Y2O3‒SiO2 SYSTEM DIAGRAM

The deoxidizing ability of yttrium has not been sufficiently studied, although it has a high affinity for oxygen. In ferrous metallurgy, yttrium is often used in the form of an alloy with silicon. The effect of each of the components of the silicoyttrium alloy on the process of liquid metal deoxidation can be established by studying the Fe‒Y‒Si‒O system. The composition of the formed non-metallic inclusions in steel in this case is mainly determined by the type of oxide state diagrams of the Y2O3‒SiO2 and FeO‒Y2O3‒SiO2 systems associated with the region of existence of metallic melts. In this work, using the method of thermodynamic modeling of phase equilibrium in oxide system state diagrams and the theory of subregular ionic solutions, we analyze and calculate liquidus lines in the Y2O3‒SiO2 oxide system. A diagram of the state of this system was constructed. According to the thermodynamic analysis, the most stable in the system are three compounds ‒ oxy- Y2O3·SiO2 and yttrium orthosilicate 2Y2O3·3SiO2 (congruent melting, 1979 and 1915 °C, respectively), as well as yttrium pyrosilicate Y2O3·2SiO2 (incongruent melting), which is consistent with the literature data. In the course of the work, the enthalpies and entropies of formation of these yttrium silicates from the components of the oxide melt, as well as the melting constants of these compounds, were obtained. The area of delamination borders on the field of cristobalite at 1668 °C in the concentration range 0.593‒0.980 (ionic fraction of SiO2) or 74.5‒99.0 % (mol.) SiO2. The values of the enthalpy and entropy of yttrium silicates obtained in this work allow us to proceed to the next stage of the study – modeling the state diagram of the ternary oxide system FeO‒Y2O3‒SiO2, which is necessary to consider the interaction of yttrium and silicon with oxygen in liquid iron.