Showing papers on "Molybdenum published in 1972"

Phase instabilities during high temperature exposure of 316 austenitic stainless steel

Abstract: Although Type 316 austenitic stainless steel is widely used in steam generating plants and nuclear reactors the knowledge about aging reactions, nature of precipitates, and precipitation kinetics during high temperature exposure is limited. Time-temperature-precipitation (TTP) diagrams were determined between 400° and 900°C for up to 3000 hr as a function of carbon content, solution treatment temperature, and cold work. The nucleation and growth phenomena, morphology, and composition of the various carbide (M23C6, M6C) and intermetallic phases (σ, χ, η were determined. The complex sequence of phase instabilities can be explained on the basis of the carbon content, effect of molybdenum and chromium on the carbon solubility, thermodynamic stability of the phases, and the kinetics of the various precipitation reactions.

The influence of molybdenum on the γ/’phase in experimental nickel-base superalloys

Abstract: The influence of 1, 3, and 5 at. pct Mo on the γ’precipitate has been studied in experimental wrought nickel-base superalloys containing about 14 at. pct Cr and 6-1/2, 9, or 12 at. pct Al, or 2 at. pct Al plus 4 at. pct Ti. Concentrations of all other elements were quite low to limit the observed effects to those of molybdenum alone. Molybdenum markedly increases the γ’ solvus temperature, as determined by the sensitive and relatively simple technique of differential thermal analysis; correspondingly, the weight fraction of γ’ increases with molybdenum additions for a given aging treatment. Molybdenum dissolves extensively in the γ’of the titanium-free alloys, but it dissolves to a considerably smaller extent in the γ’of the titanium-bearing alloys. Molybdenum substitutes for chromium in y’, but does not alter the aluminum or titanium contents of this phase. Lattice parameters of both the matrix and the γ’are increased markedly by molybdenum, in proportion to the molybdenum contents of these phases. The resulting effects on lattice-parameter mismatch correlate rather well with observed γ’morphology, which tends to change from spheroidal to cuboidal in titanium-free alloys, and from cuboidal to spheroidal in 2 at. pct Al-4 at. pct Ti alloys, as molybdenum is added to these alloys.

Molybdenum(ii) trifluoro acetate dimer

Abstract: Molybdenum(II) trifluoroacetate dimer, Mo2(O2CCF3)4, has been prepared by reaction of Mo2(O2CCH3)4 with a 10:1 mixture of CF3COOH and (CF3CO)2O under nitrogen An X-ray structure determination shows that the compound has the dinuclear, carboxylate-bridged configuration of essentially D4h symmetry previously established for a number of other transition metal carboxylates The Mo-Mo and average Mo-O distances of 2090(4) and 206 (2) A are not significantly different from those found in molybdenum(II) acetate dimer [211(1) and 210(2) A] The Mo-Mo stretching frequencies in the Raman spectrum are also similar for the two compounds: 406 cm−1 for the acetate and 393 cm−1 (389 in Et2O soln) for the trifluoroacetate The mass spectrum of the trifluoroacetate shows a strong molecular-ion peak, and a fragmentation pattern characterized by successive net loss of CF2CO2 units The infrared, Raman, electronic and mass spectra are discussed The compound crystallizes in the triclinic space group P1 with un

Refractory metals and alloys.

Abstract: The original mater ia l s f rom which the alloys were prepared were commerc ia l molybdenum (99.97~c), e lectrolyt ic rhenium (99.99%) remel ted in an a rc furnace for additional purification, and iodide zirconium. Carbon was added in the form of Mo2C and spect ra l ly pure graphite. Ingots of the al loys weighing 250 g (150 mm long and 8-10 mm in diameter) were melted in a furnace with a nonconsumable tungsten electrode and water -cooled copper hearth in an a tmosphere of helium at a p ressure of 300 mm Hg.

Elimination stabilized alkyls. Part I. Chromium, molybdenum, tungsten, and vanadium

Abstract: The interaction of chlorides of V, Cr, Mo, and W with the lithium or Grignard reagents derived from chloromethyltrimethylsilane produces thermally stable alkyls of formula V(CH2SiMe3)4, VO(CH2SiMe3)3, Cr(CH2SiMe3)4, and M2(CH2SiMe3)6(M = Mo or W). The compounds have been investigated, where feasible, by i.r., Raman, electronic, e.s.r., and n.m.r. spectroscopy and the various spectral assignments are discussed in terms of proposed structures for the compounds.

Elastic constants of niobium‐molybdenum alloys in the temperature range −190 to +100°C

Abstract: The adiabatic elastic constants were determined for niobium and niobium‐molybdenum alloys of the following nominal compositions: 15, 25, 35, 50, 75, and 90 wt.% Mo. The c11, c12, and c44 elastic constants of these bcc alloys were tabulated between −190 and +100°C. The effects of compositional changes on the elastic constants were far greater than those due to temperature. An anomalous temperature dependence for c44 was found for the niobium‐rich alloys. An analysis of the elastic constants in terms of central forces revealed that nearest‐and second‐nearest‐neighbor force constants rise with molybdenum additions, with the latter tending towards a maximum as the composition of pure molybdenum is approached. This is thought to be associated with the filling of a d subband. The Debye temperatures were computed and found to be generally in good agreement with the calorimetrically determined values reported in the literature.

Alloy hardening and softening in binary molybdenum alloys as related to electron concentration

Abstract: An investigation was conducted to determine the effects of alloy additions of hafnium, tantalum, tungsten, rhenium, osmium, iridium, and platinum on hardness of molybdenum. Special emphasis was placed on alloy softening in these binary molybdenum alloys. Results showed that alloy softening was produced by those elements having an excess of s+d electrons compared to molybdenum, while those elements having an equal number or fewer s+d electrons that molybdenum failed to produce alloy softening. Alloy softening and alloy hardening can be correlated with the difference in number of s+d electrons of the solute element and molybdenum.

Thermodynamics and phase relations in refractory metal solid solutions containing carbon, nitrogen, and oxygen

Abstract: The refractory metals Nb, Ta, Mo, and W dissolve C, N, and O by forming interstitial solid solutions The concentration of these components can be increased or decreased by annealing treatments, depending on the partial pressure of gases such as N2, O2, H2O, CH4, or CO and on the temperature of the specimen New results in binary and ternary systems combined with those obtained in the last few years now provide most of the data needed for the thermochemical analysis of the solid solution phases and for the establishment of p-T-c phase diagrams The mechanisms of the gas-metal reactions and the general feature of the constitution diagrams are similar for all refractory metals However, marked differences exist between group Va metals niobium and tantalum and group VIa metals molybdenum and tungsten in the absolute values and temperature dependence of the equilibrium pressure of gaseous species and therefore also in the amount of gas absorbed The data now available for the estimation of the final content of interstitials in solid solution after annealing treatments are compiled and discussed

Adsorbed barium films on tungsten and molybdenum (011) face

Abstract: Work function and thermal stability of Ba–W(011) and Ba–Mo(011) systems as well as the structure of adsorbed barium films on the molybdenum (011) face are studied. From the structural analysis the data on absolute surface concentration of barium atoms are obtained. The work function, adsorption that, and some characteristics of barium surface diffusion are found to correlate with the structure of films. Phase transitions in the adsorbed films are observed. [Russian Text Ignored]

Sulfur and phosphorus bearing lubricant

Abstract: The performance of lubricants having a mineral oil or synthetic oil base can be improved greatly by dithiophosphates of zinc, lead, tin, tungsten, molybdenum, niobium, lanthanum, antimony, bismuth, chromium, vanadium, or cadmium esterified with alkyl, aryl, or alkyl-aryl groups in synergistic cooperation with additives free from heavy metals, but containing sulfur and phosphorus, such as sulfides of phosphorus and known addition agents.

The interfacial free energies of solid chromium, molybdenum and tungsten

Abstract: The average surface free energies, γsv, of chromium, molybdenum, and tungsten have been measured at 0.6 to 0.8 of the absolute melting temperature, TM, by multiphase equilibrations with liquid tin or silver in tantalum-gettered argon. With grain-boundary groove angles measured by interferometry and stylus profile tracing, the respective values were 1700 ± 360, 1750 ± 390, and 1810 ± 630 ergs/cm2. Similar values for molybdenum were obtained from an analysis of the kinetics of grain-boundary grooving. Ratios involving the high-angle grain boundary, solid-liquid, and solid- foreign metal vapor interfacial free energies and γsv were consistent with theoretical considerations. The presence of surface active impurities was predicted on the basis of a positive temperature coefficient, dγ sv d T . Values of the order of +0.6 erg/cm2/ °C were calculated from the temperature dependence of grain boundary groove angles from which it was found that the relative grain boundary free energy, γ ss γ sv decreased from ~0.5 at 0.5 TM to ~0.35 at 0.95 TM. In the case of molybdenum, grain boundary groove angles were insensitive to environments ranging from 10−9 Torr residual pressure to 1.0 Torr of nitrogen. Indications of surface impurities during equilibration were given by Auger electron spectroscopy which revealed carbon and sulfur on molybdenum at 0.65 TM under ultra-high vacuum conditions. Adjusting the surface free energy values to the melting points and dividing by the surface tension of the corresponding liquid, γlv, resulted in γ sv γ lv ratios above unity, as predicted by Skapski's broken bond model.

Pitting of Molybdenum Bearing Austenitic Stainless Steel

Abstract: The effect of temperature over the range 10 to 90 C (50 to 194 F) on the pitting corrosion of a series of molybdenum bearing austenitic stainless steels in an acid chloride medium is demonstrated. The role of molybdenum in improving the corrosion resistance of these alloys is clearly shown.