The compound of interest at the conception of this research project was YInMnO3, a new bright blue inorganic pigment discovered by Mas Subramanian in 2009.1 The pigment’s unique reflective properties in the infrared region of light give this compound potential as a passive heat reducer in cool roofing. The project was conceived with a desire to find alternate routes to synthesis of this promising blue pigment. CuTiO3 and YInFeO3,2,3 other hexagonal pigments with metal ions in the same trigonal bipyramidal coordination, were made with similar experimental parameters after successful synthesis of YInMnO3 in the microwave.
Previous research has identified microwave-active elements and compounds that heat up rapidly when exposed to microwave energy. Undergraduate student Casey Young profiled various susceptors in the microwave to determine a working susceptor with the capability of heating to 1300 degrees Celsius (the literature temperature required to synthesize YInMnO3). Thermal profiles were gathered for several susceptors, collecting temperature readings at various power levels and heating interval lengths. The susceptors tested were tungsten oxide, activated and non-activated manganese dioxide, silicon carbide, cupric oxide, activated carbon mesh, and granular carbon slug. Reusability and maximum temperature were both significant limitations. The susceptor that proved most optimal for synthesis was carbon slug 6-8 mesh, which rose to 1350 degrees Celsius and was reusable after successive heatings. Casey Young determined the optimal parameters for microwave synthesis, including crucible type, crucible dimensions, type of susceptor, amount of susceptor, microwave power level, duration of heating intervals, and amount of heating intervals necessary for successful synthesis. After Casey Young determined ideal microwave synthesis conditions, the student ran several trials to synthesize YInMnO3 and YCuTiO3 and analyzed phase-purity via XRD to find optimal heating time. Using the parameters outlined by Casey Young, undergraduate student colleague Omar Rachdi ran trials of YInFeO3 to find optimal heating time for synthesis. Casey Young and Omar Rachdi then constructed a poster for CUE 2013 and presented to the general public on May 15th, 2013.
The findings of this project are significant because it shows alternative synthesis routes for YInMnO3 and other pigments of similar structure. The conventional synthesis of YInMnO3 in a furnace requires three full days of heating; microwave synthesis of this compound was shown to reduce the synthesis time to under 2 hours. This reduced heating time holds potential to reduce production cost of YInMnO3, giving this environmentally beneficial pigment greater economic potential.
1. Smith, A. E. et al. Mn 3+ in Trigonal Bipyramidal Coordination: A New Blue Chromophore. J. Am. Chem. Soc. 131, 17084–17086 (2009).
2. Smith, A. E., Sleight, A. W. & Subramanian, M. A. Synthesis and properties of solid solutions of hexagonal YCu0.5Ti0.5O3 with YMO3 (M = Mn, Cr, Fe, Al, Ga, and In). Mater. Res. Bull. 46, 1–5 (2011).
3. Jiang, P., Li, J., Sleight, A. W. & Subramanian, M. A. New Oxides Showing an Intense Orange Color Based on Fe3+ in Trigonal-Bipyramidal Coordination. Inorg. Chem. 50, 5858–5860 (2011).
This work prepared YInMnO3, YCuTiO3, and YInFeO3 solid state pigments via microwave synthesis. The microwave-prepared pigments contain optical and structural properties similar to their furnace homologues. Overall synthesis times for each pigment have been significantly reduced via microwave synthesis, while keeping the same relative phase purity as solid-state.