UBC Theses and Dissertations
Particulate fouling by iron oxide at elevated temperatures : surface chemistry, interfacial electrochemistry and sensor development Zebardast, Hamidreza
Particulate fouling as a result of corrosion product sedimentation is known to be a significant issue in the heat exchanger of nuclear power plants and thus the development of monitoring technologies for the detection of fouling is important. Since electrochemical processes are usually very sensitive to water chemistry, they provide an opportunity for the development of accurate and online sensors. The main aim of this work is to develop an electrochemical sensor to detect particulate fouling at various temperatures and pressures up to 200 ºC. In order to develop such an electrochemical sensor, knowledge of the interfacial chemistry and electrochemistry of both the suspended particles and the sensing probe are required. Potentiometric titration was used to measure the pH of zero charge (PHZC) of magnetite and hematite (both known particulate foulants) from 25 ºC to 200 ºC. Electrochemical impedance spectroscopy (EIS) was used to measure the minimum differential capacitance of a glassy carbon electrode (GC) as a function of electrode potential i.e. the potential of zero charge (PZC). The obtained results clarified the oxide particle-electrode interaction since a GC electrode was used as a detector probe. A sensor for particulate fouling detection was then investigated and a new experimental method for the detection of magnetite particles at temperatures up to 200 ºC was developed. An electromagnetic GC electrode was employed to collect the magnetite particles from the suspension solution and it was observed that changes in double-layer capacitance could be used to detect deposition at different conditions. Finally, the impact of particulate fouling on water chemistry was studied. A novel electrochemical method was employed to accurately measure the kinetics of H2O2 decomposition on the surface of magnetite at temperatures up to 200 ºC. This work provides an experimental methodology for the prediction of failures due to particulate fouling processes in heat exchangers by providing a means to estimate the extent of fouling, the interactions between colloidal foulants and their corresponding impact on water chemistry.
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