Zum thermochemischen Verhalten von Halogeniden, Oxidhalogeniden, Aluminiumhalogeniden und Ammoniumhalogeniden der Seltenerdelemente

Knudsen effusion mass spectrometric determination of the complex vapor composition of samarium, europium, and ytterbium bromides

RATIONALE

The vaporization of Sm, Eu, and Yb tri- and dibromides is accompanied by decomposition and disproportionation reactions. These result in complex vapor compositions whose analysis is an intricate problem for experimentalists. Approaches have been developed to interpret mass spectra and accurately determine the vapor composition of thermally unstable compounds.

METHODS

A sector type magnet instrument was used. A combined ion source allowed the study of both the molecular and ionic vapor compositions in the electron ionization (EI) and the thermionic emission (TE) modes. The methodological approaches were based on a joint analysis of the ionization efficiency functions, the temperature and time dependences of the ion currents, and special mathematical data evaluation.

RESULTS

The vaporization of SmBr3 , YbBr3 , SmBr2 , EuBr2 , and YbBr2 was studied in the temperature range of 850-1300 K. An initial stage of incongruent vaporization was observed in the case of the tribromides, SmBr2 , and YbBr2 . This eventually changed to a congruent vaporization stage. Various neutral (Ln, Br, Br2 , LnBr, LnBr2 , LnBr3 , Ln2 Br4 , Ln2 Br5 , and Ln2 Br6 ) and charged (Br(-), LnBr3 (-), LnBr4 (-)) species were detected at different vaporization stages.

CONCLUSIONS

The quantitative vapor composition of Sm, Eu, and Yb tri- and dibromides was determined. It was found that only EuBr2 was stable in the studied temperature range. The developed approaches can be useful in the case of other thermally unstable compounds.

Systematics and anomalies in rare earth/aluminum bromide vapor complexes: thermodynamic properties of the vapor complexes LnAl3Br12 from Ln = Sc to Ln = Lu

Systematics and anomalies in the rare earth/aluminum bromide vapor complexes have been investigated by the phase equilibrium-quenching experiments. The measurements suggest that the LnAl3Br12 complexes are the predominant vapor complexes for the 16 rare earth elements Ln = Sc, Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu in the temperature range 601-833 K and pressure range 0.01-0.22 MPa, which is different from the rare earth/aluminum chloride systems, where the predominant vapor complexes are LnAl3Cl12 from Ln = La to Ln = Lu, but LnAl2Cl9 for Ln = Sc and Y are roughly in the same ranges, which indicates the importance of the halogen anion radius on the rare earth vapor complex formation. In the temperature and pressure ranges, gaseous Al2Br6 and AlBr3 are dominant species and the molar fraction of LnAl3Br12 is normally less than 0.01. Thermodynamic functions of the reactions LnBr3(s) + (3/2)Al2Br6(g) = LnAl3Br12(g) were calculated from the measurements for the 16 rare earth elements and then smoothly interpolated for the radioelement Ln = Pm. The standard molar enthalpies and standard molar entropies show significant Gd divergences from LaAl3Br12 to LuAl3Br12 when plotted as functions of the rare earth atomic number. They also suggest nearly linear manner for ScAl3Br12, LuAl3Br12, YAl3Br12, and LaAl3Br12 when plotted as functions of the rare earth ionic radius.