In Situ Studies of Corrosion and Electrodeposition Using Atomic Force Microscopy
Rynders, Rebecca Mohr
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https://hdl.handle.net/2142/72149
Description
Title
In Situ Studies of Corrosion and Electrodeposition Using Atomic Force Microscopy
Author(s)
Rynders, Rebecca Mohr
Issue Date
1993
Doctoral Committee Chair(s)
Alkire, Richard C.
Department of Study
Chemical Engineering
Discipline
Chemical Engineering
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Chemistry, Analytical
Engineering, Chemical
Abstract
In situ atomic force microscopy was used to study corrosion and electrodeposition on a nanoscopic level. Dissolution of copper was crystallographic in 0.5 M H$\sb2$SO$\sb4$ at overpotentials up to 100 mV; addition of BTA provided corrosion inhibition up to 300 mV overpotential, where pitting occurred. Surface preparation of pure aluminum was not reproducible, and the differences altered the corrosion behavior in NaCl solutions. Shape evolution around preselected, aluminum-iron inclusions in Al-6061-T6 in 0.6 N NaCl was followed with and without applied potential. Inclusion dissolution was observed on a select iron-rich inclusion while other iron-rich inclusions did not dissolve, which indicates that the structure of aluminum-iron inclusions varies. Pit initiation at inclusion sites was geometry dependent. Results confirmed that a high local pH, resulting from oxygen reduction on the iron-rich inclusion, initiated pitting corrosion. Attempts to study pitting at intermetallic inclusions in stainless steel 304 exposed to NaCl/Na$\sb2$SO$\sb4$ solutions were unsuccessful due to an artifact that prevented dissolution beneath the cantilever substrate. Copper electrodeposition from 0.25 M CuSO$\sb4$/0.5 M H$\sb2$SO$\sb4$ onto single crystal platinum was studied. The critical overpotential for three-dimensional nucleation of copper onto Pt(111) was found to be between 70 and 120 mV. The stability of deposited clusters when the potential was returned to open circuit was dependent on surface coverage. At overpotentials above 200 mV, the nucleation followed the three-dimensional diffusion-controlled nucleation theory and shifted from progressive to instantaneous nucleation with increasing overpotentials. Copper electrodeposition onto a stepped Pt(100) surface at various current densities and 0, 10, and 100 $\mu$M benzotriazole (BTA) was investigated. With no BTA, deposition followed the classical surface diffusion model and copper selectively grew at step sites. A surface diffusivity of 10$\sp{-6}$ cm$\sp2$/s was estimated from shape evolution plots. With BTA added, surface diffusion and the growth sites were blocked by adsorbed BTA; consequently, copper deposited in a clump morphology with no preferential growth along the steps at the higher BTA concentration.
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