Electrochemistry in molten NaAlCl4 (at 210°C): Identification of dissolved oxide-containing species,solubility of alumina in terms of pCl− and properties related to H2O in this melt

It has been shown that a nickel electrode is an indicator of the presence of oxide ions dissolved in chloroaluminate melts. From quantitative interpretation of electrochemical results (voltammograms and potentiometric measurements), O^2? has appeared to behave, in terms of the chloro-acidobasicity concept, as a strong dibase, through a solvolytic reaction giving AlOCl₂^? as solvated form. AlOCl₂^? itself is a weak base, according to the system:AlOCl₂^?AlOCl+Cl^?, pK_B/mol kg^1-=4.35 (at210°C) Thus O^2? behaves cumulatively as a tribase. AlOCl is the solvated form of O^?II in very acidic melts.A saturation effect by Al₂O₃ appeared when the concentration of O^?II was increased. The solubility of Al₂O₃ in chloroaluminate melts (one third of total O^?II solubility) was determined from the electrochemical results obtained. A minimum of 0.13% in weight (solubility of O^?II=4×10^?2 mol kg^?1), is observed for pCl^?=4.5 that is in a mixture containing 51.4 moles per cent of AlCl₃. The solubility is increased by adding either more AlCl₃ (formation of AlOCl) or NaCl (formation of AlOCl₂^?). Its variation versus pCl^? has been expressed quantitatively.Through a study of the system HCl/H₂O, it was pointed out that hydrolysis of chloroaluminate melt does not occur to a great extent in basic media. On the contrary, elimination of oxide ions through H₂O formation by reaction with HCl was shown to be possible. A quantitative relation, which binds the total concentration of O^?II, pCl^? and the respective partial pressures of gaseous HCl and H₂O in equilibrium with the melt, is given.A treatment in order to carry out this purification in these melts appears necessary in order to prevent many dissolved metallic ions from precipitating under the form of oxides.     

Rapid determination of polycyclic aromatic hydrocarbons in sewage sludges using microwave-assisted solvent extraction. Comparison with other extraction methods

The presence of toxic organic micropollutants in municipal sewage sludges is a major problem on account of risks associated with the agricultural use of the sludges and therefore maximum tolerance limits are imposed. The aim of our study was to develop a reliable and fast analytical procedure for the determination of polycyclic aromatic hydrocarbons in sewage sludges, using focused microwave-assisted extraction. Optimization of the extraction conditions was performed on real matrices. The results of a 2(3) factorial design showed that extraction time was the only influential factor. The selected conditions (30 W, 10 min, 30 ml solvent) were used for real sludges and a certified marine sediment, leading to recoveries of between 56 and 75%. Results of an interlaboratory test confirmed these values. Finally, the technique was compared to traditional techniques (Soxhlet, sonication), and the more recent pressurized liquid extraction technique. Focused microwave-assisted extraction remains an attractive alternative technique due to its rapidity, the low solvent volume required and its moderate investment cost.     

Determination of methylmercury in the presence of inorganic mercury by anodic stripping voltammetry

Methylmercury is determined in a non-complexing nitrate medium by differential pulse anodic stripping voltammetry at a gold film electrode, with a detection limit of 2 × 10^-8 mol l^-1 for 5-min plating times. A method of double standard additions is proposed for determining methylmercury in the presence of mercury(II) ions.     

Preparation and characterization of MgB2 superconductor

The MgB₂ superconductor, synthesized using solid-state and liquid-phase sintering methods, have been characterized for various properties. The upper critical field, irreversibility line and critical current density have been determined using magnetization data. The current-voltage characteristics recorded under an applied magnetic field revealed the existence of vortex glass transition. The surface analysis using X-ray photoelectron spectroscopy shows that MgB₂ is sensitive to atmospheric degradation.