Electrochemical Analysis of Zirconiumin Aqueous and Organic Media

For the challenging nature of the zirconium environment analysis, this study consists to analyze the electrochemical behavior of Zirconium in both aqueous and organic media. To that end first the electrolytic media was selected on the basis of the Pourbaix potential-pH diagram, which provides informations on the predominance of Zr(IV) ion and Zr in aqueous media. In aqueous media, analyzes were first carried out in acidic media then in basic media. Studies have thus revealed that the acidic environment is not favourable for the electrochemical analysis of zirconium. Voltammograms obtained in an acidic environment show no zirconium detection signal;this is due to the strong presence of H+ ions in the solution. We have also observed in acidic media the phenomenon of passivation of the electrode surface. In aqueous alkaline media (pH = 13), we have drawn in reduction several Intensity-Potential curves by fixingsome technical parameterslike scanning speed, rotation speed of the electrode. The obtained voltammograms show cathodic waves, starting from -1.5 V/DHW and attributed to the reduction of Zr (IV) to Zr (0). The last phase of this study focused on the electrochemical analysis of zirconium in an organic media. In this media, several intensity-potential curves were plotted in reduction and in cyclic voltammetry with various parameters. Through several reduction analysis, the Zr (IV) was reduced to Zr (0) to the potential of -1.5 V/DHW. The electrochemical analysis of zirconium in organic media seems globally easier to achieve thanks to its large solvent window (i.e. dimethylformamide (DMF) solvent window > 6 V).

Stability of highly supersaturated vanadium electrolyte solution and characterization of precipitated phases for vanadium redox flow battery

The vanadium redox flow battery(VRFB)has been receiving great attention in recent years as one of the most viable energy storage technologies for large-scale applications.However,higher concentrations of vanadium species are required in the H_(2)O-H_(2)SO_(4) electrolyte in order to improve the VRFB energy density.This might lead to unwanted precipitation of vanadium compounds,whose nature has not been accurately characterized yet.For this purpose,this study reports the preparation ofⅤ^((Ⅱ)),ⅤV^((Ⅲ)),Ⅴ^((Ⅳ))andⅤ^((Ⅴ))supersaturated solutions in a 5 M H_(2)SO_(4)-H_(2)O electrolyte by an electrolytic method,from the only vanadium sulfate compound commercially available(VOSO_(4)).The precipitates obtained by ageing of the stirred solutions are representative of the solids that may form in a VRFB operated with such supersaturated solutions.The solid phases are identified using thermogravimetric analysis,X-ray diffraction and SEM.We report that dissolvedⅤ^((Ⅱ)),Ⅴ^((Ⅲ))andⅤ^((Ⅳ))species precipitate as crystals of VSO_(4),V_(2)(SO_(4))3 and VOSO_(4) hydrates and not in their anhydrous form;conversely V^((Ⅴ))precipitates as an amorphous V_(2) O_(5) oxide partially hydrated.The measured hydration degrees(respectively 1.5,9,3 and 0.26 mol of H_(2)O per mol of compound)might significantly affect the overall engineering of VRFB operating with high vanadium concentrations.

Analytical Method to Monitor Industrial Pickling Baths Initially Constituted by HF, HNO₃

The present study couples the acid/basis titration and the ICP analysis in order to monitor the concentrations of nitric and hydrofluoric acids, and presents into baths used to pickle alloys of titanium or stainless steel, largely employed in the aeronautic industry. The pickling of the alloys releases various metallic cations able to react with HF in order to lead to metal-fluoride complexes and free H+, the last being able to react with the basis. In this study, it was determined: the most significant correlations providing the number of the protons released by the complexation of the metallic cation by the fluoride. The proposed method based on: 1) these correlations;2) the titration pH = f(VKOH) curves;and 3) the content of metallic cations determined by ICP, enables the monitoring of the content of HNO3 and HF into the pickling bath. Assuming that one bath was used for one type of alloy (alloys of Titanium for example, or alloys of stainless steel), then the proposed method appears providing reliable concentration values of both acids as well as metallic cations.