Y2O3–SiO2 Phase Diagram

Abstract: The deoxidizing ability of yttrium is insufficiently studied in spite of its high affinity to oxygen. In ferrous metallurgy, yttrium is often used in the form of an alloy with silicon. The effect of each of the components of a silica–yttrium alloy on liquid metal deoxidation can be established by studying the Fe–Y–Si–O system. In this case, the composition of the formed nonmetallic inclusions in steel is mainly determined by the type of Y2O3–SiO2 and FeO–Y2O3–SiO2 oxide phase diagrams conjugated with the region of metallic melts. In this work, the liquidus lines in the Y2O3–SiO2 oxide system are analyzed and calculated using thermodynamic modeling of phase equilibria in the phase diagrams of the oxide systems and the theory of subregular ionic solutions. A phase diagram of this system is constructed. According to thermodynamic analysis results, three compounds in the system are the most stable: yttrium oxyorthosilicate Y2O3⋅SiO2, yttrium orthosilicate 2Y2O3⋅3SiO2 (congruent melting, 1979 and 1915°C, respectively), and yttrium pyrosilicate Y2O3⋅2SiO2 (incongruent melting), which is consistent with the published data. 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, are calculated. The immiscibility field borders on the field of cristobalite at 1668°C in a concentration range of 0.593–0.980 (ionic fraction of SiO2) or 74.5–99 mol % SiO2. The determined enthalpy and entropy of yttrium silicates make it possible to start the next stage of the study: modeling of the phase diagram of the ternary FeO–Y2O3–SiO2 oxide system, which is necessary to consider the interaction of yttrium and silicon with oxygen in liquid iron. © 2023, Pleiades Publishing, Ltd.