Electrode corrosion during high intensity audio frequency electric field processing

Abstract

Radio frequency electric field treatment (RFEF) is a non-thermal method of food preservation that utilizes high intensity oscillating electric field to inactivate bacteria. Past studies reported that RFEF operated at lower frequencies resulted in a higher inactivation rate of bacteria. However, the electrode may corrode at lower frequencies, especially at frequencies lower than 20 kHz, which could potentially degrade the quality of the processed liquid food. This research studied on the electrode corrosion occurred during the high intensity RFEF operated under 20 kHz, also called the audio frequency electric field treatment (AFEF), and it proposed a novel method to reduce the corrosion rate of electrodes. Inspired by the electrical double layer (EDL) and its equivalent electrical circuit, applying a high permittivity coating on the surface of electrodes was proposed to reduce the corrosion rate. Three coatings composed of titanium dioxide, barium titanate, and CCTO, having low, moderate, and high permittivities, respectively, were selected as the coatings applied on the surface of electrodes to explore how the permittivity of the coatings affect the corrosion rate. Mathematical modeling and experiments were conducted to test whether the three coatings could mitigate the electrode corrosion. In mathematical modeling, an equivalent electrical circuit of the coating-solution system was employed to calculate the phase angle and voltage drop across the three coatings and the solution (saline water). After that, the experiment of the electrode corrosion, with/without applying the three coatings on electrodes during the high intensity AFEF treatment, was conducted. Furthermore, the electrical impedance, atomic and molecular structures, surface morphology, and elemental analysis of the three coatings were conducted. Finally, the concentration of the metallic ions in the AFEF-processed saline water was measured. In conclusion, the corrosion rate generally increased with the increase of the electric field strength and the conductivity and the reduction in frequency, respectively. The CCTO coating performed the best on the reduction of the electrode corrosion among the three proactive coatings, while the titanium dioxide coating marginally reduced the electrode corrosion. However, calcium ions were detected in the processed saline water when the CCTO coating was applied, although the concentration was deficient. As a novel study in this area, this research contributes to the effective mitigation of electrode corrosion, during the electric field treatment, thereby increasing the Industrial applicability of the electric field treatments.