Molybdenum composites

Thus, for similar values of ns, the entropy at infinite dilution for TiMo/H2 is about 3.4 eu/H more negative than that for 0-Ti/H2. An explanation for this difference might be that the molybdenum atoms in the metal lattice block potentially available interstitial sites for hydrogen occupation, resulting in nonrandom occupation of sites at low hydrogen content. Rudman (24) proposed such a role for aluminum in titanium. We presently are gathering more data for alloys of varying molybdenum composition to test this hypothesis. 

Similarly 2-propanol exalts the selectivity in citronellol for the sequence B — C — E, from the values of the ratios k bg/k bj., it appears that the maximum yield in citronellol over pure nickel rises from 59% to 91%. Over molybdenum promoted catalysts the selectivity of this step increases with che molybdenum composition in the oulk to reach 100% with NiMOq 1g, i.e. citronellol is not hydrogenated to 3,7dimethyloctanol. 

The use of Fe-Cr and especially Cu-Zn-Al WCS catalysts in present-day hydrogen plants is directly connected with moderate levels of sulfur-containing compounds in natural gas and naphtha that almost completely displaced coal as the feedstock. It is likely, however, that the incentives for the use of fossil fuels rich in sulfur can be revitalized in the future. If this scenario comes into play, sulfur-tolerant catalysts will be a must for WCS process. Such catalysts are already developed, but so far they have only found a limited use in some particular cases where feed gases with high concentrations of CO and sulfur compounds had to be converted. The best known of this type are cobalt-molybdenum compositions, which are usually supported over alumina and may be promoted with alkali... 

Y. Waku, M. Suzuki, Y. Oda and Y. Kohtoku, Improving the Fracture Toughness of Mg0-Al203-Si02 Glass/Molybdenum Composites by the Microdispersion of Flaky Molybdenum Particles, J. Mat. Sci. 32, 4549 557 (1997). 

Patents claiming specific catalysts and processes for thek use in each of the two reactions have been assigned to Japan Catalytic (45,47—49), Sohio (50), Toyo Soda (51), Rohm and Haas (52), Sumitomo (53), BASF (54), Mitsubishi Petrochemical (56,57), Celanese (55), and others. The catalysts used for these reactions remain based on bismuth molybdate for the first stage and molybdenum vanadium oxides for the second stage, but improvements in minor component composition and catalyst preparation have resulted in yields that can reach the 85—90% range and lifetimes of several years under optimum conditions. Since plants operate under more productive conditions than those optimum for yield and life, the economically most attractive yields and productive lifetimes maybe somewhat lower. 

Molybdenum hexafluoride is used in the manufacture of thin films (qv) for large-scale integrated circuits (qv) commonly known as LSIC systems (3,4), in the manufacture of metallised ceramics (see MetaL-MATRIX COMPOSITES) (5), and chemical vapor deposition of molybdenum and molybdenum—tungsten alloys (see Molybdenumand molybdenum alloys) (6,7). The latter process involves the reduction of gaseous metal fluorides by hydrogen at elevated temperatures to produce metals or their alloys such as molybdenum—tungsten, molybdenum—tungsten—rhenium, or molybdenum—rhenium alloys. 

Rhenium hexafluoride is a cosdy (ca 3000/kg) material and is often used as a small percentage composite with tungsten or molybdenum. The addition of rhenium to tungsten metal improves the ductility and high temperature properties of metal films or parts (11). Tungsten—rhenium alloys produced by CVD processes exhibit higher superconducting transition temperatures than those alloys produced by arc-melt processes (12). 

Both molybdenum and tungsten can be worked in air without ductiHty loss. AH refractory metals can be made into tubing by extmsion, and most refractory metals, except chromium, are available as wine. Tungsten wines were attempted as fiber reinforcement for experimental nickel-base composites. 

DRI retains the chemical purity of the iron ore from which it is produced, therefore it tends to be very low in residual elements such as copper, chrome, tin, nickel, and molybdenum. Typical ranges of DRI chemical compositions are shown in Table 2. 

Copper and silver combined with refractory metals, such as tungsten, tungsten carbide, and molybdenum, are the principal materials for electrical contacts. A mixture of the powders is pressed and sintered, or a previously pressed and sintered refractory matrix is infiltrated with molten copper or silver in a separate heating operation. The composition is controlled by the porosity of the refractory matrix. Copper—tungsten contacts are used primarily in power-circuit breakers and transformer-tap charges. They are confined to an oil bath because of the rapid oxidation of copper in air. Copper—tungsten carbide compositions are used where greater mechanical wear resistance is necessary. 

Tungsten—silver contacts are made similarly, but can be operated in air because of the greater stabiUty of silver. The three standard compositions of this class include tungsten—silver, tungsten carbide—silver, and molybdenum—silver. 

Advanced Structural and Heating Materials. Molybdenum siHcide [12136-78-6] and composites of MoSi2 and siHcon carbide, SiC, have properties that allow use as high temperature stmctural materials that are stable in oxidizing environments (see Composite materials Metal-matrix composites). Molybdenum disiHcide also finds use in resistance heating elements (87,88). 

Vitahium FHS ahoy is a cobalt—chromium—molybdenum ahoy having a high modulus of elasticity. This ahoy is also a preferred material. When combiaed with a properly designed stem, the properties of this ahoy provide protection for the cement mantle by decreasing proximal cement stress. This ahoy also exhibits high yields and tensile strength, is corrosion resistant, and biocompatible. Composites used ia orthopedics include carbon—carbon, carbon—epoxy, hydroxyapatite, ceramics, etc. 

The physical and mechanical properties of steel depend on its microstmcture, that is, the nature, distribution, and amounts of its metaHographic constituents as distinct from its chemical composition. The amount and distribution of iron and iron carbide determine most of the properties, although most plain carbon steels also contain manganese, siUcon, phosphoms, sulfur, oxygen, and traces of nitrogen, hydrogen, and other chemical elements such as aluminum and copper. These elements may modify, to a certain extent, the main effects of iron and iron carbide, but the influence of iron carbide always predominates. This is tme even of medium alloy steels, which may contain considerable amounts of nickel, chromium, and molybdenum. 

By adjusting the content of cobalt, molybdenum, and titanium, the 18% nickel steel can attain yield strengths of 1380—2070 MPa (200,000—300,000 psi) after the aging treatment. Similarly, yield strengths of 12% nickel steel in the range of 1035—1380 MPa (150,000—200,000 psi) can be developed by adjusting its composition. 

Lubricants. TeUurides of titanium, 2irconium, molybdenum, tungsten, and other refractory metals are heat- and vacuum-stable. This property makes them useful in soUd self-lubricating composites in the electronics, instmmentation, and aerospace fields (see Lubrication and lubricants). Organic teUurides are antioxidants in lubricating oUs and greases. 

The important (3-stabilizing alloying elements are the bcc elements vanadium, molybdenum, tantalum, and niobium of the P-isomorphous type and manganese, iron, chromium, cobalt, nickel, copper, and siUcon of the P-eutectoid type. The P eutectoid elements, arranged in order of increasing tendency to form compounds, are shown in Table 7. The elements copper, siUcon, nickel, and cobalt are termed active eutectoid formers because of a rapid decomposition of P to a and a compound. The other elements in Table 7 are sluggish in their eutectoid reactions and thus it is possible to avoid compound formation by careful control of heat treatment and composition. The relative P-stabilizing effects of these elements can be expressed in the form of a molybdenum equivalency. Mo (29) ... 

Alloy Compositions and Product Forms. SteUite 21, an early type of cobalt-base high temperature alloy, is used primarily for wear resistance. The use of tungsten rather than molybdenum, moderate nickel contents, lower carbon contents, and rare-earth additions typify cobalt-base high temperature alloys of the 1990s as can be seen from Table 5. 

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