Polystyrene Coating on APTES-Primed Hydroxylated AA2024-T3: Characterization and Failure Mechanism of Corrosion

Round 1

Reviewer 1 Report

In this work, the author utilized aminopropyltriethoxysilane (APTES) as a coupling agent primed on aluminium alloy (APTES) to enhance the adhesion of polystyrene (PS). The capacitance charging-discharging mechanism was proposed for the coating system. In general, this manuscript is in good written and well-organized. Thus, I recommend it can be accepted after dealing with the following issues.

1. Among so many coating materials (e.g., epoxy, polyurethane, …) the reason for using PS as the matrix is not clearly described in the Introduction section. In addition, the textual logic should be re-arranged form the standpoint of corrosion & protection (10.1016/j.corsci.2022.110957 can be referenced); thereafter, diversified coatings can be introduced (especially those for aluminum alloy and other nonferrous metals), in which the superiority of PS can be in detailed described.

2. The mentioned advantages of safe and water-repelling are also featured by other polymeric analogues. As a thermoplastic species, the item "cross-link" may be improper.

3. How is the protection efficacy for Al alloy with the pristine APTES? A number of studies have reported that thin organosilane film affords effective corrosion inhibition effect for metals in aggressive media. The metal substrate with the pristine APTES can be a control group in this study.

4. More detailed morphological resolution should be involved in the discussion on Figures 2 to 4 (10.1016/j.matlet.2023.133979 can be referenced). By such a way, the protective power can be distinguished clearly.

5. A big problem may be presented in EIS data: there seem to be an explicit semi-infinite diffusion at the low-frequency region (Figure 5a-5c). However, the author ignored it in the fitting procedure through equivalent circuit (Figure 6). Please check it and make a proper revision.

6. Are there parallel trials for electrochemical assays? The average values for impedance parameters should be reported. Thereby, errors should be presented in Figure 7.

Author Response

Please find the author's response to the review comments in the uploaded file.  Thank you for your time!

Author Response File: Author Response.pdf

Reviewer 2 Report

This manuscript deals with the preparation of polystyrene coatings on an aluminum alloy with the aim to use APTES as an agent which promotes the compatibility between the polar aluminum ally surface and the apolar polystyrene. Notably, APTES is basically not a suited choice as the amino group of this agent is highly polar and thus not very compatible to the apolar polystyrene. Clearly, a silane with phenyl groups would have been a better choice, and accordingly the value of the study is limited. On the other hand, the characterization of the systems is fine and therefore I think the manuscript might published after major revision as indicated below.

 

p. 1, Introduction, line 1 – 2 (total line 23 – 24): It is said that “the aromatic benzene ring makes polystyrene non-polar (fat-like) and chemically non-reactive”. First, not only the benzene ring renders the polymer apolar but also the hydrocarbon segments of the main chains. Second,  polystyrene is not fat-like at all, its composition is completely different to those of fats. Fats are aliphatic esters based on glycerol. Third, it is not clear what the authors understand by non-reactive in tghe context with benzene groups. In fact, benzene groups undergo many common chemical reactions, such as sulfonation reactions of Friedel-Crafts reactions.

 

p. 1, Introduction, line 5 – 6 (total line 27 – 28): Do the authors refer to the advancing or receding contact angle?

 

p. 1, Introduction, line 9 – 10 (total line 30  – 31): It is said that “the chemically stable benzene rings also make polystyrene barely reactive and safe”. Again, it is not clear what “chemically stable” means in the context of benzene rings, and further it is not clear what the authors mean with “safe”. Why are benzene rings safe?

 

p. 2, line 11 – 13 (total line 55 – 57): References are missing for the statement in the indicated lines.

 

p. 2, 2nd paragraph, line 3 (total line 74): It is said that “silane is a silicon-based compound”. In fact, silanes are not a single compound but a class of silicon-based compounds.

 

p. 2, 2nd paragraph, line 5 (total line 74): The silane referred to in this article contain an organic aminoalkyl group and three organic alkoxy groups, i.e. all groups are organic in nature. Thus it is not clear why the authors refer to “inorganic functional groups in a silane”. There are silanes which contain inorganic groups but hose are not used in this study.

 

p. 3, section 2.1, line 4 (total line 127): To which alcohol do the authors refer to? Ethanol?

 

p. 11, line 5 – 6 (total line 348 – 349): The “Error! Reference source not found” should be corrected.

Author Response

Please find the author's response to the review comments in the uploaded file.  Thank you for your time!

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

The manuscript is proper now.

Reviewer 2 Report

The questions are answered properly and the manuscript has been revised adequately. I recommend its publication without further changes.