CO2 laser beam welding of AM60 magnesium-based alloy

The authors are grateful to FONDERIE MESSIER HONSEL group that provided the as-cast magnesium alloy workpieces. The authors would like also to acknowledge the technical support of Dr. Moraru of the LSIS Laboratory-Arts et Métiers ParisTech-Aix En Provence-France.Magnesium alloys have a 33% lower density than aluminum alloys, whereas they exhibit the same mechanical characteristics. Their application increases in many economic sectors, in particular, in aeronautic and automotive industries. Nevertheless, their assembly with welding techniques still remains to be developed. In this paper, we present a CO2 laser welding investigation of AM60 magnesium-based alloy. Welding parameters range is determinate for the joining of 3 mm thickness sheets. The effects of process parameters including beam power, welding speed, focusing position, and shielding gas flow are studied. Experimental results show that the main parameters that determine the weld quality are the laser beam power, the welding speed, and the shielding gas flow. The focal point position has a minor effect on weld quality, however, it has an influence on melting zone width. For optimized welding parameters, metallurgical observations show that after laser welding of AM60 alloy dendritic microstructure is observed on melting zone after high solidification rate. A small heat affected zone is also detected. Finally, hardness tests indicate that microhardness of the weld is higher than that of base metal

Quantitative imaging of dielectric permittivity and tunability with a near-field scanning microwave microscope

We describe the use of a near-field scanning microwave microscope to image the permittivity and tunability of bulk and thin film dielectric samples on a length scale of about 1 micron. The microscope is sensitive to the linear permittivity, as well as to nonlinear dielectric terms, which can be measured as a function of an applied electric field. We introduce a versatile finite element model for the system, which allows quantitative results to be obtained. We demonstrate use of the microscope at 7.2 GHz with a 370 nm thick barium strontium titanate thin film on a lanthanum aluminate substrate. This technique is nondestructive and has broadband (0.1-50 GHz) capability. The sensitivity of the microscope to changes in relative permittivity is 2 at permittivity = 500, while the nonlinear dielectric tunability sensitivity is 10^-3 cm/kV.Comment: 12 pages, 10 figures, to be published in Rev. Sci. Instrum., July, 200

Synthesis and electrochemical behavior of a model redox-active thiacalix[4]arene-tetrathiafulvalene assembly

Syntheses of the first bisthiacalix[4]arenes systems bridged by a tetrathiafulvalene (TTF) framework have been carried out through triethyl phosphite-mediated dechalcogenation dimerization of the corresponding 1,3-dithiole-2-ones. The cyclic voltammograms of the resulting bisthiacalix[4]arenes tethered by an electroactive TTF unit are provided, and exhibit an electrochemical response in the case of introduction of Ag+

Electroactive receptors incorporating Tetrathiafulvalene and polypyridyl units: synthesis and binding studies

Date du colloque : 07/2011</p

Récepteurs oligopyridines-tétrathiafulvalène : synthèse et propriétés

Date du colloque : 06/2012</p

Nonlinear absorption reversing between an electroactive ligand and its metal complexes

We present the nonlinear absorption investigation of an electroactive ligand and two ruthenium and iron metal complexes under 532 nm, 30 ps laser excitation, by the open aperture Z-scan technique. Significant nonlinear optical parameters have in all cases been measured, while the nonlinear attribute has been found to change from saturable to reverse saturable absorption between the initial ligand and its complexes

Tetrathiafulvalene-Polypyridyl Receptors for M2+ Recognition

Date du colloque : 06/2011</p

The parent tetrathiafulvalene-terpyridine dyad: synthesis and metal binding properties

The still unknown parent tetrathiafulvalene-terpyridine- ligand 5 (namely TTF-terpy), was synthesized through a straightforward strategy. The dyad exhibits an intramolecular charge transfer (ICT) which was evidenced by UV-vis electronic absorption. Complexation of various transition metal cations by this redox-active ligand was studied by UV-vis absorption spectroscopy as well as by cyclic voltammetry titration studies, supporting the dual functional character of this system. In addition, these results demonstrate that ligand 5 is a suitable building block for the preparation of electroactive neutral as well as charged metal complexes

A comparison of electrochemical degradation of phenol on boron doped diamond and lead dioxide anodes

This work compares two electrode materials used to mineralize phenol contained in waste waters. Two disks covered with either boron doped diamond (BDD) or PbO2 were used as anodes in a one compartment flow cell under the same hydrodynamic conditions. Efficiencies of galvanostatic electrolyses are compared on the basis of measurements of Total Organic Carbon (TOC) and Chemical Oxygen Demand (COD). Galvanostatic electrolyses were monitored by analysis of phenol and of its oxidation derivatives to evaluate the operating time needed for complete elimination of toxic aromatics. The experimental current efficiency is close to the theoretical value for the BDD electrode. Other parameters being equal, phenol species disappeared at the same rate using the two electrode materials but the BDD anode showed better efficiency to eliminate TOC and COD. Moreover, during the electrolysis less intermediates are formed with BDD compared to PbO2 whatever the current density. A comparison of energy consumption is given based on the criterion of 99% removal of aromatic compounds