Effect of LiSbO3 on the phase structure, microstructure and electric properties of Sr0.53Ba0.47Nb2O6 ceramics

LiSbO₃ doped Sr_0.53Ba_0.47Nb₂O₆ ceramics were synthesized by conventional mixed-oxide method. The phase structure, microstructure, dielectric and ferroelectric properties of obtained ceramics were investigated. Pure tungsten bronze structure could be obtained in all ceramics and LiSbO₃ additive could promote densification and reduce the sintering temperature. The dielectric characteristics showed diffuse phase transition phenomena for all samples, which was proved by linear fitting of the modified Curie-Weiss law with γ value varying between 1.65 and 1.92. With increasing LiSbO₃ content, the transition temperature T_c decreased gradually to near room temperature. Normal ferroelectric hysteresis loops could be observed in all compositions, but the remnant polarization (P_r) and coercive field (E_c) all decreased gradually. Besides, the underlying mechanism for variations of the electrical properties caused by LiSbO₃ doping was explained in this work.     

Solvothermally synthesized tungsten oxide nanowires/nanorods for NO2 gas sensor applications

One-dimensional nanorods or nanowires of W₁₈O₄₉ were synthesized by solvothermal method at 200 °C with tungsten hexachloride (WCl₆) as precursor and cyclohexanol or 1-propanol as reaction solvent. Their morphology and structure properties were systematically characterized. The NO₂-sensing properties of the sensors based on nanowires and nanorods were investigated at 100 °C up to 250 °C over NO₂ concentration ranging from 1 ppm to 20 ppm. The results indicate that both nanowires and nanorods exhibit reversible response to different concentrations of NO₂, and the highest gas response is achieved at 150 °C. In comparison with nanorods, nanowires showed a much quicker response characteristic and a relative higher response value to the same concentration of NO₂ gas due to the smaller diameter and larger specific surface area.     

钾掺杂钨合金中气相热充氘的热脱附行为

钾(K)掺杂钨(W)合金已经表现了优异的高温力学性能,成为最有希望的PFMs备选材料之一。为评估氢同位素在W-K合金中的滞留情况,采用放电等离子烧结技术(SPS),制备了纯W及K含量82μg/g的W-K合金,通过气相热充法引入氘(D)元素,考察热脱附行为。研究表明,气相热充氘释放温区从600K延伸至1200K,掺杂K后,D脱附活化能从0.86 eV下降到0.68 eV;纯W样品D滞留量在1×10^-6(原子比)左右,掺杂K后有所提高,但依然大大优于商用ITER级纯W。     

Effect of post-weld heat treatment and electrolytic plasma processing on tungsten inert gas welded AISI 4140 alloy steel

Post-weld heat treatment (PWHT) is commonly adopted on welded joints and structures to relieve post-weld residual stresses; and restore the mechanical properties and structural integrity. An electrolytic plasma process (EPP) has been developed to improve corrosion behavior and wear resistance of structural materials; and can be employed in other applications and surface modifications aspects. In this study the effects of PWHT and EPP on the residual stresses, micro-hardness, microstructures, and uniaxial tensile properties are explored on tungsten inert gas (TIG) welded AISI-4140 alloys steel with SAE-4130 chromium–molybdenum alloy welding filler rod. For rational comparison all of the welded samples are checked with nondestructive Phased Array Ultrasonic Testing (PAUT) and to ensure defect-free samples before testing. Residual stresses are assessed with ultrasonic testing at different distances from weld center line. PWHT resulted in relief of tensile residual stress due to grain refinement. As a consequence higher ductility but lower strength existed in PWHT samples. In comparison, EPP-treated samples revealed lower residual stresses, but no significant variation on the grain refinement. Consequently, EPP-treated specimens exhibited higher tensile strength but lower ductility and toughness for the martensitic formation due to the rapid heating and quenching effects. EPP was also applied on PWHT samples, but which did not reveal any substantial effect on the tensile properties after PWHT at 650 °C. Finally the microstructures and fracture morphology are analyzed using scanning electron microscopy (SEM) and optical microscope to study the evolution of microstructures.     

Densification behavior,mechanical properties and thermal shock resistance of tungsten alloys fabricated at low temperature

The low-temperature shrinkage of tungsten was greatly accelerated by the addition of trace Nb and Ni, and the addition of trace Nb and Ni also significantly promoted the final sintering density. The 99.1% of theory density for W–0.1 wt.%Nb–0.1 wt.%Ni material sintered at 1600 °C was obviously greater than 93.7% of theory density for W material sintered at 2000 °C. Ball milling treatment played an important role in promoting the sintering densification of W–0.1 wt.%Nb–0.1 wt.%Ni powder, and the powder milled for 10 h (W10) could be sintered to near full density (99.4% of theory density) at 1600 °C. The ball milling for 15 h has no effect in improving the sintering density, but it induced rapid growth of tungsten grains. The microhardness and tensile strength of the sintered tungsten alloys were highly dependent on its sintering density and grain size. Improving the sintering density while controlling the grain growth could effectively promote the microhardness and tensile strength. Furthermore, the improvement of thermal shock resistance of the W10 alloy was due to good microstructure and the increase in the tensile strength.     

Hot wire chemical vapor deposition: limits and opportunities of protecting the tungsten catalyzer from silicide with a cavity

Hot Wire Chemical Vapor Deposition (HW-CVD) is one of the most promising techniques for depositing the intrinsic microcrystalline silicon layer for the production of micro-morph solar cells. However, the silicide formation at the colder ends of the tungsten wire drastically reduces the lifetime of the catalyzer, thus limiting its industrial exploitation. A simple but interesting strategy to decrease the silicide formation is to hide the electrical contacts of the catalyzer in a long narrow cavity which reduces the probability of the silane molecules to reach the colder ends of the wire. In this paper, the working mechanism of the cavity is elucidated. Measurements of the thickness profile of the silicon deposited in the internal walls of the cavity have been compared with those predicted using a simple diffusion model based on the assumption of Knudsen flow. A lifetime study of the protected and unprotected wires has been carried out. The different mechanisms which determine the deterioration of the catalyzer have been identified and discussed.     

Electrochromism in nickel oxide and tungsten oxide thin films: Ion intercalation from different electrolytes

Electrochromic (EC) NiO_z and WO_y thin films were prepared by sputtering and were used in a feasibility study aimed at investigating mixtures of these two oxides. The object was to identify a suitable electrolyte, compatible with both NiO_z and WO_y. To that end we carried out cyclic voltammetry (CV) in potassium hydroxide (KOH), propionic acid, and lithium perchlorate in propylene carbonate (Li-PC). WO_y could be coloured in propionic acid and Li-PC, while NiO_z could be coloured only in KOH. Both films showed best stability in Li-PC, which hence is well suited for further studies of mixed NiO_z and WO_y.     

冲击台机械振实钨粉的实验研究

本文介绍了细颗粒钨粉在凸轮式冲击台上的振实实验,得出了粒度在2μm的细颗粒钨粉在不同振动参数下的振实密度.通过振动参数优化,使钨粉的最高振实密度达到了6.04g/cm3,从而满足了钨粉冷等静压的工艺要求,且钨粉粒度组成未发生明显变化,从而说明通过冲击台能够实现钨粉的机械振实及振动装料.     

The production and anatomy of a tungsten powder jet

A tungsten powder jet is a potential candidate technology for a particle production target in a future high power (i.e. Multi-MW) particle accelerator based facility, such as a so-called conventional neutrino Super Beam, a proposed Neutrino Factory, or a future neutron source. To test the viability of producing a suitable powder jet a few simple experiments were performed using standard pneumatic conveying equipment and the encouraging results are presented.     

Small tungsten carbide nanoparticles: Simulation of structure,energetics, and tensile strength

Ab initio methods of the density functional theory and pseudopotentials were used to study the structure, electronic states, total energy and tensile strength of WC nanoparticles. It has been found that the very small particles (having less than 15 WC atomic pairs) have a cube-like NaCl structure. Particles with trigonal and cubic structures have approximately the same energies in the region of 10–20 WC pairs; however, the local atomic structure keeps the NaCl-like alternation of W and C atoms. The WC₁₅ trigonal particle was used as a typical one to study the WC nanoparticle tensile strength. It has been found that W and C vacancies decrease the tensile strength, but not drastically. Electronic structure of nanoparticles looks like that of bulk fcc-WC with a large density of states at the Fermi level.