Dissertation/Thesis Abstract

Proton-conducting beta"-alumina via microwave-assisted synthesis and mechanism of enhanced corrosion prevention of a zinc rich coating with electronic control
by Kirby, Brent William, Ph.D., Princeton University, 2008, 166; 3308035
Abstract (Summary)

Proton Conducting β-alumina via Microwave Assisted Synthesis. The microwave assisted synthesis of proton conducting Mg- and Li-stabilized NH4+/H3O+ β-alumina from a solution based gel precursor is reported. β-alumina is a ceramic fast ion conductor containing two-dimensional sheets of mobile cations. Na +-β-alumina is the most stable at the sintering temperatures (1740°C) reached in a modified microwave oven, and can be ion exchanged to the K+ form and then to the NH4+/H 3O+ form. β-phase impurity is found to be 20% for Mg-stabilized material and 30-40% for Li-stabilized material. The composition of the proton conducting form produced here is deficient in NH4 + as compared to the target composition (NH4)1.00 (H3O)0.67Mg0.67Al10.33O 17.

Average grain conductivity for Li-stabilized material at 150°C is 6.6x10-3 ± 1.6x10-3 S/cm with 0.29 ± 0.05 eV activation energy, in agreement with single crystal studies in the literature. Grain boundary conductivity is found to be higher in the Li-stabilized material. A hydrogen bond energy hypothesis is presented to explain these differences. Li-stabilized NH4+/H3O + β-alumina is demonstrated as a fuel cell electrolyte, producing 28 μA/cm2 of electrical current at 0.5 V.

Mechanism of Enhanced Corrosion Prevention of a Zinc Rich Coating with Electronic Control. A corrosion inhibition system consisting of high weight-loading zinc rich coating applied to steel panels is examined. An electronic control unit (ECU) consisting of a battery and a large capacitor in series with the panel is shown to improve corrosion protection upon immersion in 3% NaCl solution. Weekly solution changes to avoid zinc saturation in solution system were necessary to see well differentiated results.

The corrosion product, hydrozincite [Zn5(CO3) 2(OH)6] is observed to deposit within the pores of the coating and on the surface as a barrier layer. Simonkolleite [Zn5(OH) 8Cl2·H2O] is found to form in place of the original zinc particles. The barrier layer is denser and more adherent with the ECU in place. A mechanism is proposed in which the characteristic time constant of the ECU is roughly matched to the time scale of ionic motion within the coating. The capacitive nature of the ECU retards the motion of ions, and affects the formation of denser corrosion products.

Indexing (document details)
Advisor: Bocarsly, Andrew
School: Princeton University
School Location: United States -- New Jersey
Source: DAI-B 69/04, Dissertation Abstracts International
Subjects: Chemistry, Materials science
Keywords: Beta-alumina, Corrosion prevention, Electronic control, Fuel cells, Proton conduction, Zinc coatings
Publication Number: 3308035
ISBN: 978-0-549-55633-6
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