Preparation of ZrO2/Gd2O3 composite ceramic materials by coprecipitation method

High burnup is a goal for further development of advanced nuclear power in the future. However, along with the increase of burnup, it becomes more diffidult to control reactor reactivity, which affects the operation safety of the nuclear reactor. Al₂O₃/B₄C burnable poison materials widely used in pressurized water reactor currently will not meet the requirements of burnable poison materials in high burnup nuclear power. Because of the better performance of ZrO₂/Gd₂O₃ burnable poison materials than that of Al₂O₃/B₄C, this paper studies the preparation of ZrO₂/Gd₂O₃ composite ceramic materials by the coprecipitation method. The experimental results show that at the sintering temperature of 1500–1650 °C, ZrO₂/Gd₂O₃ composite ceramic grains are small, compact and uniform with the generation of homogeneous solid solution. At 1600 °C, ZrO₂–10%Gd₂O₃ has the highest density and mechanical strength.     

Influence of metal ion concentration in the glycol mediated synthesis of Gd2O3:Eu nanophosphor

The solvothermal synthesis of highly luminescent and homogeneous Gd₂O₃:Eu³⁺ nanophosphor using diethylene glycol as medium, followed by controlled combustion with citric acid as fuel is reported. The influence of concentrations of carboxylic acid and metal cations on the structure, morphology and luminescence properties are investigated in detail. The microscopic investigations indicate the nanocrystalline nature and the strong influence of cation concentration on the size, shape and agglomeration of the particles. It is found that increase in concentration of metal cations lead to the reduction in agglomeration of nanophosphors. The large value of intensity parameter Ω_2, suggested that Eu³⁺ ions reside in a more asymmetric environment, resulted in intense emission due to ⁵D₀–⁷F₂ electric dipole transition. Emission decay analysis of the samples exhibited one exponential nature. The samples prepared under optimum conditions showed a quantum efficiency of 78.63% and a moderately high life time of 1.217 ms.     

Effects of grinding and firing conditions on CaAl2Si2O8 phase formation by solid-state reaction of kaolinite with CaCO3

The effects of grinding and firing conditions on CaAl₂Si₂O₈ phase formation by solid-state reaction of kaolinite with CaCO₃ were investigated by differential thermal analysis (DTA)–thermogravimetry (TG), X-ray powder diffraction (XRD) and ²⁹Si and ²⁷Al MAS NMR. Unground and ground samples showed similar crystallization behavior at about 850 °C, and the crystallizing temperature was relatively unaffected by grinding. On the other hand, the crystalline products were strongly influenced by the grinding. Gehlenite (Ca₂Al₂SiO₇) was the dominant phase in the unground samples but layer-structured CaAl₂Si₂O₈ was dominant in the ground samples, together with a small amount of anorthite, which is the stable phase. The amount of anorthite gradually increased with higher firing temperature, the sample fired at 1000 °C being almost completely anorthite. Grinding treatment before firing was effective in accelerating the decomposition of CaCO₃ and extending the temperature range for the formation of CaAl₂Si₂O₈, a phase with local structure similar to that of layered CaAl₂Si₂O₈.     

Highly uniform Gd(OH)3 and Gd2O3:Eu hexagram-like microcrystals: glucose-assisted hydrothermal synthesis,growth mechanism and luminescence property

Monodispersed and uniform Gd(OH)₃ microcrystals with novel hexagram-like morphology have been successfully prepared through a simple and green hydrothermal process with the assistance of glucose. The results of control experiments revealed that the glucose concentration in the reaction system was an important factor, which affected the morphology of the Gd(OH)₃ microcrystals significantly. On the basis of time-dependent experiments, the growth mechanism of the Gd(OH)₃ hexagrams was discussed. Furthermore, the Gd₂O₃ and Eu³⁺-doped Gd₂O₃ hexagram-like microcrystals, inheriting the Gd(OH)₃ precursors' morphology, were obtained during a direct annealing process in air. The corresponding Gd₂O₃:Eu³⁺ hexagram-like microcrystals exhibit strong red emission pertaining to the ⁵D₀→⁷F₂ transition of the Eu³⁺ ions under UV light, which have potential applications in novel optoelectronic devices.     

Microwave-assisted solvothermal preparation and photoluminescence properties of Y2O3:Eu phosphors

Europium doped yttrium oxide phosphors were synthesized by a rapid microwave-assisted solvothermal method. The microwave processing time for synthesizing the precursors of Y₂O₃:Eu³⁺ powders was as short as 5 min. After calcination at 600 °C, a well-crystallized pure phase of Y₂O₃:Eu³⁺ was obtained. The morphology of the precipitated powders was spherical and composed of nano-sized grains. As the microwave irradiation time was increased, the average particle size of the spherical powders increased, and the crystallinity of heat-treated powders was also enhanced. The synthesized powders retained the spherical morphology after heating treatments. An intense red emission at 611 nm was assigned to the ⁵D₀-⁷F₂ transition of Eu³⁺.     

Synthesis of silver/SiO2/Eu:Lu2O3 core-shell nanoparticles and their polymer nanocomposites

We report a core-shell approach that combines silver nanoparticles as the metal core component with Eu:Lu₂O₃ as the phosphor shell component. The core-shell design contains an optically transparent SiO₂ intermediate layer that separates the metallic nanoparticle core and the phosphor shell. The thickness of the SiO₂ layer is in the nanometer range and can be tuned, so as to provide for different interactions between the core and shell. To demonstrate the versatility of the design, spherical silver nanoparticles or wavelength-tunable plasmonic silver nanoplates are used as the core component. In addition, a nanocomposite phosphor was fabricated by embedding the core-shell nanoparticles into a transparent polymeric matrix. The core-shell metal-phosphor design presented here serves as framework for the fabrication of inexpensive nanocomposite scintillator.     

纳米氧化铁红颜料的室温固相合成

以FeSO4.7H2O和NH4HCO3为原料,在少量表面活性剂聚乙二醇(PEG)-400的存在下,先在室温下充分混合研磨进行固相反应,然后用水洗去反应混合物中的可溶性无机盐并烘干,即得氧化铁红的前驱体,前驱体再经热解即得氧化铁红产品。采用TG/DTA、IR、XRD和SEM对前驱体及其热解产品进行了表征。结果表明,前驱体的热解是经一步完成的,烘干后的前驱体碳酸亚铁已基本上分解成了氧化物;在550℃下热解前驱体2 h,得到了纯晶相的三方Fe2O3,其粒度约为43 nm。     

Corrosion mechanisms of Al2O3/MgAl2O4 by V2O5, NiO, Fe2O3 and vanadium slag

The effects of V₂O₅, NiO, Fe₂O₃ and vanadium slag on the corrosion of Al₂O₃ and MgAl₂O₄ have been investigated. The specimens of Al₂O₃ and MgAl₂O₄ with the respective oxides above mentioned were heated at 10 °C/min from room temperature up to three different temperatures: 1400, 1450 and 1500 °C. The corrosion mechanisms of each system were followed by XRD and SEM analyses. The results obtained showed that Al₂O₃ was less affected by the studied oxides than MgAl₂O₄. Alumina was only attacked by NiO forming NiAl₂O₄ spinel, while the MgAl₂O₄ spinel was attacked by V₂O₅ forming MgV₂O₆. It was also observed that Fe₂O₃ and Mg, Ni, V and Fe present in the vanadium slag diffused into Al₂O₃. On the other hand, the Fe₂O₃ and Ca, S, Si, Na, Mg, V and Fe diffused into the MgAl₂O₄ structure. Finally, the results obtained were compared with those predicted by the FactSage software.     

Enhanced photoluminescence property of Dy co-doped BaAl2O4:Eu green phosphors

Eu²⁺-doped BaAl₂O₄ green phosphors were prepared by a conventional solid-state reaction and the effects of Dy³⁺ co-doping on the photoluminescence property were investigated. The phosphors were characterized by X-ray powder diffraction (XRD), fluorescence spectroscopy, field-emission scanning electron microscopy (FESEM) and X-ray photoelectron spectroscopy (XPS). XRD showed that all prepared samples exhibited a hexagonal BaAl₂O₄ phase. Fluorescence spectroscopy showed that the photoluminescence efficiency increased with increasing Eu²⁺ concentration until 3 mol% then decreased at higher concentrations due to concentration quenching effect. Moreover, Dy³⁺ co-doping increased the photoluminescence efficiency of the Eu²⁺-doped BaAl₂O₄ phosphor.     

Nanocrystalline Nd2O3: Preparation,phase evolution,and kinetics of thermal decomposition of precursor

Nd₂O₃ was synthesized by calcining Nd₂(C₂O₄)₃·10H₂O in air. The precursor and its calcined products were characterized by thermogravimetry and differential scanning calorimetry, Fourier transform infrared spectroscopy, X-ray powder diffraction, and scanning electron microscopy. The results showed that high-crystallized Nd₂O₃ with hexagonal structure was obtained when the precursor was calcined at 1223 K in air for 2 h. The crystallite size of Nd₂O₃ synthesized at 1223 K for 2 h was about 48 nm. The thermal decomposition of the precursor in air experienced three steps, which are first, the dehydration of 10 crystal water molecules; then, the decomposition of Nd₂(C₂O₄)₃ into Nd₂O₂CO₃; and last, the decomposition of Nd₂O₂CO₃ into hexagonal Nd₂O₃. Based on the KAS equation, the values of the activation energies associated with the thermal decomposition of Nd₂(C₂O₄)₃?10H₂O were determined.     

Accommodation of impurities in α-Al2O3, α-Cr2O3 and α-Fe2O3

Atomic scale computer simulation was used to predict the mechanisms and energies associated with the accommodation of aliovalent and isovalent dopants in three host oxides with the corundum structure. Here we consider a much more extensive range of dopant ions than has previously been the case. This enables a rigorous comparison of calculated mechanism energetics. From this we predict that divalent ions are charge compensated by oxygen vacancies and tetravalent ions by cation vacancies over the full range of dopant radii. When defect associations are included in the model these conclusions remain valid. At equilibrium, defects resulting from extrinsic dopant solution dominate intrinsic processes, except for the largest dopant cations. Solution reaction energies increase markedly with increasing dopant radius. The behaviour of cluster binding energies is more complex.     

Phase diagram of the Al2O3-HfO2-Y2O3 system

The phase diagram of the Al₂O₃-HfO₂-Y₂O₃ system was first constructed in the temperature range 1200-2800 °C. The phase transformations in the system are completed in eutectic reactions. No ternary compounds or regions of appreciable solid solution were found in the components or binaries in this system. Four new ternary and three new quasibinary eutectics were found. The minimum melting temperature is 1755 °C and it corresponds to the ternary eutectic Al₂O₃ + HfO₂ + Y₃Al₅O₁₂. The solidus surface projection, the schematic of the alloy crystallization path and the vertical sections present the complete phase diagram of the Al₂O₃-HfO₂-Y₂O₃ system.     

Effect of Y2O3 and Er2O3 co-dopants on phase stabilization of bismuth oxide

Bi₂O₃ compositions were prepared to investigate the effect of rare earth metal oxides as co-dopants on phase stability of bismuth oxide. Compositions containing 9-14 mol% of Y₂O₃ and Er₂O₃ were synthesized by solid state reaction. The structural characterization was carried out using X-ray powder diffraction. The XRD results show that the samples containing 12 and 14 mol% total dopants had cubic structure, whereas the samples with lower dopant concentrations were tetragonal. Comparing the lattice parameters of the cubic phases of (Bi₂O₃)_0.88(Y₂O₃)_0.06(Er₂O₃)_0.06 and (Bi₂O₃)_0.86(Y₂O₃)_0.07(Er₂O₃)_0.07 revealed that lattice parameter decreases by increasing the dopant concentration. The XRD pattern and the powder density results indicated the formation of solid solution in the studied systems. After annealing samples with cubic phase at 600 °C for various periods of time, phase transformation to tetragonal and rhombohedral occurs.     

V-doped In2O3 nanofibers for H2S detection at low temperature

Pristine and vanadium-doped In₂O₃ nanofibers were fabricated by electrospinning and their sensing properties to H₂S gas were studied. X-ray diffractometry (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were used to investigate the inner structure and the surface morphology. The H₂S-sensing performances were characterized at different temperatures ranging from 50 to 170 °C. The sensor based on 6 mol% V-doped In₂O₃ nanofibers exhibit the highest response, i.e. 13.9–50 ppm H₂S at the relatively low temperature of 90 °C. In addition, the fast response (15 s) and recovery (18 s) time, and good selectivity were observed.     

The catalytic performance in oxidative coupling of methane and the surface basicity of La2O3, Nd2O3, ZrO2 and Nb2O5

The catalytic performance in oxidative coupling of methane (OCM) of unmodified pure La₂O₃, Nd₂O₃, ZrO₂ and Nb₂O₅ has been investigated under various conditions. The results confirmed that the activity of La₂O₃ and Nd₂O₃ was always much higher than that of the remaining two. The surface basicity/base strength distribution of pure La₂O₃, Nd₂O₃, ZrO₂ and Nb₂O₅ was measured using a test reaction of transformation of 2-butanol and a temperature-programmed desorption of CO₂. Both methods showed that La₂O₃ and Nd₂O₃ had high basicity and contained medium and strong basic sites (lanthanum oxide more and neodymium oxide somewhat less). ZrO₂ had only negligible amount of weak basic sites and Nb₂O₅ was rather acidic. The confrontation of the basicity and catalytic performance indicated that in the case of investigated oxides, the basicity (especially strong basic sites) could be a decisive factor in determination of the catalytic activity in OCM. Only in the case of ZrO₂ it was observed a moderate catalytic performance in spite of negligible basicity. The influence of a gas atmosphere used in the calcination of oxides (flowing oxygen, helium and nitrogen) on their basicity and catalytic activity in OCM had been also investigated. Contrary to earlier observations with MgO, no effect of calcination atmosphere on the catalytic performance of investigated oxides in OCM and on their basicity was observed.     

Selective synthesis of mixed alcohols from syngas over catalyst Fe2O3/Al2O3 in slurry reactor

The Fe₂O₃/Al₂O₃ catalyst was studied to selectively synthesize mixed alcohols from syngas in a continuously stirred slurry reactor with the oxygenated solvent Polyethylene Glycol-400 (PEG-400). The selectivity of mixed alcohols in the products reached as high as 95 wt.% and the C₂₊ alcohols (mainly ethanol) was more than 40 wt.% in the total alcohol products at the reaction conditions of 250 °C, 3.0 MPa, H₂/CO = 2 and space velocity = 360 ml/g_cat h. The hydrogen temperature programmed reduction (H₂-TPR) and X-ray photoelectron spectroscopy (XPS) measurements of the catalyst confirmed that the FeO phase was responsible for the high selectivity to mixed alcohols in the process. And the oxygenated solvent PEG-400 was also necessary for the selective synthesis of mixed alcohols in the reaction system.     

Synthesis and optical characterization of novel Sr3Ga2O6:Eu phosphor

Alkaline earth metal gallets have been identified as an important ceramic material. The crystal chemistry of many of these gallets is well explored; however, very rare studies regarding optical properties of rare earth (RE) ions doped in such gallets, particularly in Sr₃Ga₂O₆ host, have been carried out. The present study reports on synthesis and characterization of novel Sr₃Ga₂O₆:Eu³⁺ phosphors. The phosphors have been synthesized using a conventional solid state reaction method. Crystal structure, morphology and luminescence properties (excitation, emission and CIE coordinate) of these phosphors have been studied as a function of sintering temperature and Eu³⁺ concentration. X-ray diffraction study reveals that the phosphor sintered at low temperature (900 °C) contains an impurity phase which is removed at higher sintering temperatures and results into cubic crystalline phase of Sr₃Ga₂O₆. Particle size of the phosphor increases with an increase in sintering temperature which results to a red shift in the peak position of excitation band lying in a broad range from 250 to 370 nm. Optimum emission intensity is attained for 0.12 mol% concentration of Eu³⁺ ions; above this concentration, a quenching in emission intensity is observed.     

Dynamic corrosion of Al2O3-ZrO2-SiO2 and Cr2O3-containing refractories by molten frits. Part I: Macroscopic analysis

Manufacturing of enamels and frits has undergone dramatic changes since the 1980s. This has required significant efforts in research and development. Typical compositions of frits for ceramic tiles are silica-based with fluxing agents; some of the components are highly corrosive. Improvements in the production of frits would imply the selection of the most adequate refractories as a function of the chemical composition of the considered frit and the fabrication procedure.The refractories currently used in frit furnaces are Al₂O₃-ZrO₂-SiO₂ (AZS) fused cast materials and Cr₂O₃-based materials. In this work, results on dynamic corrosion studies of AZS and Cr₂O₃-based materials by two ZnO-containing frits are described. Experiments have been performed using the “Merry Go Round” test at ≅1500 °C. Macroscopic results are analysed in terms of the remaining volume after the tests, as usually done in the glass industry. The significance and limits of such an approach are discussed.     

Dynamic corrosion of Al2O3-ZrO2-SiO2 and Cr2O3-containing refractories by molten frits. Part II: Microstructural study

In this work results on dynamic corrosion studies of fused cast Al₂O₃-SiO₂-ZrO₂ and isostatically pressed and sintered Cr₂O₃-based refractories by two crystalline (transparent) frits are described. Experiments have been performed using the “Merry Go Round” test at ≅1500 °C.Microstructural and mineralogical analyses of selected areas from the corroded regions of the studied refractories were performed by reflected light optical microscopy and scanning electron microscopy with analysis by X-ray dispersive energy.Significant differences between the corrosion mechanisms acting in the two types of materials were found. In the fused cast Al₂O₃-SiO₂-ZrO₂ specimens corrosion took place by the dissolution of alumina and zirconia in the frit and in the glass formed by the reaction between the frit and the refractory. In the Cr₂O₃-based materials the corrosion process was controlled by the capillar penetration of the molten frit through the open pores. The reaction between the ZnO from the frits and Cr₂O₃ led to the formation of spinel (ZnCr₂O₄), a high-melting point bonding phase that retarded the frit penetration. Results are discussed using the relevant phase equilibrium diagrams.     

Comparison of AlPO4- and Co3(PO4)2-coated LiNi0.8Co0.2O2 cathode materials for Li-ion battery

Electrochemical and thermal properties of Co₃(PO₄)₂- and AlPO₄-coated LiNi_0.8Co_0.2O₂ cathode materials were compared. AlPO₄-coated LiNi_0.8Co_0.2O₂ cathodes exhibited an original specific capacity of 170.8 mAh g⁻¹ and had a capacity retention (89.1% of its initial capacity) between 4.35 and 3.0 V after 60 cycles at 150 mA g⁻¹. Co₃(PO₄)₂-coated LiNi_0.8Co_0.2O₂ cathodes exhibited an original specific capacity of 177.6 mAh g⁻¹ and excellent capacity retention (91.8% of its initial capacity), which was attributed to a lithium-reactive Co₃(PO₄)₂ coating. The Co₃(PO₄)₂ coating material could react with LiOH and Li₂CO₃ impurities during annealing to form an olivine Li_xCoPO₄ phase on the bulk surface, which minimized any side reactions with electrolytes and the dissolution of Ni⁴⁺ ions compared to the AlPO₄-coated cathode. Differential scanning calorimetry results showed Co₃(PO₄)₂-coated LiNi_0.8Co_0.2O₂ cathode material had a much improved onset temperature of the oxygen evolution of about 218 °C, and a much lower amount of exothermic-heat release compared to the AlPO₄-coated sample.