In situ monitoring of generation and precipitation of ferric hydroxide solwith a piezoelectric quartz crystal impedance analyzer

The piezoelectric quartz crystal (PQC) impedance technique was applied to m onitor in situ generation and precipitation of the ferric hydroxide sol in aqueous solutions at 90 degreesC. Equivalent circuit parameters and resonan t frequencies as well as the half-peak width of the electroacoustic conduct ance spectrum deltaf(G1/2) for the PQC resonance were obtained and analyzed . Three stages, sol generation and simultaneous adsorption, adsorption equi librium, and precipitation of ferric hydroxide sol could be identified in t he process of adding the ferric nitrate solution into the hot water. A sche me of two consecutive reactions occurring at the electrode/solution interfa ce was used to analyze the adsorption kinetics of ferric hydroxide sol onto the Au electrode. In addition, the electrolyte-induced precipitation of th e colloid was monitored and discussed. Temperature effect on the PQC resona nce behavior in liquid was also investigated. Since the PQC impedance techn ique provides multidimensional piezoelectric information in situ, it is hig hly recommended for studying the process of sol-gel generation and precipit ation. (C) 2001 Academic Press.