A vaporization study of the Ru–Te binary system by Knudsen effusion mass spectrometry

• Knudsen effusion mass spectrometric study of the Ru–Te binary system conducted for the first time.
• Direct confirmation of incongruent vaporization of RuTe2 – primarily to Te2(g) and to a very small extent to Te(g).
• p–T relations for Te2 and Te (860–1030 K), the relative compositions consistent with those on other M–Te systems.
• Thermodynamic data for the reaction: RuTe2(s) = Ru(s) + 2/i Tei(g) (i = 2 and 1) and for the formation of RuTe2(s).
• The Ru-rich phase boundary of RuTe2(s) close to the stoichiometric value and the Te-rich phase boundary uncertain.

Vaporization studies on some Ru–Te samples with initial compositions 40.0 and 50.5 at.% Te, corresponding to the two-phase field (Ru + RuTe2) and of initial compositions 69.5 and 71.5 at.% Te, corresponding to the two-phase field (RuTe2 + Te) were conducted by Knudsen effusion mass spectrometry. The vaporization was found to be one of incongruent in nature with the vapor phase consisting only of the component tellurium. The partial pressures of Te2(g) and Te(g) were measured over (Ru + RuTe2) in the temperature range of (860–1030) K and the p–T relations were deduced as: Log [p(Te2)/Pa] = [−(14,335 ± 148)/(T/K)] + (14.416 ± 0.154) and Log [p(Te)/Pa] = [−(13,838 ± 218)/(T/K)] + (12.480 ± 0.226). The relative mole fraction of Te(g) was < 0.05. From the partial pressures, the thermodynamic data for the vaporization reactions RuTe2(s) = Ru(s) + 2/i Tei(g) where i = 2 and 1 were deduced and so also were for the formation of RuTe2(s):ΔrHmo(298.15K)/(kJmol-1)=284.3±16.4(i=2)and537.7±24.7(i=1);ΔrSmo(298.15K)/(Jmol-1K-1)=200.2±10.4(i=2)and155.0±4.3(i=1);ΔfHmo(RuTe2,s,298.15K)/(kJmol-1)=-(121.1±16.4);ΔfSmo(RuTe2,s,298.15K)/(Jmol-1K-1)=-(39.8±10.4).The p(Te) and p(Te2) values over this two-phase field are consistent with those previously measured by us over other binary metal-tellurium systems with regard to equilibrium constant for the dissociation reaction Te2(g) = 2 Te(g). The preferential vaporization of tellurium was utilized to make the sample traverse from the (RuTe2 + Te) two-phase field to (Ru + RuTe2) two-phase field via the single phase region of RuTe2 and the evolution of Te2(g) monitored all through. That there is a composition range of existence for the RuTe2 phase and that the Ru-rich boundary composition is close to stoichiometric value became confirmed from these measurements.