The Production of aluminium is one of such industrial processes that have the potential to release great quantities of dangerous toxic material into the atmosphere. To protect the environment, the Alucam Company has put in place two collection and treatment stations. The main indicator of performance of this system is the collection and treatment efficiency. All other parameters kept constant, this efficiency is proportional to the fume flow rate at the chimney. But the key parameters to control in case of variation are poorly mastered. The collection efficiency of the treatment stations can deteriorate at any moment without any successful intervention to bring back the situation to normal. This article presents the first part of a research work which intends to solve this problem of variations in the flow rate by increasing the fume flow rate and controlling the system within specified limits. We use a Continuous Improvement Methodology which involves the use of Six Sigma tools at the completion of the analysis phase of which we get the fundamental causes of the low performance.

The collection efficiency is the major indicator for the evaluation of the pollution rate and the environmental performance of the aluminium electrolysis process. This efficiency is proportional to the flow rate of the released gases at the chimney. Since December 2009, the normal flow rate has being decreasing and fluctuating in the Alucam smelting factory. At the Analysis step of the DMAIC methodology, the fundamental causes of the variations and the decrease in the gas normal fume flow rate were identified in a previous study. We intend here to stabilize the flow rate, to Improve the efficiency and to put into place a reliable mechanism of Control in order to maintain target variables within Six Sigma limits. Therefore, we propose an appropriate model of the pipeline network which permits us to identify the causes of the process low capability by excluding the interpretation controversy of the relation between the stopping of pots and the decrease in the fume collection and treatment installation. Then, we choose to achieve the modulation of the suction fan to adapt to changes in system load, and the replacement of the fan impeller to reach the continuous regulation of the flow rate. Benefits cannot be over emphasized because the company may improve on its collection and treatment efficiency, hence an effective reduction of dangerous gaseous fluoride emissions.

One of the key issues in the development of the modern duplex stainless steels was the introduction of nitrogen as an alloying element. This was made possible by e.g. the AOD process and has meant that the problems with earlier grades regarding weldability could be solved. The prime reason for the lower weldability, namely a coarse-grained heat affected zone with inferior properties was then removed. Further beneficial effects of nitrogen increases in the new generation of duplex grades were pointed out: localized corrosion resistance particularly in chloride containing solutions, enhancement of fatigue properties, improved creep properties particularly when considering heat treatment...The paper will outline the influence of nitrogen additions in duplex grades by means of thermodynamic calculations including phase diagrams, TTT phase precipitation diagrams from metallographic investigations, mechanical and corrosion properties. Metallographic investigations, corrosion resistance properties and mechanical properties will be presented. The specific links between welded joints microstructures and properties with different nitrogen contents will be discussed.

Le but est d’innover dans le domaine des liaisons au sol en remplaçant une traverse d’un essieu arrière en acier à haute limite élastique par une traverse en matériaux composites : Fibre de verre et Epoxy; tout en conservant les mêmes fonctions qui sont : assurer une rigidité de torsion, lier et maintenir en position les bras de suspension, résister aux sollicitations mécaniques du cahier des charges (nid de poule, choc trottoir, ...), reprendre les points de fixation du bras de suspension. Cette étude tient compte de la problématique de la grande série : minimiser le nombre de pièces, géométrie simple, procédé de fabrication simple avec des cadences élevées, facilité de montage. La démarche employée est la suivante : étape de présélection et intégration des profilés dans le modèle numérique, choix de l’empilement du composite et optimisation, choix d’une solution, conception des interfaces, réalisation d’un prototype. Le gain de masse est significatif puisque la traverse composite avec fixation ne pèse que 3,9 kg à comparer avec les 12,4 kg de la traverse initiale.

In this paper, based on the practice of manganese production in China, a preliminary life cycle assessment (LCA) of the electrolytic manganese industry is provided, and an analysis of its environmental impact is carried out. A comparison is made between China and South Africa. By comparison, it can be seen that the environmental impact of the manganese production industry in China is more serious. New process technology can be expected to save energy and clean up production.

La puissance débitée par les systèmes solaires ne cesse d’augmenter, soit par l’amélioration du rendement de conversion, soit par la multiplication des techniques de fabrication des photopiles solaires. Devant l’offre de fortes sources d’énergies conventionnelles à des prix relativement bas, l’utilisation du silicium polycristallin aboutit aux cellules polycristallines à faible coût de production. Cependant, les paramètres photovoltaïques de ce type de cellules sont affectés par l’existence des joints de grains et la ségrégation des impuretés à leurs niveaux. Ceci nous a ammené à nous intéresser dans le cadre de ce travail à l’influence des traitements thermiques sur le comportement électrique des couches de silicium polycristallin destinées à des applications photovoltaïques. Les résultats obtenus ont montré que les couches dopées arsenic sont plus résistives que celles dopées bore, et que les traitements thermiques réduisent le nombre de porteurs piégés et la quantité d’atomes de dopant aux joints de grains. D’autre part, cette étude nous a permis de constater que l’élévation de la température des traitements thermiques favorise l’augmentation de la conductivité électrique. De plus, la conductivité électrique dans des couches dopées bore est plus élevée que celle dans des couches dopées arsenic.

Au cours du 19e siècle les gisements des métaux du groupe du platine en Russie ont été les gisements de type placers de platine de l’Oural. Ils furent entièrement exploités au milieu du XXe siècle À l’heure actuelle on doit considérer les dunites et les chromitites de l’Oural comme des matières premières prometteuses de platine [1]. Dans la classification moderne les gisements des métaux du groupe du platine de l’Oural sont classés «non conventionnels» et sont considérés comme des gisements potentiellement prometteurs selon d’éminents chercheurs de la ceinture de Platine de l’Oural, N.K. Vysotsky et A.N. Zavaritsky (G.V. Petrov, T.N. Greyver, V.G. Lazarenko, L’état actuel et les perspectives technologiques de production des métaux de platine à partir de minerai de chromite, Saint-Pétersbourg, 2001 [2]). Aujourd’hui les dunites sont entièrement utilisées comme matières premières pour la production des matériaux réfractaires Les métaux du groupe du platine (MGP) ne sont pas extraits. C’est pour cela qu’il a été entrepris d’examiner dans le cadre de notre étude, les particularités techniques de différents types de dunites (minerais autochtone, alluvial et éluvial), pour contribuer au mieux à l’amélioration des connaissances sur la technologie d’extraction des M.G.P. et du chrome des dunites [3].

Since contradictory data can be found in the literature, it is often difficult to assess the susceptibility of crevice corrosion of stainless steels in service conditions for a given marine application. The initiation and propagation of crevice corrosion in natural seawater were evaluated for five different duplex stainless steel grades together with some austenitic grades. A CREVCORR-type assembly was used to simulate crevice configurations involving the use of plastic crevice formers. The standard pressure applied on the crevice assembly was 3 N/mm2. Pressure of about 20 N/mm2 was also applied on some selected specimens in order to assess the effect of crevice geometry on crevice corrosion. The effect of environmental parameters (i.e. temperature, flowing conditions, residual chlorine, and dissolved oxygen content) and of surface roughness on the crevice corrosion initiation and propagation were investigated, allowing the assessment of limits of applications for some tested stainless steel grades. The less alloyed duplex stainless steels were evaluated in stagnant seawater at 5 °C and 20 °C. The duplex stainless steel UNS S32205, with PREN = 37, was also evaluated under the same conditions of exposure. The high alloyed stainless steels with PREN above 40 were evaluated in the expected most severe conditions of exposure, namely in 0.5 ppm-chlorinated seawater at 20 °C, in seawater at 30 °C (not chlorinated and with 0.5 ppm of residual chlorine) and in seawater at 50 °C (not chlorinated and with 0.5 ppm of residual chlorine). As expected the less alloyed duplex stainless steels showed limited crevice corrosion resistance in the tested media while UNS S32205 showed better resistance in the less severe tested condition of exposure. In demanding media it was shown that the limits of application of highly alloyed stainless steels are highly dependent on the crevice geometry (i.e. specimen roughness and applied pressure at gasket location).

Physical model experiments were performed to clarify the influence of orifice configuration on the volumetric mass transfer coefficient during ladle purging. Bubble behavior was recorded by a high speed video camera in the present study. And carbon dioxide desorption from an aqueous NaOH solution was used to measure the volumetric mass transfer coefficient. It is found that bubbles for multi-hole orifice are generally smaller than those for 1-hole orifice. However, when the hole distance in the multi-hole orifice is too short to avoid bubble coalescence, large bubbles will be formed. It is shown that there is a decreasing tendency of the volumetric mass transfer coefficient when the hole diameter increases. The volumetric mass transfer coefficient firstly increases with increasing the hole distance and hole number. Thereafter, it remains approximately constant with further increase in the hole distance and hole number.