The aim of this work was to use electroacoustic measurements tion on the disposition of ionic charges on the surface of a to determine the z potential of precipitated aluminum hydroxide solid in contact with water, but the normal electrokinetic particles in NaCl solutions at concentrations up to 3 M. The comtechniques are not well suited to measurement at very high mercial device used in this study, the AcoustoSizer, is not calisalt concentrations and under extremely alkaline conditions.
brated for electrolytes above about 0.1 M, and thus the first step
The electroacoustic method may be able to provide this inof this investigation involved the extension of the calibration proceformation under these difficult conditions. The AcoustoSizer dure to concentrations up to 3 M. Having calibrated the device, (Matec Applied Sciences, Hopkinton, MA) is a commercial we then determined the z potential for the aluminum hydroxide electroacoustic device that provides information on the size as a function of pH and background electrolyte concentration. The main result of the study was that at 0.5 M NaCl, the isoelectric and z potential of solid particles in colloidal dispersions. point of the aluminum hydroxide shifted up by about 2 pH units This device measures an electroacoustic effect called the for a supposedly ''indifferent'' electrolyte such as NaCl, and that electrokinetic sonic amplitude (ESA) (1). A high-frequency at 3 M NaCl, there was no isoelectric point. It appears that the (MHz) electric field is applied between two electrodes on sodium ions are preferentially adsorbed on the hydroxide surface the boundaries of the suspension. This causes the (charged) at high concentrations, and at the highest concentration studied, particles to move backward and forward in response to the the surface remains positive for all pH values. แญง 1997 Academic Press field. If there is a density difference between the particles