Mo Particles Research Articles

Size-controlled synthesis of nano Mo powders via reduction of commercial MoO3 with carbon black and hydrogen

In the present work, a novel method was proposed to synthesize pure nano Mo powder via temperature programmed pre-reduction of commercial MoO3 by carbon black, followed by deep deoxidation with hydrogen. It was found that the carbothermal reduction of MoO3 included three stages: MoO3 → MoO2 → MoO2 + Mo2C → Mo. It can be concluded that the morphology and size of the obtained Mo particles are mainly determined at the carbothermic reduction stage. The dispersed nucleation and controlled growth are critical issues for controlling the particle sizes of Mo, which could be achieved at the carbothermic reduction stage by using the raw materials of the MoO3 and carbon black. Whereas, when the MoO3 was directly reduced by hydrogen or active carbon with a larger particle size, or commercial MoO2 were reduced with the carbon black, the dispersed nucleation and controlled growth of products can't be achieved. Meanwhile, to reduce the residual carbon content in the final Mo product, in the carbothermic pre-reduction process, the small amount of MoO2 was kept in the pre-reduced Mo powders, which was removed by hydrogen at the deep deoxidation stage. The content of residual carbon content in the final produced Mo nanopowders can be reduced to about 0.02%. This method has the advantages of simplicity, low cost, and high efficiency. Therefore, it has great potential for the industrial preparation of nano Mo powders in a large-scale.

Electrostatic precipitability of TiB2-Fe-Mo-Co ceramic-metal composites

TiB2 was used as the base body, and Fe, Mo, and Co metal powder particles were used as reinforcements to pressurize TiB2-Fe-Mo-Co ceramic–metal composites and resolve the heavy weight and unevenness of the traditional wet electrostatic precipitator (WESP) plate. The performance of its electrostatic precipitator was analyzed. Results revealed that the prepared ceramic–metal composites had a hardness of 95.6 HRA, a porosity of 4.01%, a density of 6050 kg/m3, and a conductivity of 3.90 × 106 S/m, the relative rot mean square values of the barbed electrode line and the fishbone discharge electrode line plate were 3.946 × 10−3 and 2.967 × 10−3. The powder was well polymerized, and the surface can form a considerable pore size. The overall compactness was good, which was beneficial for maintaining the mechanical strength of the product. The metal was wrapped well, which was conducive for the uniform distribution of the cleaning water. Compared with conventional WESP plate, the cermet plate had lower density and superior mechanical and electrical properties. The cermet plate addresses the overweightness of the traditional plate overweight and the uneven water distribution, making the former a promising alternative to the traditional WESP plate.

Microstructure and mechanical properties of brass/Mo composites processed via pressureless and spark plasma sintering

Brass/molybdenum composites containing 30, 70 and 85 wt% Mo were synthesized by mechanical milling and densification of the brass/Mo powder mixtures. The milled powders were separately consolidated by spark plasma and pressureless sintering processes. The pressureless sintered samples were cold compacted under 300, 450 and 600 MPa before sintering. The results showed that by increasing the cold pressure up to 600 MPa, the relative density of the sintered samples with 70 and 85 wt% Mo were increased. However, the highest relative density of the brass-30 wt% Mo composites was achieved for the samples which were cold compacted under 450 MPa before sintering. The microstructural observations by scanning electron microscopy and energy dispersive spectroscopy analyses revealed that the distribution of Mo particles within the brass matrix of brass-30 wt% Mo composites was not as fine as the other samples. According to the results, the relative density and hardness of the spark plasma sintered samples was higher than that of the pressureless sintered ones. Moreover, increasing the volume percent of molybdenum has led to decreasing the relative density of the spark plasma sintered samples. The flexural strength of the spark plasma sintered composites with 30, 70 and 85 wt% Mo were 397, 376 and 114 MPa, respectively.

Thermal Pre-Treatment of Polymetallic Nodules to Create Metal (Ni, Cu, Co)-Rich Individual Particles for Further Processing

Polymetallic nodules are a potential source of industrially demanded metals such as Ni, Co, Cu, and Mo (up to 3 wt %). Even if there is no deep-sea mining of manganese nodules today, a forecasted gap between metal demand and supply as well as continuously high metal prices may make seabed mining economically viable in the future. Up to now, a well-established industrial-scale extraction method for manganese nodules has been missing. Therefore, the aim of this study is to explore how economically interesting metals can be extracted from the nodules in a cost- and energy-efficient way. Polymetallic nodules have a heterogeneous chemical and structural composition without individual metal-rich particles. The economically interesting metals are distributed between different mineral phases (Mn-Fe-(oxy)hydroxides) as well as different growth structures that are intergrown with each other on a nm‒µm scale. Because of that a typical ore processing with the beneficiation of valuable particles is not feasible. The process presented here starts with a pyro-metallurgical pre-treatment of the polymetallic nodules, with the aim of creating artificial metal-rich (Ni, Cu, Co, Mo) particles with enrichment factors up to 10 compared to the original average metal contents. Afterwards, these particles should be beneficiated by conventional mineral processing steps to create a concentrate while reducing the mass stream in the process. The resulting metal particles can be further treated in conventional hydrometallurgical and/or pyro-metallurgical processes.

A study on the mechanically equivalent surrogate plate of U Mo dispersion fuel using tungsten

Abstract When a new fuel is developed, various mechanical properties are absolutely necessary for a safety analysis of the fuel for the licensing and prediction of its mechanical behavior during operation and accident conditions. In this paper, a mechanically equivalent surrogate plate of U Mo dispersion fuel is presented using tungsten, substitute material of U Mo particle. A surrogate plate, composed of tungsten/aluminum dispersion meat and aluminum alloy cladding, is manufactured with the same fabrication process with that of fuel plate except that a tungsten powder is used instead of U Mo powder. A modal test showed that the surrogate plate and fuel plate have similar dynamic characteristics, and a tensile test demonstrated the similarity of the material property up to the yield strength range. The conducted tests proved that the surrogate tungsten plate has equivalent mechanical behaviors with that of a fuel plate, which leads to the acceptable use of a surrogate fuel assembly using tungsten/aluminum dispersion meat in various mechanical tests. The surrogate fuel assembly can be utilized for various out-of-pile characteristic tests, which are necessary for the licensing achievement of a research reactor that uses U Mo dispersion fuel as a driver.

Microstructure, residual stress and mechanical properties of Al2O3/Nb joints vacuum-brazed with two Ag-based active fillers

Vacuum brazing was applied to join Al2O3 ceramic and pure Nb with two active Ag-based fillers, Ag-Cu-Ti and Ag-Cu-Ti + Mo. The influences of the brazing parameter and the content of Mo particles on the microstructure and mechanical properties of the brazed joint were studied. The typical interfacial structure of Al2O3/Nb joint brazed with Ag-Cu-Ti filler metal at 900 °C for 10 min was Al2O3/Ti3(Cu,Al)3O/TiCu+Ti2Cu3+TiCu4+Ag(s,s)+Cu(s,s)/Nb. In the joints brazed with Mo particle-modified composite filler, the large blocky Ti-Cu compounds disappeared, and a large number of fine phases formed in the brazing seam. The dissolved Mo played a better role in refining the microstructure compared with residual Mo particles. In addition, the finite element method (FEM) calculated results showed that the residual stress peak value of Al2O3/Nb brazed joint decreased from 296 MPa to 253 MPa when 8 wt. % Mo particles were added in the composite filler. The shear strength of Al2O3/Nb brazed joints could reach up to 203 MPa at 900 °C for 10 min. The joining properties of the Al2O3/Nb brazed joint were primarily dependent on the dispersion degree of fine Ti-Cu compounds and the thickness of Ti3(Cu,Al)3O reaction layer.

Microstructure and tensile properties of Ti-Mo alloys manufactured via using laser powder bed fusion

In this work, the dense Ti-7.5Mo sample (over 99.5%) was prepared by using laser powder bed fusion (L-PBF) from powder mixture of pure Ti and pure Mo. Through the use of mechanical mixture process, Mo particles present an uniform distribution. As the laser scanning speed decreases from 1700 mm/s to 1000 mm/s, the sample's relative density increases from 85.5% to 99.5%. The microstructural analysis indicates that Mo particle was mostly fully melted during laser melting. But, some large sized Mo particles were partial melted, which possesses gradient interface structure. Then, the tensile properties of as-fabricated samples under several laser scanning speed were determined. The results shows that the as-fabricated dense sample presents Young's modulus, ultimate tensile strength and strain at failure about of 70 GPa, 740 MPa and 9.2% respectively. Given to this low Young's modulus, which is approximate to bone of 30 GPa, the L-PBF processed Ti-7.5Mo shows great application potential in implant component.

Preparation of Mo nanoparticles through hydrogen reduction of commercial MoO2 with the assistance of molten salt

In the present work, the hydrogen reduction of commercial MoO2 with the assistance of molten salt has been investigated at 720–850 °C. In the case of no salt addition, the prepared Mo particles maintained the big platelet shape of raw MoO2 powders. However, after adding a small amount of salt (0.1% NaClKCl binary salt, MgCl2KCl binary salt, or LiCl mono salt), Mo nanoparticles were prepared successfully. It was found that a small amount of molten salt can help Mo to nucleate dispersedly and its growth via chemical vapor transport (CVT) mechanism can be controlled by reducing temperature. At 750 °C, when the NaClKCl binary salt was used, the obtained Mo nanoparticles had both good dispersion and small average size of about 70 nm. Kinetics analyses indicated that the rate controlling step for the hydrogen reduction of MoO2 was the interface chemical reaction, and after adding salt, the reaction rate constant decreased dramatically, relative to that without salt. The extracted activation energies for pure MoO2, MoO2 with 0.1% NaClKCl binary salt and MoO2 with 0.1% LiCl mono salt were 76.13 kJ/mol, 117.45 kJ/mol and 97.23 kJ/mol, respectively.

A New Route to Produce Submicron Mo Powders via Carbothermal Pre-reduction Followed by Deep Magnesium Reduction

A novel route to synthesize molybdenum (Mo) powders via carbothermic pre-reduction of molybdenum dioxide followed by deep reduction by magnesium (Mg) is proposed. Molybdenum dioxide (MoO2) reacted with insufficient carbon at 1373 K for 2 h to produce a mixture of Mo and MoO2. Then, the pre-reduced samples were mixed with Mg and magnesium chloride (MgCl2), and reacted at 1023 K for 1 h to remove the residual oxygen. Acid leaching was performed at room temperature for 1 h after the magnesium reduction process. Finally, Mo particles with a small size were obtained. This new method provides a simple route to prepare submicron Mo powders.

Preparation of submicron Mo powders by the reaction between MoO2 and activated carbon

In this study, the solid-state reaction between molybdenum dioxide (MoO2) and activated carbon was investigated in the temperature range 1123–1323 K. When the reaction temperature was above 1223 K and the C/MoO2 molar ratio was 2, molybdenum (Mo) powders of particle size about 0.4 μm were obtained. It was found that a higher temperature decreased the Mo particle size and increased the reaction rate. The present method provides a simple approach to prepare submicron Mo powders.

Calcium molybdate nanoparticles formation in egg phosphatidyl choline based liposome caused by liposome fusion

In order to achieve the highly efficient 99mTc production from 100MoO3 by the 100Mo(n, 2n)99Mo reaction, we have developed a new protocol to synthesize nano-sized Mo particles, of which the size was controlled by the inner space of the liposomes. Calcium and molybdate ions were encapsulated into ∼100 nm size liposomes. The liposome suspensions were then mixed and heated to promote the membrane fusion. As a result, the insoluble CaMoO4 nanoparticles precipitated inside the liposomes. The median particle diameter of 168 nm and average diameter of 169 ± 56 nm (n = 109) were obtained from an SEM image, and the particles have a powellite-structure. The formation process of the particles was then examined. The formation of nano-sized CaMoO4 was observed by the high resolution TEM image and TEM image of negative-stained liposome. At the room temperature, the fusion of liposome did not occur significantly. These results suggest that nanocrystals of the CaMoO4 were likely formed in the liposomes because of the liposome fusion and aggregated during the drying processes of reaction solution.

Preparation of Mo nanopowders through hydrogen reduction of a combustion synthesized foam-like MoO2 precursor

In this work, Nano-sized Mo particles were fabricated by solution combustion synthesis (SCS) followed by hydrogen reduction. A foam-like MoO2 precursor was first assembled using 20–30 nm nanoparticles generated by SCS. Subsequently, hydrogen reduction of the foam-like MoO2 precursor was undertaken to prepare the nano-sized Mo particles. The reduction temperature of the final phases and morphologies of the Mo products were then systematically investigated. The hydrogen reduction mechanism of the foam-like MoO2 precursor was analyzed using thermogravimetry analysis (TG) and H2 temperature programmed reduction with MS analysis (H2-TPR-MS). The results show that the nano-sized and irregularly-shaped 60–80 nm Mo particles were successfully synthesized at 600 °C for 2 h. Increasing the temperature to 650 °C–700 °C produced larger Mo particles due to sintering of the Mo powder at a higher reduction temperature. Additionally, a Mo2C impurity formed as a result of the carbon-thermal reaction between residual carbon and MoO2 in the presence of hydrogen.

Effect of coating thickness and annealing temperature on ZrN coating failure of U-Mo particles under heat treatment

Zirconium nitride (ZrN) coating is used as a diffusion barrier layer on U-Mo powder surfaces to suppress interdiffusion layer formation. However, it has been reported that the structural integrity of the coating did not remain intact after fuel plate fabrication process. To assess the coating integrity during the fabrication process at high temperature, parametric studies were performed with different coating layer thicknesses and annealing temperatures for ZrN-coated U-7w.t.%Mo particles. The microstructure of the annealed samples was analyzed by using scanning emission microscopy (SEM) and X-ray diffraction. Finite element simulations were performed whether mechanical failure of the coating layer occurs under given annealing temperatures. The simulation results showed the effect of coating layer thickness and annealing temperature on the coating fracture. It was found that tensile hoop stress became larger to cause fracturing over the coating layers as the annealing temperature increased, which was consistent with the results of SEM analysis. By comparing experimental results with simulation results, the thresholds of coating layer thickness and annealing temperature for crack initiation was primarily determined by the U-7Mo particle size.

The Effect of Mo Particles Addition in Ag-Cu-Ti Filler Alloy on Ti(C,N)-Based Cermet/45 Steel-Brazed Joints

Reliable brazing of Ti(C,N)-based cermet and 45 steel was successfully achieved by using the Mo-particle-reinforced Ag-Cu-Ti composite filler. The effects of Mo content on the interfacial microstructure and mechanical properties of Ti(C,N)-based cermet/45 steel joints were analyzed. The results showed that the joint microstructure was primarily composed of Ni3Ti+Cu3Ti2, Ag(s,s)+Cu(s.s), CuTi+Mo, Ti-based solid solution, and FeTi+Fe2Ti. With the increase in Mo content in filler, the thickness of the Ni3Ti+Cu3Ti2 layer adjacent to the Ti(C,N)-based cermet decreases, while more blocky Ti-Cu intermetallic were observed in the brazing seam. The shear strength of the joint could be significantly improved by adding suitable amounts of Mo into the Ag-Cu-Ti filler, and the peak value of 263 MPa was achieved when the alloys were brazed with Ag-Cu-Ti+8wt.%Mo composite filler at 920 °C for 20 min.

Preparation of ultrafine Mo powders via carbothermic pre-reduction of molybdenum oxide and deep reduction by hydrogen

A novel route to synthesize molybdenum (Mo) powders via carbothermic pre-reduction of molybdenum oxide followed by deep reduction by hydrogen was proposed. The pre-reduced Mo powders containing a small amount of molybdenum dioxide (MoO2) were produced first by reacting molybdenum trioxide (MoO3) with insufficient carbon. Then the pre-reduced Mo powders were further reduced by hydrogen at 1173 K to remove the residual oxygen. Mo particle with a much smaller size could be obtained by the carbothermic reduction owing to the absence of Mo-O-H gaseous intermediate phase which leads to the increase of particle size during the hydrogen reduction process. In the carbothermic pre-reduction process, the existence of a few MoO2 can avoid the residue of carbon in the prepared pre-reduced Mo powders which is hard to remove during the following hydrogen reduction process. It was observed that increasing the C/MoO3 molar ratio was beneficial for the decrease of the particle size of Mo powders. Mo powders with submicron-size could be obtained after further hydrogen reduction. This new method provides a simple and low cost route to prepare ultrafine Mo powders.

Microstructure and mechanical behavior of Zr substrates coated with FeCrAl and Mo by cold-spraying

FeCrAl and Mo layers were cold-sprayed onto a Zr surface, with the Mo layer introduced between the FeCrAl coating and the Zr matrix preventing high-temperature interdiffusion. Microstructural characterization of the first-deposited Mo layer and the Zr matrix immediately below the Mo/Zr interface was performed using transmission electron microscopy, and near-interface elemental distributions were obtained using energy-dispersive X-ray spectroscopy. The deformation of the coated Mo powder induced the formation of microbands and mechanically interlocked nanoscale structures. The mechanical behavior of Zr with a coating layer was compared with those characteristic of conventional Zr samples. The coated sample showed smaller strength reduction in the test conducted at elevated temperature. The hardness and fracture morphology of the Zr matrix near the interface region were investigated to determine the effect of impacting Mo particles on the matrix microstructure. The enhanced hardness and cleavage fracture morphology of the Zr matrix immediately below the Mo/Zr interface indicated the occurrence of localized deformation owing to Mo particle impact.

Synthesis, microstructure and mechanical properties of bronze–molybdenum composites processed via LPS and SPS methods

In this work, synthesis, densification and properties of bronze–70wt% Mo and bronze–30wt% Mo composite powders were investigated. The composite powders were prepared by mechanical milling of bronze–Mo powder mixtures for 16h. The results of cold compressibility investigations showed that Heckel and Ge equations provided the best fit scenario for bronze–70wt% Mo and bronze–30wt% Mo, respectively. The composite powders were consolidated via pressureless and spark plasma sintering processes. The relative densities of spark plasma sintered samples with 30 and 70wt% molybdenum were about 98%. However, the relative density of bronze–70wt% Mo and bronze–30wt% Mo pressureless sintered samples were 97.1 and 94.3%, respectively. The scanning electron microscopy observations revealed that the size and dispersion of Mo particles within the bronze matrix in the pressureless sintered samples was completely different from that of the spark plasma sintered ones. Furthermore, it was found that in spite of nearly close relative densities, the hardness and flexural strength of the spark plasma sintered samples were higher than that of the pressureless sintered ones which was due to different shape, size and dispersion of the Mo particles within the matrix phase in the different samples. According to the results, the preferred densification process was SPS method.

Microbial synthesis of metallic molybdenum nanoparticles

The production of nanoparticles through biosynthesis is a reliable, non-toxic, and sustainable alternative to conventional chemical and physical methods of production. While noble metals, such as palladium, gold, and silver, have been formed via bioreduction, biologically-induced reduction of electroactive elements to a metallic state has not been reported previously. Herein, we report the reduction of an electroactive element, molybdenum, via microbial reduction using Clostridium pasteurianum. C. pasteurianum was able to reduce 88% of the added Mo6+ ions. The bioreduced molybdenum was shown to be metallically bonded in a prototypical crystal structure with an average particle size of 15 nm. C. pasteurianum was previously shown to degrade azo dyes using in situ formed Pd nanoparticles, but this study shows that in situ formed Mo particles also act as catalysts for degradation of azo dyes. C. pasteurianum cultures with the bioformed Mo nanoparticles were able completely degrade 155 μM methyl orange within 6 min, while controls with no Mo took 36 min. This research demonstrates, for the first time, that the bioreduction of active elements and formation of catalytic particles is achievable.

Interfacial Microstructure and Formation Mechanism of Zirconia Ceramic and Nb Brazed with Ag-Cu-Ti Powder without and with Mo-Particle-Reinforced

Zirconia (ZrO2) ceramic and Nb were brazed using Ag-Cu-Ti powder without and with Mo-particle-reinforced. The effects of the brazing temperature, holding time and Mo content of the composite filler on the interfacial microstructures and joining mechanism of ZrO2/Nb brazed joints were investigated. By increasing the brazing temperature and holding time, the thickness of Ti3Cu3O layer increased and the thickness of TiO layer decreased, while the total thickness of the reaction layers increased slightly with the sufficient interfacial reaction. Meanwhile, the blocky Ti-Cu compounds gradually accumulate and grow up in the brazing seam. The calculated Ti activity increased first and then decreased as the Mo content was increased from 5 to 40 wt%. When the Mo content was 5wt%, only single Ti3Cu3O reaction layers formed adjacent to the ceramic substrate. By increasing of Mo particles, TiO layer became thicker. When 40 wt% Mo particles were added to the composite filler, Mo particles aggregated into larger clumps damaged the shear strength of brazing joint.

Characterization of fresh EMPIrE and SEMPER FIDELIS U(Mo)/Al fuel plates made with PVD-coated U(Mo) particles

The HERACLES group and the US-DOE work jointly to develop dispersed U(Mo)/Al as LEU fuel for conversion of high performance nuclear research reactors. Within this frame, two irradiation programs are in progress. In the first, EMPIrE, mini-plates are tested in the ATR reactor (USA) and in the second, SEMPER FIDELIS, full-size plates are irradiated in BR2 (Belgium). In both experiments, U(Mo)/Al plates with optimized microstructure are tested under high duty conditions. This paper focuses on analyses made at CEA Cadarache on seven fresh plates made of atomized particles, with or without Mo homogenization, and with ZrN coating. Five EMPIrE mini-plates and two SEMPER FIDELIS full-size plates were examined by optical microscopy (OM), scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS). A particular attention is paid to the integrity of the ZrN coating (thickness, cracks…) and to the U(Mo) particles microstructure.