Doctoral Dissertations
Abstract
"This research is primarily focused on gaining a better understanding of the deposition and corrosion behavior of cerium-based conversion coatings (CeCCs) on AZ31B and AZ91D Mg alloys. Deposition of homogenous and protective CeCCs was highly dependent on the surface preparation steps. The best results were obtained when Mg samples underwent grinding, acid cleaning, and alkaline cleaning processes. This reduced the number of active cathodic sites and promoted the formation of a protective Al-rich Mg oxide/hydroxide layer. Electrochemical properties of the CeCCs were also strongly correlated with morphological, microstructural, and chemical characteristics. Protective CeCCs were deposited on both AZ31 and AZ91 Mg alloys using a range of deposition times (5 to 180 s) and temperatures (10 to 80 ºC). However, shorter deposition times (5 s) and lower deposition temperatures (~10 ºC) showed higher impedance and longer bath stability than other deposition conditions. The increase in impedance was related with fewer cracks and smaller nodule sizes. Additional investigations of post-treated CeCCs exposed to NaCl environments showed an increased in the total impedance. The increase in corrosion protection of the CeCCs was associated with an overall increase in coating thickness from 400 to 800 nm. A microstructural evolution from ~3 nm nodular nanocrystals of CeO₂/CePO₄·H₂O embedded in an amorphous matrix to >50 nm CePO₄·H₂O nanocrystals was responsible for the electrochemically active corrosion protection. Exposure of CeCCs to sunlight in humid environments promoted the reduction of Ce(IV) into Ce(III) species compared to unexposed coatings. This reduction process was related with photocatalytic water oxidation reaction."--Abstract, page iv.
Advisor(s)
OKeefe, Matt
Committee Member(s)
Fahrenholtz, William
Schlesinger, Mark E.
Stoffer, James O.
Miller, F. Scott, 1956-
Department(s)
Materials Science and Engineering
Degree Name
Ph. D. in Materials Science and Engineering
Sponsor(s)
National Energy Technology Laboratory (U.S.)
Roberto Rocca Fellowship
Publisher
Missouri University of Science and Technology
Publication Date
Spring 2014
Journal article titles appearing in thesis/dissertation
- A comparative study on the corrosion resistance of cerium-based conversion coatings on AZ91D and AZ31B magnesium alloys
- Effect of thickness on the morphology and corrosion behavior of cerium-based conversion coatings on AZ31B magnesium alloy
- Effect of deposition temperature on the properties of cerium-based conversion coatings on AZ31 and AZ91 magnesium alloys
- Corrosion behavior of cerium-based conversion corrosion behavior of cerium-based conversion conditions
- Photo-assisted reduction in nanostructured cerium-based coatings
- Microstructural evolution of cerium-based coatings on AZ31 magnesium alloys
- Corrosion protection of Mg-Al-galvanized steel assemblies
Pagination
xiv, 191 pages
Note about bibliography
Includes bibliographical references.
Rights
© 2014 Carlos Eduardo Castaño Londoño, All rights reserved.
Document Type
Dissertation - Open Access
File Type
text
Language
English
Subject Headings
Corrosion and anti-corrosives -- ResearchMagnesium alloysThin filmsCoating processesCerium -- ElectrometallurgySurfaces (Technology)Nanostructured materials
Thesis Number
T 10437
Electronic OCLC #
882476632
Recommended Citation
Castaño, Carlos E., "Cerium-based conversion coatings on magnesium alloys" (2014). Doctoral Dissertations. 2140.
https://scholarsmine.mst.edu/doctoral_dissertations/2140
