Investigation of Chromium Volatilization from FeCr Interconnects by a Denuder Technique

Abstract

A technique is presented for accurate and time-resolved quantification of chromium volatilization from alloys at high temperature. A denuder tube which is coated with Na2CO3 is placed downstream of the samples. CrO2(OH)(2) that evaporated from the samples is collected on the denuder and converted to the thermally stable Na2CrO4. The chromate is then dissolved in water and determined quantitatively. Three commercially available ferritic 22% Cr steels intended for use as solid oxide fuel cell interconnect materials (Sanergy HT, Crofer 22 APU, and ZMG 232) have been investigated with respect to chromium volatilization and oxidation rate. The effect on chromium volatilization of a submicrometer cobalt coating on the steel surface is reported. Comparisons are made with a conventional thick ceramic coating. The experiments are carried out at 850 degrees C in N-2 - 20% O-2 - 3% H2O atmosphere. The submicrometer Co coatings proved to be very efficient, reducing Cr volatilization by 1 order of magnitude. Microscopic studies show that both uncoated steel and steel coated with a submicrometer cobalt film develop two-layered oxide scales with the bottom part consisting of a Cr-rich corundum-type oxide. The uncoated samples develop a top layer consisting of (Cr, Mn)(3)O-4 oxide, whereas the Co-coated samples exhibit a top layer consisting of Co-rich spinel oxide. (C) 2010 The Electrochemical Society. [DOI: 10.1149/1.3462987] All rights reserved

Long term study of Cr evaporation and high temperature corrosion behaviour of Co coated ferritic steel for solid oxide fuel cell interconnects

“…It is important to note that the samples were cut after the coating was applied, thus the edges are uncoated (this is discussed in more detail in Ref. [29]. Before exposure the samples were degreased and cleaned, both in acetone and ethanol, using an ultrasonic bath.…”

“…A more detailed description can be found in Ref. [29]. The only differences between isothermal and discontinuous exposures were that in the latter case the samples were taken out for weighing and that the denuder tube was omitted.…”

“…This further requires disassembling the whole setup, with the consequence that only discontinuous measurements are possible and the time-resolution is limited. In the present study a denuder technique that was recently developed at Chalmers University of Technology has been employed [29]. This technique relies on a Na 2 CO 3 getter which collects the gaseous Cr species at high temperature using a denuder tube.…”

Coated stainless steel 441 as interconnect material for solid oxide fuel cells: Evolution of electrical properties

“…The air flow was set to a value of 6 l/min, which is equal to 27 cm/s and which was proven in previous works to be in the flow independent regime of chromium evaporation [12]. Details on the exposure setup can be found in Ref.…”

“…This is known as cathode poisoning and is another detrimental factor for the fuel cell performance [10,11]. A relatively new technique for chromium evaporation measurement was developed at Chalmers University of Technology and allows the time-resolved quantification of evaporated chromium for different samples [12].…”