Showing papers on "Molybdenum published in 2000"
TL;DR: The hemicylindrical wires prepared by this technique were self-uniform, and the wires prepared in a particular electrodeposition (in batches of 10(5) to 10(7)) were narrowly distributed in diameter.
Abstract: Metallic molybdenum (Moo) wires with diameters ranging from 15 nanometers to 1.0 micrometers and lengths of up to 500 micrometers (0.5 millimeters) were prepared in a two-step procedure. Molybdenum oxide wires were electrodeposited selectively at step edges and then reduced in hydrogen gas at 500°C to yield Moo. The hemicylindrical wires prepared by this technique were self-uniform, and the wires prepared in a particular electrodeposition (in batches of 105 to 107) were narrowly distributed in diameter. Wires were obtained size selectively because the mean wire diameter was directly proportional to the square root of the electrolysis time. The metal nanowires could be embedded in a polystyrene film and lifted off the graphite electrode surface. The conductivity and mechanical resiliency of individual embedded wires were similar to those of bulk molybdenum.
570 citations
Patent•
23 Feb 2000TL;DR: In this article, a method of forming a metal layer having excellent thermal and oxidation resistant characteristics using atomic layer deposition is provided, where the metal layer includes a reactive metal (A), an element (B) for the amorphous combination between the reactive metal and nitrogen (N), and nitrogen(N).
Abstract: A method of forming a metal layer having excellent thermal and oxidation resistant characteristics using atomic layer deposition is provided. The metal layer includes a reactive metal (A), an element (B) for the amorphous combination between the reactive metal (A) and nitrogen (N), and nitrogen (N). The reactive metal (A) may be titanium (Ti), tantalum (Ta), tungsten (W), zirconium (Zr), hafnium (Hf), molybdenum (Mo) or niobium (Nb). The amorphous combination element (B) may be aluminum (Al), silicon (Si) or boron (B). The metal layer is formed by alternately injecting pulsed source gases for the elements (A, B and N) into a chamber according to atomic layer deposition to thereby alternately stack atomic layers. Accordingly, the composition ratio of a nitrogen compound (A—B—N) of the metal layer can be desirably adjusted just by appropriately determining the number of injection pulses of each source gas. According to the composition ratio, a desirable electrical conductivity and resistance of the metal layer can be accurately obtained. The atomic layers are individually deposited, thereby realizing excellent step coverage even in a complex and compact region. A metal layer formed by atomic layer deposition can be employed as a barrier metal layer, a lower electrode or an upper electrode in a semiconductor device.
544 citations
TL;DR: In this article, the current topics of catalysts containing niobium and tantalum, especially in the field of solid acid catalysis and selective oxidation of hydrocarbons are reviewed.
184 citations
TL;DR: The synthesis of high surface area carbide and nitride materials from binary and ternary oxides of vanadium, niobium, tantalum, molybdenum, and tungsten was studied in this article.
Abstract: The synthesis of high surface area carbide and nitride materials from binary and ternary oxides of vanadium, niobium, tantalum, molybdenum, and tungsten, suitable for use as catalysts for a wide ra...
168 citations
Patent•
30 Jun 2000TL;DR: In this article, a process for depositing at least one layer based on tungsten and/or on molybdenum by chemical vapor deposition on a non-conductive substrate, such as glass, ceramic, glass-ceramic, or polymer, is described.
Abstract: The present invention is directed to a process for depositing at least one layer ( 3 ) based on tungsten and/or on molybdenum by chemical vapor deposition on a non-conductive substrate ( 1 ), such as glass, ceramic, glass-ceramic, or polymer, which includes providing at least one tungsten- and/or molybdenum-containing precursor in the form of a metal halide and/or of an organometallic compound, and at least one reducing agent, such as hydrogen or silane, to form the at least one metal layer. The present invention also relates to the substrate obtained by the preceding process and its applications, especially for producing a glazing, mirrors, or emissive screens.
167 citations
TL;DR: In this paper, a molybdenum phosphide catalyst was prepared from an aqueous solution of NH4 6Mo7O24·4H2O and NH4 2HPO4 by precipitation, calcination, and subsequent reduction in H2 at 923 K.
156 citations
TL;DR: In this article, the synthesis of high surface area molybdenum carbides from butane and butane has been studied via temperature-programmed reaction (TPRe), X-ray diffraction (XRD), scanning electron microscopy (SEM), 13C solid-state NMR, infrared (IR), and Raman spectroscopy (LR).
Abstract: The synthesis of high surface area molybdenum carbides from molybdenum oxide and butane has been studied via temperature-programmed reaction (TPRe), X-ray diffraction (XRD), scanning electron microscopy (SEM), 13C solid-state NMR, infrared (IR), and Raman spectroscopy (LR) The molybdenum oxygen/carbon system passes through four phase transitions before transforming into the pure Mo2C carbide Carbon exists in two forms within high surface area molybdenum carbide The initially produced molybdenum carbide has a face-centered-cubic (fcc) structure but is gradually converted into the hexagonal-close-packed (hcp) structure with increasing carburization temperature, and eventually at high temperature coke is deposited During the early stages, MoO3 is reduced by H2, but at higher temperatures, butane also takes part in the reduction and, besides being consumed in the formation of carbide, is catalytically converted into methane, ethane, propane, and benzene The high surface area of the molybdenum carbide mat
141 citations
TL;DR: A series of zirconia supported molybdenum catalysts were prepared and characterized by BETSA, XRD, TPR, FTIR, XPS and oxygen chemisorption as mentioned in this paper.
Abstract: A series of zirconia supported molybdenum catalysts were prepared and characterized by BETSA, XRD, TPR, FTIR, XPS and oxygen chemisorption. Thiophene, cyclohexene and tetrahydrofuran were taken as model compounds for evaluating their hydrodesulfurization (HDS), hydrogenation (HYD) and hydrodeoxygenation (HDO) activities, respectively. The XRD results indicate that Mo is present as a monolayer up to 6 wt.% loading, whereas MoO3 crystalline growth is observed beyond this loading. O2-uptake and catalytic activities also increase up to 6 wt.% Mo-loading but above this loading both start decreasing. There are good correlations between O2 uptake and all catalytic activities. TPR and FTIR results indicate that at lower loading, MoO3 is present as tetrahedra form and at moderate loading, both tetrahedral and octahedral forms are found. XPS results reveal that the electron transfer is taking place from support to molybdenum.
123 citations
TL;DR: The conditions for the heterologous expression of both untagged and His-tagged human sulfite oxidase in Escherichia coli have been optimized, and high levels of enzyme activity and molybdenum incorporation were maintained despite the increase in yield.
119 citations
TL;DR: In this article, the hydrotreatment of a petroleum residue in the presence of dispersed molybdenite was carried out within a wide range of operating conditions and catalyst loading.
Abstract: The hydrotreatment of a petroleum residue in the presence of dispersed molybdenite was carried out within a wide range of operating conditions and catalyst loading. The effect of reaction severity as well as of molybdenum concentration on product distribution and quality was studied. Based on the experimental results, a simplified reaction scheme was proposed. The hydroprocessing of the residue was described in terms of the competition between two reactions: the direct conversion of the feedstock to distillate and coke, and the catalytic hydrogenation. Compared to thermal conditions, the presence of dispersed molybdenite controls very well coke formation; however, a trend of increasing formation of solids was observed at high catalyst concentrations. The overall upgrading of the feedstock requires significant amounts of molybdenum as well as relatively high hydrogen pressure.
119 citations
TL;DR: In this paper, quantum calculations at the B3LYP level have been carried out to elucidate the reaction mechanism of the epoxidation of ethylene with the molybdenum diperoxo complex MoO(O2)2OPH3.
Abstract: Quantum-chemical calculations at the B3LYP level have been carried out to elucidate the reaction mechanism of the epoxidation of ethylene with the molybdenum diperoxo complex MoO(O2)2OPH3. All rele...
10 Mar 2000
TL;DR: A series of zirconia supported molybdenum catalysts were prepared and characterized by BETSA, XRD, TPR, FTIR, XPS and oxygen chemisorption as mentioned in this paper.
Abstract: A series of zirconia supported molybdenum catalysts were prepared and characterized by BETSA, XRD, TPR, FTIR, XPS and oxygen chemisorption. Thiophene, cyclohexene and tetrahydrofuran were taken as model compounds for evaluating their hydrodesulfurization (HDS), hydrogenation (HYD) and hydrodeoxygenation (HDO) activities, respectively. The XRD results indicate that Mo is present as a monolayer up to 6 wt.% loading, whereas MoO 3 crystalline growth is observed beyond this loading. O 2 -uptake and catalytic activities also increase up to 6 wt.% Mo-loading but above this loading both start decreasing. There are good correlations between O 2 uptake and all catalytic activities. TPR and FTIR results indicate that at lower loading, MoO 3 is present as tetrahedra form and at moderate loading, both tetrahedral and octahedral forms are found. XPS results reveal that the electron transfer is taking place from support to molybdenum.
TL;DR: The pore surface of MCM-48 mesoporous silica was functionalized with tungsten and molybdenum metal centers by the anhydrous reaction of metal alkoxides with surface silanol groups.
Abstract: The pore surface of MCM-48 mesoporous silica was functionalized with tungsten and molybdenum metal centers by the anhydrous reaction of metal alkoxides with surface silanol groups. Resulting metal−oxo species were attached via covalent M−O−Si bonds as confirmed with photoacoustic (PAS)-FTIR. Diffuse reflectance UV−visible spectroscopy indicates that the metal oxo groups are predominantly comprised of tetrahedral and octahedral coordinated monomers. MCM-48 grafted with Mo and W is active for brominating phenol red with hydrogen peroxide at neutral pH in a manner similar to Ti−MCM-48, as we reported earlier. The rates of bromination for Mo, W, and four other metals, after normalization for metal concentration, measured as absorption peak intensities of the resultant bromophenol blue, are as follows: 50:46:16:2.8:1:0 W:Mo:Ti:Zr:V:Re. The different rates of reactivity, and hence the general degree of metal−peroxo activation, can be explained on the basis of size, charge, coordination sphere, and electronegat...
TL;DR: It seems that the strong enrichment of oxidized chromium and Mo in the passive layer, andStrong enrichment of Mo and depletion of iron at the metal surface underneath the Passive layer, are responsible for the outstanding corrosion resistance of orthopedic stainless steel in physiological solution.
Abstract: The passive film formed by electrochemical oxidation on two different stainless steels differing in molybdenum (Mo) content in physiological solution with and without the addition of complexing agent, i.e., citrate, was studied using X-ray photoelectron spectroscopy. The alloys were polarized at different oxidation potentials in the electrochemical chamber attached to the spectrometer. Thus, the composition of the film formed by oxidation was analyzed by X-ray photoelectron spectroscopy without prior exposure to air (quasi in situ). The passive film formed in physiological solution consists of two predominant oxides, i.e., chromium and iron oxides. Oxides of alloying elements nickel and Mo are also detected in the film. It seems that the strong enrichment of oxidized chromium and Mo in the passive layer, and strong enrichment of Mo and depletion of iron at the metal surface underneath the passive layer, are responsible for the outstanding corrosion resistance of orthopedic stainless steel in physiological solution. Commercial AISI 304 is not suitable for orthopedic applications. The addition of complexing agent affects significantly the passivation behavior of orthopedic stainless steel, because it changes the distribution of the elements within the passive layer and at the metal surface underneath.
TL;DR: In this paper, a molybdenum oxycarbide (MoO2.42C0.23H0.78) was characterized by means of diffraction techniques and simulations.
TL;DR: In this paper, two forms of molybdenum carbide: the stable hexagonally close packed (hcp) structure β-Mo 2 C and the metastable face centered cubic (fcc) structure α-MoC 1− x can be prepared by controlled preactivation in hydrogen or hydrogen/hydrocarbon mixtures, at moderate temperature (623 K), of MoO 3.
Abstract: There exist two forms of molybdenum carbide: the stable hexagonally close packed (hcp) structure β-Mo 2 C and the metastable face centered cubic (fcc) structure α-MoC 1− x . Bulk fcc α-MoC 1− x can be prepared by controlled preactivation in hydrogen or hydrogen/hydrocarbon mixtures, at moderate temperature (623 K), of MoO 3 . Fcc structure molybdenum oxyhydride or molybdenum oxycarbide are initially formed, respectively, by a topotactic transformation and they can be further carburized to yield fcc α-MoC 1− x . However, zeolite-supported α-MoC 1− x cannot be prepared by this route when hydrogen is used, probably as a result of MoO 3 -zeolite interactions or a too small size of the MoO 3 crystals which facilitate the reduction of MoO 3 to MoO 2 . Carbon stabilization, leading to the fcc structure oxycarbide is necessary, which can be achieved by activating MoO 3 with a hydrogen/ n -butane mixture at 623 K. The latter is then easily carburized to yield fcc α-MoC 1− x . Molybdenum carbide species were identified to be active components in Mo-modified catalysts used for the direct dehydroaromatization of methane. The catalytic performance of HZSM5 modified by either hcp β-Mo 2 C, the classical catalyst well described in the literature, and fcc α-MoC 1− x , the new catalytic system we prepared, have been compared. The latter shows superior performance: higher activity, higher selectivity to benzene, and higher stability as a function of time-on-stream.
TL;DR: In this paper, it was shown that rhodium(II) monocarboxylate bridged by pyrazine form stable micropores by self-assembly of infinite linear chain complexes.
TL;DR: In this article, the effects of partial substitution of tungsten for molybdenum on the microstructure and impact properties in 22Cr-5Ni-3Mo (wt-%) duplex stainless steel (DSS) have been investigated following aging heat treatments in the temperature range 600-1000°C.
Abstract: The effects of partial substitution of tungsten for molybdenum on the microstructure and impact properties in 22Cr–5Ni–3Mo (wt-%) duplex stainless steel (DSS) have been investigated following aging heat treatments in the temperature range 600–1000°C. During aging the intermetallic σ and χ phases were precipitated, and the impact toughness was significantly decreased with an increase in the σ phase content. The χ phase had been precipitated on the α/γ boundary in the early stages of aging. Ferrite and χ phases in tungsten substituted duplex stainless steel contain a large amount of tungsten, and their decomposition rates are much lower compared with those in steel containing only molybdenum. Consequently, the precipitation of the σ phase is retarded in tungsten substituted DSSs, which results in high impact toughness. However, after aging for a long time, the α and χ phases transformed to the σ and austenite phases in the tungsten substituted steels, and the steels showed low impact toughness.
TL;DR: In this article, C-promoted cobalt molybdenum bimetallic nitride (Co3Mo3N) was synthesized by nitridation of cobalt mixture with ammonia at 973K and was stable and more active for ammonia synthesis (15 mmol h−1g−1) at 673 K under 3.1 MPa (N2 + 3H2).
Abstract: Cs promoted cobalt molybdenum bimetallic nitride (Co3Mo3N) synthesized by nitridation of cobalt molybdate hydrate with ammonia at 973K was stable and more active for ammonia synthesis (15 mmol h−1g−1) at 673 K under 3.1 MPa (N2 + 3H2) than a doubly promoted iron catalyst.
TL;DR: In this article, molybdenum silicide was non-electrolytically coated in the molten salt, where a disproportion reaction occurs between the salt composed of NaCl-KCl-NaF-Na 2 SiF 6 -SiO 2 and the Si powder Hexagonal MoSi 2 was formed as single phase with homogeneous thickness of tens of μm above 1073 K.
TL;DR: In this paper, the authors measured the oxidation, volatilization and re-deposition of molybdenum from TZM in flowing air between 400 and 800 C.
TL;DR: In this paper, the AM1 scheme extended to d orbitals, AM1/d, has been parametrized for molybdenum compounds and compared with experimental data.
Abstract: The AM1 scheme extended to d orbitals, AM1/d, has been parametrized for molybdenum. Computational results on structures and energetics of a series of molybdenum compounds are compared with experimental data. The mean absolute error of bond lengths is 0.044 A (83 comparisons) and that of X−Mo−Y angles is 3.3° (65 comparisons). The mean absolute error of heats of formation amounts to 6.5 kcal/mol (50 comparisons). This assessment demonstrates the good performance of AM1/d. Thus, the proposed method may be used for computing structural parameters as well as heats of formations, reaction enthalpies, and bond energies of rather large inorganic and organometallic compounds of molybdenum.
TL;DR: In this article, high resolution transmission electron microscopy (HRTEM) was used in the study of the structure of carbon deposits obtained on Ni/Al2O3 and Ni-Mo/Al 2O3 catalysts during steam reforming of n-butane.
TL;DR: In this paper, radio frequency (RF) sputtering from a metallic molybdenum target in a reactive atmosphere and by the sol-gel (SG) technique using moly bdenum ethoxide solutions have been examined.
Abstract: MoO3 thin films have been deposited on alumina substrates by radio frequency (RF) sputtering from a metallic molybdenum target in a reactive atmosphere and by the sol–gel (SG) technique using molybdenum ethoxide solutions. The as-deposited RF films have been annealed at 500°C for 1 h, while the SG films have been annealed at temperature range between 400°C and 700°C for 1 h. The formation of a well-developed nanoparticle structure for the RF films with respect to the SG ones was suggested by scanning electron microscopy (SEM) characterisation. X-ray diffraction (XRD) has confirmed the formation of crystalline orthorhombic MoO3 structures (JCPDS 5-508) for both the RF and SG films after annealing. The gas sensing properties towards CO have been examined. MoO3-based gas sensors developed are capable of CO down to few ppm with a very fast response.
TL;DR: A new class of chiral molybdenum and tungsten(VI) complexes of the type MO2L*2 (M=Mo, W; L*=chiral 2′-pyridinyl alcoholate), available through several synthetic pathways, and their catalytic behavior in the asymmetric epoxidation of unfunctionalized olefins are reported in this paper.
TL;DR: The solid-state reaction for condensation of {(Mo)Mo 5 } 12 Fe 30 giant spheres commences through the water ligands and leads to oxo (or hydroxo) bridging.
Abstract: The by no means trivial, solid-state reaction for the condensation of {(Mo)Mo 5 } 12 Fe 30 giant spheres commences through the water ligands and leads to oxo (or hydroxo) bridging. As the discrete icosahedral units approach each other, their oxygen atom bridges ultimately form covalent bonds (Fe-Fe 3.79 A , see picture) to result in a symmetric layered structure.
TL;DR: In this paper, the structure of a nickel-base, self-fluxing alloy coating, containing chromium and boron thermal sprayed and fused, was investigated by x-ray diffraction (XRD), scanning electron microscopy (SEM), electron probe microanalysis (EPMA), and transmission electron microscope (TEM).
Abstract: The structure of a nickel-base, self-fluxing alloy coating, containing chromium and boron thermal sprayed and fused, was investigated by x-ray diffraction (XRD), scanning electron microscopy (SEM), electron probe microanalysis (EPMA), and transmission electron microscopy (TEM). A lumpy M6C carbide, a rodlike M3B2 boride of tetragonal structure, a rodlike M7C3 carbide of hexagonal structure, and a Ni-Ni3B eutectic phase formed in the coating after fusing. Metals of M6C, M3B2, and M7C3 phases are composed of chromium, molybdenum, and nickel; chromium and molybdenum; and mainly chromium, respectively. The nickel phase in the coating has the L12 type superlattice structure.
TL;DR: In this article, dilute rhenium additions (7 and 14 wt%) to ODS molybdenum were evaluated to determine their effect on low temperature ductility.
Abstract: Oxide dispersion strengthened (ODS) molybdenum alloys being developed for high temperature applications possess excellent high temperature strength and creep resistance. In addition they exhibit a ductile-to-brittle transition temperature (DBTT) in the worked and stress-relieved condition under longitudinal tensile load well below room temperature. However, in the recrystallized condition, the DBTT may be near or above room temperature, depending on the volume fraction of oxide dispersion and the amount of prior work. Dilute rhenium additions (7 and 14 wt%) to ODS molybdenum were evaluated to determine their effect on low temperature ductility. The addition of 7 wt% rhenium to the ODS molybdenum did not significantly enhance the mechanical properties. However, the addition of 14 wt% rhenium to the ODS molybdenum resulted in a DBTT well below room temperature in both the stress-relieved and recrystallized condition. Additionally, the tensile strength of ODS Mo-14 Re is greater than the base ODS molybdenum at 1000–1250°C.