Molybdenum cleaning surface

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. 

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. )...

Much of surface science research to date has focussed on the physical and chemical properties of clean metal surfaces, a state of matter that is only obtainable under ultrahigh vacuum. However, under practical, real world conditions most metals are covered by an oxide layer or take the form of various compounds, eg. sulfide, carbide, etc. For the last several years my research group has investigated the properties of "chemically modified" molybdenum surfaces which serve as models for the surface of molybdenum compounds. Surfaces that are models for the oxides, carbides, sulfides, and borides of molybdenum are fabricated by the reaction,... 

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. 

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-... 

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). 

There has been some discussion about whether pure molybdenum will in fact react with hydrogen sulphide to produce a surface film of molybdenum disulphide. The vacuum used by Bowden and Rowe to clean the surface of their molybdenum was relatively soft, and it seems probable that some oxide remained on the surface. Later work with cleaner surfaces showed that it is very difficult or even impossible to produce a molybdenum disulphide film on a really clean molybdenum surface by reaction with hydrogen sulphide. 

Use of Lubricants. Low-viscosity oils, particularly in combination with a phosphate-treated surface, can be helpful in reducing damage if the load is not too high. Low-viscosity oils diffuse more readily to the clean metal surface produced by oscillatory slip. Molybdenum sulfide is effective as a solid lubricant, particularly if baked onto the surface, but the beneficial effects tend to be temporary because the lubricant is eventually displaced by surface movement. 

B. Frilhberger J. G. Chen. Reaction of Ethylene with Clean and Carbide-Modified Mo(llO) Converting Surface Reactivities of Molybdenum to Pt-Group Metals. Journal of the American Ceramic Society. 118, 11599-11609, 1996. 

---