FeO(OH)·0.5 H2O powders were prepared by drying portions of a FeO(OH)·0.5 H2O sol at different relative vapor pressures, and the adsorption of water on the powders was determined. The magnitude of electrostatic potential barrier for the sol is of about 9 mJ·m-2. The reduction in the immersion enthalpy and in the surface free-energy in a range of the relative vapor pressures of 0.0-0.9 is as high as 140 mJ·m-2 and 130 mJ·m-2, respectively. It follows from the foregoing that two potential barriers may form. The electrostatic barrier presumably regulates the rate of flocculation and the "hydration barrier" (at closer separations) regulates the rate of particle coalescence or sintering. Peptizability of the FeO(OH)·0.5 H2O powders dried at relative vapor pressures between 0.4 and 0.9 was found to be fairly high, presumably because the adsorbed water prevented the formation of close contacts between the primer particles. Lowering the vapor pressure, however, resulted in a notable decrease in the peptizable amount, and also a considerable increase in the particle size of the peptized sol.
- Water vapor adsorption
ASJC Scopus subject areas
- Physical and Theoretical Chemistry
- Polymers and Plastics
- Colloid and Surface Chemistry
- Materials Chemistry