Synthesis and characterization of nanocrystalline thoria obtained from thermally decomposed thorium carbonate
ABSTRACT 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.
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- "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. "
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 · 2.28 Impact Factor
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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 · 3.84 Impact Factor
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ABSTRACT: Thermal analysis is a widely used analytical technique for materials research. However, thermal analysis with simultaneous evolved gas analysis describes the thermal event more precisely and completely. Among various gas analytical techniques, mass spectrometry has many advantages. Hence, an ultra high vacuum (UHV) compatible mass spectrometry based evolved gas analysis (EGA-MS) system has been developed. This system consists of a measurement chamber housing a mass spectrometer, spinning rotor gauge and vacuum gauges coupled to a high vacuum, high temperature reaction chamber. A commercial thermogravimetric analyser (TGA: TG + DTA) is interfaced to it. Additional mass flow based gas/vapour delivery system and calibration gas inlets have been added to make it a versatile TGA-EGA-MS facility. This system which gives complete information on weight change, heat change, nature and content of evolved gases is being used for (i) temperature programmed decomposition (TPD), (ii) synthesis of nanocrystalline materials, (iii) gas-solid interactions and (iv) analysis of gas mixtures. The TPD of various inorganic oxyanion solids are studied and reaction intermediates/products are analysed off-line. The dynamic operating conditions are found to yield nanocrystalline products in many cases. This paper essentially describes design features involved in coupling the existing EGA-MS system to TGA, associated fluid handling systems, the system calibration procedures and results on temperature programmed decomposition. In addition, synthesis of a few nanocrystalline oxides by vacuum thermal decomposition, gas analysis and potential use of this facility as controlled atmosphere exposure facility for studying gas-solid interactions are also described.Bulletin of Materials Science 06/2003; 26(4):449-460. DOI:10.1007/BF02711191 · 0.87 Impact Factor