Farrel J. Martin

Carburization-induced passivity of 316 L austenitic stainless steel

A low-temperature (450-500°C) gas-phase process for introducing substantial amounts of carbon, without carbide formation, into 316L austenitic stainless steel has been developed. This process, termed low-temperature colossal supersaturation (LTCSS), provides surface carbon concentration as high as 14 atom % and dramatically improves the localized corrosion resistance of 316L austenitic stainless steel in ambient temperature seawater. In particular, the LTCSS-treated steel increases the seawater breakdown potential by more than 600 mV. This result is remarkable, as traditional carburization methods have historically decreased the corrosion resistance of stainless steels.

Anodically Generated Short-Lived Species on Boron-Doped Diamond Film Electrodes

Electrodes composed of boron-doped diamond (BDD) films on metal and semiconductor substrates have a wide range of applications in electrochemistry. This research investigated short-lived species (SLS) produced by anodic polarization of BDD electrodes in 1.0 M HClO 4 solutions. Normal pulse voltammetry experiments were performed to identify anodically produced SLS with lifetimes of less than 50 ms under open-circuit conditions. Potential step chronoamperometry experiments were performed to investigate the steady-state concentrations of SLS at the electrode-solution interface as a function of potential. Anodic potentials greater than 1.5 V with respect to the standard hydrogen electrode (SHE) were required to generate the SLS. Increasing anodic potentials between 1.5 and 3.0 V/SHE resulted in increasing concentrations of the SLS, until a saturation point was reached. Past work by other investigators suggests that the SLS likely consist primarily of HO . radicals produced from water oxidation.

Crevice corrosion of Alloy 625 in natural seawater

An experimental study was conducted to determine the influence of temperature on crevice corrosion initiation for Alloy 625 (UNS N06625) in natural seawater. These tests showed that that there was a critical potential–temperature–time relationship needed to initiate crevice corrosion. The potential necessary to cause crevice corrosion on Alloy * A. M. Grolleau contributed to this work while a visiting scientist at the Naval Research Laboratory in Key West, FL as part of the U. S./ French Defense Exchange Program 625 decreased (became less noble) when the temperature was increased from ambient to 40°C. The crevice initiation potential decreased from 300mV for ambient temperature seawater to around 100mV for 40°C seawater. Crevice initiation potentials were essentially unchanged between 40°C and 65°C, while the time required to initiate crevice corrosion decreased as temperature increased. In a second aspect of this work, natural seawater exposure studies were conducted to determine if there is a mechanistic connection between ennoblement (the gradual elevation of corrosion potential that occurs during long-term continuous immersion in natural seawater) and crevice corrosion initiation. It was found that ennoblement produced corrosion potentials for an extended period of time that exceed the crevice corrosion initiation potential in ambient temperature natural seawater. Temperature transients from ambient to elevated temperature created temporary conditions where the corrosion potential was substantially higher than the crevice initiation potential for short periods of time – but only if ennoblement had previously occurred at ambient temperatures.