Showing papers on "Molybdenum published in 1986"

Energy conversion catalysis using semiconducting transition metal cluster compounds

Abstract: Semiconductors containing transition metal clusters within their crystal lattice have recently been proposed as catalysts for multi-electron transfer reactions. This is because of the expected action of the clusters as reservoirs for electronic charge carriers and sites for cooperative electron transfer at a reasonably constant electrochemical potential1,2. Here we report the first test of the capacity of such materials for oxygen reduction in an acid medium, for operation in fuel cells. The compound Mo4.2Ru1.8Se8, which contains octahedra statistically composed of 4.2 molybdenum and 1.8 ruthenium atoms, turned out to have a catalytic behaviour comparable to platinum, which has so far been the best catalyst for fuel cells. The material costs of this new type of catalyst amount to only a few per cent of those of platinum.

A mass transfer model for copper and molybdenum in magmatic hydrothermal systems; the origin of porphyry-type ore deposits

Abstract: Equations have been derived which model element partitioning between silicate melts, aqueous fluids, and crystalline phases during crystallization. These equations can be used to calculate the efficiency of removal of elements from magmas into aqueous fluids as a function of (1) the bulk solid-liquid partition coefficient of these elements; (2) the initial and saturation water concentrations in the melt (which together determine the amount of melt crystallized before water saturation); and (3) the chlorine concentration of the melt (in the case of chlorine-complexed cations).The efficiency with which copper and molybdenum can be removed from silicate melts, E(Cu) and E(Mo), respectively, has been calculated. Based on geologic data, copper is modeled as a compatible element and molybdenum is modeled as an incompatible element. Under these conditions the ratio E(Mo)/E(Cu) increases as the initial water concentration of the melt decreases for a given depth of vapor evolution and a given Cl/H 2 O ratio and increases as the depth of vapor evolution increases for a given Cl/H 2 O ratio and a given initial water concentration of the melt.Cu is concentrated so efficiently into a moderately to highly saline aqueous phase that liquid-vapor extraction seems to be a reasonable process to account for the concentration of Cu in porphyry Cu deposits. Efficient extraction of Cu results when aqueous fluids are evolved early in the crystallization of the intrusion. The value of D(Mo) is small relative to D(Cu) at moderate to high chloride concentrations, and the extraction of Mo from the melts into aqueous fluids therefore tends to be less efficient. However, vapor-liquid partitioning can extract the requisite quantities of Mo from granitic melts of batholithic size if Mo acts as an incompatible element and if the water content of the magma at water saturation is on the order of several weight percent.

Organic molybdenum complexes

Abstract: Novel molybdenum complexes prepared by reacting (a) a fatty oil or acid, (b) 2-(2-aminoethyl)aminoethanol and (c) a molybdenum source are described. The molybdenum complexes impart antifriction, antioxidant, and antiwear properties to lubricating compositions and decrease fuel consumption in internal combustion engines using same.

Ammonia synthesis on molybdenum nitride

Abstract: Ammonia synthesis on unsupported Mo/sub 2/N powders was studied at atmospheric pressure between 557 and 717 K. Turnover rates based on titration of sites by CO decreased by a factor of 25 as the particle size of Mo/sub 2/N went from 12 to 3 nm. This confirms the structure sensitivity of the rate of ammonia synthesis. Strong inhibition of the rate by ammonia was observed. It is attributed to large values of the binding energy of nitrogen to the catalyst surface.

Study of polymerization processes in acid and base catalyzed silica sol-gels

Abstract: Raman spectroscopy has been employed in conjunction with 29 Si NMR and the molybdenum chemical technique to study the polymerization process of silica sol-gels under pH conditions ranging from 1 to 9. A qualitative correlation between the rate of hydrolysis and the size of the resulting polymeric particles has been tentatively proposed. The extent to which the relative Raman intensity simultaneously proves information regarding particle dimensions, shape and degree of condensation has been discussed. A quantitative comparison between the monomer concentration as determined by the molybdenum chemical technique and by 29 Si NMR has been provided.

Metal catalysis in oxidation by peroxides. Part 25. Molybdenum- and tungsten-catalyzed oxidations of alcohols by diluted hydrogen peroxide under phase-transfer conditions

Abstract: Effet de divers parametres sur l'oxydation d'alcools primaires et secondaires par le systeme Mo(VI) ou W(VI)-H 2 O 2

The elastic constants and structure of the vitreous system Mo-P-O

Abstract: The preparation of glasses with compositions spanning the entire vitreous range obtainable from melting phosphorous pentoxide with molybdenum trioxide, and phosphoric acid with ammonium molybdate, in open crucibles, is described. The second order elastic constants of these Mo-P-O glass systems have been obtained from ultrasonic wave velocity measurements. The most striking features of the results are two discontinuities in the compositional gradient of each elastic modulus, at compositions of ∼53 and 63 mol% MoO3 content. These compositions approximate to those of molybdenum metaphosphate and molybdenum pyrophosphate crystals. A second noteworthy feature is that the elastic moduli display a substantial overall increase with molybdenum content, 36% for bulk and 83% for shear over the entire composition range, even though the Mo-O bond stretching force constant is less than half that of the P-O bond. A detailed qualitative interpretation of these features is made, in terms of the proposed compositional dependence of the crosslink densities of the molybdenum and phosphorus atoms, and the atomic ring sizes.

Molybdenum-containing lubricant composition

Abstract: A lubricant composition comprises as essential ingredients a sulfur compound and an oil-soluble molybdenum compound, obtained by reacting one or more of hexavalent molybdenum compounds selected from the group consisting of molybdenum polyoxide, molybdic acid and the alkali salt thereof or a compound prepared by reaction of the compounds and a reducing agent, with an amino compound represented by the general formula: ##STR1## wherein R1, R2 and R3 which may be identical with or different from each other individually represent hydrogen atoms or hydrocarbon groups of 1 to 30 carbon atom The lubricant additives comprising the novel molybdenum-amine complex and the sulfur-containing compound in combination are excellent in the anti-oxidation, anti-wear and friction-reducing effect and, particularly, excellent in view of the metal corrosion

Photodecomposition of Mo(CO)6 adsorbed on Si(100)

Abstract: The photochemical properties of Mo(CO)6 adsorbed on Si(100) were investigated using temperature programmed desorption (TPD) and Auger spectroscopy. TPD experiments indicate that Mo(CO)6 physisorbs on silicon and desorbs at 210–230 K. At 150 K, KrF laser radiation (248 nm) partially decomposes the adsorbed Mo(CO)6 releasing gas‐phase CO in the process and TPD experiments after irradiation show that additional CO desorbs at 335 K. However, Auger analysis indicates that one CO molecule per molybdenum atom dissociates, leaving the molybdenum overlayer heavily contaminated with carbon and oxygen. The cross section for photodecomposition was measured to be 5±3×10−17 cm2. Decomposition of the excited molecule must compete strongly with energy relaxation to account for the magnitude of this cross section.

Effects of Argon-Ion Bombardment on the Basal Plan Surface of MoS2.

Abstract: : The surface composition and structure of the basal plane surface of Molybdenum Disulfide was modified by 10 keV argon-ion bombardment and then studied with x-ray photoelectron spectroscopy. The rigid shift of both sulfur and molybdenum core levels is demonstrated to result from the formation of a small amount of Molybdenum islands on the surface, although there is no a priori evidence for changes in oxidation state at the surface after bombardment. This conclusion is suggested by recent data on the deposition of metals on the MoS2 basal plane that indicate a strong correlation between the Mo or sulfur binding energy and the electronegativity of the metal. Our results are compared with those of previous studies and are explained in terms of recent theories on the effects of surface ion bombardment that suggest that chemical/thermal effects dominate over substrate mass effects for higher projectile-ion mass and energy.