Influence of Solids Concentration on the Isoelectric Point of Aqueous Barium Titanate

Abstract

We report on findings that the particle surface charge is influenced by solids concentration in aqueous suspensions of BaTiO 3 . Three decades in solids concentration were analyzed by combining results from two different electrokinetic methods. Combined results demonstrate a systematic acidic shift in the isoelectric pH with decreasing solids concentration. The shift is attributed to the development of a Ba-depleted, TiO 2 -rich surface layer. Using kinetic arguments, it is shown that the thickness of this layer will be proportional to the surface-tovolume ratio.

Rheological behavior of PMN gels for solid freeform fabrication

“…Such increase in the pH due to consumption of protons must be associated by the cation dissolution from the PMN surface at the acidic pH range. Such effect would be more pronounced with increasing solids content [40].…”

Microstructure and permittivity of sintered BaTiO3: influence of particle surface chemistry in an aqueous medium

“…Both models produce a similar result, in which solubility depends (in acidic media) on the amount of available surface area per unit volume (a function of solids concentration and particle size). The kinetics of dissolution, as well as the total fraction of the BaTiO 3 phase depleted of Ba (on a mass basis) are profoundly enhanced when the solid phase is of colloidal dimensions [5].…”

“…Aqueous forming methods, though environmentally friendly and cost-effective, are more difficult to control due to reactions between the solid and liquid phases. The incongruent dissolution of BaTiO 3 in aqueous media at room temperature as a result of poor thermodynamic stability is well documented [2][3][4][5], and results in the leaching of Ba 2þ . Dissolution at the BaTiO 3 surface in contact with water occurs according to the following reaction [3] Under acidic conditions, the reaction can be written [4]: BaTiO 3 ðsÞ þ 2H þ ðaqÞ ¼ Ba 2þ ðaqÞ þ TiO 2 ðrutileÞ þ H 2 O; pK ¼ À20:37 ð25 CÞ where K is the thermodynamic solubility constant.…”

“…In fact, the amount dissolved depends on both solids concentration and particle size (via specific surface area), and tends to reach a maximum at pH values below about 6. The observed solubility behavior has been explained as the result of kinetically limited diffusion through a growing surface depletion layer, with passivation by this layer [5]. The loss of Ba 2þ from BaTiO 3 has also been modeled as a Langmuir surface adsorption-desorption process [6].…”

“…In previous work [5,[7][8][9], it was demonstrated that the dissolution and adsorption/precipitation behavior of Ba are critical factors in the stability of aqueous colloidal BaTiO 3 . At acidic pH values, the formation of an oxide-rich (amorphous TiO 2 ) [2,10] surface phase leads to the development of a large positive surface potential at pH values below 5.…”