Effect of Cu and Ni Inclusion on Tribological Performance of Tribocatalytically Active Coatings in Hydrocarbon Environments
, Mohammad Eskandari, Asghar Shirani, Ali Zayaan Macknojia, Wesley Miller and Diana Berman *
Round 1
Reviewer 1 Report
Comments and Suggestions for AuthorsAttached file.
Comments for author File: 
Comments.pdf
Author Response
Reviewer 1:
The manuscript is well written and addresses a relevant topic in the field. However, there are some points that need to be modified and some questions need to be answered before the manuscript is ready for publication.
Response: We thank the reviewer for highlighting the quality and relevance of our work.
- Lines 67-69: It is not enough to say that “Cu and Ni are 67 selected based on the previous studies demonstrating their promising characteristics as 68 catalysts” especially that this is a general statement. You need recent references that are related to the study.
Response: We thank the reviewer for the valuable suggestion. The references were added to support the statements made in the paper.
- Table 1: Ni and Cu AW in g/mol. The reported values are not the AW in g/mol? What are they? Explain or remove both columns.
Response: Following the reviewer’s suggestion, we removed the columns to avoid further confusion.
- Line 181: make sure there spaces between numbers and units. See all cases.
Response: The spaces were corrected in the revised version of the manuscript.
- The signal to noise ratio in most curves is high. It would help improving the quality of the curves by smoothing or some sort of analysis. Also the quality of images in some figures needs improvement.
Response: We appreciate the reviewer’s comment. The friction graphs were smoothened. It should be noted, though, that there is still sporadic behavior observed for the uncoated steel tests as a result of wear debris formed inside the wear track and affecting the friction performance.
- What is the possibility of forming CuCl instead of CuCl2?
Response: We would like to clarify this point, CuCl2 was purchased from the outside supplier to use it during the deposition of the Cu-containing coating. The table lists the quantity of CuCl2 salt used for the deposition of the coatings of the specified composition.
Reviewer 2 Report
Comments and Suggestions for Authors
1- I suggest considering Figure 3, which illustrates measurements conducted under identical (same) loads.
2- In line 219: authors claim that Cu improves hardness and impact toughness, please explain more.
3- Line 271: mentioned reduced oxidation, please provide evidence.
4- Line 302: please provide reference.
5- Line 352: needs references.
6- Fitting on XPS results need to be well fitted, for instance Fig 8- ethanol for copper, there is a clear shoulder that not been defined properly.
Author Response
Reviewer 2:
1- I suggest considering Figure 3, which illustrates measurements conducted under identical (same) loads.
Response: We appreciate the reviewer’s comment. It should be noted that the loads were selected based on the analysis indicating the most favorable conditions in each of the lubricants. As a result, Figure 3 highlights the corresponding wear of the materials. We clarified this point further in the revised version of the manuscript.
2- In line 219: authors claim that Cu improves hardness and impact toughness, please explain more.
Response: We thank the reviewer for the valuable suggestion. We expanded the discussion of the effect of Cu incorporation in the revised version of the manuscript.
3- Line 271: mentioned reduced oxidation, please provide evidence.
Response: Our initial statement was made based on the observed contrast in the figures. However, since EDS maps does not provide quantitative assessment, we removed it to avoid reader’s confusion.
4- Line 302: please provide reference.
Response: We included additional references to support the statements.
5- Line 352: needs references.
Response: Additional references were included to clarify the statements in the revised version of the manuscript.
6- Fitting on XPS results need to be well fitted, for instance Fig 8- ethanol for copper, there is a clear shoulder that not been defined properly.
Response: We thank the reviewer for the comment. We agree that XPS can provide valuable information about the composition. Unfortunately, due to the low percentage of Cu and Ni, the XPS signals are very noisy, even for prolonged scan times. However, Raman analysis confirms no metal oxide peaks that are expected to be below 800 cm-1 (peaks for CuO and Cu2O are expected ~600-629 cm-1 [https://doi.org/10.1038/s41598-023-41631-2]) suggesting that oxygen is not bonded to Cu. We added additional discussion to clarify this point.
Reviewer 3 Report
Comments and Suggestions for AuthorsIn this manuscript, the authors study the effect of catalytic metals (specifically their composition and quantity), on the tribological performance of electrodeposited amorphous CoNiP and CoCuP coatings in different hydrocarbon-rich environments. The authors presented the results, and respective optimal combinations of Ni and Cu at different percentages. Significant reduction in the COF and wear rate is under wear is characterized by Co7CuP and the causes for the boundary lubrication sliding is discussed.
Some literature is bulk cited without detailed discussion on each for example (1-6), (19-25), Please look into some recent literature on NiP based coatings and nano-additives, refer to the recent literature with the keywords “State of art review on nickel-based electroless coatings”, “Tribology of electroless nickel coatings” “nano additives for nickel coatings”
At the end of the section-1, draw the research gaps and necessity of proposed research in detail.
Please do formatting corrections while representing chemical formula
Please state the basis for selection of weight fraction, and the authors performed/implemented optimization.
List the assumptions followed during the experimental procedures.
Discuss in-detail about the influence of parameters on performance enhancement.
The authors discussed more about the hardness and COF form the wear perspective, but please discuss on elastic behavior.
Please do a comparative assessment to draw the merits/(improvements) with reference to cited literature.
Author Response
Reviewer 3:
In this manuscript, the authors study the effect of catalytic metals (specifically their composition and quantity), on the tribological performance of electrodeposited amorphous CoNiP and CoCuP coatings in different hydrocarbon-rich environments. The authors presented the results, and respective optimal combinations of Ni and Cu at different percentages. Significant reduction in the COF and wear rate is under wear is characterized by Co7CuP and the causes for the boundary lubrication sliding is discussed.
Response: We thank the reviewer for reviewing the manuscript and for the valuable comments.
1) Some literature is bulk cited without detailed discussion on each for example (1-6), (19-25), Please look into some recent literature on NiP based coatings and nano-additives, refer to the recent literature with the keywords “State of art review on nickel-based electroless coatings”, “Tribology of electroless nickel coatings” “nano additives for nickel coatings”
Response: We appreciate the reviewer’s comment and suggestions. The introduction part has been revised to include a more detailed discussion.
2) At the end of the section-1, draw the research gaps and necessity of proposed research in detail.
Response: We have included additional discussion of the missing knowledge to highlight the novelty of the study.
3) Please do formatting corrections while representing chemical formula
Response: We thank the reviewer for noticing the minor formatting issues. We corrected them.
4) Please state the basis for selection of weight fraction, and the authors performed/implemented optimization.
Response: We thank the reviewer for the comment. In our previous study [https://doi.org/10.1038/s41598-023-37531-0] we did extended optimization to identify the most promising concentration. In this study, however, the major focus was to compare the effect of the catalytic metal nature and for this, the coatings with similar compositions were selected. It should be noted, however, that according to the prior literature, the concentration of tribocatalytic elements is usually below 10 wt% which further justifies the selected parameters.
5) List the assumptions followed during the experimental procedures.
Response: We thank the reviewer for the suggestion. We further expanded the experimental procedure to clarify the motivation for the performed experiments.
6) Discuss in-detail about the influence of parameters on performance enhancement.
Response: The discussion of the parameters has been expanded in the revised version of the manuscript.
7) The authors discussed more about the hardness and COF form the wear perspective, but please discuss on elastic behavior.
Response: We appreciate the reviewer’s comment. The major reason for including the hardness map was to analyze how the structural and chemical modifications inside the weartrack in contrast to the original coatings affect the mechanical characteristics of the coatings. In the revised version of the manuscript, we added also the changes in the elastic modulus (added in supplementary materials as Figure S2).
8) Please do a comparative assessment to draw the merits/(improvements) with reference to cited literature.
Response: We thank the reviewer for the valuable suggestions. It should be noted that including a very detailed assessment is challenging since the tribocatalysis as a wear reduction approach is not mature enough. However, to highlight the novelty and the significance of the reported results, we compared the observed wear rates with the results from the existing studies on CoP and see that in comparison to the reported 10^-5 mm3/mN wear rate for CoP in PAO, the tribocatalytic coatings show an order of magnitude lower values [http://www.electrochemsci.org/papers/vol8/80810350.pdf]. It should be noted, that there are no reports available in the literature on the cases when such materials are tested in a fuel environment.
