Experimental investigations and thermodynamic evaluation of the Sn-Cu-O system

摘要

The SnO_2 -CuO heterostructures are important with respect to sensor application for monitoring the toxic emission in the environment. This study reports experimental investigations by Thermal Analysis measurements up to 1500°C and at different oxygen partial pressures of the Sn -Cu -O system. The commercially available SnO_2 and CuO have been used as starting materials. In air, DTA/TG results evidenced thermal effects exclusively due to the CuO presence. No binary compounds were formed. The reduction process of CuO to Cu_2O over 1000°C as well as the presence of a liquid phase, extending from Cu -O system has been established. In argon atmosphere, the reduction equilibrium is shifted toward 850°C, while the liquid phase appears in the studied mixtures over 1200°C. The formation of an eutectic composition between SnO_2 -Cu_2O, melting at 1216 146L?has been experimentally evidenced. The model of the subregular solution was applied for expressing the behaviour of the liquid phase in SnO_2 -Cu_2O system. Pure liquid oxides were used as standard reference state. We imposed in our calculations a value of the oxygen fugacity for which Cu_2O is the only stable condensed phase from Cu -O system. An eutectic composition rich in copper oxides (i. e. 94% mol. Cu_2O) melting at 1218°C was found according to our calculations.