mV SHE Research Articles

Effects of phosphorus segregated at grain boundaries on stress corrosion crack initiation and propagation of rotor steel in boiling 40 wt.% NaOH solution

The effects of phosphorus segregated at grain boundaries on intergranular corrosion have been investigated by an electrochemical method. The stress corrosion crack initiation and propagation of rotor steels was studied as a function of applied stress in boiling 40 wt.% NaOH solution at an applied passive potential of −530 mV SHE using the electrical potential method. Phosphorus segregation leads to intergranular corrosion susceptibility. Intergranular attack by anodic dissolution is responsible for the crack initiation, irrespective of the applied stress and phosphorus doping. The decrease in stress corrosion crack propagation time due to phosphorus segregated at grain boundaries is enhanced with increasing applied stress and is presumably related to crack branching. Fringe patterns on the intergranular facets of the fracture surface are found to be associated with martensite lath boundaries and are inferred to be caused by strain-induced dissolution.

A voltammetric study of galena immersed in acetate solution at pH 4.6

The electrochemistry of galena in an acetate solution at pH 4.6 has been studied through the use of linear sweep voltammetry. Analysis of the voltammograms for anodic limits as high as 845 mV indicates that S0 is the sulphur-bearing species generated during the oxidative dissolution of galena. Furthermore, interpretation of the electrochemical data on the basis of thermodynamic considerations indicates that galena interacts with the acetate electrolyte and that Pb(CH3COO)2(aq) is also produced during anodic oxidation. When the scan direction is reversed in the cathodic direction, the oxidation products are removed by two reduction reactions when the solution is quiescent: the recombination of Pb(CH3COO)2 and S0 to form PbS and the reduction of S0 to H2S. In a stirred solution, only the second reaction is possible. Experiments conducted in the presence of 10−3 or 10−2 M lead acetate indicate that the presence of dissolved lead tends to inhibit the dissolution process. Furthermore, metallic lead can begin to deposit on the galena surface when the potential drops below about −330 mV SHE. The data also agree most closely with thermodynamics when Pb(CH3COO)2 is considered to be the aqueous species involved in the deposition and dissolution of metallic lead.

Cathodic Protection of Steel Embedded in Porous Concrete

AbstractThe feasibility of applying cathodic protection to carbon steel strands embedded inporous concrete exposed to a chloride-containing environment was investigated. In-situ polarisation experiments were conducted on the embedded steel using a current-interrupt technique. This enabled the magnitude of the iR drop to be determined, and the actual (or corrected) potential of the embedded steel to be monitored throughout the experiments. The results suggested that, for the porous concretes which were examined, the minimum cathodic potential required to protect the embedded steel depended on the concentration of chlorides in the environment. These potentials are −260 mV SHE (−578 mV CSE) for a 0·02 M NaCl environment and −410 mV SHE (−728 mV CSE)for 0·7 M NaCl or sea water solutions.