Doctoral Dissertations

Abstract

"Magnesium and a magnesium alloy (AZ9 1C) have been ion implanted over a range of ion s energies (50 to 150 keV) and doses (1 x 1016 to 2 x 1017 ions/cm2) to modify the corrosion properties of the metals. The corrosion tests were done by anodic polarization in chloride -free and chloride containing aqueous solutions of a borated-boric acid with a pH of 9.3. Anodic polarization measurements showed that some implantations could greatly reduce the corrosion current densities at all impressed voltages and also increased slightly the pitting potential, which indicated the onset of the chloride attack. These improvements in corrosion resistance were caused by boron implantations into both types of samples. However, iron implantations were found to improve only the magnesium alloy.

To study the corrosion in mor e detail, Scanning Auger Microprobe Spectrometer (SAM), Scanning Electron Microscope (SEM) with an X-ray Energy Spectrometry (XES) attachment, and Transmission Electron Microscope (TEM) measurements were used to analyze samples before, after, and at various corrosion stages.

In both the unimplanted pure magnesium and AZ91C samples, an odic polarization results revealed that there were three active corrosion stages (Stages A, C, and E) and two passivating stages (Stages Band D). Examination of Stages A and B in both types of samples showed that only a mild, generalized corrosion had occurred. In Stage C of the TD samples, a pitting breakdown in the initial. oxide film was observed. In Stage C of the AZ9 1C samples, galvanic and intergranular attack around the Mg17A112 intermetallic is lands and along the matrix grain boundaries were observed. Stage D of both samples showed the formation of a thick, passivating oxygen containing, probably Mg (OH) 2 film. In Stage E, this film was broken down by pits, which formed due to the presence of the chloride ions in both types of samp les.

Stages A through D of the unimplanted samples were not seen in the boron or iron implanted samples. Instead, one low current density passivating stage was formed, which was ultimately broken down by the chloride attack. It is believed that the implantation of boron modified the initial surface film to inhibit corrosion, whereas the iron implantation modified the intermetallic (Mg17Al12) islands to act as sacrificial anodes"-- Abstract, pp. ii-iii

Advisor(s)

Hale, Edward Boyd

Committee Member(s)

Gerson, Robert, 1923-2013
Park, John T.
Park, John T.
Alexander, Ralph William, Jr.

Department(s)

Physics

Degree Name

Ph. D. in Physics

Publisher

University of Missouri--Rolla

Publication Date

Fall 1985

Pagination

xviii, 159 pages

Note about bibliography

Includes bibliographical references (pages 149-148)

Rights

© 1985 Sanay Akavipat, All rights reserved.

Document Type

Dissertation - Open Access

File Type

text

Language

English

Thesis Number

T 5246

Print OCLC #

14163594

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