Effects of Lead Oxide Addition on the Electrochemical Properties of Alloy 600 in Aqueous 1 M Sodium Hydroxide Solution

Abstract

Effects of lead oxide (PbO) addition on the electrochemicalproperties of alloy 600 (UNS N06600) have been studied in aqueous 1 M sodium hydroxide (NaOH) solution at room temperature using surface analytical techniques and electrochemical methods. For the comparative study on the different roles of the surface layers in the electrochemical properties of alloy 600, two kinds of electrodes were potentiostatically prepared at the anodic and cathodic potential peaks observed in cyclic voltammograms obtained in PbO-containing caustic solution: lead dioxide (PbO 2 ) filmcovered and Pb deposit-covered alloy electrodes. The crystal structures and morphologies of the two kinds of the surface layers were characterized by x-ray diffractometry and scanning electron microscopy. From the open-circuit potential (OCP) transients and galvanic current transients, it was inferred that Ni and Fe among alloy 600 constituents as anodic sites were dissolved selectively in caustic solution caused by the lower OCP value where there was no PbO 2 film compared to that of PbO 2 film-covered surface on the alloy. Based upon the experimental results, it was suggested that an enhanced dissolution of Ni and Fe in alloy 600 in caustic solution at room temperature was a consequence of PbO 2 -induced corrosion.

Effects of NiB, PbO, and TiO[sub 2] on SCC of Sensitized Inconel Alloy 600 in RT-Tetrathionate Solution

“…It should be emphasized that the addition of PbO promotes chromium depletion from the surface oxide film of alloy 600, resulting in the low resistance of the surface oxide film to SCC. [24][25][26][27] On the other hand, the peaks for B and Ti oxides in the presence of NiB and TiO 2 were not apparent, compared to those peaks in their absence. This indicates that NiB and TiO 2 cannot be reduced and incorporated into the surface oxide film but just adsorbed on the surface film in the present work.…”

“…16 The order of the induction time for SC crack initiation given in Table II showed a similar tendency in the effects of PbO and TiO 2 reported by other researchers. 16,[24][25][26][27] It decreased in the following order: PbO Ͼ absence of additives Ϸ NiB Ͼ TiO 2 .…”