Alloys protected from corrosion by a chromia scale and LaCrO3-based perovskites are used as materials for the interconnect of solid oxide fuel cells (S0FCs). The chromium vaporization of these materials was studied by thermochemical modeling. Partial pressures of the vaporizing species were determined for different 02 and 1120 concentrations in the oxidizing gas. Cr02(OH)2(g) and Cr03(g) are the most abundant species in air with and without humidity, respectively. The potential of the Cr-containing vapor species for the degradation of the electrical properties of an SOFC was analyzed by thermodynamic computations. The electrochemical reduction of the Cr-containing vapor species at the cathode/electrolyte/gas phase boundary can lead to polarization losses.

The alloys Cr5Fe1Y 2 O 3 and the ferritic steel Crofer22APU are typical alloys used as solid oxide fuel cell ͑SOFC͒ interconnect materials. Alloy Cr5Fe1Y 2 O 3 is an oxide dispersion strengthened ͑ODS͒ alloy developed by Plansee, Reutte, Austria, for use at high temperature. A typical material for medium-temperature SOFC, is the high chromium ferritic steel Crofer22APU supplied by Thyssen Krupp VDM, Germany. The two alloys form different oxide scales which affect chromium poisoning. Chromium vaporization as source term and electrochemical degradation of La 1−x Sr x MnO 3 ͑LSM͒ and La 0.58 Sr 0.4 Co 0.2 Fe 0.8 O 3 ͑LSCF͒ describing the poisoning were studied for the two alloys. The dynamics of the chromium deposition in porous perovskite cathodes was studied by a dc method and impedance spectroscopy. Electrical degradation of the LSM cathode by alloy Cr5Fe1Y 2 O 3 was significantly higher than for Crofer22APU. The microstructure of the cells was studied after measurements by scanning and energy filtering transmission electron microscopy. Significant amounts of chromium were observed at the TPB in the functional layer of cells, with the LSM cathode giving insight into the degradation mechanism. Cells tested with the LSCF cathode clearly show Cr poisoning. Formation of large SrCrO 4 crystals was observed on the surface of the LSCF cathode.

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The vaporization of chromium species from chromia scales limits the applicability of chromia-forming steels at high temperatures and is one of the major reasons for degradation in the development of planar solid oxide fuel cells ͑SOFCs͒. Cr͑VI͒ vaporized from the interconnector is reduced at the cathode and deposits in the form of solid Cr͑III͒-oxide, thereby inhibiting the electrochemical processes. This work presents the first systematic study on the Cr vaporization of Cr-, Fe-, Ni-, and Co-based alloys in air and in H 2 atmospheres at high temperatures. The influence of outer oxide layers of ͑Cr,Mn͒ 3 O 4 , ͑Fe,Cr͒ 3 O 4 , Co 3 O 4 , TiO 2 , and Al 2 O 3 on the Cr vaporization is investigated. It is shown that the Cr vaporization of chromia-forming steels can be reduced by more than 90% by alloying. An estimate of the expected degradation effects on planar SOFC designs for the use of uncoated interconnector materials is used to show that in order to achieve the desired lifetimes for SOFC systems, additional Cr-retention coatings are necessary. Additionally, equilibrium vaporization measurements are carried out for pure Cr 2 O 3 ͑s͒ in humid air in order to elucidate controversies in the literature concerning the thermodynamic data of CrO 2 ͑OH͒ 2 ͑g͒.

Vaporization is an important property in materials research since it limits the use of the materials at high temperatures and since valuable thermodynamic data can be determined from vapour pressures. High-temperature mass spectrometry is the most versatile method for the elucidation of vaporization processes. Numerous results have been obtained. This article describes the fundamentals of the method and gives examples of its application. These examples describe the determination of thermodynamic properties for the gaseous species and condensed phases. The materials considered are salts, alloys and graphitic materials. They are of interest for metal halide lamps, superalloys, and nuclear reactors.All materials vaporize if the temperature is sufficiently high. The vaporization of materials generally limits their use. Ceramic materials, for example, often decompose at high temperatures by incongruent vaporization. On the other hand, thermodynamic data of the condensed phase can be obtained from the partial pressures of the evaporating species. The vapour pressure methods are standard for the determination of thermodynamic properties in addition to calorimetry and the galvanic cell methods. It follows from the aforementioned that vaporization is an important property in materials research.High-temperature mass spectrometry is the most important method for the analysis of vapours over condensed phases. The first investigation in this field was carried out in 1948 by Ionov.' He showed that the equilibrium vapour over the alkali halides MX(s) essentially consists of the monomer and dimer molecules MX(g) and (MX),(g). In 1953 Chupka and Inghram' as well as Honig3 studied the free vaporization of carbon at very high temperatures and thermochemical properties were evaluated. After this work the hightemperature mass spectrometric method gained wide acceptance and the number of condensed phases studied increased rapidly. Metals, alloys, oxides, sulphides, selenides, tellurides, halogenides, hydroxides, and nitrates were, for example, investigated. Numerous gaseous species were identified and their partial pressures were determined. Thermodynamic data resulted from the partial pressures and their temperature dependences. Most of the vaporization studies were carried out under equilibrium conditions using Knudsen cells.Surveys of recent mass spectrometric investigations on gaseous species and the determination of thermodynamic properties of condensed phases have been given in the review articles by Drowart (1986),4 Gorokhov (1989),5 Hilpert (1989),6 Plante and Hastie (1989),7 and Hilpert (1990.* The special fields of study of ion/ molecule and ion/ion equilibria and the determination of thermodynamic properties for the condensed phase from such data was reviewed in 1986 by Sidorov et al. cles on high-temperature mass spectrometry published before 1986 is given in reference 8.The basis of this article is a lecture given at the Fourth Summer School and Symposium on Mass Spectrometry organized by the Yugoslav Society of Mass Sp...