Influence of Alkyd Composite Coatings with Polyaniline Doped with Different Organic Acids on the Corrosion of Mild Steel
Round 1
Reviewer 1 Report
1. The error bars should be added to the corresponding graphs.
2. In lines 187-192, the authors should optically image all five Composite coatings to complete the work.
3. In the conclusion part, consider simplifying the conclusion and dividing the statement to make the logic clearer.
4. What is the engineering background and significance of the research?
5. How is the electrochemical properties of the composite coatings?
6. Could life span of the coatings be predicted?
English Language should be carefully modified.
Author Response
Dear Reviewer
Many thanks for your useful comments
- The error bars should be added to the corresponding graphs.
The error is very small and is invisible as error bar, so we add: The size of the symbols represents the experimental errors.
- In lines 187-192, the authors should optically image all five Composite coatings to complete the work.
It was done, shown and discussed.
- In the conclusion part, consider simplifying the conclusion and dividing the statement to make the logic clearer.
We bulleted the conclusion and reformulate some parts.
- What is the engineering background and significance of the research?
Nice questions. We add at the end of manuscript:
Before conclusions, we can suggest some possible applications of the results from the present study. As shown now and earlier, among solutions of sodium chloride [21, 40], polyaniline could protect mild steel in different environments, send, and wet air [41]. From the reference [20] it could be concluded that the composite coating in 3% NaCl could offer a minimum of two to three times longer corrosion protection before deterioration, and probably in less aggressive media more longer, especially due to the self-healing proper-ties. Unfortunately, due to the agglomeration of the polyaniline particles, the appearance of the coating is not for the finishing paint. Hence, at the present formulation, investigated composite coatings could be used as a primer paint for robust steel constructions, like bridges, wagons, reservoirs, trucks, industrial machinery, etc. More efforts should be in-vested, to minimize agglomerations of the polyaniline particles, for example by the functionalization of aniline monomer, using water-based paint, and maybe some other approach.
- How is the electrochemical properties of the composite coatings?
There is not electrochemical investigation in the paper, as we clearly stated at few places:
49-51: In our previous paper [20], the PANI composite with alkyd-based paint by different oxidation states doped with organic acids is qualitatively investigated using the linear polarization methods. It is observed that determined polarization resistance decreases with a decrease in the initial oxidation state of the polyaniline.
54-55: So, to extend that work, in this paper, we present results of the quantitatively determined corrosion rate using the ASTM International 1,10-phenanthroline standard test method
219-221: In order to compare the value of the polarization resistance with the determined jcorr, the same Figure 7a shows the data of the reciprocal values of the polarization resistance after 96 hours, extracted from Figure 4a from [20].
- Could life span of the coatings be predicted?
It is answered in point 4.
English language is improved
Reviewer 2 Report
The composite coatings prepared by mixing the 5 wt.% of polyaniline with commercial alkyd-based paint are applied on carbon steel. The polyaniline emeraldine chloride salt is prepared by procedure recommended by IUPAC, deprotonated by ammonia hydroxide, and reprotonated with the sulfamic, succinic, citric, and acetic acids with different doping degrees or oxidation states. The steel samples with base and composite coatings are immersed in 3% NaCl and the corrosion current density is determined after 96 h in-site using ASTM 1,10-phenanthroline method. The samples are also inspected by the optical microscope. It is shown that composite coatings reduce the possibility of blister formations and delamination. The corrosion current density and the appearance of the corrosion products, which area is determined by ImageJ softer, closely follow the initial oxidation state of the polyaniline. The role of the initial state of the polyaniline is discussed. It is suggested that such behavior could be connected with the oxygen reduction reaction mechanism that proceeds mainly via two electron paths on the polyaniline particles, releasing a much smaller amount of hydroxyl ions, responsible for the delamination and blister formations of the commercial coatings.
Author Response
Dear Reviewer
Many thanks for your useful comments
Reviewer 3 Report
The interesting results on the anti-corrosion coatings synthesized by IUPAC guidelines and tested by ASTM International 1,10-phenanthroline standard method (E 394 – 00) are showed in the present article. However, some comments can be made.
a) to verify the main degradation mechanisms, which are described in the Figure 8, the authors should prepare and analyze by SEM the cross section of the corroded samples.
b) the authors should include in the manuscript other corrosion tests, for comparison and validity of the results, such as immersion or electrochemical polarization.
Author Response
Dear Reviewer
Many thanks for your useful comments
The interesting results on the anti-corrosion coatings synthesized by IUPAC guidelines and tested by ASTM International 1,10-phenanthroline standard method (E 394 – 00) are showed in the present article. However, some comments can be made.
- a) to verify the main degradation mechanisms, which are described in the Figure 8, the authors should prepare and analyze by SEM the cross section of the corroded samples.
Dear reviewer that will be an excellent idea, but unfortunately deceased Ayad Salem took the samples to Libia after finishing his Ph.D, and due to the Covid pandemia, and civil war in Libia, we could not see each other, and he passed away last year. To prepare new samples, conduct corrosion tests, and find the available SEM is practically impossible. We are very sorry, so the mechanism is only possible. But we added micrographs of all five samples.
- b) the authors should include in the manuscript other corrosion tests, for comparison and validity of the results, such as immersion or electrochemical polarization.
We extended our manuscript including the corrosion of damaged samples.
There is no electrochemical investigation in the paper, as we clearly stated at few places:
49-51: In our previous paper [20], the PANI composite with alkyd-based paint by different oxidation states doped with organic acids is qualitatively investigated using the linear polarization methods. It is observed that determined polarization resistance decreases with a decrease in the initial oxidation state of the polyaniline.
54-55: So, to extend that work, in this paper, we present results of the quantitatively determined corrosion rate using the ASTM International 1,10-phenanthroline standard test method
219-221: In order to compare the value of the polarization resistance with the determined jcorr, the same Figure 7a shows the data of the reciprocal values of the polarization resistance after 96 hours, extracted from Figure 4a from [20].
Reviewer 4 Report
SI unit convention not followed - space between number and °C for temperature, "hour" is a name, "h" is the SI unit, so ten hours is correct, but 10 hours is not (should be 10 h), minutes is a problematic SI unit and should be avoided; SI convention uses a center dot (·) to separate units (e.g., Ah mol-1 should be A•h•mol-1, line 216. Large dot used for emphasis. Also concentration units on line 113); units are not consistent through the paper - cm3, mL, L, dm3 should be either cm3 and dm3 (note that dm is not an standard SI unit), or mL and L (standard chemical SI units, but not standard SI units); units should not be separated across lines (end of line 113, value appears to be 1 g), NOTE values should also not be separated from the unit across a carrage return.
See attached for specific comments.
Comments for author File: 
Comments.pdf
The document is generally readable, but has many critical statements that are unclear or confusing. A general comment is that the tense used is incorrect. This is a presentation of work performed (past tense) with some hypotheses to explain results (present). It is not a lab procedure to perform work (present or future tense). There are too many tense changes required to fully detail those changes in this comment section. Finally, commas are not generally correctly used, and some are missing.
Your writing is wordy, often using familiar conversational language instead of concise technical language. For example, "a lot of effort" (line 38) could be deleted and the sentence rearranged to simply say "Corrosion protection of metals and alloys was also investigated." An even better solution would be to collapse the previous sentence and this sentence (lines 36-38) to "The synthesis of PANI has been investigated (e.g., [5]) and examined for various application including the corrosion protection of metals and alloys [6]." The first sentence in the paragraph (lines 34-36) is not a sentence. By isolating the initial sentence fragment, a concise sentence is formed, and the introductory sentence can be easily converted to a sentence with a single thought - the description of the postive characteristics of PANI.
Line 70. "reported", by whom? This requires a reference. It is not clear whether reference [22] refers to the procedure only, or to both. You should clearly state both references.
Line 51. "determined" is redundant. The polarization resistance is a measured value (you state it is observed). As written, it is not grammatically correct.
Line 75, comma is incorrect, delete.
"during" means at some time in a period. You often misuse the word, instead of "for", meaning over the period
line 96, "grind" is incorrect, "ground" is correct.
line 114, "filed" is a typo, I think you mean "filled".
line 137, wavelength is plural.
line 211, "exposition" is not the correct word. Do you mean exposure?
line 269, performance is singular.
line 271, in site is not latin and should not be italisized. It is also incorrect terminology. I am not sure what you are intending, but it is not in situ either since you extract an alliquote of the solution for analysis.
Overuse of "so", often unnecessary (wordy), often grammatically incorrect.
Author Response
Dear Reviewer
Many thanks for your useful comments.
Please see attached file for detail answers.
Author Response File: Author Response.pdf
Reviewer 5 Report
This work is devoted to the study of composite coatings with polyaniline doped by organic acids on the corrosion of mild steel. Here the influence of various factors is presented, in particular the role of the initial state of the polyaniline on corrosion. A possible corrosion mechanism is also discussed. This work is a continuation of a previously published work in 2018 (https://doi.org/10.1016/j.porgcoat.2018.02.032). In my opinion, these two works strongly intersect, the results are repeated. In particular, the preparation of composite coatings with polyaniline doped by organic acids has already been detailed in a 2018 paper. The novelty of the study is one question. Here are some comments:
1. Introduction. Perhaps the authors should have given more examples of the use of polyaniline and composite materials based on it for corrosion protection.
2) Section 3.1. The description of UV-vis spectra (text and Figure 1b) fully coincides with the results of the work in 2018 (https://doi.org/10.1016/j.porgcoat.2018.02.032). Perhaps the authors should refer to these results rather than repeat material or use other methods for characterization.
3) Lines 190-192 ("Other composite coatings show the appearance of the corrosion product, but with microscope examinations, no blisters formation or delamination is observed"). The authors do not provide evidence for this claim. Perhaps authors should have used the Supplementary Materials section.
4) Lines 206-207. (It can be seen that sulfamic acid doped PANI has an average doping degree of 0.27; PANI-succinic acid 0.18, PANI-citric acid 0.15, and PANI-acetic acid 0.13.) This sentence also appears in https://doi. org/10.1016/j.porgcoat.2018.02.032 as the main conclusion.
5) Figure 8 has also already been submitted at https://doi.org/10.1016/j.porgcoat.2018.02.032
Author Response
Dear Reviewer
Many thanks for your useful comments
This work is devoted to the study of composite coatings with polyaniline doped by organic acids on the corrosion of mild steel. Here the influence of various factors is presented, in particular the role of the initial state of the polyaniline on corrosion. A possible corrosion mechanism is also discussed. This work is a continuation of a previously published work in 2018 (https://doi.org/10.1016/j.porgcoat.2018.02.032). In my opinion, these two works strongly intersect, the results are repeated. In particular, the preparation of composite coatings with polyaniline doped by organic acids has already been detailed in a 2018 paper. The novelty of the study is one question.
Dear Reviewer, we agree. We agree. Instead of Figs 1a-b, we got permission to reproduce the original Figure from ref 20. This is really important part and is difficult to only describe that part.
Novelty goal is rewritten
In our previous paper [20], the PANI composite with alkyd-based paint prepared with PANI possessing different initial oxidation states doped with organic acids is qualitatively investigated using the linear polarization methods. It is observed that determined polarization resistance decreases with a decrease in the initial oxidation state of the polyaniline. Also, the paint blistering and delamination are suppressed to a large extent in comparison with the base coating. Consequently, to extend that work, in this paper, we present results of the quantitatively determined corrosion current densities using the 1,10-phenanthroline standard test method that is already used for corrosion current determination of composite coatings contained polyaniline doped with benzoate [21], and to determine corrosion products area on the base and composite coatings surfaces. Also, a plausible mechanism of corrosion protection will be discussed in more detail. The possible applications of composite coating are also suggested.
Here are some comments:
- Introduction. Perhaps the authors should have given more examples of the use of polyaniline and composite materials based on it for corrosion protection.
We extended paper at some extent due to the Author guidance for the Metals Introduction:
The introduction should briefly place the study in a broad context and highlight why it is important. It should define the purpose of the work and its significance, including specific hypotheses being tested.
2) Section 3.1. The description of UV-vis spectra (text and Figure 1b) fully coincides with the results of the work in 2018 (https://doi.org/10.1016/j.porgcoat.2018.02.032). Perhaps the authors should refer to these results rather than repeat material or use other methods for characterization.
We agree. Instead of Figs 1a-b, we got permission to reproduce the original Figure from ref 20. This is really important part, and we rewrite description of the figure.
3) Lines 190-192 ("Other composite coatings show the appearance of the corrosion product, but with microscope examinations, no blisters formation or delamination is observed"). The authors do not provide evidence for this claim. Perhaps authors should have used the Supplementary Materials section.
Micrographs of all five samples are incorporated into the manuscript. Also we added the Figure 6. The optical images of the damaged base coating and composite coating with PANI doped with different organic acids, after 100 h of immersion in 3% NaCl.
4) Lines 206-207. (It can be seen that sulfamic acid doped PANI has an average doping degree of 0.27; PANI-succinic acid 0.18, PANI-citric acid 0.15, and PANI-acetic acid 0.13.) This sentence also appears in https://doi. org/10.1016/j.porgcoat.2018.02.032 as the main conclusion.
As we stated this is repeated due to the previously published result for what we obtain permissions for the reproduction.
5) Figure 8 has also already been submitted at https://doi.org/10.1016/j.porgcoat.2018.02.032
This is well known figure from many textbooks and journals, ad our thoughts are that especially for the younger readers will be beneficial. We slightly modified figure in the first version of the paper, but now completely new two figures are presented
Round 2
Reviewer 3 Report
There are no new comments for the authors.
Reviewer 5 Report
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