ABSTRACT
In this work, several attempts were made to prepare nanoceramic zirconate (Nd2Zr2O7) powder for pigment applications. The single pyrochlore phase, Nd2Zr2O7 was successfully synthesized with the aid of flux at relatively low temperature (1000 °C) upon milling the reaction mixture made from Nd2O3 and ZrO2 in a tungsten carbide vial. Several characterizations were done on the thermal analysis (TG/DTA), X-ray diffraction (XRD), High-resolution scanning electron microscope (HRSEM), energy dispersive X-ray (EDX) analysis, Fourier-transform infrared (FT-IR) analysis, and near-infrared (NIR spectroscopy). A single-phase nanocrystalline (Ë28 nm) pyrochlore structure (Fd3m) was confirmed through XRD analysis. A highly uniform particle in the size of Ë110 nm was observed for the Nd2Zr2O7 phase in the microimages. The vibrational (FT-IR) peaks at 423 cm-1 and 510 cm-1 in FTIR spectroscopic study confirmed the formation of pyrochlore structure. Higher NIR reflectivity recorded for this material in the 750-2500 nm region shows its novel application in color cool pigments for energy-saving paints reminiscent of Bi2-xYxCe²O7, Bi²Ce2-xTbxO7, and Gd²Ti²O7.
ABSTRACT
The recent trend of reflecting the NIR rays with cool and color pigments to reduce the transfer of heat inside the buildings is highly encouraged. In this work, the pyrochlore-type Gd2Ti2O7 nanomaterials were synthesized through a hybrid process comprising planetary ball milling and chloride salt flux method. Different combination of alkali metal chloride fluxes was used to enhance the phase formation and purity. In order to investigate the phase formation, purity, particle size, optical property, morphology and elemental composition of the prepared samples, many characterization techniques including XRD, RAMAN, FT-IR, UV-vis, NIR, PL, and HRSEM-EDX were carried out. The XRD patterns revealed that the annealed materials crystallized in cubic structure with lattice parameter, a = 1.019(1) nm, and the ball milled product annealed with LiCl:NaCl and LiCl:CsCl flux crystallized in a single cubic phase with high purity. The FT-IR analysis confirmed the presence of metal oxide bonds (Gd-O vibration and Ti-O-Ti bending vibration) in the wavenumber regions 400 cm-1 and 500 cm-1. The band gap of the Gd2Ti2O7 powder is enhanced from 2.77 eV to 3.27 eV through the addition of LiCl:CsCl flux. The PL emission property of Gd2Ti2O7 is enhanced by annealing with flux under the excitation wavelength of 230 nm. Further, the band gap and NIR reflectivity of the nanomaterials are enhanced by the conditions employed in the synthesis method.
ABSTRACT
Various BaMnO3 samples were prepared by planetary ball milling technique by varying the milling time from 1 to 20 h at a speed of 350 rpm, and all the milled powders were subsequently annealed at 1000 °C for 16 h in order to improve the phase formation and purity. While the ball milled powders are amorphous in nature, the annealed materials reveal nanocrystalline hexagonal perovskite structure with space group, P6(3)/mmc (194). The 15 h ball milled and subsequently annealed material shows lattice parameters, a = 0.5704(5) and c = 0.4801(6) nm with lowest average crystalline size of ~18 nm. It is found that, as the milling time increases (from 1 h to 15 h) the average crystalline size decreases slightly from 25.7 nm to 18.1 nm. The nano rod/needle shaped particles with the size of ~97 nm are observed through SEM images for the BaMnO3 phase. Interestingly, the present BaMnO3 nanopowder reveals photo-luminescent property under the excitation wavelengths of 270 and 350 nm. The nanocrystalline BaMnO3 powder exhibits higher reflectance, which finds application in NIR reflective pigments.
