Showing papers on "Molybdenum published in 1977"

Hardness of tempered martensite in carbon and low-alloy steels

Abstract: This paper presents the results of a systematic study of the effect of carbon, manganese, phosphorus, silicon, nickel, chromium, molybdenum, and vanadium on the hardness of martensite in low to medium carbon steels tempered for one hour at 100°F (56°C) intervals in the range 400 to 1300°F (204 to 704°C). Results show that the as-quenched hardness depends solely on carbon content. On tempering, the effect of carbon on hardness decreases markedly with increasing tempering temperature. Studies of carbon-0.5 manganese steels showed that the incremental increase in hardness from 0.5 pct manganese after a given tempering treatment was independent of carbon content. Based on this result, studies of the effects of the other alloying elements were made using a 0.2 or 0.3 pct carbon, 0.3 to 0.5 pct manganese steel base composition. The hardness of the resulting tempered martensite was assumed to be due to a given alloy addition, and when two or more alloying elements were added, their effects were assumed to be additive. Each of the seven alloying elements increased the hardness of tempered martensite by varying amounts, the increase being greater as more of each element was present. Nickel and phosphorus have substantially the same effect at all tempering temperatures. Manganese has essentially the same hardening effect at any temperature in the range 700 (371°C) to 1300°F; silicon is most effective at 600°F (316°C), chromium at 800°F (427°C), molybdenum at 1000 to 1100°F (538 to 592°C), and vanadium at 1200°F (649°C). Using the data obtained, a procedure is established for calculating the hardness of tempered martensite for carbon and alloy steel compositions in the range studied and for any combination of tempering time and temperature.

Conversion of dinitrogen in its molybdenum and tungsten complexes into ammonia and possible relevance to the nitrogenase reaction

Abstract: Treatment of trans-[M(N2)2(dppe)2](A)(dppe = Ph2PCH2CH2PPh2, M = Mo or W) with H2SO4 gives [M(HSO4)-(NNH2)(dppe)2][HSO4] and no ammonia or hydrazine. However, the complexes cis-[M(N2)2(PMe2Ph)4](B) and trans-[M(N2)2(PMePh2)4](C)(M = Mo or W) react with H2SO4 in methanol at 20 °C to give ammonia (ca. 1.9 NH3 per W atom and ca. 0.7 NH3 per Mo atom), together with a little hydrazine for (B; M = W) but not for (B; M = Mo). Treatment of (B; M = Mo and W) with a variety of other acids gives ammonia, but less effectively than with H2SO4. Anhydrous HBF4 also gives ammonia from (B; M = Mo or W), but (A; M = Mo or W) gives only trans-[MF(NNH2)(dppe)2][BF4]. Ammonia (1.6 NH3 per W atom) is also obtained when (B; M = W) but not (B; M = Mo) is treated with methanol alone, either at reflux or on irradiation at 20 °C for several hours. The mechanism of these reactions and their relevance to the action of nitrogenase is discussed.

Molybdenum cofactors from molybdoenzymes and in vitro reconstitution of nitrogenase and nitrate reductase

Abstract: A molybdenum cofactor (Mo-co) from xanthine oxidase (xanthine:oxygen oxidoreductase, EC 1.2.3.2) can be isolated from the enzyme by a technique that has been used to isolate an iron-molybdenum cofactor (FeMo-co) from component I of nitrogenase. N-Methylformamide is used for the extraction of these molybdenum cofactors. Mo-co from xanthine oxidase activates nitrate reductase (NADPH:nitrate oxidoreductase, EC 1.6.6.2) in an extract from Neurospora crassa mutant strain Nit-1; however, FeMo-co is unable to activate nitrate reductase in strain Nit-1. Mo-co from xanthine oxidase is unable to activate nitrogenase in an extract of Azotobacter vinelandii mutant strain UW45. Inactive component I in this extract can be activated by FeMo-co. These results indicate that nitrate reductase and xanthine oxidase share a common molybdenum cofactor, but this cofactor is different from the molybdenum cofactor in nitrogenase.A. vinelandii synthesizes both Mo-co and FeMo-co. Mo-co is produced when the cells fix N(2) and also when they are repressed for nitrogenase synthesis by growth in a medium containing excess ammonium. However, FeMo-co is not produced when cells are grown in an ammonium-containing medium. Partially purified preparations of component I from A. vinelandii and Klebsiella pneumoniae contain both FeMo-co and Mo-co. The presence of both FeMo-co and Mo-co activities in partially purified preparations of component I explains previous reports of activation of inactive nitrate reductase in strain Nit-1 by acid-treated component I of nitrogenase. The Mo-co can be separated from FeMo-co in these preparations by chromatography on Sephadex G-100 in N-methylformamide. Both FeMo-co and Mo-co are sensitive to oxygen.

Shock compression of molybdenum to 2.0 TPa by means of a nuclear explosion

Abstract: The principal Hugoniot of molybdenum has been determined at a pressure of 2.0 TPa by measuring directly both the shock velocity and the particle velocity behind the shock. Neutrons from an underground nuclear explosion were used to generate a high‐pressure shock in a slab of molybdenum by rapidly fission heating an adjacent slab of enriched uranium. A shock velocity of 18.2 mm/μs (±5%) was obtained by determining the transit time of the planar shock between two points in the molybdenum separated by 9.87 mm. A particle velocity of 10.7 mm/μs (±5%) was obtained by observing the Doppler shifts of six neutron resonances in the energy region from 200 to 800 eV in the moving shocked molybdenum. The pressure and density derived from this pair of measurements are 2.0 TPa (20 Mbar) and 24.8 g cm−3, respectively. This experiment represents the first direct determination of a point on the Hugoniot of any material in this pressure region, and the resulting data point is in good agreement with theoretical estimates. This measurement was a successful demonstration that the Doppler‐shift technique can be used to obtain particle velocities in this pressure region. It appears that errors in both the shock velocity and the particle velocity can be reduced to approximately ±2% in an improved measurement, resulting in a well‐defined Hugoniot for molybdenum, which can be used as a standard in future impedance‐matching experiments.

Note on the Influence of Nitrogen Content on the Resistance to Pitting Corrosion of Stainless Steels

Abstract: Pitting potentials have been measured and some gravimetric testing has been carried out on a series of experimental austenitic stainless steels with varying chromium, molybdenum and nitrogen contents. All three of these elements were found to contribute to the resistance to the initiation of pitting corrosion, and synergistic effects have been noted. The effect of nitrogen is especially potent in a steel with 22% chromium and 3% molybdenum.

Relation between electronic structure and T/sub c/ in binary and ternary molybdenum chalcogenides

Abstract: Localized orbital calculations are presented for the electronic structure of Chevrel-phase molybdenum chalcogenides. Densities of states at the Fermi energy, N (E/sub F/), are found to depend sensitively on the modification in intercluster interactions because of lattice distortions introduced by the ternary component. Calculated N (E/sub F/) values in Mo/sub 6/S/sub 8/, PbMo/sub 6/S/sub 8/, Mo/sub 6/Se/sub 8/, and PbMo/sub 6/Se/sub 8/ are 0.5, 1.7, 1.1, and 0.9 states/(spin-Mo-atom eV), respectively, and show a strong correlation with T/sub c/. States near to E/sub F/ are strongly confined within Mo/sub 6/ octahedra.

Catalytic oxide of molybdenum, vanadium, niobium and optional 4th metal

Abstract: A novel catalyst comprising the elements Mo, V and Nb is provided for oxidizing alpha-beta unsaturated aliphatic aldehydes in the vapor phase with molecular oxygen to produce the corresponding alpha-beta unsaturated carboxylic acid.

Phonon properties of niobium, molybdenum, and their alloys

Abstract: Simple lattice dynamical models have been fitted to the experimental phonon dispersion curves of niobium, molybdenum, and their alloys. The 'best-fit' parameters are used to compute the phonon distribution functions, g(v), and several properties which depend on these functions.

The influence of material purity and irradiation temperature on self-ion damage in molybdenum

Abstract: An electron microscope study has been made of vacancy loops formed as a result of displacement cascade collapse in molybdenum irradiated with 60 keV self-ions. The experiments were directed towards exposing two aspects of this process. Firstly, the influence of material purity was investigated by comparing the structures generated in three crystals, one being of high purity, the second containing a significantly higher level of substitutional impurities and the third doped specifically with nitrogen. The results demonstrated that nitrogen in solution was the most effective in reducing both the number of visible vacancy loops formed by cascade collapse and the fraction of vacancies surviving in the cascades to form loops. The second major aspect studied was the influence of irradiation temperature on vacancy loop formation in the high purity crystal. In this case the number of visible loops decreased sharply with temperature over the range studied, i.e. up to 535°C. The decrease is shown to follow...

Chemistry of compounds containing metal-to-metal triple bonds between molybdenum and tungsten. Technical report

Abstract: The preparation, properties, structures, dynamical solution behaviors and reactivities towards small unsaturated molecules (CO2, acetylenes, CO, etc.) are described for a series of molybdenum and tungsten compounds of general formula M2X6 or M2X6-nY, where X Y=R (alkyl), NR2, or, O2CNR2, O2COR or halide, and Cp2M2(CO)4, all of which contain triple bonds between the metal atoms (M=Mo or W). (Author)

Process for the preparation of unsaturated acids from unsaturated aldehydes

Abstract: Methacrylic acid or acrylic acid is produced by the oxidation of methacrolein or acrolein respectively, with molecular oxygen in the vapor phase in the presence of a catalytic oxide of molybdenum and phosphorus, promoted with chromium or at least one element selected from the group consisting of thallium, rubidium, cesium, potassium, titanium, and arsenic, or a mixture thereof, wherein at least part of the molybdenum employed in the preparation of the catalyst is supplied in the form of molybdenum trioxide The oxidation of methacrolein in the presence of a catalyst wherein all the molybdenum employed in the preparation of the catalyst has been supplied by molybdenum trioxide gives especially desirable high yields and selectivities to methacrylic acid

Carbene derivatives of molybdenum and tungsten containing metal-metal bonds

Abstract: Durch Reaktion der Ausgangskomplexe (II) mit Organolithiumverbindungen und anschliesende Alkylierung konnten die Alkoxycarbenkomplexe (IIIa) dargestellt werden.

Production of maleic anhydride and catalysts therefor

Abstract: Catalysts for the oxidation of hydrocarbons to maleic anhydride comprise a phosphorus/vanadium mixed oxide promoted by tungsten antimony, niobium, and/or molybdenum, having a surface area of at least 10m 2 /g.

Diffuse reflectance spectra of molybdenum ions supported by magnesia, γ-alumina or silica

Abstract: Supported molybdenum oxides, used as model catalysts for the oxidation of propene, have been examined by diffuse reflectance spectroscopy. Changes in the valence state and coordination number of molybdenum are functions of the support (MgO, SiO 2 or γ-Al 2 O 3 ), the preparation procedure, the oxidising pretreatment and the conditions of reduction by the olefin. Two principal types of preparation have been used: impregnation by an aqueous solution of (NH 4 ) 6 (Mo 7 O 24 ) and reaction of the support with MoCl 5 . It appears that this latter procedure is suitable for preparing molybdenum oxides of low Mo content in which the Mo 6+ and Mo 5+ coordination can be predominantly tetrahedral. The selectivity for acrolein formation during the oxidation of propene can thus be related to the presence of Mo ions in tetrahedral configuration.

Plated metallic cathode

Abstract: A highly conductive and corrosion resistant low hydrogen overvoltage cathode. The cathode comprises a copper substrate plated with an alloy of nickel, vanadium, and molybdenum.

DC conductivity of molybdenum phosphate glasses

Abstract: The temperature dependence of DC conductivity in the high-temperature range in transition metal oxide glasses containing MoO3, WO3 and V2O5 is presented. Molybdenum phosphate glass has been investigated with MoO3 contents varying from 60 to 85 mol% while vanadium and tungsten phosphate glasses have been examined for one composition only. The conductivity of a molybdenum phosphate glass is considerably lower than that of tungsten and vanadium phosphate glasses of similar composition while the activation energy is higher for the molybdenum glass. The DC conduction in molybdenum phosphate glasses can be considered to be due to hopping of polarons and is consistent with the reported results of other transition metal ion phosphate glasses.

austenitic stainless steel

Abstract: The invention relates to an austenitic stainless steel. This steel comprises by weight 10 to 14% nickel, 2-3% molybdenum, 16 to 18% chromium, up to 0.1% carbon, up to 2% mangasene up to 1% silicon, up to 0.03% sulfur, 0.1 to 0.2% phosphorus, 0 to 0.65% titanium, the remainder being constituted by iron and any impurities. Application as a structural material and fuel element sheaths in a nuclear reactor.

Molybdenum-containing enzymes

Abstract: So little is known about molybdenum enzymes other than milk xanthine oxidase that there is little to be said by way of general conclusions. In all cases where there is direct evidence (except possibly for xanthine dehydrogenase from Micrococcus lactilyticus) it seems that molybdenum in the enzymes does have a redox function in catalysis. For the xanthine oxidases and dehydrogenases and for aldehyde oxidase, the metal is concerned in interaction of the enzymes with reducing substrates. However, for nitrate reductase it is apparently in interaction with the oxidizing substrate that the metal is involved. In nitrogenase the role of molybdenum is still quite uncertain.