an imminent ROS overload, an effect that could be associated with the ability of Mfn-1 to remodel the outer mitochondrial membrane.


2017 ◽  
Vol 2017 ◽  
pp. 1-17 ◽  
Author(s):  
Gregor A. Zickler ◽  
Josef Fidler

Nanoanalytical TEM characterization in combination with finite element micromagnetic modelling clarifies the impact of the grain misalignment and grain boundary nanocomposition on the coercive field and gives guidelines how to improve coercivity in Nd-Fe-B based magnets. The nanoprobe electron energy loss spectroscopy measurements obtained an asymmetric composition profile of the Fe-content across the grain boundary phase in isotropically oriented melt-spun magnets and showed an enrichment of iron up to 60 at% in the Nd-containing grain boundaries close to Nd2Fe14B grain surfaces parallel to the c-axis and a reduced iron content up to 35% close to grain surfaces perpendicular to the c-axis. The numerical micromagnetic simulations on isotropically oriented magnets using realistic model structures from the TEM results reveal a complex magnetization reversal starting at the grain boundary phase and show that the coercive field increases compared to directly coupled grains with no grain boundary phase independently of the grain boundary thickness. This behaviour is contrary to the one in aligned anisotropic magnets, where the coercive field decreases compared to directly coupled grains with an increasing grain boundary thickness, if Js value is > 0.2 T, and the magnetization reversal and expansion of reversed magnetic domains primarily start as Bloch domain wall at grain boundaries at the prismatic planes parallel to the c-axis and secondly as Néel domain wall at the basal planes perpendicular to the c-axis. In summary our study shows an increase of coercive field in isotropically oriented Nd-Fe-B magnets for GB layer thickness > 5 nm and an average Js value of the GB layer < 0.8 T compared to the magnet with perfectly aligned grains.


2016 ◽  
Vol 30 (27) ◽  
pp. 1650200 ◽  
Author(s):  
Kang Lou ◽  
Feng Hui Wang ◽  
Yong Jun Lu ◽  
Xiang Zhao

Inhomogeneous re-oxidation, which causes graded NiO content along anode thickness, has been confirmed to be a key reason for Ni-based cell cracking during redox progress. In this paper, an analytical model is developed to estimate the impact of inhomogeneous re-oxidation on Ni-based solid oxide fuel cell (SOFC) oxidation resistance. And experiments, in which the SOFC was partially re-oxidized, were implemented for model trial. Model results show that electrolyte internal stress can be significantly reduced (from 367 MPa to 135 MPa, when the oxidation degree is 60%), and the electrolyte can remain intact even when the oxidation degree reaches about 70%, if the anode was re-oxidized uniformly. This impact of inhomogeneous re-oxidation on stress in the electrolyte decreases as the anode thickness increases. Scanning electron microscopic (SEM) images of partially oxidized anode cross-sections confirmed that Ni oxidation was inhomogeneous, in which the outer regions of the anode became almost fully oxidized, while the inner regions remained metallic. And the inhomogeneity increases with the redox times. Consequently, it is important to avoid gradients in NiO content during oxidation progress to prevent cell cracking.


2019 ◽  
Vol 2019 ◽  
pp. 1-13 ◽  
Author(s):  
Ragi Kooliyat ◽  
Joby Thomas Kakkassery ◽  
Vinod P. Raphael ◽  
Sini Varghese Cheruvathur ◽  
Binsi M. Paulson

Schiff base 2,2’-(5,5-dimethylcyclohexane-1,3-diylidene)bis(azan-1-yl-1-ylidene) diphenol (DmChDp) was synthesized and characterized using spectroscopic methods (IR, UV, NMR, and Mass) and cyclic voltammetric (CV) studies. The corrosion inhibition potency of (DmChDp) on mild steel (MS) in 1M HCl and 0.5M H2SO4 was investigated. The corrosion monitoring techniques employed for this purpose are gravimetric and electrochemical methods (EIS and potentiodynamic polarization studies). The study reveals that the Schiff base, DmChDp, acts as excellent corrosion inhibitor on mild steel in 1M HCl. DmChDp obeys Langmuir adsorption isotherm both in 1M HCl and 0.5M H2SO4 on MS. Polarization studies show that DmChDp behaves as a mixed type inhibitor in both media. Scanning electron microscopic analysis established the protective nature of DmChDp on mild steel surface. The impact of temperature on the corrosion of MS was also evaluated using gravimetric method.


Author(s):  
F.J. Sjostrand

In the 1940's and 1950's electron microscopy conferences were attended with everybody interested in learning about the latest technical developments for one very obvious reason. There was the electron microscope with its outstanding performance but nobody could make very much use of it because we were lacking proper techniques to prepare biological specimens. The development of the thin sectioning technique with its perfectioning in 1952 changed the situation and systematic analysis of the structure of cells could now be pursued. Since then electron microscopists have in general become satisfied with the level of resolution at which cellular structures can be analyzed when applying this technique. There has been little interest in trying to push the limit of resolution closer to that determined by the resolving power of the electron microscope.


Author(s):  
Charlotte L. Ownby ◽  
David Cameron ◽  
Anthony T. Tu

In the United States the major health problem resulting from snakebite poisoning is local tissue damage, i.e. hemorrhage and myonecrosis. Since commercial antivenin does not usually prevent such damage to tissue, a more effective treatment of snakebite-induced myonecrosis is needed. To aid in the development of such a treatment the pathogenesis of myonecrosis induced by a pure component of rattlesnake venom was studied at the electron microscopic level.The pure component, a small (4,300 mol. wt.), basic (isoelectric point of 9.6) protein, was isolated from crude prairie rattlesnake (Crotalus viridis viridis) venom by gel filtration (Sephadex G-50) followed by cation exchange chromatography (Sephadex C-25), and shown to be pure by electrophoresis. Selection of the myotoxic component was based on light microscopic observations of injected mouse muscle.


Author(s):  
J. W. Horn ◽  
B. J. Dovey-Hartman ◽  
V. P. Meador

Osmium tetroxide (OsO4) is a universally used secondary fixative for routine transmission electron microscopic evaluation of biological specimens. Use of OsO4 results in good ultrastructural preservation and electron density but several factors, such as concentration, length of exposure, and temperature, impact overall results. Potassium ferricyanide, an additive used primarily in combination with OsO4, has mainly been used to enhance the contrast of lipids, glycogen, cell membranes, and membranous organelles. The purpose of this project was to compare the secondary fixative solutions, OsO4 vs. OsO4 with potassium ferricyanide, and secondary fixative temperature for determining which combination gives optimal ultrastructural fixation and enhanced organelle staining/contrast.Fresh rat liver samples were diced to ∼1 mm3 blocks, placed into porous processing capsules/baskets, preserved in buffered 2% formaldehyde/2.5% glutaraldehyde solution, and rinsed with 0.12 M cacodylate buffer (pH 7.2). Tissue processing capsules were separated (3 capsules/secondary fixative.solution) and secondarily fixed (table) for 90 minutes. Tissues were buffer rinsed, dehydrated with ascending concentrations of ethanol solutions, infiltrated, and embedded in epoxy resin.


Author(s):  
Ralph M. Albrecht ◽  
Scott R. Simmons ◽  
Marek Malecki

The development of video-enhanced light microscopy (LM) as well as associated image processing and analysis have significantly broadened the scope of investigations which can be undertaken using (LM). Interference/polarization based microscopies can provide high resolution and higher levels of “detectability” especially in unstained living systems. Confocal light microscopy also holds the promise of further improvements in resolution, fluorescence studies, and 3 dimensional reconstruction. Video technology now provides, among other things, a means to detect differences in contrast difficult to detect with the human eye; furthermore, computerized image capture, processing, and analysis can be used to enhance features of interest, average images, subtract background, and provide a quantitative basis to studies of cells, cell features, cell labelling, and so forth. Improvements in video technology, image capture, and cost-effective computer image analysis/processing have contributed to the utility and potential of the various interference and confocal microscopic instrumentation.Electron microscopic technology has made advances as well. Microprocessor control and improved design have contributed to high resolution SEMs which have imaging capability at the molecular level and can operate at a range of accelerating voltages starting at 1KV. Improvements have also been seen in the HVEM and IVEM transmission instruments. As a whole, these advances in LM and EM microscopic technology provide the biologist with an array of information on structure, composition, and function which can be obtained from a single specimen. Corrrelative light microscopic analysis permits examination of living specimens and is critical where the “history” of a cell, cellular components, or labels needs to be known up to the time of chemical or physical fixation. Features such as cytoskeletal elements or gold label as small as 0.01 μm, well below the 0.2 μm limits of LM resolution, can be “detected” and their movement followed by VDIC-LM. Appropriate identification and preparation can then lead to the examination of surface detail and surface label with stereo LV-HR-SEM. Increasing the KV in the HR-SEM while viewing uncoated or thinly coated specimens can provide information from beneath the surface as well as increasing Z contrast so that positive identification of surface and subsurface colloidal gold or other heavy metal labelled/stained material is possible. Further examination of the same cells using stereo HVEM or IVEM provides information on internal ultrastructure and on the relationship of labelled material to cytoskeletal or organellar distribution, A wide variety of investigations can benefit from this correlative approach and a number of instrumentational configurations and preparative pathways can be tailored for the particular study. For a surprisingly small investment in time and technique, it is often possible to clear ambiguities or questions that arise when a finding is presented in the context of only one modality.


Author(s):  
Nico Vogler ◽  
Philipp Drabetzki ◽  
Mathias Lindemann ◽  
Hans-Carsten Kühne

AbstractThe thermal gravimetric analysis (TG) is a common method for the examination of the carbonation progress of cement-based materials. Unfortunately, the thermal properties of some components complicate the evaluation of TG results. Various hydrate phases, such as ettringite (AFt), C–S–H and AFm, decompose almost simultaneously in the temperature range up to 200 °C. Additionally, physically bound water is released in the same temperature range. In the temperature range between 450 °C and 600 °C, the decomposition of calcium hydroxide and amorphous or weakly bound carbonates takes place simultaneously. Carbonates, like calcite, from limestone powder or other additives may be already contained in the noncarbonated sample material. For this research, an attempt was made to minimise the influence of these effects. Therefore, differential curves from DTG results of noncarbonated areas and areas with various states of carbonation of the same sample material were calculated and evaluated. Concretes based on three different types of cement were produced and stored under accelerated carbonation conditions (1% CO2 in air). The required sample material was obtained by cutting slices from various depths of previously CO2-treated specimen and subsequent grinding. During the sample preparation, a special attention was paid that no additional carbonation processes took place. As reference method for the determination of the carbonation depth, the sprayed application of phenolphthalein solution was carried out. Microscopic analysis was examined to confirm the assumptions made previously. Furthermore, the observed effect of encapsulation of calcium hydroxide by carbonates caused by the accelerated carbonation conditions was examined more closely.


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