The Effect of Curing Temperature and Thickness of Polybutyl Methacrylate Siloxane Coatings on the Corrosion Protection of Structural Steel S355

Round 1

Reviewer 1 Report

The paper through the proposed subject is of practical interest (decreasing the effect of steel corrosion through coating, over time). The paper is largely well written, but there are still some omissions, namely:

1. It is important to check the English language and grammar, because you used some words (I think) from the national cornet speech, which do not sound good in English. For example: in line 48-49 'linker' I think it should be 'link'; row 65-66 'dense' I think it should be 'frequently'; line 80 'ground' replace it with 'polished' or 'glazed';; line 145, not 'giving' but obtaining' or 'resulting' etc.

2. Not '... least squares...', but I think '... method of least squares...', line 195, 204, etc.

3. In line 380-381, say "as explained in the Experimental section."; which section? There is no such section! Maybe you had the intention and it wouldn't have been wrong!

4. In fig. 5, on the ordinate you wrote 'Impedance' which you noted with 'Z' and on the abscissa "frequency" which you noted with 'f' towards the end of the 'Results and Discussion' section; change in Fig. 7 you put only 'Z' in the ordinate; be consistent, wear the same everywhere!

5. In the 'Conclusions' it was good to specify the optimal coating thickness and the optimal curing temperature, not only the minimum values or, otherwise, the minimum and maximum values.

Author Response

The paper through the proposed subject is of practical interest (decreasing the effect of steel corrosion through coating, over time). The paper is largely well written, but there are still some omissions, namely:

Dear reviewer. Thank you very much for positive opinion about the content of the prepared manuscript. The comments to your revision are given below; the changes are yellow-shadowed in the manuscript.

1. It is important to check the English language and grammar, because you used some words (I think) from the national cornet speech, which do not sound good in English. For example: in line 48-49 ‘linker’ I think it should be ‘link’; row 65-66 ‘dense’ I think it should be ‘frequently’; line 80 ‘ground’ replace it with ‘polished’ or ‘glazed’;; line 145, not ‘giving’ but obtaining’ or ‘resulting’ etc.

Thank you for the comments. We rechecked the manuscript and corrected the grammar errors. We also omit the phrases (I think, it should be) and change the sentence to passive. The manuscript's grammar was checked with the program Grammarly. After acceptance, the MDPI language-editing service will also recheck the manuscript by native English speaker. 

The expression “linker” is often used in sol-gel chemistry (a.g. https://pubs.rsc.org/en/content/articlehtml/2021/ma/d0ma01009j, or https://pubs.rsc.org/en/content/articlelanding/2016/ra/c5ra26094a) when the inorganic and organic components are combined in one hybrid material. Therefore this expression remained in the manuscript.

The expression “ground” has also remained in the manuscript because the surface was ground using SiC emery papers (Struers, Denmark) 80, 120, 240, 500, 1200, and 2400-grit. This expression is also used by the producer of these grinding machines and papers: https://www.struers.com/en/Products/Grinding-and-Polishing/Grinding-and-polishing-equipment/LaboSystem#labosystemfacts. The polishing procedure of the steel surface was not performed in this study because the coating can be evenly deposited also on the ground steel surface. 

The expression ‘giving’ in the manuscript was replaced with “obtaining”. 

The expression ‘dense’ has remained in the manuscript because it refers to a dense coating structure. To improve the meaning, the sentence was modified to: “produce dense and protective coating structure” (in line 66) 

2. Not ‘... least squares...’, but I think ‘... method of least squares...’, line 195, 204, etc.

Thank you very much for the comment. The sentence was corrected in the manuscript (in line 212). 

3. In line 380-381, say “as explained in the Experimental section.”; which section? There is no such section! Maybe you had the intention and it wouldn’t have been wrong!

Thank you for the comment. We modified the sentence and added the section number (2.2.4. Coating porosity). The changes are in lines 399-400.

4. In fig. 5, on the ordinate you wrote ‘Impedance’ which you noted with ‘Z’ and on the abscissa “frequency” which you noted with ‘f’ towards the end of the ‘Results and Discussion’ section; change in Fig. 7 you put only ‘Z’ in the ordinate; be consistent, wear the same everywhere!

Thank you for the comment. We modified the y-axis in Figure 6. The abbreviation IZI at 5 mHz remained in the text.  

5. In the ‘Conclusions’ it was good to specify the optimal coating thickness and the optimal curing temperature, not only the minimum values or, otherwise, the minimum and maximum values.

Thank you for the comment and suggestion. The conclusions of the manuscript were modified by replacing the expression “minimum” with “optimal” (in line 566 and line 569). 

Reviewer 2 Report

(1) In page 3, line 113, it is better to use the word “polished” than “ground”.

(2) In Figure 5, the unit for impedance should be “Ω cm^-2”.

(3) According to the experimental section, the resolution of 3D topography was 0.167 μm/per point, however, this value did not match the resolution of the Y-axis in Figure 3, which was ~0.01 μm. Furthermore, the 3D maps used to determine the thickness are needed to be shown.

Author Response

Dear reviewer. The comments to your revision are given below; the changes are yellow-shadowed in the manuscript.

(1) In page 3, line 113, it is better to use the word “polished” than “ground”.

Thank you for the comment. We prefer to use the expression “ground” because the surface was ground using SiC emery papers (Struers, Denmark) 80, 120, 240, 500, 1200, and 2400-grit. This expression is also used by the producer of these grinding machines and papers: https://www.struers.com/en/Products/Grinding-and-Polishing/Grinding-and-polishing-equipment/LaboSystem#labosystemfacts. The polishing procedure of the steel surface was not performed in this study because the coating can be evenly deposited also on the ground steel surface.

(2) In Figure 5, the unit for impedance should be “Ω cm-2”.

Thank you for the comment. The y-axis in the Bode diagram is correct Ω cm2. More information is available: https://www.sciencedirect.com/topics/engineering/bode-diagram or bit.ly/3Jgzv6c. Therefore the impedance unit in the y-axis has remained Ω cm2.

(3) According to the experimental section, the resolution of 3D topography was 0.167 μm/per point, however, this value did not match the resolution of the Y-axis in Figure 3, which was ~0.01 μm. Furthermore, the 3D maps used to determine the thickness are needed to be shown.

Thank you very much for the comment. The resolution stated in the experimental section refers to the resolution of the instrument used to measure the 3D topography (minimum distance between two adjacent measurement points on the X and Z-axes), while the Y-axis resolution in Figure 3 refers to the resolution of the graph that was created from the measurements. These values may not be the same because the graph may have been scaled for visualization.
The coating thickness was made using 3D map to determine the step, which would accurately represent the coating thickness as the step height. Since the substrate is smooth, we can claim that the area below the layer is the substrate. The coating thickness was similarly determined in previous papers (see references 30, 32, and 33). We suggest not including 3D maps in this manuscript because they are not crucial. 

Reviewer 3 Report

My comments

 Thank you very much for giving me the chance to cooperate with your respected journal in reviewing this interesting work.

The work is dealing with “ The Effect of Curing Temperature and Thickness of Polybutyl 2 Methacrylate Siloxane Coatings on the Corrosion Protection of 3 Structural Steel S355”. This work is very important for readers to improve their awareness regarding how to design successful coating materials for corrosion protection of metallic structures. This work is very important for coating materials selection especially the polymeric materials according to their suitability and reproducibility in corrosion protection approaches. The paper is carefully prepared but some points must be fixed before the publication of this manuscript.

1.      The title is long but precise for the core message of this research.

2.      The word application is mentioned only in the introduction and results so, please I hope to see it in the abstract (the best results in applications).

3.      The introduction is well-written and covered the period from 1944 to 2022 and this literature is satisfactory. Some recent and related references on polymeric coating for corrosion protection.

·         Abdel‑Karim AM, El‑Shamy AM, Reda Y, Corrosion and Stress Corrosion Resistance of Al Zn Alloy 7075 by Nano‑Polymeric Coatings, Journal of Bio- and Tribo-Corrosion, 2022, 8: 57. https://doi.org/10.1007/s40735-022-00656-2

·         Megahed MM, Abdel Bar MM, Abouelez ESM, El-Shamy AM, Polyamide Coating as a Potential Protective Layer Against Corrosion of Iron Artifacts, Egyptian Journal of Chemistry, 2021, 64(10), 5693–5702. DOI: 10.21608/ejchem.2021.70550.3555

·         Reda Y, Abdelbar M, El-Shamy AM, Fortification performance of polyurethane coating in outdoor historical ironworks, Bull. Natl. Res. Cent., 2021, 45, 69. https://doi.org/10.1186/s42269-021-00532-y

·         El-Shamy A. M., Abdelfattah I., Elshafie O. I., Shehata M. F., Potential removal of organic loads from petroleum wastewater and its effect on the corrosion behavior of municipal networks, J. Environ. Management, 2018, 219, 325-331. https://doi.org/10.1016/j.jenvman.2018.04.074

·         El-Shamy AM, Mouneir SM, Medicinal Materials as Eco-friendly Corrosion Inhibitors for Industrial Applications: A Review, Journal of Bio- and Tribo-Corrosion, 2023, 9(1): 3. https://doi.org/10.1007/s40735-022-00714-9

4.      The effect of pH is very important and not covered well in this manuscript, just mentioned on page 5,6  part 2.2.6 Salt-spray test. So it was not mentioned in depth. For more benefits of this manuscript, I recommend adding a title specified to the effect of pH variation on the efficacy of coating efficiency for corrosion protection. As you know the coatings are used in different pH ranges from acidic to alkaline media (variation of pH from 1.5 to 10). The variations of pH in different parts of the different steps of applications this issue is very important for readers so please give more illustrations of the benefits of the coating techniques and their potential effect against corrosion in pH variation and how to control the degradation of the metallic structure under alkaline and acidic conditions.

This part needs more illustration, especially how it works. This reference may help you in this part.

·         Zohdy KM, El-Sherif RM, El-Shamy AM, Effect of pH Fluctuations on the Biodegradability of Nanocomposite Mg-Alloy in Simulated Bodily Fluids, Chemical Paper, 2022, 2022: 1-21. https://doi.org/10.1007/s11696-022-02544-y

5.      The performance of Figures and tables is accepted.

6.      I saw the word mechanism only in the introduction and I hope to see a specific part under this title (structure effect relationship) I think it will help readers to get the highest benefits from this manuscript. Just illustrate short notes about the chemical structure of coating and their effect on corrosion control.  

7.      This work is very important for industrial applications so please in the conclusion add one or more sentences to highlight the benefits of the application of this coat in different industries.

8.       The references are listed according to the requirements of the journal.

9.      The manuscript contains some editing and grammatical mistakes. Please check it before the publication.

My decision is: acceptance after a minor revision

Author Response

Thank you very much for giving me the chance to cooperate with your respected journal in reviewing this interesting work.
The work is dealing with “ The Effect of Curing Temperature and Thickness of Polybutyl 2 Methacrylate Siloxane Coatings on the Corrosion Protection of 3 Structural Steel S355”. This work is very important for readers to improve their awareness regarding how to design successful coating materials for corrosion protection of metallic structures. This work is very important for coating materials selection especially the polymeric materials according to their suitability and reproducibility in corrosion protection approaches. The paper is carefully prepared but some points must be fixed before the publication of this manuscript.

Dear reviewer. Thank you very much for positive opinion about the content of the prepared manuscript. The comments to your revision are given below; the changes are yellow-shadowed in the manuscript.

1.    The title is long but precise for the core message of this research.

Thank you for the comment. We prefer to keep the current title of the manuscript because it presents both researched effects (curing temperature and thickness) and explains the main topic (corrosion protection) and studied substrate (structural steel S355). 

2.    The word application is mentioned only in the introduction and results so, please I hope to see it in the abstract (the best results in applications).

Thank you for the comment. This manuscript presents the results of basic research (most of the tests were performed in the laboratory); therefore, the application of this coating was not explicitly given in the abstract. In addition, the abstract length is limited to up to 200 words. 
However, we are aware of the application of this type of coating, and they were already tested in a real environment. These results are published in ref 34: Hamulić, D.; Putna-Nimane, I.; Liepina-Leimane, I.; Dimante-Deimantovica, I.; Rodič, P.; Milošev, I. Field Testing and Ecotoxicity of Acrylate-BasedSol–Gel Coatings in Fresh and Seawater. J. Coat. Technol. Res. 2022, doi:10.1007/s11998-022-00701-2. 
However, the sentence related to the application of the coating was added to the Conclusions: “The studied coating presents a promising approach to corrosion protection of structural steel for applications where only a few micrometres thick coating is required.”

3.      The introduction is well-written and covered the period from 1944 to 2022 and this literature is satisfactory. Some recent and related references on polymeric coating for corrosion protection.
·         Abdel Karim AM, El Shamy AM, Reda Y, Corrosion and Stress Corrosion Resistance of Al Zn Alloy 7075 by Nano Polymeric Coatings, Journal of Bio- and Tribo-Corrosion, 2022, 8: 57. https://doi.org/10.1007/s40735-022-00656-2
·         Megahed MM, Abdel Bar MM, Abouelez ESM, El-Shamy AM, Polyamide Coating as a Potential Protective Layer Against Corrosion of Iron Artifacts, Egyptian Journal of Chemistry, 2021, 64(10), 5693–5702. DOI: 10.21608/ejchem.2021.70550.3555
·         Reda Y, Abdelbar M, El-Shamy AM, Fortification performance of polyurethane coating in outdoor historical ironworks, Bull. Natl. Res. Cent., 2021, 45, 69. https://doi.org/10.1186/s42269-021-00532-y
·         El-Shamy A. M., Abdelfattah I., Elshafie O. I., Shehata M. F., Potential removal of organic loads from petroleum wastewater and its effect on the corrosion behavior of municipal networks, J. Environ. Management, 2018, 219, 325-331. https://doi.org/10.1016/j.jenvman.2018.04.074
·         El-Shamy AM, Mouneir SM, Medicinal Materials as Eco-friendly Corrosion Inhibitors for Industrial Applications: A Review, Journal of Bio- and Tribo-Corrosion, 2023, 9(1): 3. https://doi.org/10.1007/s40735-022-00714-9-inhibitorji??

Thank you for the comment. We tried to give a comprehensive literature overview focus was on sol-gel coatings, which are only a few micrometres thick and mainly deposited on the steel. The current version of the manuscript contains 67 references. The suggested papers are not strictly related to the topic of corrosion protection with hybrid sol-gel coatings (1 – coating deposited on AA7075, 2- Polyamide Coating on iron, 3- polyurethane coating in outdoor historical ironworks, 4- Potential removal of organic loads from petroleum wastewater, 5- Eco-friendly Corrosion Inhibitors for Industrial Applications), and are not crucial for this manuscript. Therefore we did not include them in the manuscript.

4.    The effect of pH is very important and not covered well in this manuscript, just mentioned on page 5,6  part 2.2.6 Salt-spray test. So it was not mentioned in depth. For more benefits of this manuscript, I recommend adding a title specified to the effect of pH variation on the efficacy of coating efficiency for corrosion protection. As you know the coatings are used in different pH ranges from acidic to alkaline media (variation of pH from 1.5 to 10). The variations of pH in different parts of the different steps of applications this issue is very important for readers so please give more illustrations of the benefits of the coating techniques and their potential effect against corrosion in pH variation and how to control the degradation of the metallic structure under alkaline and acidic conditions.

We agree with the comment on the effect of pH on corrosion, but this is an additional parameter we did not study explicitly. This manuscript is focused on two issues i) the effect of curing temperature and ii) the thickness of polybutyl methacrylate siloxane coatings in chloride-containing medium (3.5 wt. %), which is enough for one manuscript. In addition, the selected corrosion medium represents the average seawater salinity in the world’s oceans (https://en.wikipedia.org/wiki/Seawater). Such a high chloride concentration is very aggressive in terms of corrosion attack of this type of steel. This was confirmed with electrochemical measurements and salt-spray tests. To sum up, the effect of the corrosive media pH can be studied in the additional study, and the reference was not included in the manuscript.

5.       This part needs more illustration, especially how it works. This reference may help you in this part.
·         Zohdy KM, El-Sherif RM, El-Shamy AM, Effect of pH Fluctuations on the Biodegradability of Nanocomposite Mg-Alloy in Simulated Bodily Fluids, Chemical Paper, 2022, 2022: 1-21. https://doi.org/10.1007/s11696-022-02544-y

The suggested reference presents the study of magnesium alloy in Simulated Bodily Fluids, which is not the same topic as the one in the manuscript. Therefore the reference was not included in the manuscript.
 
6.      The performance of Figures and tables is accepted.

Thank you very much for the positive opinions about the figures and tables. 

7.      I saw the word mechanism only in the introduction and I hope to see a specific part under this title (structure effect relationship) I think it will help readers to get the highest benefits from this manuscript. Just illustrate short notes about the chemical structure of coating and their effect on corrosion control.  

A more detailed description of coating preparation is given in references 33: Hamulić, D.; Rodič, P.; Milošev, I. The Influence of Length of Alkyl Chain on the Chemical Structure and Corrosion Resistance of Silica-Polyacrylic Hybrid Coatings on Structural Steel. Prog. Org. Coat. 2021, 150, 105982, doi:10.1016/j.porgcoat.2020.105982. and reference 32. Milošev, I.; Hamulić, D.; Rodič, P.; Carrière, C.; Zanna, S.; Budasheva, H.; Korte, D.; Franko, M.; Mercier, D.; Seyeux, A.; Marcus P. Siloxane Polyacrylic Sol-Gel Coatings with Alkyl and Perfluoroalkyl Chains: Synthesis, Composition, Thermal Properties and Long-Term Corrosion Protection. Appl. Surf. Sci. 2022, 574, 151578, doi:10.1016/j.apsusc.2021.151578. There reference 32 was also added in section 2.1.2. Synthesis of sols. 

8.   Just illustrate short notes about the chemical structure of coating and their effect on corrosion control.

The chemical structure of the coating and its corrosion control are given in references 32 and 33.

9.      This work is very important for industrial applications so please in the conclusion add one or more sentences to highlight the benefits of the application of this coat in different industries.

Thank you for the suggestion. The sentence was added in the Conclusions: “The studied coating presents a promising approach to corrosion protection of structural steel for applications where only a few micrometres thick coating is required.”

10.       The references are listed according to the requirements of the journal.

Thank you very much for the positive opinion. 

11.      The manuscript contains some editing and grammatical mistakes. Please check it before the publication.

Thank you for the comment. We rechecked the manuscript and corrected the grammar errors. All changes are yellow-shaded in the manuscript. The manuscript’s grammar was checked with the program Grammerly. Additionally, the MDPI will recheck the paper by native English speakers after acceptance.
 
My decision is: acceptance after a minor revision. 

Thank you very much for your opinion. We tried to include all your suggestions. 

Round 2

Reviewer 2 Report

In this manuscript, the authors presented an investigation on the effects of curing temperature and thickness of the polybutyl methacrylate siloxane coatings on the anti-corrosion property of S355, however, I may have several concerns as provided below.

(1)    The process and equation used to determine the roughness may need to be provided in the experimental section to better evaluate the accuracy of the experiments. The values of the actual and geometrical surface areas may need to be shown as they are important for the determination of the surface roughness.

(2)    In Figure 8, both of the thickness and roughness increase with increasing withdrawing rates, please explain the phenomenon. On the other hand, the 3D maps can be shown in order to provide direct visualization of the coating thickness.

(3)    In page 3, line 114, it is correct to use “grounded” than “ground”.

Author Response

The answers are listed below and given in the attached file (the file also includes figures). 

In this manuscript, the authors presented an investigation on the effects of curing temperature and thickness of the polybutyl methacrylate siloxane coatings on the anti-corrosion property of S355, however, I may have several concerns as provided below.

Dear Reviewer, Thank you very much for the constructive comments. The replies are given below. The changes in the manuscript are highlighted in green highlighted to differentiate from the changed made in the previous version of the manuscript (yellow highlighted).

1) The process and equation used to determine the roughness may need to be provided in the experimental section to better evaluate the accuracy of the experiments.

Thank you very much for your comment. The process (scientific background) and the equation is now added to the experimental part of the manuscript (lines 184-189).

The arithmetical mean height (S_a) expands the profile (line roughness) parameter into three dimensions. It is generally used to evaluate the surface roughness of 3D profile according to equation (1).

(1).

Reference for equation (1): https://www.olympus-ims.com/en/metrology/surface-roughness-measurement-portal/parameters/#!cms[focus]=022 Equations in the text are renumbered accordingly.

New reference (45) is added: Leach, R. Chapter 8 - Surface Topography Characterisation. In Fundamental Principles of Engineering Nanometrology (Second Edition); Leach, R., Ed.; Micro and Nano Technologies; William Andrew Publishing: Oxford, 2014; pp. 241–294 ISBN 978-1-4557-7753-2.

The values of the actual and geometrical surface areas may need to be shown as they are important for the determination of the surface roughness.

Thank you very much for your comment. The actual values are given in Fig. 8, and geometrical surface areas are shown in Fig. 9.  

2) In Figure 8, both of the thickness and roughness increase with increasing withdrawing rates, please explain the phenomenon.

Thank you for the comment. Figure 8 was modified (the right y-axis was renamed to surface roughness).

The dip-coating process involves immersing into a liquid coating material and withdrawing it at a controlled rate to obtain a uniform coating. Several factors, including the withdrawing rate, can influence the thickness and roughness of the resulting coating.

The thickness of the coating increases linearly with the withdrawing rate. At a certain point, a limiting withdrawal rate is reached when the influence of gravity becomes comparable to that of evaporation. In addition, there may be some limitations to this relationship due to the physical properties of the coating material and surface properties (a.g., surface tension and density/viscosity of the sol).

When the withdrawing rate increases during the dip-coating process, the coating material cannot flow and spread evenly on the substrate. This can result in a thicker coating as more material accumulates on the substrate.

In addition to affecting the thickness of the coating, increasing the withdrawing rate can also increase the roughness of the resulting surface. This is because the coating material is more likely to form irregularities and defects as it is pulled away from the substrate. These irregularities can create peaks and valleys on the coating surface, resulting in a rougher texture.

Overall, the withdrawing rate can have a significant impact on the thickness and roughness of coatings produced by the dip-coating process. By carefully controlling the rate at which the substrate is withdrawn, it is possible to optimize the properties of the resulting coating for a given application.

The changes in the manuscript are green highlighted in the manuscript (lines 485-490 and lines 501-503).

In addition, new reference 59 is added:

Rebrov, E.V.; Schouten, J.C. Limiting Withdrawal Rate and Maximum Film Thickness during Dip-Coating of Titania Sols onto a Si Substrate. Chem. Eng. Process. Process Intensif. 2011, 50, 1063–1068, doi:10.1016/j.cep.2011.05.025.

On the other hand, the 3D maps can be shown in order to provide direct visualization of the coating thickness.

Thank you very much for the comment. Here is an example of 3D maps along with the delaminated coating, where the scan of the area and determined step was performed. Here we also attached some photos below to better illustrate the description, Figure 1.    

Figure 1. Optical image of the analised area along the performed scribe, 3D map of the analysed area (Bruker DektakXT profilometer) and determining the coating thickness (step height) using TalyMap Gold 6.2 software.

The main goal of the manuscript is to study the effect of curing temperature and thickness. Therefore, we think that these 3D maps are not essential to be part of the manuscript.

(3)    In page 3, line 114, it is correct to use “grounded” than “ground”.

Thank you very much for the comment. The correct verb is ground because the grind is irregular, which means it doesn’t follow the regular rules used by most verbs: “ground” is the past tense and past participle form of the verb “grind.” See explanation:

English.https://writingexplained.org/grinded-or-ground

Therefore we kept the verb »ground« in the manuscript.

Author Response File: Author Response.docx

Round 3

Reviewer 2 Report

  The authors have made significant improvements on the manuscript, however, the resoltuion of Figure 1 and Figure 2 may need to be further enhanced before publication.