Fiscal year 1989 annual report for the Sensors Development Program: Inert Electrodes Program

Abstract

Activities in support of the Sensors Development Program for FY 1989 were conducted under three major tasks: Digital Signal Analysis (DSA), Development of the Reference Anode, and Field Test of the Reference Anode. DSA of current and voltage signals colleCted from PNL bench-scale laboratory cells suggest there may be correlations between certain quantification parameters derived from these data and the current density of the working anode. Although some data show a dependence on alumina concentration, additional effort is required to determine whether a correlation of DSA with this important cell operating parameter can be unequivocally shown. If successful, such a correlation would form a viable basis for a DSA-based alumina sensor. Digital current and voltage signals collected during the Prototype Inert Anode Test gave correlations involving current density that were similar to those obtained using data from the PNL bench-scale laboratory cells. This suggests a DSA-based sensor may work in a large-scale aluminum reduction cell if it can be shown to work in a bench-scale test. In other words, there may be no serious effects on DSA data resulting from scale-up considerations. Analog current and voltage data were generally stable throughout the Prototype Inert Anode Test and therefore did not signal the onset of the corrosion of the prototype anode that was observed in post-test analysis. This indicates that monitoring de signals may not be a suitable approach to determining, in every case, when an inert anode is undergoing degradation during its operation. Despite the magnitude of effort expended in FY 1989 to develop the reference anode, serious issues regarding its operation and durability remain. Problems were also encountered in trying to use the reference anode in the Prototype Inert Anode Test. Consequently, PNL recommended that further development of the reference anode be suspended. Future tests, including the Pilot Cell Test, will use an Al/Alz03 reference electrode. The Pilot Cell Test was postponed to FY !99D because of delays in obtaining the required materials and manufacture of the anodes from commercial vendors. v Electrochemical impedance data collected on inert anodes in PNL benchscale laboratory cells during the evaluation of the reference anode show a dependence on current density and alumina concentration that is consistent with the formation of a resistive reaction layer. The formation of a resistive reaction layer is not the only possible mechanism for the observed results. Alternative mechanisms are being considered based on separate experimental studies. However, an alumina sensor based on the dependency of the impedance data is not expected to viable because significant hysteresis was observed in these data. vi ACKNOWLEDGMENTS The authors wish to acknowledge the technical assistance of N.

Final report on DSA methods for monitoring alumina in aluminum reduction cells with cermet anodes. Inert Electrodes Program

“…These results were discussed in a previous PNL report (Windischet al 1990). The present report focuseson the results of additionalanalyses using laboratory cells in FY 1990and the pilot cell in FY 1991and FY 1992 The principal result discussed in Windisch et al (1990)was that the relationshipbetween selected DSA quantificationparametersand current density for data collectedfrom laboratorycells showed a t:"endthat was consistent with data from the prototype anode test. This result suggestedthat laboratorycells were a re'liable "provingground" for the developmentof a showing significantsensitivityonly between 20% and 40% of saturation.…”

“…3.1 separately,that was discussed in Windisch et al (1990). Later analysis using laboratorydata labelled "Set#3 data" and the pilot cell data reduced some of the initial optimism regardingreproducibleapplicationof these three parametersto monitor alumina concentration.…”

Final report on DSA methods for monitoring alumina in aluminum reduction cells with cermet anodes

“…The principal result discussed in Windisch et al (1990)was that the relationshipbetween selected DSA quantificationparametersand current density for data collectedfrom laboratorycells showed a t:"endthat was consistent with data from the prototype anode test. This result suggestedthat laboratorycells were a re'liable "provingground" for the developmentof a (a) Operated for the U.S. Departmentof Energy by Battelle Memorial Instituteunder Contract DE-ACO6-76RLO1830.…”

Inert Electrodes Program: Characterization of the reaction layer or film on PNL (Pacific Northwest Laboratory) inert anodes: Progress Report for April-December 1989

“…Attempts to use impedance measurements to monitor alumina concentration (Windisch 1990) also may have been unsuccessful because of the source of the anode impedance. Although surface roughness may be affected by alumina concentration, the relationship would probably be much less precise than one involving, for example, the thickness of a reaction layer or film (as previously proposed).…”