Nanocrystalline thoria was synthesized by temperature programmed decomposition of Th(CO3)2 in an evolved gas analysis mass spectrometer set-up. The structural and stoichiometric changes encountered in the decomposition pathway were studied by off-line thermogravimetry (TGA), X-ray diffraction and X-ray photoelectron spectroscopy (XPS). Accurate conversion temperature for transformation of Th(CO3)2→ThO2 was arrived from the XPS measurements. Fourier transform infrared (FT-IR) measurements were used to compare vibrational activities of nano and bulk polycrystalline thoria. Raman spectroscopic studies indicated optical phonon confinement effects in nanocrystalline thoria. High resolution transmission electron microscopic examination on starting material, intermediates and nanocrystalline final product were carried out for studying the microstructure in the nanometer scale.
"aqueous systems, different hydroxilated species of thorium(IV) can be formed (Mompean et al. 2008), which together with the thorium(IV) ion are usually bound to different types of particle surfaces (Geibert and Usbeck 2004), such as colloids and/or solid hydroxides and oxides (Altmaier et al. 2004; Neck et al. 2003; Bitea et al. 2003; Rothe et al. 2002; Ansoborlo et al. 2006). Notwithstanding, important applications of thoria nanoparticles in the nuclear industry are still in use (IAEA 2005), although synthesis of thoria nanomaterial has received little attention (Dash et al. 2002). Therefore, there is a great interest in the study of nanocrystalline thoria with minimum carry over of impurity phases during synthesis. "
[Show abstract][Hide abstract] ABSTRACT: Thoria materials have been largely used in the nuclear industry. Nonetheless, fluorescent thoria-based nanoparticles provide additional properties to be applied in other fields. Thoria-based nanoparticles, with and without arsenic and cysteine, were prepared in 1,2-ethanediol aqueous solutions by a simple precipitation procedure. The synthesized thoria-based nanoparticles were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), energy disper-sive X-ray spectrometry (ED-XRS), Raman spectros-copy, Fourier transform infrared (FT-IR) spectroscopy and fluorescence microscopy. The presence of arsenic and cysteine, as well as the use of a thermal treatment facilitated fluorescence emission of the thoria-based nanoparticles. Arsenic-doped and cysteine-capped thoria-based nanoparticles prepared in 2.5 M 1,2-ethanediol solutions and treated at 348 K showed small crystallite sizes and strong fluorescence. How-ever, thoria nanoparticles subjected to a thermal treatment at 873 K also produced strong fluorescence with a very narrow size distribution and much smaller crystallite sizes, 5 nm being the average size as shown by XRD and TEM. The XRD data indicated that, even after doping of arsenic in the crystal lattice of ThO 2 , the samples treated at 873 K were phase pure with the fluorite cubic structure. The Raman and FT-IR spectra shown the most characteristics vibrational peaks of cysteine together with other peaks related to the bonds of this molecule to thoria and arsenic when present.
Journal of Nanoparticle Research 07/2013; 15(9). DOI:10.1007/s11051-013-1895-8 · 2.18 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Bandpass filters without inductors can be realized by using all-pass frequency-sensitive phase-shift networks. Filters with Q values approaching 1000 have been constructed. A method of reducing the Q sensitivity is reported.
IEEE Transactions on Circuit Theory 01/1969; CT-15(4-15):501 - 503. DOI:10.1109/TCT.1968.1082852
[Show abstract][Hide abstract] ABSTRACT: We report the trimethylamine (TMA) sensing properties of thoria-incorporated tin oxide. The tin oxide pellet having 3 wt.% of thoria exhibits a high sensitivity of 1500 towards 800 ppm of TMA compared to only 18 of pure tin oxide at a lower operating temperature of 225 °C. The incorporation of thorium in tin oxide enhances the sensitivity towards TMA with improved selectivity. The effect of surface coverage, morphology and oxidation state on the sensitivity has been studied using techniques like scanning electron microscopy (SEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The correlation between thoria incorporation in the tin oxide at different sintering temperatures and the improvement in the selectivity and sensitivity towards TMA is discussed.
Sensors and Actuators B Chemical 12/2002; 87(3-87):406-413. DOI:10.1016/S0925-4005(02)00288-5 · 4.10 Impact Factor
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