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Abstract.A design of and initial results from a Knudsen Effusion Mass Spectrometer (KEMS) are presented. The design was adapted from high temperature alloy studies with a view to using it to measure vapour pressures for low volatility organics. The system uses a temperature controlled cell with an effusive orifice. This produces a molecular beam which is sampled by a quadropole mass spectrometer with electron impact ionization calibrated to a known vapour pressure. We have determined P (298 K) and H sub of the first 5 saturated straight chain dicarboxylic acids: 2.15±1.19×10 −2 Pa and 75±19 KJ mol −1 respectively for oxalic acid, 5.73±1.14×10 −4 Pa and 91±4 KJ mol −1 for Malonic acid, 1.13±0.47×10 −4 Pa and 93±6 KJ mol −1 for Succinic acid, 4.21±1.66×10 −4 Pa and 123±22 KJ mol −1 for Glutaric acid and 6.09±3.85×10 −6 Pa and 125±40 KJ mol −1 for Adipic acid.

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.

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