Investigation of inhibition effects of l-hydroxy-ethane-l,l-diphosphonic acid by radiotracer technique IT., Adsorption processes on polycrystalline gold in the presence of Zn2+ ions. The effect of zinc ion on potential and time dependent adsorption processes of 1-hydroxy-ethane-l,l-diphosphonic acid (HEDP) on polycrystalline gold have been investigated by combined application of an in situ radiotracer method and voltammetry. In the potential range below and above E=0.2 V, the extent, time dependence as well as the mechanism of HEDP adsorption are different in solutions containing zinc ions. At E>0.2 V, a slight decrease in HEDP sorption has been observed in the presence of zinc ion, which is presumably due to the differences in projected areas occupied by HEDP and HEDP-Zn complexes. At E<0.1 V quasi-reversible oxidationreduction current peaks of zinc redox processes were observed. The current peaks shifted toward the anodic direction and the hydrogen evolution potential shifted continuously toward the cathodic direction with increasing HEDP/Zn2+ molar ratio. The induced adsorption of HEDP in the course of zinc reduction reveals formation of an adsorbed layer of HEDP-zinc complexes on the gold surface. At E< 0.1 V the surface excess values of HEDP are much higher (Γmax = 1.45·10-9 mol-cm-2, E = -0.6 V, t = 12 min) than those in the potential range of E>0.2 V (Γmax = 4-10-10 mol-cm-2). These experimental data also support the formation and accumulation of HEDPzinc complexes on the gold surface, which increases during cathodic polarization as a result of the reduction processes below 0.1 V. The adsorption of HEDP in the presence of zinc ion is polymolecular, the coverage reaches n~3 (E = -0.6 V, t -12 min), and the formation of the layer is continuous in time. These results are in accordance with the experimental facts that the required protective effect of HEDP-zinc salt inhibitor blends is developed after several hours in corrosion systems.
|Number of pages||7|
|Journal||Magyar Kemiai Folyoirat, Kemiai Kozlemenyek|
|Publication status||Published - Dec 1 1998|
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