Metals molybdenum

In addition, molybdenum has high resistance to a number of alloys of these metals and also to copper, gold, and silver. Among the molten metals that severely attack molybdenum are tin (at 1000°C), aluminum, nickel, iron, and cobalt. Molybdenum has moderately good resistance to molten zinc, but a molybdenum—30% tungsten alloy is practically completely resistant to molten zinc at temperatures up to 800°C. Molybdenum metal is substantially resistant to many types of molten glass and to most nonferrous slags. It is also resistant to hquid sulfur up to 440°C. 

In a vacuum, uncoated molybdenum metal has an unlimited life at high temperatures. This is also tme under the vacuum-like conditions of outer space. Pure hydrogen, argon, and hehum atmospheres are completely inert to molybdenum at all temperatures, whereas water vapor, sulfur dioxide, and nitrous and nitric oxides have an oxidizing action at elevated temperatures. Molybdenum is relatively inert to carbon dioxide, ammonia, and nitrogen atmospheres up to about 1100°C a superficial nitride film may be formed at higher temperatures in the latter two gases. Hydrocarbons and carbon monoxide may carburize molybdenum at temperatures above 1100°C. 

Manufacturing Processes. Ammonium molybdate or molybdenum trioxide is reduced to molybdenum metal powder by hydrogen in a two-stage process. In the first stage, MoO or ammonium molybdate is reduced to molybdenum dioxide, M0O2, at temperatures around 600°C in the... 

The same properties that make molybdenum metal effective in high temperature furnace appHcations make it useful as support wires for tungsten filaments in incandescent light bulbs and as targets in x-ray tubes. 

Because of its high modulus of elasticity, molybdenum is used in machine-tool accessories such as boring bars and grinding quills. Molybdenum metal also has good thermal-shock resistance because of its low coefficient of thermal expansion combined with high thermal conductivity. This combination accounts for its use in casting dies and in some electrical and electronic appHcations. 

Additions of selected alloying elements raise the recrystaUization temperature, extending to higher temperature regimes the tensile properties of the cold-worked molybdenum metal. The simultaneous additions of 0.5% titanium and 0.1% zirconium produce the TZM aUoy, which has a corresponding... 

Molybdenum Metal, Climax Molybdenum Co., Ann Arbor, Mich., 1960. 

Figure 2 Molybdenum K-edge X-ray absorption spectrum, ln(i /i ) versus X-ray energy (eV), for molybdenum metal foil (25- jjn thick), obtained by transmission at 77 K with synchrotron radiation. The energy-dependent constructive and destructive interference of outgoing and backscattered photoelectrons at molybdenum produces the EXAFS peaks and valleys, respectively. The preedge and edge structures marked here are known together as X-ray absorption near edge structure, XANES and EXAFS are provided in a new compilation of literature entitled X-rsy Absorption Fine Structure (S.S. Hasain, ed.) Ellis Norwood, New York, 1991.

Figures Background-subtracted, normalized, and ili -weighted Mo K-edge EXAFS, versus k (A ), for molybdenum metal foil obtained from the primary experimental data of Figure 2 with Eq = 20,025 eV.

The Fourier transform of the EXAFS of Figure 5 is shown in Figure 6 as the solid curve It has two large peaks at 2.38 and 2.78 A as well as two small ones at 4.04 and 4.77 A. In this example, each peak is due to Mo—Mo backscattering. The peak positions are in excellent correspondence with the crystallographically determined radial distribution for molybdenum metal foil (bcc)— with Mo—Mo interatomic distances of2.725, 3.147, 4.450, and 5.218 A, respectively. The Fourier transform peaks are phase shifted by -0.39 A from the true distances. 

Nair, F. B. and Briggs, J. Z., Corrosion Resistance of Molybdenum and Molybdenum Base Alloys, Molybdenum Metal... 

In the preparation of Mo/HUSY, the cluster 1 amounting to 2.5 wt% (as molybdenum metal) of HUSY was added to the suspension of HUSY 92% of the molybdenum was loaded onto HUSY. The Cl/Mo ratio of Mo/HUSY was found to be 0.34, suggesting that in ion exchange the cluster 1 acted as a trivalent cation on the average. These findings indicate that the protons in HUSY are less exchangeable by the cluster cation than the Na cations in NaY. 

Pure molybdenum trioxide, a higher quality product, is in great demand with regard to chemicals and catalyst manufacturers, superalloy producers, and molybdenum metal producers. This refined quality oxide is produced by the volatilization of the technical grade... 

This proposed catalytic mechanism (Chong and Sharpless, 1977) requires four reaction steps (3 bimolecular and 1 unimolecular), which take place on a molybdenum metal center (titanium and vanadium centers are also effective), to which various nonreactive ligands (L) and reactive ligands (e g., O-R) are bonded. Each step around the catalytic cycle is an elementary reaction and one complete cycle is called a turnover. 

A mixed-valent polymolybdate on active carbon was prepared from molybdenum metal and H202, followed by the addition of active carbon to the aqueous solution [114,115], This catalyzed the epoxidation of several alkenes in 2-propanol using H202 as an oxidant, while the efficiency of H202 utilization was very low (< 25%). The epoxidation likely proceeded mainly on the surface of the catalyst because the recovered catalyst showed almost similar catalytic activity. 

Ammonium molybdates are used to prepare high purity grade molybdenum metal powder, sheet, or wire for colorimetric analysis of phosphates and arse-... 

Elemental composition H 4.11%, Mo 48.94%, N 14.29% O 32.65. (NH4)2Mo04 is digested with nitric acid and the molybdenum metal is analyzed by atomic absorption or emission spectrophotometry. It is dissociated to ammonia, which may be measured by titration or by an ion-specific electrode technique (see Ammonia). Ammonium molybdate reacts under acid conditions with dilute orthophosphate solution to form molybdophosphoric acid which, in the presence of vanadium, forms yellow vanadomolybdophosphoric acid the intensity of the yeUow color may be measured by a spectrophotometer at 400 to 490 nm and is proportional to the trace amount of ammonium molybdate. 

When bromine vapor is passed over molybdenum metal at 600 to 700°C in an atmosphere of nitrogen, the product is trimeric molybdenum dibromide (trimolybdenum hexabromide) (Mo3Bre) ... 

Among molybdate salts, sodium and ammonium molybdates have commercial applications. The normal salt, sodium orthomolyhdate, Na2 M0O4, is used in pigments. It also is used as a corrosion inhibitor and as an additive to soil. Lead molybdate, Pb M0O4, occurs in nature as mineral ulfenite, from which molybdenum metal is recovered. 

Molybdenum hexacarbonyl usually is made by treating molybdenum pen-tachloride with zinc dust in carbon monoxide under high pressure (90 to 120 atm). Also, it can be prepared by direct combination of molybdenum metal powder with carbon monoxide under pressure. 

Thermal dissociation of molybdenum hexacarbonyl yields molybdenum metal and carbon monoxide. 

Elemental composition Mo 36.34%, C 27.30%, 0 36.36%. A benzene solution of the hexacarbonyl may be analyzed by GC/MS. Molybdenum metal digested in nitric acid solution may be analyzed by various instrumental techniques. Also, the compound may be thermally dissociated and the liberated CO may be identified by GC using a TCD or by GC/MS using an appropriate capillary column. 

Alternatively, the oxide may be prepared by heating a molybdate salt, such as ammonium molybdate, with a reducing agent such as zinc. The dioxide also may be obtained along with other oxides of molybdenum when molybdenum metal is heated in air. 

The dioxide readily oxidizes to trioxide when heated in air. It also is oxidized to M0O3 by nitric acid. When heated with hydrogen above 470° C, the oxide is reduced to molybdenum metal. 

Also, the compound may be prepared by the action of chlorine on molybdenum metal at elevated temperatures (500°C) ... 

When heated with hydrogen at 400°C or the vapors passed over heated molybdenum metal, the pentachloride converts to trichloride ... 

However, when the pentachloride is heated with hydrocarbons, a beta-form of M0CI4 forms. The product always is contaminated with carbon. Heating the pentachloride with molybdenum metal forms the same beta-MoCR. Reaction with hydrogen bromide yields molybdenum tetrabromide. 

Existence of technetium was predicted from the vacant position in the Periodic Table between manganese and rhenium. Noddack, Tacke, and Berg reported its discovery in 1925 and named it masurium. The metal actually was never isolated from any source by these workers. Its existence, therefore, could not be confirmed. Perrier and Segre in 1937 produced this element by bombarding molybdenum metal with deuterons in a cyclotron. They named the element technetium derived from the Greek word technetos, meaning artificial. 

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