In situ and ex situ surface investigations of thiosulfate, sulfate and chloride accumulation on stainless steel and aluminum

In the United States alone it is estimated that annual corrosion-related damages cost approximately 100 billion dollars. Clearly, much effort is needed to reduce the detrimental efforts of corrosion. One approach to accomplishing this task is to understand fundamental corrosion mechanisms. Specifically, characterizing anionic accumulation on technologically-important substrates such as stainless steel and aluminum is of paramount importance, particularly in the development of effective corrosion inhibitors. This is largely attributed to the fact that anion interaction with passive films may promote either film degradation or corrosion inhibition.To date, attempts to gain information regarding anionic accumulation on stainless steel and aluminum have primarily been obtained via electrochemical methods or ex-situ surface analytical techniques such as Auger electron spectroscopy (AES), X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy/energy dispersive X-ray spectroscopy (SEM/EDX). Moreover, data describing accumulation processes such as reversibility, immobilization, kinetics and competitive anion accumulation are virtually nonexistent.Seeking to fill this void, my thesis provides scientific insight into corrosion mechanisms by employing an in-situ radiochemical method. This technique furnishes surface concentration, competitive accumulation, anion exchange and accumulation reversibility with respect to electrode potential information. Moreover, it is well suited for corrosion-related accumulation studies since smooth, commercial stainless steel and aluminum electrodes can be employed.The general investigative approach involves correlating radiochemical data with information acquired from electrochemical techniques (i.e., cyclic voltammetry and chronoamperometry). Electrochemistry is used to determine dissolution or repassivation potentials, the effect(s) of anion addition on voltammogram morphology and general redox processes occurring at the electrode/solution interface. AES, XPS and SEM/EDX are then employed to obtain elemental qualitative and quantitative information about adsorbed and/or immobilized species, surface and bulk composition as well as surface topography.Specific accumulation studies presented in my thesis are thiosulfate on 316 and 304 stainless steels, sulfate on pure aluminum and aluminum alloy (Al 2024) and chloride versus sulfate on 316 stainless steel and pure aluminum. Experimental methods, measurement procedures and correlation of electrochemical and surface analytical data with radiotracer results are discussed.U of I OnlyETDs are only available to UIUC Users without author permissio