Showing papers on "Molybdenum published in 1970"

Yield Point Phenomena in Metals and Alloys

Abstract: 1 Yield Point Phenomena and their Theoretical Background.- The effects of tensile machine and specimen stiffness.- Types of yield point effects.- The upper yield point-experimental.- The upper yield point-theoretical.- The lower yield point.- Strain ageing.- Pseudo yield points.- 2 Iron and its Alloys.- Effects of carbon, nitrogen and other elements.- Quench ageing.- Yielding behaviour.- Strainageing kinetics.- Effects of radiation damage-Single crystals.- Steels.- 3 The Group Va and VIa Metals.- Vanadium.- Chromium.- Niobium.- Molybdenum.- Tantalum.- Tungsten-Alloys of these metals.- Discussion.- 4 Hydrogen in Metals.- Hydrogen embrittlement.- Solubility of hydrogen in metals.- Mild steel.- Group Va and VIa metals.- Nickel.- Palladium.- Titanium and zirconium.- 5 Aluminium and its Alloys.- The unloading yield point effect.- 'Commercially pure' aluminium.- Aluminium-copper alloys - Aluminium-magnesium alloys.- Other aluminium alloys.- Theories of yield points in aluminium alloys.- 6 Other Face-Centred Cubic Metals and Alloys.- Copper and its dilute alloys.- Brass.- Silver and its alloys.- Nickel and its alloys.- Thorium.- Ordered alloys.- 7 Miscellaneous Materials.- Whiskers.- Ionic crystals.- Semiconducting materials.- Hexagonal metals and alloys.- 8 Discussion.

The surface energies of solid molybdenum, niobium, tantalum and tungsten

Abstract: The surface energies of solid molybdenum, niobium, tantalum, and tungsten at 1500 °C have been determined using the multi-phase equilibration technique The values obtained were 2050, 2550, 2680 and 2830 erg/cm2, respectively The grain boundary energy/surface energy ratios for the four metals varied from 028 to 038 with an average of 032

Sintering steel-bonded carbide hard alloy

Abstract: A sintered alloy comprising a carbide of preferably titanium and a steel matrix of an alloy steel containing chromium, molybdenum, copper and vanadium as alloying elements provide high temperature hardness and wear resistance. Preferred alloys contain 0.8 to 1.9% by weight of manganese and up to 80% by weight of carbide.

Solid solution strengthening in Nb-Ta and Nb-Mo alloy single crystals

Abstract: The strength of Nb, Nb-Ta, and Nb-Mo alloys was investigated in tension and compression as a function of composition, temperature, and strain rate. The room-temperature properties show molybdenum to have a significant effect on the strength of niobium while the effects of tantalum are nearly zero. The room-temperature strength is shown to be well correlated with the atomic misfit parameter. Analysis of the low-temperature behavior of Nb-Ta alloys indicates that they behave similarly to the pure metal while Nb-Mo alloys show a marked deviation from this behavior. The strengthening phenomena occurring in the Nb-Mo alloys at low temperature is interpreted as being an impurity interaction. A transition between the mechanism operating in the pure metal and the impurity interaction occurs at low solute contents.

Thermochemistry and the Oxidation of Refractory Metals at High Temperature

Abstract: Recent developments in the thermochemical data for the condensed oxide phases and volatile oxide species for the refractory metals has made possible an analysis of the several types of high temperature oxidation processes. The analyses show the following factors to be important: (1) the presence or absence of oxide films or scales on the metals, (2) the melting points of the one or more oxide phases, (3) the equilibrium pressures of the several volatile oxides, and (4) the flow rate of reactant gases. The thermochemical predictions are compared to experimental observations for molybdenum and tungsten.

Complexes of molybdenum(VI) and molybdenum(V) with dithiocarbamate, dithiocarbonate, and phosphorothiolothionate

Abstract: Complexes Mo2O3B4(B = diethyl dithiocarbamate, O-ethyldithiocarbonate, or diethyl or diphenyl-phosphorothiolothionate), MoO2B2, and Mo2O3B2(CH3CO2)2(B = diethyl dithiocarbamate), and MoOB2(C5H5N)(B = ethyldithiocarbonate) have been prepared. Their electronic, i.r., and 1H n.m.r. spectra are reported. For these and other oxomolybdenum(V) complexes a correlation is found between Mo–O stretching frequencies and the frequency of the first d–d transition.

Ellipsometric Technique for Obtaining Substrate Optical Constants

Abstract: A method for determining substrate optical constants, surface film thickness, and surface film optical constants has been devised by measuring the ellipsometer angles Δ and ψ at several angles of incidence. This method, previously reported as impossible, solves in a simple fashion the ellipsometry equations for one consistent values of surface film thickness in association with compatible values of substrate optical constants. The technique is advantageous in that vacuum ellipsometry is eliminated and previously unmeasured materials such as alloy structures may be studied readily. Data on aluminum, molybdenum, and silicon are presented illustrating the technique.

Spectroscopic investigation of bismuth–molybdenum–oxide catalysts

Abstract: Bismuth–molybdenum–oxide catalysts have been studied by i.r. and u.v. reflectance spectroscopy. Both tetrahedral and octahedral oxomolybdenum(VI) species were at the catalyst surface. The proportion of octahedral species increased with increasing molybdenum concentration and with increasing calcining temperature. The i.r. spectra showed the presence at the surface of an octahedral oxomolybdenum(VI) species with terminal and bridging oxygen. The most active catalysts, including silica-supported catalysts, had characteristic u.v. and i.r. spectra. Molybdenum–terminal oxygen stretching frequencies were in the range found in model compounds with three terminal oxygens per molybdenum. The effect of silica in supported catalysts was to promote formation of the same active species as in the unsupported catalyst but at a higher molybdenum concentration. The relevance of our results to the mechanism of the catalysis of oxidative dehydrogenation of olefines is discussed. We suggest that the bifunctional nature of the bismuth molybdate catalyst is due to the presence of two types of molybdenum–oxygen bond in the particular structure adopted by MoO3 in association with Bi2O3.

Superconductivity and lattice parameters in the zirconium-molybdenum, zirconium-tungsten, hafnium-molybdenum and hafnium-tungsten alloy systems

Abstract: Superconductivity and lattice parameters have been measured on annealed alloys of ZrMo 2 , ZrW 2 , HfMo 2 and HfW 2 Polymorphism for HfMo 2 was reconfirmed and the compound was found to be superconducting at 007 °K in the C 15 structure and normal down to 005 °K in the C 36 modification The C15 compounds ZrMo 2 , ZrW 2 and HfW 2 were normal down to at least 12 °K The bcc phase was investigated by rapid quenching from the melt It was possible to obtain single phase bcc alloys in the range 3–41 at% Mo in ZrMo alloys and about 9 to at least 67 at% Mo in HfMo alloys The lattice parameters at room temperature for these alloys could be accurately determined and extrapolated to room temperature bcc values for Zr and Hf It was possible to obtain HfMo 2 alloys in three different crystal structures The superconducting transition temperature is about 1 °K for the bcc modification and decreases with decreasing lattice symmetry The rapid quenching technique was less successful in the tungsten alloys, but superconductivity in the bcc phase could be observed in all four alloy systems A maximum in the transition temperature was found in all systems at an electron/ atom ratio between 4 and 5 In the ZrW system, a dip in the transition temperature versus concentration was observed at the composition of the compound ZrW 2 Some aspects of the superconductivity in the bcc phase are discussed It is found that the rigid band model is a good approximation in the dilute Zr region An extrapolation to bcc Zr gives 15 °K as the estimate for the transition temperature

Ammoxidation of saturated hydrocarbons

Abstract: Method for the production of acrylonitrile or methacrylonitrile from propane or isobutane employing a catalyst containing the oxides of molybdenum, boron and tin.