Study of Hillock and Zinc Whisker Evolution in Five Different Cable Tray Coatings

Round 1

Reviewer 1 Report

According to the authors, the main objective of this work is the study of the hillocks and zinc whiskers evolution of five commercial different zinc coatings manufactured by a leading company in the field of cable tray manufacturing: white zinc alkaline electrolyte, yellow zinc trivalent electrolyte, acid zinc electrolyte, hot dip galvanized, and zinc nickel coating, manufactured.

The research was carried out over the period of one year and concerned the measurements of hardness, coating thickness, roughness and surface topography by scanning electron microscopy.

The conducted research shows that practically only the hardness is a significant determinant of the analyzed coatings, while there were no clear differences in the development of zinc hillocks and tendrils within one year. It can be assumed that all the obtained values are within the limits of measurement errors, although they have not been marked in the figures. This also applies to the results of the research of hillocks and whiskers density evolution with and with- and out presence of compression stresses, which, according to the authors, are one of the most influencing parameters. On the basis of the obtained test results, no conclusions can be drawn about any influence of stresses on hillocks and whiskers density evolution.

A valuable component of the article is the state of the art concerning the current state of knowledge regarding the phenomena affecting the development of zinc whiskers and hillocks on the coating surface. Moreover, the results of the research can provide important information for cable tray companies. However, they do not contribute to the development of science.

Author Response

Thank you for your time revising our work and the analysis you have done. As you state, the research provides important information for cable tray companies, but also to the development of the science; not being purely basic science, this work is the result of applied science to industrial processes. This is a clear example of transfer of knowledge from research centers to the productive sector, which is becoming more and more relevant within the functions of 21st century researchers, who must contribute to the development of science but also to their practical applications, which are the ultimate goal for the advancement of society.

Reviewer 2 Report

The authors have done a good job, the systematic analysis of coatings is conducted and the datas are well organized. I recommend the publication of this manuscript. 

Author Response

Thank you very much for the time analyzing our work. We are glad to have met your expectations.

Reviewer 3 Report

I have read the article entitled “Study of hillocks and zinc whiskers evolution in five different cable tray coatings manufactured by VALDINOX Ltd by B. Arroyo et al. submitted to Metals, MDPI Journal. The formation and growth of the zinc whiskers, from different coatings, which could readily be grown from bright zinc electrodeposits have been reported in this work.

In recent years, there has been a renewed industrial interest in whisker growth, mainly due to the miniaturization of electronic devices and the environmental regulations forbidding the use of lead. Electroplated zinc coatings are used as anticorrosive protection for low alloy steels in diverse industries such as automotive, aerospace or energy, as well as for support structures or raised-floor tiles in computer data centers. In order to mitigate, prevent, and predict the failures caused by the zinc whiskers, the mechanisms of growth must be understood. Therefore, the reported work is significant and suitable to the chosen journal. The evolution of hillocks and zinc whiskers from five different commercial zinc coatings and their relative performances are reported. Work is well presented and be useful to the Zn industry for decision making and for the reliability of electrical devices. Having said that, some of the ambiguity in the manuscript need to be resolved. Therefore, revision is required before rendering a final decision. Heaps of micrographs can be grouped, and numbers can be reduced.

Some specific comments that may require attention:

• The first two lines of the abstract are not relevant (or) appropriate, can be taken elsewhere. Can start from the sentence “the main objective..”
• In the introduction (section 1) terminology whiskers/hillocks need to be described from a metallurgical perspective. Classification of these (whiskers) can be provided.
• Section 2.1 coating thickness is coupled with texture for at least some substrates, please include this in the discussion.
• Section 2.2 To justify the intermetallic compounds, the phase diagram of Fe-Zn can be shown.
• Section 2.2 While defining the dimensions, the behavior of zinc electrodes in alkaline electrolyte reported in the literature (such as Electrochem Solid-State Lett. 13 (2010) A77; Solid State Ionics 179 (2008) 355; International Journal of Hydrogen Energy 35 (2010) 7618) need to be cited. This will give a big picture of the Zn from different applications.
• Section 2.3 Whiskers growth kinetics could be briefly explained. Is this due to recrystallization or dislocations?

General comments

• It appears the alkaline electroplating electrolyte favors the activation energy of both stress relaxation and whiskers growth when compared to acid-electrolyte. However, on the other hand, whiskers growth activation energy is favored by zinc coating thickness and disfavoured by steel substrate thickness. How this can be seen?
• The presence of brightening agents causes whisker initiation and growth and that growth is probably related to electrodeposits micro stress, has this been verified?
• In the electroplating electrolyte, dull zinc deposits are usually produced from cyanide baths, without organic additives, do not produce zinc whiskers. Can this be influenced?
• Figure 1 caption “differences respecting ZW growth after 10 months in service” unclear.
• Figure 7 and its relevant text may not be so essential.
• Figures 8-9 need to be well explained, currently, it is left almost unattended.
• Figures 10 – 14 can be grouped together while showing the higher magnification as inset.
• Few of the areas, language need to be polished.

Author Response

Dear reviwer, thank you for your time revising our manuscript. We have addressed all your comments, please find rebuttal file attached.

Author Response File: Author Response.pdf

Reviewer 4 Report

The manuscript addresses the specific challenges associated with the formation of Zn whiskers in many sectors such as buildings,  airports, data centers. The work is interesting. However, lot of works on the characterization, correlation of the points needs to be made in order to demonstrate its novelty

Comments:

• Figure 4, 20-21 is not clear
• Figure numbers are mismatching and,  needs to be checked, corrected.
• There are few typo errors that needs to be checked and corrected throughout the manuscript [highlighted in yellow]
• Figures 6-9: are they representative images for one of the conditions? Figure caption needs to be specific and match with the text.
• Figure 12-13: Optical images of magnification (x500) needs to be presented.
• Though it was pointed out that the results would have had an influence on the texture, there is no physical characterisation data such as XRD to support this fact. Also, temperature effects were not studied in this manuscript. Proper correlation should be made in the discussion.
• The reason for inhibition of hillocks, whiskers with electrodeposited Zn-Ni was not discussed in detail. Also, the responsible factors for whisker formation, hillock formation in alkaline deposition conditions while inhibition in acidic deposition conditions was not explained
• Deposition conditions were not mentioned in the manuscript like mode of deposition,  deposition time, anode, temperature used??. For the acidic bath, was it a chloride bath or sulphate bath?
• Recommended inclusion of few more physical characterisation techniques  in the manuscript for better analysis and discussion.

 

Author Response

Dear reviwer, thank you for your time revising our manuscript. We have addressed all your comments, please find rebuttal file attached.

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

I maintain the position that the presented research has no impact on the development of science, in particular surface engineering. However, they prove that the five VALDINOX® patented EASYCONNECT system cable trays made out of the same base steel wires but finished in different coatings is of good quality. As confirmed by a 12-month study of the hillock and whisker density evolution in the presence and without the influence of compression bending stresses.

Taking into account the amendments made by the authors to improve the quality of the article, I am inclined to accept the conclusion that "this is a example of transfer of knowledge from research centers to the productive sector" and withdraw from the decision to reject the article.

Author Response

Dear reviewer, thank you for your time revising our work for a 2nd time. We are glad thay after the changes and improvements done to the work you consider that it represents an example of transfer of knowledge from research centers to the productive sector, and by this way it could be published. Regards.

Reviewer 4 Report

Thanks for addressing some of the comments. I fully understand the complexity of dealing with a commercial manufacturing company. The overall quality of the paper has improved significantly, but there are some typos and grammatical errors that need to be addressed. This is best done by a thorough revision by a native English writer. Please seek help to get this arranged.

Author Response

Dear reviwer, thank you for your time revising our work for a 2nd time. The paper has been sent to a native English speaker who has revised it in order to correct these issues.