DFT Analysis of Ethanol Electro-Oxidation on Fe(110) and Fe<sub>3</sub>c(110) and Its Correlation with the Stress Corrosion Cracking of Carbon Steel
Bibliographic record
Abstract
Stress Corrosion Cracking (SCC) of carbon steel in fuel-grade ethanol is typically intergranular in service, but it is nearly always transgranular, in short-term laboratory experiments. While this might be considered an inconvenience, it provides an important clue about the SCC mechanism. The important point is that the transgranular cracking occurs under much milder mechanical conditions than any known form of hydrogen embrittlement in ordinary carbon steel. For this and other reasons, hydrogen is not considered to be the cause of this form of SCC. Transgranular SCC of carbon steel occurs in a very particular set of environments. Anhydrous liquid ammonia, anhydrous ammonia-methanol and CO-CO2-H2O are the key systems to be considered, apart from alcohols. High-temperature water containing oxygen also causes transgranular SCC, but is a less severe environment, probably because a magnetite film imposes a compressive stress that partially opposes any embrittlement effect. In our view, the important factor connecting these examples is embrittlement by interstitials. Just as hydrogen can embrittle iron, so can nitrogen or carbon (or oxygen). The main distinction is the diffusivity of the interstitial in iron. Ammonia can be oxidized to N, and CO can be reduced to C (or, in the language of surface chemistry, this could be dissociative adsorption). Still, at ambient temperature, those interstitials can only diffuse a few nm in relevant times of seconds. But we know little about the effect of such near-surface embrittlement on the propagation of a crack, and research on such surface effects is very important. Striking mechanical and morphological similarities of the SCC of carbon steel in ethanolic media with those governed by a cleavage-like mechanism in CO-CO2 aqueous solutions prompted the investigation of the possibility of ethanol electrochemical oxidation into CO on ferrite (Fe) and cementite (Fe3C) surfaces. Density functional theory computations on (110) surfaces revealed that the catalytic activity of Fe and Fe3C through the α dehydrogenation pathway can significantly reduce the energy barrier of electro-oxidation of ethanol and production of CO to 0.575 and 0.480 eV, respectively. These first principle calculations indicate that at the anodic potentials applied during potentiostatic slow strain rate testing, ethanol electro-oxidation to CO is thermodynamically viable on carbon steel, giving further credit to the involvement of cleavage type SCC of carbon steel in ethanolic environments.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.001 | 0.000 |
| Insufficient payload (model declined to judge) | 0.004 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".