Fundamental Study on the Phase Diagram of SnO-SiO2 System.

In the pyrometallurgical treatment of tin, it is necessary to identify the proper chemical composition of slag based on the thermodynamic behavior and phase diagram for decreasing of tin losses with effective recovery of tin from slag. Although some studies were reported about the phase diagram of SnO-SiO2 binary system, which is basic system of slag in the tin smelting, those results show always disagreement. W hereas it is necessary to consider closely the stability of solid SnO with increasing in temperature when the specimen contains SnO component, because solid SnO decomposes easily by a disproportionation with increasing in temperature.In the present study, firstly, the disproportionation of solid SnO with increasing in temperature was examined, and then the liquidus of SnO-SiO2 binary system was also investigated by SnO or SiO2 saturation method.Furthermore the influence of CaO and FeO addition on the liquidus in SnO-SiO2 system was investigated. The results obtained were summarized as follows:Solid SnO decomposed with increasing in temperature in the following manner: SnO→Sn, SnO, Sn3O4→Sn, Sn3O4→Sn, Sn3O4, SnO2→Sn, SnO2.It was confirmed that the phase diagram of SnO-SiO2 system is an eutectic type and the rising of liquidus at SiO2 side is very sharp. And it was thought to be appropriate that a metasilicate phase, such as SnO·SiO2is existed in this system, and it seemed metastably intermediate product.The melting point of SnO-SiO2 system raised by CaO addition, while it lowered by FeO addition.