Tungsten Nanopowders Research Articles

Processing of Tungsten Nanopowder into a Micropowder Consisting of Spherical Particles

Processing of Tungsten Nanopowder into a Micropowder Consisting of Spherical Particles

Сфероидизация нанопорошковых микрогранул вольфрама в термической плазме электродугового разряда

A method for producing tungsten powder consisting of spherical microparticles with dimensions of 20 – 50 µm is considered when processing a granular tungsten nanopowder in a flow of argon electric arc thermal plasma. Experimental studies of plasma chemical synthesis of tungsten nanopowder in a plasma reactor with a limited jet flow during the interaction of tungsten trioxide with a flow of hydrogen-containing plasma generated in an electric arc plasma torch have been carried out. The conditions of spray drying and the properties of a suspension consisting of tungsten nanoparticles have been experimentally determined, ensuring the production of mechanically strong nanopowder microgranules of rounded shape with a homogeneous internal nanostructure that does not contain cavities, with the yield of microgranules with a size of less than 60 µm at the level of 65 %. The influence of the parameters of the plasma processing of nanopowder microgranules in the thermal plasma flow on the degree of spheroidization and the microstructure of the resulting particles has been established.

Effect of Tungsten Nanopowder Content on Electrode Coating Properties and the Structure of the Deposited Metal

Effect of Tungsten Nanopowder Content on Electrode Coating Properties and the Structure of the Deposited Metal

Influence of Tungsten Nanopowders on the Kinetics of Cement Stone Strength Gain

The paper presents the results of research of influence of nanopowders of tungsten compounds obtained from hard-alloy waste on structure formation and kinetics of cement stone strength gain. The positive effect of additives on the mechanical and structural characteristics of the cement stone in the concentration range of 1...5 wt.% has been established.

Joining and cycling performance of ultra-thick tungsten coatings on patterned steel substrates for fusion armour applications

Tungsten is the leading candidate to provide a critical protective coating for copper and steel-based plasma facing components in nuclear reactors. However, fabrication of thick tungsten coatings on copper or steel is challenged by the significant difference in the melting points and the thermal expansion coefficients of the materials, which leads to severe thermal expansion mismatch strains during manufacture and in service. This challenge is investigated using a new processing approach — field assisted sintering of tungsten nanopowders directly onto pre-sculptured steel component surfaces to induce controlled, vertical segmentation cracks that provide strain relief. Tungsten coatings up to 2 mm thick were fabricated with uniform density and with a microstructure consisting of ultrafine grains of ∼200 nm. The coatings showed outstanding thermal cycling durability and survived for at least 50 cycles under pulsed temperature cycles between 300 to 800 °C. Microscopy and in situ thermal imaging revealed that a previously unachievable thermal expansion mismatch strain tolerance was provided by a combination of enhanced tungsten coating adhesion and deliberate coating segmentation by vertical cracking. The approach should be readily adaptable to other dissimilar materials systems to facilitate a range of durable, ultra-thick low ductility coatings on metallic substrates.

Development of a Lightweight Tungsten Shielding Fiber That Can Be Used for Improving the Performance of Medical Radiation Shields

Radiation exposure in medical institutions is mainly due to low doses. Low-dose radiation mainly means scattered radiation, and such scattered radiation can be shielded with a lightweight shielding suit. In this study, the shielding performance of shielding fabrics woven by winding polyethylene (PE) yarn around a 30 μm tungsten wire was evaluated. To improve the shielding performance, an air pressure dispersion process of coating tungsten nanopowder on the fiber was developed. The radiation shielding effectiveness of the shielding fibers with and without dispersed tungsten nanopowder were compared by measuring the spatial dose inside the diagnostic X-ray imaging room of a medical institution. The results of the experiment confirmed that the fabric coated with tungsten nanopowder improved the shielding performance of the general tungsten fiber by approximately 15% and provided relatively effective low-dose radiation shielding at approximately 1.2 m of the X-ray imaging equipment. This study shows that tungsten fiber can be helpful in manufacturing lightweight shielding clothing for protection from scattered radiation in medical institutions.

Investigation of the Effect of Tungsten Carbide (WC) Nanopowder on Iron-Based Powder Structural Materials

Studies of a powder used as a modifier obtained from solid-alloy waste, such as tungsten carbide (drill balls), are presented. Dispersion, particle morphology and phase analysis of the powder were studied. The powder obtained from solid-alloy waste is a phase – it is tungsten carbide WC, it consists of nanoobjects of various shapes (nanoparticles, nanoplastics) up to 100 nm in size, with a slight presence of agglomerates up to 250 nm in size. The influence of tungsten carbide nanopowder as a modifier on the mechanical properties (strength and hardness) of PK70D3 iron-based powder structural steel has been studied. For the study, two different modes of preparation of powder alloy have been used with the use of one-stage and two-stage sintering. The influence of additive nanopowder of tungsten carbide on the mechanical properties of structural alloy powder based on iron PK70D3 has been defined: strength increases by more than 23% (in single-stage sintering), by more than 28% (in double-sintering), hardness decreases by more than 6% in single-stage sintering and increases by more than 26% with two stages of sintering, compared to the initial alloy. It has been shown that samples, obtained using double sintering with a tungsten nanopowder modifier (2.5%), have higher values of strength (more than 80%) and hardness (more than 13%), compared to modified samples, obtained by single-stage sintering technology. Thus, the modification of a 2.5 % nanoprobe of tungsten carbide, a widely used structural powder alloy based on iron PC70D3 allows for a significant change in mechanical properties. The use of powder alloys in double sintering technology provides the material hardness and the strength increase.

Effect of surface modification on the microstructure and sintering characteristics of tungsten nanopowders prepared by a wet chemical method

ABSTRACT In order to prepare high-performance tungsten alloys, surface modification of tungsten nanopowders prepared by a wet chemical method was carried out by acid pickling at room temperature. The low-temperature sintering characteristics of tungsten nanpowders before and after pickling was compared and analysed. The surface modification was carried out by pickling with a solution of hydrofluoric acid, concentrated nitric acid and ammonium fluoride at room temperature. After this surface treatment, uniformly distributed step-shaped defects formed on the surface of the tungsten nanopowders. After low-temperature sintering, the grain size of the tungsten alloy corresponding to the surface-modified powder precursor was reduced by 20% compared to the alloy using untreated powder as precursor. In addition, the step-shaped defects also increase the sintering activity of the pickled tungsten powder and promote its sintering densification, making the final density of pure tungsten sintered at 1600°C as high as 96.7%, and its hardness greatly increased to 521 HV0.2. The results show that room-temperature pickling and subsequent low-temperature sintering is a promising method for preparing high-performance nanotungsten alloys.

Effect of La2O3 content on the densification, microstructure and mechanical property of W-La2O3 alloy via pressureless sintering

In the present work, the influences of La2O3 content (0–5.0 wt%) on the densification and grain growth of tungsten (W) nanopowders during pressureless sintering were systematically investigated. The densification inhibitory effect was enhanced with the increase of the amount of La2O3 addition, resulting in that the densification rate decreases from pure W to W/5.0wt%La2O3 composite powder. However, the grain size of W first decreases from 0 wt% to 2.0wt%La2O3 addition due to the increase of number density of La2O3 particles, and then increases from 2.0 wt% to 5.0wt%La2O3 addition because of the significant increase of the particle size and the decrease of the number density. On the premise of achieving near full density, the grain size of all W-La2O3 alloys sintered by pressureless sintering is very small, only 0.47–1.90 μm. The W-2.0wt%La2O3 alloy sintered at 1650 °C with the grain size of 0.47 μm possesses the highest Vickers microhardness of 739.3 HV0.2.

Facile Synthesis of Single-Phase Alpha-Tungsten Nanopowders from Ammonium Paratungstate by RF Induction Thermal Plasma and Thermochemical Reduction

Facile, economic methods of preparing tungsten (W) nanopowder are critically needed to meet industrial demand. Herein, we report a method of preparing single-phase alpha-W (α-W) nanopowders using ammonium paratungstate (APT) as a starting material and the optimum synthesis conditions. The process involves two stages: i) the radio-frequency (RF) induction thermal plasma treatment of APT, followed by ii) thermochemical reduction at 600-900 <sup>o</sup>C. The crystallographic phase and morphological evolution of all products were systematically investigated using X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), and transmission electron microscopy (TEM), and the effects of the annealing temperature on the phase and particle size of the obtained powders were also evaluated. When the RF induction thermal plasma treatment was conducted with and without H<sub>2</sub>, the XRD and FESEM results showed the formation of mixed-phase α- and beta-W (β-W) nanopowder and WO<sub>3</sub> nanopowder, respectively. Single-phase α-W nanopowder was achieved by annealing the WO<sub>3</sub> nanopowder in an H<sub>2</sub> reductive atmosphere at 700 <sup>o</sup>C for 10 min, resulting in homogenous nanoparticles with a small particle size (d50) of 21.16 nm without any aggregation.

Effect of La2O3 addition on the synthesis of tungsten nanopowder via combustion-based method

In this study, the influences of La2O3 added on the phase, morphology and reduction process of tungsten oxide prepared by solution combustion synthesis (SCS) were investigated for the first time. And tungsten nanopowders with different La2O3 doping amount (0.5∼5.0 wt%) were successfully prepared by SCS and followed hydrogen reduction. The results showed that with the increase of La2O3 addition, the product synthesized by SCS changed from needle-like W18O49 to irregularly granulated H0.53WO3 and the complete reduction temperature also increased form 700 ℃ to 850 ℃. The densification behavior of as-prepared W nanopowders revealed that the densification inhibitory effect of La2O3 was enhanced as the La2O3 addition increased. Nevertheless, due to the optimal size and distribution of La2O3 particles, the sample with 2.0 wt% La2O3 addition has a smallest grain size of 0.47 μm and a highest microhardness value of 739.3 Hv0.2, which are the best compared with the literature.

Obtaining of tungsten nanopowders by high energy ball milling

The objective of the work is identifying the modes of ball milling of the W16,5 and PWT grade tungsten that ensure obtaining nanosized powders. Milling was performed with the AGO-2U planetary-centrifugal mill for 5, 15, 60, and 120 min at the carrier rotation frequencies of 400, 800, and 1000 rpm. After milling, the shape and size of tungsten powder particles was studied by scanning electron microscopy. The effect of work hardening and aggregation on milling of the powders has been demonstrated. As a result of ball milling, nanoparticles of tungsten sized from 25 nm have been obtained. It has been found that the minimum size of particles is achieved at the carrier rotation frequency of 800 rpm and milling duration of not less than 60 min.

Comparison of different tungsten precursors for preparation of tungsten nanopowder by RF induction thermal plasma

Tungsten nanopowders were synthesized using three different precursors: commercial tungsten (W), tungsten trioxide (WO3), and ammonium paratungstate (APT) by radio-frequency (RF) induction thermal plasma in the presence and absence of H2. The crystalline structure, morphology, and particle size of the synthesized tungsten nanopowders were analyzed by X-ray diffraction, field emission scanning electron microscopy, and transmission electron microscopy. The W nanopowder obtained using APT precursor was found to be the most homogeneous and smallest nanoparticles and showed the largest α-W phase (stable) fraction, which is the preferred phase for tungsten because of its superior properties to those of the β-W phase (metastable).

Synthesis of tungsten nanopowders and modes of their combustion and passivation

Tungsten nanopowders were synthesized by a chemical metallurgy method at 440–640 °C from WO3 precursors possessing different specific surfaces. The α-W nanopowder synthesized at 640 °C was not pyrophoric, while the α-W containing the traces of oxides obtained at 480 °C was pyrophoric. The temperature interval for the α-W synthesis was revealed as very narrow, from 470 to 490 °C.

Получение наноразмерных порошков оксида вольфрама и вольфрама

AbstractNanopowder tungsten oxide and metallic tungsten are obtained via pyrolysis of ammonium metatungstate. Two methods are used for the synthesis of tungsten oxide: the use of a fibrous matrix and pyrolysis of aerosol particles. Tungsten oxide particles are formed during the pyrolysis in air. Metallic tungsten nanoparticles are obtained via subsequent thermal reduction of tungsten oxide in hydrogen. The structure and morphology of the samples are studied with X-ray diffraction and scanning electron microscopy. Tungsten nanopowders with average sizes from 7 to 30 nm are obtained depending on synthesis temperature. The electrochemical characteristics of electrodes coated with tungsten nanoparticles are studied with cyclic voltammetry, impedance spectroscopy, and galvanostatic charge–discharge methods. An electrode with W nanoparticles exhibited a specific low-frequency capacitance of about 90 F/g due to thin tungsten oxide film on the surface of tungsten nanoparticles.

Применение метода испарения вещества высокоэнергетическим пучком электронов для получения нанопорошка вольфрама

The method of producing nanopowder by evaporation by a high-energy electron beam has a great potential for refractory substances, since the electron beam makes it possible to obtain high the power density in the interaction spot is not more than 3–4 cm2 and, as a result, high temperature gradients. The accelerator and electron beam have a high efficiency of transferring energy from the power grid to evaporation (up to 70 %). The electron beam does not introduce pollution and is not selective to the material. Work specifics with an electron accelerator is associated with radiation caused by electron deceleration and high temperatures. These phenomena greatly complicate the monitoring of processes occurring in the evaporation zone. Therefore, at present, the method requires development and adaptation to specific materials. In this work, we studied the process of obtaining nanosized tungsten powder by the indicated method. Experiments were tested that allow obtaining data on the processes of nanopowder synthesis by calorimetry of the evaporation zone and measurements of the radiation level near it. The technology was developed and the parameters of the obtained tungsten nanopowders were determined. Showing ways to increase productivity This method is applied to tungsten.

Preparation of Nanosized Tungsten and Tungsten Oxide Powders

Nanopowder tungsten oxide and metallic tungsten are obtained via pyrolysis of ammonium metatungstate. Two methods are used for the synthesis of tungsten oxide: the use of a fibrous matrix and pyrolysis of aerosol particles. Tungsten oxide particles are formed during the pyrolysis in air. Metallic tungsten nanoparticles are obtained via subsequent thermal reduction of tungsten oxide in hydrogen. The structure and morphology of the samples are studied with X-ray diffraction and scanning electron microscopy. Tungsten nanopowders with average sizes from 7 to 30 nm are obtained depending on synthesis temperature. The electrochemical characteristics of electrodes coated with tungsten nanoparticles are studied with cyclic voltammetry, impedance spectroscopy, and galvanostatic charge–discharge methods. An electrode with W nanoparticles exhibited a specific low-frequency capacitance of about 90 F/g due to thin tungsten oxide film on the surface of tungsten nanoparticles.

A low-cost, efficient, and industrially feasible pathway for large scale preparation of tungsten nanopowders

Tungsten (W) is the most commonly used high-temperature refractory metal in many critical fields such as aerospace, military and electronic industries etc. This paper proposes a low-cost, efficient, and industrially feasible pathway for large scale preparation of tungsten nanoparticles via the combination of carbothermic reduction and hydrogen reduction processes. The new strategy involves the preparation process of pre-reduction W powder by reducing commercial WO3 with insufficient carbon black at 1050 °C or 1150 °C to avoid the residue of carbon, and the deep reduction process of pre-reduction W powder by hydrogen 725 °C. By this process, most of the oxygen in WO3 was reduced by carbon, and W particles with a much smaller size could be obtained owing to the absence of the volatile tungsten oxide, such as WO2(OH)2, which leads to the serious increase of particle size during the hydrogen reduction process. Tungsten nanoparticles with average particle sizes of about 40 nm and 75 nm have been successfully synthesized at 1050 °C and 1150 °C, respectively, with the residual carbon content as low as about 0.01%. This process can be readily extended to a large-scale industrial production of W nanopowders. Additionally, this new strategy has great potential to prepare other pure metals (or nanopowders) from their metal oxides via combining of carbothermic reduction (main process) and further reduction of other reducing agents.

Porous Pellets of Tungsten Nano Powder: Investigation of Surface Porosity of Machined Surfaces

The pressed dispenser cathodes are showing problem in machining due to their less strength because of low sintering temperature. In this paper, the synthesis of Nano tungsten powders and the fabrication of machinable porous Nano tungsten matrices were discussed. The Nano tungsten powders were synthesized by two different routes. One is by using Ammonium Meta Tungstate in sol gel technique and other is dissolving micron sized tungsten particles in Hydrogen Peroxide (H2O2). Using these synthesized Nano powders, the pellets were fabricated and the results were compared with the pellet made of commercially available tungsten powder (particle size 0.6–1 μ). The pressed porous tungsten buttons are sintered at high temperature and machining is carried out after copper infiltration. In this paper, surface morphology, hardness and machinability of porous tungsten Nano pellets were discussed.

Fabrication of fine-grained W-Cu composites with high hardness

W-Cu composite powders were prepared by ball milling method using quasi-spherical tungsten nanopowders as starting materials, and further used to fabricate W-Cu composites. The sintering behavior of obtained composite powders was investigated and experimental results reveal that composite powders exhibit high sintering activity and nanosized tungsten spheres could effectively suppress the grain growth of prepared W-Cu compacts. Importantly, composite compacts with high hardness of 409 ± 9 Hv are obtained when sintered at 1200 °C for 1.5 h, which could be attributed to the fine grain size and homogeneous constituents distribution of sintered composites. Furthermore, 96.5% of theoretical density (TD) of obtained compacts could be achieved by liquid phase sintering process due to enhanced grain rearrangement. Kinetic analysis indicates that liquid phase diffusion is the dominant mass transfer mechanism during liquid phase sintering. The grain size comparison of products prepared by pure tungsten nanopowders and W-Cu composite powders confirms fine-grained W-Cu composites could be obtained using quasi-spherical tungsten nanopowders.