Development and testing of an additively manufactured lattice for DEMO limiters

In the conceptual design of EU-DEMO, damage to plasma-facing components under disruption events is planned to be mitigated by specific sacrificial limiter components. A new limiter concept has been proposed using lattice structures fabricated with tungsten powder by additive manufacturing techniques. The major potential benefits of using a lattice structure for limiters are the possibility to customise the thermal conductivity and structural compliance of the structure to manage temperatures and stress within material limits and lower sensitivity to crack propagation. This paper presents the results of the first investigations into the production, characterisation, and high heat flux testing of the lattices to assess their suitability for DEMO limiters. First stage prototypes have been manufactured from tungsten and tungsten tantalum mixed powder with two distinct laser power bed fusion processes, namely pulsed laser and continuous laser with heated bed. The samples are characterised in terms of mass, volume, density, extent of microcracks and voids, level of un-melted or partially melted particulates, texture and grain size, as well as tantalum segregation when applicable. High transient (0.25ms) heat load testing, with hydrogen plasma of energy density up to ~3 MJm-2 was carried out at KIPT on the QSPA Kh-50. These tests have shown that the energy absorbed by latticed targets preheated at 500°C is close to that absorbed by solid tungsten, suggesting that they may be used for limiter applications with the added advantage of adjustment of the heat transfer and stiffness performance by geometry design or material properties.

Hydrogen Diffusion and Adsorption on WO3 (001) based on First Principles Calculation

Hydrogen reduction of tungsten oxide is currently the most widely applied ultrafine tungsten powder production process. The process has the advantage of short, pollution free and simple production equipment. But it is difficult to effectively control the morphology and particle size of the tungsten powder because of lacking in-depth understanding of the dynamic mechanism of the process. The first-principles calculations are carried out to explore the diffusion and internal adsorption of hydrogen on the WO-terminated surface of WO3 based on the density functional theory. The results show that hydrogen can diffuse from the WO terminal surface to the inside of WO3, the activation energy of diffusion is 46.682 Kcal/mol. It’s preferable for hydrogen to diffuse from the surface to the inside than diffuse within the WO3 lattice. The adsorption energy of hydrogen on the WO termination surface of WO3 is 15.093 Kcal/mol, the adsorption energy of hydrogen inside the WO termination surface of WO3 is 14.116 Kcal/mol, which means the hydrogen is easier to adsorb inside the WO3 lattice.

Manufacturing and performance evaluation of medical radiation shielding fiber with plasma thermal spray coating technology

Lead, which has been used for radiation shielding in medicine, is currently sought to be replaced by an eco-friendly shielding material. Therefore, it should be replaced with shielding materials possessing excellent processability and radiation shielding performance similar to that of lead. In this study, a new process technology was developed focusing on the processability of tungsten, a representative eco-friendly shielding material. It is difficult to reproduce the shielding performance when using the method of coating nonwoven fabrics with a liquid using tungsten powder on a polymer material, which is adopted to ensure the flexibility of the shielding fabric. To address this, tungsten powder was sprayed on the fabric using a plasma thermal spray coating process and coated to a thickness of 0.2 mm to evaluate the shielding performance. Compared to standard lead with a thickness of 0.2 mm, the shielding efficiency differed by approximately 15%. Since the developed process can maintain the amount of injection in an area, it is possible to ensure the reproducibility of the shielding performance and automated process for mass production. This approach is economically feasible as it does not entail the mixing of polymer materials; hence, it can be used for preparing radiation shielding clothing for medical institutions.

Effect of Peak Current and Pulse On Time on the Coating Layer Thickness using Electrical Discharge Coating

The present study focused on the surface modification of aluminum 6061 by using electrical discharge coating (EDC) with powder suspension. The effects of peak current (Ip) and pulse on time (Ton) on the coating layer thickness were investigated. This study used Tungsten powder as an additive and mixed it with the kerosene oil and surfactant Span 83. The results indicated that peak current and pulse on-time significantly affected the coating layer thickness. The thinnest coating layer was observed at 3A, 150 µs, while the thickest coating layer with an average value of 17.239 µm was obtained at parameter 4A and 250 µs. In conclusion, the high value of peak current and longer pulse duration on time increased the thickness of the coating layer.

Effect of tungsten nanoparticles on sintering of the Sn-Cu-Co-W powder material

The effect of tungsten nanoparticles on the kinetics of sintering of the Sn-Cu-Co-W powder material used as a binder in diamond tools was studied. The W16,5 grade tungsten powder was mechanically activated in the AGO-2U planetary centrifugal mill for 60 minutes at the carrier rotation frequencies of 800 RPM. The mixture of tungsten, tin, copper, and cobalt powders was compacted by static pressing in press dies and then sintered in vacuum at the temperature of 820°C. The morphology and sizes of powder particles, as well as the structure of the sintered samples, were studied by the methods of scanning electronic microscopy. It has been demonstrated that tungsten nanoparticles have a noticeable effect on the process of dissolution-reprecipitation of cobalt in liquid-phase sintering.

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.

Soluble tungsten compounds Determination in workplace air

Tungsten is a transition metal which occurs in the Earth’s crust as minerals which after being mined is extracted. There is no data on chronic effects of contact with tungsten, although fine tungsten powder is flammable and can cause mechanical irritation to skin and eyes. However, there are soluble tungsten compounds, which are classified as toxic, causing damage to the eyes, and being harmful to the aquatic environment. The aim of the study was to amend Standard No. PN-Z-04221-3 determination of soluble tungsten compounds in workplace air using spectrophotometric method with potassium thiocyanate. The amendment was performed because Standard No. PN-Z-04221-3 describes a method in which the quantification is 0.25 mg/m3, according to European Standard No. EN 482 the quantification of method must be in range of 0.1 – 2 mg/m3. The method is based on depositing soluble tungsten compounds on a cellulose esters filter and then dissolving them in water. Then tungsten is reduced with tin chloride, after reaction with potassium thiocyanate, tungsten becomes a complex. Tungsten complex should be extracted with isoamyl alcohol and then absorbance should be measured on a UV-Vis spectrophotometer. The tests were performed with the UV-Vis Heλios spectrophotometer by ThermoSpectronic model Beta. The validation requirements of European Standard No. EN 482 were met. With this method soluble tungsten compounds in air can be determined at concentration of 0.1 – 2 mg/m3. The limit of quantification (LOQ) is 1.875 ng. The overall accuracy of the method is 5.06% and its relative total uncertainty is 22.09%. The method for determining tungsten has been recorded in a form of an analytical procedure (see Appendix). This article discusses problems of occupational safety and health, which are covered by health sciences and environmental engineering.

Effect of Jet Grading Technology on the Properties and Structural Characteristics of Tungsten Products

Jet grading technology is an efficient process in different industries. In this research, tungsten powder with different particle size distribution was used as a raw material to produce tungsten products via isostatic pressing as well as sintering. The mechanism of jet grading and the morphology and particle size distribution of different precursors were analyzed. The results showed that jet grading technology had remarkable effect on tungsten powder classification. The appropriate grading treatment was helpful to the formation of tungsten products with high performance. After jet grading and the following process like pressing and sintering, the tungsten products with better properties were manufactured which was used fischer particle size of 3.0~3.5μm as the raw material. The obtained products’ density was 18.77g/cm3 and its hardness was 372.15HV0.3.

Structure forming of Cu–W pseudoalloys prepared in different routes

The microstructures of alloys formed during the sintering of tungsten powder mixtures (PV2, 3.8–6.0 μm average particle size) and copper (PMS-11, 45–60 μm fraction) prepared by various methods were compared. The methods included simple metal powder mixing, mechanical activation (MA) of metal powders, copper precipitation from the solution of its sulfate (CuSO4·5H2O) on tungsten powder with simultaneous mechanical activation. The molar ratio of metals in mixtures Cu/W = 1. An aqueous solution for copper deposition included diethylene glycol (up to 30 %), glycerin (up to 8 %), hydrofluoric acid (up to 0.1 %), wetting agent OP-10 (up to 0.8 %). Mechanical activation was carried out in an AGO-2 planetary mill with 200 g of steel balls charged into the drums rotating at 2220 rpm for 5 min. Reduced copper in the solution and in the air rapidly oxidizes to the Cu2O oxide, so the composite powders obtained were washed, dried, and stored in an argon atmosphere. Samples pressed from the powders obtained (tablets 3 mm in diameter, 1.5–2.0 mm in height with a density of 7.7–8.0 g/cm3) were sintered in argon at atmospheric pressure and temperatures from 1000 to 1500 °C. During the sintering of Cu–W composite particles, several areas of the process can be distinguished. «Solid phase» sintering occurs at the contact points of composite particles at temperatures lower than the copper melting point. When samples are heated from the melting point to 1200 °C, samples are sintered by the liquid-phase mechanism from the conventional mixture of metal powders to form a low-porous cake. When composite powders obtained by MA during the copper deposition and MA of metal powder mixtures are sintered, samples are delaminated with the formation of large pores elongated perpendicular to the pressing axis and partially filled with copper melt. When samples obtained by powder MA are heated above 1400 °C, phase separation occurs and almost all copper is displaced from the sample to the surface.