Calculation and tabulation of efficiencies for tungsten foil positron moderators

2019 ◽  
Vol 125 (20) ◽  
pp. 205304
Author(s):  
Raed Alsulami ◽  
Mubarak Albarqi ◽  
Safwan Jaradat ◽  
Shoaib Usman ◽  
Joseph Graham
Keyword(s):  
Tungsten Foil

scholarly journals Characteristics of Microstructure Evolution during FAST Joining of the Tungsten Foil Laminate

Metals ◽  
2021 ◽  
Vol 11 (6) ◽  
pp. 886
Author(s):  
Xiaoyue Tan ◽  
Wujie Wang ◽  
Xiang Chen ◽  
Yiran Mao ◽  
Andrey Litnovsky ◽  
...  
Keyword(s):  
Critical Current ◽  
Current Density ◽  
High Current Density ◽  
Operation Mode ◽  
Sharp Peak ◽  
Advanced Materials ◽  
Peak Current ◽  
Tungsten Foil ◽  
Field Assisted Sintering ◽  
Joining Process

The tungsten (W) foil laminate is an advanced material concept developed as a solution for the low temperature brittleness of W. However, the deformed W foils inevitably undergo microstructure deterioration (crystallization) during the joining process at a high temperature. In this work, joining of the W foil laminate was carried out in a field-assisted sintering technology (FAST) apparatus. The joining temperature was optimized by varying the temperature from 600 to 1400 °C. The critical current for mitigating the microstructure deterioration of the deformed W foil was evaluated by changing the sample size. It is found that the optimal joining temperature is 1200 °C and the critical current density is below 418 A/cm2. According to an optimized FAST joining process, the W foil laminate with a low microstructure deterioration and good interfacial bonding can be obtained. After analyzing these current profiles, it was evident that the high current density (sharp peak current) is the reason for the significant microstructure deterioration. An effective approach of using an artificial operation mode was proposed to avoid the sharp peak current. This study provides the fundamental knowledge of FAST principal parameters for producing advanced materials.

scholarly journals Numerical and Experimental Studies on the Explosive Welding of Tungsten Foil to Copper

Materials ◽  
2017 ◽  
Vol 10 (9) ◽  
pp. 984 ◽  
Author(s):  
Qiang Zhou ◽  
Jianrui Feng ◽  
Pengwan Chen
Keyword(s):  
Explosive Welding ◽  
Experimental Studies ◽  
Tungsten Foil

Tungsten foil laminate for structural divertor applications – Basics and outlook

2012 ◽  
Vol 423 (1-3) ◽  
pp. 1-8 ◽  
Author(s):  
Jens Reiser ◽  
Michael Rieth ◽  
Bernhard Dafferner ◽  
Andreas Hoffmann
Keyword(s):  
Tungsten Foil

Some work functions of vapour deposited uranium on polycrystalline tungsten foil

1967 ◽  
Vol 7 (3) ◽  
pp. 365-379 ◽  
Author(s):  
D.E. Barry ◽  
B.J. Hopkins ◽  
A.J. Sargood
Keyword(s):  
Polycrystalline Tungsten ◽  
Tungsten Foil ◽  
Work Functions

Mechanism of Ammonia Decomposition on Tungsten; NH3 and ND3 Isotope Effect

1979 ◽  
Vol 34 (1) ◽  
pp. 96-98 ◽  
Author(s):  
H. Shindo ◽  
C. Egawa ◽  
T. Onishi ◽  
K. Tamara
Keyword(s):  
Isotope Effect ◽  
Nitrogen Uptake ◽  
Dynamic Balance ◽  
Nitride Layer ◽  
Ammonia Decomposition ◽  
Tungsten Foil ◽  
Nitride Layers ◽  
Kinetics Of ◽  
Rate Determining Steps

Abstract Light and heavy ammonia were decomposed on a clean tungsten foil at 973-1123 K and at pNH₃, ND₃ ≈ 0.2 Torr. The nitrogen uptake and the kinetics of the formation of nitride layers were examined during the course of the reaction. The amount of nitrogen chemisorbed (or the thickness of the nitride layers formed) at higher pressures was found to be appreciably larger from NH3 than from ND3. Addition of hydrogen had no effect on the thickness of the nitride layer nor on the rate of ammonia decomposition. These facts support the concept of a dynamic balance between two consecutive rate determining steps: supply of chemisorbed nitrogen from ammonia into the surface and consumption of the chemisorbed nitrogen through its desorption from the surface to form nitrogen molecules.

Ordered and twinned structure in hexagonal-based potassium tungsten bronze nanosheets

2013 ◽  
Vol 46 (6) ◽  
pp. 1817-1822 ◽  
Author(s):  
Shuangfeng Jia ◽  
Hongqian Sang ◽  
Wenjing Zhang ◽  
Han Zhang ◽  
He Zheng ◽  
...  
Keyword(s):  
Electron Microscopy ◽  
Potassium Hydroxide ◽  
Structural Investigation ◽  
Tungsten Bronze ◽  
X Ray Diffraction ◽  
Rotation Symmetry ◽  
X Ray ◽  
Tungsten Foil ◽  
Diffraction Patterns ◽  
Microscopy Techniques

Non-stoichiometric hexagonal-based potassium tungsten bronze (KxWO3) nanosheets were synthesized by oxidizing tungsten foil in potassium hydroxide. The tungsten bronze nanosheets exhibited an ordered monoclinic superstructure as revealed by X-ray diffraction patterns. Further detailed structural investigation by employing electron microscopy techniques showed the coexistence of 120° rotation twinning variants in the superstructure phase, which may result from the rotation symmetry reduction induced by the ordered arrangements of K vacancies during crystal growth.

Photoelectron- and Thermionic- Emission Microscopy of Barium/Scandium Thin Films on Tungsten

2008 ◽  
Vol 1088 ◽  
Author(s):  
Joel M. Vaughn ◽  
Martin Kordesch
Keyword(s):  
Thin Films ◽  
Thermionic Emission ◽  
Barium Oxide ◽  
Scandium Oxide ◽  
Unequivocal Identification ◽  
Tungsten Foil ◽  
Cathode Structure ◽  
Current Densities ◽  
Emission Microscopy ◽  
Sputter Deposited

AbstractCommercial scandium oxide doped thermionic cathodes have demonstrated current densities over 100 A/cm2. In order to understand the effect of Sc- and Ba- oxides on the emissivity of these cathodes we have imaged thin films of scandium oxide and barium oxide on tungsten foils using photoelectron emission microscopy and thermionic emission microscopy. Arrays of 100 um × 100 um squares of scandium and 25 um × 25 um squares of barium, 200 nm thick, were sputter deposited onto 50 um thick sheets of tungsten foil. Imaging squares of different sizes gives an unequivocal identification of each material and a completely consistent comparison of each material and cathode structure under identical conditions in one image.The metal squares oxidize in air before imaging. Each sample was heated in situ in a Bauer-Telieps style LEEM/PEEM used primarily in the ThEEM mode. The barium oxide squares emit below 875 K, and diffuse over the scandium below 875 K. Thermionic emission from scandium oxide squares is observed at temperatures significantly larger than 875 K. Failure of the barium oxide film cathode is through barium desorption. AES spectra show that the Sc does not desorb.While the origin of reduced emission temperature is commonly believed to be a result of a low work function monolayer of Ba and Sc oxides, in our study, the benefits of a combined Ba/Sc cathode are present in a thick (multi-layer), layered structure of barium oxide on top of a thick scandium oxide layer.

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