Rhenium Powder Research Articles

Production of rhenium nanoparticles by low-temperature aqueous-phase reduction of NH4ReO4 using NaBH4

The synthesis of refractory rhenium (Re) powders is significant for the production of rhenic products. In this work, the ultra-fine Re nanoparticles were synthesized via a combination of aqueous-phase reduction and rapid hydrogen reduction using NH4ReO4 as Re source. The theoretical reduction route was determined by investigating the Eh-pH diagram of the Re-H2O system and conducting thermodynamic calculations. The optimal results were achieved by adjusting the experimental parameters like acid type, initial acidity, molar ratio of BH4−: ReO4−, feed rate of reductant, reaction temperature (T), and reaction time (t). The amorphous Re powders with minor oxide inclusions can be prepared under the optimized conditions of [HCl] = 1.35 mol L−1, BH4−: ReO4− molar ratio = 5.32, feed rate = 15 mL min−1, reaction temperature = 30 °C, and reaction time = 30 min. The maximum reduction efficiency reaches 99.5%. After annealing in hydrogen for 30 min, the crystalline Re nanoparticles with low oxygen content can be obtained. This work demonstrates the feasibility and efficacy of rapidly synthesizing ultra-fine Re nanoparticles in a solution-based approach.

The preparation process of ultrafine gain W-Re powder by wet chemical method and its effect on alloy properties

Tungsten-rhenium (W-10Re) powder was successfully prepared by wet chemistry method followed by spark plasma sintering technique to fabricate W-10Re alloy. The synthesis mechanism and reduction behavior of the W-10Re powders were investigated by using X-ray diffraction (XRD), thermogravimetric experiments, and X-ray photoelectron spectroscopy. The reduction process of W-10Re powders from 100 °C to 1200 °C was divided into four stages, and the optimal reduction temperature region is 1000 °C–1100 °C. The reduced powders with irregular cube-shape were examined by transmission electron microscope. The XRD results of powders reduced at 1000–1200°C showed an overall right shift with the increase in temperature, indicating the solid solution of Re into W. The microstructure and mechanical properties of the alloys were studied using XRD, transmission electron microscopy, scanning electron microscopy, and Vickers hardness. The relative densities and grain sizes were comparable for the W-10Re alloys prepared from the powders reduced at 1000 °C, 1100 °C, and 1200 °C, whereas the Vickers hardness was decreased with the increase in the reduction temperature for those samples. The characterization of fracture toughness for these W-10Re alloys showed largely intergranular fracture with a small number of transgranular features. • Tungsten rhenium powder with an irregular cube shape and evenly distributed sizes could be prepared by the wet chemical method. • The particle size, oxygen content, and formation of solid solution were related to reduction temperature. • The reduction process of the precursor was studied and analyzed, and the reason for incomplete powder reduction was proposed, which was different from earlier studies.

Preliminary Study of the Rhenium Addition on the Structure and Mechanical Properties of Tungsten Heavy Alloy.

The results of structure and mechanical property investigations of tungsten heavy alloy (THA) with small additions of rhenium powder are presented. The material for the study was prepared using liquid phase sintering (LPS) of mixed and compacted powders in a hydrogen atmosphere. From the specimens, the samples for mechanical testing and structure investigations were prepared. It follows from the results of the microstructure observations and mechanical studies, that the addition of rhenium led to tungsten grain size decreasing and influencing the mechanical properties of W-Ni-Fe-Co base heavy alloy.

Physicochemical and Catalytic Properties of Rhenium-Containing Zeolites in the Course of Straight-Run Gasoline Upgrading

Catalysts for upgrading of the straight-run gasoline fraction of oil were prepared on the basis of a ZSM‑5 zeolite via dry mechanical mixing with an ultrafine rhenium powder. It was shown how the structural and acidic characteristics of zeolite ZSM‑5 changed when it was modified with rhenium. The concentration and nature of carbon condensation products formed on the prepared catalysts during the processing of straight--run gasoline have been determined. An enhancement of operating efficiency of rhenium--containing zeolite catalysts in comparison with an unmodified zeolite was established, which consisted in increasing their capacity and reducing the rate of deactivation in the process under study

Characterization of Wear and Corrosion Resistance of Stellite 6 Laser Surfaced Alloyed (LSA) with Rhenium

This paper presents the method of preparation and study results of the Stellite 6 laser surface alloyed (LSA) with rhenium using na LDF diode laser (4000 W). During this process, a rhenium powder was introduced onto the surface of the Co-based alloy. The possibility of improving wear and corrosion resistance properties is interesting and worth investigating. The selected process parameters: the laser power of 900 W, powder feed rate in the range 1.92–3.83 g/min, and necessarily preheating of the substrate up to 200 °C—allowing to obtain the LSA layers on the Stellite 6 substrate. Depending on the process parameters, it is possible to modify the substrate’s surface layer in terms of rhenium concentration and geometrical characteristics of the laser tracks. It was found that undissolved particles of rhenium in laser-alloyed layers have a non-significant effect on their hardness and abrasion resistance. The laser surface-alloyed corrosion potential is better than the corrosion potential of the Stellite 6 substrate, including reducing resistance to pitting corrosion with a high ability to repassivation.

Reaction Mechanism and Process Control of Hydrogen Reduction of Ammonium Perrhenate

The preparation of rhenium powder by a hydrogen reduction of ammonium perrhenate is the only industrial production method. However, due to the uneven particle size distribution and large particle size of rhenium powder, it is difficult to prepare high-density rhenium ingot. Moreover, the existing process requires a secondary high-temperature reduction and the deoxidization process is complex and requires a high-temperature resistance of the equipment. Attempting to tackle the difficulties, this paper described a novel process to improve the particle size distribution uniformity and reduce the particle size of rhenium powder, aiming to produce a high-density rhenium ingot, and ammonium perrhenate is completely reduced by hydrogen at a low temperature. When the particle size of the rhenium powder was 19.74 µm, the density of the pressed rhenium ingot was 20.106 g/cm3, which was close to the theoretical density of rhenium. In addition, the hydrogen reduction mechanism of ammonium perrhenate was investigated in this paper. The results showed that the disproportionation of ReO3 decreased the rate of the reduction reaction, and the XRD and XPS patterns showed that the increase in the reduction temperature was conducive to increasing the reduction reaction rate and reducing the influence of disproportionation on the reduction process. At the same reduction temperature, reducing the particle sizes of ammonium perrhenate was conducive to increasing the hydrogen reduction rate and reducing the influence of the disproportionation.

Synthesis of Rhenium–Scandia doped tungsten nanoparticles for shrinkage investigation

Scandate cathode made out of tungsten nanoparticles have several advantages such as high current density, uniform emission, and long life over conventional cathode. Fabrication of porous tungsten pellet out of tungsten nanoparticles by pressing and sintering is a critical challenge. Cold pressing followed by sintering of nanoparticles results shrinkage of pellet size and uncontrolled porosity, which motivate us to work on sintering of nanoparticle. A new chemical synthesis approach was adopted for precisely controlling the powder particle parameters. The present technology relates to the preparation of an ultra-fine nano-scandate powder using chemical route, dissolving tungsten, and rhenium powder in special solvent under ultra-agitation, wherein the other constituents (such as Ba, Ca, Sc, and alumina) are uniformly distributed throughout the powder. Dissolving tungsten and rhenium in the solution, and further sol–gel process, resulted in the formation of spherical shaped particles. Nanoparticles were characterized using: (1) X-ray diffraction (XRD) for phase purity of powder, (2) Field Emission Scanning Electron Microscopy (FE-SEM) for particle size and distribution, (3) Scanning Electron Microscopy (SEM) to study the surface micro-features such as pore dimension and pore distribution and (d) Energy Dispersive Analysis of X-rays (EDAX) for elemental composition. The results showed that the powder has uniform grain size with an average particle diameter of ~100 nm. In this proposed work, rhenium has been co-doped with scandia doped tungsten nanoparticles in order to improve shrinkage. Addition of rhenium in scandia doped tungsten nanoparticles showed about 10% less shrinkage compared with scandia doped tungsten nanoparticle.

The Influences of Stirring on the Recrystallization of Ammonium Perrhenate

Ammonium perrhenate is widely used in alloy manufacturing, powder processing, the catalytic industry, and other fields. Recrystallization can improve the specific surface area of ammonium perrhenate, reduce its particle size, and improve its particle size distribution uniformity. Therefore, recrystallized ammonium perrhenate can obtain better application benefits in the above fields. Stirring is an important factor that affects the recrystallization of ammonium perrhenate, and this paper systematically analyzes the influence of the stirring paddle types and stirring intensities on ammonium perrhenate during the homogeneous recrystallization process, ultimately revealing the relationship between the growth rate of ammonium perrhenate and the stirring process. Particle image velocimetry physical simulation results showed that the flow field in the reactor was more evenly distributed when using the disc turbine impeller, and a relatively uniform velocity liquid flow area was formed in the whole reactor, while the low-velocity liquid flow area was smaller. Therefore, this information, combined with SEM test results, suggests that under the same recrystallization time and stirring intensity, the stirring effect of a disc turbine impeller is more suitable than a propelling propeller and an Intermig impeller for the recrystallization process of ammonium perrhenate. Moreover, the XRD patterns and SEM analysis showed that if the agglomeration in the systems was too strong or too weak, the growths of the (101) crystal plane and (112) crystal plane were restrained, which caused an attenuation in the growth rates along the crystallographic directions that were orthogonal to the crystal faces. Finally, the reduction experiments show that the recrystallization of ammonium perrhenate could improve the phase parameters of rhenium powders.

Effect of Oxygen Flow Rate on the Particle Size Distribution and Morphology of the Ultrafine Rhenium Powders Prepared by CVD

Ultrafine rhenium (Re) powders were prepared by a chemical vapor deposition method at different oxygen flow rates. Results show that the particle size ranges between 100 nm and 1300 nm and that the size distributions are close to the normal distribution. The d-values (d10, d50, and d90) of the ultrafine Re powders initially decrease and then increase with increasing oxygen flow rate from 20 to 80 mL/min. The morphology of the ultrafine Re powders is irregular polyhedron, and these powders grow through either coagulation or continuous deposition. In addition, the amount of residuals after the experiment reduces with the increase of oxygen flow rate from 20 to 40 mL/min. Above 40 mL/min, no appreciable residuals could be observed. X-ray diffraction analysis of the residuals indicates that the samples were low valence Re oxides of ReO3 and ReO2.

Investigation on ammonium perrhenate behaviour in nitrogen, argon and hydrogen atmosphere as a part of rhenium extraction process

ABSTRACTAmmonium perrhenate (APR) is an intermediate product in rhenium extraction process, by which it is possible to produce rhenium powder. The main purpose of this research is to investigate the behaviour of APR in different atmospheres as a part of reduction process. In this research, differential thermal analysis and thermo gravimetric analysis are used to peruse the APR behaviour in nitrogen, argon and hydrogen atmospheres. Also for further validation, X-ray diffraction analysis and the scanning electron microscopy were used. The results indicate that APR behaves almost the same in the argon and nitrogen atmospheres. In these conditions, APR decomposes to rhenium oxides during thermal decomposition. However, APR in hydrogen reductive atmosphere is reduced to pure rhenium powder without any reactions. SEM images showed that hydrogen reduced APR had a spherical morphology, but on the other hand the directly reduced rhenium powder in hydrogen atmosphere showed flake morphology.

Refractory metal alloying: A new method for improving mechanical properties of tungsten heavy alloys

Abstract Influence of mechanically alloyed tungsten-rhenium powders on the microstructure and mechanical properties of liquid phase sintered 89W-7Ni-3Fe-1Re heavy alloy was studied. Heat treatment and swaging were conducted on alloys prepared using both conventionally blended and mechanically milled powders. The results indicated the formation of bcc solid solution by high energy milling of tungsten and rhenium powders. The corresponding particle and the crystallite size decreased after high energy milling. Grain size and contiguity of the milled alloy were significantly lower than those of conventional counterpart. The alloy prepared using high energy milled W-Re powder exhibited relatively superior balance of strength, ductility and impact toughness. These findings suggest that refractory powder mechanical alloying prior to sintering is beneficial for improving the mechanical properties of tungsten heavy alloys.

Crystal structures of [M(Еn)3](ReO4)2 (M = Ni, Zn)

The structures of two isostructural phases of [M(Еn)3](ReO4)2 (M = Ni, Zn; Еn is ethylenediamine) are studied. The crystal structures belong to the triclinic system, but demonstrate a pseudohexagonal packing motif. It is shown that the product of thermal decomposition of [Zn(Еn)3](ReO4)2 (hydrogen atmosphere, 400 °C) is a homogeneous mixture of nanocrystalline zinc and rhenium powders with coherent scattering regions of ~30 nm.

Study of Alloys Ir<sub>x</sub>Re<sub>1-x </sub>(x = 0.65, 0.75 and 0.85)

Ir-Re alloys were synthesized from nanocrystalline iridium and rhenium powders under high pressure (4 GPa) und temperature (2000° C). They were characterized using powder X-ray diffraction and scanning electron microscopy.

Preparation of ultrafine rhenium powders by CVD hydrogen reduction of volatile rhenium oxides

A novel CVD process for the preparation of ultrafine rhenium powders was investigated using ammonium perrhenate as starting materials. In the process, volatile rhenium oxides, such as ReO4 and Re2O7, were vaporized under a controlled oxidizing atmosphere via the pyrolysis of ammonium perrhenate, and carried into reduction zone by carrier gas, and there reduced into rhenium powders by hydrogen gas. Thermodynamic calculations indicated that Re2O7 could be prevented from further decomposition through controlling the oxygen partial pressure higher than 10−1.248 Pa in the pyrolysis of ammonium perrhenate. This result was further validated via DSC-TGA analysis of ammonium perrhenate. The typical rhenium powders prepared by the CVD method proposed show irregular polyhedron morphology with particle size in the range of 100-800 nm and a D50 of 308 nm. The specific surface area and oxygen content were measured to be 4.37 m2/g and 0.45%, respectively.

Production of high-purity microcrystalline molybdenum and rhenium powders by reduction in hydrogen-nitrogen media

Possibilities of producing high-purity microcrystalline molybdenum and rhenium powders by direct single-stage reduction of ammonium compounds of molybdenum [(NH4)6Mo7O24 · 4H2O] and rhenium [NH4ReO4] in hydrogen-nitrogen media are considered. Based on the results of investigations of the influence of technological parameters (degree of purity of the initial reactants, temperature, gas mixture composition, reactant feed rate) on the quality of target products, an optimum regime of the reduction process has been established, which ensures the production of high-purity microcrystalline molybdenum and rhenium powders.

The Effect of Sintering on the Properties of Ultrafine Rhenium Powders Prepared by CVD Method

A novel CVD method of preparing ultrafine rhenium powders was investigated in this paper. The Re2O7 gas obtained by decomposing NH4ReO7 was transported to the reduction chamber and then reduced by H2 to form rhenium powders. In order to evaluate the effects of sintering on properties of rhenium particles, such as crystal size, morphology, surface conditions and particle size, the samples of rhenium powders prepared at different reduction temperatures were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and laser particle size analyzer. The experimental results show that the sintering effect among particles is enhanced with increasing of reduction temperature, resulting in larger crystal size, smoother surface and larger average particle size of the rhenium powder.

Modification of W and Re Powders by Plasma Technique

Selected measurement results of plasma spheroidization of tungsten and rhenium powders are presented in the paper. The powders can be applied for production of sinters intended for armor-piercing penetrating cores (kinetic energy penetrators) or high-current electric contacts. Spheroidization of these powders was carried out on the stand for plasma spraying in a chamber filled with neutral gas. Changes of shape and size of powder particles after spheroidization are demonstrated. Measurement results of internal stresses in powder particles are presented.

Investigation of Influence of Rhenium Addition on W-Ni-Fe-Re Heavy Alloys Properties

The method of rhenium powder fabrication was presented in the paper. The powder was received by reduction of ammonium perrhenate. Rhenium was added to W+Ni+Fe powder mixture, then pressed (in the isostatic press), and next sintered in a vacuum furnace. Sinters containing rhenium are more fine-grained as compared to WNiFe alloys. Their average grain diameters are 11,7 µm and 25,6 µm respectively. Sinters with addition of rhenium are charac-terized by higher hardness, higher tensile and yield stress but lower density and elongation as com-pared to classical heavy alloys.

Lutetium(III) oxide iodide

Single crystals of lutetium oxide iodide, LuOI, were obtained as a by-product of the reaction of lutetium metal, rhenium powder and lutetium triiodide, LuI3, in a sealed tantalum container. LuOI crystallizes in the tetra­gonal PbFCl-type of structure (matlockite), where Lu, O and I are situated on positions with 4mm, \overline{4}m2 and 4mm symmetry, respectively.

Microstructural Characterization of Rhenium Powder Obtained at Various Temperatures

This work deals with the measurement of particle-size distribution of rhenium powder obtained by reduction of ammonium perrhenate under hydrogen flux. Depending upon the reduction temperature, variable amounts of hydrogen, nitrogen and oxygen remain interstitially located in the material, causing large X-ray diffraction line broadening, which accounts for particle-size domains in the microstructure of the metallic particles. The present study was carried out in the range of 400 to 1000 °C, where the oxidized species can be reduced to rhenium powder. All calculations regarding the line-broadening effects made use of the powerfull Warren-Averbach method, while the experimental diffraction profiles were modeled by non-linear least-squares fitting, using pseudo-Voigt functions. The average particle size increased from 8.7 to 120 nm with increasing temperature from 400 to 750 °C, with no further change above this last temperature. On the other side, strain distribution within the same temperature range varied from 15 to 735x10 -5 .