The effect of current reversal on coated titanium electrodes

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Title The effect of current reversal on coated titanium electrodes
Publication Type dissertation
School or College College of Mines & Earth Sciences
Department Metallurgical Engineering
Author Elnathan, Francis
Date 2012-05
Description Coated titanium electrodes have applications in the electrochemical industry, including water treatment and swimming pool chlorination. Current/polarity reverse electrolysis is a technique used for "self-cleaning" of the coated titanium anodes employed in water disinfection and treatment. However, the literature holds very little information about the effects of polarity reversal on these anodes. The present work appears to be the first to investigate coated titanium anodes in polarity reversal in a systematic method. Two commercial titanium electrodes (RuTi and IrTa) were studied. Polarity reversal was the main electrochemical technique employing a current density of 1200 A/m2, except when current density was studied. The effects of NO3-, SO42-, ClO4-, HPO42-, CO32-, Mg2+ and Ca2+ on electrode lifetime were examined. Analysis of the electrochemical results showed that plateau time (?P), for gas evolution, is highly important to the lifetime of the coated titanium anodes. The effects of three electrolysis variables on the coated titanium anode life were examined. Current density was observed to have an inverse relationship with anode life while reversal cycle time had a direct relation with lifetime. NaCl concentration had no discernible effect. In general, the RuTi electrode exhibited longer lifetimes than IrTa except for a few specific conditions. The influence of the concentration of five anions (NO3-, SO42-, ClO4-, HPO42-, and CO32-) was determined. Changing the composition and concentration of anions affected the lifetimes of the two electrodes, especially nitrate, hydrogen phosphate and carbonate. The lifetime of IrTa was highest in nitrate, and increased as a function of nitrate concentration. The service life of RuTi was highest in hydrogen phosphate, and increased with increasing hydrogen phosphate concentration. Lifetime of both anodes decreased with increasing carbonate ions. The effects of Mg2+ and Ca2+ on electrode lifetime were examined with three anions (NO3-, HPO42-, ClO4-) electrolytes. While there were numerous effects and interactions between Mg2+ or Ca2+ and anions on lifetime, these effects were found to mainly affect the amount of time the electrodes spent in the charging and discharging reactions. The times related to gas evolution (which is the plateau time, ?P) were found to be strikingly similar. The charging times (?C), which are related to adsorption and desorption of species, were not also any significantly different. Coating dissolution, substrate and/or coating passivation mechanisms were identified as being responsible for coated titanium anode failure in current reverse and hard water electrolysis. IrTa is believed to have failed predominantly by the dissolution mechanism in nitrate, hydrogen phosphate and perchlorate. RuTi failed predominantly by substrate and/or coating passivation in hydrogen phosphate, nitrate and carbonate. Anode failure is believed to be the result of plateau (?P) and charging (?C) reactions occurring at the coating/electrolyte and/or substrate/coating interface. The ?P and ?C are useful determinants for the process of anode failure.
Type Text
Publisher University of Utah
Subject Charging time; Coated titanium anodes; Coated titanium electrodes; Failure mechanisms; Lifetime of anodes; Lifetime of electrodes; Plateau time; Current reversal; Polarity reversal
Dissertation Institution University of Utah
Dissertation Name Doctor of Philosophy
Language eng
Rights Management Copyright © Francis Elnathan 2012
Format application/pdf
Format Medium application/pdf
Format Extent 6,472,516 bytes
Identifier us-etd3,82013
Source Original housed in Marriott Library Special Collections, TP7.5 2012 .E46
ARK ark:/87278/s6wm1v5r
Setname ir_etd
ID 194736
Reference URL https://collections.lib.utah.edu/ark:/87278/s6wm1v5r
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