ABSTRACT This research presents a novel one–step solution combustion synthesis to obtain nano-structured Cr2O3 from chrome nitrate solution and one fuel such as aspartic acid (Asp) or Lysine (Lys), or Autor Restrihydroxymethylaminomethane (Tris) or ethylenediaminetetraacetic acid (Edta). Once obtained, the ashes were calcined at 500°C. The powders were characterized by x-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), infrared spectroscopy with Fourier transform (FTIR), UV-Visible Spectroscopy (UV-VIS) spectroscopy and Brunauer–Emmett–Teller (BET) techniques. These powders will be used in solar absorbing surfaces: in composites (o cermets) and painted coatings. Within the obtained ashes and calcined powders, it was identified a Cr2O3 crystalline structure corresponding to the rhombohedral system and to the R-3c spatial group. The average crystallite size was determined for ashes and calcined powders, this value was in nanometric range between 29 and 45 nm, where for ashes were in general minor than calcined powders in all cases. It is probable that with an increment of the temperature, crystallite size would grow. A specific area of 167 m2/g was determined for asp-ashes. This was a highest value observed in specific literature and it could be used in catalysis reactions, while the area values of ashes was higher than calcined powders value for each fuel. The average particle size observed through TEM resulted in 50 nm to 100 nm approximately. The determined Energy band gap resulted in 3.055eV to 3.078 eV approximately. The Energy band gap slightly increased with calcination temperature. Further trials and investigation will confirm the mentioned tendencies.

RESUMEN Esta investigación presenta un nuevo método de síntesis de un solo paso para obtener Cr2O3 nanoestructurado a partir de una solución de nitrato de cromo y un combustible como ácido aspártico, o lisina, o trihidroximetilaminometano, o etilendiaminotetraacético. Una vez obtenido los polvos fueron calcinados a 500ºC. Luego se caracterizaron mediante difracción de rayos X (DRX), microscopía electrónica de barrido (MEB), microscopía electrónica de transmisión (TEM), espectroscopía infrarroja por transformada de Fourier (FTIR), espectroscopía por UV-Visible y técnicas de Brunauer–Emmett–Teller (BET). Estos polvos serán utilizados en superficies absorbedoras como cermts o pinturas selectivas solares. En las cenizas y los polvos calcinados obtenidos se identificó la estructura cristalina del Cr2O3, correspondiente al sistema romboédrico y al grupo espacial R-3c. El tamaño promedio de cristalita de los productos obtenidos estuvo entre 29 y 45 nm, donde para las cenizas el tamaño fue menor en comparación a los polvos obtenidos para todos los combustibles utilizados. Es probable que para un incremento de la temperatura el tamaño de cristalita crezca. Un área específica de 167 m2/g fue determinada para las cenizas obtenidas con ácido aspártico. Este fue el mayor valor observado en la literatura específica y podría utilizarse para reacciones de catálisis, mientras que el resto de los valores obtenidos para las cenizas fue mayor en comparación a los polvos calcinados para todos los combustibles. El tamaño promedio de partícula observado a través de TEM resultó entre 50 y 100 nm aproximadamente. La energía de Band Gap determinada resultó entre 3.055 eV y 3.078 eV, esta variable aumenta suavemente con la temperatura de calcinación. Para confirmar esta tendencia se deberían realizar mayor cantidad de experimentos.

ABSTRACTTernary spinel-like oxides such as CuFeMnO4, CoCuMnOxand CuCr2O4 are attractive materials due to their absorbent properties when used as pigments for selective surfaces thus improving solar heaters efficiency. These materials are obtained through sol-gel and sol-gel-combustion methods. This work proposes the synthesis of mixed oxides of Co, Cu and Mn by means of original one-step stoichiometric combustion methods starting from Mn(NO3)2,Co(NO3)26H2O, Cu(NO3)23H2O and Aspartic acid (Asp) or Lysine( Lys) as fuels. The resulting ashes after the combustion were calcined at 500 °C. The obtained ashes and the calcined powders were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FTIR), and by Brunauer-Emmett-Teller method (BET), and TG-DTA analysis. In calcined powders obtained with Lys (CoCuMnOx-Lys), the phase corresponding to CoCuMnOx and others segregated phases were identified. However, in calcined powders obtained with Asp (CoCuMnOx-Asp) only the phase corresponding to CoCuMnOxwas identified. The sample CoCuMnOx-Lys presented an average crystallite size of 44 nm and a specific surface area of 23 m2/g while in CoCuMnOx-Asp, 54 nm and 13 m2/g values were obtained throughout FT-IR vibrational modes associated with spinel metallic oxides for both calcined powders (Asp and Lys) were observed. Additionally, by means of TEM, polyhedral particles with an average size of 20 to 100 nm were observed. In particular, it was determined in CoCuMnOx-Lys an average size of 44nm. According to the different fuels used (Asp and Lys), an evident variation in the obtained phases was observed. However, it was not obtained any difference in crystallite size and specific area surface values. It is of considerable importance the study of further syntheses processes to verify this trend.