Effects of Sodium and Calcium Ions on the Aggregation of Titanium Dioxide, at High pH, in Aqueous Dispersions

• Published in: Journal of colloid and interface science Vol. 159; no. 1; pp. 58 - 67
• Main Authors: Mange, F., Couchot, P., Foissy, A., Pierre, A.
• Format: Journal Article
• Language: English
• Published: San Diego, CA Elsevier Inc 01.08.1993; Elsevier
• Subjects: 400201 - Chemical & Physicochemical Properties; ADSORPTION; AGGLOMERATION; ALKALI METALS; ALKALINE EARTH METALS; AQUEOUS SOLUTIONS; CALCIUM; CATALYTIC EFFECTS; CHALCOGENIDES; Chemistry; Colloidal state and disperse state; DISPERSIONS; ELEMENTS; Exact sciences and technology; General and physical chemistry; HYDRATION; INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL CHEMISTRY; METALS; MICROSCOPY; MIXTURES; OPTICAL MICROSCOPY; OXIDES; OXYGEN COMPOUNDS; PH VALUE; Physical and chemical studies. Granulometry. Electrokinetic phenomena; POTENTIALS; RHEOLOGY; SEDIMENTATION; SODIUM; SOLUTIONS; SOLVATION; SORPTION; SURFACE POTENTIAL; SURFACE PROPERTIES; TITANIUM COMPOUNDS; TITANIUM OXIDES; TRANSITION ELEMENT COMPOUNDS; Sodium Ions; Binary compound; Salt effect; Medium effect; Transition metal Compounds; pH; Electrokinetic potential; Aqueous solution; Particle suspension; Calcium Ions; Experimental study; Titanium Oxides
• ISSN: 0021-9797; 1095-7103
• DOI: 10.1006/jcis.1993.1297

This paper investigates how sodium and calcium ions affect the aggregation of TiO2 particles in aqueous solutions of high pH. Optical microscopy and sedimentation rate and rheological measurements are used to characterize the aggregation. The surface charge and calcium adsorption densities are measured as a function of the total calcium concentration. The aggregates' size is maximum at a negative electrokinetic potential (-35 to -40 mV) when the surface excess of calcium equals almost half the ionized surface sites' density. Similar results are obtained at three values of the solid-to-solution volume ratio, provided that the calcium content is expressed in terms of moles per gram of solid. We propose that this aggregation between strongly negative particles is due to an attractive potential created by an ion-ion correlation, a phenomenon expected in systems with a high surface charge and divalent counter ions. In the presence of sodium ions, at pH 11, the dispersion stability increases to above 10-1M. This phenomenon is attributed to the occurrence of hydration forces.