Ecofriendly Protic Ionic Liquid Lubricants for Ti6Al4V

Round 1

Reviewer 1 Report

This manuscript studies the lubrication effect of three kinds of diprotic ionic liquids on Ti6Al4V/sapphire friction pairs, and provides a halogen-free, water soluble protic ionic liquid additive that can improve the tribological properties of water on Ti6Al4V friction pairs and avoid corrosion and pollution. According to the research in this manuscript, the new (Water+1wt.% PILs) lubricants were tested under room temperature and 100℃，which show greater lubrication performance and best lubrication performance, respectively. However, the characterization results are not well related to the conclusion of the corresponding aqueous lubricants friction performance test in the manuscript, which lacks logical reasoning and is difficult to convince people. I think it is necessary to add some cohesive explanations to summarize the role of the characterization part. In addition, there are some issues should be addressed :

1.        The legend in Figure 2b in the manuscript is beyond the border of the diagram.

2.        The borders of the legends in Figures 3 and 4 should be removed.

3.        Line 170-172, the mechanism for the influence of contact angle change on friction performance should be added.

4.        Lines 176-188: The friction coefficient of water in Table 4 is 0.90, but there is no friction data of water in Figure 3.

5.        Line 193:Why the mass fraction of PILs in water is only 1%, and the lubricating effect of other proportions is unknown?

6.        Line 206:The friction coefficient is greater than 0.2. It is unreasonable to use the phrase “ultralow friction values”.

7.        Line 211:It is mentioned in the paper that the formation of PIL surface layers by evaporation of water indicates that the lubrication may be affected by humidity, but the experimental humidity value is not mentioned in the experimental conditions.

8.        Figure 5 already contains Figure 4, so it is unreasonable to divide it into two figures.

9.        In Figure 12, (a) is “Neat water”; in Figure 13, (a) is “Water”. The expression should be consistent.

10.    The SEM images in the upper right corner of Figure 17 and Figure 18 are not placed in the same way.

11.    In the section of “Results and Discussion”, it is necessary to add some links and summaries of the tribological performance test and characterization test done previously in the conclusions part.

12.    The manuscript only mentions that the lubrication effect of adding protic ionic liquid into water is better than that of water, and whether the performance of this lubricant can be better than that of other lubricants used in Ti6Al4V.

Author Response

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Reviewer 2 Report

The topic of the article is very interesting and innovative. The authors studied three diprotic ionic liquids (PILs) containing bis(2-hydroxyethyl)ammonium cations and citrate (DCi); lactate (DL) or salicylate (DSa) hydroxycarboxylate anions were tested as lubricants for Ti6Al4V-sapphire contact. At room temperature, pure PILs are non-Newtonian fluids that exhibit up to 70% reduction in the coefficient of friction relative to water. New aqueous lubricants have been developed using PIL as 1% by weight. additives in the water. The lowest coefficients of friction at room temperature are obtained for thin layers of lubricant deposited on Ti6Al4V from (water + 1 wt.% PIL) after water evaporation. Electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX) and X-ray photoelectron spectroscopy (XPS) were used in the research. In the abstract, please articulate the innovativeness of the work in relation to other authors in one sentence. In the introduction, please enter the works: https://doi.org/10.1108/00368791111112180; https://doi.org/10.1016/j.energy.2022.126002, will complement the introduction. The work is written in very good technical language. It contains a lot of interesting information. The results are compiled correctly. The photos are prepared reliably. Chapter 2 informs the reader well about the need for research. The results in Chapter 3 are well presented. They are reliable and well discussed. The work is of very good quality. The conclusion contains the most important information. The work is innovative.

Author Response

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Round 2

Reviewer 1 Report

Accept.