Kinetcis of silicothermic reduction of clacined dolomite in flowing argon atmosphere
The magnesium vapour extracted is removed using vacuum condition to condense as a dense metal. Thermodynamic analysis of this process has been carried out in the past to predict the distribution of the metal impurities in condensed magnesium. The results suggested that a number of impurities in different phases formed in the region between reaction zone and condenser. The thermodynamic results only are not sufficient to describe the process, and the knowledge of the kinetics of the Pidgeon process is required. Kinetics plays important role to give more insight to the process such as for process design and control.
Silicothermic Reduction of Dolomite Ore Under Inert Atmosphere
Abstract Magnesium metal was produced from dolomite ore under inert atmosphere using ferrosilicon as a reducing agent. The kinetics of the silicothermic reduction process was studied at a temperature range from 1150-1300 °C. The charges studied are in the form of briquettes. The parameters studied are silicon stoichiometry, temperature and time of preheating, calcium fluoride additive, molar ratios of calcium oxide/magnesium oxide, flow rate of inert gas, briquetting pressure, temperature and time of reduction process. The maximum reduction extent of about 92% was achieved when using charges in the form of briquettes containing 2.5 wt.% CaF2, CaO/MgO molar ratio of 1.6 and using silicon as reductant with its weight ratio/MgO equals 1.45 at 1300 °C for 5 hours. The discussion takes into considerations the type of intermediate compounds formed during the reduction and the mechanism of the silicothermic reduction process. It was found that the silicothermic reduction process of dolomite ore is a solid-state reaction controlled by diffusion of reacted species and the apparent activation energy obtained equals 306 KJ.mol-1. On a produit du magnésium-métal à partir de minerai de dolomite en atmosphère inerte en utilisant du ferrosilicium comme agent de réduction. On a étudié la cinétique du procédé de réduction silico-thermique dans une gamme de température de 1150-1300 °C. Les charges étudiées avaient la forme de briquettes. Les paramètres étudiés incluent la stoechiométrie du silicium, la température et la durée de préchauffage, l’addition de fluorure de calcium, les rapports molaires oxyde de calcium/oxyde de magnésium, le taux d’écoulement du gaz inerte, la pression de mise en briquette, la température et la durée du procédé de réduction. La réduction maximum d’environ 92% a été obtenue lorsqu’on utilisait des charges en forme de briquettes contenant 2.5% en poids de CaF2, avec un rapport molaire CaO/MgO de 1.6 et avec du silicium comme agent de réduction, avec un rapport de son poids/MgO égal à 1.45, à 1300 °C pendant 5 heures. La discussion prends en considération le type de composés intermédiaires formés lors de la réduction et le mécanisme du procédé de réduction silico-thermique. On a trouvé que le procédé de réduction silico-thermique du minerai de dolomite était une réaction à l’état solide contrôlée par la diffusion des espèces ayant réagi; on a obtenu une énergie d’activation apparente égale à 306 kJ.mol-1.
ROOM- AND HIGH-TEMPERATURE MAGNETIC PROPERTIES OF Sm(CobalFexCu0.088Zr0.025)7.5 (x=0.30) SINTERED MAGNETS
The effect of Fe content on room- and high-temperature magnetic properties of Sm(CobalFexCu0.088Zr0.025)7.5 (x=0-0.30) sintered magnets, prepared by the conventional powder metallurgy method, has been systematically studied. With increasing Fe content, the remanences BT and maximum energy products (BH)max at room temperature gradually increase and reach optimal values of 1.055 T with x=0.27 for BT, and 205 kJ/m3 with x=0.21 for (BH)max, respectively, and then drop sharply with further Fe increase. An excessive addition of Fe (x≥0.24) results in rapid deterioration of permanent magnetic properties due to the formation of a considerable amount of FeCo soft magnetic phase. It was found that the effect of Fe content on high temperature stability is huge. The lower the Fe content, the smaller the temperature coefficient of coercivity. When x=0.07, a temperature coefficient of coercivity of -0.14%/K (293-723 K) can be achieved, as compared with -0.23%/K for x=0.21. BT of 0.725 T, bHc of 517 kA/m, iHc of 764 kA/m, and (BH)max of 95 kJ/m3 at 723 K were obtained, and the B-H demagnetization curve remains a straight line.