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[en] The authors report the analysis of the oxygen isotopic composition of sulfates dissolved in 102 samples of thermal waters coming from different contexts: sedimentary (Parisian Basin), volcanic (New Mexico, West Indies, Mont Dore in France), or base (France), with the objective of a better understanding of the behaviour of oxygen isotopes of dissolved sulfates in order to use them as a geochemical tool in geothermal exploration. Some of these thermal waters contain colloids of silica, sulphur or iron which disturb oxygen extraction, and the authors therefore reconsidered handling conditions. After a recall of knowledge about the sulfate-water geo-thermometer (thermodynamic balance, kinetic parameters), the authors address mechanisms which disturb the SO4-H2O thermometer (cases of overestimated or underestimated temperature). They describe the experimental methodology: sampling, chemical processing, oxygen extraction, isotopic analysis by using a mass spectrometer. Then applications to the different studied fields are reported.
[en] At a time when greenhouse gas emissions must be reduced, the use of the aluminium alloys is expanding, in particular in the transportation industry. In order to extend the possibilities of aluminium assembly design, new Metal Inert Gas (MIG) welding processes have been conceived. They work at lower temperatures than usual arc processes (classic MIG or Tungsten Inert Gas). This study compares four arc welding processes, applied to the 6061 aluminium alloy. These four weld processes have been studied through the metallurgical analysis of the weld beads. Metallography, micro-hardness testings, X Ray radiography have been carried out on the produced weld beads. The processes are classified according to the quality of the beads like geometry of beads, size of the heat affected zone and presence of defects.