Coupled radiotracer and voltammetric study of the adsorption of 1-hydroxy-ethane-1,1-diphosphonic acid on polycrystalline gold

Coupled application of a version of the in-situ radiotracer ‘foil’ method and voltammetry provided information on the time-, potential-, concentration- and pH-dependent adsorption of 1-hydroxy-ethane-1,1-diphosphonic acid (HEDP) on a polycrystalline gold electrode, and on the effect of Zn²⁺ ions on the adsorption phenomena. Adsorption processes on the oxide-free surface of gold were observed to be potential-dependent in the potential range 0.05–1.00 V (versus RHE), while formation and irreversible accumulation of oxidation products of HEDP could be detected at E>1.00 V. The relative adsorption strength of HEDP (its dissociation and/or oxidation products) was found to be higher on an oxide-free gold surface than on an oxide-covered one. The surface excess of HEDP increased with increasing pH. Addition of Zn²⁺ ions to the solution exerted a substantial effect on the HEDP accumulation. Namely, significant differences in the surface coverage, as well as in the kinetics and mechanism of HEDP adsorption could be detected in the potential regions below and above E=0.2 V. Reduction of Zn(II) species at E≤0.1 V is probably coupled with the induced adsorption of HEDP on an Au electrode, leading to the formation of a polymolecular HEDP–Zn surface complex layer.     

Effects of AP-CITROX Decontamination Procedure on the Surface Oxide Layer Composition of Stainless Steel Originating from the Primary Circuit of a VVER-Type Nuclear Reactor

A real specimen originating from the primary circuit of a VVER-440 type pressurized water cooled nuclear reactor has been studied by Conversion Electron Mössbauer Spectroscopy (CEMS) in order to find out how the AP-CITROX decontamination procedure modifies the structure and composition of the surface oxide layer of stainless steel which is used in the steam generator. Other methods like voltammetry, gravimetry, and SEM-EDAX were also applied to characterize the samples and to help the interpretation of CEMS results. It was found that, in contradiction with expectations, the presence of the surface magnetite layer could not be convincingly identified even on the non-decontaminated sample. This finding together with the relatively weak Mössbauer signals indicated that the surface oxide layer is strongly Fe-depleted. It was also concluded that the upper layer of the bulk steel (under the oxide layer) has an altered composition probably due to irradiation-enhanced diffusion of the metallic constituents. It was established that the AP-CITROX decontamination procedure does not exert detrimental effects on the thickness and composition of the surface oxide layer.     

A Mössbauer Study of Austenitic Steel Originating from the Steam Generator of a VVER-440 Type Nuclear Reactor,Paks, Hungary

Real specimens after more than ten years of operation in the steam generator of a VVER-440 type nuclear reactor, Paks, Hungary have been studied. Conversion electron Mössbauer spectroscopy was used for phase analysis of the primary side surfaces of austenitic stainless steel pipes. From the measurements, we concluded that the surface layer of the pipes consisted of a thin (<100 nm) and highly iron depleted oxidic film of nickel and chromium rich compounds. The ratio of the metallic constituents was found to be substantially different from that of the bulk steel to a depth of about 1–1.5 microns as revealed by independent SEM-EDAX studies. These findings may most likely be attributed to the irradiation enhanced diffusion and selective dissolution of iron.The bulk steel was investigated by transmission Mössbauer spectroscopy and X-ray diffraction. The samples originated from different sections of the collector head of the steam generator representing different contact times with steam and liquid water. Besides the paramagnetic peak of austenite, the Mössbauer spectra contained a magnetic sextet of ferrite in various amounts. This difference in phase composition may be attributed to the combination of irradiation effect and different thermal stress.