Thermodynamische Eigenschaften von Halogeniden der Lanthaniden
Gietmann, C. (Corresponding author)
Hilpert, K. / Nickel, Hubertus
Publikationen vor 2000; PRE-2000; Retrocat
Jülich Forschungszentrum Jülich GmbH Zentralbibliothek, Verlag 1997
171 p.
Report
Book
Addenda
Berichte des Forschungszentrums Jülich 3337
OpenAccess
OpenAccess
Please use the identifier: http://hdl.handle.net/2128/21798 in citations.


Rare earth halides are important components in metal halide discharge lamps. Due to the high temperature from 1100 to 6000 K, the press ure up to 30 bar duringoperation and the strong corrosion behaviour of the halides it is difficult to achieve the thermochemical stability of the arc tubes. The stability of the lamps has to beguaranteed to render possible operation time periods of more than 6000 h. For a better understanding of the chemical conditions in the arc tube it is necassary to know the thermochemical properties of the used components and their behaviour of evaporation. Vaprization studies by Knudsen effusion mass spectrometry were carried out for the determination of the thermochemical data. The vaporization of LnBr$_{3}$(s) with Ln = La, Ce, Pr, Nd, Gd, Tb, Er, Tm and HoI$_{3}$(s) was investigated in a temperature range between 750 and 1020 K, HoI$_{3}$ between 773 and 898 K. The equilibrium partial pressures of LnX$_{3}$ and Ln$_{2}$X$_{6}$ were determined. Enthalpies and entropies of sublimation of LnX$_{3}$ and Ln$_{2}$X$_{6}$ as well as enthalpies and entropies of dimerization were evaluated by using the seeond and third law methods. The quasi binary sytem HoBr$_{3}$ - HoI$_{3}$ was investigated in the temperature range between 800 and 1000 K by using the mass spectrometric Knudsen effusion method. The gaseous species HoBr$_{3}$(g), HoI$_{3}$(g), HoBrI$_{2}$(g) and HoBr$_{2}$I(g) as well as Ho$_{2}$Br$_{6}$(g), Ho$_{2}$I$_{6}$(g), Ho$_{2}$Br$_{5}$I(g), Ho$_{2}$Br$_{4}$I$_{2}$(g), Ho$_{2}$Br$_{3}$I$_{3}$(g), Ho$_{2}$Br$_{2}$I$_{4}$(g) and Ho$_{2}$BrI$_{5}$(g) are present in the equilibrium vapour. Gas-phase equilibria of homocomplexes and heterocomplexes in a quasi binary system of halides were determined for the first time. Finally, enthalpies and entropies of different reactions of mixed monomers and dimers were determined.