Iron-molybdenum Alloys Research Articles

Effect of elemental composition on structure and corrosion resistance of electrolytic iron-based alloys

The article deals with the formation of electrolytic coatings taking into account the participation of basic components and elements of nonmetallic nature by the example of iron-phosphorus and iron-molybdenum alloys. The data of X-ray photoelectron spectroscopy of surface layers are presented, which confirm the presence of nonmetallic inclusions in the coatings under study. The influence of the structure being formed on the corrosion resistance of coatings is also studied.

Cover Picture: Materials and Corrosion. 6/2017

Cover:False‐coloured scanning electron micrograph of corrosion products (yellow) on a base material (blue) consisting of a binary iron molybdenum alloy after exposure to hydrogen sulfide containing solution. More detailed information can be found in: G. Genchev, C. Bosch, E. Wanzenberg, A. Erbe, Role of molybdenum in corrosion of iron‐based alloys in contact with hydrogen sulfide containing solution, Materials and Corrosion 2017, 68, page 595.

Carbon nanotube synthesis via the catalytic chemical vapor deposition of methane in the presence of iron, molybdenum, and iron–molybdenum alloy thin layer catalysts

In this study, we documented the catalytic chemical vapor deposition synthesis of carbon nanotubes (CNTs) using ferrocene and molybdenum hexacarbonyl as catalyst nanoparticle precursors and methane as a nontoxic and economical carbon source for the first time. Field emission scanning electron microscopy, energy dispersive X-ray spectroscopy, wavelength dispersive X-ray spectrometry and transmission electron microscopy of the thin layer catalyst as a simple and cost effective catalyst preparation after methane decomposition reaction, along with Fourier transform infrared spectroscopy and Raman spectroscopy confirmed the growth of CNTs, from bimetallic nanoparticles, which are converted into iron–molybdenum alloy nanoparticles at 700 °C for pretreatment by hydrogen after chemical vapor deposition of thin layers. An investigation of the weight percentages of the chemical elements present in the CNTs synthesized from iron–molybdenum catalyst using quartz sheet substrate at 750 °C, confirmed a significant carbon yield of 75.4% which represents high catalyst activity. Additionally, multi-walled carbon nanotubes (∼16–55 nm in diameter and 1.2 µm in length) were observed in the iron–molybdenum alloy sample after methane decomposition reaction at 750 °C for 35 min. To show the role of iron and molybdenum coated on silicon substrate as two thin layer catalysts, samples were considered for CNTs growth (diameter ∼47–69 nm) at 800 °C and 830 °C, respectively. Moreover, the effect of hydrogen pretreatment was evaluated in terms of active metal coating properly. The best graphitic structure due to Raman spectroscopy outcomes (ID/IG ratio) was obtained for iron coated on a quartz sheet, which was estimated at 0.8505. Thermogravimetric analysis proved the thermal stability of the synthesized CNTs using iron thin-layer catalyst up to 350 °C.

Role of molybdenum in corrosion of iron‐based alloys in contact with hydrogen sulfide containing solution

A sample iron molybdenum alloy with 3.4 wt% (2 at%) molybdenum, and pure iron, are exposed to hydrogen sulfide saturated saline solution for up to 56 days. In addition, their behavior under anodic polarization in the same electrolyte is investigated. The initially fast dissolution of the iron molybdenum alloy slows down significantly over time, while iron corrodes with a constant rate. The observed slow down of the corrosion rate can be described well with an exponential decay of the instantaneous corrosion rate with a time constant of (0.15 ± 0.03)/day, which implies stop in corrosion in practical terms after 2 weeks. Relationships are discussed between the instantaneous corrosion rate, and the time‐averaged integral corrosion rate. Dissolution under anodic polarization of the iron molybdenum alloy is slower than for pure iron. While at certain times, pyrite, FeS2, is found as corrosion product, the main corrosion product is mackinawite, FeS. The latter likely contains a certain fraction of molybdenum in case of the iron molybdenum alloy. On iron molybdenum, corrosion products forming a sealing layer are observed, which slow down further corrosion. The corrosion products on iron molybdenum show better adhesion to the base material surface.

On the reliability of powder diffraction Line Profile Analysis of plastically deformed nanocrystalline systems.

An iron-molybdenum alloy powder was extensively deformed by high energy milling, so to refine the bcc iron domain size to nanometer scale (~10 nm) and introduce a strong inhomogeneous strain. Both features contribute to comparable degree to the diffraction peak profile broadening, so that size and strain contributions can be easily separated by exploiting their different dependence on the diffraction angle. To assess the reliability of Line Profile Analysis, results were compared with evidence from other techniques, including scanning and transmission electron microscopy and X-ray small angle scattering. Results confirm the extent of the size broadening effect, whereas molecular dynamics simulations provide insight into the origin of the local atomic, inhomogeneous strain, pointing out the role of dislocations, domain boundaries and interactions among crystalline domains.

Electrodeposition of iron–molybdenum alloy from ammonium–citrate solutions and properties of produced materials

The structure and properties of Fe–Mo alloys is studied. It is shown that the iron–molybdenum alloys formed in the electrolysis are highly hydrogenated, and the content of hydrogen in them increases with increasing atomic fraction of molybdenum in the cathodic deposit. The kinetics of hydrogen evolution reaction in the alkaline solutions on the obtained materials is studied.

Chemical composition of Fe–Mo alloys obtained by electrodeposition

Iron–molybdenum alloys prepared by electrodeposition from ammonia-citrate solutions contain iron and molybdenum in metallic states and a large amount of sorbed hydrogen.

Development of TiB<sub>2</sub>-Based Cermets with Fe-Mo Binder

In this study, the wettability and interaction of TiB2with melted iron and iron-molybdenum alloys have been investigated. The wetting contact angles were determined, the structure and phase composition of the drops have been investigated by the methods of energy dispersive X-ray microanalysis. The results showed that TiB2–(Fe-13%Mo) system prove to be an optimum one for the new cermets production because of good wetting and minimal interaction between components. The TiB2-(Fe-13wt.%Mo) cermets were produced by sintering in vacuum. The influence of initial TiB2particles size on the structure formation of the cermets above has been established.

Synthesis and Characterization of a Self-Lubricating Film on Bearing Balls

In this work, the feasibility of using planetary ball milling for coating bearing balls with a self-lubricating film was investigated. Bearing balls with appropriate amount of MoS2 powder were put into vacuumed stainless steel vials and ball milled. With proceeding of ball milling, thickness of the self-lubricating film increased at first and then decreased. X-ray diffraction (XRD) and X-ray photoelectron spectrum (XPS) results revealed that the surface of the self-lubricating film was MoS2 and the inner region was a mixture of iron molybdenum alloys (Fe3Mo, FexMoy), MoS2 and FeS. Friction coefficient between the self-lubricating film and bear steel was 0.06~0.1.

Spin and charge density on iron nuclei in the BCC Fe–Mo alloys studied by 57Fe Mössbauer spectroscopy

Iron molybdenum alloys were prepared for the molybdenum concentration range 0–50 at.% by the arc melting method. X-ray diffraction patterns show single BCC phase for the Mo concentration up to 18 at.% with the lattice constant increasing upon addition of Mo. Sample with 21 at.% of Mo looks like composed of many BCC phases differing by the lattice constant. Finally, sample with 50 at.% of Mo looks like being composed of two BCC phases with various lattice constants and some amount of the non-stoichiometric λ-phase having symmetry P6 3/ mmc. Mössbauer data indicate random solutions up to 12 at.% of Mo with magnetic order at room temperature. Room temperature paramagnetic phase appears for the sample with 18 at.% of Mo and its content increases with the increasing concentration of Mo. Traces of magnetically ordered phase (at room temperature) are seen for the sample with 40 at.% of Mo. Sample with 50 at.% of Mo is paramagnetic at room temperature. Contributions to the hyperfine field and isomer shift on the iron nuclei have been determined as the function of the distance between iron nucleus and Mo impurity up to the third co-ordination shell within the single-phase random solution range. Mo atom as the nearest iron neighbor changes iron hyperfine field by −4.18 T, as the second neighbor makes change by −2.30 T and finally as the third neighbor changes the field by +0.51 T. Corresponding changes in the isomer shift are as follows: −0.033 mm/s, −0.005 mm/s and +0.003 mm/s. The average hyperfine field and the isomer shift decrease linearly versus Mo concentration at rates −0.383 T/at.% and −5.06 × 10 −4 mm/(s at.%), respectively. Hence, addition of Mo increases the electron density on the iron nucleus at the rate +1.7 × 10 −3 electron a.u. −3(at.%) −1.

Self-diffusion in iron-based Fe–Mo alloys

Tracer diffusion coefficients of 59Fe and 99Mo in high-purity iron–molybdenum alloys containing up to 1.8 at.% molybdenum have been determined in the temperature range 823–1173 K by use of a serial sputter-microsectioning technique. The diffusion coefficient of iron (solvent) increases with increasing molybdenum content, whereas the diffusion coefficient of molybdenum (solute) decreases. The influence of magnetic transformation on the diffusion of iron in the iron–molybdenum alloys decreases with increasing molybdenum content, while that on the diffusion of molybdenum in the alloys is a maximum at about 0.8 at.% molybdenum. Analysis of jump frequency ratios shows that a vacancy is weakly bound by a molybdenum atom.

Influence of the Catalyst Type on the Growth of Carbon Nanotubes via Methane Chemical Vapor Deposition

The preparation of the catalyst is one of the key parameters which governs the quality of carbon nanotubes (CNTs) grown by catalyzed chemical vapor deposition (CVD). We investigated the influence of three different procedures of catalyst preparation on the type and diameter of CNTs formed under identical growth conditions via methane CVD. In the first one, chemically synthesized colloidal iron oxide or iron molybdenum alloy nanoparticles were used, which were homogeneously deposited on silicon substrates by spin coating to prevent them from coalescence under CVD growth conditions. The obtained multiwall CNTs (MWNTs) exhibited diameters corresponding to the catalyst particle size, whereas no formation of single-wall CNTs (SWNTs) was observed. In the second method, commercial porous alumina nanoparticles were used in association with iron and molybdenum salts and the Fe/Mo catalyst was formed in situ. We determined that the alumina concentration significantly influenced the morphology of the catalyst and that below a critical value of the range of 1 g/L no CNTs were formed. While yielding nearly defect-free SWNTs, their diameter could not be controlled using this procedure, resulting in a large distribution of tube sizes. In a third, new preparation method, associating alumina and iron-based nanoparticles, SWNTs of a different size and narrower diameter distribution as compared to the second method were obtained. Our results are evidence of the essential role of alumina particles in the formation of SWNTs, and the newly developed method opens up a way to the synthesis of diameter-controlled SWNTs via catalyzed CVD.

Diffusion of molybdenum in high-purity iron-molybdenum alloys

Diffusion of molybdenum in high-purity iron-molybdenum alloys

Structure and hyperfine interactions in mechanosynthesized iron–molybdenum alloys

X-ray diffraction and Mössbauer spectroscopy were used to study the structure and hyperfine interactions in Fe80Mo20 and Fe50Mo50 prepared by mechanical alloying. Two solid solutions, i.e. Fe(Mo) and Mo(Fe) with b.c.c. lattice were formed during milling of Fe80Mo20. Mössbauer spectra revealed different magnetic arrangements in these solid solutions. In the case of Fe50Mo50 no amorphisation was observed, as literature data suggest. During mechanosynthesis of Fe50Mo50 a paramagnetic Mo(Fe) solid solution was probably formed.

Influence of molybdenum on the anodic dissolution of iron in acidic solutions

The anodic dissolution of pure iron and binary iron-molybdenum alloys (10 and 20 wt% Mo) in molar H2SO4 and HCl solutions was studied by d.c. polarization and a.c. impedance techniques. Molybdenum additive influences both the steady state polarization curves and the impedance spectra in the two media, the impact being stronger for the Fe-20 wt % Mo alloy. In general, two-slope polarization curves are obtained for the alloys; impedance spectra exhibit two time constants in addition to the charge transfer one implying the existence of two reaction intermediates. Differences between spectra measured in H2SO4 and HCl are discussed. A kinetic model advanced on the basis of literature data for pure iron and molybdenum was able to reproduce quantitatively both the steady state and a.c. impedance results for both alloys in the two media. Kinetic parameters for the anodic dissolution of Fe-Mo alloys are thereby determined.

アルミナ磁器と鉄・モリブデン合金の焼結接合

Joinning ceramic to metal without interlayer was tried using process from emulsifying of suspension to sintering. Alumina-kerosene suspension (0) was mixed with iron oxide-molybdenum-water suspension (W) and (W/O) emulsion was formed. After casting the emulsion, the (W)particles submerged to bottom due to difference in density between (O) and(W). The dried body was sintered in a reducing atmosphere and transformed to double layer consisting of alumina ceramic and iron-molybdenum alloy. At the area between these layers, protrusions of the alloy were locked in the alumina ceramic and this was considered to be a source of joint strength.

Effect of process conditions on ion nitrided sintered iron-molybdenum alloys : E. Stagno et al (University of Genoa, Genoa, Italy)

Effect of process conditions on ion nitrided sintered iron-molybdenum alloys : E. Stagno et al (University of Genoa, Genoa, Italy)

Theoretical analysis of co-reduced iron-molybdenum alloy powders

W-Cu composite materials with various molar ratio of constituent metals (W:Cu = 2:1 and 1:3) were synthesized via co-reduction of WO3 and CuO oxides precursors with Mg + C combined reducer in the combustion mode by applying reaction's thermo-kinetic coupling approach. The interaction mechanism and phase and microstructure formation laws in the 2WO3-CuO-yMg-xC and WO3-3CuO-yMg-xC quaternary systems were explored. According to experimental results obtained by stopped combustion front technique in bulk copper wedge, it was shown that firstly the copper oxide carbothermal reduction into copper and then magnesio-carbothermal reduction of the tungsten oxide into tungsten take place. It was revealed that the growth of C/Mg ratio leads to decrease both the combustion temperature and velocity conditioned by growth in the portion of low-caloric reaction and allows to control interaction conditions for the preparation of nanosized 2 W-Cu and W-3Cu composite powders. Combustion products obtained at optimum conditions represent as W-Cu nanocomposite powder with 30–50 nm in size.

Mechanical alloying (MA) of iron-molybdenum alloys : J. Kuyama et al. (Kyoto University, Kyoto, Japan.) J. Japan Soc. Powder and Powder Metallurgy, Vol 38, No 7, 1991, 910–913. (In Japanese.)

Mechanical alloying (MA) of iron-molybdenum alloys : J. Kuyama et al. (Kyoto University, Kyoto, Japan.) J. Japan Soc. Powder and Powder Metallurgy, Vol 38, No 7, 1991, 910–913. (In Japanese.)

Raman studies of corrosion films grown on Fe and Fe-6Mo in pitting conditions

Raman spectroscopy is used to identify the corrosion films grown on iron and iron-molybdenum alloy in presence of Cl − or SO 4 2−. Pure iron in pitting corrosion is covered by an inner spinel layer and an outer green rust layer. The Raman spectrum of green rust is given for the first time. When molybdenum is present in the alloy the green rust is less crystalline, and a molybdate layer is detected at the metal/film interface. The pitting seems to be associated with the presence of Mo 4+ in this inner layer, but in passive conditions the film contains FeMoO 4.