Mo Powder Research Articles

Physical, mechanical, and corrosion properties of Ti–12Mo and Ti–15Mo alloys fabricated by elemental blend and mechanical alloying techniques

Ti–Mo alloys have received increased attention and concern in several applications, especially in biomedical, because of their appropriate properties, non-toxicity, and reasonable cost. This work investigated the different Mo powder content (12 and 15 wt%) fabricated by elemental blended and mechanical alloying. The microstructure, density, microhardness, compressive, wear, and corrosion properties were characterized. It was found that the volume fraction of β-phase increases with increasing Mo content to around 85%, mainly due to the robust β-phase stabilizer effect. Moreover, the microhardness and compressive properties were enhanced with Mo addition and MA fabrication by 11.5 and 27%, respectively, mainly due to solid solution strengthening, plastic deformation, high dislocations, and lattice defects. However, the strain at failure decreased with decreasing sintered density and increasing porosity. From this study, the corrosion rate decreased with decreasing the porosity, reaching 0.226 × 10−3 mm/year for Ti–12Mo alloy fabricated by elemental blend with a minimum porosity of 3.6%. Ti–Mo alloys can also tolerate properties and impurities, making them suitable for biomedical applications.

Improvement of Fe(Ⅲ)/percarbonate system by molybdenum powder and tripolyphosphate: Co-catalytic performance, low oxidant consumption, pH-dependent mechanism

The homogeneous sodium percarbonate (SPC) systems are limited by narrow pH range, ineffective consumption of oxidant, and weak reusability of catalyst. Herein, molybdenum (Mo) powder and sodium tripolyphosphate (STPP) were selected to overcome these challenges. Sulfamethoxazole (SMX), as a model contaminant, was almost completely degraded in 60 min with higher removal rate (0.1367 min−1) than the Mo or STPP-absent system. In addition, Mo/STPP-Fe(Ⅲ)/SPC system was cost-effective in terms of oxidant consumption, requiring only 0.2 mM SPC. About activation mechanism, the main active species for SMX degradation was pH-dependent, with hydroxyl radical (·OH) as the dominant active species at pHi = 7 and ·OH, carbonate radical (CO3·-), and superoxide radical (O2·-) derived from a series of chain reaction at pHi = 10, respectively. Due to the generation of various electrophilic free radical, the system exhibited excellent performance towards electron-rich pollutants under a wide pH range. Furthermore, Mo exhibited excellent stability and reusability. SMX was degraded through hydroxylation, N-S cleavage, amino and sulfanilamide oxidation into intermediates whose toxicities were evaluated by Toxicity Estimation Software Tool (T.E.S.T.) software. This work provided new insights to Fe/SPC system towards high-efficiency and low consumption treatment of practical application.

Deep decarburization of molybdenum and tungsten powders by wet hydrogen

The control of residual carbon content is an urgent problem to be solved for the preparations of molybdenum and tungsten powders by method of carbothermic reduction of their oxides. In this paper, finer Mo (W) powder with a low residual carbon content was prepared by a two-step reduction process consisting of carbothermal pre-reduction of MoO3 (WO3) at 1050 °C and following deep hydrogen reduction. During the deep hydrogen reduction process, with the increases of hydrogen reduction temperature and dew point, the residual carbon contents of the finally prepared Mo and W powders gradually decreased, while the particle sizes of Mo and W powders gradually increased. The lowest residual carbon and oxygen contents of Mo and W powders obtained after hydrogen reduction at 1100 °C with the hydrogen dew point of 41 °C were 0.007 wt% (carbon content) and 0.104 wt% (oxygen content), as well as 0.010 wt% and 0.086 wt%, respectively. In addition, the mean particle sizes of them were 1032 nm and 998 nm under this condition, respectively.

Closed-loop recovery of molybdenum and value-added reuse of tungsten from alloy waste in additive manufacturing

As metal additive manufacturing (MAM) technology is booming in the aerospace sector, alternatives to the traditional production methods of metals such as mining, processing, and refining with severe emissions are urgently needed. This study proposed a closed-loop route for efficient recovery of molybdenum (Mo) and value-added reuse of tungsten (W) from Cr–Co–Ni–Mo–W alloy waste in MAM. The results showed that the leaching efficiency of Mo and W reached 99.3% and 99.9%, respectively, using the dual chemical-physical means of mixed-alkali roasting and leaching by microwave heating, while the discharge of waste liquor containing Cr6+ was reduced. Leaching kinetic studies revealed that the metal leaching process was controlled by chemical reaction mechanism. Moreover, the 10%N1923 (primary amine)–5%TRPO (tri-alkyl phosphine oxide)–kerosene extraction system exhibited a synergistic extraction effect on Mo and W. After purification, Mo was recovered as Mo powder for MAM. Simultaneously, the recovered product of W, MnWO4, was applied as a photocatalytic material with excellent degradation of methylene blue dye. Ultimately, the proposed method obtained recovery efficiencies of 98.4% and 99.3% for Mo and W, respectively, achieving efficient and environmentally-friendly reuse of these key metals.

Effect of molybdenum release on UO2/MOX fuel oxidation under severe light water reactor accident conditions

To investigate the Mo release behavior and its influence on the oxidation of UO2/mixed oxide (MOX) fuel, the oxidation and evaporation (O&E) behaviors of Mo powders and their influencing mechanisms with respect to oxygen partial pressure around powders (pO2s) were researched by using a thermogravimetric analysis technique under Ar-0.1 % O2, Ar-1.0 % O2, and Ar-1.5 % O2 atmospheres in the temperature range from 1473 to 1673 K. The study results reveal that Mo O&E could quickly consume oxygen, substantially decreasing pO2s. This decrease in pO2s facilitates the attainment of an oxygen mass balance by enhancing the diffusion rate of O2(g) towards the powder surfaces and decelerating the O&E rates of the powders. Subsequently, the oxygen consumption rate with respect to Mo release (FO-con) and the potential oxidation rate of UO2 nuclear fuels (FO-ads) under the typical accident conditions created in VERCORS were estimated using the latest analytical model of Mo and the existing fuel oxidation model, respectively. The results demonstrate that, as accident proceeds, FO-con has the potential to surpass FO-ads, thereby retarding the oxidation of nuclear fuel.

Effect of powder milling on sintering behavior and monotonic and cyclic mechanical properties of Mo and Mo–Si lattices produced by direct ink writing

Molybdenum is a refractory metal regarded as a promising basis for producing high-temperature components. However, the potential of manufacturing molybdenum-based structures by direct ink writing (DIW) has not been explored. In this study, three-dimensional porous molybdenum (Mo) and molybdenum-silicon (Mo–Si) composite lattices were fabricated using DIW with non-milled and milled powders. The effects of Mo powder morphology (resulting from milling) and chemical composition (alloying Mo with 3 and 10 wt% of Si) on the microstructure, phase composition, and static and cyclic compression properties at room temperature were investigated. Lattices fabricated from commercial spherical Mo powder exhibited the highest intra-filament porosity. Conversely, lattices fabricated from milled Mo powder were denser and had higher compressive strength, offset stress, and quasi-elastic gradient. Alloying Mo with Si during sintering resulted in composite lattices with Mo + Mo3Si microstructure. A low content of Mo3Si slightly decreased monotonic compression properties but did not affect the cyclic compression response compared to Mo lattices made from milled powder. In contrast, a high content of Mo3Si produced quasi-brittle lattices with reduced compressive strength and increased damage accumulation during cyclic loading. The cyclic behavior of all lattices was characterized by a ratcheting-dominated stress-strain response. Lattices fabricated from milled Mo and milled Mo-3 wt.%Si powders demonstrated superior performance compared to those fabricated from commercial spherical Mo and milled Mo-10 wt%Si powders. The results suggest that using milled powders can enhance the mechanical reliability and promote the use of DIW as preferred additive manufacturing technology for the fabrication of Mo–Si composite lattices.

High-Temperature Oxidation Properties of Ti-Hf-Mo-Ta-Nb-B Composite Coating Deposited on Ti60 Alloy with Laser Cladding

In order to improve the high-temperature oxidation resistance of Ti60 alloy, a Ti-Hf-Mo-Ta-Nb-B composite coating was prepared on Ti60 alloy with Ti, Hf, Mo, Ta and Nb powder and B powder as raw materials using laser cladding. The microstructure and oxidation behavior of the coating before and after oxidation at 1100 °C × 120 h in static air were studied with XRD, SEM, EDS and isothermal oxidation techniques. The results show that the coating was mainly composed of six phases, (Ti0.2Hf0.2Mo0.2Ta0.2 Nb0.2)B2, TiB, HfB2, Mo4.00 B3.40, TiHf and Hf1.86Mo0.14. The high-temperature oxidation of the coating and Ti60 alloy followed parabolic law, and the oxidation weight gain rate of the coating after 110 °C × 120 h was only 1/4.8 of that of the Ti60 alloy. The improvement of the high-temperature oxidation resistance of the coating may benefit from high-temperature oxidation resistance (Ti0.2Hf0.2 Mo0.2Ta0.2Nb0.2)B2, HfB2 and TiB boride ceramic phases.

Cuprous-mediated peroxymonosulfate activation for Fenton-like removal of micropollutants: The function of co-catalyst and the accelerated degradation mechanism

Introducing co-catalysts to enhance the activation of cuprous-mediated peroxymonosulfate (PMS) and induce the continuous generation of highly reactive oxygen species is promising. The function, effectiveness, and acceleration mechanism of co-catalysts in the cuprous-mediated PMS activation process were fully explored in this work, which focused on rhodamine B as the target contaminants. The results demonstrated that molybdenum (Mo) powder was a superb co-catalyst, and that the reaction of cuprous-mediated PMS system was carried out by surface Mo species as opposed to Mo ions in the solution. The Cu (II)/Cu(I) cycle was primarily encouraged by the Mo0, which also caused abundant ·HO and 1O2 and minimal SO4·− and ·O2− to be produced from PMS. The Mo/Cu2+/PMS system exhibited high removal efficiency towards typical pollutants, especially ciprofloxacin, methyl orange, malachite green, and crystal violet, with removal rates up to 93%, 99%, 97%, and 92%, respectively. Additionally, this system showed excellent adaptability to complex water environments. After four cycles, the Mo powder retained its properties and morphology, and the target pollutants could still maintain an 82% degradation efficiency. This study provides a basis for enhancing cuprous-mediated PMS activation for wastewater treatment.

A fast and environment-friendly method for preparing nanopowders Mo through electro- desulfidation of MoS2 in LiCl melt

Fast–reaction rate production of Mo with energy-saving and environmental protection is important for industries. However, the present preparation of Mo by pyrometallurgical process in industry is challenging. Here we demonstrate a solution route through direct electro- desulfidation solid MoS2 at 973 K in LiCl melt with a fast and environment-friendly method. When the scan rate was 50 mV/s, the total reduction (0.5 mg MoS2 in the MCE.) time was less 16 s, and the peak current density was as high as 38 A/cm2 with reference to the geometric surface of the cavity (ca. 0.004 cm2)Nano molybdenum powder can be obtained on cathode and element sulfur on anode. The current efficiency was 95% and energy consumption was 1.02 kWh/kg- Mo. The details of the electro-desulfidation mechanism of solid MoS2 was also investigated by cyclic voltammetry, potentiostatic and constant voltage electrolysis. Accordingly, the electro-desulfidation mechanism may be speculated as followings: the intercalation compound containing Li+ (LixMoS2) was first generated and then LixMoS2 was reduced to nanometer Mo powder.

Mechanism and kinetics of hydrogen reduction of ultrafine MoO2 for preparing ultrafine Mo powder

In this study, ultrafine Mo powder was synthesized via hydrogen reduction of MoO2 at various temperatures for different durations. The outcomes indicated that the higher temperature (in the range of 650–900 °C) could effectively enhance the reaction rate, leading to a substantial reduction in the time needed to complete the reduction reaction. Nevertheless, the obtained ultrafine Mo powder exhibited little change in overall particle morphology, and basically retained the sheet shape of the precursor MoO2, attributed to the dominance of pseudomorphic transformation mechanism in the reduction process. Additionally, various phase compositions of the products were observed across diverse material layers, illustrating the impact of gaseous mass transfer in the material layer on the reduction reaction. Moreover, a comprehensive kinetic model incorporating the diffusion of gases within the material layer and the interfacial chemical reaction of single particle was introduced. The utilization of this model confirmed its effectiveness in accurately characterizing the reduction kinetics of ultrafine MoO2, with the extracted apparent activation energy of 74.5 kJ/mol.

Impact of Sintering Temperature Variation on Porous Structure of Mo2TiAlC2 Ceramics.

Mo, TiH2, Al and graphite elemental powders were used as starting materials for the activation reaction sintering process, which was employed to fabricate porous Mo2TiAlC2. The alteration of phase constitution, volume expansion, porosity, pore size and surface morphology of porous Mo2TiAlC2 with sintering temperatures ranging from 700 °C to 1500 °C were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and pore size tester. Both the pore formation mechanism and activation reaction process at each temperature stage were investigated. The experimental results illustrate that the sintered discs of porous Mo2TiAlC2 exhibit obvious volume expansion and pore structure change during the sintering process. Before 1300 °C, the volume expansion rate and porosity increase with the increment of temperature. However, with the sintering temperature above 1300 °C, the volume expansion rate and porosity decrease. At the final sintering temperature of 1500 °C, porous Mo2TiAlC2 with a volume expansion rate of 35.74%, overall porosity of 47.1%, and uniform pore structure was synthesized. The pore-forming mechanism of porous Mo2TiAlC2 is discussed, and the evolution of pressed pores, the removal of molding agents, the decomposition of TiH2, and the Kirkendall effect caused by different diffusion rates of elements in the diffusion reaction are all accountable for the formation of pores.

Preparation of ultrafine Mo powder by the H2 reduction of MoO2: Parameter optimization, reaction kinetic, and its reduction mechanism

The influences of different parameters, such as reaction temperature, yttrium (Y) content, and H2 concentration, on the particle size and morphological structure of Mo powder prepared via the H2 reduction of MoO2, were investigated in the work. TG, XRD, FE-SEM, laser particle size analysis, model fitting, and orthogonal design experiment methods were adopted to analyze the reaction kinetic and reduction mechanism. The results showed that the optimum conditions for preparing ultrafine Mo powder were recognized as 1073 K, 1 mass% Y content, and a H2 concentration of 0.000576 mol·cm−2·min−1, which enabled the as-prepared Mo powder with a particle size as small as 107 nm. A new interfacial chemical reaction model with the consideration of reaction temperature, H2 concentration, and sample thickness, was proposed to analyze the reaction kinetic. It was found that the curves predicted by the model agreed well with the experimental data, with the apparent activation energy extracted to be 94.686 kJ/mol. The effect of different individual parameter on the reaction rate and the possible reduction mechanism were also elucidated.

Microstructure and reduction behavior of Mo powders doped with La2O3 and ZrO2 oxides using the spray drying method

In the present contribution, we used the spray drying method for the preparation of molybdenum-based composite powders, which belong to an important class of high-temperature structural materials – oxide dispersion strengthened molybdenum alloys (ODS-Mo). Three types of materials were prepared via spray drying and subsequent steps of calcination and reduction, including undoped reference Mo, ODS-Mo doped with 1 wt% of La2O3, and ODS-Mo doped with 1 wt% of La2O3 and 1 wt% of ZrO2. The particular focus was given to precursor solution; specifically, the effects of type (aqueous or water-ethanol mixture) and chemical composition (the addition of La and Zr precursors) were studied in detail, which was rarely given attention in previous research. The morphological and microstructural changes of the particles during oxidation and reduction of sprayed-dried powders were extensively analysed by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDX), X-ray diffractometry (XRD), and X-ray photoelectron spectroscopy (XPS). The morphology and crystallinity of spray dried powders were controlled by the state of spraying precursor solution, i.e. homogeneous solution or particle suspension. Calcination at the temperatures of 500 °C and 650 °C produced spherical polycrystalline and slab-shaped monocrystalline MoO3 oxide particles. Subsequent reductive treatment of transformed calcined powders into metal-based powders took place with efficiency that depended mainly on the type of spraying solution (aqueous solution or water-ethanol suspension) and its chemical composition, in which case, the addition of La and Zr precursors resulted in lower efficiency than the addition of La alone. In terms of powder particle size, homogeneity of alloying elements, and reduction efficiency, the powders produced from water-ethanol suspensions were clearly superior to those produced from aqueous solutions.

Structural, mechanical and tribological performance of a nano structured biomaterial Co–Cr–Mo alloy synthesized via mechanical alloying

The influence of milling time on the tribological behavior of a Co–Cr–Mo alloy designed for biomedical applications, synthesized via mechanical alloying is investigated. Elemental Co, Cr and Mo powders are milled using different milling times (2, 6, 12 and 18 h) in a high-energy ball mill. The resulting powders were subjected to cold uniaxial and hot isostatic pressing respectively, followed by sintering to obtain cylindrical samples, which were evaluated for their structural, mechanical and the wear behavior. Results showed that the grain and crystallite sizes of the powders decreased with increasing milling time, reaching low values of <10 μm and 32 μm respectively, at higher milling times. Furthermore, the wear rates and the coefficients of friction were lower, at higher milling times due to high densities (96%), and higher elasto-plastic resistance, as presented by the H/E and H3/E2 values of 0.026 and 0.0021 GPa, respectively. Increased milling time enables the refinement of grains and reduction in porosity in the Co–Cr–Mo alloy, which in turn increases the alloy's elasto-plastic resistance and enhances its wear resistance.

Study on the preparations of Mo and W powders via carbothermal pre-reduction process of MoO3 or WO3

In this paper, ultrafine Mo (W) powders were obtained by a two-stage reduction process consisting of carbothermal pre-reduction of MoO3 (WO3) and deep hydrogen reduction. The increase of reaction time was conducive to reduce the residual carbon contents of carbothermally pre-reduced products without significantly affecting the particle sizes. The particle sizes of carbothermic reduction products of MoO3 and WO3 were 186–192 nm and 141–146 nm as increasing holding time from 1 h to 4 h, respectively, while the residual carbon contents decreased from 0.036 wt% to 0.025 wt%, as well as from 0.045 wt% to 0.032 wt%, respectively. In addition, with the decrease in particle size of carbon black from 200 to 300 nm to 50 nm, the particle sizes of carbothermic reduction products of MoO3 and WO3 were gradually decreased from 322 nm to 188 nm and from 261 nm to 146 nm, respectively, while their residual carbon contents were 0.025–0.028 wt%, as well as 0.028–0.031 wt%, respectively. After the deep hydrogen reduction of carbothermal reduction products, the residual carbon contents of finally obtained ultrafine Mo and W powders were further reduced.

Unveiling the formation of Mo2C coating on diamond particles along with anisotropic etching by Mo powder

Unveiling the formation of Mo2C coating on diamond particles along with anisotropic etching by Mo powder

Preparation and properties of HfB2-HfC and HfB2-HfC-MoB composites by reactive spark plasma sintering

ABSTRACT Ultra-high-temperature ceramics are required for many aerospace applications. In this work, HfB2-30 vol.% HfC and HfB2-26 vol.% HfC-43 vol.% MoB high-density composites were prepared by one-step in-situ reactive spark plasma sintering (R-SPS) using Hf, B4C and Mo powders as starting materials. The influences of sintering temperature on the densification mechanism, microstructural evolution, mechanical properties and oxidation resistance of the composites were thoroughly investigated. The results demonstrate that the raw materials undergo a complete chemical reaction to form new binary HfB2-HfC and ternary HfB2-HfC-MoB composite structures at a temperature of 1300°C. The HfB2-HfC and HfB2-HfC-MoB composites prepared at the optimal conditions (pressure = 50 MPa, temperature = 1800°C, holding time = 5 min) had highre densities of 97% and 98%, respectively. The Vickers hardness, Young’s modulus and fracture toughness of the HfB2-HfC composite were 18.3 GPa, 525 GPa and 6.34 MPa·m1/2, respectively. However, after molybdenum was added, the Vickers hardness of the ternary HfB2-HfC-MoB composite increased to 19.4 GPa but its fracture toughness decreased slightly to 6.1 MPa·m1/2. Compared with the binary composite, the ternary composite exhibited a low and thermally stable oxidation rate up to a temperature of 1400°C, and the test was conducted in air atmosphere.

Plasma surface enrichment versus volumetric alloying of Fe + 0.6% C + 3% SiC self-lubricating sintered composites: Microstructural and tribological evaluation

In the present study, the addition of molybdenum as an alloying element to the Fe + 0.6% C + 3% SiC self-lubricating composite was carried out by two different processing routes: In a novel and original processing route, the addition of Mo is carried out through plasma treatment, creating an average content of 1.6 wt % Mo in the first 10 μm. In the long-established route, Mo powder was added to the powder mix to reach 1.6 wt % Mo average volumetric composition. The two groups of samples were produced by powder injection mould, plasma-assisted debinded and sintered and subjected to a soaking stage to promote bainite formation. Tribological characterisation (scuffing resistance, steady-state friction coefficient, specimen and counter-bodies wear rates) was performed using dry, constant and variable load reciprocating sliding tests. The results, discussed in terms of microstructural modifications and wear mechanisms, indicated that Mo enrichment presented the best results, with a significant increase (4500%) in scuffing resistance and an order of magnitude reduction in the average steady-state friction coefficient. In addition, the wear rate of the volumetric specimens was notably higher (1000%) and even more pronounced in the counter-bodies (four orders of magnitude), proving that surface enrichment of self-lubricating composites is viable, cost-effective, and reliable alternative for improving their tribological properties.

Effect of Nano-La2O3 and Mo on Wear Resistance of Ni60a/SiC Coatings by Laser Cladding

To improve the wear resistance of the TMR blade and investigate the effect of nano-La2O3 and Mo on the wear resistance of laser cladding coating. 65Mn blade as the substrate, La2O3, Mo and Mo-La2O3 composite powders were added into Ni60a/SiC composite powder. Using scanning electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy and the CFT-I surface synthesizer, the phase composition, element distribution and friction and wear properties of the coating were analyzed to obtain the best composition of the composite coating. The results showed that the wear resistance of Mo-La2O3-Ni60a/SiC composite coating was the best. The coating was analyzed by X-ray diffraction and X-ray photoelectron spectroscopy. The coating contained hard phases such as CrB, CrC and Cr7C3, and the element distribution was uniform. It can be seen from the scanning electron microscope that the addition of nano-Mo and La2O3 improves the toughness and compactness of Ni60a/SiC composite coating, and the microstructure is refined. The friction coefficient of Mo-La2O3-Ni60a/SiC composite coating is 0.5, and the wear depth is 12.35 μm, 23% and 89% lower than that of 65Mn substrate, respectively. The surface roughness of the Mo-La2O3-Ni60a/SiC coating after wear is 2.06 μm, and the wear amount is 0.001 g. The wear mechanism of the coating is mainly adhesive wear, abrasive wear, and oxidation wear. The wear surface of the Mo-La2O3-Ni60a/SiC composite coating is mainly composed of micro furrows, accompanied by the generation of new wear-resistant layers.

Enhanced Photocatalytic Performance of Visible-Light-Driven BiVO4 Nanoparticles through W and Mo Substituting

Bismuth vanadate (BiVO4), W-doped BiVO4 (BiVO4:W), and Mo-doped BiVO4 (BiVO4:Mo) nanoparticles were synthesized at pH = 4 using a green hydrothermal method. The effects of 2 at% W or Mo doping on the microstructural and optical characteristics of as-prepared BiVO4 nanoparticles and the effect of combining particle morphology modification and impurity dopant incorporation on the visible-light-derived photocatalytic degradation of dilute Rhodamine B (RhB) solution are studied. XRD examination revealed that these obtained BiVO4-based nanoparticles had a highly crystalline and single monoclinic phase. SEM and TEM observations showed that impurity doping could modify the surface morphology, change the particle shape, and reduce the particle diameter to enlarge their specific surface area, increasing the reactive sites of the photocatalytic process. XPS and FL measurements indicated that W- and Mo-doped nanoparticles possessed higher concentrations of oxygen vacancies, which could promote the n-type semiconductor property. It was found that the BiVO4:W and BiVO4:Mo powder samples exhibited better photocatalytic activity for efficient RhB removal than that shown by pristine BiVO4 powder samples under visible light illumination. That feature can be ascribed to the larger surface area and improved concentration of photogenerated charge carriers of the former.