DETERMINATION OF ZETA-POTENTIAL AND PH OF ZERO CHARGE OF OXIDES AT HIGH-TEMPERATURES

High-temperature zeta potentials of oxides are important in understanding and preventing the deposition of corrosion products, particularly in nuclear power plants. They are also important in separation of minerals from coal/mineral aggregates and sol-gel processing of high-density advanced ceramics at supercritical temperatures. In this paper, a computer-interfaced experimental arrangement for the determination of high-temperature zeta potential via streaming potential measurements is described. Zeta potentials of oxides were calculated from the slopes of streaming potential versus differential pressure plots, avoiding any errors associated with the asymmetry of electrodes. The same measurement technique can be modified to determine the zeta potentials of solid conducting surfaces and coating materials. The oxides show the ability to retain a higher surface charge at high temperatures, presumably due to stronger acid/base dissociation of the surface hydroxyl groups. Consequently, the pH of zero charge of the oxides are shifted to lower values at higher temperatures as reported in the literature, indicating the importance of making these measurements at the desired temperature.