Surface compositional changes

As high-alloy steels are used, the surface compositions change with use such changes occur in a matter of hours or even minutes. First, major increases occur in the chromium and manganese content. At or near the surface, the chromium content often increases from about 20% to 50-70 /o. The manganese content increases from <1% to 15-20 /o. Meanwhile the iron and nickel concentrations decrease from 40-50%i and 25-35% to less than 5 /o. Significant increases of... 

A comparison of catalytic and corrosion properties is possible, of course, only if the alloy happens to corrode without change of surface composition. For alloys, one component of which is relatively much more noble compared with other components, enrichment of the noble metal or its intermetallic compounds may occur at the surface. This makes it difficult to predict the corrosion behavior of Hume-Rothery alloys based on their catalytic behavior as described, for example, by Schwab 26). Copper-nickel alloys and transition metal alloys involving Fe, Cr, Ni, etc., corrode apparently without evidence of surface composition change of this kind. 

Compute the surface concentration of a Au-Ag solid solution that contains only 5 atom% silver. Assume ideal solution behavior. How does the surface composition change upon heating from 300 K to 700 K ... 

Similar behavior is observed with superalloys, but the mechanisms are more complicated because the surface composition changes with time due to the selective oxidation of alloy components. Figure 9.38 shows the mass variation as a function of... 

S. Rambert and D. Landolt, /Anodic dissolution of binary single phase alloys. I. Surface composition changes on Ag-Pd studied by Auger election spectroscopy, Electrochim. Acta3l Ul (1986). 

The top end of the Couette flow usually presents fewer problems, since it is open to a gas interface. Provision should be made in the design for exact maintenance of L without the need for precise volumetric filling. This can be accomplished by the spillover cup shown in Figure 5.3.7. Two problems can occur at the upper end surface composition changes and normal stress climbing. 

During vaporization of carbides (MC) the surface composition changes with time due to... 

Pyrite oxidation is not only important because of its environmental impact resulted from AMD. It affects directly the surface composition, changing its interaction with collectors in flotation, impacting economically on extraction of other minerals. The first step in order to understand the oxidation of pyrite is the analysis of its surface structure. The first question to answer is which is the preferential surface cleavage, i.e., the surface with lower surface energy (y). The surface energy is related with the formation of a surface from the solid. Because it is related with the breaking of chemical bonds, y is a positive quantity that depends on the area of the surface. Usually, surface energy is in the order of 0.1-1.0 I the lower values are related to more stable surfaces.y can be calculated by eq. (19), in which... 

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