Calcium titanate (CaTiO(3), perovskite) has been used to determine its apatite nucleation ability and propose a possible nucleation initial step. Measurements of calcium leaching from the calcium titanate surface and phosphate adsorption experiments were carried out separately by using commercial calcium titanate suspensions at room temperature. Adsorption behaviour determined by zeta potential measurements shows that phosphate is strongly adsorbed on the calcium titanate surface. It was found that the higher the pH, the higher the Ca present on the calcium titanate surface, but phosphate adsorption followed this trend only up to pH 7.4. Results suggest that phosphate ions are not adsorbed only on Ca sites but also on TiO(2) groups sites of the surface, formed after calcium leaching from the surface. When both ions are simultaneously added in a modified simulated body fluid containing calcium titanate, at 37 degrees C, apatite growth occurs on its surface after 1 week of immersion.
This work describes the preparation of four Ti|Ir-Sn-Sb oxide anodes by the Pechini method under different conditions and the evaluation of their service life, envisaging a future application in electrochemical advanced oxidation processes for water treatment. This was estimated by means of accelerated life tests (1 A cm-2 , 1 M HClO4), which highlighted the dependence of durability on the Ir and Sn content in the mixed metal oxide (MMO) as well as on the required heat treatment time for its preparation. The best MMO anode reached up to 351 h of service life under such extreme conditions. SEM-EDS and XRD analyses were performed before and after the accelerated life tests, evidencing that the failure of the MMO coatings occurred by detachment from the titanium substrate, thus losing the anode electroactivity. Great amounts of acid sites in the range 0.21-0.26 meq g-1 were determined on the MMO surfaces by Boehm titrations. From the apparent rate constants determined for the decay of N,N-dimethyl-4-nitrosoaniline used as spin trap, before and after acid sites neutralization, a higher activity of adsorbed hydroxyl radicals at the MMO surface cannot be correlated with a greater amount of acid sites. The results obtained suggest that other active sites affect the formation of such radicals from water discharge.
Titania powders have been prepared by the sol-gel route from Ti (IV) ethoxide under acidic conditions. Adsorption experiments of calcium and phosphate ions on gel-derived titania suspensions were performed to suggest a likely initial step of apatite growth on its surface. Experiments were performed as a function of time and pH at 37 degrees C with and without NaCl present in the suspensions. Also, zeta (zeta) potential experiments were performed to determine the kind of calcium adsorption. Results suggest that, apparently, calcium and phosphate adsorption can act as two different initial steps for apatite growth.
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