Analysis of the Isoelectric Point in Moderately Concentrated Alumina Suspensions Using Electroacoustic and Streaming Potential Methods

ABSTRACT

Alumina suspended in aqueous electrolytic solution was used as a model ceramic suspension to investigate the measurement precision and influencing factors for the determination of the isoelectric point (IEP) in moderately concentrated systems. Techniques used in this study include colloid vibration current (CVI), electrokinetic sonic amplitude (ESA), and particle charge detection (PCD). A number of important factors were examined, focusing on those related to sample preparation, measurement methodology and instrumentation. A total of 145 acid-base titrations were included in the analysis. Although sample preparation factors influence the magnitude of the measured signal, primarily due to agglomeration effects, these factors do not significantly impact the determination of the IEP for alumina. The primary factor affecting IEP precision and accuracy is the level of sample agitation during titration. Poor mixing gives rise to hysteresis phenomena that introduce large systematic errors. Colloid vibration current, ESA, and PCD produce comparable electrokinetic data over the solids volume fraction range between 1% and 10%, although some systematic differences are apparent. Further refinements in methodology and greater fundamental understanding are necessary to improve measurement agreement between different techniques and to reduce variability in IEP results.