Space Charge Layers in Polycrystalline Cerium Oxide

2002 ◽  
Vol 756 ◽  
Author(s):  
Andreas Tschöpe
Keyword(s):  
Electrical Conductivity ◽  
Space Charge ◽  
Cerium Oxide ◽  
Oxygen Deficiency ◽  
Electronic Conductivity ◽  
Electrical Potential ◽  
Theoretical Models ◽  
Excess Charge ◽  
Two Phase ◽  
Space Charge Model

ABSTRACTThe effect of space charge layers in polycrystalline cerium oxide was analyzed by comparing experimental results of grain size-dependent electrical conductivity with theoretical models. Modeling included the calculation of space charge segregation of acceptor ions and of the effective electrical conductivity of polycrystalline cerium oxide in both the macroscopic and mesoscopic range of grain sizes. It is shown that an L-3 power law for the electronic conductivity in the nm-regime is characteristic for the equilibrium space charge model and different from the scaling behavior of alternative models. The origin of space charge potential was investigated by numerical calculation of the electrical potential in a two-phase model. It was found, that a positive excess charge at grain boundaries of cerium oxide is caused by an enhanced oxygen deficiency at the grain boundary core. The influence of acceptor ion doping in the dilute limit and of non-equilibrium distribution of acceptor ions on electrical conductivity was also studied.

Numerical analysis of space charge layers and electrical conductivity in mesoscopic cerium oxide crystals

2004 ◽  
Vol 95 (3) ◽  
pp. 1203-1210 ◽  
Author(s):  
Andreas Tschöpe ◽  
Christof Bäuerle ◽  
Rainer Birringer
Keyword(s):  
Electrical Conductivity ◽  
Numerical Analysis ◽  
Space Charge ◽  
Cerium Oxide ◽  
Oxide Crystals

Electrical Conductivity in Praseodymium-Cerium Oxide

2002 ◽  
Vol 756 ◽  
Author(s):  
Todd S. Stefanik ◽  
Harry L. Tuller
Keyword(s):  
Electrical Conductivity ◽  
Ionic Conductivity ◽  
Cerium Oxide ◽  
Electronic Conductivity ◽  
Impurity Band ◽  
Defect Model ◽  
Valence States ◽  
Partial Pressures ◽  
Wide Range ◽  
Low Levels

ABSTRACTThe electrical conductivity of PrxCe1-xO2-δ (PCO) for 0 ≤ × ≤ 0.20 was examined over a wide range of temperatures and oxygen partial pressures. A defect model based on multiple Pr valence states was found to be qualitatively consistent with the observed data. A unique pO2-dependent ionic conductivity is observed at high pO2 values in compositions containing low levels of Pr (0 ≤ × ≤ 0.01). In compositions containing higher amounts of Pr (0.05 ≤ × ≤ 0.20), formation of a Pr induced impurity band results in a significant electronic conductivity at high pO2 values.

Revisiting the passivation of stainless steels and other passive CRAs

2018 ◽  
Vol 106 (1) ◽  
pp. 107 ◽  
Author(s):  
Jean- Louis Crolet
Keyword(s):  
Electrical Conductivity ◽  
Metal Ions ◽  
Base Metal ◽  
Stainless Steels ◽  
Electronic Conductivity ◽  
Transport Processes ◽  
General Knowledge ◽  
Inorganic Polymers ◽  
Faraday Cage

All that was said so far about passivity and passivation was indeed based on electrochemical prejudgments, and all based on unverified postulates. However, due the authors’ fame and for lack of anything better, the great many contradictions were carefully ignored. However, when resuming from raw experimental facts and the present general knowledge, it now appears that passivation always begins by the precipitation of a metallic hydroxide gel. Therefore, all the protectiveness mechanisms already known for porous corrosion layers apply, so that this outstanding protectiveness is indeed governed by the chemistry of transport processes throughout the entrapped water. For Al type passivation, the base metal ions only have deep and complete electronic shells, which precludes any electronic conductivity. Then protectiveness can only arise from gel thickening and densification. For Fe type passivation, an incomplete shell of superficial 3d electrons allows an early metallic or semimetallic conductivity in the gel skeleton, at the onset of the very first perfectly ordered inorganic polymers (- MII-O-MIII-O-)n. Then all depends on the acquisition, maintenance or loss of a sufficient electrical conductivity in this Faraday cage. But for both types of passive layers, all the known features can be explained by the chemistry of transport processes, with neither exception nor contradiction.

scholarly journals Transport Properties of Natural and Artificial Smart Fabrics Impregnated by Graphite Nanomaterial Stacks

Nanomaterials ◽  
2021 ◽  
Vol 11 (4) ◽  
pp. 1018
Author(s):  
Carola Esposito Corcione ◽  
Francesca Ferrari ◽  
Raffaella Striani ◽  
Antonio Greco
Keyword(s):  
Electrical Conductivity ◽  
Transport Properties ◽  
Low Cost ◽  
Empirical Relationship ◽  
Theoretical Models ◽  
Expandable Graphite ◽  
Easy Method ◽  
Textile Materials ◽  
Fabric Materials ◽  
The Impact

In this work, we studied the transport properties (thermal and electrical conductivity) of smart fabric materials treated with graphite nanomaterial stacks–acetone suspensions. An innovative and easy method to produce graphite nanomaterial stacks–acetone-based formulations, starting from a low-cost expandable graphite, is proposed. An original, economical, fast, and easy method to increase the thermal and electrical conductivity of textile materials was also employed for the first time. The proposed method allows the impregnation of smart fabric materials, avoiding pre-coating of the fibers, thus reducing costs and processing time, while obtaining a great increase in the transport properties. Two kinds of textiles, cotton and Lycra®, were selected as they represent the most used natural and artificial fabrics, respectively. The impact of the dimensions of the produced graphite nanomaterial stacks–acetone-based suspensions on both the uniformity of the treatment and the transport properties of the selected textile materials was accurately evaluated using several experimental techniques. An empirical relationship between the two transport properties was also successfully identified. Finally, several theoretical models were applied to predict the transport properties of the developed smart fabric materials, evidencing a good agreement with the experimental data.

Electrical Properties of Y0.06Sr0.94Ti0.6Fe0.4O3-δ-YSZ Composites as Electrode Materials

2016 ◽  
Vol 697 ◽  
pp. 327-330 ◽  
Author(s):  
Ke Shan ◽  
Xing Min Guo ◽  
Feng Rui Zhai ◽  
Zhong Zhou Yi
Keyword(s):  
Electrical Conductivity ◽  
Electrode Materials ◽  
Electronic Conductivity ◽  
Ionic Conductivities ◽  
Conductivity Measurement ◽  
Transference Numbers ◽  
Secondary Phases ◽  
Electrical Conductivity Measurement ◽  
Total Electrical Conductivity ◽  
Phase Compatibility

Y0.06Sr0.94Ti0.6Fe0.4O3-δ-YSZ composites were prepared by mixing Y, Fe co-doped SrTiO3 (Y0.06Sr0.94Ti0.6Fe0.4O3-δ known as YSTF) and 8 mol% Y2O3 stabilized ZrO2 (YSZ) in different weight fractions. The phase stability, phase compatibility, microstructure and mixed ionic-electronic conductivity of composites were investigated. Phase analysis by XRD showed no clearly detectable secondary phases. The electrical conductivity measurement on the YSTF-YSZ composites showed a drastic decrease in total electrical and ionic conductivities when more than 10 wt% of YSZ was used in the composites. The total electrical conductivity was 0.102 S/cm for Y0.06Sr0.94Ti0.6Fe0.4O3-δ and 0.043 S/cm for YSTF-20YSZ at 700 oC, respectively. The value at 700 oC is approximately 2.4 times higher than that of YSTF-20YSZ. The ionic conductivity of Y0.06Sr0.94Ti0.8Fe0.2O3-δ varies from 0.015S/cm at 700 oC to 0.02 S/cm at 800 oC, respectively. The value at 800°C is approximately 12.5 times higher than YSTF-20YSZ. The ion transference numbers of YSTF-YSZ composites vary from 0.14 to 0.28 at 800 °C.

An Investigation of the Distribution of Electric Potential and Space Charge in a Silicon Nanowire

2014 ◽  
Vol 69 (10-11) ◽  
pp. 597-605 ◽  
Author(s):  
A. Wesam Al-Mufti ◽  
Uda Hashim ◽  
Md. Mijanur Rahman ◽  
Tijjani Adam
Keyword(s):  
Finite Element Method ◽  
Space Charge ◽  
Electric Potential ◽  
Silicon Nanowire ◽  
Electrical Potential ◽  
Comsol Multiphysics ◽  
The Finite Element Method ◽  
Simulation Experiments ◽  
Different Dimensions

AbstractThe distribution of electric potential and space charge in a silicon nanowire has been investigated. First, a model of the nanowire is generated taking into consideration the geometry and physics of the nanowire. The physics of the nanowire was modelled by a set of partial differential equations (PDEs) which were solved using the finite element method (FEM). Comprehensive simulation experiments were performed on the model in order to compute the distribution of potential and space charge. We also determined, through simulation, how the characteristic of the nanowire is affected by its dimensions. The characterization of the resulting nanowire, calculated by COMSOL Multiphysics, shows different dimensions and their effect on space charge and electrical potential

scholarly journals Experimental Investigation of Droplet Injections in the Vicinity of the Critical Point: A comparison of different model approaches

2017 ◽  
Author(s):  
Christoph Steinhausen ◽  
Grazia Lamanna ◽  
Bernhard Weigand ◽  
Rolf Stierle ◽  
Joachim Groß ◽  
...  
Keyword(s):  
Experimental Investigation ◽  
Raman Scattering ◽  
High Pressures ◽  
Region Of Interest ◽  
Theoretical Models ◽  
Nitrogen Atmosphere ◽  
Material Surface ◽  
Atmospheric Conditions ◽  
Mixing Processes ◽  
Two Phase

The disintegration process of liquid fuel within combustion chambers is one of the most important parameters forefficient and stable combustion. Especially for high pressures exceeding the critical value of the injected fluids the mixing processes are not fully understood yet. Recently, different theoretical macroscopic models have been introduced to understand breakdown of the classical two phase regime and predict the transition from evaporation to a diffuse-mixing process. In order to gain deeper insight into the physical processes of this transition, a parametric study of free-falling n-pentane droplets in an inert nitrogen atmosphere is presented. Atmospheric conditions varied systematically from sub- to supercritical values with respect to the fluid properties. An overlay of a diffuse lighted image with a shadowgram directly in the optical setup (front lighted shadowgraphy) was applied to simultaneously detect the presence of a material surface of the droplet as well as changes in density gradients in the surrounding atmosphere. The experimental investigation illustrates, that the presence of a material surface cannot be shown by a direct shadowgram. However, reflections and refractions caused by diffuse ambient illumination are able to indicate the presence of a material surface. In case of the supercritical droplet injections in this study, front lighted shadowgraphy clearly revealed the presence of a material surface, even when the pre-heated droplets are released into a supercritical atmosphere. This detection of the droplet interface indicates, that the droplet remains subcritical in the region of interest, even though it is injected into a supercritical atmosphere. Based on the adiabatic mixing assumption recent Raman-scattering results in the wake of the droplet are re-evaluated to compute the temperature distribution. Presented experimental findings as well as the re-evaluation of recent Raman scattering results are compared to thermodynamic models to predict the onset of diffuse-mixing and supercritical disintegration of the droplet. Additionally, a one dimensional evaporation model is used to evaluate the validity of the adiabatic mixing assumption in the estimation of the droplet temperature. The presented findings contribute to the understanding of recent theoretical models for prediction of spray and droplet disintegration and the onset of diffuse-mixing processes.DOI: http://dx.doi.org/10.4995/ILASS2017.2017.4635

scholarly journals A Mini Review on Lanthanum Ferrites-based Exsolved Perovskites as Fuel-flexible Anode for Solid Oxide Fuel Cells

2020 ◽  
Author(s):  
Massimiliano Lo Faro ◽  
Sabrina Campagna Zignani ◽  
Antonino S. Aricò
Keyword(s):  
Substrate Surface ◽  
Electronic Conductivity ◽  
Solid Oxide ◽  
Full Density ◽  
Thermal Treatments ◽  
Direct Oxidation ◽  
Ni Doping ◽  
Shell Nanoparticles ◽  
Two Phase ◽  
Sulphur Poisoning

Exsolved perovskites can be obtained from lanthanum ferrites, such as La0.6Sr0.4Fe0.8Co0.2O3, as result of Ni doping and thermal treatments. Ni can be simply added to the perovskite by an incipient wetness method. Thermal treatments include calcination in air (e.g., 500 °C) and subsequent reduction in diluted H2 at 800 °C to favor the exsolution process. The chemistry of the nanoparticles exsoluted on the substrate surface can be further modulated by a post treatment in air. These processes allow to produce a two-phase material consisting of a Ruddlesden-Popper type structure and a solid oxide solution e.g. α-Fe100-y-zCoyNizOx oxide. The formed electro-catalyst shows sufficient electronic conductivity under reducing environment at the SOFC anode. Outstanding catalytic properties are observed for the direct oxidation of dry fuels in SOFCs, including H2, methane, syngas, methanol, glycerol and propane. This anode electrocatalyst can be combined with full density electrolyte based on Gadolinia-doped Ceria or with La0.8Sr0.2Ga0.8Mg0.2O3 (LSGM) or BaCe0.9Y0.1O3-δ (BYCO) to form a complete perovskite structure-based cell. Moreover, the exsolved perovskite can be used as a coating layer or catalytic pre-layer of a conventional Ni-YSZ anode. Beside the excellent catalytic activity, this material also shows proper durability and tolerance to sulphur poisoning. In this mini review, preparation methods, physico-chemical characteristics, surface properties of exsoluted and core-shell nanoparticles encapsulated on the metal-depleted perovskite substrate surface, electrochemical properties for the direct oxidation of dry fuels and related electrooxidation mechanisms are examined and discussed.

Sign in / Sign up

Export Citation Format

Share Document