Thermogravimetric study of reduction and sulfurization of Y₂(SO₄)₃ using carbon disulfide

The reaction of Y₂(SO₄)₃ with CS₂ was studied using thermogravimetry. Anhydrous yttrium sulfate Y₂(SO₄)₃ first decomposes to Y₂O₂SO₄ at temperatures which depend upon the heating rate, namely 550-650°C at 1 K min^-1 and 550-750°C at 5 K min^-1. With increasing temperature, Y₂O₂SO₄ is further deoxidized to Y₂O₂S, and in this step the heating rate exerts a larger effect than in the first step. This reaction is complete at 700 and 875°C at heating rates of 1 and 5 K min^-1, respectively. The last step involves the reaction of Y₂O₂S to form δ-Y₂S₃. Single phase Y₂S₃ was formed at ≈ 950°C when the heating rate was as low as 1 K min^-1. When the heating rate was increased to 5 K min^-1, a small amount of unreacted Y₂O₂S was found in the Y₂S₃ product. The compound YS_{2 - x}, which was determined as YS_1.85, was stable below ≈ 600°C and decomposed to Y₂S₃ at higher temperatures. The difference of the present reaction from the reaction of Nd₂(SO₄)₃ with CS₂ lies mainly in the decomposition of sulfate to oxysulfate and the sulfurization of oxysulfide to sesquisulfide.