Surface iron atoms, measurement

Extensive information concerning distribution of the promoters, penetration below the promoters of adsorbed atoms, and chemical behavior of the promoters was obtained by Brunauer and Emmett (25,26). They used chemisorption of carbon monoxide, carbon dioxide, nitrogen, hydrogen, and oxygen, individually and successively measuring the influence of one type of chemisorption upon another type. It was concluded that CO and C02 were chemisorbed as molecules, H2 and N2 as atoms, and 02 probably as ions. C02 is chemisorbed on the alkali molecules located at the surface, whereas H2, N 2, CO, and 02 are chemisorbed on the iron atoms. From the effect of presorbed CO upon the chemisorption of C02 and vice versa it was concluded that the promoters are concentrated on the surface and are distributed so effectively that most surface iron atoms are near to a promoter atom. Strong indication... 

For iron, cobalt, nickel, and their alloys, the most sensitive technique for characterizing the particle surface is the measurement of magnetic properties. Thus, we synthesized cobalt nanoparticles of 1.6 nm (ca. 150 atoms), 2 nm (ca. 300 atoms) and 4 nm (a few thousand atoms) mean size. The structure of the particles is hep in the latter case and polytetrahedral in the first two cases. The 4 nm particles display a saturation magnetization equal to that of bulk... 

For elements such as silicon, alumina and sodium, there is a fairly good agreement between atomic absorption (AA) determination and EDS data for the parent Mg-rectorite. However, there are differences with respect to other elements, as shown in Table 6-1. This is not unexpected, since AA determination reports bulk analysis, whereas EDS reports the composition of the individual clay ciystal surface. The iron content measured by EDS is much higher than reported by AA analysis indicating that Fe is preferentially concentrated on the clay platelets surface, and that FejOj-containing phase impurities are negligible. The magnesium distribution is similar to that observed for Fe. 

The interchange reaction implies the removal of one atom of /I at the surface for each atom of B deposited. It therefore takes place with a minimum change in weight or dimensions of the article (A). U A and B have similar atomic weights, as in the case of iron and chromium, interchange reaction will produce little change in weight and no measurable increase in dimension, whatever the thickness of the diffusion layer. 

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