Vapor Composition and Thermodynamic Characteristics of Gaseous Molecules of Alkaline Earth Metal Tungstates

Calculated and experimental mass spectra of gaseous tungstates of alkaline earth metals MgWO 4(g) , CaWO 4(g) , SrWO 4(g) , and BaWO 4(g) in the temperature range from 1600 to 2000 K are presented. The partial vapor pressures are determined and equations are derived for the temperature dependences of the partial pressures of gaseous molecules of alkaline earth metal tungstates for liquids in the following form ( P , atm): On the basis of experimental data on vapor pressure, the enthalpies of evaporation ( ), formation ( ), and atomization ( ) of gaseous tungstates of alkaline earth metals are calculated, which, respectively, amount to (Δ H 0 , kJ/mol) 652, 890, and 2855 for MgWO 4 ; 644, 974, and 2968 for CaWO 4 ; 615, 1045, and 3056 for SrWO 4 ; and 548, 1045, and 3095 for BaWO 4 . It is determined that the enthalpy of sublimation of alkaline earth metal tungstates decreases from magnesium to barium.