An electrophoretic study of nickel ferrite particles in high-temperature aqueous solutions using particle image velocimetry

Abstract

Metal oxide deposition on the inner surfaces of power plant systems reduces heat transfer efficiency and promotes localized corrosion. Nickel ferrite (NixFe1-xFe2O4; 0 ≤ x ≤ 1) is a common yet understudied corrosion product in pressurized water reactors. Conventional electrophoretic studies inaccurately addressed background thermal convection, complicating the isolation of electrophoretic components. Herein, we integrated particle image velocimetry into a hydrothermal cell, to enable precise electrophoretic mobility measurements up to 250 °C. This approach was first validated by measuring the mobilities of zirconium dioxide at 25 °C and 200 °C. Electrophoretic mobilities of Ni0.37Fe0.63Fe2O4 particles were measured up to 250 °C at 50 bar, using HNO3 and KOH as pH modifiers. Results showed the isoelectric point decreased from 5.9 ± 0.1 at 150 °C, plateauing at 5.6 ± 0.1 above 230 °C indicating that higher temperatures favored further deprotonation of surface sites. Thermodynamic analysis indicated surface deprotonation was spontaneous (ΔG° = −43 ± 1 kJ mol−1) and exothermic (ΔH° = − 40 ± 0.8 kJ mol−1) with its favorability increasing due to its positive entropy (ΔS° = 10 ± 2 J mol−1 K−1). This study highlights PIV as a reliable and rapid tool for electrophoretic data acquisition, providing insights into surface chemistry of oxide solution interfaces. (Figure presented.)