Molybdenum Particles Research Articles

The influence of ball milling conditions on the powder characteristics and sintering densification of Mo[sbnd]Cu alloy

Mechanical alloying was utilized to produce Mo-30Cu(wt%) composite powder. The effects of milling conditions on the powder characteristics and sintering densification were investigated. The morphological evolution during the mechanical alloying process can be categorized into four stages: 1-individual Mo and Cu particles, 2-coexistence of Mo particles and blocky MoCu composite particles, 3-coarse irregular composite particles, and 4-refined near-spherical composite particles or lamellar MoCu composite particles, depending on whether process control agent (PCA) is added. The mechanical alloying degree of the MoCu composite powder was deepened gradually from stage 1 to 4, which is influenced by the ball milling parameters. As the milling speed and milling time increase, the lattice strain and the alloying degree of the MoCu composite powders increase while the grain size of molybdenum particles decreases, which is conducive to accelerating the sintering density. Among these ball milling parameters, an elevated milling speed notably accelerates the mechanical alloying process and the sintering density. Under the milling speed of 600 r/min, ball to powder ratio (BPR) of 10:1, and milling time of 4 h, the grain size, lattice strain, and average particle diameter of the composite powder were measured to be 48.4 nm, 0.247 %, and 21.04 μm, respectively, with the particle morphology being nearly spherical. The sintered density of the MoCu composite reached 98.1 %, larger than the other composites.

Investigation on the Enhancement of the Flotation Performance in Fine Molybdenum Particles Based on the Probability of Collision Model

Investigation on the Enhancement of the Flotation Performance in Fine Molybdenum Particles Based on the Probability of Collision Model

Parallel additions of molybdenum and copper particles for boosted peroxydisulfate activation process: Performance, mechanism, and application

Molybdenum (Mo) has been certified as a benign cocatalyst in homogenous Fenton/Fenton-like reactions. To improve zero-valent copper (Cu) induced peroxydisulfate (PDS) reaction, Mo and Cu were parallelly added to enhance the activation of (PDS for metronidazole (MTZ) degradation in this work. The efficient MTZ elimination (96.01 %) was reached after 20 min by Cu/Mo/PDS process in terms of 0.10 g⋅L−1 PDS, 0.08 g⋅L−1 Cu, 0.30 g⋅L−1 Mo, and initial pH 6.5. This ternary system presented a broad pH adaptive capacity (pH 3.5–9.5) and well cycling effect (above 80 % after three cycles). The addition of Mo enhanced Cu(II)/Cu(I) circulation and PDS decomposition, and electrochemical test testified that could be attributed to the electron migration between Cu and Mo. The cycle of Cu(II)/Cu(I) triggered by the conversion of Mo0 and Mo4+ was further proved by X-ray photoelectron spectroscopy result. Singlet oxygen and sulfate radicals were identified as the dominant reactive substances by scavenger test, probe measurement, and electron paramagnetic resonance spectroscopy. By density functional theory calculation and mass spectrometry analyses, two possible decomposed pathways of MTZ were raised. At last, Mo and Cu powders were immobilized together by a simple physical mixing with methacrylate, which also showed the integrated catalytic property and good reusability. This work could advance the development of Cu-catalyzed Fenton-like reaction with inorganic co-catalysis in water purification.

Investigation into elevated dielectric properties of molybdenum particle /PVDF composites by engineering insulating silica shell as an interlayer

The urgent requirement for high reliability and increasingly miniaturized electronic devices necessitates packaging polymers with giant dielectric constant (ε′), low loss and high breakdown strength (Eb). To significantly restrain the dielectric loss and leakage current of molybdenum (Mo)/poly (vinylidene fluoride, PVDF) while still holding a large ε′, the silica (SiO2) encapsulated Mo core@shell structured particles were prepared in this work utilizing a sol-gel method, and then composited with PVDF to explore the silica shell's impact and regulating effect on the dielectric properties of the PVDF composites. The findings on the relationship between microstructure and dielectric properties showcase that the introduced SiO2 interlayer not only enhances the interface interactions but also mitigates the great interfacial mismatch in both ε′ and conductivity between the two components, resulting in elevated Eb of the composites. Moreover, the dielectric loss and conductivity of the composites can be remarkably reduced because the silica shell introduces deep traps inhibiting the passage of long-distance electron migration. And the overall dielectric properties of the Mo@SiO2/PVDF can be effectively tuned by modifying the Mo@SiO2's electric resistivity and optimizing the shell thickness. This work provides a beneficial strategy for the design and preparation of dielectric composites with superior dielectric performances for prospective applications.

The influence of the condensation rate on the structure of Cu-Mo pseudoalloys

The structure and microhardness of Cu-0.3 at. % Mo vacuum condensates obtained at different deposition rates, both in the initial state and after isothermal annealings carried out up to 800 °C, were studied in the work. It has been established that molybdenum has a dispersing effect on the grain structure of the copper matrix, which consists of the blocking effect of monoatomic molybdenum adsorption layers formed on the surface of growing copper grains during the condensation of a two-component vapor. The structure of Cu-0.3 at. % Mo condensates demonstrates increased thermal stability, retaining the size of the original grain upon annealing up to 800 °C. The thermal stabilization of the grain structure of condensates is explained by the influence of grain-boundary segregations of molybdenum atoms and particles, which reduce the free energy of grain boundaries and the rate of their migration.

Irradiation performance of a U-7Mo in Al-Si matrix dispersion full-size fuel plate assembly

The Korea Atomic Energy Research Institute (KAERI) is leading the Ki-Jang Research Reactor (KJRR) project with the intent to develop a new reactor for medical isotope production and other nuclear research purposes. The KJRR core is designed to use high density fuel system where uranium alloyed with 7 wt% molybdenum (U-7Mo) particles are dispersed in a matrix of aluminum alloyed with 5 wt% silicon (Al-5Si) and clad in aluminum alloy 6061 (Al-6061) to form fuel plates. KAERI developed a fabrication facility to construct KJRR fuel assemblies and partnered with the Idaho National Laboratory (INL) to irradiate a full-size fuel assembly, with 21 total fuel plates, in the Advanced Test Reactor (ATR). Irradiation testing and subsequent Post Irradiation Exam (PIE) campaigns were performed successfully over a multi-year project. Monte Carlo neutronic calculations, coupling with a depletion code, were performed based on ATR’s as-run power history which showed that the highest power plate (plate 20) reached 83.1 % end-of-life (EOL) local burnup based on initial 235U content. Finite element thermal modeling was performed based as-run power history which showed a beginning-of-life (BOL) peak local heat flux of 184 W/cm2. No anomalous fuel performance was observed during the irradiation and target test conditions were achieved. PIE showed favorable performance of the fuel assembly regarding all important phenomena. This paper describes the KJRR fuel assembly irradiation conditions and PIE data to support the conclusion that it performed well, without evidence of unexpected or problematic fuel performance, within an irradiation test designed to bound the KJRR design environment.

Quench initiation and normal zone propagation characteristics of smart insulated high-temperature superconducting coil

A smart insulation (SI) winding technique utilizing vanadium trioxide (V2O3) as a turn-to-turn insulation material is an effective means of achieving a suitable time constant and thermal stability in high-temperature superconducting (HTS) coils. However, the low electrical conductivity of the V2O3 makes the SI coil vulnerable to damage during quenching. To address this problem, this study explored a mixture of V2O3 and molybdenum (Mo) particles to improve the thermal stability of the SI coil. Two GdBCO coils, insulated with V2O3 and V2O3:Mo, respectively, were fabricated, and quench tests were performed at various operating currents in liquid nitrogen at 77 K. The findings revealed that the V2O3:Mo-insulated coil demonstrated improvements of 82%, 25%, and 160% in the minimum quench energy, and the normal-zone propagation velocities in the longitudinal and transverse directions, respectively, at 60% of the current-carrying capacity of the coil, which are essential performance parameters in the operation of a superconducting magnet.

Effect of Vanadium Oxide on the Crystallization of CaO-Al2O3-SiO2 Glass.

This study investigated the effect of vanadium oxide on the crystallization of CaO-Al2O3-SiO2 (CAS) glass. Specifically, this study subjected CAS glass-ceramics (GCs) with precipitated hexagonal platy particles of metastable CaAl2Si2O8 (CAS GC-H), a layered crystal, that was prepared using metallic molybdenum (Mo) particles as nucleation agents. When the parent glass of CAS GC-H was crystallized with the addition of vanadium oxide in the 0.052-0.21 wt % range, the obtained platy particles of metastable CaAl2Si2O8 displayed an increase in the aspect ratio from 20 to 15 compared with conventional CAS GC-Hs. In addition, no crystallization occurred in the CAS glass with vanadium oxide in the 0.052-0.21 wt % range in the absence of metallic Mo particles. Meanwhile, a CAS glass containing 1.0 wt % vanadium oxide without the addition of metallic Mo particles showed the precipitation of metastable CaAl2Si2O8. Therefore, these results indicated that the aspect ratio of layered crystals in glass was controlled by the addition of a relatively small content of vanadium oxide, and a new nucleation agent for the precipitation of metastable CaAl2Si2O8 in CAS glass using a relatively high content of vanadium oxide was developed.

Process maps and regression models for the physio-thermo-mechanical properties of sintered Al7075-Molybdenum composite

The need for high strength and high-temperature performance Al 7075 is on the rise. Moreso, the process map and model for such a process is necessary. Present report involved the design of a process map for property optimization/minimization in the development of Al-7075 composite infused with thermally stable molybdenum (Mo) particles. Mo particles were varied at 5, 10, and 15 wt% while sintering temperature was varied at 350, 450, and 550 °C. Properties evaluated are porosity, sintered density, hardness, yield strength, elongation, elastic modulus, specific heat capacity and thermal conductivity. The obtained process maps showed varying proportions in minimizing/maximizing each response property. The developed models for each property response were validated to be fit in predicting the responses.

NRF2 is a critical regulator and therapeutic target of metal implant particle-incurred bone damage

Aseptic metal implant loosening due to wear particle-induced bone damage is a major complication of total joint arthroplasty often leading to revision surgery, of which the key regulators mediating the processes are not clearly defined. Here we reported that in a mouse model of calvarial osteolysis, titanium particles (TiPs) and cobalt–chromium–molybdenum particles induced severe osteolysis accompanied by marked suppression of a master redox transcriptional factor NRF2 (Nuclear factor erythroid derived 2-related factor 2). Nfe2l2 knockout mice treated with TiPs developed worse osteolytic alterations compared with wild-type mice. On the contrary, NRF2 restoration by an NRF2 agonist TBHQ (tert-butylhydroquinone) effectively alleviated the osteolysis and the abnormal expression of NRF2 downstream antioxidant enzymes, inflammatory cytokines and osteogenic factors. Further, TiPs induced adverse osteoblastogenesis and osteoclastogenesis in cultured bone cells, which were substantially blocked by TBHQ in an NRF2 inhibition-sensitive manner. Consistently, the osteoprotective effects of TBHQ observed in wild-type mice were largely limited in Nfe2l2 knockout mice. Collectively, our data suggest that NRF2 suppression is a critical causal event of metal wear particle-incurred osteolysis, and the strategies reinstating NRF2 are effective to lessen the bone damage and potentially reduce the incidence of metal implant loosening.

Selective laser sintering of alumina-molybdenum nanocomposites

Alumina/molybdenum nanocomposites were obtained from alumina and molybdenum particles. Alumina with different molybdenum contents (0, 1, 2.5, 5, 10 and 20 wt %) was first uniaxially pressed at 100 MPa to obtain green compacts that were later sintered using a carbon dioxide (CO2) laser. Samples were characterized by X-ray diffraction and Scanning Electron Microscope to evaluate the morphological and microstructural characteristics of the composites. SEM results show that for mixtures with 1, 2.5, 5 and 10 wt % Mo, metallic Mo appears dispersed within the alumina grains (grain boundaries and triple points). Nevertheless, for the mixture with 20 wt % Mo, it also appears in the alumina matrix as Mo in triple points and grain boundaries, although MoO3 is also identified (as inclusion). The presence of these phases was confirmed by X-ray Diffraction technique. These metallic molybdenum particles distributed in the alumina matrix at triple points and grain boundaries promote the densification of the composite. Metallic molybdenum has also a pinning effect, which drastically affects the microstructural evolution during the sintering, mainly on the grain size of alumina. The best results were observed for the composite Al2O3-10 wt % Mo, with an average alumina grain size <10 μm and few pores.

Evidence of ammonia synthesis by bulk diffusion in cobalt molybdenum particles in a CLAS process

For the first time ammonia-synthesis-on-nitridation has been reported in CoMo during a chemical looping ammonia synthesis experiment. The observation lends evidence to the existence of a dynamic surface, a shrinking core and counter diffusion. The Mars-van Krevlen mechanism involving surface and bulk exchange has been established for the CoMo system under H2:N2 atmospheres was extended into the CLAS domain and complicated by the existence of an unreacted oxide core containing molybdenum bronzes, HxMoO3. This OH−1 diffuses outward as the core is stabilized by N−3, resulting in the observation of gas phase H2O and NH3 in the absence of gaseous H2.

Line identification of extreme ultraviolet spectra of Mo V to Mo XVIII in EAST tokamak

The presence of high-&lt;i&gt;Z&lt;/i&gt; impurities in magnetically confined fusion devices has different influences on the confinement property of the plasma due to the high cooling rate of high-&lt;i&gt;Z&lt;/i&gt; impurities. The first wall of EAST is equipped with molybdenum tiles, molybdenum particles sputtered from inevitable plasma-wall interaction enter into the plasma and become high-&lt;i&gt;Z&lt;/i&gt; impurity. In this paper, four fast-time-response extreme ultraviolet (EUV) spectrometers, a system which is upgraded in the EAST 2021 campaign, are used to monitor the line emission from impurity ions in the 5–500 Å wavelength range simultaneously. The in-situ wavelength calibration is carried out accurately using several well-known emission lines of low- and medium-Z impurity ions. The observed spectral lines are carefully identified based on the National Institute of Standards Technology (NIST) database, previously published experimental data and the time evolution of the normalized line intensity of emission lines from impurity ions. At the lower electron temperature (&lt;i&gt;T&lt;/i&gt;&lt;sub&gt;e0&lt;/sub&gt; = 1.5 keV), the EUV spectra emitted from molybdenum ions in the range of 5–485 Å are systematically identified in EAST discharges accompanied with spontaneous sputtering events. As a result, two unresolved transition arrays of molybdenum spectra composed of Mo&lt;sup&gt;19+&lt;/sup&gt;-Mo&lt;sup&gt;24+&lt;/sup&gt; (Mo XX-Mo XXV) and Mo&lt;sup&gt;16+&lt;/sup&gt;-Mo&lt;sup&gt;29+&lt;/sup&gt; (Mo XVII-Mo XXX) are observed in the ranges of 15–30 Å and 65–95 Å. In addition, several spectral lines of lower molybdenum ions of Mo&lt;sup&gt;4+&lt;/sup&gt;-Mo&lt;sup&gt;17+&lt;/sup&gt; (Mo V-Mo XVIII) in the ranges of 27–60 Å and 120–485 Å are observed and identified on EAST for the first time, including a few strong and isolated forbidden and resonant lines, e.g. Mo XII at 329.414 Å, 336.639 Å and 381.125 Å, Mo XIII at 340.909 Å and 352.994 Å, Mo XIV at 373.647 Å and 423.576 Å, Mo XV at 50.448 Å, 57.927 Å and 58.832 Å. Six spectral lines are newly observed in the range of 27–32 Å, i.e. (27.21 ± 0.01) Å, (27.37 ± 0.01) Å, (28.99 ± 0.01) Å, (30.81 ± 0.01) Å, (31.54 ± 0.01) Å and (31.83 ± 0.01) Å, which may be Mo XV-Mo XVIII spectral lines. As a result, twelve strong and isolated spectral lines are chosen in routine observation for impurity transport physical study. The identification of these spectral lines not only enriches the molybdenum atom database, but also provides a solid experimental data base for magnetically confined devices to study the behavior and transport in core and edge plasmas of high-Z impurity.

Research of surface layer properties of piston rings after gas thermal spraying

Today, one of the important problems of mechanical engineering is to increase the reliability and durability of machines. A special place in this matter is occupied by increasing the wear resistance of parts. As for diesel construction, the problem of increasing the hardness and wear resistance of piston rings is very important. Goal. The goal is study of the structure and nature of changes in the hardness of the surface layer obtained by gas-thermal combined spraying, after grinding, running-in and mileage of the diesel engine, i. e., at all stages of the production cycle. Methodology. The coating on the rings was applied by the method of two-wire metallization with independent supply of wires made of 11X18M steel and molybdenum. Metallographic analysis was used to study the structure of the obtained coating. The condition of the surface layer after coating, grinding, running-in and diesel run was studied by measuring the microhardness. Results. Metallographic analysis of the interface between steel and molybdenum coating – cast iron for many rings and different parts of one ring shows that the coating interacts closely with the substrate along the entire application profile. The structure of molybdenum particles demonstrates their fineness. This is due to the fact that the rapid crystallization under pressure contributes to the creation of a fine-grained structure. Comparison of the microhardness of molybdenum and steel wires with steel-molybdenum coating indicates a significant strengthening of molybdenum and steel particles during spraying, due to the processes of structure formation. Experimental data indicate the stability of the hardness of both molybdenum particles and steel particles, which is important for the coating in operation. Originality. Features of formation of a gas-thermal covering at a simultaneous electric arc spraying of molybdenum and 11Х18М steel on piston rings from pig-iron are established. It is shown that a layered structure is formed, which consists mainly of steel and molybdenum particles. The reasons for the wide range of properties of steel and molybdenum particles have been clarified. It is proved that the operational properties of steel-molybdenum coating are due to its antifriction properties, porosity, which provides self-lubrication of the friction surface, good adhesion to the substrate, which increases by 3–4 times compared to traditional methods. Practical value. The proposed technology of gas-thermal spraying significantly increases the service life of piston rings operating in wear conditions.

Liquid zinc assisted electro-extraction of molybdenum

• Co-deposition of Mo and Zn were investigated which lead Mo ions to deposit under a less cathodic potential. • Electrolytic cell was designed utilizing liquid zinc as cathode arranged according to the density. • Pure molybdenum was obtained by removing zinc in Zn-Mo alloy, where Zn-Mo alloy was produced through liquid zinc assisted electro-extraction. Improvements of the direct electro-desulfurization of molybdenum disulfide in NaCl-KCl eutectic molten salt by employing a liquid zinc electrode was studied in this work. According to the previous studies, one of the rate controlling step of the MoS 2 desulfurization process is the sulfur ions’ diffusion through solid MoS 2 pellet, and a decreasing reaction rate is considered to result from the poor conductivity between the loosely connected partial reduced molybdenum particles. Based on these facts, liquid zinc electrode, along with a graphite crucible as the container, was employed to collect the reduced molybdenum particles as long as keep providing a fresh three-phase interline (3PI) as the current collector. Transient electrochemical technologies were introduced to study the electrochemical behavior of molybdenum ions with and without the appearance of zinc ions. Zn-Mo alloy was obtained through the potentiostatic electrolysis process, and molybdenum powders mainly sank into the bottom of liquid zinc due to the gravity. Metallic molybdenum shall be obtained by distilling the electrolysis product.

Direct laser deposition of Cu-Mo functionally graded layers for dissimilar joining titanium alloys and steels

The dissimilar joining of titanium alloys and steel is more challenging due to the formation of brittle Ti-Fe intermetallic compounds (IMCs). The use of Cu-Mo interlayer successfully prevented the mixing of Ti and Fe to avoid the formation of FexTiy brittle phases. Near Ti-(Cu + Mo) interlayer boundary typical CuTi2, CuTi and Cu3Ti2 phases are formed. Intermetallic stoichiometry, morphology are discussed. The tensile strength of the Grade1/316 L joints with the Cu-Mo interlayer is 175 MPa, and the joints exhibited the ductile–brittle fracture. The fracture region formed at the interlayer along the molybdenum particles.

Formation of Molybdenum Blue Nanoparticles in the Organic Reducing Area.

Molybdenum blue dispersions were synthesized by reducing an acidic molybdate solution with glucose, hydroquinone and ascorbic acid. The influence of the H/Mo molar ratio on the rate of formation of molybdenum particles was established. For each reducing agent, were determined the rate constant and the order of the particle formation and were established the conditions for the formation of aggregative stable dispersion with the maximum concentration of particles. The dispersed phase is represented by toroidal molybdenum oxide nanoclusters, which was confirmed by the results of UV/Vis, FTIR, XPS spectroscopy and DLS.

Mechanical and Thermal Properties of Harmonic Structured Composites by MM/SPS Process

Harmonic structured composites consist of a low fraction metal region like network and a dispersed another major metal region like island. The harmonic structured composites were produced via mechanical milling (MM) followed by spark plasma sintering (SPS), and its mechanical and thermal properties were investigated in detail. Microstructural observation of the MM powders and SPS compacts was achieved using scanning electron microscopy (SEM). The mechanical properties of the harmonic structured composites were evaluated using results of the Vickers hardness and the tensile tests. The thermal properties of a part of the harmonic structured composites were evaluated using results of thermo-mechanical analysis and laser flash method. High speed steel / mild steel harmonic structured composite exhibited high strength and enough ductility in spite of the trade-off relationship between strength and ductility. In addition, the high speed steel / mild steel harmonic structured composite also demonstrates a superior wear properties and low hardness simultaneously. On the other hand, molybdenum / copper harmonic structured composite demonstrate low coefficient of linear expansion and enough thermal conductivity compared to the conventional copper / molybdenum particle dispersed composite. The coefficient of linear expansion and thermal conductivity are the trade-off relation in this composite. In summary, the harmonic structure control is effective for improvement of the trade-off mechanical and thermal properties in the composite.

Non-Equilibrium Synthesis of Highly Active Nanostructured, Oxygen-Incorporated Amorphous Molybdenum Sulfide HER Electrocatalyst.

Molybdenum sulfide emerged as promising hydrogen evolution reaction (HER) electrocatalyst thanks to its high intrinsic activity, however its limited active sites exposure and low conductivity hamper its performance. To address these drawbacks, the non-equilibrium nature of pulsed laser deposition (PLD) is exploited to synthesize self-supported hierarchical nanoarchitectures by gas phase nucleation and sequential attachment of defective molybdenum sulfide clusters. The physics of the process are studied by in situ diagnostics and correlated to the properties of the resulting electrocatalyst. The as-synthesized architectures have a disordered nanocrystalline structure, with nanodomains of bent, defective S-Mo-S layers embedded in an amorphous matrix, with excess sulfur and segregated molybdenum particles. Oxygen incorporation in this structure fosters the creation of amorphous oxide/oxysulfide nanophases with high electrical conductivity, enabling fast electron transfer to the active sites. The combined effect of the nanocrystalline pristine structure and the surface oxidation enhances the performance leading to small overpotentials, very fast kinetics (35.1 mV dec-1 Tafel slope) and remarkable long-term stability for continuous operation up to -1 A cm-2. This work shows possible new avenues in catalytic design arising from a non-equilibrium technique as PLD and the importance of structural and chemical control to improve the HER performance of MoS-based catalysts.

Combined promoting effect of molybdenum on the bimetallic Al2O3-La2O3 catalysts for NOx reduction by CO

Promotional effect of molybdenum on bimetallic Al2O3-La2O3-based catalysts was investigated in the selective catalytic reduction (CO-SCR) reaction. The physicochemical properties of the solids were evaluated through X-ray powder diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), Scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM-EDS), nitrogen physisorption analyses, Temperature programmed reduction (TPR), NH3-temperature programmed desorption (NH3-TPD) and Transmission electron microscopy (TEM). Structural characterizations confirmed the formation of porous nanostructured solids with molybdenum helping the dispersion of the Ni or Pt active sites close to the molybdenum particles. The catalysts have acid sites of medium to low strengths effectively enhancing the catalytic activity of the solids. Investigation of the various active sites revealed PtMo supported on Al2O3-La2O3 as the best catalyst using distinct temperatures and poisoning conditions in the CO-SCR reaction, rather than NiMo and CoMo counterparts. The oxidation of the species and phase transformation were more significant on the CoMo than NiMo catalyst, with the latter having a modest performance. The low interaction of the PtMo with the support provided the formation of a Pto and Mo6+ redox pair, which resulted in high CO and NOx adsorption to form CO2 and N2. This was due to the synergistic effect of valence-rich Mo transition oxides with Pt species, resulting in the inhibition of irreversible sulfatation and coking over PtMo/Al2O3-La2O3 catalyst.