Cs. Vértes

Mössbauer spectroscopy studies of Sn-Pt/Al2O3 catalysts prepared by controlled surface reactions

Abstract Mossbauer spectroscopy was used to study the chemical state of tin in a new type of Sn-Pt/Al2O3 catalysts. Controlled surface reaction of tin tetraethyl with hydrogen preadsorbed on platinum resulted in the exclusive formation of a Pt-SnEt3 surface complex, which decomposed in hydrogen at 773 K to PtxSn alloy (3

Electrochemical and Conversion Electron Mössbauer Studies of Low Carbon Steel Polarized in Aqueous Sulfate Solution Containing Sulfite in Low Concentration

The passivation of low carbon steel was studied in aqueous solution of 0.5M and of at . The electrochemical methods (potentiodynamic, chronopotentiometric, and voltammetric) showed that the presence of 0.001M increased the thickness of the oxide film by about one order of magnitude. The spectrophotometric analysis of the solutions demonstrated that the rate of the dissolution of iron was much higher through the thick passive film, in the presence of ions, than through the thin passive film formed in the solution of 0.5M without ions. This is good evidence for the protective properties of the passive film being very weak if sulfite ions are present in the solution, even in a very low concentration. The conversion electron Mossbauer spectroscopy (CEMS) provides information about the compositions and thicknesses of the passive films formed in a solution containing both sulfate and sulfite ions. The major components found are and , and also could be identified on the surface of the low carbon steel as a minor component.

Conversion electron Mössbauer study of low carbon steel polarized in aqueous sulfate and sulfite containing sulfate solutions

Abstract The passivation of low carbon steel was studied in aqueous solutions of 0.5 M Na 2 SO 4 (pH = 3.5 and 6.5) and of 0.5 M Na 2 SO 4 + 0.001 M NaHSO 3 (pH 3.5 and 6.5). The used conversion electron Mossbauer spectroscopy (CEMS) with the complementary electrochemical, microscopic and spectrophotometric investigations proved that the presence of sulfite ion induces pitting corrosion. The compositions and thichnesses of the passive films formed during the electrochemical treatments are determined from the conversion electron Mossbauer spectra. γ-FeOOH was found in each case as a major component. At pH = 3.5, the sextet belonging to Fe 3 C appears in the spectra in most cases, and also FeSO 4 · H 2 O and could be detected after the shortest (90 min) polarization time.

Electrochemical and conversion electron mössbauer study of corrosion induced by acid rain

Abstract The passivation of low carbon steel was studied in aqueous solution of 0.5M Na2SO4 +0.001M NaHSO3 (pH 3.5, 6.5 and 8.5) which can be considered as a model of acid rain. The used conversion electron Mossbauer spectroscopy (CEMS) with the complementary electrochemical investigations proved that the sulfite ions induce pitting corrosion at pH 3.5 and 6 5 while the measurements showed much weaker pitting at pH 8.5. The compositions and thicknesses of the passive films formed during the electrochemical treatments are determined from the CEM spectra. Only γ-FeOOH was found on the surface of the samples at pH 6.5 and 8.5. Nevertheless, at pH 3.5 the sextet belonging to Fe3C appears in the spectra, and also FeS04H2O could be detected in low concentration.

A Mössbauer study of the crystalline structure of the passive film formed on iron in aqueous sulfate solution containing sulfite in low concentration

Electrochemically induced passivation of evaporated, enriched 57Fe in 0.5 mol dm−3 Na2SO4 + 0.001 mol dm−3 NaHSO3 aqueous solution (pH 6.5) was followed by conversion electron Mossbauer spectroscopy. The transformation of amorphous iron oxide or hydroxide into crystalline γ-FeOOH could be observed with the increase of the polarization time. The comparison of the original quantity of evaporated, enriched 57Fe layer on the surface of the samples with the dissolved iron, measured in the solutions after the polarization, proved the existence of pitting corrosion at this pH.

A study of electrochemically-induced corrosion of low carbon steel in a medium modelling acid rain

Complementary electrochemical, spectrophotometric and electron microsopic investigations were made in addition to the conversion electron Mössbauer spectroscopic (CEMS) measurements to learn more about the mechanism of corrosion of low carbon steel samples in aqueous sulfate and sulfite containing sulfate solutions (pH 3.5, 6.5 and 8.5). Passivation of iron in pure sulfate solution was studied in detail in earlier papers. In the present work, we used a solution containing both sulfate and sulfite anions to obtain more information about the effect of acid rain on low carbon steel samples. The compositions and thicknesses of the passive films formed due to the electrochemical treatments were determined from the CEM spectra. γ-FeOOH was found in each case on the surface of the samples; nevertheless, at pH 3.5 the sextet belonging to Fe3C appears in the CEM spectra, and also FeSO4 · H2O was detected in low concentration after the shortest polarization time (90 min). The results of the applied methods proved that the sulfite ions induce pitting corrosion at pH 3.5 and 6.5, while the measurements referred to suppressed pitting at pH 8.5.

conversion electron Mössbauer study of low carbon steel polarized in aqueous sulfate solution containing sulfite in low concentration

The passivation of low carbon steel was studied in aqueous solution of 0.5 M Na2SO4+0.001 M NaHSO3 at pH=3.5 and 6.5. The found major components at pH-3.5 were: γ-FeOOH and Fe3C, and also FeSO4.H2O could be identified on the surface of the low carbon steel as a minor component. At pH-6.5, the passive film contained only amorphous iron(III)-oxide or oxyhydroxide.

Comparative Mössbauer study of short-range ordering in electrodeposited and rapidly quenched amorphous alloys

We have found significant differences between the low temperature Mossbauer spectra of rapidly quenched and electrochemically prepared samples in the investigated cases even if the room temperature spectra were similar. In the spectra of electrodeposited alloys a new component appears at low temperature. The results can be interpreted in terms of differences between the structures of rapidly quenched and electrodeposited amorphous alloys.

Electrochemical behaviour of electrodeposited Fe—8P amorphous alloys

Mössbauer spectroscopy was used in order to study the influence of electrochemical behaviour of electrochemically deposited Fe—8P amorphous alloy. Electrochemically deposited amorphous samples were exposed to corrosion in the solution of H2SO4 and Na2SO4 containing NaHSO3 at pH=3.5. CEM spectra of as-deposited samples exhibit a typical sextet of ferromagnetic amorphous state. Even with samples being kept under corrosion condition for 10 minutes, the Mössbauer spectra reveal an extra Fe(III) component.

Conversion electron Mössbauer and XPS study on the effect of polishing of a stainless steel sample

Conversion electron Mössbauer spectroscopy (CEMS) and XPS has been used for the surface analysis of an “X10CrNiTi 18/9 (DIN 1.7440)”-type stainless steel in order to determine the supposed structural and/or chemical changes in the surface layer caused by polishing. Both, CEMS and XPS results can be associated with the appearance of Fe nitride in the outer layer of steel samples after polishing, while no sign of nitrogen was detected in the bulk material.