Showing papers on "Molybdenum published in 1968"

Lattice parameter measurements on molybdenum disulphide

Abstract: The lattice parameter a0 of thin single crystals of molybdenum disulphide was shown to be independent of crystal thickness and to have the value 31475 A at 293°K. The variation of a0 with temperature was measured from 77 to 373°K.

Resistor thin films formed by low-pressure deposition of molybdenum and tungsten

Abstract: High resistivity, low temperature coefficient of resistance films are formed by evaporating a molybdenum or tungsten source in a low-pressure atmosphere, e.g. 5 X 10 4 torr, of a nitrogen bearing gas, a carbon bearing gas or an inert gas and depositing a resistor film atop a preferably unheated dielectric substrate.

Cobalt–molybdenum–alumina hydrodesulphurisation catalysts. Part I. A spectroscopic and magnetic study of the fresh catalyst and model compounds

Abstract: The u.v., visible, and i.r. spectra of the following compounds containing cobalt, molybdenum, and aluminium in tetrahedral and octahedral co-ordination in oxide lattices, and the magnetic susceptibilities over the temperature range 80–380°K of the first four compounds are reported: hydrated cobalt molybdate, calcined cobalt molybdate (CoMoO4), cobalt(II) molybdenum(IV) oxide (Co2Mo3O8), cobalt aluminate, cobalt(II) oxide, cobalt(II,III) oxide (Co3O4), sodium molybdate, ammonium paramolybdate, molybdenum trioxide, and γ-alumina. The spectroscopic and magnetic properties of a fresh (i.e., unsulphided) cobalt–molybdenum–alumina hydrodesulphurisation catalyst are reported and compared with the properties of the above compounds in order to determine the chemical and structural environment of cobalt and molybdenum in the catalyst. Cobalt is present as cobalt(II), approximately 50% in octahedral co-ordination and 50% in tetrahedral co-ordination by oxide. There is very little magnetic interaction between the cobalt ions which are well dispersed in the catalyst. Molybdenum is present as molybdenum(VI) in tetrahedral co-ordination by oxide. There is no evidence for the presence in the catalyst of Co3O4 or any well defined compound of cobalt, molybdenum, or aluminium. The relevance of the results to the preparation of the catalyst is discussed.

Molybdenum–Cysteine Complex

Abstract: RECENT measurements of electron spin resonance1 have indicated that, in the reduced form of the molybdoflavo-protein enzyme xanthine oxidase, molybdenum(V) is coordinated with one or more sulphur atoms, probably ionized thiol groups of cysteine. Molybdenum–sulphur complexes have therefore attracted considerable interest as possible models for molybdenum in enzymes2. Although the chemistry of molybdenum–sulphur complexes is becoming well understood3, there has been little work on complexes with cysteine. Stability constants of complexes of molybdenum(V) and (VI) with cysteine have been reported4, but no complexes have been isolated. We now report the preparation and properties of a molybdenum(V)–cysteine complex, sodium di-μ-oxo-bis {oxo[cysteinato(2-)]aquomolybdate(V)} trihydrate, Na2 {Mo2O4[SCH2CH(NH2)CO2]2(H2O)2}3H2O, and discuss how far it can be regarded as a model for molybdenum in enzymes.

Elastic Constants of Molybdenum-Rich Rhenium Alloys in the Temperature Range -190°C to +100°C

Abstract: The adiabatic elastic constants of molybdenum and molybdenum alloyed in solid solution with 7.0, 16.6, and 26.9 at.% rhenium were measured in the temperature range −190°C to +100°C. Rhenium additions decrease (c11−c12)/2 and the twinning shear (c11−c12+c44)/3, and increase the bulk modulus and c44. The 26.9 at.% alloy is elastically isotropic. Alloy additions strengthen nearest‐neighbor interactions and weaken second‐nearest‐neighbor interactions. Debye temperatures calculated from the measured elastic constants agree well with those determined by calorimetry. Thermal expansion of the alloys was found to be essentially the same as for molybdenum in this temperature range.

Spectroscopic Studies of Mixed Amine Carbonyl Complexes of d6 Structure. II. Solvent Effect on the Ultraviolet and Visible Absorption Spectra of Diamine-tetracarbonyl Complexes of Chromium(0), Molybdenum(0) and Tungsten(0)

Abstract: Absorption bands, especially metal to amine charge transfer bands of bipyridyl- and phenanthroline-tetracarbonyl chromium (0), molybdenum (0) and tungsten (0) are shifted in various solvents by less than 4500 cm−1. The shift is discussed in accordance with McRae’s equation, which was derived with the point-dipole approximation. The solvents can be classified into two groups, the alcohol and the ester group. When three constants corresponding to (1) the interaction between induced dipoles of the solute and of the solvent, (2) the interaction between permanent dipole of the solute and induced dipole of the solvent, and (3) the interaction between permanent dipoles of the solute and of the solvent, are duely chosen for the two groups of solvent individually, the experimental values are satisfactorily accounted for. Short range interactions, such as hydrogen bonding can be ignored.

Spectroscopic Studies of Mixed Amine Carbonyl Complexes of d6 Structure. I. Visible and Ultraviolet Absorption Spectra of Diamine-tetracarbonyl Complexes of Chromium(0), Molybdenum(0) and Tungsten(0)

Abstract: Chromium(0), molybdenum(0) and tungsten(0) complexes of [M·(CO)4AA]0 type (AA=ethylenediamine (en), l-propylenediamine (l-pn), trimethylenediamine (tn), bipyridyl (bp), and phenanthroline (phen); l-pn and tn derivatives are new compounds) have been synthesized and their absorption spectra, rotatory dispersion (RD) and circular dichroism (CD) measured in methanol at room temperature. The nature of the absorption bands has been discussed by comparing them with one another and with those of hexacarbonyl- and piperidinepentacarbonyl complexes of these elements. The peaks in the region 23000 to 25000 cm−1 seem to be due to spinallowed d–d transition. The bands at 30000 to 33000 cm−1 appears to correspond to the metal to carbonyl charge transfer band of hexacarbonyls at ca. 36000 cm−1. Besides them, complexes of aromatic amines (bp and phen) show broad and strong bands at 21000 to 22000 cm−1 which seem to owe to metal to amine charge transfer.

Molybdenum(ii) cluster compounds involving alkoxy groups.

Abstract: : Molybdenum(II) halides readily react with alcoholic solutions of either sodium methoxide or ethoxide at room temperature to give crystalline coordination compounds of the type Na2((Mo6X8)(OR)6) in which the (Mo6X8)(4+) cluster behaves like a hexacoordinate coordination center. More vigorous treatment of molybdenum(II) chloride with sodium methoxide in methanol yields the crystalline compound Na2((Mo6(OCH3)8)(OCH3)6) in which both ligand and cluster chloride ions are replaced by methoxy groups. This compound appears to contain the cluster (Mo6(OCH3)8)(4+) analogous to the well known (Mo6X8)(4+) on the basis of magnetic properties, oxidation state of the molybdenum, proton magnetic resonance, conductivity, molecular weight, and infrared spectra. (Author)

Mos device with a metal-silicide gate

Abstract: A semiconductor device obtains in which a silicide film of 3d, 4d and 5d transition metal such as iron (Fe), cobalt (Co), nickel (Ni), molybdenum (Mo), palladium (Pd), platinum (Pt), or the like, is used as a conductive means in place of the conventional simple metal and whose structure is semiconductor-insularsilicide.

Effects of Composition on the Stress Corrosion Cracking of Ferritic Stainless Steels

Abstract: U-bend and axially loaded tensile-type specimens were used in stress corrosion tests performed in boiling 140 C (284 F) magnesium chloride solution. The experimental ferritic alloys tested contained 17 to 25% chromium, 0 to 4% nickel, 0 to 2% copper, and 0 to 5% molybdenum. Alloys essentially free of nickel and copper did not undergo stress corrosion cracking. (Tests on Types 430 and 434 stainless steels confirmed this behavior.) However, alloys containing more than 1% nickel or 0.5% copper were subject to transgi anular stress corrosion cracking in boiling magnesium chloride solution. Critical concentrations of copper and nickel that produce susceptibility to cracking were determined at various chromium and molybdenum levels. Experiments at controlled potentials indicated that cracking in boiling magnesium chloride was not the result of hydrogen embrittlement.

Some electronic properties of the molybdenum bronzes

Abstract: Measurements of the e.s.r. and optical spectra of the potassium and sodium molybdenum bronzes have been made. It is concluded that the observed e.s.r. signals arise from Mo5+ donor levels situated < 1 eV below the conduction band of the host MoO3 matrix. A model for the electronic structures of these compounds is proposed.