<p>Metal oxide deposition on the inner surfaces of power plant systems reduces heat transfer efficiency and promotes localized corrosion. Nickel ferrite (Ni_xFe_1-<i>x</i>Fe₂O₄; 0 ≤ <i>x</i> ≤ 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 Ni_0.37Fe_0.63Fe₂O₄ 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 (Δ<i>G</i>° = −43 ± 1 kJ mol⁻¹) and exothermic (Δ<i>H</i>° = − 40 ± 0.8 kJ mol⁻¹) with its favorability increasing due to its positive entropy (Δ<i>S</i>° = 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.</p><p></p>