Corrosion Behavior of Electrochemical and Thermal Treated Titanium into Artificial Saliva: Effect of pH and Fluoride Concentration

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

Recommendations for Authors

Manuscript Number: CMD3808167

Corrosion Behavior of Electrochemical and Thermal Treated Titanium into Artificial Saliva: Effect of pH and Fluoride Concentration

Although the proposed manuscript is very interesting, there are some weaknesses that suggesting to a major revision. This based on the follow:

• The objective of the study is not clear; it must justify the scope of the investigation.
• Authors should enrich the introduction with recent works.
• Indicate why the chemical composition of the alloys was obtained using analytical technique.
• A section must be included: 2.2 Electrochemical oxidation
• Section 2.3 should be corrected and read: Electrochemical corrosion or electrochemical tests or electrochemical measurements
• In Electron Microscopy, the authors must indicate which sensor they use: secondary or back-dispersed electrons.
• The abstract and objective mention that they used linear polarization (LPR) and the materials section says potentiodynamic polarization curves (PPC). Which is correct? What is the repeatability of their tests?
• Why use PPC and LPR if one technique is high field and the other is low field?
• The materials section, Says: And energy dispersive spectroscopy …. The correct is: energy-dispersive X-ray Spectroscopy (EDS)
• In section 3.1 and 3.2 there is no discussion of results, they are only described
• Figure 2, 11, 14, should say Figure X. SEM-SE according to the sensor used, the magnification of the images should be indicated (for example 2000X),
• In the morphologies there must be indications about the particles, phases, etc.
• Figures 3. 5, 8, 12 are NOT linear polarization curves. It is a serious error of the authors; they do not know how to distinguish what each technique is, between LPR and PPC?
• In table 2, 4, 8 and 10, it must be corrected: remove Ref. put the type of reference electrode, the standard deviation values should be attached
• In the EIS results, Nyquist diagrams should include the fit and place the "Y" axis legend, and Bode diagrams should be integrated to see if there is really a single time constant.
• In figure 6 in the Nyquist diagram which means sample B, it is necessary to window it (Zoom)
• There is no discussion of results; it should be enriched with references.
• What is the mechanism of corrosion by electrochemical tests?
• The first paragraph of conclusions should be eliminated
• The paragraphs of the conclusions are very long and have no value, the authors must correct and redo the conclusions that have been punctual and that comply with the objectives of each of the techniques used.
• The authors present 43 references. It only has two references from 2023, you must attach updated references.
• References should be corrected as indicated in the Journal: Authors are in an order such as 1. Rojo, R; Gharibi, R; ..... the journal names are abbreviated, the word Vol. pp, etc. should be eliminated.

Author Response

Rewiever 1

Corrosion Behavior of Electrochemical and Thermal Treated Titanium into Artificial Saliva: Effect of pH and Fluoride Concentration

Although the proposed manuscript is very interesting, there are some weaknesses that suggesting to a major revision. This based on the follow:

• The objective of the study is not clear; it must justify the scope of the investigation.
• Authors should enrich the introduction with recent works. 36-38
• Indicate why the chemical composition of the alloys was obtained using analytical technique.

We thank the reviewer for these valuable comments. In this revised version, we have provided further explanations, enriched the introduction, and indicated why the chemical composition was obtained using an analytical technique.

• A section must be included: 2.2 Electrochemical oxidation

Okay; it has been done.

• Section 2.3 should be corrected and read: Electrochemical corrosion or electrochemical tests or electrochemical measurements

It has been done.

• In Electron Microscopy, the authors must indicate which sensor they use: secondary or back-dispersed electrons.

In this revised version, we have clarified the type of detector used.

• The abstract and objective mention that they used linear polarization (LPR) and the materials section says potentiodynamic polarization curves (PPC). Which is correct? What is the repeatability of their tests?

We sincerely thank the reviewer for these valuable comments. In this revised version, we have added further clarifications regarding the technique employed and have also addressed the aspect of repeatability.

As mentioned in the text, to ensure reproducibility, all electrochemical measurements were repeated three times. The curves obtained by potentiodynamic polarization being almost superimposable (the margins of error were around 5% on the extrapolated values, which led to 10% on Rp), only one curve will be presented per experiment. The measurement uncertainties have been added.

• Why use PPC and LPR if one technique is high field and the other is low field?

In this study, we employed a single technique, namely PPC. This high-field electrochemical method allows the analysis of corrosion mechanisms by investigating both anodic and cathodic reactions under varying polarization conditions. Moreover, PPC is particularly suitable for identifying localized forms of corrosion, such as pitting, at elevated potentials.

• The materials section, Says: And energy dispersive spectroscopy …. The correct is: energy-dispersive X-ray Spectroscopy (EDS)

Thanks, it has been corrected.

• In section 3.1 and 3.2 there is no discussion of results, they are only described.

Some comments about the color of the layers were added in 3.1. The amorphous aspect of the layers is well known (we add a sentence about this point).

Some changes were added in section 3.2, but we don’t see how to improve the discussion beyond what has been written: “Both surface treatments led to an increased concentration of oxygen, indicating the thickening of the oxide film”.

• Figure 2, 11, 14, should say Figure X. SEM-SE according to the sensor used, the magnification of the images should be indicated (for example 2000X),

In the revised version, the captions of Figures 2, 11, and 14 have been corrected to indicate “SEM-SE” according to the detector used, and the magnifications (e.g., 55000×) have been added.

• In the morphologies there must be indications about the particles, phases, etc.

The description of the morphologies has been reviewed: The titanium surface is composed by faceted crystallites approximately 100 nm in size, the TT surface appears denser and more homogeneous, while the EO surface exhibits some parts with cracks and holes, each around 100 nm or smaller. to clearly indicate the size of the particles.

Given the nanometric size of the particles or surface defects, it was not possible to be more precise except by carrying out examinations with a transmission microscope (analysis too expensive given our limited budget).

• Figures 3. 5, 8, 12 are NOT linear polarization curves. It is a serious error of the authors; they do not know how to distinguish what each technique is, between LPR and PPC?  PPC not LPR

We appreciate the reviewer’s valuable comment. The issue has been corrected accordingly in the revised manuscript.

• In table 2, 4, 8 and 10, it must be corrected: remove Ref. put the type of reference electrode, the standard deviation values should be attached

We thank the reviewer for this valuable comment. Tables were corrected and standard deviation values were added.

• In the EIS results, Nyquist diagrams should include the fit and place the "Y" axis legend, and Bode diagrams should be integrated to see if there is really a single time constant.

We thank the reviewer for this valuable comment. Bode diagrams and comments have been included in the revised manuscript.

• In figure 6 in the Nyquist diagram which means sample B, it is necessary to window it (Zoom)

It has been included in the revised manuscript.

• There is no discussion of results; it should be enriched with references. 

Accordingly, the discussion section has been expanded and improved following the reviewer’s recommendations.

• What is the mechanism of corrosion by electrochemical tests?

The mechanism of corrosion has been clarified in this revised version through additional electrochemical tests.

• The first paragraph of conclusions should be eliminated

Ok, it has been done.

• The paragraphs of the conclusions are very long and have no value, the authors must correct and redo the conclusions that have been punctual and that comply with the objectives of each of the techniques used.

We thank the reviewer for the comment. This point has been improved in the revised manuscript.

• The authors present 43 references. It only has two references from 2023, you must attach updated references.  

In the revised version, 15 references were added, including works published in 2023 and 2024.

• References should be corrected as indicated in the Journal: Authors are in an order such as 1. Rojo, R; Gharibi, R; ..... the journal names are abbreviated, the word Vol. pp, etc. should be eliminated.

All references have been revised and reformatted according to the journal’s guidelines.

Reviewer 2 Report

Comments and Suggestions for Authors

 The submitted manuscript presents an interesting and valuable study.
 Few details should be considered by the authors:

• Lines 96-97: please remove the TT and EO abbreviation, as they are introduced in lines 100 and 105
• Section 2.2 Present the scanning velocity (deg/min)
• Table 2: present in the text the Tafel slope values.
• Table 3: define "n"; do the same in the other tables related to Nyquist diagrams. 
• Lines 577 - 588 (end of the manuscript) The meaning of the info presented is not clear. explain or delete the text.

Author Response

The submitted manuscript presents an interesting and valuable study.
 Few details should be considered by the authors:

• Lines 96-97: please remove the TT and EO abbreviation, as they are introduced in lines 100 and 105

We thank the reviewer. It has been done in the revised version.

• Section 2.2 Present the scanning velocity (deg/min)

It has been done in the revised version.

• Table 2: present in the text the Tafel slope values.

The explanation of the Tafel’s slope method used here was added in paragraph 2.4. Tafel slopes values were added for the bare material at neutral pH.

Table 3: define "n"; do the same in the other tables related to Nyquist diagrams. 

This has been demonstrated in the revised version of the manuscript.

• Lines 577 - 588 (end of the manuscript) The meaning of the info presented is not clear. explain or delete the text.

This was an error (copy of the instructions for the authors concerning how to write the bibliography). The corresponding text has been deleted.

Reviewer 3 Report

Comments and Suggestions for Authors

This work has studied the corrosion behavior of pure titanium under surface treatment, as well as the effects of pH and fluoride concentration. This study is important, and the results can provide useful insights for biomedical applications. Please see the comments below for revision.

1. In the first paragraph of the introduction, Line 35, it states: “favorable mechanical properties including high Young’s modulus”. However, for orthopedics and dentistry, titanium is normally valued for its relatively low Young’s modulus.
2. Surface treatments such as introducing compressive stress on the surface and refining surface grains have been among the most widely used approaches for enhancing the corrosion performance of titanium alloys. These should be mentioned to provide a broader background, followed by a comparison of how the thermal treatment method adopted in this work compares with other methods.
3. The introduction section mainly cites literature published before 2014 and overlooks more recent studies on titanium alloys with different heat and surface treatments aimed at understanding and improving the corrosion resistance of biomedical titanium alloys. Examples include: “Corrosion behavior and mechanisms of the heat-treated Ti5Cu produced by laser powder bed fusion”, “Corrosion and passivation behavior of Ti-6Al-4V surfaces treated with high-energy pulsed laser: A comparative study of cast and 3D-printed specimens in a NaCl solution”, “Corrosion behavior of an ultrafine-grained Ti6Al4V-5Cu alloy in artificial saliva containing fluoride ions”, and “Corrosion behavior and microstructural effects on passivation film mechanisms in forged Ti-5Al-5Mo-5V-1Cr-1Fe titanium alloy under laser surface remelting”. Including a discussion of recent literature would strengthen the context, after which the authors could highlight why pure titanium was chosen and the significance of this work.
4. In Section 2.1, how were the pure titanium discs made? It would be helpful to provide some details so that readers can follow the methodology.
5. On Page 3, Line 96, providing more details on why TT and EO durations ranged from 20 minutes to 4 hours would enhance the readers’ understanding. Additionally, a description of how these treatments were conducted and under what environment should be included.
6. On Page 6, Line 197, it states “the corrosion potential and oxidation currents are lowest in the neutral medium (pH 6.5)”. While the lowest corrosion and passive currents in Table 2 indicate high corrosion resistance for the pH 6.5 sample, the relatively low corrosion potential for the pH 6.5 sample, as shown in Figure 3 and Table 2, presents a somewhat unusual phenomenon.
7. Line 226, “pH6.6” should be corrected as “pH6.5”.
8. The fitting results in Table 3 should add standard deviation.
9. It is unclear why there is a dashed line in Figure 6. Additionally, the caption for Figure 6 is incorrect. Please carefully check and edit the manuscript during the revision.
10. Similar to Comment 6, the untreated titanium (B) at 0 ppm F⁻ shows the best corrosion performance, but the corrosion potential is obviously the lowest according to Figure 8 and Table 8, which is inconsistent with other figures.
11. The scale bar and numbers in Figure 11 and Figure 14 could be made it larger for easier reading.
12. The conclusion section is somewhat lengthy and could be made slightly more concise.

Author Response

This work has studied the corrosion behavior of pure titanium under surface treatment, as well as the effects of pH and fluoride concentration. This study is important, and the results can provide useful insights for biomedical applications. Please see the comments below for revision.

1. In the first paragraph of the introduction, Line 35, it states: “favorable mechanical properties including high Young’s modulus”. However, for orthopedics and dentistry, titanium is normally valued for its relatively low Young’s modulus.

 We are grateful to the reviewer for the pertinent comments. The manuscript has been corrected in accordance with these recommendations.

1. Surface treatments such as introducing compressive stress on the surface and refining surface grains have been among the most widely used approaches for enhancing the corrosion performance of titanium alloys. These should be mentioned to provide a broader background, followed by a comparison of how the thermal treatment method adopted in this work compares with other methods. 

A paragraph and references have been introduced in accordance with these recommendations.

1. The introduction section mainly cites literature published before 2014 and overlooks more recent studies on titanium alloys with different heat and surface treatments aimed at understanding and improving the corrosion resistance of biomedical titanium alloys. Examples include: “Corrosion behavior and mechanisms of the heat-treated Ti5Cu produced by laser powder bed fusion”, “Corrosion and passivation behavior of Ti-6Al-4V surfaces treated with high-energy pulsed laser: A comparative study of cast and 3D-printed specimens in a NaCl solution”, “Corrosion behavior of an ultrafine-grained Ti6Al4V-5Cu alloy in artificial saliva containing fluoride ions”, and “Corrosion behavior and microstructural effects on passivation film mechanisms in forged Ti-5Al-5Mo-5V-1Cr-1Fe titanium alloy under laser surface remelting”. Including a discussion of recent literature would strengthen the context, after which the authors could highlight why pure titanium was chosen and the significance of this work.

We are grateful to the reviewer for the pertinent comments and suggestions. The manuscript has been thoroughly improved in accordance with these recommendations, and additional references have been included for further clarification.    

1. In Section 2.1, how were the pure titanium discs made? It would be helpful to provide some details so that readers can follow the methodology.  ok

The following sentence has been added to the revised version of the manuscript for clarification: “Pure titanium bars with a diameter of 15 mm (Mayitr, cp-Ti, ASTM B265, Grade 2) were cut into 3 mm-thick discs with a thickness of about 2 mm and used as working electrodes.”

1. On Page 3, Line 96, providing more details on why TT and EO durations ranged from 20 minutes to 4 hours would enhance the readers’ understanding. Additionally, a description of how these treatments were conducted and under what environment should be included.

We thank the reviewer for this remark. In the revised version, we have clarified that the choice of heat treatment (TT) and electrochemical treatment (EO) durations was based on previous work conducted by the Madirel-Marseille laboratory group. Several treatment times were tested, and the most effective condition was selected for the fluorinated solution. EO treatments were carried out at room temperature, a separated paragraph has been added to the revised version to satisfy the request of another reviewer. For TT, as mentioned in the text: the samples were annealed ex-situ in air at 450 °C using a standard furnace (Nabertherm 30/3000 °C) with a controlled heating rate of 5 °C/min.

1. On Page 6, Line 197, it states “the corrosion potential and oxidation currents are lowest in the neutral medium (pH 6.5)”. While the lowest corrosion and passive currents in Table 2 indicate high corrosion resistance for the pH 6.5 sample, the relatively low corrosion potential for the pH 6.5 sample, as shown in Figure 3 and Table 2, presents a somewhat unusual phenomenon.

We appreciate the reviewer’s insightful comment. In the revised version, we highlight this unusual phenomenon and discussed this point (see section 3.3.1.a)

1. Line 226, “pH6.6” should be corrected as “pH6.5”. 

The pH value has been corrected.

1. The fitting results in Table 3 should add standard deviation.   

Chi-squared values (c² ) were directly added in the tables coming from EIS extrapolations. As you know this value is directly related to the quality of the fitting. In our case, the c² values being very low (in the range of 10^-3) the deviations between experimental and simulated values are small (1). Standard deviations have not been added to avoid overloading the tables and make reading easier

• Lasia,A., Electrochemical Impedance Spectroscopy and its Applications, Springer, 2014.

1. It is unclear why there is a dashed line in Figure 6. Additionally, the caption for Figure 6 is incorrect. Please carefully check and edit the manuscript during the revision.

We thank the reviewer. The line in Figure 6 has been removed, and the caption has been revised.

1. Similar to Comment 6, the untreated titanium (B) at 0 ppm F⁻ shows the best corrosion performance, but the corrosion potential is obviously the lowest according to Figure 8 and Table 8, which is inconsistent with other figures.

The unusual behavior of _Ecorr could be explained as previously by the slowing down of the cathodic reaction.

1. The scale bar and numbers in Figure 11 and Figure 14 could be made it larger for easier reading.              

Thanks, it has been done. 

1. The conclusion section is somewhat lengthy and could be made slightly more concise. 

We thank the reviewer for this constructive criticism. We have taken it into consideration and revised the conclusion accordingly, in line with the reviewer’s remarks.

Round 2

Reviewer 3 Report

Comments and Suggestions for Authors

The authors have revised the manuscript and it can be accepted.

However, some errors (special characters) in the x- and y-axis labels in Figures 3, 4, 5, 6, 7, 8, 9, 12, and 13 were noted and should be corrected.

Author Response

Comment 1: The authors have revised the manuscript and it can be accepted. However, some errors (special characters) in the x- and y-axis labels in Figures 3, 4, 5, 6, 7, 8, 9, 12, and 13 were noted and should be corrected.

Answer : We thank the reviewer. The new figures have been introduced.