Date of Award

August 2013

Degree Type

Thesis

Degree Name

Master of Science

Department

Engineering

First Advisor

Ben Church

Second Advisor

Hugo Lopez

Committee Members

Ben Church, Hugo Lopez, Nidal Abu-Zahra, Ilya Avdeev

Keywords

Ceria, Coating, Corrosion Inhibitor, High Temperature, Humidity, Nanoparticles

Abstract

A solution of 20 wt. % colloidal dispersion of Cerium Oxide (CeO2) in 2.5% of acetic acid, was used for depositing a coating film on an austenitic stainless steel 316L. Cerium compounds have been distinguished as potential corrosion inhibitors in coatings over several alloys. The oxidation behavior of the cerium oxide coating on 316L austenitic stainless steel alloy was evaluated in dry and humid environments, the weight changes (W/A) was monitored as a function of time using a custom built Thermogravimetrical Analysis (TGA) instrument at temperatures of 750C, 800C and 850C, and different relative humidity levels (0%, 10% and 20%) respectively. The parabolic oxidation rate and activation energy is calculated experimentally for each relative humidity level.

A measurement of the effective diameter size of the ceria nanoparticles was performed using a Light Scattering technique. A characterization of the film morphology and thickness before the oxidation was executed using Atomic Force Microscopy (AFM)

Microstructure and chemical composition of the oxidized coated substrates were analyzed using Scanning Electronic Microscopy (SEM) with energy dispersive spectroscopy (EDS). X-Ray Diffractometer (XRD) was used to characterize oxides formed in the surface upon isothermal treatment. A comparison of activation energy values obtained to identify the influence of relative humidity in the oxidation process at high temperature was conducted.

Cerium oxides coating may prevent crevice corrosion and increase pitting resistance of 316L relative to the uncoated substrate at high temperatures and different levels of relative humidity acting as a protective oxidation barrier.

The calculated parabolic rate constants, kp, at the experimental temperatures tend to increase as a function of humidity levels. The activation energy tends to increase proportionally to higher level of humidity exposures.

At 0% relative humidity a value of 319.29 KJ/mol of activation energy is being obtained and at 20% is 366.10 KJ/mol. For the 10% an approximate value of 343.00 KJ/mol has been estimated based on the projection of the kp values at 750C and 800C.

The presence of the CeO2 coating film, reduced the oxidation kinetics and provided good cyclic oxidation resistance at increments of relative humidity.

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