Abstract
The thermochemical hydrogen generation process has been developed at Japan Atomic Energy Research Institute. This process has a severely corrosive environment, such as sulfuric and hydriodic acids. A silicon-iron alloy with fractional gradient is one of the candidate materials in a boiling sulfuric environment. So, the corrosion resistance and the passive film of Fe-20 mass%Si alloy in boiling sulfuric acids were studied in this work.
The Fe-20 mass%Si alloy was prepared by arc melting of iron (99.9 mass%) and silicon (99.99 mass%). The specimens were ground to a 600 grit finish and rinsed with distilled water and acetone. The specimens were immersed in 50 vol% or 95 vol% sulfuric acids at the boiling temperature (140°C or 320°C) and then weighed to yield a corrosion rate. The passive films on the specimens were evaluated in terms of the appearance, Auger electron spectroscopy (AES) analysis and X-ray photoelectron spectroscopy (XPS) analysis.
The alloy showed good resistance in boiling 50 vol% and 95 vol% sulfuric acids. By AES, the passive film of the specimen exposed 50 vol% sulfuric acid consisted of O and Si. The passive film of the specimen exposed to 95 vol% sulfuric acid consisted of O, Si and S. It seems that S in the passive film of the specimen exposed to 95 vol% sulfuric acid is attributable to the cathodic reduction of sulfuric acid. The growth rate of the passive film of the specimen exposed to 95 vol% sulfuric acid is about 30 times as fast as that of the specimen exposed to 50 vol% sulfuric acid. It is considered that the faster growth rate is attributable to the low density of the film. From the result of XPS, the passive films on the specimens exposed to 50 vol% and 95 vol% sulfuric acids can be described as SiO2 and as a composite of SiO2 and SiO, respectively.
