Abstract
X-ray diffraction (XRD), electron probe microanalysis (EPMA), and scanning transmission electron microscopy (STEM) with focused ion beam (FIB) lift-out sample preparation techniques were used to study corrosion products in a 304L (UNS30403) stainless steel fluidized-bed reactor segment from Iowa State University's Pyrolysis Process Development Unit Facility (PPDU). This reactor segment is particularly valuable because a detailed history of operation time, temperature, and biomass feedstock was available. As previously reported for a range of stainless steel pyrolysis-related equipment, external scaling and internal attack along alloy grain boundaries were observed. The scaling was primarily associated with O, although S, Ca, K, Si, Mg, and P were also detected in the outer scale regions. However, unlike other recent advanced characterization analyses we have conducted, in this instance the internal alloy grain boundary attack was not directly related to S. Rather, only internal oxidation and localized nanoporosity were observed along the alloy grain boundaries, with associated local nanoscale Cr depletion and Ni enrichment. Mechanistic implications of this finding are discussed.
