共查询到20条相似文献,搜索用时 15 毫秒
1.
Sepideh ArastehAmir Maghsoudipour Masoud AlizadehAli Nemati 《Ceramics International》2011,37(8):3451-3455
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. 相似文献
2.
Hirotomo Inoue Satoshi Sato Ryoji Takahashi Yusuke Izawa Hironobu Ohno Kazunari Takahashi 《Applied Catalysis A: General》2009,352(1-2):66-73
Vapor-phase catalytic dehydration of 1,4-butanediol was investigated over rare earth oxides supported on ZrO2. In the dehydration of 1,4-butanediol, 3-buten-1-ol was mainly produced, together with tetrahydrofuran (THF) and γ-butyrolactone. The heavy group of rare earth oxides, such as Dy2O3, Ho2O3, Er2O3, Tm2O3, Yb2O3, and Lu2O3, supported on monoclinic ZrO2 showed higher selectivity to 3-buten-1-ol than pure monoclinic ZrO2 and supported light rare earth oxides, such as La2O3 and Pr6O11. Supported Yb2O3 catalysts dispersed on other oxides, such as alumina, silica, and tetragonal ZrO2 catalyze the formation of THF. X-ray diffraction (XRD) measurements reveal that cubic Yb2O3 crystallites dispersed on monoclinic ZrO2 provide active sites in the dehydration of 1,4-butanediol to produce 3-buten-1-ol. 相似文献
3.
《Ceramics International》2016,42(16):18425-18430
Erbium oxide (Er2O3) has been used in a variety of microelectronic, optoelectronic, thermophotovoltaic, and biomedical applications, and especially in nuclear reactor systems. Electrochemical synthesis of rare earth oxides has conventionally been based upon base generation under the application of anodic or cathodic potential and subsequent sintering of as-deposited rare earth hydroxides. In this study, we investigated a direct, room-temperature electrochemical synthesis of Er2O3 onto titanium base metal by applying cathodic potentials. Iminodiacetate (IDA) ligand was added to form Er(IDA)2− complexes with Er3+ in a neutral electrolyte. A cathodic reaction for the direct deposition of Er2O3 from Er(IDA)2− was suggested as the mechanism of Er2O3 synthesis. The formation of cubic Er2O3 phase at all applied potentials was verified by means of X-ray diffractometry and X-ray photoelectron spectroscopy. The relationship between the diffusion characteristics of the reacting ions and the resulting microstructures of Er2O3 deposits was also studied as a function of applied potential. 相似文献
4.
Electrochemical noise measurements have been performed on various electrode materials during oxygen evolution reaction. Fluctuations of both electrode potential and electrolyte resistance, recorded under galvanostatic polarization, have been analysed in order to separate ohmic and non-ohmic contributions. The anode materials compared in this study were PbO2 and composite oxides consisting of a PbO2 matrix and variable amounts of catalytic dispersed phases (Co3O4, RuO2 and hydrous Co oxides); the composite oxide layers were generally obtained by anodic codeposition of fine particles (typically 0.1-1 μm in size) with a PbO2 matrix electrochemically grown by Pb2+ oxidation. The power spectral density (PSD) of the electrolyte resistance fluctuations is very similar for PbO2 and composite electrodes, suggesting a similar gas evolution profile. On the contrary, the potential PSD is markedly different for PbO2 and composites containing catalytic particles. In the latter case, the potential fluctuations are entirely due to ohmic effects, while non-ohmic components are clearly dominant in the case of O2 evolution on pure PbO2, probably because of the much higher activation overpotential. Furthermore, on PbO2 electrodes a plateau was obtained at intermediate frequencies (0.1-10 Hz), which was tentatively explained by bubble coalescence phenomena. 相似文献
5.
Electrochemical experiments on titanium electrodes were coupled with electron backscattered diffraction (EBSD) experiments. The substrates were thermally treated and electropolished in order to have flat and reproducible polycrystalline surfaces, leading to EBSD orientation mapping. Afterwards, the samples were anodised by a galvanostatic procedure. It was shown that electrodeposition of PbO2 from a 0.5 M Pb(NO3)2+2.5 M HNO3 solution occurs selectively on the near {0 0 0 1} grains, whereas lead electrodeposition occurs on all the grains, whatever their orientation. These results are discussed, taking into account the fact that on {0 0 0 1} grains, the oxide layers are thinner than on other grains. It was concluded that electrodeposition is observed locally on Ti/TiO2 electrodes for (i) cathodic electrodeposition of metals at low overvoltage; (ii) anodic electrodeposition of PbO2, in potentiostatic or galvanostatic conditions. 相似文献
6.
Structure and properties of PbO2-CeO2 anodes on stainless steel 总被引:1,自引:0,他引:1
Yuehai Song 《Electrochimica acta》2007,52(24):7022-7027
The lack of ideal anodes with excellent activity and stability is one of the critical problems in electrochemical oxidation for organic wastewater treatment. It is reported in this paper that the PbO2-CeO2 films electrodeposited on stainless steel were used as catalytic electrodes for treating antibiotic wastewater. The PbO2-CeO2 films on stainless steel were proved to be high stability, good activity and relatively low cost. Because of these properties, the films are more attractive than any other electrocatalytic materials among conventional dimensionally stable anodes (DSA). Experimental results showed that the PbO2-CeO2 electrode has a service life of 1100 h in 3 M H2SO4 solution under a current density of 1 A cm−2 at 35 °C, compared with 300 h for PbO2 under the same conditions. The X-ray diffraction (XRD) patterns and SEM images indicated that the PbO2-CeO2 films on stainless steel have a dense structure and the preferred crystalline orientation on the substrate surface was changed. Color and chemical oxygen demand (COD) of antibiotics wastewater were studied by electrolysis by using these electrodes as anode and stainless steel as cathode. The results indicated that the anodes have excellent activity in antibiotic wastewater treatment. The PbO2-CeO2 electrodes have high chemical stability which contributed by the superstable nature of the electrode, dense microstructure, good conductivity and the improvement of bonding with the stainless steel during electrodeposition. 相似文献
7.
Two oxides, Er2O3 and Nb2O3, are used to stabilize delta-phase Bi2O3 used as electrolyte of solid oxide fuel cell. Optimization of dopant ratio and total doping concentration (TDC) is determined by X-ray diffraction, and successfully reduce the TDC (Er + Nb) to 10-15 mol.%. Conductivities of different compositions are measured by two-probe method. The results show that highest conductivity appears at the minimum doping concentrations. Phase stability of ENSB samples with Er/Nb ratio of 2/1 and TDC of 10-20 mol.% at 650 °C up to 300 h is analyzed showing two newly formed (alpha- and gamma-) phases in the samples. Degradation of conductivity at 650 °C is studied in detail by DTA and TEM. The abnormity of lattice contraction of delta-phase is discussed. 相似文献
8.
Qing Yi Shengming Zhou Hao TengHui Lin Xiaorui Hou Tingting Jia 《Journal of the European Ceramic Society》2012,32(2):381-388
The paper reports the use of La2O3 and ZrO2 co-doping as a composite sintering aid for the fabrication of Tm:Y2O3 transparent ceramics. Two groups of experiments were conducted for investigating the influences of composite sintering aids on the microstructures and the optical properties of Tm:Y2O3 transparent ceramics in contrast to single La3+ and single Zr4+ doped Tm:Y2O3. Samples with composite sintering aids could realize fine microstructures and good optical properties at relatively low sintering temperatures. Grain sizes around 10 μm and transmittances close to theoretical value at wavelength of 2 μm were achieved for the 9 at.% La3+, 3 at.% Zr4+ co-doped samples sintered at 1500-1600 °C. The influences of the composite sintering aids on the emission intensities and the phonon energies of Tm:Y2O3 ceramics were also investigated. 相似文献
9.
Electro-oxidation tests with different electrolytes (Na2SO4, NaCl, H2SO4) and anode types (Pt, Ti lined with Ir and Ta oxides, PbO2, activated carbon) were performed on aqueous solutions containing phenol to assess the mechanism and nature of electrode deactivation phenomena. For the Pt electrode, the nature of the electro-deposited organic species was investigated by ATR-FTIR and FESEM-EDS analyses, which showed adsorption of intermediate oxidation products (e.g. benzoquinone, hydroquinone) is likely responsible for the early deactivation stages. Conversely, in the longer term, formation of polymeric films is promoted. Potentiostatic tests showed that anode regeneration can be achieved by anodic polarisation above 1.1 V (vs Hg/Hg2SO4). This reactivation was found to be easier in the presence of significant amounts of chloride ions. Conversely, the deactivated state is maintained for the Ti/IrO2/Ta2O5 electrode even though anodic polarisation at high positive potentials is applied. Cyclic voltammetric curves on PbO2 electrodes did not provide satisfactory results as the intensity of the lead-dioxide reduction peak was so high that peaks for phenol oxidation were hardly detectable. Finally, the activated carbon based electrode was found to be promising as it enables simultaneous adsorption of the organic pollutant and oxidation of the pollutant itself to constitute a sort of self-regenerating adsorber unit. 相似文献
10.
Ca0.28Ba0.72Nb2O6 (CBN28) ceramics with addition of CeO2 and La2O3, were prepared by the conventional ceramic fabrication technique. XRD results showed that the single tungsten bronze structure of CBN28 was not changed by adding CeO2 or La2O3. SEM results indicated that both CeO2 and La2O3 dopants were effective in inhibiting the grain growth and suppressing the anisotropic growth behavior in tungsten bronze structure. It was also found that both two kinds of dopants had remarkable effects on the dielectric and ferroelectric properties of CBN28 ceramics. Compared with CBN28 ceramics, the dielectric constant around room temperature εr, dielectric loss tan δ, the degree of diffuseness γ and coercive field Ec were all ameliorated when doping proper amount of CeO2 or La2O3. The comprehensive electric performance was obtained in CBN28–0.3 wt% CeO2 and CBN28–0.4 wt% La2O3 ceramics. Besides, the underlying mechanism for variations of the electrical properties due to different dopants was explained in this work. 相似文献
11.
Sang Mun Jeong Ho-Sup Shin Sun-Seok Hong Jin-Mok Hur Jae Bum Do Han Soo Lee 《Electrochimica acta》2010,55(5):1749-1755
The reduction path of the U3O8 powder vol-oxidized at 1200 °C has been determined by a series of electrochemical experiments in a 1 wt.% Li2O/LiCl molten salt. Various reaction intermediates are observed by during electrolysis of U3O8. The formation of the metallic uranium is caused from two different reduction paths, a direct reduction of uranium oxide and an electro-lithiothermic reduction. As the uranium oxide is converted to the metallic uranium, the lithium metal is more actively formed in the cathode basket. The reducibility of the rare earth oxides with the U3O8 powder has been tested by constant voltage electrolysis. The results suggest the advanced vol-oxidation could lead to the enhancement in the reducibility of the rare earth fission products. 相似文献
12.
George Ting-Kuo Fey P. Muralidharan Cheng-Zhang Lu Yung-Da Cho 《Electrochimica acta》2006,51(23):4850-4858
An enhanced electrochemical performance LiCoO2 cathode was synthesized by coating with various wt.% of La2O3 to the LiCoO2 particle surfaces by a polymeric method, followed by calcination at 923 K for 4 h in air. The surface-coated materials were characterized by XRD, TGA, SEM, TEM, BET and XPS/ESCA techniques. XRD patterns of La2O3-coated LiCoO2 revealed that the coating did not affect the crystal structure, α-NaFeO2, of the cathode material compared to pristine LiCoO2. TEM images showed a compact coating layer on the surface of the core material that had an average thickness of about ∼15 nm. XPS data illustrated that the presence of two different environmental O 1s ions corresponds to the surface-coated La2O3 and core material. The electrochemical performance of the coated materials by galvanostatic cycling studies suggest that 2.0 wt.% coated La2O3 on LiCoO2 improved cycle stability (284 cycles) by a factor of ∼7 times over the pristine LiCoO2 cathode material and also demonstrated excellent cell cycle stability when charged at high voltages (4.4, 4.5 and 4.6 V). Impedance spectroscopy demonstrated that the enhanced performance of the coated materials is attributed to slower impedance growth during the charge-discharge processes. The DSC curve revealed that the exothermic peak corresponding to the release of oxygen at ∼464 K was significantly smaller for the La2O3-coated cathode material and recognized its high thermal stability. 相似文献
13.
《Journal of the European Ceramic Society》2014,34(12):2865-2874
Silicon carbide (SiC) ceramics have been fabricated by pressureless liquid phase sintering with Al2O3 and rare-earth oxides (Lu2O3, Er2O3 and CeO2) as sintering additives. The effect was investigated of the different types of rare earth oxides on the mechanical property, thermal conductivity and microstructure of pressureless liquid phase sintered SiC ceramics. The room temperature mechanical properties of the ceramics were affected by the type of rare earth oxides. The high temperature performances of the ceramics were influenced by the triple junction grain boundary phases. With well crystallized triple junction grain boundary phase, the SiC ceramic with Al2O3–Lu2O3 as sintering additive showed good high temperature (1300 °C) performance. With clean SiC grain boundary, the SiC ceramic with Al2O3–CeO2 as sintering additive showed good room temperature thermal conductivity. By using appropriate rare earth oxide, targeted tailoring of the demanding properties of pressureless liquid phase sintered SiC ceramics can be achieved. 相似文献
14.
《Ceramics International》2017,43(3):3356-3362
Mullite/hBN composites were fabricated with different rare earth oxides additives (ReO: Er2O3, CeO2, La2O3, Lu2O3) by pressureless sintering at 1600 °C for 4 h. The impacts of ReO on the phase composition, microstructure, mechanical, dielectric and tribological properties of the composites were investigated. XRD results showed that all the ReO additives were beneficial to the formation of mullite phase. With the decrease in the ionic radius of the ReO, the mullite grains of the composite were refined while their mechanical properties were increased. The sample sintered with Lu2O3 showed the smallest grain size and the most excellent mechanical properties, e.g., its relative density, flexure strength, fracture toughness and hardness reached 93.7%, 222 MPa, 3.2 MPa m1/2 and 6.02 GPa, respectively. Due to the different porosity and phase composition of the composites, the sample sintered with La2O3 had the lowest dielectric constant while the sample sintered with Er2O3 exhibited the lowest dielectric loss. Attributing to the highest hardness and fracture toughness, the sample sintered with Lu2O3 showed the best tribological properties. 相似文献
15.
Nano-size Ca1−χLa2χ/3Cu3Ti4O12 (χ = 0.00, 0.05, 0.10, 0.15 and 0.20) precursor powders were prepared via the sol–gel method and the citrate auto-ignition route and then processed into micro-crystal Ca1−χLa2χ/3Cu3Ti4O12 ceramics under heat treatment. Characterization of the as-obtained ceramics with XRD and SEM showed an average grain sizes of ∼1–2 μm, indicating La3+ amount to have little impact on grain size. The room-temperature dielectric constant of the Ca1−χLa2χ/3Cu3Ti4O12 ceramics sintered at 1000 °C was of the order of 103–104 despite the variation of χ values. Compared with CaCu3Ti4O12, La3+-doped CaCu3Ti4O12 showed a flatter dielectric constant curve related to frequency. It was found that the loss tangent of the Ca1−χLa2χ/3Cu3Ti4O12 ceramics was less than 0.20 in ∼600–105 Hz region, which rapidly decreased to a minimum value of 0.03 by La3+doping with χ = 0.05. Our measurement of the ceramics conductivities (σ) also indicated that the appropriate introduction of La3+ into CaCu3Ti4O12 would distinctly result in its dielectric properties. 相似文献
16.
Shaobin Wang G
Q Lu 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》2000,75(7):589-595
Catalytic reforming of methane with carbon dioxide was studied in a fixed‐bed reactor using unpromoted and promoted Ni/γ‐Al2O3 catalysts. The effects of promoters, such as alkali metal oxide (Na2O), alkaline‐earth metal oxides (MgO, CaO) and rare‐earth metal oxides (La2O3, CeO2), on the catalytic activity and stability in terms of coking resistance and coke reactivity were systematically examined. CaO‐, La2O3‐ and CeO2‐promoted Ni/γ‐Al2O3 catalysts exhibited higher stability whereas MgO‐ and Na2O‐promoted catalysts demonstrated lower activity and significant deactivation. Metal‐oxide promoters (Na2O, MgO, La2O3, and CeO2) suppressed the carbon deposition, primarily due to the enhanced basicities of the supports and highly reactive carbon species formed during the reaction. In contrast, CaO increased the carbon deposition; however, it promoted the carbon reactivity. © 2000 Society of Chemical Industry 相似文献
17.
Fabrication and Upconversion Luminescent Properties of Er3+‐Doped and Er3+/Yb3+ Codoped La2O2CN2 Nanofibers
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Xiaomin Guo Wensheng Yu Xiangting Dong Jinxian Wang Qianli Ma Guixia Liu Ming Yang 《Journal of the American Ceramic Society》2015,98(4):1215-1222
La2O2CN2:Er3+and La2O2CN2:Er3+/Yb3+ upconversion (UC) luminescence nanofibers were successfully fabricated via cyanamidation of the respective relevant La2O3:Er3+ and La2O3:Er3+/Yb3+ nanofibers which were obtained by calcining the electrospun composite nanofibers. The morphologies, structures, and properties of the nanofibers are investigated. The mean diameters of La2O2CN2:Er3+ and La2O2CN2:Er3+/Yb3+ nanofibers are 179.46 ± 12.58 nm and 198.85 ± 17.07 nm, respectively. It is found that intense green and weak red emissions around 524, 542, and 658 nm corresponding to the 2H11/2→4I15/2, 4S3/2→4I15/2, and 4F9/2→4Il5/2 energy levels transitions of Er3+ ions are observed for La2O2CN2:Er3+ and La2O2CN2:Er3+/Yb3+ nanofibers under the excitation of a 980‐nm diode laser. Moreover, the emitting colors of La2O2CN2:Er3+ and La2O2CN2:Er3+/Yb3+ nanofibers are all located in the green region. The upconversion luminescent mechanism and formation mechanism of the nanofibers are also proposed. 相似文献
18.
Hot corrosion behaviors of gas tunnel type plasma sprayed La2Zr2O7 thermal barrier coatings 总被引:1,自引:0,他引:1
Subramaniam YugeswaranAkira Kobayashi P.V. Ananthapadmanabhan 《Journal of the European Ceramic Society》2012,32(4):823-834
Gas tunnel type plasma sprayed free-standing La2Zr2O7 coating specimens with a thickness of 300-400 μm were prepared under optimized operating conditions and were subjected to hot corrosion test in the presence of corrosive impurities such as V2O5, Na2SO4, and Na2SO4 + V2O5 mixtures (60:40 wt%) at two different temperatures for duration of 5 h, i.e. 1000 and 1350 K for V2O5 and Na2SO4 + V2O5 mixtures, 1200 and 1350 K for Na2SO4. For temperatures at 1350 K, the reaction mechanism of V2O5 and the mixture of Na2SO4 + V2O5 are similar and LaVO4 is formed as the corrosive product, which leads to massive phase transformation from pyrochlore to tetragonal and monoclinic phases. Microstructural observations from planar reaction zone (PRZ) and melt infiltrated reaction zone (MIRZ) reveals that the present La2Zr2O7 coating exhibits good hot corrosion resistance in V2O5 environment and moderate for the mixture of Na2SO4 + V2O5, but is worst in Na2SO4 environment. 相似文献
19.
A series of PbO2 coatings on planar carbon substrates has been prepared by anodic deposition in aqueous methanesulfonic acid (MSA) under galvanostatic conditions. The effect of four experimental parameters, i.e., lead(II) methanesulfonate and MSA concentrations, current density, and temperature was analysed. Surface characterisation by XRD, SEM-EDX, and AFM has provided information about the structural (phase distribution, degree of crystallinity, and crystallite size), morphological (crystallite shape, degree of porosity), and tribological (surface roughness) properties of the PbO2 coatings, respectively. Electrochemical studies based on linear and cyclic voltammetry allowed comparison between electrodes prepared in MSA and classical electrodes prepared in HNO3. Pure α- or β-PbO2 and α + β mixtures were obtained depending on the conditions, being temperature the most influential deposition parameter. A temperature rise caused a transition to pure β-PbO2 and led to a higher degree of crystallinity with a progressive increase of crystallite size, always within the range of 10-30 nm, as well as to a remarkably higher roughness, from smooth (35-50 nm rms) to rough (up to 500 nm rms) surfaces. Low MSA and high lead(II) methanesulfonate concentrations were required to avoid the formation of excessively porous powdery coatings, as well as cracks, pits, and holes. Most of the coatings obtained in MSA were uniform, nanocrystalline, and moderately rough. Their electrocatalytic behaviour was comparable to that of the electrodes prepared in HNO3, showing an O2-overpotential of +0.66 V in 0.05 M Na2SO4 at pH 3.0. Such coatings can then be envisaged as suitable anodes for energy and water treatment applications. Prolonged electrolysis has shown their stability against leaching. 相似文献
20.
The electrochemical oxidation of chloranilic acid (CAA) has been studied in acidic media at Pb/PbO2, boron-doped diamond (Si/BDD) and Ti/IrO2 electrodes by bulk electrolysis experiments under galvanostatic control. The obtained results have clearly shown that the electrode material is an important parameter for the optimization of such processes, deciding of their mechanism and of the oxidation products. It has been observed that the oxidation of CAA generates several intermediates eventually leading to its complete mineralization. Different current efficiencies were obtained at Pb/PbO2 and BDD, depending on the applied current density in the range from 6.3 to 50 mA cm−2. Also the effect of the temperature on Pb/PbO2 and BDD electrodes was studied.UV spectrometric measurements were carried out at all anodic materials, with applied current density of 25 and 50 mA cm−2. These results showed a faster CAA elimination at the BDD electrode. Finally, a mechanism for the electrochemical oxidation of CAA has been proposed according to the results obtained with the HPLC technique. 相似文献