Gel-Combustion synthesis to obtain Co3O4 nanopowders for solar selective surfaces

M,C. GARDEY MERINO; R. BELDA; G. E. LASCALEA; J. M. MARTIN MARTINEZ; DRA. PATRICIA VÁZQUEZ

Rio de Janeiro

Conferencia; 11th International Conference on Advanced Materials (ICAM); 2009

The use of selective surfaces for solar collectors improve the efficiency of solar heaters because of their high absortance in the solar spectrum (0.25 a 3m) and their low emittance in the infrared range (>3m). In this work, two combustion syntheses of Co3O4 powders using lysine and ethylenediaminetetraacetic acid (EDTA) as fuels, are presented: i) Samples were prepared by two stoichiometric process (EDTA/Co molar ratio=0.17 (a), Lysine/Co molar ratio=0.26) (b)); ii) Two other samples were prepared using two nitrate- and fuel-rich process (EDTA/Co molar ratio=1.12 (c), Lysine/Co molar ratio=1.32 (d)). After all processes, ashes were calcined at 500 ºC for 2 h. By XRD, in all samples, was found the face-centered cubic structure of Co3O4. It was assessed their morphology by SEM, observing that their agglomerates are: (a) composed of filaments, (b) porous sheets, (c) only sheets without evident porosity, and (d) composed of micrometric particles. By TEM, it was verified that (a), (b) and (c) samples are agglomerations of polyedric nanoparticles (average size ~50 nm), but in (d) sample, particles are cubic (size ~1 m). A criterion based on theoretical models claims that a selective surface will be effective in solar radiation absorption only if their particles have a size minor than the incident wavelength, so (a), (b) and (c) samples are suitable as pigments in paints for this purpose.