Reduction Of Molybdenum Oxide Research Articles

Characterization and electrodeposition mechanism of Ni–Mo coatings from self-regulating electrolyte

Electrochemical Ni–Mo coatings were obtained on a low-carbon steel substrate using a stable, environmentally safe, self-regulating electrolyte containing 0.2 M NiCl2, 0.3 M Na3C6H5O7, and SrMoO4 (saturated). The effects of electrolyte pH, temperature, deposition current density, and hydrodynamic conditions on chemical composition and morphology of the coatings were studied. It was established that the addition of ammonia to the electrolyte contributes to the deposition of a more uniform, globular, nonporous coatings morphology. The effect of ammonia on the formation mechanism of coatings was substantiated. The stages of deposition and the limiting stage of the formation of Ni–Mo coatings from citrate-ammonia electrolytes, which involves the chemical reduction of molybdenum oxide (IV) to molybdenum, were determined using cyclic voltammetry.

SUBSTANTIATING THE PROCESS OF PRODUCTION OF FERROMOLYBDENUM FROM TEGHUT MOLYBDENITE CONCENTRATE UNDER PRODUCTION CONDITIONS

Studies of the production process of ferromolybdenum under industrial conditions feom Teghut molybdenite concentrate by using different reducing materials are carried out. Molybdenum can be reduced by carbon at low energy costs. However, the reduction of molybdenum oxides with carbon is accompanied by the formation of undesirable carbides Mo2C and MoCl-x. Due to the limitation of the carbon content in ferromolybdenum (≤0.05…0.5% C), it is obtained by the metallothermal method. In production, ferromolybde¬num is smelted by the out-of-furnace silicoaluminothermal method with an upper fuse from fired molybdenum concentrate (50.% Mo) and the use of ferro-silicon-aluminum (FSA) containing 60…65% Si and 10…12% Al, aluminum grains, iron ore, steel shavings and lime. The process takes place only due to the heat released by the reduction reactions of molybdenum, iron and other elements oxides with silicon and aluminum. From the standpoint of thermodynamics, the reduction reaction of molybdenum oxides by the carbothermal method has a positive value of enthalpy and entropy (due to the formation of CO), the total value of the change in Gibbs energy (∆G_T^0) remains negative and becomes smaller in absolute terms. That is why carbohydrate recovery requires external energy expenditure. On the contrary, when reducing by the aluminothermic and silicothe¬r¬m¬ic methods, the reactions are too negative, since these reactions are highly exothermic, and here the entropy factor does not affect the negative value of the change in Gibbs energy (∆G_T^0) (all reactants and the resulting products are in solid form), therefore the reactions are recovered due to the exothermicity of their own reactions and do not require external energy costs, which is the potential advantage of this method.

ELECTROLYSIS MODES VARIATION АS A UNIVERSAL METHOD FOR CONTROL THE ELECTROLYTIC COATING COMPOSITION

The possibility of electrosynthesis and control of the composition of galvanic coatings by alloys based on metals of the iron group with refractory metals, in particular molybdenum, from a complex citrate electrolyte by varying the electrolysis modes has been proved. It has been established that coatings with a high oxygen content are formed by direct current, namely, more molybdenum oxides are fixed in these coatings in comparison with coatings used in unipolar pulsed electrolysis. In the latter case, the oxygen content on the protrusions and depressions is much lower and is respectively 21 at.% And 25 at.%. It was shown that during pulsed electrolysis, the content of the metal form of molybdenum is higher as a result of the reduction of molybdenum oxides with intermediate oxidation levels by hydrogen ad-atoms, which are formed in the partial cathodic reaction. The reduction occurs due to the spillover effect, the implementation of which is most effective during a current interruption. The formation of the oxide phase of inclusions directly during electrolysis without introducing it into the electrolyte as a second phase is justified. Depending on the completeness of this process, conditions are created for the formation of a metal coating from ternary alloys or metal oxide composites, the second phase of which consists of molybdenum oxides of an intermediate oxidation state, that is, a process is formed directly in the electrode. According to the results of atomic force microscopy, it was found that coatings synthesized in the galvanostatic mode can be classified as composite electrolytic materials, and the cathode deposit obtained as a result of unsteady electrolysis can be attributed to metal. The doped coatings obtained in a pulsed mode are characterized by lower porosity. The surface free energy for metal and composite coatings was calculated, the values of which are 127.74 mJ/m2 and 118.10 mJ/m2. When testing the electrocatalytic activity of Fe-Co-Mo ternary alloys in the reaction of electrolytic hydrogen evolution, high values of the hydrogen exchange current density were obtained both for metal and composite coatings.

An investigation on aluminothermic reduction of MoO3 in domestic microwave oven

In the present study, feasibility of aluminothermic reduction of molybdenum oxide by microwave oven was studied. Furthermore, the effect of compaction pressure and the amount of used Al and CaO as flux on aluminothermic reduction of molybdenum oxide were investigated. Thermodynamic analysis of the corresponding reaction indicated that, aluminothermic reduction of MoO3 was possible at all temperatures. XRD patterns and thermodynamic investigation of reaction products indicated that aluminothermic reduction of molybdenum oxide progressed through the formation of intermediate phases such as Al2 (MoO4)3 and MoO2, where the final products were elemental Mo and Al2O3. Results revealed that by increasing the compaction pressure of the pellet, undesired phases of molybdenum dioxide (MoO2) and aluminum molybdate Al2(MoO4)3 can be detected among the final products. By increasing the amount of Al more than stoichiometric ratio, the intermediate phases, such as MoO2, were produced. The results indicated that by adding CaO to the MoO3-Al system, the unwanted molybdenum dioxide (MoO2) and aluminum molybdate (Al2 (MoO4)3) compounds were successfully reduced to Mo.. In the present work, metallic molybdenum could easily and successfully be separated from Al2O3 slag, as the side product of the reaction, in molten phase, based on the difference in their densities.

Microscopy and spectroscopy study of nanostructural phase transformation from β-MoO3 to Mo under UHV – MBE conditions

We report a simple reduction of molybdenum oxide (β-MoO3) grown on reconstructed Si(100) by thermal annealing in ultra-high vacuum (UHV) using molecular beam epitaxy (MBE). By increasing the substrate temperature during deposition or the annealing temperature after growth, the morphologies of as-deposited structures were found to vary from nanoribbons (NRs) of β-MoO3 to nanoparticles (NPs) of Mo. The change in morphologies have been associated with a structural transition from β-MoO3 to MoO2 at 400 °C and MoO2 to Mo at 750 °C. The in-situ X-ray photoelectron spectroscopy (XPS) measurements revealed a shift of the Mo 3d peaks towards lower binding energies, representing the reduction in Mo oxidation states until a pure Mo 3d peak at 750 °C was observed. The ex-situ KPFM measurements showed a decrease in the local work function (Φ) (from ≈ 5.27 ± 0.05 eV to ≈ 4.83 ± 0.05 eV) with increasing substrate temperature. A gradual reduction of the band gap from ≈ 3.32 eV for β-MoO3 NRs to zero band gap for Mo NPs is also observed during the annealing up to 750 °C.

Synthesis of a MoSi2-Based Powder Material Under the Influence of Pressure and Shearing

The SHS-grinding method was employed to prepare molybdenum disilicide powder material through the reduction of molybdenum oxide by aluminum and silicon. It is shown that the mechanical action applied to the material after the passing of an SHS-combustion wave through it can destroy the synthesized briquette created by the conventional self-propagating high-temperature synthesis (SHS) method. The increase in the intensity of mechanical action in the course of SHS-grinding breaks the agglomerated particles up into finer fractions, and also changes the morphology of the synthesized powder.

A study on direct alloying with molybdenum oxides by feed wire method

Direct alloying with molybdenum oxides has been regarded in years; the main addition methods are adding to the bottom of electric arc furnace (EAF) with scrap, adding to the ladle during the converter tapping and mixing molybdenum oxide, lime and reductant to prepare pellet added to basic oxygen furnace (BOF). In this paper, a new method for direct alloying with molybdenum trioxide is proposed, adding molybdenum trioxide molten steel by feeding wire method in ladle furnace (LF) refining process. The feasibility of molybdenum oxide reduction, the influence rules of bottom-blown on liquid steel fluidity and the yield of molybdenum by feeding wire method were analyzed. Results show that molybdenum oxide can be reduced by [Al], [Si], [C], and even [Fe] in molten steel. Bottom blowing position has a significant influence on the flow of molten steel when the permeable brick is located in 1/2 radius. The yields of Mo are higher than 97% for the experiments with feed wire method, the implementation of direct alloying with molybdenum trioxide by feed wire method works even better than that uses of ferromolybdenum in the traditional process.

Thermodynamic model of metallothermic smelting of ferromolybdenum

ABSTRACTFerromolybdenum, used in alloy steel production, is made by the batch reduction of molybdenum oxide by silicon and aluminium at high temperatures. In this work, the technology of the process has been reviewed and representative charge mixes compared. A computational thermodynamics model was developed and used to investigate the relationships between charge composition and ferroalloy grade and quality, indicated by its silicon content. The model predicted satisfactorily the composition of the ferromolybdenum and waste slag from a typical charge mixture. The silicon content depended on the ratio of silicon to molybdenum oxide in the charge and was not sensitive to the assumed smelting temperature or activity coefficient of silicon in the alloy. Losses of molybdenum to slag as dissolved oxide were predicted to be much lower than published industrial data, suggesting that losses in practice are mostly due to the inclusion of unsettled ferromolybdenum droplets.

Comparison of transesterification and thermal cracking methods on fuel specifications of castor oil biodiesel

A series of NiMo/γ-Al2O3 carbides were synthesized with the temperature programmed carburization method for the tri-reforming of methane. The relationship between the catalytic behavior and the impregnation sequence was investigated by XRD, TG-DSC, XPS, SEM, and so on. It was found that Mo2C species were the active species for the tri-reforming of methane. The amounts of Mo2C species on the fresh NiMo carbides decreased in the order of co-impregnated NiMo carbide > Ni-first NiMo carbide > Mo-first NiMo carbide. In contrast, Mo2C species on the latter two carbides would continue to be formed during the tri-reforming of methane. NiMoO4 species only existed on the co-impregnated NiMo oxidic precursor, exhibiting a strong synergistic effect between Ni and Mo species. NiMoO4 species were reduced more easily than MoO3 species on the step-impregnated NiMo oxides. Ni0 species promoted the dissociation of methane, induced the reduction of molybdenum oxide and supplied active hydrogen and carbon species for the carburization process. The co-impregnation method was conducive to refine the particles.

Effect of impregnation sequence on the catalytic performance of NiMo carbides for the tri-reforming of methane

A series of NiMo/γ-Al2O3 carbides were synthesized with the temperature programmed carburization method for the tri-reforming of methane. The relationship between the catalytic behavior and the impregnation sequence was investigated by XRD, TG-DSC, XPS, SEM, and so on. It was found that Mo2C species were the active species for the tri-reforming of methane. The amounts of Mo2C species on the fresh NiMo carbides decreased in the order of co-impregnated NiMo carbide > Ni-first NiMo carbide > Mo-first NiMo carbide. In contrast, Mo2C species on the latter two carbides would continue to be formed during the tri-reforming of methane. NiMoO4 species only existed on the co-impregnated NiMo oxidic precursor, exhibiting a strong synergistic effect between Ni and Mo species. NiMoO4 species were reduced more easily than MoO3 species on the step-impregnated NiMo oxides. Ni0 species promoted the dissociation of methane, induced the reduction of molybdenum oxide and supplied active hydrogen and carbon species for the carburization process. The co-impregnation method was conducive to refine the particles.

Electrochemical Reduction of Molybdenium Compounds to Form Molybdenium Powder

Molybdenum (Mo) is a refractory metal and mostly used as an alloying agent in cast iron, steels and superalloys to enhance hardenability, strength, toughness and corrosion resistance. It also finds other uses either in the form of a pure metal or an element in, for example, lubricants and catalysts. Traditional metal production methods are not suitable for molybdenum because pure molybdenum has very high melting point and has a tendency to get oxidized at low temperatures. Hydrogen reduction of molybdenum oxide is a very common way for Mo production but, it has two stages during process. At the second stage, the reduction process needs very high temperatures, therefore, high energy consumption and special equipment requirement is essential. FFC Cambridge process [1] based on electrochemical reduction of solid compounds was considered as an alternative way to produce molybdenum at relatively low temperatures. Similar to reduction of WO3 [2], loss of molybdenum as molybdenum oxychloride from MoO3 in CaCl2 containing molten salts is inevitable [3]. MoS2 powder pressed and sintered at 400oC to form pellets were used as starting material for electrochemical formation of pure Mo in molten CaCl2-NaCl salt mixture under argon gas at 800oC. A constant voltage in the range 1 to 3.0V was applied between MoS2 cathode and graphite anode. When the process was terminated at a prescribed time, the cathode was removed from the molten salt, cooled in argon, washed with water in air to dissolve the solidified salt, and then dried at about 100oC in vacuum before further analysis employing XRD, SEM and EDS. [1] G.Z. Chen, D. J. Fray, T. W. Farthing, Direct Electrochemical Reduction of Titanium Dioxide to Titanium in Molten Calcium Chloride, Nature, 407 (2000), 361-364. [2] M. Erdoğan, İ. Karakaya, Electrochemical Reduction of Tungsten Compounds to Produce Tungsten Powder, Metallurgical and Materials Transactions B, 41B (2010), 798-804. [3] W.T. Thompson, C.W. Bale, and A.D. Pelton: Facility for the Analysis of Chemical Thermodynamics (FACT), McGill University Montreal, Royal Military College of Canada in Kingston, E´cole Polytechnique, Montreal, Canada, 1985.

Hydrogen reduction of molybdenum oxide at room temperature

The color changes in chemo- and photochromic MoO3 used in sensors and in organic photovoltaic (OPV) cells can be traced back to intercalated hydrogen atoms stemming either from gaseous hydrogen dissociated at catalytic surfaces or from photocatalytically split water. In applications, the reversibility of the process is of utmost importance, and deterioration of the layer functionality due to side reactions is a critical challenge. Using the membrane approach for high-pressure XPS, we are able to follow the hydrogen reduction of MoO3 thin films using atomic hydrogen in a water free environment. Hydrogen intercalates into MoO3 forming HxMoO3, which slowly decomposes into MoO2 +1/2 H2O as evidenced by the fast reduction of Mo6+ into Mo5+ states and slow but simultaneous formation of Mo4+ states. We measure the decrease in oxygen/metal ratio in the thin film explaining the limited reversibility of hydrogen sensors based on transition metal oxides. The results also enlighten the recent debate on the mechanism of the high temperature hydrogen reduction of bulk molybdenum oxide. The specific mechanism is a result of the balance between the reduction by hydrogen and water formation, desorption of water as well as nucleation and growth of new phases.

Molybdenum oxide reduction using syngas and heat from an inert porous media reactor

A method of molybdenum oxide (MoO3) reduction using both the heat released and gaseous products from hydrocarbon fuels partial oxidation (H2 and CO) in a novel inert porous media reactor is studied. The numerical approach considered a two-temperature model for filtration combustion of methane with a four-step reaction mechanism to solve temperature, H2 and CO production, and MoO3 reduction through shrinking core model. A maximum for molybdenum oxide reduction was found with an increasing equivalence ratio (ϕ). Use of propane resulted in a low reduction degree and a maximum temperature of 641 K for the molybdenum oxide powder. SEM and XRD analysis were conducted on the tested powders. Empirical data predicts a favorable reduction degree for the new reactor proposed.

On the removal of a-C:H films deposited onto Mo, Mo oxidation, and MoO x reduction in O2 and D2 discharges

The peculiarities inherent to a-C:H film removal, Mo oxidation in a flowing glow discharge of oxygen, and molybdenum-oxide reduction in deuterium discharge are investigated at T = 300–320 K. After carbon is removed under O2 discharge conditions, a steady-state MoO3 layer with a limiting thickness of 25–30 nm is formed on large-block molybdenum with the predominant orientation Mo(110). Oxide films are reduced in deuterium plasma at a selective sputtering yield on the order of 0.01 O atom/D+2 ion. If the interior Mo surfaces of a thermonuclear reactor are cleaned of hydrocarbon sediments via oxygen discharge, the working chamber must be additionally exposed to deuterium plasma for 8–10 h to remove oxygen from the generated a-MoO3 layers with the greatest possible oxygen content of 4–4.5 µg/cm2.

Reduction characteristics of molybdenum trioxide with aluminum and silicon

Thermodynamics for reduction of molybdenum oxides by aluminum and silicon were calculated, and the results show that reduction reaction is feasible at a certain temperature region. Compared to the presence of CaO or CaCO3, reduction products of molybdenum trioxide with aluminum and silicon at various temperatures were detected by X-ray diffraction (XRD). Results show that molybdenum trioxide is reduced by aluminum or silicon step by step, and the intermediate product is MoO2. At 1000 °C, molybdenum trioxide could be reduced to metal Mo by aluminum, and in the presence of CaO, metal Mo as the reduction product appears even at 800 °C. In contrast, silicon could barely reduce molybdenum trioxide to metal Mo even at 1200 °C. In the presence of CaO or CaCO3, reducibility of silicon increases significantly, and the reduction products are metal Mo and MoSi2. Altogether, CaO or CaCO3 performs two major roles in reduction process: restraining sublimation of MoO3 and decreasing the temperature of reducing MoO3 to metal Mo.

DTA/TGA study of molybdenum oxide reduction by Mg/Zn & Mg/C combined reducers at non-isothermal conditions

In this work the reduction mechanisms of molybdenum oxide by single (Mg, Zn, C) and complex (Mg/C, Mg/Zn) reducers are reported. It is revealed that in the case of Mg and Zn the reduction undergoes before Mg/Zn melting, i.e. by solid-state mechanism. Unlike these systems, in the case of carbon, a stepwise reduction takes place. First stage (<600°C) is exothermic and corresponds to MoO3→MoO2 reaction; next one is endothermic reduction (>900°C) of MoO2 to the mixture of Mo and Mo2C. When combined reducer is used, such as Zn/Mg, then before reduction process the Zn melts and reduction takes place by liquid–solid mechanism. In this case apart MoO2 (and MgO∗MoO2) MgZn2 also is formed. When the MoO3 is reduced by Mg/C mixture, the reduction process starts by carbon at 520–650°C forming MoO2. Next the Mg melts and molten Mg reduces MoO2 yielding Mo. Based on the results obtained by DTA/TGA investigations the effective activation energy values are calculated for reduction stages for all studied mixtures.

A study on mechanochemical behavior of MoO3–Mg–C to synthesize molybdenum carbide

The influence of Mg value in the MoO3–Mg–C mixture on the molybdenum carbide formation and the mechanism of reactions during mechanochemical process were investigated. In keeping with this aim, magnesium and carbon contents of the mixture were changed according to the following reaction: 2MoO3+(6−x) Mg+(1+x) C=(6−x) MgO+Mo2C+x CO. The value of x varied from 0 to 6. Differential thermal analysis (DTA) results for sample with stoichiometric ratio (x=0) revealed that in the early stage, carbon reduced the MoO3 to MoO2 and subsequently highly exothermic magnesiothermic MoO2 reduction occurred after magnesium melting. Also, it was indicated that the exothermic reaction temperature shifted to before magnesium melting in the 11h-milled sample (x=0) and all the exothermic reactions happened, simultaneously. According to the experimental findings, molybdenum carbide (Mo2C) was synthesized in the mixture powder with stoichiometric ratio (x=0) after 12h milling process and the type of reactions was mechanically induced self-sustaining reaction (MSR). However, at lower Mg content in the MoO3–Mg–C mixture (0<x≤2), the magnesiothermic reduction occurred in MSR mode and activated the carbothermal reaction. Further decrease in Mg value (2<x≤3) resulted in MSR mode magnesiothermic reaction and gradual carbothermal reduction. In samples with lower magnesium contents, partial molybdenum oxide reduction proceeded through a gradual mode magnesiothermic reaction.

Mo Powders Fabricated from MoO3 by Reduction in Hydrogen Gas

We studied the effect of temperature and reaction time by investigating the various temperatures and reaction times in the reduction of molybdenum oxide (MoO3) to molybdenum (Mo) powder in hydrogen gas. We also studied the effect of the reaction of reduction according to the various hydrogen gas flow rates. We surveyed the reduction from molybdenum oxide to molybdenum powder in hydrogen gas and checked two temperature ranges, one from 400℃ to 600℃ and the other from 700℃ to 900℃. We found that the reaction ratio of molybdenum oxide increased with an increasing temperature and also increased with an increasing reaction time, but hydrogen gas did not influence the reduction ratio of molybdenum oxide. We examined molybdenum powders fabricated by ball milling for two hours, using with X-ray diffraction (XRD) and a scanning electron microscopy (SEM).

Reduction of molybdenum oxide from steelmaking slags by pure liquid iron

The effects of reaction temperature, slag basicity and FeO concentration on the reduction of molybdenum oxide from steelmaking slags by pure liquid iron were investigated experimently. The reduction kinetics of molybdenum oxide by liquid iron was analysed. The reaction models were developed based on the condition that diffusion of [Mo] in liquid iron and CaMoO4 in slag is the control steps, respectively. These reaction models were tested using data from a series of experiments. The results indicate that under the present experimental conditions, the temperature and the FeO content, other than slag basicity, have some effects on the reduction of molybdenum oxide from steelmaking slags by pure liquid iron. Both the molybdenum oxide reduction rate and final reduction ratio increase with an increase of temperature and a decrease of FeO content. The diffusion of CaMoO4 in slag which dominated overall reduction process is the only one ratecontrolling step with its apparent activation energy 294 kJ/mol. The reduction of molybdenum oxide used directly as alloy additive can be further enhanced by strong stirring in the converter practice.

Self-sustaining reduction of MoO3 by the Mg–C mixture

Abstract The possibility of the molybdenum oxide (MoO3) reduction by the Mg–C mixture was investigated under the self-sustaining combustion regime. Thermodynamic analyses for the MoO3–xMg–yC system were performed. Optimal ranges of x and y coefficients to ensure complete reduction of MoO3 to metallic molybdenum were found. The influence of x and y values on the process parameters (e.g. temperature, front propagation velocity), phase composition and the structure of products were investigated experimentally. Optimum reduction conditions of MoO3 to fine (1–3 μm) molybdenum powder were defined. Possible mechanism of the molybdenum oxide reduction to metallic molybdenum was proposed.