Corrosion of Cu in Antifreeze Solutions with Triazine- or Triazole-Type Corrosion Inhibitors for 3 Weeks

Round 1

Reviewer 1 Report

1. Why do you select Cu but not Cu alloys?

2. The microstructure of Cu should provided.

3. The polarization curves should be further analysed.

Author Response

1. Why do you select Cu but not Cu alloys?

<answer> Cu, not a Cu alloy, is generally used for the heat exchanger system for now. This study is driven by a company's request, which is to seek a commercially usable inhibited antifreeze solution in the very near future. 

 

2. The microstructure of Cu should provided.

<answer> The research project, from which the data of this manuscript was obtained, was closed several years ago. It is very unfortunate that the microscopic images of some specimens were lost so we cannot show them. However, we think the AFM images in Fig. 1 are adequate to show the surface condition in view of the degree of corrosion damage. 

 

3. The polarization curves should be further analysed.

<answer>  Some comments on the overall polarization behavior and cathodic current density was added. (p. 10 in revised manuscript) 

Reviewer 2 Report

General remarks

In the Introduction: please, give more examples on the applications of different imidazole-, triazole-, triazine-type inhibitors that are applied in antifreeze systems.

It is interesting that the authors did not mention their own paper on this topic where the same inhibitors were used: Journal of the Korea Academia-Industrial cooperation Society; Vol. 21, No. 2 pp. 619-626, 2020. Though this paper is written in Korean language the abstract and the tables are in English. The chemicals under investigation are identical with those examined in this paper.

It is necessary to correct the formulas of Inhibitor A and B in Table 2 as the “right ends” of the molecules (COOH groups) are missing.

The real composition of the basic antifreeze solution is missing. It is necessary to give the correct composition of “commercial ethylene glycol-based antifreeze solutions, which contain molybdate or nitrite,” (Experimental, line 2) and mentioned later in the section Results “K, Mo, and Na are constituents of the antifreeze solution,” (below Figure 1 line 3).

 

Please, inform the readers why the Mo concentration in the cases of solution 5 and 6 is so small (Table 3), if, according to the Experimental section in all cases the same basic antifreeze solution was used.

How do the authors explain that in the presence of solution (1) and (2) there is not any copper ion in the antifreeze solution in the first week though according to the AFM images the surface is corroded?

Experimental results done without any inhibitor (i.e. test done in the presence of the commercial ethylene glycol with molybdate and/or nitrite) are missing in Figure 1 and in Table 3.

It would be necessary to give some explanation about the connection between inhibition efficiency and the inhibitor structures. The authors often mention the high molecular weight but is there any influence of the molecular structure, of the presence of hetero atoms and ionic substituents in the molecules on the differences between the inhibitor efficacy?

 

Special remark

 Introduction, line 7: “The global interests in sustainable technology urge the development of new corrosion inhibitors which are environmentally benign but highly resistant to corrosion.” Please, rephrase this sentence as this suggests that “new corrosion inhibitors are highly resistant to corrosion”.

 

Author Response

<reviewer's comment 1> It is interesting that the authors did not mention their own paper on this topic where the same inhibitors were used: Journal of the Korea Academia-Industrial cooperation Society; Vol. 21, No. 2 pp. 619-626, 2020. Though this paper is written in Korean language the abstract and the tables are in English. The chemicals under investigation are identical with those examined in this paper.

<answer> It is a good point and we reviewed this previous work of ours. The results were comparatively discussed in the revised manuscript, p.6. The compositions of some solutions in the previous work were the same as those used in this work and the others contained the same inhibitors but the concentrations were different. We also found that we made a mistake in describing the solution temperature in this manuscript, which is actually 98 °C, thanks to the reviewer's comment. 

 

<reviewer's comment> It is necessary to correct the formulas of Inhibitor A and B in Table 2 as the “right ends” of the molecules (COOH groups) are missing. 

<answer> We are sorry but the COOH groups are included on both left and right ends in Table 2. If the reviewer did not find them, probably a technical problem occurred. A pdf version of the manuscript is attached, please see that page again. 

 

<reviewer's comment> The real composition of the basic antifreeze solution is missing. It is necessary to give the correct composition of “commercial ethylene glycol-based antifreeze solutions, which contain molybdate or nitrite,” (Experimental, line 2) and mentioned later in the section Results “K, Mo, and Na are constituents of the antifreeze solution,” (below Figure 1 line 3). 

<answer> We obtained the detailed composition of the antifreeze solution by the company's cooperation. Table 1 was revised. 

 

<reviewer's comment> Please, inform the readers why the Mo concentration in the cases of solution 5 and 6 is so small (Table 3), if, according to the Experimental section in all cases the same basic antifreeze solution was used. 

<answer> Molybdate was not contained in the solution no5 and no6, as shown in revised Table 1 and the last sentence of the first paragraph in 2. Experimental Procedures section. 

 

<reviewer's comment> How do the authors explain that in the presence of solution (1) and (2) there is not any copper ion in the antifreeze solution in the first week though according to the AFM images the surface is corroded?

<answer> The AFM images were taken after 3 weeks, so they do not show the corrosion surface within the first week. 

 

<reviewer's comment> Experimental results done without any inhibitor (i.e. test done in the presence of the commercial ethylene glycol with molybdate and/or nitrite) are missing in Figure 1 and in Table 3.

<answer> Unfortunately we could not take the blank test while the research project running, partly due to the cooperating company's requests. Now the project is closed and we have difficulty getting the same blank solution.  

 

<reviewer's comment> It would be necessary to give some explanation about the connection between inhibition efficiency and the inhibitor structures. The authors often mention the high molecular weight but is there any influence of the molecular structure, of the presence of hetero atoms and ionic substituents in the molecules on the differences between the inhibitor efficacy?

<answer> The molecular weight is a crucial factor for corrosion inhibition efficiency. The structure will affect the inhibiting role, of course, but in this work the role of the molecular weight is much stronger. 

 

 

Author Response File: Author Response.pdf