2015 Volume 55 Issue 12 Pages 2677-2685
This paper provides an answer to the ever-lasting discussion concerning the interpretation of the hydrogen-related peak at 300 to 400°C in hydrogen-detecting Thermal Desorption Spectrum which often appears in a hydrogen-introduced steel sample, particularly which has undergone an outdoor exposure or wet/dry cyclic accelerated-corrosion test and/or by acid immersion. Up to now, the focus of the discussion of the peak has been held with respect to whether the reaction is caused by diffusible hydrogen or not. However, the peak does not correspond either to a typical diffusible hydrogen peak at around 200°C or to a typical non-diffusible peak at over 400°C. Rather, the 300 to 400°C peak in TDS comes from the formation of hydrogen through a rust-related chemical reaction where iron (III) oxide-hydroxide (oxyhydroxide) of goethite “FeOOH” reacts into iron (III) oxide of hematite “Fe2O3”. It should be noted that the origin of FeOOH comes from rust which is too small to detect and which, even if you are sure that the surface is perfectly smooth and cleaned off by hand-polishing, is not removed due to deeply-rooted and small-diameter rust particles, and cannot be detected by the naked eye. In addition, following on from this new interpretation of the controversial spectrum, this phenomenon is re-interpreted as a new process to produce hydrogen gas, and the potentiality and the mechanism are also discussed.