Feasibility Of Directional Solidification Of Lanthanum Hexaboride In a Boron Matrix

1981 ◽  
Vol 12 ◽  
Author(s):  
Kathryn V. Logan
Keyword(s):  
Directionally Solidify ◽  
Eutectic Mixture ◽  
Lanthanum Hexaboride ◽  
Hydrogen Atmosphere ◽  
Zone Melting ◽  
Circular Cylinders ◽  
Pure Hydrogen ◽  
Directional Growth ◽  
Internal Zone ◽  
Cold Pressed

Attempts were made to directionally solidify lanthanum hexaboride as uniformly spaced rods, less than one micron in diameter, in a boron matrix. Lanthanum hexaboride and boron powders were combined in a near eutectic mixture, formed into right circular cylinders and melted by RF induction heating in a pure hydrogen atmosphere using a modified internal zone melting technique.Ball milling, uniaxial cold pressing, isostatic pressing and hot pressing were investigated as possible means of increasing the sample density before melting in the RF induction furnace. RF coupling was achieved directly in the hot pressed pellet, and indirectly through the use of a molybdenum preheater in the uniaxially cold pressed pellets. Internal zone melting and conventional crucible melting in various materials were tried.Directional growth was observed in the pellets that were uniaxially cold pressed and preheated with a molybdenum tube sleeve. Lanthanum hexaboride fibers with an ℓ/d ratio of about ten to one and other forms of aligned microstructures were observed in selected areas of the pellet.

The Research of Non-Oriented Electrical Steel Processed by Stress Relief Annealing Experiments

2014 ◽  
Vol 887-888 ◽  
pp. 252-256
Author(s):  
Zhun Li ◽  
Jing Liu ◽  
Shi De Li ◽  
Ze Lin Zheng
Keyword(s):  
Magnetic Properties ◽  
Electrical Steel ◽  
Core Loss ◽  
Reference Method ◽  
Stress Relief ◽  
Hydrogen Atmosphere ◽  
Silicon Steel ◽  
Pure Hydrogen ◽  
Final Annealing ◽  
Annealing Experiments

A high grade non-oriented electrical steel final annealing product was processed by stress relief annealing experiments under pure hydrogen atmosphere using different process parameters. The samples were compared in the aspects of magnetic properties and anisotropy, then analyzed the phenomena concerned with grain size, texture and precipitates aspects. The experiments showed that the samples magnetic properties were most improved in the 850 degrees stress relief annealing experiment, thus providing a reference method for non-oriented silicon steel stress relief annealing experiments and to obtain low core loss non-oriented silicon steel.

scholarly journals A Spectroscopic Survey in the EUV of the “Coolest” Hot DA Stars

1996 ◽  
Vol 152 ◽  
pp. 217-222
Author(s):  
Jean Dupuis ◽  
Stéphane Vennes
Keyword(s):  
Effective Temperature ◽  
White Dwarfs ◽  
Heavy Element ◽  
Extreme Ultraviolet ◽  
Diffusion Theory ◽  
Hydrogen Atmosphere ◽  
Element Abundance ◽  
Pure Hydrogen ◽  
Element Abundances ◽  
The One

We present an analysis of the extreme ultraviolet (EUV) spectroscopy of a sample of 10 DA white dwarfs observed by the Extreme Ultraviolet Explorer (EUVE). We have selected white dwarfs cooler than about 50,000 K and with presumably low heavy element abundances. The goal of this study is to determine the fundamental atmospheric parameters, namely the effective temperature and chemical composition, of these stars by fitting their continua with synthetic spectra computed from pure hydrogen LTE/line-blanketed model atmospheres. The question of the presence (or absence) of trace elements is explored by comparing EUV-determined effective temperatures to the one obtained from a fit of hydrogen balmer lines. It is found that the majority of the DA in the sample are consistent with having a pure hydrogen atmosphere. One of the star, MCT0027-634, is another possible example of a HZ 43-type white dwarf, having an effective temperature above 50000 K and a low heavy element abundance, i.e., much lower than predicted by diffusion theory.

Surface Chemical Behavior of Uranium Metal in Hydrogen Atmosphere Studied by XPS

2003 ◽  
Vol 10 (02n03) ◽  
pp. 325-330 ◽  
Author(s):  
Xiaolin Wang ◽  
Xiaoguo Fu ◽  
Zhengping Zhao
Keyword(s):  
Chemical Structure ◽  
Uranium Oxide ◽  
Main Product ◽  
Profile Analysis ◽  
Hydrogen Atmosphere ◽  
Pure Hydrogen ◽  
Surface Chemical ◽  
Chemical Behavior ◽  
Uranium Metal ◽  
Good Agreement

The surface chemical behavior of clean uranium metal in a hydrogen atmosphere at 80°C and 120°C has been studied using XPS and thermodynamic calculation. The main product is uranium oxide rather than hydride uranium on the uranium surface after the exposure of uranium to extremely pure hydrogen, and the U4f7/2 binding energy of UH3 has been found to be 378.6 ± 0.1 eV. An elevated temperature (120°C) is beneficial to the formation of UH3 species at the same hydrogen exposures. The depth profile analysis of XPS indicates that the chemical structure of the surface layer was UO2/UH3/U after the exposure of hydrogen reached 1.31 × 10-6 L (1 L = 10-6 Torr·s). Results of thermodynamic calculations are in good agreement with the above conclusions.

Fabrication of Lotus-Type Porous Ni-(15, 28 and 31) at.% Al Alloys by Unidirectional Solidification in Hydrogen Atmosphere

2007 ◽  
Vol 544-545 ◽  
pp. 323-326
Author(s):  
Soong Keun Hyun ◽  
Teruyuki Ikeda ◽  
Hideo Nakajima
Keyword(s):  
Liquid Metals ◽  
Hydrogen Atmosphere ◽  
Zone Melting ◽  
Al Alloys ◽  
Unidirectional Solidification ◽  
Hydrogen Gas ◽  
Solidification Velocity ◽  
Melting Technique ◽  
Cylindrical Pores ◽  
High Frequency Induction

Lotus-type porous Ni- (15, 28 and 31) at.% Al alloys whose long cylindrical pores are aligned in one direction were fabricated by continuous zone melting technique under high-pressure gas of hydrogen of 2.5 MPa. A part of 5-10 mm in length of the rod in the vicinity of the coil was melted by high frequency induction heating, and was moved downwards by electric motors at a constant velocity of 330 μms-1 to 500 μms-1 for unidirectional solidification. The pores are formed as a result of precipitation from the supersaturated hydrogen gas when the liquid metals dissolved with gas atoms is solidified. The porosity and the pore size decrease with increasing aluminum content. An increase of solidification velocity from 330 μms-1 to 500 μms-1 leads to a decrease of pore diameter and an increase of pore number in the porous Ni-28at%Al.

Properties of Binary Si:H Materials Prepared by Hydrogen Plasma Sputtering

1989 ◽  
Vol 164 ◽  
Author(s):  
Shoji Furukawa ◽  
Tatsuro Miyasato
Keyword(s):  
Substrate Temperature ◽  
Room Temperature ◽  
Hydrogen Plasma ◽  
Rf Sputtering ◽  
Hydrogen Atmosphere ◽  
Pure Hydrogen ◽  
Rf Power ◽  
Optical Gap ◽  
Plasma Sputtering ◽  
X Ray Scattering

AbstractBinary Si:H materials are prepared by means of the rf sputtering technique in pure hydrogen atmosphere on low temperature (about 100 K) and room temperature substrates. The physical properties of the obtained materials are very much affected by the rf power and substrate temperature during the deposition. The material prepared at a low substrate temperature with a low rf power has a wide optical gap, and shows a visible photoluminescence at room temperature. On the other hand, the material prepared at room temperature with a high rf power contains many Si microcrystals, whose diameters are relatively large, and its optical gap becomes very small. The latter condition causes the dependence of the crystalline direction of the material film on the substrate crystal even at the room temperature. An rf power-modulated multi-layered structure (superlattice) is also proposed, and an apparent diffraction peak can be observed in the low-angle X-ray scattering measurement.

scholarly journals Isothermal and Non-Isothermal Reduction Behaviors of Iron Ore Compacts in Pure Hydrogen Atmosphere and Kinetic Analysis

2020 ◽  
Author(s):  
Abourehab Hammam ◽  
Ying Li ◽  
Hao Nie ◽  
Lei Zan ◽  
Weitian Ding ◽  
...  
Keyword(s):  
Heating Rate ◽  
Iron Ore ◽  
Reduction Rate ◽  
Reduction Process ◽  
Gas Diffusion ◽  
Hydrogen Atmosphere ◽  
Pure Hydrogen ◽  
Degree Of Reduction ◽  
Isothermal Reduction ◽  
Co Gas

Abstract This study examines the isothermal and non-isothermal reduction behaviors of iron ore compacts in a pure hydrogen atmosphere and compares the results obtained during the reduction process by CO. The different phases accompanying the reduction reactions were identified using X-ray diffraction (XRD) and its morphology was microscopically examined. In isothermal experiments, temperature plays a significant role in the reduction process. At any given temperature, the reduction rate during the initial stages is higher than that during the final stages. The reduction rate in H2 atmosphere was faster than in CO gas. The comparison of activation energy values suggested that reduction with H2 is more efficient than with CO. At the same temperature, the time required to achieve a certain degree of reduction was lower when using H2 gas than CO atmosphere. In non-isothermal tests, the heating rate has a significant effect on the reduction rate and reduction extent. At the same heating rate, the degree of reduction was higher in H2 atmosphere than in CO gas. Based on experimental data, the parameters of reaction kinetics were deduced by application of model-free and model-fitting methods. The reduction in H2 atmosphere was controlled by nucleation model (Avrami-Erofeev model), while the CO reduction reaction was controlled by gas diffusion.

scholarly journals Convective overshoot and macroscopic diffusion in pure-hydrogen-atmosphere white dwarfs

2019 ◽  
Vol 488 (2) ◽  
pp. 2503-2522 ◽  
Author(s):  
Tim Cunningham ◽  
Pier-Emmanuel Tremblay ◽  
Bernd Freytag ◽  
Hans-Günter Ludwig ◽  
Detlev Koester
Keyword(s):  
Diffusion Coefficients ◽  
White Dwarfs ◽  
Hydrogen Atmosphere ◽  
Theoretical Description ◽  
Time Variability ◽  
Pure Hydrogen ◽  
Temperature Range ◽  
Tracer Particles ◽  
Order Of Magnitude ◽  
Convective Overshoot

Abstract We present a theoretical description of macroscopic diffusion caused by convective overshoot in pure-hydrogen DA white dwarfs using 3D, closed-bottom, radiation hydrodynamics co5bold simulations. We rely on a new grid of deep 3D white dwarf models in the temperature range $11\, 400 \le T_{\mathrm{eff}} \le 18\, 000$ K where tracer particles and a tracer density are used to derive macroscopic diffusion coefficients driven by convective overshoot. These diffusion coefficients are compared to microscopic diffusion coefficients from 1D structures. We find that the mass of the fully mixed region is likely to increase by up to 2.5 orders of magnitude while inferred accretion rates increase by a more moderate order of magnitude. We present evidence that an increase in settling time of up to 2 orders of magnitude is to be expected, which is of significance for time-variability studies of polluted white dwarfs. Our grid also provides the most robust constraint on the onset of convective instabilities in DA white dwarfs to be in the effective temperature range from 18 000 to 18 250 K.

Improved Epilayer Surface Morphology on 2˚ Off-Cut 4H-SiC Substrates

2014 ◽  
Vol 778-780 ◽  
pp. 206-209 ◽  
Author(s):  
Louise Lilja ◽  
Jawad ul Hassan ◽  
Erik Janzén ◽  
J. Peder Bergman
Keyword(s):  
Surface Morphology ◽  
Defect Density ◽  
Hydrogen Atmosphere ◽  
Pure Hydrogen ◽  
Morphological Defects ◽  
Homoepitaxial Layers ◽  
Epilayer Surface

Homoepitaxial layers of 4H-SiC were grown with horizontal hot-wall CVD on 2˚ off-cut substrates, with the purpose of improving the surface morphology of the epilayers and reducing the density of surface morphological defects. In-situ etching conditions in either pure hydrogen or in a mixture of silane and hydrogen prior to the growth were compared as well as C/Si ratios in the range 0.8 to 1.0 during growth. The smoothest epilayer surface, together with lowest defect density, was achieved with growth at a C/Si ratio of 0.9 after an in-situ etching in pure hydrogen atmosphere.

Fabrication of Copper-Alumina Nanocomposites by Mechanochemical Routes

2009 ◽  
Vol 6 ◽  
pp. 51-60 ◽  
Author(s):  
F. Shehata ◽  
M. Abdelhameed ◽  
A. Fathy ◽  
S.F. Moustafa
Keyword(s):  
Aqueous Solution ◽  
Ammonium Hydroxide ◽  
Copper Matrix ◽  
Hydrogen Atmosphere ◽  
Aluminum Nitrate ◽  
Mechanochemical Method ◽  
Composite Powders ◽  
Alumina Particles ◽  
Cold Pressed ◽  
Fine Copper

Nanostructure composites of Copper-Alumina were successfully produced by new mechanochemical method using two different routes. First, route A was carried out by addition of coarse copper to aqueous solution of aluminum nitrate, and second, route B was also carried out by addition of coarse copper to aqueous solution of aluminum nitrate and ammonium hydroxide. In both routes, the mixtures were heated in air and milled mechanically to get the oxides powders of CuO and Al2O3. The CuO was reduced in preferential hydrogen atmosphere into fine copper. The composite powders have been cold pressed into briquettes and sintered in hydrogen atmosphere. The structure and characteristics of powders as well as sintered composites produced from both routes were examined by XRD, SEM, EDS, TEM and metallographic techniques. The results showed that, in both routes, nano-sized particles of alumina were formed and dispersed within the copper matrix. The structure revealed the formation of CuAlO2 spinel structure at copper alumina interface. Nanocomposites produced by route-B showed finer alumina particles of 30 nm compared to 50 nm produced by route-A resulting in improved properties in terms of relative density, macro and microhardness values.

High Purity Liquid Phase Epitaxial GaAs For Radiation Detectors

1997 ◽  
Vol 487 ◽  
Author(s):  
D. I. Wynne ◽  
C. S. Rossington Tull ◽  
E. E. Haller
Keyword(s):  
Liquid Phase ◽  
Schottky Barrier ◽  
High Purity ◽  
Ohmic Contacts ◽  
Far Infrared ◽  
Radiation Detectors ◽  
Hydrogen Atmosphere ◽  
Pure Hydrogen ◽  
Detector Performance ◽  
Gaas Substrates

AbstractWe report on the growth of high purity n-GaAs using Liquid Phase Epitaxy (LPE) and the fabrication of room temperature p-i-n radiation detectors. Our epilayers are grown from a Ga solvent in a graphite boat in a pure hydrogen atmosphere. Growth is started at a temperature of approximately 800 °C. Our best epilayers show a net-residual-donor concentration of 2×1013 cm−3, confirmed by Hall effect measurements. The residual donors have been analyzed by far infrared spectroscopy and found to be sulfur and silicon. Epilayers with thicknesses of up to 120 µm have been deposited on 650 µm thick semi-insulating GaAs substrates and on 500 µm thick n+-type GaAs substrates. We report the results obtained with Schottky barrier diodes fabricated from these high purity n-type GaAs epilayers and operated as X-ray detectors. The Schottky barrier contacts consisted of evaporated circular gold contacts on epilayers on n+ substrates. The ohmic contacts were formed by evaporated and alloyed Ni-Ge-Au films on the back of the substrate. Several of our diodes exhibit currents of the order of 1 to 10 nA at reverse biases depleting approximately 50 µm of the epilayer. This very encouraging result, demonstrating the possibility for fabricating GaAs p-i-n diodes with depletion layers in high purity GaAs instead of semi-insulating GaAs, is supported by similar results obtained by several other groups. The consequences of using high purity instead of semi-insulating GaAs will be much reduced charge carrier trapping. Diode electrical characteristics and detector performance results using 55Fe and 241Am radiation will be discussed.

Sign in / Sign up

Export Citation Format

Share Document