The high temperature vaporization and thermodynamics in the lutetiumndash;sulfur system

摘要

The high temperature vaporizations of Lu3S4and nonstoichiometric LuSx(0.75x1.30) compositions in the lutetiumndash;sulfur system were investigated by mass spectrometric and target collection Knudsen effusion techniques. Lu3S4vaporizes congruently according to: (1) LuS1.33(s) =Lu(g)+1.33S(g) and (2) LuS1.33(s) =LuS(g)+0.33S(g). The equilibrium partial pressures are: logPLu(atm) = minus;(29162plusmn;239)/T+(7.117plusmn;0.112); logPS(atm) =minus;(29513plusmn;338)/T+ (7.104plusmn;0.159); and logPLuS(atm) =minus;(31366plusmn;675)/T+(8.052plusmn;0.317). The secondhyphen;law thermodynamic values are: Reaction (1) Dgr;Hdeg;298= 317.6plusmn;2.5 kcal molminus;1; Dgr;Sdeg;298=79.6plusmn;1.5 eu; Reaction (2) Dgr;Hdeg;298=196.9plusmn;3.3 kcal molminus;1; Dgr;Sdeg;298=55.9plusmn;1.8 eu; and for LuS1.33(s), Dgr;Hdeg;f,298=minus;126.5plusmn;2.5 kcal molminus;1;Sdeg;298= 18.0plusmn;1.5 eu. The dissociation energy of LuS(g) is computed asDdeg;0= 120.6plusmn;3.2 kcal molminus;1from the mass spectrometric slopes for logI+LuTand logI+LuSTvs 1/T, and with an iterated slope for logI+STconsistent with the congruency of the vaporization reactions. The activity of Lu across the homogeneity range of the monosulfide was measured. Together with the Gibbsndash;Duhem derived values for the activity of sulfur, the thermodynamic properties of stoichiometric LuS1.0were calculated. These are: (in kcal molminus;1) Dgr;Hdeg;atom,298=268.5plusmn;3.0; Dgr;Hdeg;subl,298= 147.7plusmn;3.0; and Dgr;Hdeg;f,298=minus;99.6plusmn;3.1.