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[en] Highlights: • Tungsten coatings were electroplated on cooper alloy by pulse plating. • Increasing current density resulted in an increase in grain size of tungsten coating. • With the increase in duty cycle, the grain size of tungsten coating increased. • The pulse period had an insignificant effect on the tungsten grain size. - Abstract: The tungsten coatings with low oxygen content were prepared on copper alloy substrate by pulse electroplating in Na_2WO_4–WO_3–NaPO_3 molten salt. A series of tungsten coatings with compact morphologies were successfully obtained under various conditions. The influences of current density, duty cycle and period on tungsten grain size and coatings thickness were investigated. The results demonstrated that current density was the most important factor influencing tungsten grain size, which had a positive correlation with current density. The thickness of coating decreased when the current density was up to 80 mA cm"−"2. However, the tungsten grain size, tungsten coating thickness and current efficiency changed a little with the increase in pulse periods
[en] Highlights: • Tungsten coatings were electroplated on molybdenum substrate for the first time. • The electrodeposition was studied in the air atmosphere. • The coating has columnar structure with preferential growth orientation of (1 1 0). • The columnar structure was disappeared after high-temperature annealing. • The coating has an extremely low oxygen content with the value of 0.032 wt%. - Abstract: Compact and smooth tungsten coating on molybdenum substrate was obtained by electrodeposition from Na_2WO_4–WO_3 molten salt at 1173 K in atmosphere. Microstructure, morphology and properties were performed on the tungsten coating. The tungsten coating had columnar structure with the preferential growth orientation of (2 0 0). There was about 2 μm thick diffusion layer of tungsten in the molybdenum substrate. The bending test and thermal shock test showed the tungsten coating had good adhesion with the molybdenum substrate. The microhardness of the coating was about 492 HV and the oxygen content of the coating was 0.032 wt%. The high-temperature could enhance the high-temperature oxidation resistance and bond strength of the tungsten coating
[en] Graphical abstract: Coupling CdS with CeO_2 can effectively improve the light-harvesting ability of wide-band gap CeO_2 NRs as the photoinduced electrons on the conduction band of CdS are transfered to the conduction band of CeO_2. - Highlights: • Coupling CdS can effectively improve the light-harvesting ability of wide-band gap CeO_2. • CdS/CeO_2 composites show high photocatalytic activity under visible light irradiation. • The mechanism of photocatalytic H_2 evolution over CdS/CeO_2 was proposed. - Abstract: Different mole ratios of CdS nanoparticles (NPs)/CeO_2 nanorods (NRs) composites with effective contacts were synthesized through a two-step hydrothermal method. The crystal phase, microstructure, optical absorption properties, electrochemical properties and photocatalytic H_2 production activity of these composites were investigated. It was concluded that the photogenerated charge carriers in the CdS NPs/CeO_2 NRs composite with a proper mole ratio (1:1) exhibited the longest lifetime and highest separation efficiency, which was responsible for the highest H_2-production rate of 8.4 mmol h"−"1 g"−"1 under visible-light irradiation (λ > 420 nm). The superior photocatalytic H_2 evolution properties are attributed to the transfer of visible-excited electrons of CdS NPs to CeO_2 NRs, which can effectively extend the light absorption range of wide-band gap CeO_2 NRs. This work provides feasible routes to develop visible-light responsive CeO_2-based nanomaterial for efficient solar utilization.
[en] Tungsten is considered as plasma facing material in fusion devices because of its high melting point, its good thermal conductivity, its low erosion rate and its benign neutron activation properties. On the other hand, carbon based materials like C/C fiber composites (CFC) have been used for plasma facing materials (PFMs) due to their high thermal shock resistance, light weight and high strength. Tungsten coatings on CFC substrates are used in the JET divertor in the frame of the JET ITER-like wall project, and have been prepared by plasma spray (PS) and other techniques. In this study, tungsten coatings were electro-deposited on CFC from Na2WO4–WO3 molten salt under various deposition parameters at 900 °C in air. In order to obtain tungsten coatings with excellent performance, the effects of pulse duration ratio and pulse current density on microstructures and crystal structures of tungsten coatings were investigated by X-ray diffraction (XRD, Rigaku Industrial Co., Ltd., D/MAX-RB) and a scanning electron microscope (SEM, JSM 6480LV). It is found that the pulsed duration ratio and pulse current density had a significant influence on tungsten nucleation and electro-crystallization phenomena. SEM observation revealed that intact, uniform and dense tungsten coatings formed on the CFC substrates. Both the average grain size and thickness of the coating increased with the pulsed current density. The XRD results showed that the coatings consisted of a single phase of tungsten with the body centered cubic (BCC) structure. The oxygen content of electro-deposited tungsten coatings was lower than 0.05%, and the micro-hardness was about 400 HV
[en] Highlights: • Tungsten coatings were successfully electroplated on vanadium alloy substrate. • Tungsten coatings with various thicknesses were obtained. • Tungsten coating was electroplated with c low oxygen content. • High heat flux property of tungsten coatings on V-4Cr-4Ti substrate was investigated. • Helium ion irradiation property of tungsten coatings on V-4Cr-4Ti substrate was investigated. - Abstract: Tungsten coatings were prepared by electrodeposition on vanadium alloy (V-4Cr-4Ti) substrate from Na2WO4-WO3 molten salt at 1173 K in atmosphere. The crystal structure, microstructure, microhardness, oxygen content of the coating as well as bond strength between coatings and substrates were investigated. Pure and compact tungsten coatings were successfully obtained with columnar structure. The tungsten coatings thickness is 505 μm and the oxygen weight ratio is 0.025 wt.%, when the electrodeposited time is 80 h. The tungsten coatings adhesive strength determined by tensile test exceeds 39.28 MPa
[en] The computer code DHRSC is used for the calculation of natural convection and decay hear removal in China experimental fast reactor. The model of the stratification occurred in hot and cold sodium pool due to natural convection and the model for passive decay hear removal are described
[en] Highlights: • Tungsten coatings were successfully electroplated on vanadium alloy substrate. • Tungsten coatings consisted of two sub-layers. • Tungsten coatings plated at lower duty cycle has a better surface quality. • High heat flux property of tungsten coatings was investigated. • Helium ion irradiation property of tungsten coatings was investigated. - Abstract: Tungsten coatings with high (2 2 0)-orientation were formed on V alloy substrate by pulse current electrodeposition in air atmosphere. The coatings’ microstructure, crystal structure and adhesive strength between coatings and substrates were investigated. It could be observed the tungsten coatings consisted of two sub-layers with the inner tooth-like layer, and the outer columnar layer. The tungsten coatings deposited at lower duty cycle have a better surface quality with a little change in the adhesive strength. The tungsten coating was exposed to electron beam with power density of 200 MW/m"2 in the thermal shock test, the tungsten crystal grain surface melt, the microcracks are found among the crystal grains. Exfoliation, flaking and dense needle-like holes were observed on the tungsten coating after irradiation with helium ions at an energy of 65 keV and an implanted dose of 22.67 × 10"1"8 cm"−"2
[en] Zigzag graphene nanoribbons with edges modified by different chemical groups are investigated by first principles calculations. The chemical groups considered include hydrogen, hydroxyl, ketone, and combination of hydrogen and hydroxyl. Band structures. DOS and charge difference density have been calculated. The results show that, the effect of different groups could be essentially ascribed to different types of edge. The structures of sp2 type have little influence on electron state of the inner atoms of GNRs whose metallicity still remains. However the structures of sp3 type generate a band gap which will decrease with the increase of ribbon's width. The shift from metallicity to semiconducting occurs in both structures of GNRs-H2 and GNRs-H2O, while the structure of GNRs-O remains its metallicity as its Fermi level increases into the conduction band. By using this method of edge hybridization, the GNRs' band structure is prone to be controlled. (authors)
[en] The W coating with the thickness over 1 mm was obtained by pulse electrodeposition on large CuCrZr alloy in a Na2WO4–WO3 molten salt. The composition of this system keeps unchanged with the duration of electrodeposition. The coating’s structure, morphology and contents were investigated by XRD, XPS and SEM. The electrodepostion tungsten coating was compact and without void. The residual stress in surface of W coating was calculated to be a compressive stress with the value of 225 MPa. The W coating comprised an inner tooth-like layer and an outer columnar layer. The bonding strength between W coating and CuCrZr susbtrate was near 60 MPa; the thermal conductivity parallel to the crystal growth direction was measured to be 150.86 W m−1 K−1.
[en] We present a 10 Gsps 8 bit digital-to-analog converter (DAC) with a novel built-in self-test (BIST) circuit, which makes it possible to evaluate the DAC's performance without a complicated test setup. Design considerations and test results are included. According to the test results, the DAC core and the BIST circuit are able to work under 10 GHz. The chip is fabricated in 0.18 μm SiGe HBTs with f_t of 100 GHz. The DAC core occupies a die size of 260 × 250 μm"2. (semiconductor integrated circuits)