Scaling behavior of two Fe- x Cr-5Si alloys under high and low oxygen pressures at 700 °C

Effects of Cr Addition and a Magnetron Sputtered Film on the Oxidation-Sulfidation Behavior of Fe-xCr-5Si Alloys in H2-CO2-H2S Mixture at 800°C

“…The chromium and silicon contents of the bare cast alloy Fe-5Cr-5Si are sufficient to form an externally protective layer of Cr 2 O 3 and SiO 2 at 800 • C in a purely oxidizing atmosphere with the same low oxygen partial pressure as that used in this study, 9 but are not completely sufficient to form this type of scale when sulfur is also present in the atmosphere. However, the deposition of the sputtered film led to the formation of a continuous layer of a mixture of Cr 2 O 3 and SiO 2 at the initial surface of the base alloy, showing that the presence of the coating on the base cast alloy favors the formation of an oxide scale on the base alloy during corrosion.…”

“…7 In particular, the addition of chromium presenting a reactivity intermediate between those of iron and silicon toward both oxygen and sulfur decreases the partial pressures of oxygen and sulfur prevailing at the scale/alloy interface via the formation of chromium oxide and sulfide, resulting in the selective oxidation of silicon since it is believed that the critical content of silicon needed to form the continuous SiO 2 layer is lower in environments with lower oxygen partial pressures. 9 The selective oxidation of silicon results in the formation of a silica layer directly between the base alloy and the outer scale and is responsible for the great decrease of k p , because further scale growth resulting from transport of reactants through the protective SiO 2 layer is negligible. 28 However, the corrosion rate of the previous stage of Fe-5Cr-5Si is very high and is in the same order of magnitude with that of Fe-5Si.…”

“…According to the theory of the third-element effect (TEE), 6,7 the addition of an element with oxygen affinity intermediate between those of iron and silicon could be one of the options. The beneficial effect of TEE on enhancing the oxidation resistance of Fe-Si alloys in both high 8,9 and low 9 oxygen pressures has already been demonstrated. For instance, adding 15 wt% Cr to Fe-1Si (wt%) alloy enhanced the formation of a continuous layer of SiO 2 at the scale/alloy interface during oxidation at 900 • C in Ar-15%O 2 , 8 while the critical silicon content needed for the formation of a SiO 2 layer on Fe-Cr-Si alloys decreases with an increase of the chromium content by exposure to 10 −20 atm O 2 at 800 • C. 9 Although the influence of silicon on the transition from the formation of oxide scales to that of sulfide scales on Fe-Cr-Si alloys in oxidizing-sulfidizing environments has already been studied by Wang et al, 10 the effect of chromium on the selective oxidation of silicon in such alloys in similar atmospheres has not been investigated.…”

The corrosion behavior of a sputtered micrograin film on Fe-5Cr-5Si alloy in H 2 -CO 2 -H 2 S mixture at 700 °C

“…Guo et al [14] have studied the oxidation behavior of the as-cast Fe-5Cr-5Si alloy in H2-CO2 mixture with oxygen partial pressure equal to 10 -20 atm at 700 o C.…”

“…First, we could raise the content of the Cr or Si in the alloy or prepare a coating containing high contents of Cr and Si on the surface of the alloy. For example, Bamba [13] and Guo [14] reported that the addition of Cr to Fe-Si alloy can induce the formation of SiO2 layer in pure oxidizing atmosphere. Second, we also could decrease the grain size of the alloy to improve the outward diffusion of the Cr and Si to achieve the selective oxidation of Si and form the protective scale [11,12].…”