Molybdenum Particles Research Articles

Characterization of molybdenum particles reinforced Al6082 aluminum matrix composites with improved ductility produced using friction stir processing

Aluminum matrix composites (AMCs) reinforced with various ceramic particles suffer a loss in ductility. Hard metallic particles can be used as reinforcement to improve ductility. The present investigation focuses on using molybdenum (Mo) as potential reinforcement for Mo(0,6,12 and 18 vol.%)/6082Al AMCs produced using friction stir processing (FSP). Mo particles were successfully retained in the aluminum matrix in its elemental form without any interfacial reaction. A homogenous distribution of Mo particles in the composite was achieved. The distribution was independent upon the region within the stir zone. The grains in the composites were refined considerably due to dynamic recrystallization and pinning effect. The tensile test results showed that Mo particles improved the strength of the composite without compromising on ductility. The fracture surfaces of the composites were characterized with deeply developed dimples confirming appreciable ductility.

Quantitative characterization of material surface — Application to Ni + Mo electrolytic composite coatings

A new approach to numerical analysis of maps of material surface has been proposed and discussed in detail. It was concluded that the roughness factor RF and the root mean square roughness Sq show a saturation effect with increasing size of the analysed maps what allows determining the optimal map dimension representative of the examined material. A quantitative method of determining predominant direction of the surface texture based on the power spectral density function is also proposed and discussed. The elaborated method was applied in surface analysis of Ni+Mo composite coatings. It was shown that co-deposition of molybdenum particles in nickel matrix leads to an increase in surface roughness. In addition, a decrease in size of the embedded Mo particles in Ni matrix causes an increase of both the surface roughness and the surface texture. It was also stated that the relation between the roughness factor and the double layer capacitance Cdl of the studied coatings is linear and allows determining the double layer capacitance of the smooth nickel electrode.

Study of a nickel-copper filter for the future conditioning of insoluble residues

This paper deals with the feasibility of a separate conditioning for insoluble residues coming from spent nuclear fuel reprocessing. The two possible conditioning routes considered for insoluble residues were (i) added with cladding hulls with the considered filter (route #1) or (ii) melted with a nickel copper alloy already studied (route #2). Only route #2 was dealt with in this study. In France, the current practice is to store insoluble residues in a water suspension. For the two conditioning routes described here, dry insoluble residues are required for safety with melted metals. A nickel-copper filter was developed that can serve for the two types of conditioning. A filtration test performed with molybdenum particles as insoluble residue surrogates was done. The particle-charged filter was sintered, and Mo particles were kept inside the filter. Thus an integrated flowsheet for the filtration and immobilization of insoluble residues was demonstrated.

A Method for Image Decomposition and Particle Quantification in Multiphase Systems

X-ray tomography has proven to be an effective tool for three-dimensional analysis of particle deposition in deep bed filtration. A major challenge in terms of quantitative data evaluation of such tomographic images is the implementation of a reliable image decomposition method in quantifying the various materials in a filter bed which has been flooded with water and contains particle depositions. Therefore, a multistage method, based on basic image processing operations, has been developed to decompose grayscale images of multiphase systems into sets of concentrations for each phase. In that regard, the quantification of strong absorbing particles below the resolution limit is of particular interest in order to enable the detection of particle deposition sites at the beginning of a filtration process. The method was tested on three model samples, consisting of glass, molybdenum particles and polyurethane, as a substitute for water, with entrapped air. It could be shown that the particle concentration can be determined for all samples with a maximum error of 14.5 %.

Facile and novel synthetic method to prepare nano molybdenum and its catalytic activity.

This study reports on a facile and economical synthetic method to prepare nano molybdenum by solid-state reaction technique. Metallic nano molybdenum was synthesised from molybdenum trioxide, molybdenum IV oxide and molybdenum VI oxide through thermal decomposition technique. Metallic nano molybdenum prepared from molybdenum IV oxide was used to study the catalytic effect of molybdenum nanoparticles on the growth of Anabaena sp. The increase in concentration of nano molybdenum from 0.1 to 100% in BG11 (N⁻ Mo⁻ + nano Mo) medium increases heterocyst frequency. The chlorophyll and protein content in Anabaena sp. was found to improve when compared with bulk molybdenum particles and showed a positive influence to be used as a nano nutrient for Anabaena sp.

Combustion features in the Mo–Si–B system. Part 1. Mechanism and kinetics

The article describes the investigation of reaction mix combustion kinetics and mechanisms as well as to producing ceramic materials in the Mo–Si–B ternary system by SHS method. For mixes enriched by silicon, the driving force of the SHS-reaction is shown to be silicon fusion, produced melt sprea- ding over the surface of molybdenum and boron solid particles with dissolution of the latter in it and formation of Mo 3 Si intermediate silicide film. The subsequent silicon diffusion in molybdenum results in occurrence of MoSi 2 grains, thus molybdenum boride grains are formed as a result of mo- lybdenum diffusion into the melt. In the compositions with high boron content and low silicon fraction, MoB formation can carry by means of gas- phase mass transfer of МоО 3 suboxide to boron particles. Investigations of chemical transformation succession have been carried out in combustion wave. The obtained data testify of the possibility of parallel and subsequent flowing of molybdenum silicide and boride formation reactions, this sti- pulates the combustion transfer from fusion mode to detachment mode and vice versa. In the detachment mode, molybdenum silicide formation re- action is leading one, and molybdenum boride formation occurs with short time detachment. Using the power SHS-compaction, targets for magne- tron deposition are produced.

Effect of dry-ice blasting on the deposition behavior of molybdenum particles onto aluminum and stainless steel substrates using plasma spraying: From single splat to coating

Molybdenum splats usually exhibit splitting morphology onto aluminum and stainless steel substrates due to substrate melting and their own high surface tension using plasma spraying. In this study, Mo particles were sprayed onto different substrates, which were treated by dry-ice blasting combined with substrate preheating. The splats were studied using detailed microstructural characterization with an emphasis on the splat shape. Moreover, the corresponding Mo coatings deposited onto different substrates were obtained. The results showed that the splitting splat formed on stainless steel was different from that on the aluminum surface. Dry-ice blasting combined with substrate preheating slightly modify the morphology of Mo splat sprayed on aluminum and stainless steel surfaces.

A cellular automaton method to simulate the microstructure and evolution of low-enriched uranium (LEU) U–Mo/Al dispersion type fuel plates

Low-enriched uranium (LEU) fuel plates for high power materials test reactors (MTR) are composed of nominally spherical uranium–molybdenum (U–Mo) particles within an aluminum matrix. Fresh U–Mo particles typically range between 10 and 100μm in diameter, with particle volume fractions up to 50%. As the fuel ages, reaction–diffusion processes cause the formation and growth of interaction layers that surround the fuel particles. The growth rate depends upon the temperature and radiation environment. The cellular automaton algorithm described in this paper can synthesize realistic random fuel-particle structures and simulate the growth of the intermetallic interaction layers. Examples in the present paper pack approximately 1000 particles into three-dimensional rectangular fuel structures that are approximately 1mm on each side. The computational approach is designed to yield synthetic microstructures consistent with images from actual fuel plates and is validated by comparison with empirical data on actual fuel plates.

Diamond Machining of Rapidly Solidified Aluminium for Optical Mould Inserts

In this study, we conducted a series of machining tests on an ultra-high precision machining centre to investigate the wear mechanism of diamond inserts when rough turning a rapidly solidified aluminium grade, having increased contents of hard elements such as iron, nickel and molybdenum particles. This aluminium grade (RSA 905) produced by melt-spinning process could be used for making optical moulds for plastic lens injection as a re-placement of other traditionally used aluminium grades. The study yields some recommendations on the best combination of machining parameters that will result in maximum material removal rates with smallest possible damage to the tool edge. In this work, standard non-controlled waviness mono-crystalline diamond inserts are used to cut the aluminium alloy. The initial results of tool wear measurements indicate that diamond machining of this particular aluminium grades results in relatively intensive tool wear compared to other optical material. The study concludes that the tool wear is very noticeable on the diamond inserts operated at high feed rates.

Influence of in situ formed MoSi2 inclusions on the thermoelectrical properties of an N-type silicon–germanium alloy

An N-type Si92Ge08 (7000at. ppm P doping) powder (matrix) prepared by mechanical alloying was homogeneously mixed with 1.3vol.% nanosized molybdenum. The “composite” and matrix powders were sintered by spark plasma sintering, using optimized parameters. The as-sintered “composite” material exhibits a dimensionless thermoelectrical figure of merit (ZT) of ∼1.0 at 700°C. For the same temperature, the ZT value is only 0.7 for the as-sintered matrix alone. In the composite material, transmission electron microscopy observations enable the detection of nanosized (average diameter of ∼30nm) MoSi2 inclusions that formed in situ during sintering via the reaction between the native silicon–germanium matrix and the added molybdenum particles. The presence of such nanosized inclusions reduces significantly the lattice contribution to the thermal conductivity of the sintered “composite” material, explaining the strong increase of the ZT parameter in comparison to the sintered matrix alone.

Al2O3–Mo cutting tools for machining hardened stainless steel

This article presents the result of the study of the properties of alumina ceramics–molybdenum cutting tools in dry machining of hardened steel. Dry machining process leads to the oxidation of molybdenum particles and formation of MoO3 and MoO2 oxides. The MoO3 oxide structure is very similar to that of graphite and serves the function of a solid lubricant, thereby a frictional coefficient between cutting edge and the machined material is decreased. Produced alumina ceramics–molybdenum composites are characterized with self-lubricating properties in dry machining condition. In addition, composite cutting tools edges wear uniformly without cracking and chipping and have the average tool life of over 2h.

A Study of 5%Mo-Cu Nanocomposite Prepared by SHS Route

Thermodynamic calculations indicate that molybdenum particles reinforced copper-matrix composite can be fabricated in CuO-Al-MoO3 powder system. Thermit reaction and self-propagation high-temperature synthesis (SHS) were applied to prepare samples. Then the phases, structure morphologies and properties were studied through the instruments of XRD, SEM and microhardness tester. The results show that nanocrystals are formed in Cu matrix and molybdenum particles are dispersive distributed in Cu matrix. The microhardness of 5﹪Mo-Cu nanocomposite is 110HV，and the relative electric conductivity is 58.6﹪IACS.

Microstructure and electrical conductivity in shape and size controlled molybdenum particle thick film

We study the effects of particle morphology on the microstructure and electrical conductivity of Mo particle thick films. In our study, the shape and size of molybdenum (Mo) particles are modified by mechanical ball-milling and atomic layer deposition (ALD). As the total number of collisions between Mo particles and ball-milling media increases, Mo particles are deformed, and the shape of Mo particles changed from irregular polyhedrons to thin flakes. In the ball-milling process, stress frequency is an important processing parameter governing the deformation and breakage of Mo particles. In addition, ALD-grown TiO2 layer is found to significantly suppress the growth of Mo particles at high temperature. After 1000 °C annealing, the particle size of the TiO2 layer-coated film is only half of that of bare Mo particle films. The shape of the particles changes electrical conductivity of the Mo thick films. Large contact area between flake shape particles can increase the carrier mobility of the film and the 5-nm thick TiO2 layer can provide the inter-particle carrier transport path via a tunneling mechanism. Our results show that the combined use of the ball-milling and the ALD coating leads to Mo thick films with high electric conductivity and large surface area.

Electrochemical ammonia production on molybdenum nitride nanoclusters

Theoretical investigations of electrochemical production of ammonia at ambient temperature and pressure on nitrogen covered molybdenum nanoparticles are presented. Density functional theory calculations are used in combination with the computational hydrogen electrode approach to calculate the free energy profile for electrochemical protonation of N2 and N adatoms on cuboctahedral Mo13 nanoparticles. Pathways for electrochemical ammonia production via direct protonation of N adatoms and N2 admolecules with an onset potential as low as -0.5 V and generally lower than -0.8 V on both a nitrogen covered or a clean Mo nanoparticle. Calculations presented here show that nitrogen dissociation at either nitrogen vacancies on a nitrogen covered molybdenum particle or at a clean molybdenum particle is unlikely to occur under ambient conditions due to very high activation barriers of 1.8 eV. The calculations suggest that the nitrogen will be favored at the surface compared to hydrogen even at potentials of -0.8 V and the Faradaic losses due to HER should be low.

Solidification of SiMo Nodular Cast Iron for High Temperature Applications

During the 1960s and 70s research was aimed at developing a material withstanding the ever higher temperatures in a combustion engine. This work resulted in what have later been named SiMo and D5S. SiMo is a nodular cast iron typically containing 4–6 % Si and 0.5–2 % Mo and can be used in temperatures up to 850–860 °C. D5S is a nickel base material. High silicon and silicon–molybdenum content improves the dimensional stability of ductile iron. Silicon increases the transformation temperature where austenite transforms to ferrite. Molybdenum partly segregates and freezes in intercellular regions, promoting carbides while during the solid state transformation molybdenum particles precipitate around grain boundaries. The solidified material shows a range of interesting structures and phases which will be presented.

The influence of addition of nanosized molybdenum and nickel particles on creep behavior of Sn–Ag lead free solder alloy

The effect of addition of nano-sized Ni and Mo particles on creep behavior of Sn–3.5Ag lead free solder alloy was investigated using a constant load method in a nanoindenter. Modified Garofalo’s equation was found to show an excellent fit to indentation creep data. It was observed that the steady state creep rate as well as primary creep stage displacement and primary creep stage time decreased with increasing addition of Mo and Ni to the base alloy.

Spark plasma sintering of TiC particle-reinforced molybdenum composites

In order to improve the recrystallization resistance and the mechanical properties of molybdenum, TiC particle-reinforcement composites were sintered by SPS. Powders with TiC contents between 6 and 25 vol.% were prepared by high energy ball milling. All powders were sintered both at 1600 and 1800°C, some of sintered composites were annealed in hydrogen for 10h at 1100 up to 1500°C. The powders and the composites were investigated by scanning electron microscopy and XRD. The microhardness and the density of composites were measured, and the densification behavior was investigated. It turns out that SPS produces Mo–TiC composites, with relative densities higher than 97%.The densification behavior and the microhardness of all bulk specimens depend on both the ball milling conditions of powder preparation and the TiC content. The highest microhardness was obtained in composites containing 25 vol.% TiC sintered from the strongest milled powders. The TiC particles prevent recrystallization and grain growth of molybdenum during sintering and also during annealing up to 10h at 1300°C. Interdiffusion between molybdenum and carbide particles leads to a solid solution transition zone consisting of (Ti1−x Mox)Cy carbide. This diffusion zone improves the bonding between molybdenum matrix and TiC particles. A new phase, the hexagonal Mo2C carbide, was detected by XRD measurements after sintering. Obviously, this phase precipitates during cooling from sintering temperature, if (Ti1−x Mox)Cy or molybdenum, are supersaturated with carbon.

Influence of Nano Nutrients on Heterocyst-Forming Cyanobacterium Anabaena ambigua Rao

The present study is deals with the influence of nanoparticles on the growth of heterocyst-forming cyanobacterium Anabaena ambigua Rao [A100]. The nano molybdenum and iron particles have been synthesized respectively from molybdenum trioxide (MoO3) and iron chloride (FeCl3) employing sodium borohydride (NaBH4) as a reducing agent and characterized comprehensively. BG11 (N−) media containing micronutrients like molybdenum and iron were replaced respectively by different concentrations of nano molybdenum [BG11 (N−Mo− + nano Mo)] (0, 5, 10, 15, 20, 25, 40, 60, 80, and 100%) and nano iron [BG11 (N−Fe− + nano Fe)] (0, 0.1, 0.2, 0.3, 0.4, 0.5, 1, 2, 3, 4, 5, 10, 15, 20, 25, 40, 60, 80, and 100%) particles for the cultivation. The effect of nano nutrients on cyanobacterial growth parameters like heterocyst formation, chlorophyll content, and protein content was analyzed. The obtained results showed that the high concentrations of nano molybdenum induce heterocyst formation, increase protein content, and decrease chlorophyll content when compared to the control, whereas the nano iron suppresses the growth of cyanobacteria Anabaena ambigua Rao [A 100].

Effect of atmosphere and heating rate on mechanism of MoSi2 formation during self-propagating high-temperature synthesis

To study the effect of atmospheric type and heating rate on formation mechanism of MoSi2, the Mo + 2Si powder mixture was exposed to simultaneous thermal analysis (STA) in air atmosphere at different heating rates (10, 15, and 20 °C/min). To further study the changes, thermal analyses of molybdenum powders and consumed silicon were also performed separately. An amount of aluminum powder (5 wt.%) was also added to Mo + 2Si powder mixture and exposed to thermal analysis at different heating rates (10, 15, and 20 °C/min) to study the effect of the presence of active elements (like aluminum) on the trend of the performance of changes. To perform phase studies on the products of the thermal analysis at a later stage, each product was separately tested by an X-ray diffraction (XRD) method. Contrary to expectations, the XRD patterns showed that the trends of changes during thermal analysis were not in the direction of MoSi2, and the DTA–TG peaks obtained from these analyses were in fact related to other changes. Ultimately, the results showed that the peaks on the DTA curves resulted from the oxidation of molybdenum particles; and the (MoO3) melt of the product, and in continuation of the reduction of a part of this oxide, it resulted during the silicothermic and aluminothermy reactions. The results of this research also showed that with regard to the presence of intensive oxidation tendency of molybdenum particles, there is no chance for the formation of MoSi2 by heating the powder mixture of Mo + 2Si in air atmosphere and at low heating rates.

A New Approach to Preparing Crystalline Nano Molybdenum Particles*

Simple and cost-effective new method is developed to synthesize crystalline nano molybdenum particles from molybdenum trioxide (MoO3) using sodium borohydride (NaBH4) as a reducing agent. Nano molybdenum particles were studied using comprehensive characterisation. Crystallite size of prepared nano molybdenum was in the range of 24–35 nm. Particle size of nano molybdenum was around 100 nm whereas its surface area was in the range of 3.13–3.24 m2 g−1. The observed results are compared with existing results and the solid-phase technique in a muffle furnace was simple, rapid, reliable, reproducible, and cost effective in comparison with the currently available conventional methods.