The thermochemical properties of Y2Si2O7and Dy2Si2O7

Abstract The enthalpy increments of Y 2 Si 2 O 7 and Dy 2 Si 2 O 7 have been measured by drop-calorimetry from T =(516.7 to 928.4) K, and T =(516.7 to 918.2) K, respectively. The standard molar enthalpy of formation of monoclinic Y 2 Si 2 O 7 has been deduced from its enthalpy of solution in (6.20 mol·dm −3 HCl + 0.147 mol·dm −3 HF)(aq), and the value Δ f H m °(298.15 K)=−(3854.8±6.8) kJ·mol −1 has been obtained. For Dy 2 Si 2 O 7 the standard molar enthalpy of formation −(3776.1±4.6) kJ·mol −1 has been estimated.