CEMS Mossbauer spectrum

CEMS Mossbauer spectrum of the corroded mild steel surface. 

Typical Mossbauer spectra for the fresh, reduced, carblded and used Fe/ZSM-5 system are shown in a composite Fig. 5. Similar spectra were obtained for the Fe-Co/ZSM-5 system. The product distribution for the F-T reaction, using the Fe and Fe-Co systems, are shown in Table 1. The gasoline range hydrocarbon yield increased from 75 to 94%, when the Fe-Co clusters were used in place of Fe only. In a typical CEMS (Conversion Electron Mossbauer Spectroscopy) of the Fe-Co system, no spectrum for 57pg vas observed even after one week from this. It was concluded that in the Fe-Co clusters Co was predominantly in the "mantle" and Fe species were In their "core," in the parlance of metallurgy/geophysics. This model Is sometimes referred to as the cherry model. 

The Mossbauer-effect experiment can also be applied to the study of surfaces in the variation known as conversion electron Mossbauer spectroscopy (CEMS). Here, what is monitored as a function of incident y-ray energy is not absorption, but the emission of electrons through a process of internal conversion (i.e., as a byproduct of the absorption of Mossbauer y rays). Since the conversion electrons can only escape from the surface layers of the solid, data are selectively acquired for the surface region, arising from the Mossbauer effect in the (most commonly iron) atoms of the surface layers. The monitoring of emitted electrons results in a mirror image of the usual absorption spectrum. Transmission and CEM spectra of vivianite [Ee3(P04)2-8H20] are illustrated in Fig. 2.49 (after Tricker et al., 1979]. 

Fine coal samples were pressed into briquettes to simulate the compacting occurring during transportation and it was found that the amount of water contained in the coal declined by a factor of about 2 as compaction pressures increased from an initial pressure of 51 to a final pressure of 251. The amount of water in the samples compacted at 51 was 8.3% for the coal containing 3% pyrite and 11.9% for the coal containing only 0.6% pyrite. The briquettes pressed at a 51 compaction pressure were then placed on cleaned steel coupons for predetermined times and CEMS mode Mossbauer spectroscopy was conducted on the steel samples with the resulting spectrum presented in Fig. 30.11. 

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