Adsorption of tannic acid on ?-Al2O3 and its effect on the suspension stability and particles dispersion

Reference Presenter Authors
13-029 Jaíne Webber Webber, J.(Universidade de Caxias do Sul); Cruz, R.C.(Universidade de Caxias do Sul); Zorzi, J.E.(Universidade de Caxias do Sul); Surfaces interactions dominates the properties of colloidal particles suspension. The balance between particles surface sites, solvent, and other active species determines the properties related to the solid/liquid interface interactions and reactivity. Tannic acid is a natural compound extracted from plants, which can be used as a stabilizing and dispersing agent in colloidal ceramic suspensions. The control of alumina surface properties and the mechanisms that determine the alumina-tannin interactions is fundamental to adjust its effects on colloidal processing. Bearing this in mind, it is necessary to ensure a contaminant-free surface to evaluate the contribution and effect of each suspended species. In this work, it has been realized the adsorption of contents up to 3 wt% tannic acid on ?-Al2O3 particles and it has been investigated the effect on the suspensions stability and the particles dispersion. In addition, the effect of the ionic strength also has been investigated for 0.1, 0.01 and 0.001 mol/L NaCl. The net electrical contribution of the suspended tannic acid was mainly defined by the pH of the medium, since this solvent property defined the state of protonation and deprotonation of the polar groups in both alumina and molecules. The stability of the suspensions resulting from the tannic acid adsorption lowered as adsorption raised up, specially above 1 wt%. Increasing of ionic strength also lowered the stability of suspension for a given concentration of tannic acid. For 0.1 mol/L NaCl the suspensions were unstable for all adsorbed contents of tannic acid. The particles remained dispersed for conditions which the suspensions were stables (??25 mV) and for the unstable suspensions, agglomerates formation has been observed.
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