Spherical Molybdenum Research Articles

Enhancing the physical properties of Mo-Cu composites through plasma spheroidized spherical molybdenum powder

ABSTRACT This paper investigates the preparation of spherical molybdenum-copper (Mo-Cu) composites through the utilization of plasma spheroidization1 of molybdenum powder, followed by ‘Carbon thermal pre-reduction + Hydrogen deep reduction2’ processes. The properties of these composites are analyzed. By adjusting the mass ratio of molybdenum to copper and employing mechanical activation during high-temperature sintering, Mo and Cu are dispersed more uniformly, resulting in improved fluidity and a reduced tendency to agglomerate in x% Mo-Cu (x = 20, 40, 60, 80) composites. Experimental results demonstrate that compared to original powder Mo-Cu composites, the prepared spherical Mo-Cu composites exhibit uniform elemental distribution, regular arrangement, and reduced porosity. Among these, the 60% Mo (spherical)-Cu composites show the best dispersion and superior performance. At the optimal sintering temperature of 1250°C, the thermal conductivity of the sintered product increased from 137 Wm−1K−1 to 148 Wm−1K−1, the electrical conductivity increased from 18.9 MS/m to 21.8 MS/m, and the Vickers hardness increased from 177 HV to 209 HV.

Study on synergistic mechanism of molybdenum disulfide/sodium carboxymethyl cellulose composite nanofiber mats for photothermal/photodynamic antibacterial treatment

Innovative antibacterial therapies using nanomaterials, such as photothermal (PTT) and photodynamic (PDT) treatments, have been developed for treating wound infections. However, creating secure wound dressings with these therapies faces challenges. The primary focus of this study is to prepare an antibacterial nanofiber dressing that effectively incorporates stable loads of functional nanoparticles and demonstrates an efficient synergistic effect between PTT and PDT. Herein, a composite nanofiber mat was fabricated, integrating spherical molybdenum disulfide (MoS2) nanoparticles. MoS2 was deposited onto polylactic acid (PLA) nanofiber mats using vacuum filtration, which was further stabilized by sodium carboxymethyl cellulose (CMC) adhesion and glutaraldehyde (GA) cross-linking. The composite nanofibers demonstrated synergistic antibacterial effects under NIR light irradiation, and the underlying mechanism was explored. They induce bacterial membrane permeability, protein leakage, and intracellular reactive oxygen species (ROS) elevation, ultimately leading to >95 % antibacterial activity against Staphylococcus aureus (S. aureus) and Escherichia coli (E. coli), which is higher than that of single thermotherapy (almost no antibacterial activity) or ROS therapy (about 80 %). In addition, the composite nanofiber mats exhibited promotion effects on infected wound healing in vivo. This study demonstrates the great prospects of composite nanofiber dressings in clinical treatment of bacterial-infected wounds.

Quality Diagnostics of Parts Produced by Combined Additive Manufacturing Technology

The work is focused on the combined process of obtaining bimetallic parts that involve laser-directed energy deposition (LDED) additive technology and the conventional casting process. In this research, molybdenum powder was deposited by LDED on a cast 25L steel substrate. The choice of materials is motivated by demands for replacing the traditional technique of brazing molybdenum with a copper interlayer on low-carbon steel to eliminate shortcomings. The influence of powder particle morphology on the quality of deposited layers was studied. Spherical molybdenum powder PMS-M99.9 facilitated stable deposition of good layers and was found to be suitable for the LDED. Quality diagnostics were performed by studying microstructure, hardness, and wear resistance properties. Preferential parameters of the LDED of molybdenum were found through parametrical analysis. Microstructural studies showed that LDED of PMS-M99.9 powder results in a homogeneous stable layer with a strong bond to the steel substrate, which was confirmed by mutual diffusion of Mo and Fe in the boundary. It is also demonstrated that the found working parameters of LDED assure high hardness, wear, and fretting wear resistance. The three studied coatings (LDED of powders PMS-M99.9 and PM-M; VM1 brazing) had the same friction coefficient value of ~0.25. Compared to others, PMS-M99.9 coating had the lowest volumetric wear, while abrasive wear was measured to be the highest.

Identifying the dominant effect of electron-feeding on molybdenum phosphonates to decipher the activity origin for oxidative desulfurization of fuel

Electronic structure of active sites is crucial for oxidative desulfurization (ODS) process, while there is still a lack of direct experimental evidence to identify its real role on ODS activity. Herein, hollow spherical molybdenum phosphonate is designed through a facile hydrothermal method with the assistance of urea. The well-defined hollow spherical structure and homogeneous integration of organic moieties improve mass transfer during the heterogeneous ODS reaction. The combination of systemic characterizations, selective bromination and quenching experiment suggests that the introduction of –OH functional groups with strong electron-donating ability can modulate the electronic structure at molecular level, which provides continuous electron-feeding to Mo active sites, thus accelerating the ODS process. Correspondingly, the obtained catalyst delivers superior ODS performance with 100 % DBT conversion in 40 min at 60 ℃ and stable recyclability up to 10 times. This work can supply new inspiration for manipulating the nanostructures and electronic states of metal phosphonates for green catalysis.

Controllable Preparation of Spherical Molybdenum Nano-Powders by One-Step Reduction of APM in Radio Frequency Hydrogen Plasma

Spherical molybdenum nano-powders were in-situ ultrafast synthesized from ammonium paramolybdate (APM) raw materials in a one-step reduction method by radio frequency (RF) hydrogen plasma. Due to the extreme conditions of the RF plasma torch such as its high temperature and large temperature gradient, the injected raw APM powder was quickly gasified and then reduced into nano-sized metal molybdenum (Mo) powder. The influences of APM powder delivery rate and H2 concentration on the properties of the obtained powders were investigated. Field-emission scanning electron microscope (FESEM), transmission electron microscope (TEM), X-ray diffraction (XRD), nanolaser particle analyzer, and specific surface area method were used to characterize the morphology, phase, and particle size distribution of the powders. The results showed that the nano-sized Mo powder obtained by hydrogen plasma treatment had a quasi-spherical morphology and an average particle size of about 30 nm. The particle size could be successfully adjusted by varying H2 concentrations. In addition, spherical nano-sized MoO3 powder could be obtained when no H2 was added into the RF plasma.

MoS2-based nanofluids as heat transfer fluid in parabolic trough collector technology

Concentrating solar power is becoming one of options for producing energy to replace conventional polluting energy sources. However, improving the efficiency and reducing the cost of technologies based on this type of energy to make it more competitive is still a work in progress. This study proposes replacing the thermal oil used as the heat transfer fluid in the absorber tubes of parabolic trough solar collectors (PTCs) with nanofluids based on spherical molybdenum disulphide nanoparticles with the aim of improving the thermal efficiency of concentrating solar power plants. The colloidal stability of the nanofluids was verified by Ultraviolet–Visible spectroscopy, Zeta potential and Dynamic Light Scattering monitoring. The presence of spherical MoS2 nanoparticles resulted in an increase of up to 13% in specific isobaric heat and 6% in thermal conductivity compared to thermal oil. Finally, the efficiency of parabolic trough solar collectors was estimated to increase by 5%, which also favours the decrease of pumping power and the elimination of selective coatings on the absorber tube. To our knowledge, this is the first time that MoS2-based nanofluids are tested as heat transfer fluids in PTCs analysing its implementation in the solar energy application.

Laser additive manufacturing of pure molybdenum using freeze-dry pulsated orifice ejection method-produced powders

Preparing appropriate initial powders is a key factor in using laser powder bed fusion (L-PBF) for high-performance refractory materials. In this study, we developed a novel technology, the freeze-dry pulsated orifice ejection method (FD-POEM), for producing spherical molybdenum powders with controllable particle size and distribution and good flowability without melting. The Mo powders, which had unique mesh-structures, exhibited higher laser absorptivity than the dense ones. Pure Mo builds were fabricated using L-PBF. Fine MoO2 particles were formed and uniformly distributed along the grain boundaries and inside the equiaxed grains. High-resolution transmission electron microscopy revealed an interfacial orientation correlation between Mo [1 -1 -1]//MoO2 [0–1 0] and Mo (1 1 0)//MoO2 (0–1 2). The Vickers hardness of the Mo build increased compared to that of pure Mo owing to grain refinement and the oxide-dispersion-strengthening effect of in-situ MoO2. This study provides the basis for powder fabrication using FD-POEM and the processability of Mo parts via L-PBF in ultrahigh-temperature applications.

Aqueous Al-N2 battery assembled by hollow molybdenum phosphate microspheres for simultaneous NH3 production and power generation

Hollow molybdenum phosphate microspheres derived from molybdenum phosphonates exhibit an excellent electrocatalytic activity for simultaneous electrochemical N 2 -to-NH 3 and power generation in the aqueous Al-N 2 battery during discharge process. • Hollow spherical molybdenum phosphates derived from molybdenum phosphonates were prepared. • MoPi/HSNPC exhibits high performance toward NRR in alkaline electrolyte. • The phosphate groups of MoPi/HSNPC as the active contributor for NRR. • Aqueous Al-N 2 battery was fabricated for simultaneous NH 3 production and power generation during discharge process. Developing controllable and facile devices beyond traditional N 2 electrocatalysis cell is critical for the commercial production of NH 3 through electrochemical N 2 reduction reaction (NRR) under ambient condition. Herein, the aqueous Al-N 2 battery, fabricated by coupling the hollow molybdenum phosphate microspheres as cathode and the Al plate as anode within KOH electrolyte, was assembled for the electrochemical reduction of N 2 to NH 3 and power generation during the discharge process. Benefiting from the desirable active components and the structural advantages, the hollow molybdenum phosphate microspheres derived from molybdenum phosphonates exhibit high NH 3 yield rate of 18.66 μg h −1 mg cat. -1 with the Faradaic efficiency of 9.04% at − 0.2 V vs. reversible hydrogen electrode, associated with excellent robustness for cycling operation. The Mo 4+ species of molybdenum phosphates are verified as the active components for NRR through the associative reaction pathway. When measured in the flow battery configuration with flowing N 2 during discharge, the formed Al-N 2 battery delivers the high NH 3 yield rate of 13.47 μg h −1 mg cat. -1 and Faradaic efficiency of 5.06% at 1.0 V vs. Al(OH) 4 − /Al, which can be stably maintained in discharge cycling tests over 20 cycles. Moreover, the peak power density of 2.37 mW cm −2 and the long-term energy output are still achieved by this Al-N 2 battery during the discharge process. This work not only supplies some guidelines for the rational design of active NRR electrocatalysts from earth-abundant elements but also provides a reasonable and promising devices for efficient electrochemical N 2 fixation and power generation.

Preparation and Properties of Spherical Mo Powders by Plasma Rotating Electrode Process for Additive Manufacturing

Since molybdenum has very high melting point of 2620 °C, there are many difficulties in its forming and post-processing, especially for deep processing. Furthermore as molybdenum is expensive, the utilization rate is important for the molybdenum processing. Additive manufacturing can directly manufacture the parts without mold and increase the utilization rate, and brings an opportunities for the new direction of deep processing for molybdenum. Due to the high quality requirements of molybdenum powder in additive manufacturing technology, the high-quality spherical molybdenum powder was prepared by plasma rotating electrode process method in the present study. The morphology, particle size and particle size distribution, chemical and physical properties were investigated. The molybdenum powder prepared by plasma rotating electrode process method showed to have high purity, high sphericity, good fluidity and high bulk density, proper particle size distribution and low gap element within the powder. The microstructure of the powder was a mixed structure of dendrites and cell crystals formed by rapid solidification, and as the particle size of the powder gradually decreased, the microstructure of the powder surface was remarkably refined. Within a certain range, the molybdenum powder with a wide particle size distribution had better fluidity and higher bulk density. The high-quality spherical molybdenum powder was prepared by plasma rotating electrode process method, which can meet the requirements of additive manufacturing technology for powder material performance.

Application of Molybdenum oxide nanoparticles in H2S removal from natural gas under different operational and geometrical conditions

Microporous and nanoporous metal oxides are potential adsorbents for separating H2S from natural gas. Structured porous adsorbents have the potential to improve the energy and production costs in gas separation and catalysis applications by providing higher production rates. Zinc, Manganese, and Iron oxide nanoparticles are among the most potential and most extensively employed materials. Applying this framework, other novel metal oxides have been recognized for separation of H2S from representative H2S/CH4. In the present study, we investigate the performance of Molybdenum oxide nano-particles as an adsorbent for H2S removal and compare it with the performance of zinc oxide nano-particles. The effects of operating conditions such as temperature (65–89 °C), pressure (10–19 bar), initial concentration of H2S in the feed stream (38–73 ppm), and space velocity (0.018–0.045 m s−1) on H2S adsorption from sour gas are evaluated. Our analysis shows that Molybdenum oxide nano-particles have an adsorption capacity of 0.081 and 0.074 g H2S/g Molybdenum oxide in low temperature and low concentration of H2S using non-spherical and spherical Molybdenum oxide sorbent, respectively. Proceeding by two adsorption isotherms, the Langmuir and Freundlich isotherms, analysis of variance displayed that both models can fit the adsorption data of H2S on Molybdenum oxide nanoparticles very well, while the Freundlich isotherm seems to provide R2 value of 0.98–0.99, indicating a better prediction of our experimental data.

Fabrication of homogeneous Mo-Cu composites using spherical molybdenum powders prepared by thermal plasma spheroidization process

In this work, spherical and dense molybdenum particles with the average particle size of 16.6 μm were synthesized by thermal plasma spheroidization process, and further used to fabricate homogeneous Mo-25 wt% Cu composites by infiltration method. The influence of infiltration temperature and holding time on the microstructure and properties of obtained Mo-Cu composites was investigated, and experimental results show that homogeneous Mo-Cu composites with high densification are obtained and the smooth surface of pores could facilitate the infiltration process. Specially, 98.6% of relative density of Mo-Cu composites is achieved and less than 10% irregular particles existing in spherical powders induce closed or half-connected pores in porous Mo skeleton, which shows adverse effect on full dense Mo-Cu composites obtaining. In addition, the highest microhardness of Mo-Cu composites (199 ± 3.6 Hv) is obtained when infiltrated at 1300 °C for 1 h. Moreover, the maximum value of thermal conductivity (TC) of Mo-Cu composites is 154 W/(m·K), and this is lower than that predicted by theoretical models, which may be due to the small amounts of carbon in Mo-Cu composites and non-full dense of Mo-Cu composites. Furthermore, the carbon in porous skeleton could be well removed by controlling the atmosphere of sintering process. Importantly, Mo-25 wt% Cu composites fabricated by irregular particles exhibit non-uniform microstructure and low TC compared to that prepared by spherical particles, which would be due to the uneven pore distribution and closed pores in porous skeleton fabricated by irregular particles. These results well illustrate the superiority of spherical molybdenum particles on fabrication homogeneous Mo-Cu composites.

Stress control of heterogeneous nanocrystalline diamond sphere through pressure-temperature tuning

The hollow nanocrystalline diamond (NCD) sphere, a promising ablator material for inertial confinement fusion capsule, is generally fabricated by the chemical vapor deposition method. Herein, we report on a method to transform hydrogenated tetrahedral amorphous carbon coatings on spherical molybdenum (Mo) substrates into nanocrystalline diamond films via a designed high pressure high temperature (HPHT) treatment that balances the mismatch in the thermal expansion coefficient between a diamond coating and the Mo substrate through the difference in the bulk modulus. The results show that the density and strength of the diamond shell increase significantly and the residual stress is eliminated as well. The methodology of the designed HPHT treatment can not only provide an alternative way to fabricate NCD spheres but also can apply to other heterogeneous material stress control applications.

Development of hierarchical layered nanostructured α-MoO3 thin films using dc magnetron sputtering

The synthesis of environmentally friendly, catalyst free, hierarchical molybdenum oxide nanostructured thin films of different morphologies by a DC magnetron sputtering technique is reported. With increase in the annealing temperature, the spherical molybdenum nanoparticles arrange themselves in the form of vertically aligned nanorods and platelets stacked over one another. The preliminary phase analysis was carried out using x-ray diffraction. The sample annealed at 600 °C shows the formation of highly crystalline orthorhombic α-MoO3. Field emission scanning electron microscopy and transmission electron microscopy images confirm the formation of a layered structure at higher annealing temperatures, while the Raman spectroscopy revealed the stretching vibration modes of Mo–O bonds in the formation of the orthorhombic α-MoO3 layered structure. The Raman peaks at 667, 820 and 995 cm−1 correspond to the layered structure of orthorhombic α-MoO3. The electrical properties and possible growth mechanism of the as-prepared samples at different annealing temperatures are also discussed.

Reduction-Triggered Self-Assembly of Nanoscale Molybdenum Oxide Molecular Clusters.

Understanding the formation mechanism of giant molecular clusters is essential for rational design and synthesis of cluster-based nanomaterials with required morphologies and functionalities. Here, typical synthetic reactions of a 2.9 nm spherical molybdenum oxide cluster, {Mo132} (formula: [Mo(VI)72Mo(V)60O372(CH3COO)30(H2O)72](42-)), with systematically varied reaction parameters have been fully explored to determine the morphologies and concentration of products, reduction of metal centers, and chemical environments of the organic ligands. The growth of these clusters shows a typical sigmoid curve, suggesting a general multistep self-assembly mechanism for the formation of giant molecular clusters. The reaction starts with a lag phase period when partial Mo(VI) centers of molybdate precursors are reduced to form {Mo(V)2(acetate)} structures under the coordination effect of the acetate groups. Once the concentration of {Mo(V)2(acetate)} reaches a critical value, it triggers the co-assembly of Mo(V) and Mo(VI) species into the giant clusters.

Synthesis of molybdenum disulfide particles by aerosol-assisted chemical vapor deposition

It was shown that dimethylformamide can be, in principle, used as a solvent of ammonium thiomolybdate for obtaining molybdenum disulfide particles by the aerosol-assisted chemical vapor deposition method. IR Fourier spectroscopy was used to examine (NH4)2MoS4–C3H7NO liquid solutions and the thermal stability of dimethylformamide and ammonium thiomolybdate vapors. It was demonstrated that pyrolysis at temperatures of 700–900°C yields spherical molybdenum disulfide microparticles with average diameters in the range 0.6–1 µm and “onion” structure.

Spheroidization of molybdenum powder by radio frequency thermal plasma

To control the morphology and particle size of dense spherical molybdenum powder prepared by radio frequency (RF) plasma from irregular molybdenum powder as a precursor, plasma process parameters were optimized in this paper. The effects of the carrier gas flow rate and molybdenum powder feeding rate on the shape and size of the final products were studied. The molybdenum powder morphology was examined using high-resolution scanning electron microscopy. The powder phases were analyzed by X-ray diffraction. The tap density and apparent density of the molybdenum powder were investigated using a Hall flow meter and a Scott volumeter. The optimal process parameters for the spherical molybdenum powder preparation are 50 g/min powder feeding rate and 0.6 m3/h carrier gas rate. In addition, pure spherical molybdenum powder can be obtained from irregular powder, and the tap density is enhanced after plasma processing. The average size is reduced from 72 to 62 µm, and the tap density is increased from 2.7 to 6.2 g/cm3. Therefore, RF plasma is a promising method for the preparation of high-density and high-purity spherical powders.

In-situ molybdenum nano-attached particle synthesis from spent Mo scrap.

Radio frequency thermal plasma is a versatile process for engineering powder preparation owing to its high energy density and reactivity. Molybdenum powders were prepared from molybdenum sheet scrap by RF thermal plasma in association with powder comminution process. Molybdenum scrap which was used in high temperature environment was friable enough to be broken into micropowders by hammer milling. Spherical molybdenum micro-powder was obtained from the hammer milled powders were treated via thermal plasma. On the other hand, vaporization and condensation pathway for nanoparticle synthesis is largely dependent on both thermo-physical properties and thermal plasma properties. In this regard, molybdenum trioxide was chosen for the feedstock of nanoparticle synthesis. Additional reactivity of argon-hydrogen thermal plasma, oxide feedstock was fully reduced to bcc molybdenum. Considering different reaction pathway of each feedstock, molybdenum nanoparticle attached molybdenum spherical micro-powder could be effectively synthesized by feeding a blended feedstock of molybdenum micro-powder and molybdenum trioxide micro-powder into argon-hydrogen thermal plasma.

The production of entropy of a supercooled liquid in the electrostatic levitation method

The change in the production of entropy with time and the connection between the force and the flux are investigated using an experimental thermogram for a spherical molybdenum sample by the electrostatic levitation method. It is found that during supercooling of the molybdenum liquid phase, the reliability of the linear relation between the force and the flux does not exceed 25%. Estimates of the maximum values of the amplitude of temperature fluctuations and of the production of entropy during supercooling of liquid nickel are given.

The Preparation Technology of Spherical Molybdenum Powder in Continous Induction Plasma

In this paper, the preparation technology of spherical molybdenum powder has been studied by using of continuous induction plasma powder synthesis system, and the flow-ability, particle size , the impurity content of powder before and after plasma treatment have been measured and compared. The result shows that, by applying for induction plasma preparation technology ,the powder’s flow-ability is improved, oxygen and carbon content is decreased markedly. the continuous induction plasma powder synthesis system shows high performance on particle size control.

Synthesis of molybdenum nanoparticle by in situ γ-radiation

This paper reports the synthesis of various types of molybdenum nanoparticles using in-situ minuscule amount of radioactivity. The radioisotope 99Mo was introduced into the solution of (i) 10−5M ammonium molybdate and (ii) mixture of 10−5M ammonium molybdate and anionic surfactant sodiumdodecyl sulphate (SDS). The molybdate ions were changed to nanoparticles due to radiolysis initiated by γ-irradiation in both the cases. The transmission electron microscopic images showed 4–15nm size nanoparticles with spherical shape in ammonium molybdate solution. However, the aggregation of nanoparticles could not be avoided in this case. The addition of SDS to the solution helped to obtain 10–60nm size of spherical molybdenum nanoparticle and 2–10nm wire like molybdenum nanoparticle. Interpretation of spectral data advocates that the molybdenum nanoparticles might be in MoO3 form.