In Situ Studies of Corrosion and Electrodeposition Using Atomic Force Microscopy

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 μM 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.

Name thesis:degree_name

Ph.D.

Level thesis:degree_level

Dissertation

Discipline thesis:degree_discipline

Chemical Engineering

Grantor

University of Illinois at Urbana-Champaign

Year dc:date

2014

Author dc:creator

• Rynders, Rebecca Mohr

Contributors dc:contributor

• Alkire, Richard C.

• Chemistry, Analytical
• Engineering, Chemical

Identifier

(UMI)AAI9411771

OAI identifier oai:identifier

oai:www.ideals.illinois.edu:2142/72149