Phase Relations Between Palladium Oxide and the Rare Earth Sesquioxides in Air

The equilibrium phase relations were determined in an air environment between PdO and each of the following: La₂O₃, NH₂O₃, Sm₂O₃, Eu₂O₃, Gd₂O₃, Dy₂O₃, Ho₂O₃, Y₂O₃, Er₂O₃, Tm₂O₃, Yb₂O₃, and Lu₂O₃. In air PdO dissociates to Pd metal at 800 °C. The dissociation of PdO is apparently a reversible process. The Nd₂O₃-PdO and Sm₂O₃-PdO systems were studied in detail inasmuch as they typified several of the Ln₂O₃-PdO systems. Three compounds, 2Nd₂O₃ · PdO, metastable Nd₂O₃ · PdO, Nd₂O₃ 2PdO occur in the Nd₂O₃-PdO system. The 2:1, 1:1, and 1:2 compounds, of unknown symmetry, dissociate or decompose at 1135, 860, and 1085 °C, respectively. The 2:1 compound dissociates to the solid phases, Nd₂O₃ and Pd. No further reactions occur between Nd₂O₃ and Pd up to 1300 °C Three compounds, 2:1, metastable 1:1, and 1:2 occur in the Sm₂O₃-PdO and Eu₂O₃-PdO systems. Two compounds, 2:1 and 1:2 occur in the La₂O₃-PdO system. Other compounds detected were the 1:1 and 1:2 in the Gd₂O₃-PdO system and the metastable 1:1 in the Dy₂O₃-PdO system. Each of these compounds subsequently dissociated upon heating. No apparent reaction occurred between PdO and either Ho₂O₃, Y₂O₃, Er₂O₃, Tm₂O₃, Yb₂O₃, or Lu₂O₃.