INSTITUTO ARGENTINO DE NIVOLOGIA, GLACIOLOGIA Y CIENCIAS AMBIENTALES
Unidad Ejecutora - UE
congresos y reuniones científicas
Synthesis of CoCuMnOx pigments for selective enamels for solar collectors
MARÍA CELESTE GARDEY MERINO; M. RODRIGUEZ; A. ESTRELLA; ALONSO, J.A; S. LASSA; ARRECHE ROMINA; PATRICIA VAZQUEZ; G. LASCALEA; R.ROMAGNOLI; R. ECHAZÚ
Conferencia; The Energy & Materials Research Conference - EMR2015; 2015
In order to improve the energy yield of solar collectors, selective coatings presenting a high absorbance of the solar spectrum (0.3< < 3m) and a high emittance in the infrared region >3m) are used . The selective coatings formed by enamels applied on substrates represent the most economical alternative for the heat transfer to the collectors, among other types. The pigments used in selective painted surfaces are, in general, black in color and posses a high absorption of the solar spectrum. Among the most utilized we can mention the spinel-type oxides containing transition metals like Fe, Co, Cr, Mn y Cu, exhibiting a high absoption in all the solar spectrum . Pigments with spinel-like structure such as CuCrxMn2-xO4  or CoCuMnOx  have been obtained by gelification-combustion synthesis using citric acid as a fuel, but other types of fuels have not been studied yet. In this work we propose the synthesis of pigments by combustion chemistry from stoichiometric mixtures of metal nitrates of CoCuMnOx oxides utilizing novel fuels such as aspartic acid (Asp), etylen-diamin-tetra-acetic acid (Edta) and lysine (Lys). Once obtained the ashes they were calcined to 500°C in order to get the pigments with the desired phase. The powders were characterized by x-ray diffraction (XRD), scanning electron mycroscopy (SEM), transmission electron microscopy (TEM), infrared spectroscopy with Fourier transform (FT-IR), and Brunauer?Emmett?Teller (BET) techniques, and the crystal structures were refined by the Rietveld method. Finally the selected pigment was that obtained with Asp, and the corresponding enamel of alkyl base was prepared with Al powder aggregate; the enamel was applied on an aluminum substrate in order to obtain a selective surface independent of the thickness. The spectral absorbance curve of those substrates was determined with a spectro-radiometer in a wavelengths range between 500 and 1000 nm. The Rietveld analysis allowed the refinement of the spinel structure with a model assuming that Cu occupies the tetrahedral A positions and Co and Mn are located at random at the octahedral B sites of the AB2O4 structure, ie Cu(CoMn)O4, with unit cell parameters in the range 8.18 to 8.21 Å, as described in literature for this composition. The Scherrer formula yielded crystalline sizes between 22 and 26 nm. The surface area BET was ranging between 2 and 11 m2/g. The IR bands corresponding to metal oxides were observed between 550 y 750 cm-1 by means of FT-IR spectroscopy; by TEM an agglomeration of particles with polygonal shapes with an average size between 50 and 100nm. With respect to the selective surfaces (enamels applied on Al substrates) an extraordinary value of absorption between 96 and 97% was observed. These superior absorption ranges, in comparison with literature values, suggest the possibility of utilizing these oxides as active pigments if selective solar enamels. In the near future we are aiming to determine the formulation of enamels with an optimal thermal emittance.