The Point Defect Model (PDM) has been shown to accurately describe the properties of passive films that form on metal surfaces in contact with aggressive environments under both open circuit and anodic polarization conditions. However, the commonly-employed PDM, known henceforth as PDM-II assumes that passivity arises from the properties of the barrier layer and that the outer layer, if present, contributes negligibly to the interfacial impedance. In this paper, we describe PDM-III, in which a resistive outer layer exists on the surface and contributes substantially to the impedance of the interface. The outer layer is shown to have a profound impact on the properties of the barrier layer and under certain circumstances the barrier layer is predicted to disappear. This new form of depassivation has been observed experimentally. The use of electrochemical impedance spectroscopy to characterize passive films having resistive outer layers is describe and illustrated with reference to the passive state on zirconium in simulated PWR (Pressurized Water Reactor) primary coolant.
Bert Hayslip Jr and Julie Hicks Patrick (eds), Custodial Grandparenting: Individual, Cultural, and Ethnic Diversity, Springer Publishing Company, New York, 2006, 334 pp., pbk $48.95, ISBN 0 8261 1998 0. - Volume 27 Issue 1
Abstract Investigated in this paper is the question: Can seismic demands on steel moment‐frame buildings due to maximum considered earthquake (MCE R ) design‐level ground motions (GMs) be estimated satisfactorily using linear viscous damping models or is a nonlinear model, such as capped damping, necessary? This investigation employs an enhanced model with several complex features of a 20‐story steel moment‐frame building. Considered are two linear viscous damping models: Rayleigh damping and constant modal damping; and one nonlinear model where damping forces are not allowed to exceed a predefined bound. Presented are seismic demands on the building due to two sets of GMs: MCE R design‐level GMs (2% probability of exceedance [PE] in 50 years) and rarer excitations (1% PE in 50 years). Based on these results, we conclude that linear damping models are adequate for estimating seismic demands on steel moment‐frame buildings—designed to satisfy current story drift and plastic rotation limits due to MCE R design‐level GMs. Between the two linear damping models, constant modal damping is preferred; it is available in commercial computer codes for earthquake structural analysis.
This introduction presents an overview of the key concepts discussed in the subsequent chapters of this book. The book deals with heterogeneous catalysis and allows several leading practitioners to describe examples of materials and processes in heterogeneous catalysis under investigation by nuclear magnetic resonance (NMR) techniques. Modern solid-state NMR makes it possible to detect signals from distinguishable sites in molecules and materials and to monitor the connectivities, correlations, and dynamics of these sites. Furthermore, NMR spectroscopy is essentially noninvasive and can be carried out in the presence of gases or liquids over a wide range of temperatures and pressures. While the principal use of NMR spectroscopy is to obtain information about the chemical environment of elements in catalysts or species adsorbed on catalysts, the technique can also be used to characterize atomic and molecular motions. The types of information that may be derived from NMR signals include site identification and intersite correlations.
Here, we demonstrate an approach for the selective growth of Pt, PtNi, and PtCo on CdS nanorods. The hybrid nanostructures prepared via an organometallic synthesis have promise for photocatalytic and magnetic applications.
Abstract The synthesized title complex (III) (space group P1, Z=2) is characterized by NMR, IR, and MS data as well as by an X‐ray structure analysis.
Se resenan algunas de las propiedades fisico-electroquimicas de las peliculas de oxido pasivo que se forman sobre la superficie de metales y aleaciones reactivos, y que protegen a los metales subyacentes de la reaccion con ambientes corrosivos, dentro del contexto del Modelo de Defecto Puntual (PDM) y del Modelo de Potencial Mixto (MPM). Estos modelos rinden expresiones (PDM) o algoritmos numericos rapidamente convergentes (MPM) para la corriente del estado estacionario y el grosor de la pelicula, que se pueden usar para predecir de manera determinista la acumulacion de los danos de corrosion general de las superficies de los metales, siempre que la evolucion hacia el estado futuro sea continua y se pueda especificar. El calculo del dano se ilustra por estimacion de la perdida de grosor de la pared de contenedores de Aleacion-22 que contienen residuos nucleares de alta actividad en un deposito geologico ?seco? (por encima del nivel de las aguas freaticas). Los modelos predicen que los contenedores perderan unos 1,6 mm de grosor de pared, comparado con un grosor disenado de 2 cm, durante su vida disenada de 10.000 anos. Finalmente, se realiza una breve discusion sobre las condiciones que se han de dar para que un metal reactivo se transforme en pasivo, ya que es la retencion del caracter pasivo lo que hace posible emplear metales reactivos en nuestra civilizacion basada en los metales.
