Untersuchungen zur Verdampfung und Thermodynamik von Perowskiten auf der Basis von LaCrO_3 fuer Hochtemperatur-Brennstoffzellen mit Festelektrolyt (SOFC)

LaCrO_3 based perovskites are generally used as material for the ceramic interconnect of solid oxide fuel cells (SOFC). The stability of the used interconnect materials has to be guaranteed under oxidizing and reducing condition as well as for operating temperatures up to 1000 C in order to render possible operation time periods of more than 40000 h. Knowledge on the vaporization, the thermochemical data, and the phase diagrams belonging to the used perovskites is, therefore, necessary. This knowledge is also necessary for the development of welldefined production processes. Vaporization studies by Knudsen effusion mass spectrometry and phase diagram studies were carried out for the determination of the missing data. Reliable data for the Gibbs energy and entropy of formation were determined for LaCrO_3 for the first time. Contributions to the SrO-Cr_2O_3-La_2O_3 and CaO-Cr_2O_3-La_2O_3 phase diagrams were experimentally determined. Thermodynamic activities resulted for the oxide components at 2000 K in the phases La_1_-_xSr_xCrO_3_-_#delta#, La_1_-_xCa_xCrO_3_-_#delta#, La_0_._8Sr_0_._2_-_xCa_xCrO_3_-_#delta#, and LaCr_1_-_xMg_xO_3_-_#delta#. Gibbs free energies of formation were determined for the first and last mentioned phases as well as for the Ruddlesden-Popper phases (La_3A)Cr_3O_1_0, (La_2A)Cr_2O_7 and (LaA)CrO_4 (A=Sr or Ca) as well as for the spinel phase MgCr_2O_4. Finally, thermochemical computations were carried out in order to determine the chromium vaporization from the metallic interconnect (Cr containing alloy protected from corrosion by a Cr_2O_3 scale) and from the ceramic interconnect (LaCrO_3 and La_0_._8_4Sr_0_._1_6CrO_3_-_#delta#). (orig.)Dissertation submitted by D.H. Peck, 164 refs.Available from TIB Hannover: RA 831(3253) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman