Oxygen transfer properties of ion-implanted yttria-stabilized zirconia

The influence of surface modification by ion implantation on oxygen transfer in yttria-stabilized zirconia (YSZ) has been studied. Implantation of 15 keV 56Fe in YSZ with a maximum dose of 8×1016 atoms cm−2 yields reproducible surface layers of approximately 20 nm deep with a maximum Fe cation fraction of 0.5 at the surface. After annealing these layers are stable up to 700–800°C. The exchange current densities for the Fe-implanted layers, measured using porous gold electrodes, are a factor of 10–50 larger than observed for not-implanted YSZ. 18O isotope exchange experiments show that for Fe-implanted samples the surface oxygen exchange rate is at least a factor 30 larger than for normal YSZ. The electrode kinetics has been studied for normal and implanted YSZ using current-overvoltage measurements and impedance measurements under bias. An electrode reaction model for the transfer of oxygen has been developed. This model is able to explain the low frequency inductive loop in the impedance diagram which is observed at high cathodic and anodic polarizations for implanted as well as normal YSZ.\u

Electrode polarization at the Au, O2(g)/yttria stabilized zirconia interface. Part II: electrochemical measurements and analysis

The impedance of the Au, O2 (g) / yttria stabilized zirconia interface has been measured as function of the overpotential, temperature and oxygen partial pressure. At large cathodic overpotentials (η < −0.1 V) and large anodic overpotentials (η > +0.1 V) inductive effects are observed in the impedance diagram at low frequencies. Those inductive effects result from a charge transfer mechanism where a stepwise transfer of electrons towards adsorbed oxygen species occurs. A model analysis shows that the inductive effects at cathodic overpotentials appear when the fraction of coverage of one of the intermediates increases with more negative cathodic overpotentials. The steady state current-voltage characteristics can be analyzed with a Butler-Volmer type of equation. The apparent cathodic charge transfer coefficient is close to c=0.5 and the apparent anodic charge transfer coefficient varies between 1.7< a<2.8. The logarithm of the equilibrium exchange current density (Io) shows a positive dependence on the logarithm of the oxygen partial pressure with a slope of m= (0.60 ± 0.02). Both the apparent cathodic charge transfer coefficient and the oxygen partial pressure dependence of Io are in accordance with a reaction model where a competition exists between charge transfer and mass transport of molecular adsorbed oxygen species along the electrode/solid electrolyte interface. The apparent anodic charge transfer coefficients deviate from the model prediction.\u

Electrode polarization at the Au, O2(g)/Fe implanted yttria-stabilized zirconia interface

Ion implantation has been applied to modify the surface properties of yttria-stabilized zirconia (YSZ). A three-electrode cell was used for measuring steady state current-overpotential curves and for determining the electrode impedance. An increase of the equilibrium exchange current density at the Au, O2(g)/yttria stabilized zirconia interface with a factor 10–50 has been observed after the implantation of 15 kV 56Fe up to a dose of 8 × 1016 at.cm−2. This increase results from a broadening of the active surface area due to an increase in the electronic conductivity of the Fe implanted YSZ surface and from an increase of the fraction of coverage of the adsorbed oxygen molecules. The double layer capacitance of the Au, O2,g/YSZ interface increases with a factor 10–100 after the Fe implantation. This is most likely due to the variable oxidation state of the implanted Fe ions, thus providing an additional way for charge accumulation. In comparison with the not implanted Au, O2,g/YSZ interface no changes in the rate-determining steps of the oxygen exchange mechanism occur after Fe implantation. Similar apparent charge-transfer coefficients have been determined. A slight decrease in the oxygen partial pressure dependence of Io is observed. The experimental results can still be explained with a reaction model where the charge-transfer process is in competition with the surface diffusion of molecular adsorbed oxygen species along the noble metal-solid electrolyte interface. At cathodic and anodic overpotentials inductive effects appear at low frequencies in the impedance diagram. The inductive effects result from a charge-transfer mechanism where a step-wise transfer of electrons to adsorbed oxygen species takes place.\u

Electrode polarization at the Au, O2(g)/yttria stabilized zirconia interface. Part I: Theoretical considerations of reaction model

Three different reaction models are discussed which describe the oxygen exchange reaction at the Au, O2(g)/yytria stabilized zirconia interface. The first model assumes the charge transfer process to be rate determining. If the electron transfer to the adsorbed oxygen species occurs in a stepwise fashion low frequency inductive effects can be simulated in the frequency dispersion of the electrode impedance. If the charge transfer process is in competition with mass transport of oxygen along the Au, O2(g)/stabilized zirconia interface the second model can predict “apparent” Tafel behaviour of the current-overpotential curve. The real charge transfer coefficients change from c = a = 1 to apparent values of c = 0.5 and c = 1.5. Due to a gradient in the fraction of coverage of the molecular adsorbed oxygen species along the Au, O2(g)/stabilized zirconia interface, the oxygen partial pressure dependence of the equilibrium exchange current density changes from I0 ∝ PO21/4 to I0 ∝ PO25/8. Depending on the basic charge transfer mechanism inductive effects at the electrode remain possible. The electrode impedance derived from this model under equilibrium conditions thus far revealed only capacitive effects. This makes this reaction model difficult to distinguish from the electrode impedance of a pure charge transfer process with an adsorbed intermediate. In case the mass transport process is rate determining limiting currents are predicted at moderate values of the applied overpotential. The electrode impedance then consists of a finite-length Warbung diffusion element and inductive effects cannot be predicted

Quantum differential forms

Formalism of differential forms is developed for a variety of Quantum and noncommutative situations

Developing reflective practice in LIS education: The SEA-change model of reflection

This paper presents the SEAchange model of reflection. It was developed to support the growing interest in reflective practice within the library domain. The model was developed from experience gained teaching and training reflective writing to students and practitioners within librarianship. The model was tested using data gathered from the reflective journals of 22 MA Librarianship students, who submitted 116 reflective journal entries from October 2007 toMay 2008. The model has three core process elements: a consideration of the situation (S); consideration of the evidence used during the practice of reflection (E); and action (A) needed as a result of what has been learnt from the reflective process. An earlier study identified significant benefits that could be gained from engaging in reflective writing, particularly in relation to student learning outcomes, selfdevelopment and empowerment. These outcomes, identified as change or the need for change are integrated into the SEAchange model. Reflection is discussed in relation to teachers or mentors applying a progressive “descaffolding” approach to learning support in order to facilitate student autonomy. Further validation of the model is recommended in a range of different settings. The model provides a framework for the teaching, support and guidance of reflective practice

GIS application to boost fish production in Nigeria

The paper discusses the application of Geographic Information System (GIS) to fisheries management. The paper presents the importance of the emerging technology of GIS and how it can be utilized to greatly speed up and make more efficient location optimizing processes and how the technology can allow for a through examination of the many spatially variable factors which might affect or control fish production both from aquaculture and inland fisheries in Nigeri

Reflective writing: a management skill

Purpose – The purpose of this paper is to analyze students' reflective writing in terms of identifiable outcomes and explore students' thoughts on reflection and reflective writing as a process. Design/methodology/approach – A mixed methods approach is taken with a qualitative analysis of 116 written reflections from MA Librarianship studying management over an eight-month period. A quantitative statistical analysis assesses the relationships between reflective writing and a number of possible outcomes identified from the literature. Findings – A significant relationship is found between seven of eight outcomes tested; academic learning, the need for self-development, actual self-development, critical review, awareness of ones' own mental functions, decision making and empowerment and emancipation. There is some evidence of a relationship between non-academic learning and reflective writing, but it is not significant. A number of themes emerged from the reflective writings regarding reflection itself, with students seeing reflection as a positive activity, with benefits for the individual, groups and in the workplace, and identifying reflection as a skill that can be practiced and developed. Practical implications – Reflection and reflective writing as a management skill has potential benefits for personal and professional development and improving work-based practice. Originality/value – This paper differs from the previous literature in presenting statistical evidence to confirm the relationships between reflective writing and a range of potential outcomes

What a classical r-matrix really is

The notion of classical $r$-matrix is re-examined, and a definition suitable to differential (-difference) Lie algebras, -- where the standard definitions are shown to be deficient, -- is proposed, the notion of an ${\mathcal O}$-operator. This notion has all the natural properties one would expect form it, but lacks those which are artifacts of finite-dimensional isomorpisms such as not true in differential generality relation \mbox{End}\, (V) \simeq V^* \otimes V for a vector space $V$. Examples considered include a quadratic Poisson bracket on the dual space to a Lie algebra; generalized symplectic-quadratic models of such brackets (aka Clebsch representations); and Drinfel'd's 2-cocycle interpretation of nondegenate classical $r$-matrices

Illinois beef cow handbook : management, health, pastures, economics / 1068

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