SIMS studies of Ca and Mg distributions in sintered Al2O3

1992 ◽  
Vol 50 (2) ◽  
pp. 1772-1773
Author(s):  
K. K. Soni ◽  
A. M. Thompson ◽  
M. P. Harmer ◽  
D. B. Williams ◽  
J. M. Chabala ◽  
...  
Keyword(s):  
Grain Boundaries ◽  
Analytical Techniques ◽  
Solute Drag ◽  
Ion Microprobe ◽  
Grain Boundary Mobility ◽  
High Lateral Resolution ◽  
Significant Research ◽  
The University

The addition of MgO to α-Al2O3 has been practiced for over 30 years in order to improve greatly the properties of the sintered material. However, a complete understanding of the role of MgO has not been achieved despite significant research efforts by various groups. The most difficult obstacle is microchemical characterization of MgO doped Al2O3. Surface analytical techniques, primarily AES and XPS, have been employed by past researchers in order to analyze the grain boundaries on fractured surfaces of sintered Al2O3. This prior work has met with limited success due to poor sensitivity and spatial resolution. MgO is believed to segregate to the grain boundaries and to retard the grain boundary mobility via a solute drag mechanism; this hypothesis has not been verified experimentally.In this study, the distribution of Ca and Mg was characterized by a high lateral resolution scanning ion microprobe (SIM) developed at The University of Chicago (UC).

Microchemistry of ZnO Varistors

1992 ◽  
Vol 50 (2) ◽  
pp. 1694-1695
Author(s):  
K. K. Soni ◽  
J. Hwang ◽  
V. P. Dravid ◽  
T. O. Mason ◽  
R. Levi-Setti
Keyword(s):  
Grain Boundaries ◽  
Multiple Roles ◽  
Grain Boundary Engineering ◽  
Ion Microprobe ◽  
Dopant Distribution ◽  
Important Ingredient ◽  
Zno Varistor ◽  
Zno Varistors ◽  
Zno Powder ◽  
The University

ZnO varistors are made by mixing semiconducting ZnO powder with powders of other metal oxides e.g. Bi2O3, Sb2O3, CoO, MnO2, NiO, Cr2O3, SiO2 etc., followed by conventional pressing and sintering. The non-linear I-V characteristics of ZnO varistors result from the unique properties that the grain boundaries acquire as a result of dopant distribution. Each dopant plays important and sometimes multiple roles in improving the properties. However, the chemical nature of interfaces in this material is formidable mainly because often trace amounts of dopants are involved. A knowledge of the interface microchemistry is an essential component in the ‘grain boundary engineering’ of materials. The most important ingredient in this varistor is Bi2O3 which envelopes the ZnO grains and imparts high resistance to the grain boundaries. The solubility of Bi in ZnO is very small but has not been experimentally determined as a function of temperature.In this study, the dopant distribution in a commercial ZnO varistor was characterized by a scanning ion microprobe (SIM) developed at The University of Chicago (UC) which offers adequate sensitivity and spatial resolution.

Observation of grain boundary segregation in advanced ceramics using high-resolution imaging SIMS

1995 ◽  
Vol 53 ◽  
pp. 324-325
Author(s):  
R. Levi-Setti ◽  
K. K. Soni ◽  
J. M. Chabala ◽  
A. M. Thompson
Keyword(s):  
Grain Boundary ◽  
Grain Boundaries ◽  
High Spatial Resolution ◽  
Imaging Techniques ◽  
Boundary Segregation ◽  
Ion Microprobe ◽  
Broad Beam ◽  
Resolution Imaging ◽  
Boundary Chemistry

The significance of grain boundaries in controlling processing and properties of ceramics is widely acknowledged. Through the addition of suitable dopants to ceramics, their processability and properties can be improved. These dopants may segregate to grain boundaries, but the characterization of boundary chemistry is a challenging task. Studies of segregation phenomena require the application of high-lateralresolution techniques such as STEM/AEM or surface sensitive techniques such as AES, XPS. These techniques require rigorous sample preparation and have their limitations.The scanning ion microprobe is a powerful tool that has exhibited unprecedented potential in the characterization of grain boundaries in ceramics. When interfaced to a mass spectrometer (magnetic sector in our case), this instrument allows mapping of many trace elements at nanometer level in bulk specimens. The combination of excellent sensitivity and high spatial resolution enables direct imaging of grain boundary segregants. The results thus obtained are free from artifacts that typically complicate analysis with broad beam, non-imaging techniques.

scholarly journals Revascularization of Transplanted Pancreatic Islets and Role of the Transplantation Site

2013 ◽  
Vol 2013 ◽  
pp. 1-13 ◽  
Author(s):  
Andrew R. Pepper ◽  
Boris Gala-Lopez ◽  
Oliver Ziff ◽  
A. M. James Shapiro
Keyword(s):  
Pancreatic Islets ◽  
Cell Mass ◽  
Graft Function ◽  
Beta Cell Mass ◽  
Limiting Factors ◽  
Clinical Settings ◽  
Vascular Networks ◽  
Significant Research

Since the initial reporting of the successful reversal of hyperglycemia through the transplantation of pancreatic islets, significant research efforts have been conducted in elucidating the process of revascularization and the influence of engraftment site on graft function and survival. During the isolation process the intrinsic islet vascular networks are destroyed, leading to impaired revascularization after transplant. As a result, in some cases a significant quantity of the beta cell mass transplanted dies acutely following the infusion into the portal vein, the most clinically used site of engraftment. Subsequently, despite the majority of patients achieving insulin independence after transplant, a proportion of them recommence small, supplemental exogenous insulin over time. Herein, this review considers the process of islet revascularization after transplant, its limiting factors, and potential strategies to improve this critical step. Furthermore, we provide a characterization of alternative transplant sites, analyzing the historical evolution and their role towards advancing transplant outcomes in both the experimental and clinical settings.

The Role of Zirconium Additions in Recrystallization of Aluminum Alloys

2007 ◽  
Vol 558-559 ◽  
pp. 383-387 ◽  
Author(s):  
Hasso Weiland ◽  
Soon Wuk Cheong
Keyword(s):  
Grain Size ◽  
Aluminum Alloys ◽  
Grain Boundary ◽  
Solute Drag ◽  
Heat Treatments ◽  
Boundary Mobility ◽  
Grain Boundary Mobility ◽  
Structural Applications ◽  
Zn Alloys

Control of grain size during recrystallization of aluminum alloys is critical when tailoring material properties for structural applications. Most commonly the grain size is controlled by adding alloying elements which form second phases during homogenization heat treatments small enough to impose a Zener drag on the grain boundary mobility. These phases are known as dispersoids and are in the 10 to 200 nm in diameter range. In Al-Zn alloys, zirconium has been successfully used in controlling the degree of recrystallization after solution heat treatments. It is commonly understood that the Al3Zr dispersoids of about 20 nm in diameter present in the microstructure are the key features affecting grain boundary mobility. With the success of controlling recrystallization in Al- Zn alloys, zirconium has been added to other alloy systems, such as Al-Cu-Mn, and a similar retarding effect in recrystallization kinetics has been observed as seen in the Al-Zn systems. However, in Al-Cu-Mn alloys, zirconium bearing dispersoids are not observable in the microstructure. Consequently, additional microstructural effects such as solute drag need to be considered to explain the experimental observations. In this paper, the role of zirconium additions in aluminum alloys will be summarized.

The effect of time and temperature on the segregation of foreign ions to grain boundaries in growing α-Al2O3 scales

1993 ◽  
Vol 51 ◽  
pp. 950-951
Author(s):  
B. A. Pint ◽  
A. J. Garratt-Reed ◽  
L. W. Hobbs
Keyword(s):  
Grain Boundaries ◽  
Incident Angle ◽  
Oxidation Mechanism ◽  
X Ray Diffraction ◽  
Temperature Oxidation ◽  
Glancing Angle ◽  
Α Al2o3 ◽  
Oxide Adhesion

The addition of small quantities of certain oxygen-active or “reactive” elements (REs) such as Y, Zr, Hf and Ce produces a tremendous improvement in the oxidation behavior of both chromia and alumina-forming alloys. However, few of the hypotheses that have been put forth to explain this phenomenon have been confirmed by careful characterization of the oxidation process.The segregation theory emphasizes the role of RE segregation to oxide grain boundaries and has been successful in correlating the presence of Y and Zr segregants to changes in the oxidation mechanism (thus reducing the oxidation rate) of chromia and alumina scales. Improvements in oxide adhesion have been attributed to the segregation of REs to the metal-alumina interface on doped β-NiAl and FeCrAl alloys. All of these studies employed FEG-STEM equipped with XEDS in order to detect the interfacial segregation.The RE is also found in the scale as RE-rich particles which have been observed after high temperature oxidation using XEDS on SEM and FEG-STEM and detected using glancing-angle (0.5° incident angle) x ray diffraction.

Investigating the role of arginine 21 in the structure and function of human [alpha]a-crystallin

2018 ◽  
Author(s):  
◽  
Ashutosh Shripad Phadte
Keyword(s):  
Functional Characterization ◽  
Lens Fiber Cell ◽  
University Of Missouri ◽  
Mutant Proteins ◽  
Plausible Mechanism ◽  
And Function ◽  
The University

[ACCESS RESTRICTED TO THE UNIVERSITY OF MISSOURI AT AUTHOR'S REQUEST.] Cataractogenesis in the eye lens occurs as a result of protein aggregation. Of the multiple mutations in [alpha]A-crystallins associated with the development of congenital hereditary cataract, three identified mutations target R21 within the N- terminal domain of the protein. On structural and functional characterization of a recently identified mutant of [alpha]A-crystallin, [alpha]A-R21Q, we revealed the contribution of R21 in dictating the interaction of [alpha]A-crystallin with other proteins. [alpha]A-R21Q showed and enhanced chaperone-like function, and increased binding to lens fiber cell membranes. Transduction of mutant proteins in ARPE-19 cells prevented their apoptosis in the presence of oxidative stress, suggesting a role for R21 in modulating the anti-apoptotic function of [alpha]A-crystallin. In addition, the R21Q point mutation rescued the chaperone-like activity of [alpha]A-G98R crystallin as well as palliated [alpha]A-G98R mediated cytotoxicity otherwise observed in transduction experiments. Although another mutation, R157Q rescued the chaperone-like activity of [alpha]A-G98R, the double mutant exhibited a loss of its cytoprotective function. The results therefore implicate an important role of R21 in regulating the functional aspect of [alpha]A-crystallin. [alpha]A-crystallin derived peptides have been shown to prevent non-specific aggregation of unfolding proteins in vitro. We show that the [alpha]A-crystallin derived mini-chaperone (mini-[alpha]A) mediated stabilization of self-aggregating [alpha]A-G98R crystallin and bovine [subscript]-crystallin occurs via compensation of lost surface charge. The observation therefore suggests a plausible mechanism of action of [alpha]A-crystallin derived peptides of therapeutic interest.

The Role of Crystallization of an Intergranular Glassy Phase in Determining Grain Boundary Residual Stresses in Debased Aluminas

1989 ◽  
Vol 170 ◽  
Author(s):  
Nitin P. Padture ◽  
Helen M. Chan ◽  
Brian R. Lawn ◽  
Michael J. Readey
Keyword(s):  
Grain Size ◽  
Grain Boundary ◽  
Residual Stresses ◽  
Glassy Phase ◽  
Analytical Techniques ◽  
Ceramic Materials ◽  
Strength Test ◽  
Second Phase

AbstractThe influence of microstructure on the crack resistance (R-curve) behavior of a commercial debased alumina containing large amounts of glassy phase (28 vol %) has been studied using the Indentation-Strength test. The effect of two microstructural variables, viz. grain size and the nature of the intergranular second phase (glassy or crystalline) has been evaluated. Crystallization of the intergranular glass was carried out in order to generate residual stresses at the grain boundaries, which have been shown to enhance R-curve behavior in ceramic materials. Enhancement of the R-curve behavior was observed with the increase in grain size. However, no effect of the nature of the intergranular second phase on the R-curve behavior, in small and large grain materials, was observed. The results from characterization of these materials using various analytical techniques is presented, together with possible explanations for the observed effects.

Characterization of grain growth, nature and role of grain boundaries in microcrystalline silicon—review of typical features

2006 ◽  
Vol 501 (1-2) ◽  
pp. 107-112 ◽  
Author(s):  
J. Kočka ◽  
T. Mates ◽  
H. Stuchlíková ◽  
J. Stuchlík ◽  
A. Fejfar
Keyword(s):  
Grain Boundaries ◽  
Grain Growth ◽  
Microcrystalline Silicon

scholarly journals Two New Reference Materials Based on Tobacco Leaves: Certification for over a Dozen of Toxic and Essential Elements

2012 ◽  
Vol 2012 ◽  
pp. 1-16 ◽  
Author(s):  
Zbigniew Samczyński ◽  
Rajmund S. Dybczyński ◽  
Halina Polkowska-Motrenko ◽  
Ewelina Chajduk ◽  
Marta Pyszynska ◽  
...  
Keyword(s):  
Reference Materials ◽  
Interlaboratory Comparison ◽  
Statistical Evaluation ◽  
Certified Reference Materials ◽  
Analytical Techniques ◽  
Essential Elements ◽  
Tobacco Leaves ◽  
Certified Values

The preparation, certification, and characterization of two new biological certified reference materials for inorganic trace analysis have been presented. They are based on two different varieties of tobacco leaves, namely, Oriental Basma Tobacco Leaves (INCT-OBTL-5), grown in Greece, and Polish Virginia Tobacco Leaves (INCT-PVTL-6), grown in Poland. Certification of the materials was based on the statistical evaluation of results obtained in a worldwide interlaboratory comparison, in which 87 laboratories from 18 countries participated, providing 2568 laboratory averages on nearly 80 elements. It was possible to establish the certified values of concentration for many elements in the new materials, that is, 37 in INCT-OBTL-5 and 36 in INCT-PVTL-6, including several toxic ones like As, Cd, Hg, Pb, and so forth. The share and the role of instrumental analytical techniques used in the process of certification of the new CRMs are discussed.

scholarly journals Natural Products in the Prevention of Metabolic Diseases: Lessons Learned from the 20th KAST Frontier Scientists Workshop

Nutrients ◽  
2021 ◽  
Vol 13 (6) ◽  
pp. 1881
Author(s):  
Seung J. Baek ◽  
Bruce D. Hammock ◽  
In-Koo Hwang ◽  
Qingxiao Li ◽  
Naima Moustaid-Moussa ◽  
...  
Keyword(s):  
Natural Products ◽  
Metabolic Diseases ◽  
Current Knowledge ◽  
Analytical Techniques ◽  
Lessons Learned ◽  
Bioactive Components ◽  
Underlying Causes ◽  
The University ◽  
And Oxidative Stress

The incidence of metabolic and chronic diseases including cancer, obesity, inflammation-related diseases sharply increased in the 21st century. Major underlying causes for these diseases are inflammation and oxidative stress. Accordingly, natural products and their bioactive components are obvious therapeutic agents for these diseases, given their antioxidant and anti-inflammatory properties. Research in this area has been significantly expanded to include chemical identification of these compounds using advanced analytical techniques, determining their mechanism of action, food fortification and supplement development, and enhancing their bioavailability and bioactivity using nanotechnology. These timely topics were discussed at the 20th Frontier Scientists Workshop sponsored by the Korean Academy of Science and Technology, held at the University of Hawaii at Manoa on 23 November 2019. Scientists from South Korea and the U.S. shared their recent research under the overarching theme of Bioactive Compounds, Nanoparticles, and Disease Prevention. This review summarizes presentations at the workshop to provide current knowledge of the role of natural products in the prevention and treatment of metabolic diseases.

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