Influence of Heat Treatment on the Anelastic Properties of MgB2

2010 ◽  
Vol 660-661 ◽  
pp. 832-836
Author(s):  
Marcos Ribeiro da Silva ◽  
Carlos Roberto Grandini
Keyword(s):  
Heat Treatment ◽  
Grain Boundaries ◽  
High Vacuum ◽  
Ultra High Vacuum ◽  
Crystalline Lattice ◽  
Relaxation Processes ◽  
Mechanical Spectroscopy ◽  
Critical Temperatures ◽  
Dislocation Movement ◽  
Binary Compounds

The discovery of the superconductivity of MgB2 was of great importance, because this material is one of the few known binary compounds and has one of the highest critical temperatures (39° K). As MgB2 is a granular compound, it is fundamentally important to understand the mechanisms of the interaction of the defects and the crystalline lattice, in addition to the eventual processes involving the grain boundaries that compose the material. In this sense, the mechanical spectroscopy measurements constitute a powerful tool for this study, because through them we can obtain important information about phase transitions, the behavior of interstitial or substitutional elements, dislocations, grain boundaries, diffusion, instabilities, and other imperfections of the lattice. For this paper, the samples were prepared using the PIT method and were characterized by density, X-ray diffraction, scanning electron microscopy, electric resistivity, magnetization, and mechanical spectroscopy. The samples were measured in their as-cast condition and after an ultra-high-vacuum heat treatment. The results showed complex spectra, in which were identified relaxation processes due to dislocation movement, interaction among interstitial elements and dislocations, auto-diffusion, and movement of grain boundaries. Some of these processes disappeared with the heat treatment.

Exoelectron emission from unexcited metallic glasses Fe78B13Si9 during heat treatment

1992 ◽  
Vol 7 (6) ◽  
pp. 1396-1399 ◽  
Author(s):  
Yoshihisa Watanabe ◽  
Tadayoshi Kubozoe ◽  
Yoshikazu Nakamura
Keyword(s):  
Heat Treatment ◽  
Metallic Glasses ◽  
High Vacuum ◽  
Ultra High Vacuum ◽  
Exoelectron Emission ◽  
Radiation Chemical ◽  
Temperature Range ◽  
High Vacuum Condition ◽  
Before And After ◽  
Ultra High Vacuum Condition

Exoelectron emission from the surface of unexcited metallic glasses Fe78B13Si9 during heat treatment has been studied under ultra high vacuum condition. In the first heating cycle, exoelectrons are emitted from the as-cast ribbon in the temperature range from approximately 423 K to 773 K (150 °C to 500 °C), although the surface of the specimen is not excited by ionizing radiation, chemical processes, or mechanical treatments prior to measurements. In the second and subsequent heating cycles, however, there is no anomalous emission observed in the same temperature range. In order to elucidate the mechanism of emission, the surface of the specimen is observed by the atomic force microscope (AFM) before and after measurements. In the AFM image, many crystallites in the amorphous matrix can be found in the surface of the heated specimen. These experimental results show that exoelectrons are emitted in the same temperature range as the early stages of crystallization on the surface of metallic glasses. We hypothesize that the two effects are correlated.

Substitutional Impurity Segregation to the Σ 5 (310)/[001] Stgb in Cu Doped Aluminum and Ag Doped Copper

2001 ◽  
Vol 7 (S2) ◽  
pp. 246-247
Author(s):  
J. M. Plitzko ◽  
G. H. Campbell ◽  
W. E. King ◽  
S. M. Foiles ◽  
C. Kisielowski
Keyword(s):  
Grain Boundaries ◽  
High Vacuum ◽  
Ultra High Vacuum ◽  
Face Centered Cubic ◽  
Substitutional Impurity ◽  
Fcc Metals ◽  
Impurity Segregation ◽  
Symmetric Tilt ◽  
Impurity Species ◽  
Face Centered

The phenomenon of segregation is of long standing scientific interest and has been studied extensively, both theoretically as well as experimentally. For our investigations we have chosen the Σ5 symmetric tilt grain boundaries (STGB) in two face-centered cubic (FCC) metals, aluminum and copper. Both metals were doped with only 1 at% of the impurity species (Cu and Ag). One of our major goals in this study was to investigate the size effect on segregation of an impurity to distinct sites at the grain boundary. Therefore we have selected the Ag as an impurity in Cu and Cu as an impurity in Al. The latter one is of special interest for applications like interconnects in microcircuits, where one of the major controlling factors of electromigration is expected to be the diffusion or segregation of Cu atoms at Al grain boundaries.The model grain boundaries have been fabricated with ultra-high vacuum diffusion bonding of single crystals which bonds the bicrystals under highly controlled environmental conditions.

scholarly journals Surface structures of β- FeSi2 formed by heat-treatment in ultra-high vacuum and their influence on homoepitaxial growth

2011 ◽  
Vol 11 ◽  
pp. 174-176 ◽  
Author(s):  
S. Matsumura ◽  
K. Ochiai ◽  
H. Udono ◽  
F. Esaka ◽  
K. Yamaguchi ◽  
...  
Keyword(s):  
Heat Treatment ◽  
High Vacuum ◽  
Ultra High Vacuum ◽  
Surface Structures ◽  
Homoepitaxial Growth

Surface Properties of GaAs Passivated With (NH4)2Sx Solution

1995 ◽  
Vol 386 ◽  
Author(s):  
Kyung-Soo Suh ◽  
Hyung-Ho Park ◽  
Jong-Lam Lee ◽  
Haechon Kim ◽  
Kyung-Ik Cho ◽  
...  
Keyword(s):  
Heat Treatment ◽  
Surface Properties ◽  
Photoelectron Spectroscopy ◽  
High Vacuum ◽  
Ultra High Vacuum ◽  
Gaas Surface ◽  
X Ray ◽  
Partial Decomposition

ABSTRACTSurface properties of GaAs passivated with (NH4)2Sx solution have been compared with HCl-treated GaAs using X-ray photoelectron spectroscopy, Sulfur treatment on GaAs surface results in the formation of S-Ga and S-As bonds, which remain after successive rinsing for I minute in DI water. The evolution of Ga 2p3 and As 3d peaks in the sulfidation treated GaAs was monitored with the exposing time to air. After 10 days exposure to air, the Ga-O and As-O bonds slightly increased, but maintained almost constant for further exposure. The increase of Ga-O and As-O bonds induces the partial decomposition of sulfur bonds. Decomposition and evaporation behaviors of sulfur and oxygen were observed through the heat treatment of sulfidation treated GaAs under ultra high vacuum (less than l × 10-9 torr). After anneal at 350 – 450 °C, slight decrease of sulfur and oxygen due to the decomposition of As-O bond were observed. No more sulfur was found after anneal at 550 – 650 °C, where the decomposition of Ga-O bond was completed.

Influence of Oxidation On Boron Sgregation to Grain Boundaries of In-Situ Fractured Ni3Al Alloys

2000 ◽  
Vol 654 ◽  
Author(s):  
S. A. Koch ◽  
D. T. L van Agterveld ◽  
G. Palasantzas ◽  
J. Th. M. De Hosson
Keyword(s):  
Grain Boundaries ◽  
Room Temperature ◽  
High Vacuum ◽  
Spot Size ◽  
Ultra High Vacuum ◽  
Nucleation Sites ◽  
Ni Oxidation ◽  
Subsequent Exposure ◽  
Auger Microscopy

AbstractScanning electron and scanning Auger microscopy studies were performed on in-situ fractured B-doped hypostoichiometric Ni3Al alloys. The Auger measurements on the fracture surface showed a very small amount or the total absence of B. Further, B segregated to the grain boundaries during subsequent exposure to the ambient system ultra-high vacuum environment at room temperature. The B segregation appeared to be driven by a mechanism of electronic nature related to Ni enrichment and O supplied from the environment. Ni-oxidation at room temperature is in accordance with model predictions for small beam sizes (≤10 µm) based on the premise that the electron beam creates additional nucleation sites around of which oxide growth occurs. With increasing the size of the e-beam the oxidation process becomes slower and chemisorption of oxygen plays a significant role. As a result the Ni-oxide depth decreases drastically with increasing spot size and offers an alternative route for monitoring the thickness of NiO in a nanometer range.

Thin Pyrolytic Graphite Films for Electron Microscope Substrates

1971 ◽  
Vol 29 ◽  
pp. 226-227 ◽  
Author(s):  
George H. N. Riddle ◽  
Benjamin M. Siegel
Keyword(s):  
Vacuum Chamber ◽  
Pyrolytic Graphite ◽  
High Vacuum ◽  
Dark Field ◽  
Ultra High Vacuum ◽  
Graphite Substrate ◽  
Nickel Substrate ◽  
Routine Procedure ◽  
Field Electron Microscopy ◽  
Dark Field Electron

A routine procedure for growing very thin graphite substrate films has been developed. The films are grown pyrolytically in an ultra-high vacuum chamber by exposing (111) epitaxial nickel films to carbon monoxide gas. The nickel serves as a catalyst for the disproportionation of CO through the reaction 2C0 → C + CO2. The nickel catalyst is prepared by evaporation onto artificial mica at 400°C and annealing for 1/2 hour at 600°C in vacuum. Exposure of the annealed nickel to 1 torr CO for 3 hours at 500°C results in the growth of very thin continuous graphite films. The graphite is stripped from its nickel substrate in acid and mounted on holey formvar support films for use as specimen substrates.The graphite films, self-supporting over formvar holes up to five microns in diameter, have been studied by bright and dark field electron microscopy, by electron diffraction, and have been shadowed to reveal their topography and thickness. The films consist of individual crystallites typically a micron across with their basal planes parallel to the surface but oriented in different, apparently random directions about the normal to the basal plane.

A High Voltage Electron Microscopy Study of Sub-Oxide Formation in Vanadium

1971 ◽  
Vol 29 ◽  
pp. 212-213
Author(s):  
R. H. Geiss ◽  
R. L. Ladd ◽  
K. R. Lawless
Keyword(s):  
High Vacuum ◽  
Microscopy Study ◽  
Electron Microscopy Study ◽  
Ultra High Vacuum ◽  
Pure Oxygen ◽  
Pressure Oxidation ◽  
High Voltage Electron Microscopy ◽  
Oxidation Study ◽  
Voltage Electron ◽  
Good Agreement

Detailed electron microscope and diffraction studies of the sub-oxides of vanadium have been reported by Cambini and co-workers, and an oxidation study, possibly complicated by carbon and/or nitrogen, has been published by Edington and Smallman. The results reported by these different authors are not in good agreement. For this study, high purity polycrystalline vanadium samples were electrochemically thinned in a dual jet polisher using a solution of 20% H2SO4, 80% CH3OH, and then oxidized in an ion-pumped ultra-high vacuum reactor system using spectroscopically pure oxygen. Samples were oxidized at 350°C and 100μ oxygen pressure for periods of 30,60,90 and 160 minutes. Since our primary interest is in the mechanism of the low pressure oxidation process, the oxidized samples were cooled rapidly and not homogenized. The specimens were then examined in the HVEM at voltages up to 500 kV, the higher voltages being necessary to examine thick sections for which the oxidation behavior was more characteristic of the bulk.

The High Resolution Scanning Transmission Electron Microscope

1974 ◽  
Vol 32 ◽  
pp. 316-317
Author(s):  
A. V. Crewe
Keyword(s):  
Electron Microscope ◽  
High Resolution ◽  
High Vacuum ◽  
Scanning Transmission Electron Microscope ◽  
Ultra High Vacuum ◽  
Resolving Power ◽  
Imaging Characteristics ◽  
Transmission Electron ◽  
Scanning Transmission ◽  
The Moment

The high resolution STEM is now a fact of life. I think that we have, in the last few years, demonstrated that this instrument is capable of the same resolving power as a CEM but is sufficiently different in its imaging characteristics to offer some real advantages.It seems possible to prove in a quite general way that only a field emission source can give adequate intensity for the highest resolution^ and at the moment this means operating at ultra high vacuum levels. Our experience, however, is that neither the source nor the vacuum are difficult to manage and indeed are simpler than many other systems and substantially trouble-free.

Structure of Palladium Single-Crystal Films Prepared by Flash Evaporation onto (001) NaCl Substrates

1970 ◽  
Vol 28 ◽  
pp. 456-457
Author(s):  
L. E. Murr ◽  
G. Wong
Keyword(s):  
Single Crystal ◽  
High Vacuum ◽  
Ultra High Vacuum ◽  
High Rate ◽  
Flash Evaporation ◽  
Optimum Load ◽  
Single Crystal Films ◽  
Crystal Films ◽  
A Current

Palladium single-crystal films have been prepared by Matthews in ultra-high vacuum by evaporation onto (001) NaCl substrates cleaved in-situ, and maintained at ∼ 350° C. Murr has also produced large-grained and single-crystal Pd films by high-rate evaporation onto (001) NaCl air-cleaved substrates at 350°C. In the present work, very large (∼ 3cm2), continuous single-crystal films of Pd have been prepared by flash evaporation onto air-cleaved (001) NaCl substrates at temperatures at or below 250°C. Evaporation rates estimated to be ≧ 2000 Å/sec, were obtained by effectively short-circuiting 1 mil tungsten evaporation boats in a self-regulating system which maintained an optimum load current of approximately 90 amperes; corresponding to a current density through the boat of ∼ 4 × 104 amperes/cm2.

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