کد مقاله | کد نشریه | سال انتشار | مقاله انگلیسی | نسخه تمام متن |
---|---|---|---|---|
193613 | 459774 | 2009 | 8 صفحه PDF | دانلود رایگان |
![عکس صفحه اول مقاله: Effects of phosphate species on localised corrosion of steel in NaHCO3 + NaCl electrolytes Effects of phosphate species on localised corrosion of steel in NaHCO3 + NaCl electrolytes](/preview/png/193613.png)
Pitting corrosion of carbon steel electrodes in 0.1 M NaHCO3 + 0.02 M NaCl solutions was induced by anodic polarisation. The evolution of the breakdown potential Eb with the phosphate concentration was investigated by linear voltammetry. Eb increased from −15 ± 5 mV/SCE for [HPO42−] = 0 to 180 ± 40 mV/SCE for [HPO42−] = 0.02 mol L−1. During anodic polarisation (E = 50 mV/SCE), the behaviour of the whole electrode surface, followed by chronoamperometry, was compared to the behaviour of one single pit, followed via the scanning vibrating electrode technique (SVET). The addition of a Na2HPO4 solution after the beginning of the polarisation did not lead to the repassivation of pre-existing well-grown pits. The corrosion products forming in the pits were identified in situ by micro-Raman spectroscopy. They depended on the phosphate concentration. For [HPO42−] = 0.004 mol L−1, siderite FeCO3 was detected first. It was oxidised later into carbonated green rust GR(CO32−) by dissolved O2. The beginning of the process is therefore similar to that observed in the absence of phosphate. Finally, GR(CO32−) was oxidised into ferrihydrite, the most poorly ordered form of Fe(III) oxides and oxyhydroxides. Phosphate species, adsorbing on the nuclei of FeOOH, inhibited their growth and crystallisation. For [HPO42−] = 0.02 mol L−1, siderite was accompanied by an amorphous precursor of vivianite, Fe2(PO4)3·8H2O. This shows that, in any case, phosphate species interact strongly with the iron species produced by the dissolution of steel.
Journal: Electrochimica Acta - Volume 54, Issue 18, 15 July 2009, Pages 4389–4396