SULPHUR CAPACITIES OF CaO—Na20—Si02 SLAGS

Abstract

Quality raw materials having lower percentage of unwanted elements like sulphur are depleting with time and at the same time development of new special alloys warrants very low sulphur Content. These constraints are sufficient to keep the metallurgists and material scientists engaged in study of behaviour of sulphur in metals, alloys and slags necessary to develop processes to produce quality alloys at econaeical price. Extensive work has been done in past on removal of sulphur during extraction and refining but at the cost of productivity and economy. However, external desulphur-isation has off•late proved to be quite useful process for removal of sulphur in between iron making and steel making stages. Still, substantial work may be done to optimiee the external desulphurization process with regard to the technology and desulphurising agents used to improve the economy of the process. Soda base slags have been established to be very useful for bringing down the sulphur level in the melts. However, they can not be used successfuly during smelting and refining as they attack the refractory lining and give out irritating fumes. In external or ladle desulphurisation use of soda base slags may be made more efficiently because of low temperatures prevalent bringing down the magnitude of slags attack on refractories. However, only a few studies carried iii out on external desulphurization using soda-slags but the data obtained has evoked the need for detailed study on soda-based slags. The present work has, therefore, been taken up to study systematically the soda-silica binary system and the effect of lime additions on the sulphur capacity of soda- silica .slags. Thus, the binary Na20-Si02 and ternary CaO-Na20-Si02 slag systems of varying compositions have been selected for experimental study using gas condensed phase ee;uilibria technique. The slag samples have been ecjpilibrated with a gas phase of known sulphur and oxygen potentials.The sulphur capacities of binary soda-silica slags with varying Na20/Si02 molar ratios, namely, 0.25,0.40, 0.52, 0.84, and 1.03 at temperatures 1373,1423,1473, 1523 and 1573 K have been determined. Effects of lime additions in soda-silica slags of the above mentioned Na20/8i02 ratios on their sulphur capacities at the same temperatures have also been studied. Oxygen and sulphur-di-oxide potentials ranged in between 10-11 to 108 and 0.07 to 0.10 atm. respectively. Oxygen potentials were measured in different gaseous mixtures using a suitably designed oxygen sensor. The entire text of the dissertation has been spread over five chapters. Chapter 1 has been devoted to the brief introduction of the problem and critical review of literature comprising of different technicues used and various systems studied for iv determination of sulphur capacity. Design and fabrication of experimental set-up has been described in detail in Chapter 2. A detailed description has also been given on materials and methods used in the present work. Chapter 3 deals with the experimental results and discussion for the binary Na20-Si02 system. Results of present investigations have been analysed and compared with the existing data on soda-silica slag and other binary silicate systems. In Chapter 4 the experimental results and discussion for the ternary CaO-Na20-Si02 system have been reported. Results of present work are compared with the earlier work on this system and other ternary siliccte systems. In Chapter 5, the experimental results on sulphur capacity of soda base binary and ternary slag systems have been summarized and concluded.