Preparation of nano-crystalline tungsten powders from gaseous WO2(OH)2

The industrial production of tungsten powder is carried out by the reduction of tungsten oxide powder via hydrogen. In this process, the size of the W particles is limited to particle sizes larger than 100 nm. To get below this limit, alternative processes are needed. In the current work, the possibility of preparing W powder below 100 nm via a vapour phase reduction of volatile WO2(OH)2 by hydrogen was investigated. The process consists of two stages. In the first stag,e WO2(OH)2 is formed by reacting WO3 with water vapour at temperatures of 1000–1100 °C. In the second stage, WO2(OH)2 is reduced by hydrogen at about 1000 °C to form metallic tungsten. The influence of process parameters such as furnace temperature, humidity and gas flow on the WO2(OH)2 evaporation and formation of tungsten powder was investigated. The characterization of the resulting powders was performed by X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM) and transmission electron microscopy (TEM). By optimization of the reaction conditions, powder with a metallic tungsten content of about 70 at% besides tungsten oxides was produced with metal particle sizes down to 5 nm. Further optimization should lead to a high tungsten content and a high product yield. Due to the small particle size, applications in catalysis might be possible, although an industrial realization of the process seems unrealistic at moment.

Influence of W Addition on Microstructure and Resistance to Brittle Cracking of TiB2 Coatings Deposited by DCMS

The aim of this work was to determine the influence of the tungsten addition to TiB2 coatings on their microstructure and brittle cracking resistance. Four coatings of different compositions (0, 7, 15, and 20 at.% of W) were deposited by magnetron sputtering from TiB2 and W targets. The coatings were investigated by the following methods: X-ray diffraction (XRD), transmission electron microscopy (TEM), atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS). All coatings had a homogeneous columnar structure with decreasing column width as the tungsten content increased. XRD and XPS analysis showed the presence of TiB2 and nonstoichiometric TiBx phases with an excess or deficiency of boron depending on composition. The crystalline size decreased from 27 nm to 10 nm with increasing W content. The brittle cracking resistance improved with increasing content of TiBx phase with deficiency of B and decreasing crystalline size.

NH3-Selective Catalytic Reduction of NOx to N2 over Ceria Supported WOx Based Catalysts: Influence of Tungsten Content

A series of HPW/CeO2 catalysts generated from 12-tungstophosphoric acid, H3PW12O40 (HPW), supported on ceria and presenting different tungsten loadings (2, 4.5, 9, 16, and 40 wt% W) were prepared and characterized by N2 physisorption, XRD, IR, Raman, and UV-Vis. The different characterization techniques suggested that low loading of tungsten resulted in mainly isolated sites, while high tungsten loading produced polymeric or tungsten clusters. Those materials exhibited high activity in NH3-SCR of NOx into N2. Moreover, the series of experiments indicated that low loading in tungsten (2% HPW/CeO2) displayed the highest activity with a remarkable N2 selectivity (99%) at medium-high temperature (300–515 °C), owing to the high amount of monomeric tungstate coverage on the catalyst surface.

Experimental Investigations on The Effect of Tungsten Content on the Machining Behaviour of Tungsten Heavy Alloys

The present work attempts to assess the machinability of tungsten heavy alloys (WHAs) with varying tungsten content in terms of different machining characteristics such as chip thickness, material removal rate, cutting force and surface roughness under varied cutting conditions. The feed rate is found to have major influence on the machining characteristics; whereas the effect of rake angle appears to be marginal. With increase in W content both cutting force and material removal rate increase whereas surface roughness decreases. Since WHAs are difficult to machine, an additional objective of the study is to optimize machining parameters. An optimal balance of the experimental cutting parameters using Grey relational analysis has been achieved, which can be effectively employed for the machining of the alloys with close dimensional tolerances and desirable surface finish.

Mechanical Properties and Gamma-Ray Shielding Performance of 3D-Printed Poly-Ether-Ether-Ketone/Tungsten Composites

Nuclear energy provides enduring power to space vehicles, but special attention should be paid to radiation shielding during the development and use of nuclear energy systems. In this paper, novel composite materials containing poly-ether-ether-ketone (PEEK) as a substrate and different tungsten contents as a reinforcing agent were developed and tested as shielding for gamma-ray radiation. Shielding test bodies were quickly processed by fused deposition modeling (FDM) 3D printing, and their mechanical, shielding properties of composite materials were evaluated. The results revealed shielding materials with excellent mechanical properties which can further be improved by heat treatment. Under 0.45 MPa load, the heat deflection temperature of PEEK/tungsten (metal) composites was significantly lower than that of PEEK/boron carbide (non-metal) composites. The new shielding materials also demonstrated better shielding of low-energy 137Cs than high-energy 60Co. The gamma-ray shielding rates of test pieces shielding materials made of the same thickness changed exponentially with the tungsten content present in the composite materials. More tungsten led to a better shielding effect. At the same tungsten content, the gamma-ray shielding effect showed a proportional relationship with the thickness of the shielding test bodies, in which thicker test bodies induced better shielding effects. In sum, the integration of 3D printing in the mechanical design and manufacturing of shielding bodies is an effective and promising way for quick processing when considering diverse rays and complex environments. Lighter shielding bodies, at lower costs, can be achieved by structural design in limited space to maximize the material utilization rate and reduce waste.