The Effect of Pre-Treatment on Steel-Topcoat Interface Using Three Complementary Non-Destructive Techniques
Bibliographic record
Abstract
Approximately 3.4% of the global gross domestic product is lost annually due to metal corrosion, which is primarily mitigated by coating techniques. N-heterocyclic carbenes (NHCs), which were discovered in 1991 and are metallophilic organic materials, are applied as surface-functionalizing ligands for a wide range of applications. Recently, NHCs have shown excellent bonding to metal surfaces and can decrease the surface oxide on copper and mild steel [1, 2]. A pre-treatment of a NHC compound ( iPr NHC as in [1]) improved the adhesion between the steel and the epoxy topcoat. However, it is challenging to quantitatively and qualitatively probe the interface of a substrate and topcoat under an intact non-transparent coating. Here, we utilized three complementary non-destructive and electrochemical techniques to probe this interface and the heterogeneity of the extent of corrosion between the steel and the intact epoxy topcoat. First, we utilized synchrotron-based X-ray absorption near edge structures (XANES) spectroscopy to “see through” an up to 60 µm thick epoxy coating and probe the chemical speciation, heterogeneity, and extent of corrosion products in the coating-steel interface. Fe K-edge XANES showed that the NHC pre-treatment reduced the amount of iron oxides and hydroxides, which were several nanometers in thickness, on the cold-rolled steel surface from 11 wt% down to 8 wt% of the total Fe signal. Second, we utilized non-destructive high-voltage electrochemical impedance spectroscopy (ISO 16773) to compare the corrosion resistance of various coatings (with pre-treatments of NHC or without). To accelerate the coating characterization of an intact anticorrosive coating, we also utilized a sequential electrochemical test alternating electrochemical impedance spectroscopy with an applied negative voltage (cathodic disbondment), following ISO 17463. This test was able to quantitatively distinguish different coating candidates with one test taking 24 h, which is significantly shorter than other coating characterization methods. The NHC pretreatment significantly improved the adhesion of automotive epoxy e-coat on cold-rolled steel. Third, we applied scanning Kelvin probe to measure the work function of the e-coated cold-rolled steel with and without NHC pretreatment over up to one week at 85% relative humidity. The coating on top of NHC-pre-treated epoxy showed a significantly different work function, implying a chemical difference at the interface. In all, non-destructive test methods are necessary to develop the next-generation leading coating technology. References: [1] L. Laundry-Mottiar, T. Susuwella, W. Senanayake, M. Turnbull, A. Juneau, E. Kaur, M. Aloisio, T. Selva, J. Henderson, H.-Y. Nie, M. Biesinger, J. Noël, Y. Hedberg, C. Crudden, J. Mauzeroll, N-Heterocyclic Carbene Overlayers on Mild Steel. Chemistry of Materials , 2025, 37, 1, 76–86. [2] J. Selva, Y. Li, J. Kaur, A. Juneau, A. Diraki, S. Bendahmane, J. Henderson, M. Aloisio, A. Messina, A. Nezamzadeh, C. Viasus Pérez, M. Biesinger, A. Levasseur, C. Crudden, J. Mauzeroll. N-Heterocyclic Carbene Deposition on a Copper Powder Surface Using Mechanochemistry. ACS Appl. Mater. Interfaces 2025, 17, 6, 10004–10013. Figure 1
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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 | 0.001 |
| Meta-epidemiology (narrow) | 0.001 | 0.000 |
| Meta-epidemiology (broad) | 0.001 | 0.001 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.001 | 0.000 |
| Open science | 0.001 | 0.000 |
| Research integrity | 0.001 | 0.001 |
| Insufficient payload (model declined to judge) | 0.001 | 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".