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Several members of the order Thermotogales in the domain Bacteria, viz., Thermotoga neapolitana, Thermotoga maritima, Thermosipho africanus, Fervidobacterium islandicum, and Thermotoga strain SEBR 2665, an isolate from an oil well, reduced thiosulfate to sulfide. This reductive process enhanced cellular yields and growth rates of all the members but was more significant with the two hyperthermophiles T. neapolitana and T. maritima. This is the first report of such an occurrence in this group of thermophilic and hyperthermophilic anaerobic bacteria. The results suggest that thiosulfate reduction is important in the geochemical cycling of sulfur in anaerobic thermal environments such as the slightly acidic and neutral-pH volcanic hot springs and oil reservoirs

Role of the reversible electrochemical deprotonation of phosphate species in anaerobic biocorrosion of steels

Sulphate reducing bacteria are known to play a major role in anaerobic microbiological influenced corrosion of steels, but mechanisms behind their influence are still source of debates as certain phenomena remain unexplained. Some experiments have shown that hydrogen consumption by SRB or hydrogenase increased the corrosion rate of mild steel. This was observed only in the presence of phosphate species. Here the cathodic behaviour of phosphate species on steel was studied to elucidate the role of phosphate in anaerobic corrosion of steel. Results showed: a linear correlation between reduction waves in linear voltammetry and phosphate concentration at a constant pH value; that phosphate ions induced considerable anaerobic corrosion of mild steel, which was sensitive to hydrogen concentration in the solution; and that the corrosion potential of stainless steel in presence of phosphate was shifted to more negative values as molecular hydrogen was added to the atmosphere in the reaction vessel. Phosphate species, and possibly other weak acids present in biofilms, are suggested to play an important role in the anaerobic corrosion of steels via a reversible mechanism of electrochemical deprotonation that may be accelerated by hydrogen removal

Analysis and modeling of burr formation during the plane milling of cast aluminium alloy using Polycrystalline Diamond Tools

Burr formation is a significant problem during manufacturing, and leads to a lack of geometrical quality through the appearance of undesired and undefined shapes on the workpiece. Thus, understanding the burr formation and elaborating of predictive models are helpful for process design in order to avoid or to reduce burrs and to optimize the strategies for eventual deburring. This study presents both an experimental approach and a model for the plane milling of openwork parts, where burrs are a significant factor. A large-scale analysis of relevant geometrical parameters and their interactions is performed. A phenomenological burr size model is established considering local parameters and the specificities of 3D cutting in milling. Based on local parameters, this article proposes a new methodology to simulate burr height along any part edge and for most face-milling trajectories. Simulations and validations during tool path exits, with changing local parameters, are presented. In addition to the quantitative approach, new 3D aspects of face milling in relation with Exit Order Sequence are developed.contrat ARTS avec MONTUPE

Etude de la formation des bavures en coupe orthogonale à l’outil carbure dans un alliage d’Aluminium – Silicium.

Le but de cet article est d’étudier l’influence des paramètres de coupe sur la formation des bavures en coupe orthogonale. Pour ce faire, une étude en rabotage est réalisée avec des plaquettes carbures, sur un alliage d’Aluminium-Silicium, communément utilisé pour la fonte de culasses automobiles. Cette étude consiste à analyser l’influence de différents paramètres de coupe sur la formation des bavures dans le matériau. Les résultats obtenus permettent de conclure sur l’influence de certains paramètres de coupe sur la formation de la bavure, ainsi que son caractère aléatoire en coupe orthogonale, dû à l’hétérogénéité du matériau

Etude de la formation des bavures en coupe orthogonale à l’outil carbure dans un alliage d’Aluminium – Silicium.

Le but de cet article est d’étudier l’influence des paramètres de coupe sur la formation des bavures en coupe orthogonale. Pour ce faire, une étude en rabotage est réalisée avec des plaquettes carbures, sur un alliage d’Aluminium-Silicium, communément utilisé pour la fonte de culasses automobiles. Cette étude consiste à analyser l’influence de différents paramètres de coupe sur la formation des bavures dans le matériau. Les résultats obtenus permettent de conclure sur l’influence de certains paramètres de coupe sur la formation de la bavure, ainsi que son caractère aléatoire en coupe orthogonale, dû à l’hétérogénéité du matériau

Investigations on exit burr formation mechanisms based on digital image correlation and numerical modelling

Requirements on burr height and burr amount on machined parts are getting stricter. This leads to method development from manufacturing companies to predict burr distribution and its size along part edges. A deeper understanding of burr formation mechanisms will assist to more accurate model development. This study aims to analyze the exit burr formation, which is formed during orthogonal cutting of a brittle cast aluminum alloy. A customized Digital Image Correlation (DIC) system with the help of a high-speed camera was used to measure the displacements fields. It calculates strain fields during burr initiation and development in orthogonal cutting of T7 heat-treated cast Aluminum alloy ENAC-AlSi7Mg0.3 as well. Those results are then qualitatively compared with a numerical model of the burr with chamfer formation developed and simulated using a Finite Element Method (FEM), to ensure a good correspondence between experiments and simulation. This model is used to complete the DIC study of burr with chamfer formation mechanisms during crack propagation leading to chamfer formation. The analysis of numerically obtained stress triaxiality fields and of DIC observations from experiments are compared to the assumptions made from analytical models. Finally, necessary improvements of an existing burr formation analytical model are proposed

Experimental Investigation and Modelling of Burr Formation during Orthogonal Cutting of A356+0.5Cu Aluminium Alloy

Burr formation during parts manufacturing is a significant problem that companies try to minimise or eliminate. The present work aims to study the burr formation mechanisms in a cast aluminium alloy. Orthogonal cutting tests are performed using different uncut chip thicknesses and tool rake angles. To analyse burr formation mechanisms, the work material state of stress and triaxiality distribution in the chip root was investigated via numerical simulations. Results show that the uncut chip thickness has an effect on burr morphology and burr cumulation while tool rake angle influences burr height on high uncut chip thicknesses