Molybdenum cleaning

The molybdenum cleaning process is necessary to remove surface scale, general contamination, and any basis metal that may be present. Among the potential contaminants in wrought products, iron is of primary concern. Others, such as aluminum, carbon, cadmium, copper, and nickel, may also be present as elements, but they are more frequently present in the form of oxides. Removal of a controlled amount of basis metal may be desired to insure complete removal of contaminants. There are three main methods for cleaning molybdenum and molybdenum alloys. 

Natural gas contains both organic and inorganic sulfur compounds that must be removed to protect both the reforming and downstream methanol synthesis catalysts. Hydrodesulfurization across a cobalt or nickel molybdenum—zinc oxide fixed-bed sequence is the basis for an effective purification system. For high levels of sulfur, bulk removal in a Hquid absorption—stripping system followed by fixed-bed residual clean-up is more practical (see Sulfur REMOVAL AND RECOVERY). Chlorides and mercury may also be found in natural gas, particularly from offshore reservoirs. These poisons can be removed by activated alumina or carbon beds. 

In cases where very high adherence is necessary an undercoating of sprayed molybdenum is applied. Owing to the volatile nature of its oxide this metal presents a clean surface to the workface and with most metals (except copper) very high adhesion is obtained. To a limited extent arc-sprayed aluminium bronze will also form a strongly adherent base coating. 

D.G. Kelly, M. Salmeron, and G.A. Somorjai, The adsorption and reactions of hydrocarbons on molybdenum single crystal surfaces when clean and in presence of coadsorbed sulfur or carbon, Surf. Sci. 175,465 (1986). 

A schematic flowsheet for molybdenum recovery from porphyry coppers is shown in Figure 2.34. Here the important role is played by flotation. The first stage involves collective flotation of copper and molybdenum. The floated product is upgraded through two or three cleaning flotations. Finally, molybdenum is recovered by depressing copper values. In order to depress a mineral, some kind of oxidation should be implied on its surface, or re-... 

Measurements of the EDS emission were limited to Cu and In edges since the EDS emissions for sulfur and molybdenum overlapped. SEM-EDS data on several regions on the film gave atomic percents representative of CuInS2 (Table 6.3), and no evidence of phosphorous could be detected under the typical detection limit of EDS (0.02 wt%), verifying that the precursor decomposes cleanly, as evidenced in EGA-TGA studies. 

The ruthenium carbene catalysts 1 developed by Grubbs are distinguished by an exceptional tolerance towards polar functional groups [3]. Although generalizations are difficult and further experimental data are necessary in order to obtain a fully comprehensive picture, some trends may be deduced from the literature reports. Thus, many examples indicate that ethers, silyl ethers, acetals, esters, amides, carbamates, sulfonamides, silanes and various heterocyclic entities do not disturb. Moreover, ketones and even aldehyde functions are compatible, in contrast to reactions catalyzed by the molybdenum alkylidene complex 24 which is known to react with these groups under certain conditions [26]. Even unprotected alcohols and free carboxylic acids seem to be tolerated by 1. It should also be emphasized that the sensitivity of 1 toward the substitution pattern of alkenes outlined above usually leaves pre-existing di-, tri- and tetrasubstituted double bonds in the substrates unaffected. A nice example that illustrates many of these features is the clean dimerization of FK-506 45 to compound 46 reported by Schreiber et al. (Scheme 12) [27]. 

Platinum electrodes were cleaned with the same procedure. Then sodiiun molybdenum oxide (Johnson Matthey, 99.998%) was added to obtain 0.01 M molybdenum concentration. Then the potential was held at 50 mV for 10 s. Then the electrode was rinseed with hydrogen saturated water and transferred to the measurement cell. The potential was set to 50 mV immediately after the transfer. 

An attempt at a direct determination of the number of silver atoms in a nucleus just able to initiate physical development was made by Reinders and his co-workers (Reinders and Hamburger, 41 Reinders and deVries, 42). Silver was deposited on glass plates by sublimation in a high vacuum. The source of the silver was a molybdenum wire coated with silver and heated electrically to 500-600°. The glass plates were carefully cleaned and outgassed before use. 

Table 1. Reflection of He at normal incidence from clean surfaces of Tungsten, Molybdenum, and Silicon. is the energy of the incident ion and R is the probability that it will be reflected from the surface as an ion. (From Ref. )...

In this latter reaction, the iridiabenzene complex cleanly displaces the para-xylene ligand so as to form complex 68, in which the iridiabenzene acts as if it were a normal pMigand coordinated to the molybdenum tricarbonyl moiety. 

There are two principal synthetic routes to dicarboxylate complexes. One of these uses an aqueous solution of the alkali metal dicarboxylate and the corresponding metal halide,93 while the other depends upon the dicarboxylic acid reduction of higher oxidation state metals. This reductive property of oxalic acid results in its ready dissolution of iron oxides and hence a cleaning utility in nuclear power plants.94 Mention must also be made of the successful ligand exchange synthesis of molybdenum dicarboxylates, Mo(dicarboxylate)2 H2 O, from the corresponding acetate complex. Unfortunately the polymeric, amorphous and insoluble nature of these complexes has restricted the study of these systems, which may well provide examples of multiple M—M bonding in dicarboxylate coordination chemistry.95... 

Materials such as graphite, molybdenum disulfide, and Teflon emit few or no electrons when disturbed. Meanwhile, fresh surfaces of such metals as aluminum and steel produce a large number of emitted electrons (Connely Rabinowicz 1983). This emission occurs when plastic deformation, abrasion, or fatigue cracking disturbs a material s surface. Electron emission from freshly formed surface reaches a maximum immediately and then decays with time. Emission has been observed for both metals and metal oxides. There is strong evidence that the existence of oxides is necessary. The exoelectron emission occurs from a clean, stain-free metallic surface upon adsorption of oxygen (Ferrante 1977). 

Prior to deposition, polish the Si substrate for 15 min with diamond powder on a felt polishing pad. The scratches serve as nucleation sites for the diamond growth. Clean the polished substrate with 2-propanol twice, and dry it by air blowing. Then, place on molybdenum holder in the CYD reactor, and reduce the system pressure to less than ICC3 Torr. 

This conversion is a clean reactivity model for the Mo enzyme trimethylamine A-oxide reductase. The molybdenum(VI) bis(oxido) complex has a distorted octahedral geometry [181],... 

Figure 24 Auger spectrograph of molybdenum silicide film both (a) before and (b) after sputter cleaning.

Catalysts help customers comply cost-effectively with clean-air regulations. Hydrocarbons, carbon monoxide, and nitrogen oxides can be removed using supported precious metal catalysts. Organic sulfur compounds are converted to H2S using nickel/molybdenum or cobalt/molyb-denum on alumina catalysts. Sulfur can be recovered in a Claus process unit. The Claus catalytic converter is the heart of a sulfur recovery plant. 

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