共查询到20条相似文献,搜索用时 31 毫秒
1.
S. Vandarkuzhali Nibedita Gogoi Suddhasattwa Ghosh B. Prabhakara Reddy K. Nagarajan 《Electrochimica acta》2012
The electrochemical behaviour of lanthanum was studied at inert tungsten electrode and reactive aluminium electrode in LiCl–KCl eutectic melt in the temperature range 698–798 K using transient electrochemical techniques. Reduction of La(III) to La(0) at the tungsten electrode takes place in a single step. The reduction shows quasi-reversible behaviour for polarization rates, 25 ≤ ν ≤ 150 mV s?1 and is predominantly controlled by charge transfer of La(III) ions for scan rates higher than 75 mV s?1. The heterogenous rate constant of the process was estimated from impedance spectroscopy and from the semi-integrals of the cyclic voltammograms. The redox potential of the La(III)/La couple at the Al electrode was observed to be more positive than that at the inert electrode. This potential shift is due to the lowering of the activity of La in the metal phase caused by the formation of the intermetallic compound Al11La3. Thermodynamic properties such as Gibbs energy of formation of Al11La3, excess Gibbs energy and the activity coefficient of La in Al were calculated from the open circuit potential measurement. 相似文献
2.
Mei-Yu Chen Ching Yu Chiu Chia-Ta Chia J.F. Lee J.J. Bian 《Journal of the European Ceramic Society》2010,30(2):335-339
A-site deficient perovskite compounds, La(2?x)/3NaxTiO3 (0.02 ≤ x ≤ 0.5) and Nd(2?x)/3LixTiO3 (0.1 ≤ x ≤ 0.5) microwave ceramics, were investigated by Raman scattering. Nd(2?x)/3LixTiO3 (0.1 ≤ x ≤ 0.5) was also investigated by extended X-ray absorption fine structure (EXAFS) measurement. The Raman shifts of the E (239 cm?1) and A1 (322 cm?1) modes of La(2?x)/3NaxTiO3 were found to decrease with x. However, the E (254 cm?1) and A1 (338 cm?1) of Nd(2?x)/3LixTiO3 were found to blueshift with x, which was caused by Li substitution. The redshift of the A1 (471 cm?1) phonon of Nd(2?x)/3LixTiO3 (0.1 ≤ x ≤ 0.3) indicates that O–Ti–O bonding forces lessen with Li concentration, which is consistent with the EXAFS result that Ti–O bond lengths increase for 0.1 ≤ x ≤ 0.3. For x > 0.3, the EXAFS result shows that Ti–O bond lengths decrease. Moreover, Ti–O bond lengths show strong correlation with the microwave dielectric constants of Nd(2?x)/3LixTiO3. 相似文献
3.
A modular impactor was designed to remove large droplets from aerosols generated by a pneumatic nebulizer, the Six-Jet Atomizer from TSI Inc. (Shoreview, MN), with the aim of generating dry nanoparticles. Three interchangeable nozzle heads were designed to provide droplet cutoff diameters of 0.5, 1, and 2 μm at an air flow rate of 8.3×10?4 m3 s?1 (50 L min?1), which corresponds to all six jets of the nebulizer operated at 25 °C and an air pressure of 241 kPa (35 psi). The collection and output characteristics of the 0.5 μm impactor were evaluated from dry particle size distributions produced by nebulizing an aqueous solution with a NaCl mass fraction of 1% both with and without the impactor present. The impactor characteristic cutoff curve was sharp (impactor geometric standard deviation, GSDimp=1.15–1.19) with a 50% cutoff diameter d50 that ranged from 0.48 μm at 3.0×10?4 m3 s?1 to 0.74 μm at 11.7×10?4 m3 s?1. The rate of dry NaCl particle generation ranged from 0.5 to 5 g s?1 (0.04 to 0.4 g day?1) with mass median diameters MMDp=80–123 nm and geometric standard deviations GSDp=1.6–1.8 (depending on flow rate). Anomalous negative impactor efficiencies were observed at flow rates >8.3×10?4 m3 s?1 for 100 to 400 nm droplets and at all flow rates for droplets smaller than 100 nm. This phenomenon will be investigated further as a way to increase the generation rate of nanoparticles. A step-by-step procedure is presented for the selection of an appropriate impactor design and operating flow rate for a desired maximum aerosol particle size. 相似文献
4.
Ana C.F. Ribeiro Marisa C.F. Barros Ana S.N. Teles Artur J.M. Valente Victor M.M. Lobo Abílio J.F.N. Sobral M.A. Esteso 《Electrochimica acta》2008,54(2):192-196
Experimental values for mutual diffusion coefficients (interdiffusion coefficients) for CaCl2 aqueous solutions at 298.15 K and 310.15 K, not available in the literature, were experimentally determined between 0.005 mol dm?3 and 0.1 mol dm?3. The measurements were performed by using a conductimetric open-ended capillary cell. Values at infinitesimal concentration, D0, were also obtained. These data were analysed using the Onsager–Fuoss and Gordon models. In addition, molar conductance data were measured at 310.15 K for CaCl2 aqueous solutions at the same concentration range and the value at infinitesimal concentration determined. Afterwards, it was split into the ionic limiting values. By replacing them into the Nernst equation, diffusion coefficients at infinitesimal concentration were derived (1.335 × 10?9 m2 s?1 and 1.659 × 10?9 m2 s?1) at both temperatures (298.15 K and 310.15 K, respectively). They agree well with the extrapolated experimental ones (1.312 × 10?9 m2 s?1 and 1.613 × 10?9 m2 s?1). 相似文献
5.
6.
Whilst there are numerous experimental, theoretical and computational studies of Taylor flow in microchannels, the intermittent slug–annular regime has largely been neglected. In this paper time-resolved micro-PIV data are collected and used to study the flow characteristics of a gas–liquid system for flow regimes spanning Taylor to annular flow. The experimental work used a 1.73 mm diameter channel with water and nitrogen as the working fluids, for gas and liquid superficial velocity ranges of 0.35–8.65 m s?1 (40<ReG<1000) and 0.071–0.18 m s?1 (120<ReL<300), respectively. Time-averaged velocity profiles were obtained in the liquid film surrounding the gas bubbles (or the gas core in the pseudo-annular flow regime) and in the liquid slugs (which changed from regular slugs to annular rings as the gas superficial velocity was increased). These data showed that the velocity in the liquid film relaxed back to an equilibrium value following the passage of each liquid slug or annular ring. In contrast rather flat velocity profiles were observed in the liquid slug. Based on a simple representation of the flow structure, average gas holdups were estimated using independent experimental data obtained by the micro-PIV technique and by direct observation of the flow structure. A phenomenological model of intermittent slug flow, based on the representation of the flow structure as a train of slugs and bubbles moving over a liquid film, is used to interpret the experimental data. The modelling work highlights the different behaviour of the limiting cases of slug and annular flow, in terms of the gas–liquid interfacial shear and its influence on the pressure field. 相似文献
7.
A new series of rare earth solid solutions Yb2?xLaxW3O12 were successfully synthesized by the solid-state method. Effects of substituted ion lanthanum on the microstructures and thermal expansion properties in the resulting Yb2?xLaxW3O12 ceramics were investigated by X-ray diffraction (XRD), thermogravimetric analyzer (TGA), field emission scanning electron microscope (FESEM) and thermal mechanical analyzer (TMA). Results indicate that the structural phase transition of the Yb2?xLaxW3O12 changes from orthorhombic to monoclinic with increasing substituted content of lanthanum. The pure phases can form in the composition range of 0 ≤ x < 0.5 with orthorhombic structure and 1.5 < x ≤ 2 with monoclinic one. High lanthanum content leads to a low hygroscopicity of Yb2?xLaxW3O12. Negative thermal coefficients of the Yb2?xLaxW3O12 (0 ≤ x ≤ 2) also vary from ?7.78 × 10?6 K?1 to 2.06 × 10?6 K?1 with increasing substituted content of lanthanum. 相似文献
8.
Samples of SmxCe1 ? xO2 ? δ (0.05 ≤ x ≤ 0.55) were prepared by solid-state reactions and the disorder–order phase transition and grain ionic conductivity were investigated using XRD and ac impedance spectroscopy technique, respectively. For 0 ≤ x ≤ 0.35 the material has a fluorite structure and gradually stabilizes into a C-type rare-earth structure at 0.40 ≤ x ≤ 0.55 because of oxygen-vacancy ordering. The highest grain ionic conductivity observed is 0.0565(37) S cm?1 at 700 °C for Sm0.20Ce0.80O2 ? δ with an associated activation energy (EA) of 0.791(7) eV. The slopes for EA and pre-exponential factor change during phase transition and the conductivity decreases monotonically. Upon comparison of the EA between the SmO1.5–CeO2 and NdO1.5–CeO2 systems, it is seen EA for the SmO1.5–CeO2 system is lower than NdO1.5–CeO2 system at compositions with less than 25% trivalent rare earth element while higher EA is observed for the SmO1.5–CeO2 system at Nd/Sm concentrations above 25%. 相似文献
9.
D. Manara H.F. Jackson C. Perinetti-Casoni K. Boboridis M.J. Welland L. Luzzi P.M. Ossi W.E. Lee 《Journal of the European Ceramic Society》2013,33(7):1349-1361
A fast spectro-pyrometer has been employed for radiance measurements of zirconium carbide samples laser-heated to very high temperature, for compositions 0.7 ≤ C/Zr ≤ 2.61 and in a spectral range 0.550 μm ≤ λ ≤ 0.900 μm. The ZrC–C eutectic temperature has been taken as the radiance reference. The measured normal spectral emissivity (NSE) ?λ of solid zirconium carbide is close to 0.6 at 0.650 μm, in agreement with previous literature. Its high-temperature behaviour, value in the liquid, carbon-content and wavelength dependences in the visible-near infrared range have been determined here for the first time. Liquid zirconium carbide seems to interact with electromagnetic radiation in a more metallic way than the solid. A considerable NSE increase has been observed at increasing carbon content, which can be interpreted on the basis of preferential growth along the “c” plane of the carbon lamellae in the eutectic structure. 相似文献
10.
I.N. Andryushina L.A. Reznichenko I.M. Shmytko L.A. Shilkina K.P. Andryushin Yu.I. Yurasov S.I. Dudkina 《Ceramics International》2013,39(4):3979-3986
Solid solution (SS) ceramics of the PZT (PbTixZr1?xO3, 0≤x≤1.0) system were studied in broad temperature (10≤T≤1000 K) and electric field frequency (10?2≤f≤107 Hz) ranges. Several groups of SS were distinguished, which differ by nonmonotonic behavior of dielectric parameters in the cryogenic temperature range and at Т>300 K, which results both from the defective state and from the polymorphism of SS. A conclusion is made on the expediency of use of the obtained data during the application of materials based on the PZT system in the broad range of external actions. 相似文献
11.
The microstructural and compositional changes that occurred in the solid electrolyte interphase (SEI) formed on graphite electrodes subjected to voltammetry tests (vs. Li/Li+) at different voltage scan rates were investigated. The microstructure of the SEI layer, characterized using high-resolution transmission electron microscopy, consisted of an amorphous structure incorporating crystalline domains of ~5–20 nm in size. Evidence of lithium compounds, namely Li2CO3 and Li2O2, and nano-sized graphite fragments was found within these crystalline domains. The morphology and thickness of the SEI depended on the applied voltage scan rate (dV/dt). The variations in the Li+ diffusion coefficient (DLi+) at the electrode/electrolyte interface during the SEI formation process were measured and two regimes were identified depending on the scan rate; for dV/dt ≥ 3.00 mV s?1, DLi+ was 3.13 × 10?8 cm2 s?1. At lower scan rates where DLi+ was low, 0.57 × 10?8 cm2 s?1, a uniform and continuous SEI layer with a tubular morphology was formed whereas at high dV/dt, the SEI formed had a columnar morphology and did not provide a uniform coverage. 相似文献
12.
Effect of CaO addition on the structure and electrical conductivity of the pyrochlore-type GdSmZr2O7
Polycrystalline GdSm1?xCaxZr2O7?x/2 (0 ≤ x ≤ 0.20) ceramics have been prepared by the solid-state reaction method. The effects of CaO addition on the microstructure and electrical properties of the pyrochlore-type GdSmZr2O7 ceramic were investigated. GdSm1?xCaxZr2O7?x/2 (x ≤ 0.05) ceramics exhibit a pyrochlore-type structure; however, GdSm1?xCaxZr2O7?x/2 (0.10 ≤ x ≤ 0.20) ceramics consist of the pyrochlore-type structure and a small amount of CaZrO3. The total conductivity of GdSm1?xCaxZr2O7?x/2 ceramics follows the Arrhenius relation, and gradually increases with increasing temperature from 723 to 1173 K. GdSm1?xCaxZr2O7?x/2 ceramics are oxide-ion conductors in the oxygen partial pressure range of 1.0 × 10?4–1.0 atm at each test temperature. The highest total conductivity is about 1.20 × 10?2 S cm?1 at 1173 K for the GdSm0.9Ca0.1Zr2O6.95 ceramic. 相似文献
13.
The purpose of this study is to investigate transverse mixing enhancement by superposition of periodic time dependence, in the form of pulsation, on a twisted pipe flow in which the fluid particles trajectories are spatially chaotic. The pulsation makes the secondary flow structure more complex, resulting in stronger velocity gradients that enhance stretching and folding, the main mechanisms of chaotic mixing. Here, the chaotic configuration is six alternating 90° curved pipes. The imposed pulsating conditions range as follows: steady Reynolds numbers 420 ≤ Rest ≤ 1000, velocity component ratios 1 ≤ (β = Umax,osc/Um,st) ≤ 4 and frequency parameters 8.37 < (α = r0(ω/ν)0.5) < 24.5. The secondary velocity fields are measured by particle image velocimetry. The axial vorticity and transverse strain rate at the outlet of each curved pipe in pulsatile flow are compared with those of the steady flows. Analysis of these criteria for mixing assessment shows that β ≥ 2 and α ≤ 15 are favourable pulsating conditions for transverse mixing enhancement. Moreover, in some pulsation conditions, the cell centres visit a zone in the flow cross-section that is much larger than in the steady case, implying that pulsation also contributes to mixing homogenization. 相似文献
14.
Adel Mesbah Céline Cau-dit-Coumes Guillaume Renaudin Fabien Frizon Fabrice Leroux 《Cement and Concrete Research》2012,42(8):1157-1165
Decommissioning of old nuclear reactors may produce waste streams containing chlorides and carbonates, including radioactive 36Cl? and 14CO32?. Their insolubilization by calcium monosulfoaluminate hydrate was investigated. Carbonates were readily depleted from the solution, giving at thermodynamic equilibrium monocarboaluminate, monocarboaluminate + calcite, or calcite only, depending on the initial ratio between the anion and calcium monosulfoaluminate hydrate. Chloride ions reacted more slowly and were precipitated as Kuzel's salt, Kuzel's and Friedel's salts, or Friedel's salt only. Rietveld refinement of X-Ray powder diffraction patterns was successfully used to quantify the phase distributions, which were compared to thermodynamic calculations. Moreover, analysing the lattice parameters of Kuzel's salt as a function of its chloride content showed the occurrence of a restricted solid solution towards the sulfate side with general formula 3CaO·Al2O3·xCaCl2·(1 ? x)CaSO4·(12 ? 2x)·H2O (0.36 ≤ x ≤ 0.50). 相似文献
15.
Sharon S.Y. Leung Yang Liu David F. Fletcher Brian S. Haynes 《Chemical engineering science》2010,65(24):6379-6388
The flow and heat transfer behaviours of gas–liquid, non-boiling, Taylor flow in the vertical upward direction were studied experimentally using a 2.00 mm diameter channel. Nitrogen and water at atmospheric pressure were employed as the working fluids. Three circular T-junction mixers with different diameters were used to generate gas bubbles and liquid slugs of different lengths (1–220d) with controlled mixture velocities (0.11<UTP<0.53 m s?1, 200<ReTP<1100) and homogeneous void fractions (0.03<β<0.90). High-speed visualization of adiabatic flow and heat transfer rate determination for constant wall heat flux conditions were performed. The heat transfer enhancement brought about by Taylor flow is found to be larger with shorter slugs and higher mixture velocities. An enhancement up to 3.2-fold over the liquid-only flow was observed. Based on the experimental data, a correlation between the apparent slug Nusselt number (NuL?) with a Graetz number, where the characteristic length is that of the slug, is proposed. 相似文献
16.
Andrei V. Kovalevsky Eugene N. Naumovich Aleksey A. Yaremchenko Jorge R. Frade 《Journal of the European Ceramic Society》2012,32(12):3255-3263
Iron-based oxides are considered as promising consumable anode materials for high temperature pyroelectrolysis. Phase relationships, redox stability and electrical conductivity of Fe3?xAlxO4 spinels were studied at 300–1773 K and p(O2) from 10?5 to 0.21 atm. Thermogravimetry/XRD analysis revealed metastability of the sintered ceramics at 300–1300 K. Low tolerance against oxidation leads to dimensional changes of ceramics upon thermal cycling. Activation energies of the total conductivity corresponded to the range of 16–26 kJ/mol at 1450–1773 K in Ar atmosphere. At 1573–1773 K and p(O2) ranging from 10?5 to 0.03 atm, the total conductivity of Fe3?xAlxO4 is nearly independent of the oxygen partial pressure. The conductivity values of Fe3?xAlxO4 (0.1 ≤ x ≤ 0.4) at 1773 K and p(O2) ~10?5 to 10?4 atm were found to be only 1.1–1.5 times lower than for Fe3O4, showing high potential of moderate aluminium additions as a strategy for improvement of refractoriness for magnetite without significant deterioration of electronic transport. 相似文献
17.
Diffusional NaCl transport across a microporous ceramic membrane was studied by measurements carried out at a constant feed concentration (Cf = 0.01 equiv./l) but different solutions stirring rates (0 ≤ ν (rpm) ≤ 1000), which allows the determination of both membrane system and true membrane diffusional permeability (Psm and Ps, respectively). Differences between both values are related with the stagnant solution layer on the membrane surface, and its thickness was also determined from these measurements. Moreover, modification in diffusional permeability and polarization layer thickness as a result of membrane static protein fouling due to membrane–protein contact for two different protein solution concentrations (0.5 and 2 g/l of bovine serumalbumin) was also studied and correlated with the system structure. 相似文献
18.
《Journal of the European Ceramic Society》2017,37(7):2673-2678
A series of Zr1-xNd xO2-x/2 (0 ≤ x ≤ 1) ceramics was prepared by solid-state reaction method. The effects of Nd content on the phase evolution were investigated. The chemical durability of resulting waste forms was also examined. The results show that the ceramics with x < 0.1 show monoclinic and cubic zirconia phase, with 0.2 ≤ x < 0.4 exhibit a single cubic phase, with 0.4 ≤ x ≤ 0.6 exhibit a single pyrochlore phase, with 0.6 < x < 0.8 exhibit a single cubic phase and remain cubic phases and hexagonal Nd2O3 when 0.8 ≤ x ≤ 1. The unit cell parameters of the Nd-doped zirconia samples increase as the Nd content increases. Moreover, the normalized element release rates of Nd element in Nd-doped zirconia ceramics firstly decrease with leaching time and almost no change after 21 days (∼0−6 g m−2 d−1), demonstrating its good chemical durability. 相似文献
19.
Four novel Cr(III) complexes, Bis(ethylenediamine-κ2N,N′)(R-SA-κ2O,O′)chromium(III) chloride (H2SA = salicylic acid, R = 5-F, 5-Cl, 5-Br, 4-CH3 ethylenediamine = en) have been synthesized and three of them are determined by X-ray crystallography. The competition reaction with EDTA and apoovotransferrin (apoOTf) was monitored by UV–Visible (UV–vis) and fluorescence spectra at 37 °C. The reaction with EDTA is only a simple competitive process and no specific selectivity was observed (kEDTA/F410 = 4.07 × 10?3–4.37 × 10?3 M?1 s? 1). While for the reaction with apoOTf, an instable intermediate species (R-SA)–Cr(III)–OTf forms (kOTf/F336 = 1.70 × 10? 1–2.08 × 10?1 M?1 s? 1), where R-SA2? act as the role of synergistic anion. The intermediate is instable and the R-SA2? ligand will then be released with the rate constants of 1.17 × 10? 1 (5-F-SA2?) ≈ 1.01 × 10? 1 (4-CH3-SA2?) > 3.19 × 10? 2 (5-Cl-SA2?) > 3.25 × 10? 3 (5-Br-SA2?) M?1 s? 1. The substitutive groups R on SA have positive influence on charge density of O donor atom, which directly affect the stability of the (R-SA)–Cr(III)–OTf intermediate. 相似文献
20.
Single-walled carbon nanotube (SWCNT)/silicone rubber composites that can be used in fabricating compliant electrodes are prepared by spraying a mixed solution of ionic-liquid-based SWCNT gel and silicone rubber onto an elastic substrate. Subsequently, the composites are exposed to nitric acid vapor. Scanning electron microscopy and atomic force microscopy images of the composites show that the SWCNTs are finely dispersed in the polymer matrix due to the addition of the ionic liquid. Doping of the SWCNTs by nitric acid can significantly lower the sheet resistance (Rs) of the composites; samples with 4 wt% of SWCNT content exhibit the lowest Rs value (50 Ω sq?1). This sheet resistance corresponds to a conductivity value of 63 S cm?1. In addition, the composites retain a high conductivity after several tensile strains are applied. Stretching the composite sample to 300% of the original length increased the Rs value to 320 Ω sq?1 (19 S cm?1). Even after 20th stretch/release/stretch cycle, the conductivity remains constant at a value of 18 S cm?1. These results provide a scalable route for preparing highly stretchable and conductive SWCNT composites with relatively low SWCNT concentrations. 相似文献