Performance of Ti/Pt and Nb/BDD anodes for dechlorination of nitric acid and regeneration of silver(II) in a tubular reactor for the treatment of solid wastes in nuclear industry

One of the problems frequently encountered in the processing of nuclear fuels is the recovery of plutonium contained in various solid wastes. The difficulty is to make soluble the plutonium present as the refractory oxide PuO2. The dissolution of this oxide in nitric acid solutions is easily performed by means of silver(II) a strong oxidizing agent which is usually electrochemically generated on a platinum anode. However, certain solid residues that must be treated to separate actinides contain important quantities of chloride ions that require after dissolution in nitric acid a preliminary electrochemical step to be removed before introducing Ag(I) for Ag(II) electrogeneration. Research is conducted to find electrocatalytic materials being able to replace massive platinum in view to limit capital costs. In the present work a set-up including a two-compartment tubular reactor with recirculation of electrolytes was tested with anodes made of boron doped diamond coated niobium (Nb/BDD) and platinum coated titanium (Ti/Pt) grids for the removal of chlorides (up to 0.1 M) and for silver(II) regeneration. The study showed that these two anodes are effective for the removal of chlorides contained in 6 M HNO3 solution as gaseous chlorine, without producing the unwanted oxyanions of chlorine. Furthermore, the regeneration rate of silver(II) on Nb/BDD anode is approximately equal to that obtained on Ti/Pt anode for the same hydrodynamic conditions in the tubular reactor. Accordingly, dechlorination as well as silver(II) regeneration can be performed in the same reactor equipped either with a Nb/BDD or a Ti/Pt anode. Besides, the service life of Nb/BDD anodes estimated by accelerated life tests conducted in 6 M HNO3 can be considered as very satisfactory compared to that observed with Ti/Pt anodes

High frequency carbonate cycles in Middle Devonian of northwestern Meseta (Morocco).

Communication et Abstract, p 162-163info:eu-repo/semantics/nonPublishe

Microfaciès et isotopes stables (carbone, oxygène): deux outils en faveur du contrôle orbital de la cyclicité du Dévonien de la Meseta Nord-Occidentale du Maroc

Communication et Abstract; p 213info:eu-repo/semantics/nonPublishe

A meter-scale cyclicity in the Middle Devonian of northwestern Meseta (Morocco): Is it a Milankovitch signature?

info:eu-repo/semantics/publishe

Ionic conductivity of an extruded Nafion 1100 EW series of membranes

The proton conductivity of a series of extruded Nafion membranes @of equivalent weight ~EW! of 1100 and nominal dry thickness of 51, 89, 127, and 178 mm# has been studied. Measurements were made in 1 M H2SO4 at 298 K using a four-electrode, dc technique. The membrane area resistance increases with thickness, as expected, from 0.07 to 0.16 V cm2 for Nafion 112 and Nafion 117, respectively. However, in contrast to the published literature, after correcting for the membrane thickness, the conductivity of the membranes decreases with decreasing membrane thickness. For example, values of 0.083 and 0.16 S cm21 were obtained for Nafion 112 and 117 membranes, respectively. In situ current-interrupt measurements in a proton exchange membrane fuel cell confirmed the relatively poor conductivity of the membrane electrode assemblies ~MEAs! based on the thinner membranes. While a high contact resistance to the electrodes may have contributed to the in situ MEA resistance, water balance measurements over the MEA showed that the high resistance was not due to a low water content or to an uneven water distribution in the MEAs. The implications of the findings for the understanding of the membrane properties are discussed

Proton Conductivity of a Fuel Cell|Membrane with Nanoscale Resolution

The present work demonstrates that EC-AFM is a very useful new tool for identification and spatially resolved characterization of proton conductivity at the membrane surface in comparison with topography, however it does not provide insight into the 3D pore structure within the membrane. The results are consistent with those of conventional macroscopic measurements, confirming the reliability of the method. It will allow careful analysis of the homogeneity, the nature and the consequences of microphase separation as well as the effect of humidity on novel alternative membranes, and it will thus be essential for tailored developments of new materials for fuel-cell membranes. The present initial work is followed up with further experiments which provide a more complete understanding of the proton conductivity of the polymers, determine the influence of relative humidity on the size of conductive regions and investigate the reproducibility of the results

Structure and Local Reactivity of Supported Catalyst/Nafion® Layers studied by in-situ STM

The electrodes are crucial components for fuel cells, since this is where the electrochemical reactions take place. In order to provide an insight into the structure/activity relationships of the rather complex electrodes, a high-resolution measuring technique, based on a scanning tunneling microscope operating in an electrochemical cell, has been developed. The structure of the electrode surface can be imaged from the microscale to the nanoscale, under conditions quite close to those in a working fuel cell. The relative reactivity is measured by using the STM tip as a sensor electrode for the ORR. Here, the first results of the surface structure of the electrode materials are presented, as well as measurements of the local reduction current, related to the oxygen reduction reaction, giving a relative measure for the local reactivity