title: Stability of mixtures of charged silica, silica-alumina, and magnetite colloids.
abstract: We report experiments on the stability of aqueous mixtures of charged colloidal magnetite and charged silica and silica covered with alumina particles of similar size. First, positively charged magnetite dispersions were mixed with negatively charged silica dispersions at pH 4, at different volume ratios and low colloid volume fractions, producing mixtures which were stable over a period of weeks despite the expected electrostatic attraction between the oppositely charged particles. When magnetite particles were mixed with positively charged silica covered with alumina at pH 4 under exactly the same conditions, some of the systems separated to form a magnetite sediment. When the volume fraction of the initial dispersions was increased, the behavior of the mixtures was the opposite: positive magnetite/negative silica mixtures were unstable at intermediate volume ratios. The unexpected behavior of the mixtures was investigated by means of electrophoretic mobility, initial susceptibility, and dynamic light scattering measurements as well as sedimentation experiments.
authors.affiliation: Van 't Hoff Laboratory for Physical and Colloid Chemistry, Debye Research Institute, University of Utrecht, Padualaan 8, 3584 CH Utrecht, The Netherlands. julianlv@ugr.es
authors.forename: J L
authors.initials: JL
authors.lastname: Viota
authors.forename: M
authors.initials: M
authors.lastname: Raşa
authors.forename: S
authors.initials: S
authors.lastname: Sacanna
authors.forename: A P
authors.initials: AP
authors.lastname: Philipse
mesh_terms: D000537:Aluminum Oxide / Q000737:chemistry*; D003102:Colloids / Q000737:chemistry; D052203:Ferrosoferric Oxide / Q000737:chemistry*; D008027:Light; D008280:Magnetics; D010316:Particle Size; D012542:Scattering, Radiation; D012822:Silicon Dioxide / Q000737:chemistry*; D013499:Surface Properties
chemical_list: D003102:Colloids; D012822:Silicon Dioxide; D000537:Aluminum Oxide; D052203:Ferrosoferric Oxide