M. G. Coelho

Experimental and theoretical studies of the thermal behavior of titanium dioxide-SnO2 based composites.

In this paper we report experimental and theoretical studies concerning the thermal behavior of some organotin-Ti(IV) oxides employed as precursors for TiO(2)/SnO(2) semiconducting based composites, with photocatalytic properties. The organotin-TiO(2) supported materials were obtained by chemical reactions of SnBu(3)Cl (Bu = butyl), TiCl(4) with NH(4)OH in ethanol, in order to impregnate organotin oxide in a TiO(2) matrix. A theoretical model was developed to support experimental procedures. The kinetics parameters: frequency factor (A), activation energy, and reaction order (n) can be estimated through artificial intelligence methods. Genetic algorithm, fuzzy logic, and Petri neural nets were used in order to determine the kinetic parameters as a function of temperature. With this in mind, three precursors were prepared in order to obtain composites with Sn/TiO(2) ratios of 0% (1), 15% (2), and 30% (3) in weight, respectively. The thermal behavior of products (1-3) was studied by thermogravimetric experiments in oxygen.

Thermal Decomposition of Dibutyltin(IV) Sulphide Supported on α-Αl2ο3

In this paper we report the preparation of tin sulphides on the surface of α-Α1203. The starting material was prepared by a mixture of dibutyltin(IV) sulphide dissolved in ethanol with a suspension of alumina in the same solvent. The residues were obtained after removing the solvent and subsequent pyrolysis of the supported product. The samples were prepared in order to have, after pyrolysis, ratios of Sn/a-Al203 of 5% (1), 10% (2), 15% (3), 30% (4), 40% (5) and 60% (6) in weight. The X-ray powder diffraction results were not conclusive since lines of some phases of SnS, SnS2, Sn2S3 and Sn3S4 are too close one to another. However, Sn Mössbauer experiments suggest that SnS2 is formed at first, and then Sn2S3 and finally Sn3S4, as the Sn(IV) concentration increases. Scanning electron microscopy (SEM) revealed that crystals of tin sulphides have grown on the surface of big crystals of α-Α1203. Finally, X-ray electron probe microanalyses (ΕΡΜΑ) shows the presence of ΑΙ, Ο, S and Sn in all samples.