The zeta potential of alumina particles in aqueous dispersion is significantly influenced by the pH and ionic strength of the solution. The zeta potential is an important parameter that determines the stability of colloidal dispersions, such as alumina particles in water. It represents the electrostatic potential at the slipping plane between the particle surface and the surrounding liquid.1. Effect of pH:Alumina Al2O3 particles have amphoteric surface properties, meaning they can exhibit both acidic and basic behavior depending on the pH of the solution. At low pH values, the surface of alumina particles becomes positively charged due to the protonation of surface hydroxyl groups Al-OH + H+ Al-OH2+ . Conversely, at high pH values, the surface becomes negatively charged due to the deprotonation of surface hydroxyl groups Al-OH Al-O- + H+ . The isoelectric point IEP is the pH at which the zeta potential is zero, and for alumina particles, it typically occurs around pH 8-9.As the pH increases from the acidic to the basic range, the zeta potential of alumina particles shifts from positive to negative values, passing through the isoelectric point. This change in zeta potential affects the stability of the dispersion. Dispersions with high absolute zeta potential values either positive or negative are more stable due to the electrostatic repulsion between particles, which prevents aggregation. Near the isoelectric point, the zeta potential is low, and the dispersion is less stable, leading to particle aggregation and sedimentation.2. Effect of ionic strength:The ionic strength of the solution also plays a crucial role in determining the zeta potential of alumina particles. As the ionic strength increases, the thickness of the electrical double layer surrounding the particles decreases, leading to a reduction in the electrostatic repulsion between particles. This effect is known as the screening or shielding effect.At low ionic strength, the zeta potential is less affected, and the dispersion remains stable due to the strong electrostatic repulsion between particles. However, as the ionic strength increases, the zeta potential decreases, and the electrostatic repulsion between particles weakens. This reduction in repulsion can lead to particle aggregation and sedimentation, resulting in a less stable dispersion.In summary, the zeta potential of alumina particles in aqueous dispersion is highly dependent on the pH and ionic strength of the solution. The pH influences the surface charge of the particles, while the ionic strength affects the electrostatic repulsion between particles. To maintain a stable dispersion, it is essential to control both the pH and ionic strength of the solution.