Corrosion behaviour of new quaternary ZrNbTiAl alloys in simulated physiological solution using electrochemical techniques and surface analysis methods

The potential biomedical application of three new quaternary Zr alloys, namely Zr6Ti15Nb4Al, Zr32Ti15Nb4Al, and Zr49Ti15Nb4Al, was evaluated in vitro using electrochemical methods complemented with surface analysis of corrosion resistance. Cyclic potentiodynamic polarization (CCP) and electrochemical impedance spectroscopy (EIS) tests were performed in Ringer’s solution at 37 ºC. The electrochemical behavior of the ZrTiNbAl quaternary alloys was consistent with the formation of passivating oxide films on the surfaces of these materials. Localized breakdown of the oxide layer occurred on Zr6Ti15Nb4Al and Zr32Ti15Nb4Al alloys subjected to positive anodic polarization, a feature confirmed by scanning electron microscopy (SEM) on retrieved samples. The Zr49Ti15Nb4Al alloy, which had the highest titanium (49 wt.%) content, exhibited a larger passive range in the polarization curve and was immune to localized corrosion breakdown in a simulated physiological solution for the range of polarizations that can occur in the human bod

Fluid flow induced by non-uniform AC electric fields in electrolytes on microelectrodes III: Observation of streamlines and numerical simulation

The application of a nonuniform ac electric field to an electrolyte using coplanar microelectrodes results in steady fluid flow. The flow has its origin in the interaction of the tangential component of the nonuniform field with the induced charge in the electrical double layer on the electrode surfaces. Termed ac electro-osmosis, the flow has been studied experimentally and theoretically using linear analysis. This paper presents experimental observations of the fluid flow profile obtained by superimposing images of particle movement in a plane normal to the electrode surface. These experimental streamlines demonstrate that the fluid flow is driven at the surface of the electrodes. Experimental measurements of the impedance of the electrical double layer on the electrodes are also presented. The potential drop across the double layer at the surface of the electrodes is calculated numerically using a linear double layer model, and also using the impedance of the double layer obtained from experimental data. The ac electro-osmotic flow at the surface of the electrodes is then calculated using the Helmholtz-Smoluchowski formula. The bulk fluid flow driven by this surface velocity is numerically calculated as a function of frequency and good agreement is found between the numerical and experimental streamlines

Revista española de orientación y psicopedagogía

Resumen tomado de la publicaciónSe ha generado una línea de investigación a partir de la creación del concepto de Aprendizaje Autorregulado (AAR), que pretende aunar los conocimientos y experiencia existentes en relación con las variables cognitivas, afectivo-motivacionales y del entorno de aprendizaje. Pese a estar todavía en proceso de definición y explicación, puede proporcionar una base teórica para la comprensión y evaluación del proceso de aprendizaje de los estudiantes. Se pretende destacar los grandes rasgos que van a conducir en el futuro a la elaboración de recursos dirigidos a su evaluación. En este trabajo, se presentan sus principales características, componentes, líneas actuales de investigación e instrumentos que se sitúan próximos a su evaluación. Se persigue ayudar al desarrollo de los estudiantes desde los centros educativos, en lo que se ha denominado aprender a aprender.MadridBiblioteca de Educación del Ministerio de Educación, Cultura y Deporte; Calle San Agustín, 5 - 3 Planta; 28014 Madrid; Tel. +34917748000; [email protected]

Electrochemical characteristics of titanium based biomaterials in artificial saliva

In the last decade, new titanium alloys have been developed in different areas of dentistry, such as Ti6Al7Nb, Ti6Al2Nb1Ta1Nb, and Ti5Al2.5Fe. The aim of this study was to compare the Ti6Al7Nb, Ti6Al2Nb1Ta1Nb, Ti5Al2.5Fe, and Ti6Al4V alloys with the commercial titanium, regarding the corrosion resistance in artificial saliva. In the electrochemical estimations the polarization data are converted into instantaneous corrosion rate values (I-corr). The passivation properties were comparable for the four alloys. The EIS spectra are best fitted using an equivalent circuit (EC), which corresponds to the model of a two-layer structure for the passive film. High impedance values (in the order of 10(6) Omega cm(2)) were obtained from medium to low frequencies for all materials suggesting high corrosion resistance in artificial saliva.The electrochemical and corrosion behavior of Ti6Al4V is not affected on substituting vanadium with niobium, iron, molybdenum, and tantalum.856848SCI