Increasing Molybdenum Content Research Articles

Molybdenum-Doped ZnO Thin Films Obtained by Spray Pyrolysis.

A batch of ZnO thin films, pure and doped with molybdenum (up to 2 mol %), were prepared using the spray pyrolysis technique on glass and silicon substrates. The effect of molybdenum concentration on the morphology, structure and optical properties of the films was investigated. X-ray diffraction (XRD) results show a wurtzite polycrystalline crystal structure. The average crystallite size increases from 30 to 80 nm with increasing molybdenum content. Scanning electron microscopy (SEM) images demonstrate a smooth and homogeneous surface with densely spaced nanocrystalline grains. The number of nuclei increases, growing over the entire surface of the substrate with uniform grains, when the molybdenum concentration is increased to 2 mol %. The estimated root mean square (RMS) roughness values for the undoped and doped with 1 mol % and 2 mol % of ZnO thin films, defined by atomic force microscopy (AFM), are 6.12, 23.54 and 23.83 nm, respectively. The increase in Mo concentration contributes to the increase in film transmittance.

Electrocatalytic behavior of Ni–Mo alloy electrodeposited from deep eutectic solvents-assisted plating baths: electrochemical impedance spectroscopy study

The electrocatalytic behavior of electrodeposited Ni and Ni–Mo alloy coatings in the hydrogen evolution reaction in a 1 M NaOH aqueous solution was investigated by means of the electrochemical impedance spectroscopy method. The electrochemical deposition of electrocatalytic coatings was carried out using electrolytes based on deep eutectic solvents (eutectic mixtures of choline chloride with ethylene glycol or urea). To simulate the recorded Nyquist plots reflecting the electrocatalytic performance of deposited coatings, a modified Armstrong-Henderson equivalent circuit was employed, which accounts for the involvement of adsorbed intermediates in the reaction. The equivalent circuit included three polarization resistances and three constant phase elements, allowing for the consideration of the localization of the electrochemical process on different surface microdomains. It was found that the electrocatalytic activity of nickel coatings deposited from deep eutectic solvents exceeded the activity of nickel fabricated in an aqueous electrolyte. The increase in molybdenum content in the coating was shown to enhance electrocatalytic activity. It was established that the main reasons for improving the electrocatalytic properties of the Ni–Mo alloy coatings are structural-morphological factors (increase in the degree of microheterogeneity of the surface and the development of the surface area available for electrochemical reaction) and the formation of a favorable electronic structure of the metal, leading to the acceleration of the rate-determining Volmer step.

Properties of high-strength complex-alloy steel for casing pipes in cold-resistant and corrosion-resistant versions

The influence of alloying on the properties of high-tempered steels used for the production of casing pipes has been studied. It has been shown that an increase of molybdenum content from 0.15 to 0.53% provides a noticeable increase of the mechanical characteristics in chromium-molybdenum steels after tempering at 600‒690 °C. Alloying with vanadium and niobium contributes to an additional increase in strength properties. The influence of vanadium on the highly viscoplastic properties of steels is shown. It has been established that the greatest strengthening of steel with 0.32% molybdenum in a highly tempered state is provided by complex alloying with niobium and vanadium. The influence of austenitization and tempering temperature on the structure and properties, including resistance to cracking in an environment saturated with hydrogen sulfide, of chromium-molybdenum steel grade 26CrMoVNb-2 with micro-alloying additives of vanadium and niobium was determined. Alloying with molybdenum, vanadium and niobium makes it possible to obtain steels for high-strength casing pipes that are resistant to brittle fracture and sulfide stress corrosion cracking, subject to comprehensive consideration of the main factors such as austenitization temperature, tempering temperature and duration, dispersion and homogeneity of microstructure

ELECTRODEPOSITION OF THIN MOLYBDENUM COATINGS FROM SULPHATE SOLUTIONS

Based on the study of current-voltage dependencies during electroreduction of molybdenum ions from sulfate electrolytes on Pt electrode, the conditions of deposition of Mo-nanocoatings were established. The influence of various factors such as temperature, content of components in the electrolyte, current density, acidity of solutions, etc., on the composition and quality of coatings was studied. It was found that, with an increase in the concentration of molybdenum and current density, the molybdenum content increases and the quality of coatings improves. Based on the determination of the nature of the cathodic polarization, it was found that the process of electrodeposition of molybdenum from sulfate electrolyte is mainly accompanied by chemical polarization. According to the experimental data, the following electrolyte composition (mol/l) is recommended for obtaining molybdenum nanocoatings: 2.0·10-2– 1.5·10-3 Na2MoО4 +2.0 H2SO4; pH=0.4; EV=0,005 Vs-1; t=750C, electrod – Pt

Corrosion resistant behaviour of titanium – Molybdenum alloy in sulphuric acid environment

The present work focuses on the corrosion prevention behaviour of pure titanium metal (Ti) and its alloy with various percentages of molybdenum (Mo) in sulphuric acid environment. The alloying of pure Ti was made using 5, 10, 15% of Mo and their corrosion resistance in acidic environment was evaluated by electrochemical techniques namely potentiodynamic polarization and electrochemical impedance spectroscopy (EIS). The effectiveness of the alloy in improving the corrosion resistance was monitored by means of Nyquist and Bode plots resulted from impedance studies. Potentiodynamic polarization studies were also carried out for the pure Ti metal and its alloy with different concentration of Mo in acid environment. The data resulted from the above two electrochemical studies reveal that Ti 85- Mo 15 was found to offer the maximum corrosion resistance than pure Ti and its other alloys with Mo. It was also interesting to note that with increase in molybdenum content the corrosion resistance of the Ti alloy kept on increasing.

Corrosion of austenitic stainless steels and nickel-based alloys in concentrated phosphoric acid at elevated temperatures

The corrosion sensitivity of several austenitic stainless steels (316L, 316Ti, Sanicro28, Sanicro35) and nickel-based alloys (Hastelloy G30 and Hastelloy G35) was determined at elevated temperatures in food grade phosphoric acid (FGPA). The materials were submerged in a harsh environment of >85 wt% FGPA at temperatures ranging from 80 to 160°C. The main aim was to understand the corrosion phenomena occurring in such environment and define the temperature range for which corrosion is within acceptable limits for these materials. Moreover, the role of a material's chemical composition on the corrosion resistance in phosphoric acid was experimentally elucidated. The corrosion sensitivity was determined by weight loss measurements, scanning electron microscopy and energy dispersive X-ray spectroscopy. The high concentrations of alloying elements in the selected metals allow them to form a protective passive surface film, which inhibits further oxidation. Depending on the stability of the passive film, materials will be corrosion resistant up to higher temperatures. Alloys with an increased molybdenum content showed a higher general and pitting corrosion resistance up to 140°C. Moreover, copper alloying resulted in an improved corrosion resistance at higher temperatures.

Microstructure and Mechanical Properties of the ((CoCrFeNi)95Nb5)100−xMox High-Entropy Alloy Coating Fabricated under Different Laser Power

In this paper, the ((CoCrFeNi)95Nb5)100−xMox (x = 1, 1.5 and 2) high-entropy alloy (HEA) coatings were fabricated on the substrate of 45# steel by laser cladding process under different laser beam power. The influence of laser beam power and molybdenum element content on the microstructure and microhardness of the HEA coatings was investigated. Results show that the HEA coatings were composed of face-centered cubic (FCC) phase and Laves phase, had low porosity, and bonded well to the substrate. The Mo1 coating is composed of cellular dendritic structures and columnar dendritic structures. With the increase of molybdenum element content, the columnar dendritic structures disappeared, the grains are refined, and the arrangement of grains is more compact. The volume fraction of the interdendritic phase under the laser beam power of 800 W was small and irregular. After the laser beam power was increased to 1000 W, the volume fraction of the interdendritic phase was increased. Under the laser beam power of 1200 W, the volume fraction of the interdendritic phase was small again. Therefore, the coatings fabricated under the laser beam power of 1000 W had a larger volume fraction of the interdendritic phase and higher microhardness. With the increase in molybdenum content, the grain changed from columnar dendrite to cellular dendrite, and the microhardness of the coating increased. The characteristics of the laser cladding process, the formation of Laves phase, and the fine grain strengthening lead to high microhardness of the coatings.

The effect of molybdenum on the microstructure and mechanical behaviour of the sintered Fe-Mo-Mn-Si-C composite

Experimental sintered Fe-Mo-Mn-Si-C composites were prepared from 3 different pre-alloyed Fe-Mo-Mn powders, namely Fe-0.50Mo-0.15Mn, Fe-0.85Mo-0.15Mn and Fe-1.50Mo-0.15Mn, mixed with fixed 4 wt.% silicon carbide powder. Sintered Fe-SiC composite was also prepared, as a reference material, from pure Fe powder mixed with fixed 4 wt.% silicon carbide powder. All specimens were processed by using the ‘press and sinter’ method. Sintering was performed in a vacuum furnace at 1250ºC for 45 minutes and slow cooling in the furnace. The microstructures of most sintered alloys showed a common feature consisting of a black particle enveloped with ferrite and pearlite. Sintered composites produced from high-molybdenum powders showed different matrices, in which some pearlite regions were replaced by BF/M- A structures. The Tensile and hardness test showed that the sintered alloys exhibited an increase of tensile strength, yield strength, and hardness with increasing molybdenum content. The pearlite + BF/M-A fractions of sintered composites played important roles in material strengthening. In the sintered composites produced from high-molybdenum powders, the carbide-free BF/M-A structure showed a promising strengthening effect.

The influence of phosphorus substitution by molybdenum on the chemical composition and certain properties of the zinc metaphosphate glass

xMoO3-50ZnO-(50-x)P2O5, i.e. (1-x/50)Zn(PO3)2-(x/50)ZnMoO4, glasses were prepared up to x = 25. It has been proved that the glasses are not a mixture of boundary components, but that chemical reactions taking place in the melt during synthesis produce in equilibrium a more complicated chemical mixture. Molybdenum is incorporated into the glass structure as a molybdate(2-) and also as complex cations, a colorless molybdenyl MoO4+ (d0 system) and blue colored MoO3+ (d1). The chemical model of the studied glasses was designed indicating that the glassy matrix gradually changes with increasing molybdenum content from pure anionic metaphosphate to the cationic-anionic network with the help of molybdenyl cation strongly bonded by four covalent donor-acceptor bonds with non-bonding phosphate oxygens. The compositional dependencies of some physical properties agree with the proposed chemical model. The melts or glasses of chemical compositions near the glass-forming border are less stable and immiscibility of glass phases was found.

Microstructure and Properties of Oil and Gas Range Pipe Steel Subjected to Improvement

The effect of alloying on the properties of highly tempered steels used for production of a range of petroleum pipes is studied. It is shown that an increase in molybdenum content from 0.15 to 0.53% improves the mechanical characteristics of chromium-molybdenum steels tempered at 600–690°C significantly. Alloying with vanadium and niobium facilitates an additional increase in strength properties. The best hardening of steel with 0.32% molybdenum in a highly tempered condition is provided by combined microalloying with niobium and vanadium, although stress corrosion cracking resistance is reduced.

Steam reforming of toluene as model of tar compound over Mo catalysts derived from hydrotalcites

This study evaluated the catalytic activity of Mo catalysts derived from hydrotalcite-like compounds for steam reforming of toluene as a model compound for tar. The catalysts with 1.5, 3 and 4.5 Mo loadings (wt%), denoted as Mo1.5MgAl, Mo3MgAl and Mo4.5MgAl respectively, were prepared by coprecipitation and characterized by BET, XRD, SEM, TEM, FT-IR and UV–VIS. The results showed that toluene conversion increased with increasing molybdenum content. The hydrogen amount depended on two factors: the presence of molybdate species on the surface and the presence of aluminum cations in tetrahedral sites (Mo3MgAl), with molybdenum influence being more pronounced. The H2/CO ratio decreased at increasing temperature while, the H2/CO2 ratio increased proportionally with temperature. Mo1.5MgAl catalyst was more selective for CO2 and H2, while, Mo3MgAl and Mo4.5MgAl were more selective for CO and H2.

Effect of Micro-Alloying with Boron and Niobium on Properties of Cr-Mn-Mo Steels

Economically alloyed steels for critical details of drill pipes have been studied. Effect of microalloying on structure and properties has been investigated. The article shows that boron and niobium additives change the structure and properties of Cr-Mn-Mo steels after quenching and high tempering. Methods of optical and electron microscopy have been used. Basic mechanical properties and impact strength of investigated steels are determined. Optical and electronic fractography has been carried out. The quantitative content of the ductile component is determined in steel fracture. It is shown that steel microalloying leads to a substantial structure refinement. This is due to the influence of niobium on the austenite grain value. An increase in the amount of carbide particles leads to structure refinement with an increased molybdenum content. Boron microadditives allow obtaining the tempered martensite structure throughout the product section. This provides an increase in both the strength and ductile properties. Combined microalloying of chromium-manganese-molybdenum steel with additions of boron up to 0.005 % and niobium up to 0.05 % makes it possible to increase the strength and reduce the tendency to brittle fractures significantly. The nature of the fracture becomes completely ductile. Distinct cleavage fracture surface feature “river patterns” are observed in unmodified steels. Сleavage facetes are large enough, it proves the presence of large grains in the steel. Microalloying changes the destruction mechanism, it becomes a ductile “dimple rupture”. An increase in the molybdenum content to 0.6 % makes it possible to obtain strength above 1100 MPa in microalloyed steel.

YÜKSEK KROMLU BEYAZ DÖKME DEMİRLERDE FAZ DENGESİNİN BENZETİMİ

In this study, using the Materials Calculator software program, the pseudo binary phase diagrams (i.e. isoplethal maps) of high chromium white cast irons (~19% in weight) with different molybdenum contents were simulated. In order to test the accuracy of the calculated phase diagrams, the transformation temperatures read from the diagrams at certain compositions were compared with the phase transformation temperatures measured using Differential Scanning Calorimetry (DSC) analysis of the samples produced by casting in the same composition followed by slow cooling. With the same purpose, low temperature phases read from the phase diagrams were compared with the crystalline phases determined by X-Ray Diffraction (XRD) of the casted samples. Simulated diagrams predicted an increase in the amount of secondary M 23 C 6 carbides with increasing molybdenum content. The validity of this prediction was tested by determining the phase distribution and phase compositions in the casted samples by means of metallographic examinations and Scanning Electron Microscopy (SEM) - Energy Dispersive Spectroscopy (EDS) analyzes. When the hardness values of the samples were taken into consideration, it was seen that the hardness increased from 44.90 to 51.05 HRC with a 1% increase in Mo content and a corresponding increase in the amount of secondary carbides without any heat treatments. Results show that theoretical predictions and experimental measurements are in accord and estimating phase equilibria in multi-component systems is of practical importance.

Sintered Fe-Mo-Si-C alloys with ductile cast iron microstructure

Sintered Fe-Mo-Si-C alloys, produced by admixing 4.0 wt.% silicon carbide to two different pre-alloyed powders with compositions of Fe-0.85Mo and Fe-1.5Mo, sintering at 1250 °C for 45 minutes and cooling in a vacuum furnace, showed a microstructure similar to that of a ductile cast iron. The microstructure of the sintered alloys was characterized by the bull’s eye structure consisting of a black particle surrounded by ferrite shell and harder shell of pearlite/bainite, respectively. With the influence of alloying element content in the pre-alloyed powders, the proportion of the harder shell, particularly the bainite fraction, increased with increasing molybdenum content. Due to the matrix hardenability via bainite formation by the molybdenum influence, tensile strength of the sintered alloys increased but elongation decreased with increasing molybdenum content.

Nanostructured magnetic films based on iron with refractory metals

Abstract The electrolysis modes affect on the quantitative and phase composition of the ternary Fe-Co-W and Fe-Co-Mo coatings is studied. It was established that the distribution of refractory components over the thickness of the coating varies in the opposite way with increasing duration of electrolysis – the molybdenum content increases and the tungsten one decreases. Amorphous-crystalline structure of alloys has been visualized by X-ray spectroscopy, including inter-metallic phases Co7W6, Fe7W6, Fe7Mo, Fe7Co, FeCo along with α-Fe and Fe3C. The size of coherent-scattering region of the amorphous part is of 6–8 nm. The formation of metallic tungsten and molybdenum additional phases has been detected for alloys deposited at pulse current which contributes microhardness Hμ increase up to 700 compared with direct current mode. Magnetic characteristics of Fe-Co-W(Mo) films were measured depending of deposition time. It was concluded that the content of magnetic phases in upper layers of Fe-Co-W deposits is higher than in the bottom ones and superior Fe-Co-Mo coatings. It qualitatively corresponds to W(Mo) content changes over the thickness.

Wear and corrosion performance of laser-clad low-carbon high-molybdenum Stellite alloys

Low-carbon Stellite alloys such as Stellite 21 exhibit good high-temperature and corrosion properties but need improved wear resistance in some applications. In this research, two low-carbon Stellite alloys with highly increased molybdenum content are produced via laser cladding. The microstructures of the laser cladding hardfacings are studied using scanning electron microscopy (SEM) with an energy dispersive X-ray (EDS) spectroscopy, and X-ray diffraction. The wear resistance of the hardfacings is evaluated using a pin-on-disc tribometer. The corrosion performance of the hardfacings is investigated under electrochemical tests in 3.5 wt.% sodium chloride (NaCl) solution and in Green Death solution. The experimental results show that the presence of Mo-rich intermetallic compounds enhances the wear resistance of the alloy hardfacings significantly. Since Stellite alloys are all able to form protective oxide films due to high chromium content against corrosion of the substrates, the bonding strength and repair ability of the oxide films dominate the corrosion resistance of the hardfacings in the corrosive environments. Stellite 21 hardfacing is also studied under the same testing conditions for comparison.

Mechanism for Improving the Mechanical Properties of Sintered Iron–Copper Composites Alloyed with Molybdenum

The structure of Fe–Cu composites after solid-phase and liquid-phase sintering was studied. It is shown that 2–10 wt.% molybdenum additions have an activating effect on the diffusion processes in densification, grain growth, and recrystallization, as well as on the amount and composition of copper and iron solid solutions. Molybdenum additions to 70 wt.% Fe–30 wt.% Cu composites simultaneously influence their strength and ductility properties. With increasing molybdenum content, the solubility of iron in copper decreases, promoting higher ductility of the composites, and the solid solutions of copper and molybdenum in iron preserve their strength characteristics. Solidphase sintering results in fine-grained FeCuMo samples with high relative density (up to 98.8%) and high ductility.

Single-phase mixed molybdenum-niobium carbides: Synthesis, characterization and multifunctional catalytic behavior in toluene conversion

Single-phase mixed molybdenum-niobium carbides were synthesized to establish structure–activity relationships. Precursors for carburization were obtained by hydrothermal synthesis or, to achieve high molybdenum content (metal fraction xMo=0.86), by flash-freezing of salt solutions and subsequent freeze-drying. Thermogravimetric and evolved gas analysis during carburization showed that bimetallic precursors were more easily reduced than monometallic ones; and as the niobium content increased, the removal of oxygen shifted to higher temperatures and from H2O to CO formation (from H2 or CH4, respectively), and the final carburization temperature rose from 650 to 950°C. Carbides crystallized in cubic NbC/MoC(cF8) structure for xNb≥0.38 and hexagonal Mo2C(hP3) structure for xNb≤0.14. After passivation, mixed metal carbides could be reduced at lower temperatures than Mo2C. With increasing molybdenum content of the carbides, CO uptake per gram increased, and turnover frequencies for hydrogenation of toluene to methylcyclohexane increased from 0 to 3.1s−1 (at a temperature of 250°C, 21bar pressure, and H2/toluene=36). At 400°C, mixed carbides with xNb≥0.38 were more selective toward acid-catalyzed products and less selective toward hydrogenolysis products than carbides with lower niobium content.

Electrochromism in sputter deposited W1-y MoyO3 thin films

Electrochromic (EC) properties of tungsten-molybdenum oxide (W1-y MoyO3) thin films were investigated. The films were deposited on indium tin oxide covered glass by reactive DC sputtering from tungsten and molybdenum targets. Elemental compositions of the W1-y MoyO3 films were determined by Rutherford back scattering. Voltammetric cycling was performed in an electrolyte of 1 M LiClO4 in propylene carbonate. An increase in molybdenum content in the EC films caused both a shift towards higher energies and a lowering of the maximum of the optical absorption band, as compared with WO3 EC films. Durability under electrochemical cycling was diminished for W1-y MoyO3 EC films.

Effects of Molybdenum on the Wear Resistance and Corrosion Resistance of Carbidic Austempered Ductile Iron

The effects of molybdenum on the microstructure, wear resistance, and corrosion resistance of carbidic austempered ductile iron were studied. The results show that the microstructures of as-cast samples are mainly composed of nodular graphite, pearlite and carbides, and the nodularization grade is 2–3 and graphite size is 6–7 magnitude in all samples. With the increase of Mo content, the amount of nodular graphite decreases, but the pearlite and carbides increase. The microstructures of all heat-treated samples mainly consist of nodular graphite, acicular ferrite, retained austenite, and a certain number of carbides. As the molybdenum content increases, the quantity of retained austenite and carbides increases, the acicular ferrite becomes finer, and the wear resistance and corrosion resistance increased. When the concentration of molybdenum reaches 0.570 wt%, the average wear weight loss decreased to 0.218 mg/m, the corrosion potential reached to −0.5626 V, and the corrosion current density decreased to 6.361 × 10−8 A/cm2.