Papers by Keyword: Tungsten

Abstract: Higher solar absorptance and lower thermal emittance are the key factors for solar collectors. The use of thin films that are having mechanically resistant coatings are common practice in industries. The primary motivation of carrying this research work is to lower thermal emittance and maximize solar absorptance on SS304 substrate material. W-Al₂O₃ composite coatings are developed using magnetron sputtering process by considering the process parameters. The experimental plan is achieved based on Taguchi L9 orthogonal under various levels for deposition parameters. The tungsten and alumina thin films deposited using a co-sputtering were characterized using 410 - solar instrument for measuring solar absorptance and ET 100 Emissometer for measuring thermal emittance. The optimization for process parameters on thermal emittance and absorptance were carried out. It was found that for deposition parameters of DC power 750W, RF power 1050W and Argon gas flow rate of 250 sccm, absorptance of 0.758 with thermal emittance of 0.061 is observed with deposition was carried out on SS304 substrates.

Abstract: KENS-II is the second generation of the spallation neutron source at KEK which was operated from December 1, 2000 to March 22, 2006 supplying neutron beam to the neutron spectrometers of material science. The present paper reviews history of the KENS-II from its design to removal together with its performance for the neutron scattering experiments.

Abstract: Tungsten (W) is a principal candidate as target material because of its high density and extremely high melting point. W inherently has a critical disadvantage of its brittleness at around room temperature (low temperature brittleness), recrystallization embrittlement, and irradiation embrittlement. TFGR (Toughened, Fine Grained, Recrystallized) W-1.1%TiC has been considered as a realized solution to the embrittlement problems. We started to fabricate TFGR W-1.1%TiC in 2016 under collaboration between KEK and Metal Technology Co. LTD (MTC). The TFGR W-1.1%TiC samples were successfully fabricated in June, 2018. As a result, the specimen showed slight bend ductility and 2.6 GPa of fracture strength.

Abstract: For validating the number of displacements per atom (dpa) for tungsten under high-energy proton irradiation, we measured displacement cross sections related to defect-induced electrical resistivity changes in a tungsten wire sample under irradiation with 389-MeV protons under 10 K. The Gifford–McMahon cryocooler was used to cool the sample using a conductive coolant via thermal conduction plates of oxygen-free high-conductivity copper and electrical insulation sheets of aluminum nitride ceramic. In this experiment, the displacement cross section was 1612 ± 371 b for tungsten at 389 MeV. A comparison of the experimental displacement cross sections of tungsten with the calculated results obtained using Norgett–Robinson–Torrens (NRT) dpa and athermal recombination-corrected (arc) dpa cross sections indicates that arc-dpa was in better agreement with the experimental data than NRT-dpa; this is similar to the displacement cross sections of copper. From the measurements of damage recovery of the accumulated defects in tungsten through isochronal annealing, which is related to the defect concentration of the sample, approximately 20% of the damage was recovered at 60 K. This trend was similar to those observed in other experimental results for reactor neutrons.

Abstract: Tungsten (W) is suitable for solid targets of spallation neutron source due to its high neutron yield. The prediction of radiation effects of W is, therefore, of importance; especially, the influence of solute elements are complex and are not clearly known to date. We discuss here the solute effects using the first principles and kinetic Monte Carlo (KMC) calculations and show that Re and Os, which are nuclear transmutation products of W, can largely change the stability and mobility of radiation defects. Such influences of the solute elements seem to explain the unsolved mechanism of the microstructural evolution of W-based materials under irradiation.

Abstract: Characterization of advanced materials by neutron powder diffraction provides information not accessible by other techniques. Thanks to the low absorption of neutrons, the bulk of the material and large-grain samples can be investigated, moreover in situ at elevated temperatures. The neutron diffraction use is demonstrated on two types of technologically important materials: Ti-Zr alloy and Co-Re high temperature alloy. In Ti-Zr alloy, the residual stress relief and microstrain evolution after ECAP was established. Boron influence on TaC strengthening precipitates in Co-Re high temperature alloys was shown not to be significant at the foreseen alloy operation temperatures, although boron content has a strong influence on the matrix phase.

Abstract: In this paper, visible-light-active monoclinic WO₃ powders were synthesized by thermal oxidation of W powders at 200 – 1000 °C in air atmosphere. Morphology and crystal structure of annealed W powders were characterized by Scanning Electron Microscopy (SEM) and X-ray Diffraction (XRD), respectively. Based on SEM and XRD results, a spherical orthorhombic-W₃O₈ obtained at 200 °C was transformed into a dendritic monoclinic WO₂ + tetragonal WO₃ + monoclinic WO₃ structures at 400 °C accompanied by a color transition from grey into green. At 600 °C, yellow monoclinic WO₃ + monoclinic WO_2.96 powder was produced that ascribed to oxygen vacancies. Photocatalytic activity of annealed W powders demonstrated 70.7% Cr (VI) removal after 150 min on sample annealed at 1000 °C. This ascribed to high photoactivity of monoclinic WO₃. Nevertheless, the dendritic monoclinic WO₂ + tetragonal WO₃ + monoclinic WO₃ obtained at 400 °C exhibited the lowest Cr (VI) photoreduction i.e. 45.2% implies less photoactive monoclinic WO₂ and sluggish electron transport at oxide-oxide interfaces.

Abstract: The oxidation behaviors of tantalum-tungsten alloy with 10-20% W was investigated between temperature range of 700 to 900 °C exposed in air. The kinetics of Ta-W alloy was determined by TG-DTA, the characteristics of oxides were analyzed by SEM, EDS and XRD. The oxidation tests revealed that the alloys obeyed parabolic kinetic in the initial stage, then translated in linear law. The addition of W has a good effect on the oxidation resistance of Ta-W alloys at experimental temperature. Solid solution of Ta₂O₅ form in case of oxidation product of Ta-10W, Ta-15W alloys, while the complex oxide Ta₂₂W₄O₆₇ form after Ta-20W alloy oxidized. The formation of solid solution and complex oxide impeded the volatilization. The compact oxide film protects the penetration of oxygen in the initial oxidation stage. The large compressive stresses and mismatch of the coefficient of thermal expansion between oxide scale and matrix alloys make the oxides layer be broken, which cause kinetic of oxidization obeying linear law.

Abstract: The effect of tungsten nanoparticles and microparticles on the structure and hardness of sintered Sn–Cu–Co–W alloys has been studied. Tungsten powder of 19–24 μm sized particles was milled in a planetary-centrifugal mill, after which the size of particles was 25 nm to 20 μm. The milled and non-milled tungsten was then mixed with powders of tin, copper and cobalt. The specimens were compacted in moulds and sintered in vacuum at 820°C for 20 minutes. The structure of sintered materials was studied using X-ray diffraction analysis and scanning electron microscopy. Microhardness (HV_0.01) of structural constituents and hardness of the materials were measured. It has been determined that it is alloys containing mechanically milled tungsten that have the highest hardness. The main factor influencing the rise of hardness is dispersion hardening with nanoparticles. A further factor is work hardening of tungsten microparticles during ball milling. The highest hardness of 109–111 HRB has been obtained in the Sn–Cu–Co–W alloy containing 23% wt. of milled tungsten, with the proportion of tin, copper and cobalt being 1/2.6/1.6.

Abstract: In this report we report a simplest way to synthesis inorganic Tungsten disulfide (WS₂) nanorods. In this research work we used Tungsten trioxide (WO₃) to produce tungsten disulfide with hydrogen gas and sulfur gas to synthesis WS₂ nanorods at ambient temperature. This synthesis was done by two steps. The first step is oxide reduction and the second step is Sulfuration. And we have analyzed the changes in the nanorod structure when the reaction time is increased and when the temperature is changed at constant gas flow. The synthesized nanorods are analyzed by SEM, EDS and XRD. We report that we have successfully synthesized WS₂ nanorods with the dimension of 100 to 300 nm in diameter and few micrometers in length. And we also report the changes in the structural morphology when the temperature was increased. When the temperature was increased to 1000oC the structure become very ranom.