Determination of the Thermodynamic Properties of Rare Earth-Oxygen-Sulfur Systems at High Temperatures

Abstract

<p>The thermodynamics of rare earth-oxygen-sulfur systems was studied at high temperatures using the following four types of oxygen concentration cells.</p> <p>Type I Cells:</p> <p>[equation removed]</p> <p>Type II Cells:</p> <p>[equation removed]</p> <p>Type III Cells:</p> <p>[equation removed]</p> <p>Type IV Cells:</p> <p>[equation removed]</p> <p>Type I and II cells were used to yield the standard free energy changes corresponding to the reaction</p> <p>[equation removed]</p> <p>at two different sulfur partial pressures. Type III cells were used to determine the standard free energy changes for the reaction.</p> <p>[equation removed]</p> <p>Type IV cells were used to determine the standard free energy changes for the reaction</p> <p>[equation removed]</p> <p>Combining the experimental results for the above three-reactions with the values of ΔGfº for Cu₂S and Ag₂S, the standard free energies of formation of La₂O₂SO₄, Pr₂O₂SO₄, Nd₂O₂SO₄, Sm₂O₂SO₄, Eu₂O₂SO₄, Gd₂O₂SO₄, La₂O₂S, Pr₂O₂S, Nd₂O₂S, Sm₂O₂,S, Eu₂O₂S, Gd₂O₂S, Y₂O₂S and Ce₂O₂S were determined at high temperatures. In addition, the standard free energy changes for oxidation of Tb₂O₂S and Dy₂O₂S to Tb₂O₂SO₄ and Dy₂O₂SO₄ were determined.</p> <p>The above data were used to construct the phase stability diagrams for the rare earth-oxygen-sulfur systems at high temperatures.</p>