Positron Trapping within the Grain and at Grain Boundaries in Sintered Alumina of High Impurity Content

2004 ◽  
Vol 445-446 ◽  
pp. 177-179 ◽  
Author(s):  
A. Si Ahmed ◽  
Jerzy Kansy ◽  
Kamel Zarbout ◽  
Gérard Moya ◽  
Dominique Gœuriot
Keyword(s):  
Grain Boundaries ◽  
Impurity Content ◽  
Positron Trapping ◽  
High Impurity

Consequences of Silicon Segregation on the Dielectric Properties of Sintered Alumina

2006 ◽  
Vol 249 ◽  
pp. 281-0 ◽  
Author(s):  
Kamel Zarbout ◽  
Gérard Moya ◽  
Jean Bernardini ◽  
Denise Moya-Siesse ◽  
A. Si Ahmed ◽  
...  
Keyword(s):  
Grain Boundaries ◽  
Positron Lifetime ◽  
Dielectric Breakdown ◽  
Breakdown Strength ◽  
Impurity Content ◽  
Impurity Level ◽  
Dielectric Breakdown Strength ◽  
High Impurity ◽  
Potential Traps ◽  
Shallow Traps

The dielectric breakdown strengths of two series of sintered alumina samples of low and high impurity content (where Si is the dominant element with, respectively, 90 and 1500 ppm) and impurity level (25 ppm of Si and 12 ppm of Ti) are compared with positron lifetime measurements. The dielectric breakdown strength of sintered alumina is found higher than that of single crystal. This improvement is stronger when silicon is the only major foreign element. If, in addition to SiO2, MgO and CaO are present in substantial amounts, the improvement is lessened. This is attributed to the enhanced bulk solubility of Si. These results are discussed by calling for the potential traps for positrons and electrons that are located at grain boundaries. It is deduced that the improvement of the dielectric breakdown strength stems from the consequences of Si segregation at grain boundaries via electron trapping in shallow traps, which are likely the x '' Al • Al ) V : (3Si clusters.

Positron trapping at grain boundaries

1982 ◽  
Vol 27 (3) ◽  
pp. 149-152 ◽  
Author(s):  
C. Hidalgo ◽  
N. Diego
Keyword(s):  
Grain Boundaries ◽  
Positron Trapping

Runaway electron dynamics in tokamak plasmas with high impurity content

2015 ◽  
Vol 22 (9) ◽  
pp. 092512 ◽  
Author(s):  
J. R. Martín-Solís ◽  
A. Loarte ◽  
M. Lehnen
Keyword(s):  
Runaway Electron ◽  
Impurity Content ◽  
Tokamak Plasmas ◽  
Electron Dynamics ◽  
High Impurity

scholarly journals PURIFICATION AND QUANTITATION OF GLUTARALDEHYDE AND ITS EFFECT ON SEVERAL ENZYME ACTIVITIES IN SKELETAL MUSCLE

1967 ◽  
Vol 15 (11) ◽  
pp. 652-661 ◽  
Author(s):  
PAUL J. ANDERSON
Keyword(s):  
Skeletal Muscle ◽  
Surface Area ◽  
Enzyme Activities ◽  
Absorption Maximum ◽  
High Surface ◽  
High Surface Area ◽  
Impurity Content ◽  
Ultraviolet Spectrophotometry ◽  
Enzyme Recovery ◽  
High Impurity

Glutaraldehyde was quantitated by chemical titration, osmometry and ultraviolet spectrophotometry. Pure glutaraldehyde exhibited an absorption maximum at 280 mµ and absorbance at this wavelength conformed to Beer's law. A second maximum at 235 mµ indicated the presence of "impurities" (probably of polymeric origin), and effective purification was achieved by distillation or by repeated washing with charcoal of high surface area (Norit EX). Purified glutaraldehyde was stable when stored under nitrogen or freon at 4°C. Representative oxidoreductase, transferase and hydrolase activities were measured in supernatants and sediments of skeletal muscle homogenates that had been treated with glutaraldehyde samples of low, intermediate and high impurity content (based on relative absorbance at 235 mµ). Enzyme recovery was inversely related to impurity content, the highest levels being obtained from tissue treated with the purest glutaraldehyde.

scholarly journals Ice crystal properties of amber ice and strain enhancement at the base of cold Antarctic glaciers

2005 ◽  
Vol 40 ◽  
pp. 185-190 ◽  
Author(s):  
Denis Samyn ◽  
Anders Svensson ◽  
Sean J. Fitzsimons ◽  
Reginald D. Lorrain
Keyword(s):  
Impurity Content ◽  
Ice Crystal ◽  
Fine Grained ◽  
Automated Method ◽  
Lattice Preferred Orientation ◽  
High Impurity ◽  
Deformation Properties ◽  
Crystal Properties ◽  
Analytical Accuracy

AbstractTo improve our understanding of the deformation properties of cold-based polar glaciers, we examine here some of the factors leading to the localization of strain within the amber ice facies. We present a crystallographic case study of amber ice (a fine-grained bubbly ice containing a relatively high impurity content) sampled at the base of two Antarctic glaciers. The crystal fabrics and textures of amber ice were computed by application of a recently developed automated method. To date, it was tedious and awkward to determine amber ice facies accurately because of the sub-millimetric crystal size and relatively high debris content of this facies. The authomatic analytical method applied in this study allows not only for improving analytical accuracy in this task but also for considerably reducing the time of analysis. Our investigations reveal highly homogeneous crystallographic properties for the studied amber ice. The ice crystals are mainly polygonal, equant and sub-millimetric, and show a strong lattice-preferred orientation. These properties, beside the relatively high impurity content, are likely to exert a major control on strain enhancement in amber ice when this facies is present at the base of cold glaciers.

Positron-trapping mechanism at grain boundaries

1985 ◽  
Vol 31 (11) ◽  
pp. 6941-6946 ◽  
Author(s):  
C. Hidalgo ◽  
N. de Diego ◽  
F. Plazaola
Keyword(s):  
Grain Boundaries ◽  
Trapping Mechanism ◽  
Positron Trapping

Temperature dependence of positron trapping at grain boundaries

1997 ◽  
Vol 9 (31) ◽  
pp. 6749-6759 ◽  
Author(s):  
S Aina ◽  
A Dupasquier ◽  
P Folegati ◽  
N De Diego ◽  
J del Rio ◽  
...  
Keyword(s):  
Temperature Dependence ◽  
Grain Boundaries ◽  
Positron Trapping

Normal and Abnormal Grain Growth in Ceramics - NbC-Co and Alumina

2006 ◽  
Vol 11-12 ◽  
pp. 47-52
Author(s):  
Jong Hoon Lee ◽  
Min Cheol Chu ◽  
Seong Jai Cho ◽  
Duk Yong Yoon
Keyword(s):  
Grain Boundaries ◽  
Grain Growth ◽  
Impurity Content ◽  
Normal Growth ◽  
Abnormal Grain Growth ◽  
Alumina Powder ◽  
Liquid Matrix ◽  
Diffusion Controlled ◽  
Interface Roughening ◽  
Grain Growth Behavior

Normal and abnormal grain growth has been observed in 70NbC-30Co with varying B concentrations at 1450°C and in alumina with varying impurity and additive concentrations at 1600°C -1650°C as typical systems with and without liquid matrix. The grain growth behavior depends on the roughening of the interfaces as indicated by the grain and grain boundary shapes. When 4% B is added to 70NbC-30Co, the NbC grains in Co-rich liquid matrix are spherical and undergo diffusion controlled normal growth, because the grain-liquid interface is rough. As the B concentration is decreased to 3, 2, 1, and 0%, the NbC grains become more cubic and the tendency for abnormal grain growth increases because of the step growth mechanism of the flat singular surface segments. When compacts of high purity alumina powder are sintered at 1650°C, the grain boundaries are smoothly curved, indicating their atomically rough structures. With increasing impurity content—in particular SiO2—in the alumina powder, abnormal grain growth becomes more pronounced with increasing number of flat grain boundaries. These singular grain boundaries are expected to move by a step mechanism and thus cause the abnormal grain growth. These results show that the interface roughening and hence the grain growth mode changes gradually with the additive or impurity concentrations. Therefore, the abnormal grain growth cannot be sharply distinguished from the normal grain growth as has been previously suggested in general and for alumina in particular.

Modification of Copper

2018 ◽  
Vol 284 ◽  
pp. 357-362
Author(s):  
A.V. Sulitsin ◽  
Raisa K. Mysik ◽  
Sergey V. Brusnitsyn
Keyword(s):  
Crystal Structure ◽  
Rare Earth ◽  
Rare Earth Elements ◽  
Grain Boundaries ◽  
Cross Section ◽  
Impurity Content ◽  
Metallographic Analysis ◽  
Plastic Properties ◽  
Average Area ◽  
Misch Metal

The requirement of modification of copper is proved in the article. As a modifier for copper the misch metal is proposed. The misch metal contains rare earth elements having greatest modifying ability. The results of experiments of the influence of misch metal in an amount from 0.0025 to 0.0125 wt. % on the formation of crystal structure of cast copper with different impurity content are presented. The metallographic analysis of macrostructure of copper is made and the average area of cross section of grains in the structure of copper is determined. The average area of cross section of grains in the structure of copper of brand M00 decreases from 5 to 0.9 mm2 with addition of 0.005 wt. % of misch metal. The average area of cross section of grains in the structure of copper of brand M1 decreases from 6 to 0.45 mm2 with addition of 0.005 wt. % of misch metal. An increase of quantity of added misch metal more than 0.005 wt. % dose does not lead to significant decrease of average area of cross section of grain in the structure of copper. The investigation of microstructure of samples of cast copper of brands of M00 and M1 is made. It is established that the addition of misch metal in the copper dose does not lead to increase in the thickness of the grain boundaries. The results of experiments are shown that addition of misch metal in the copper leads to increase of stregth and plastic properties of copper. Based on the results of experiments the mechanism of modification of copper is proposed.

Positron Trapping Effection at the Grain Boundaries of Fe73.5Cu1Nb3Si13.5B9 Nanocrystalline Alloys

1994 ◽  
Vol 175-178 ◽  
pp. 605-608
Author(s):  
Ya Zen Zhang ◽  
Li Jun Wang ◽  
Lin Hua Zhe ◽  
Zi Bin Zhou
Keyword(s):  
Grain Boundaries ◽  
Nanocrystalline Alloys ◽  
Positron Trapping
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