Volatilization kinetics of chromium oxide, manganese oxide, and manganese chromium spinel at high temperatures in environments containing water vapor

Abstract

Performance degradation of solid oxide fuel cells due to chromium volatilization is a well‐investigated issue in the literature. Therefore, retention coatings were developed to distinctly reduce the chromium volatilization. One approach was by alloying with manganese to ferritic steels to form manganese chromium spinel which is reported to decrease chromium volatilization by 61–75%. In the present paper, the volatilization rates of pure manganese chromium spinel ceramics were examined as well as those of the two oxides forming this spinel—pure chromium oxide and pure manganese oxide—in synthetic air containing 10% water vapor (high p(O2)) and argon/hydrogen containing 10% water vapor (low p(O2)) at 850°C, 950°C, and 1,050°C. Chromium oxide showed higher volatilization rates in high p(O2), whereas manganese oxide demonstrated higher volatilization rates in low p(O2). Contradictory to the literature, manganese chromium spinel displayed the highest volatilization rates in both atmospheres and nonlinear kinetics behavior. This deviation from linear behavior can be attributed to diffusion‐controlled volatilization in high p(O2).

Anticoking Performance of Electrodeposited Mn/MnO Surface Coating on Fe–Ni–Cr Alloy during Steam Cracking

“…72−75 The degree of nonstoichiometry (δ) typically increases with temperature and oxygen partial pressure. 76 The Frenkel-and Schottky-type defects that occur in the MnO crystal structure create cation/anion vacancies that are balanced by the oxidation of some Mn 2+ species to Mn 3+ . 64,75 During coking with ethylene-steam, we hypothesize that these vacancies result in more active Mn 3+ sites that can reduce and release oxygen to gasify coke and/or coke precursors on the surface.…”

“…In our previous work, we have deposited coke onto a MnO powder catalyst and shown that it has considerably higher coke gasification activity (under steam and steam-H 2 mixtures) compared to a Cr 2 O 3 powder catalyst . Several studies have shown that MnO is a metal-deficient oxide with varying degrees of nonstoichiometry: Mn 1−δ O, where 0 < δ < 0.15. − The degree of nonstoichiometry (δ) typically increases with temperature and oxygen partial pressure . The Frenkel- and Schottky-type defects that occur in the MnO crystal structure create cation/anion vacancies that are balanced by the oxidation of some Mn 2+ species to Mn 3+ . , During coking with ethylene-steam, we hypothesize that these vacancies result in more active Mn 3+ sites that can reduce and release oxygen to gasify coke and/or coke precursors on the surface.…”

High-Temperature Oxidation in Dry and Humid Atmospheres of the Equiatomic CrMnFeCoNi and CrCoNi High- and Medium-Entropy Alloys

“…The Cr 2 O 3 layer is not dense and H 2 O continues to react with Cr 2 O 3 . Especially in mixed gas environments (for instance O 2 + H 2 O), it is known that the reaction of Cr 2 O 3 with O 2 and H 2 O leads to further volatilization of chromia by the formation of CrO 2 (OH) 2 according to reaction IX [31,33,57] The volatilization rate is also reported to be enhanced when the chromia layer is porous [58]. However, in the low-p O2 humid atmosphere, it was reported for Fe10Cr and Fe20Cr exposed to Ar-7% H 2 O at 900 °C for 72 h that the formation of volatile Cr-oxy-hydroxide is not the main reason for the suppression of a protective chromia scale growth [31].…”

Effect of B-Site Order–Disorder in the Structure and Magnetism of the New Perovskite Family La2MnB′O6 with B′ = Ti, Zr, and Hf

“…Reaction with the crucible is thoroughly informed for CoO (crucibles turn blue, which is the color of the Co doped alumina); however, we did not observe changes in the color of the alumina crucible after the reaction. On the other hand, MnO has been shown to be volatile between 850 and 1050 °C . It is sensible to think that volatilization increases with temperature and therefore at 1350 °C MnO might volatilize.…”

“…On the other hand, MnO has been shown to be volatile between 850 and 1050 °C. 21 It is sensible to think that volatilization increases with temperature and therefore at 1350 °C MnO might volatilize.…”