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13477-34-4Relevant articles and documents
Synthesis and red luminescence of Pr3+-doped CaTiO3 nanophosphor from polymer precursor
Pan, Yuexiao,Su, Qiang,Xu, Huifang,Chen, Tianhu,Ge, Weikun,Yang, Chunlei,Wu, Mingmei
, p. 69 - 73 (2003)
Uniform and sphere-like nanoparticles of crystalline Pr3+-doped CaTiO3 have been prepared from complex polymer precursor at 600°C, in which, metal atoms are previously dispersed by citric acid in ethylene glycol solvent. The decomposition process of the precursor, crystallization, and particle sizes of CaTiO3 have been investigated by using thermal analysis, powder X-ray diffraction and transmission electron microscopy. Diffuse reflectance spectra, photoluminescence and decay curve indicate that a strong red emission located at the nearly NTCS ideal red site is deduced from the energy transfer from the band gap absorption to doping Pr3+ ions. The thermoluminescence curves exhibit that a potential long phosphorescent material based on Pr3+-doped CaTiO3 will be explored in future.
Kinetics of heterogeneous reaction of CaCO3 particles with gaseous HNO3 over a wide range of humidity
Liu,Gibson,Cain,Wang,Grassian,Laskin
, p. 1561 - 1571 (2008)
Heterogeneous reaction kinetics of gaseous nitric acid (HNO3) with calcium carbonate (CaCO3) particles was investigated using a particle-on-substrate stagnation flow reactor (PS-SFR). This technique utilizes the exposure of substrate deposited, isolated, and narrowly dispersed particles to a gas mixture of HNO3/H2O/N2, followed by microanalysis of individual reacted particles using computer-controlled scanning electron microscopy with energy-dispersive X-ray analysis (CCSEM/EDX). The first series of experiments were conducted at atmospheric pressure, room temperature and constant relative humidity (40%) with a median dry particle diameter of Dp = 0.85 μm, particle loading densities 2 × 104 ≤ Ns ≤ 6 × 106 cm -2 and free stream HNO3 concentrations of 7, 14, and 25 ppb. The apparent, pseudo first-order rate constant for the reaction was determined from oxygen enrichment in individual particles as a function of particle loading. Quantitative treatment of the data using a diffusion-kinetic model yields a lower limit to the net reaction probability γnet ≥ 0.06 (x 3/÷-2). In a second series of experiments, HNO3 uptake on CaCO3 particles of the same size was examined over a wide range of relative humidity, from 10 to 80%. The net reaction probability was found to increase with increasing relative humidity, from γnet ≥ 0.003 at RH= 10% to 0.21 at 80%.
Sintering densification of CaO-UO2-Gd2O3 nuclear fuel pellets
Wang, Yun,Sun, Huidong,Wang, Hui,Pan, Xiaoqiang,Li, Tongye,Liu, Jinhong,Zhang, Yong,Wang, Xinjie
, p. 626 - 631 (2015)
CaO-doped UO2-10 wt% Gd2O3 burnable poison fuel was prepared by co-precipitation reaction method. It was found that 0.3 wt% CaO-doping significantly improved the sintered density, grain sizes and crushing strength of UO2-Gd2O3 fuel pellets at the sintering temperature of 1650 C in the sintering atmosphere of hydrogen for 3.5 h. In addition, homogeneous solid solution without precipitation of free phases of CaO and Gd2O3 was successfully achieved. CaO doping in UO2-Gd2O3 fuel pellet system accelerated the thermally activated material transport, so the onset temperature of densification as well as the temperature of the maximum densification rate shifted to a lower temperature region.
Particle size dependence on the structural, transport and optical properties of charge-ordered Pr0.6Ca0.4MnO3
Kumar, Satyam,Dwivedi,Lourembam,Kumar, Shiv,Saxena,Ghosh,Chou,Chatterjee, Sandip
, p. 1094 - 1101 (2015)
Abstract Structural, transport and optical properties of nano-crystalline Pr0.6Ca0.4MnO3 have been investigated to emphasize on the semiconducting properties of charge-ordered manganite. Rietveld refinement of X-ray diffraction pattern of Pr0.6Ca0.4MnO3 nanoparticles show that due to increase in sintering temperature, MnO6 octahedra elongated along z-direction and compressed in x-y plane. Both Mn-O-Mn angles are found to decrease with increasing sintering temperature. Fourier transform infrared (FTIR) spectroscopy measurements reveal that the stretching and bending vibration of Mn-O-Mn is responsible for the change in Mn-O-Mn bond length and bond angle respectively. With increasing sintering temperature, these vibrations tend to increase, which resulted in the further distortion of MnO6 octahedra. Magnetic measurements suggest that charge ordering is established and system becomes antiferromagnetic with increasing particle size. Resistivity behavior of Pr0.6Ca0.4MnO3 nanoparticles clearly exhibit semiconducting nature of these systems, which is due to the formation of charge-ordered state of Mn3+ and Mn4+. Estimated optical band-gap of ～3.7 eV for Pr0.6Ca0.4MnO3 nanocrystals, makes it a potential candidate for wide band-gap magnetic semiconductors.
Universal transport coefficient behaviour in ionic melts
Veliyulin,Shasha,Voronel,Machavariani,Seifer,Rosenberg,Shumsky
, p. 8773 - 8784 (1999)
Precise resistivity and viscosity measurements for ionic mixed melts, regular and glass-forming, have been performed on the liquid state over a wide range of viscosity variation. Their universal behaviour in the high-temperature region allows us to scale them relative to their activation energy. The resistivity-viscosity relation reveals a fractional-power character over the whole range of parameters investigated. This interdependence suggests a fractional character of the Stokes-Einstein law of the viscosity-diffusion relation for ions in melts.
The oxidation of calcium sulphite by calcium nitrate
Galwey, Andrew K.,Ettarh, Clodagh
, p. 57 - 73 (1998)
Crushed powder mixtures of calcium sulphite and calcium nitrate exhibit an exothermic reaction between 650 and 700 K. This rate process has been investigated by dynamic and isothermal DSC experiments, complemented with isothermal rate studies based on gas evolution in a vacuum apparatus, together with some product analyses. It is concluded that the overall reaction is complicated, including several concurrent contributing chemical changes, in which sulphite oxidation to sulphate is a dominant process, accompanied by some nitrate decomposition. On heating to higher temperatures (above 800 K) a second endothermic reaction was identified as the melting and breakdown of calcium nitrate. These processes occurred at temperatures somewhat less than those characteristic of the pure salt, possibly due to the presence of products from the first reaction including small amounts of Ca(NO2)2. The dominant exothermic reaction was accompanied by fusion, at temperatures significantly below the melting point of either reactant. This may be due to the intermediate formation of Ca(NO2)2, melting point 551 K, or the generation of liquid product following hydrolysis reactions with water evolved during dehydration of reactant CaSO3·1/2H2O, with which the exothermic oxidation overlapped. This dehydration step was a precursor to sulphite oxidation. A detailed reaction mechanism is not proposed here due to the difficulties of separating the contributions from the several probable concurrent participating reactions. The role of the fluid reactant believed to be active in the oxidation process, and containing NO-3, NO-2, SO2-3 and possibly SO2-4, in desulphurization processes, is discussed as a possible route towards removing the precursors to acid rain from coal combustion emissions. It is known that CaCO3 reacts with NOx to form Ca(NO3)2. The present work identifies the liquid medium recognized in the exothermic reaction as enabling the oxidation of CaSO3→CaSO4 to proceed to completion at a lower temperature than the slow and product-opposed reaction of CaSO3 with oxygen gas. Aspects of the chemistry of this complicated reaction and its potential value in pollution abatement are discussed.
Synthesis of pure cementitious phases by sol-gel process as precursor
Stephan, Dietmar,Wilhelm, Patrick
, p. 1477 - 1483 (2004)
Calcium silicates and aluminates are the main constituents of ordinary Portland cement (OPC) and calcium aluminate cements (CAC) and therefore the pure phases are of great importance for the investigation of interactions between binder and additives or admixtures. Additionally, investigations on clinker phases doped with foreign ions enable the improvement of the performance of cements. For this purpose great amounts of pure phases are needed. These phases are hard to synthesize via a solid state reaction of solid educts. Thus there is a need for a new, more efficient route to synthesize these phases. The sol-gel process as precursor provides an alternative to the conventional method. In this paper experimental evidence is presented for an improved synthesis of calcium silicates and aluminates via sol-gel processes, the characterisation of these clinker phases and their hydration behaviour.
Structural and optical characterization of Eu and Dy doped CaWO4 nanoparticles for white light emission
Kaur, Puneet,Khanna, Atul,Singh, M. N.,Sinha, A. K.
, (2020)
The structural and light emission properties of calcium tungstate (CaWO4) nanoparticles containing Eu3+ and Dy3+ are studied. CaWO4 nanoparticles were prepared by chemical routes followed by drying at 80°C, doping with 1, 3, 5, 7 and 10 mol% of Eu2O3 and/or Dy2O3 and final annealing at 800oC. The samples were characterized by field emission-scanning electron microscopy (FE-SEM), energy dispersive X-ray spectroscopy (EDS), synchrotron X-ray diffraction (XRD), Raman and photoluminescence (PL) spectroscopy. FE-SEM studies show that CaWO4 sample dried at 80°C contains spherical particles of diameter ～5 μm, and upon annealing at 800°C, dense and irregular shaped structures are formed. EDS mapping found a uniform distribution of Eu and Dy ions and only a small segregation in the CaWO4 matrix is observed. XRD studies revealed the co-existence of the tetragonal CaWO4 and cubic Dy2O3 and/or Eu2O3 phases in the doped samples and rule out the replacement of Ca2+ by rare-earth ions. The structural parameters: crystallite size, lattice strain, unit cell dimensions, atomic position coordinates, bond-lengths, bond-angles and cation-oxygen coordination numbers were determined. The short-range structure of CaWO4 consists of interconnected CaO8 and WO4 units. All the W–O bonds in WO4 units have the same length whereas two types of Ca–O bond-lengths exist in CaO8 units. The undoped CaWO4 sample annealed at 800°C, has the smallest Ca–O bond-lengths and unit cell dimensions due to the compressive macrostrain induced by heat-treatment. On incorporating Eu3+ and Dy3+, the W–O and Ca–O bond-lengths increase slightly. Raman spectra of all the samples are similar and show W–O vibrational modes. PL studies found that the undoped CaWO4, Eu and Dy-doped CaWO4 samples emit blue, red and yellow light respectively. The co-doped sample: 2 mol% Eu2O3–5 mol% Dy2O3–CaWO4 was closest to the ideal white light emission properties.
Synthesis & characterization of Dy and Ca Co-doped ceria based solid electrolytes for IT-SOFCs
Tanwar, Khagesh,Jaiswal, Nandini,Kumar, Devendra,Parkash, Om
, p. 683 - 690 (2016)
Numerous compositions in the system, Ce1-x-yDyxCayO2-δ have been synthesized using citrate-nitrate auto-combustion route. Samples sintered at 1350 °C for 4 h have density more than 93% of the theoretical value. Single phase formation has been confirmed by X-ray diffraction in all the samples. Reitveld refinement has been carried out to confirm the cubic fluorite structure with space group Fm3 m. Surface morphology of the sintered samples show the distinct grains and grain boundaries. Complex plane impedance analysis has been employed to separate the contribution of the grains, grain boundaries and electrode/specimen interface polarizations. A significant improvement in the electrical conductivity has been observed by partial replacement of Dy3+ with Ca2+ in Ce0.80Dy0.20O1.90 (keeping total number of oxygen vacancies fixed). Composition, Ce0.83Dy0.14Ca0.03O1.90 shows the highest conductivity, 1.45 × 10-2 S/cm at 600 °C. This value is about two orders of magnitude higher than that of singly Dy3+ doped ceria (6.01 × 10-4 S/cm) at the same temperature.
Heterogeneous reactivity of gaseous nitric acid on Al2O3, CaCO3, and atmospheric dust samples: A Knudsen cell study
Hanisch,Crowley
, p. 3096 - 3106 (2001)
The heterogeneous reaction between HNO3 and various authentic and synthetic mineral dust/mineral oxide surfaces has been investigated using a low-pressure Knudsen reactor operating at 298 K. The surfaces used were Saharan dust from Cape Verde, Arizona dust, CaCO3, and Al2O3. In all cases, a large irreversible uptake was observed. An uptake coefficient of γ = (11 ± 3) × 10-2 was determined for Saharan dust, and γ= (6 ± 1.5) × 10-2 was obtained for Arizona dust. The uptake coefficients for HNO3 on heated CaCO3 and on unheated CaCO3 are given by γ = (10 ± 2.5) × 10-2 and (18 ± 4.5) × 10-2, respectively, and are in good agreement with previous results. CO2 and H2O were formed as gas-phase products. Measurements of the uptake coefficient of HNO3 on grain-size selected samples of Al2O3, γ = (13 ± 3.3) × 10-2, and systematic variation of sample mass enabled us to show that the geometrical surface area of the dust sample is appropriate for calculation of uptake coefficients in these experiments. The high reactivity of HNO3 toward dust samples highlights the potentially important role of mineral dust in redistributing nitrate from the gaseous to the particulate phase and modifying tropospheric photochemical oxidation cycles.