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

Library of Congress Subject Headings

Corrosion and anti-corrosives -- Research
Magnesium alloys
Thin films
Coating processes
Cerium -- Electrometallurgy
Surfaces (Technology)
Nanostructured materials

Thesis Number

T 10437

Electronic OCLC #

882476632

Share

 
COinS