Physical properties of molybdenum

Other physical properties of molybdenum are given under Chemical Elements. See also summary of properties of refractory metals under Niobium. 

The chemical and physical properties of molybdenum(IV) chloride are well established.9,10,12,19 It is a black, nonvolatile compound which readily disproportionates to molybdenum (III) chloride and molybdenum (V) chloride at moderate tempera-... 

The mechanical properties reported in the literature for molybdenum and its alloys are frequently at variance. That this should be so is not surprising as the properties of molybdenum and its alloys are greatly affected by the prior history of the material, both thermal and mechanical. Far too often values are used without reference to the sources of the material, various states of heat treatment, etc. When mechanical properties are an important feature of the design application, advice should always be sought on the suitability as only the manufacturer has the complete data on the history of his own product. Physical and some typical mechanical properties given for general guidance are shown in Tables 5.2 and 5.3. 

Mo4 clusters have been identified in many solid phases of molybdenum chalcogenides including PbMo6S8,278 MoSX (X - Cl, Br,I)2 and GaMo4(YY ) (Y, Y - S, Se, Te)-290 the physical properties of these systems are of particular significance. Tetrahedral arrays of... 

For a comparison of the physical properties of tantalum, tungsten, molybdenum, platinum, oopper and nickel, see Balke, Chem. Met. Mng., 1922, 27, 1273. 

Physical Properties of Coked Catalysts. Surface areas for a series of Shell 244 (cobalt-molybdenum (Co-Mo) on alumina) catalysts varying from 0 to 22% coke were determined. The surface area is inversely proportional to coke deposition as shown in Figure 3. The catalysts with 10% coke deposit lose approximately 20% of their original surface areas. 

The most selective catalysts for the oxidation of methanol to formaldehyde are molybdates. In many commercial processes, a mixture of ferric molybdate and molybdenum trioxide is used. Ferric molybdate has often been reported to be the major catalytically active phase with the excess molybdenum trioxide added to improve the physical properties of the catalyst and to maintain an adequate molybdenum concentration under reactor conditions(l,2). In some cases, a synergistic effect is claimed, with maximum catalytic activity for a mixture with an Fe/Mo ratio of l.T( 3j. A defect solid solution was also proposed( ). Aging of a commercial catalyst has been studied using a variety of analytical techniques(4) and it was concluded that deactivation can largely be account for by loss of molybdenum from the catalyst surface. 

Nuclear applications of nanocapsules are related to the emitting physical properties of the encapsulated material. Emitted radiation can be electromagnetic of high energy (y), electrons or positrons (/3), alpha particles (" He nucleus), or fission products [67]. These emitters can be in themselves radioactive or can be activated by a nuclear reaction, usually a neutron capture. The particular advantage of carbon nanocapsules in nuclear applications is related to the protective characteristics that the carbon capsule confers to the interior product. Experiments on irradiation of fullerenes have shown that knocked carbon atoms from one cage are foimd in another fuUerene and even form dimers and trimers by a recoil-implantation mechanism [68]. The observed major damage of capsules in nanoencapsulated molybdenum irradiated in a nuclear reactor was produced by... 

Metallo-Flavoproteins. As was mentioned in the case of cytochrome reductase, enzymes are known that contain metal cofactors in addition to flavin. These are called metallo-flavoproteins. The presence of metals introduces complexity into the reaction, since the metals involved, iron, molybdenum, copper, and manganese, all exist in at least two valence states and can participate in oxidation-reduction reactions. The enzymes known to be metallo-flavoproteins include xanthine oxidase, aldehyde oxidase, nitrate reductase, succinic dehydrogenase, fatty acyl CoA dehydrogenases, hydrogenase, and cytochrome reductases. Before these are discussed in detail some physical properties of flavin will be presented. 

Catalyst selection should be based on catalyst reactivity, reaction selectivity, and physical properties such as particle size, density, and resistance to attrition. For process development, heat and mass transfer phenomena together with reactivity and physical properties of catalysts must be taken into account. The catalytic process begins with gas reactant transferring to the catalyst outer surface and subsequent intraparticle diffusion of the reactant through the pores of the catalyst. Reactants then absorb onto the catalyst surface and react to form product. These products desorb from the surface, and, through intraparticle diffusion, the products exit from the pores and outer catalyst surface. Consider the example of the ammoxidation of propylene to produce acrylonotrile over multicomponent molybdenum/bismuth catalysts ... 

Malyshev, V.V. (1998) Physical and chemical properties of molybdenum carbide coatings on various materials. Fiz. Khim. Mekh. Mater, 63. 

Nemanic, V., Zumer, M., Zajec, B., Pahor, J., Remskar, M., Mrzel, A., Panjan, P. and Mihailovic, D., Field emission properties of molybdenum disulfide nanombes. Applied Physics Letters, 82 (25), 2003, 4573 575. 

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