Next Article in Journal
Numerical Prediction and Reduction of Hat-Shaped Part Springback Made of Dual-Phase AHSS Steel
Previous Article in Journal
A General Vision for Reduction of Energy Consumption and CO2 Emissions from the Steel Industry
Article
Peer-Review Record

Effects of Chloride Ions and Nitrate Ions on the Anodic Dissolution of Iron in Sulfuric Acid Solution

Metals 2020, 10(9), 1118; https://doi.org/10.3390/met10091118
by 1,2,*, 3, 1,2 and 1,2
Reviewer 1: Anonymous
Reviewer 2: Anonymous
Reviewer 3: Anonymous
Metals 2020, 10(9), 1118; https://doi.org/10.3390/met10091118
Received: 16 July 2020 / Revised: 7 August 2020 / Accepted: 11 August 2020 / Published: 20 August 2020

Round 1

Reviewer 1 Report

Dear Authors:

this  a nice paper about a subject seldom discussed in pitting studies

The introduction of the new technique is interesting but is not fully exploited

Need to improve the experimental part by indicating the characteristics of the experimental design adopted for the study

 

Please check the attached document

Comments for author File: Comments.pdf

Author Response

Reviewer 1:

  1. “During the electrodissolution processes of iron in 0.5 mol dm-3 H2SO4 solution, Cl- ions and/or NO3- ions are injected onto the electrode/electrolyte interface by using FI.” redundant

Answer: The “Abstract” has been re-written as MDPI required.

 

  1. “…of the behavior of target irons”

Not clear what you mean here.

Answer: The sentence has been modified. “…, so as to enable close examination of the behavior of target irons.” has been changed into “…, so as to obtain more information about the composition and the stability of the passive film, the anodic dissolution of the electrode, the effects of the injections and so on.”.

 

  1. “2. Materials and Methods”

There are no details of the experimental design. No mention of independen variables and the ranges considered as well of the characteristics of the measured response whatever it is.

Answer: The details of the experimental design have been added in the “Materials and Methods”.

    As shown in Figure 1, the working electrode is placed in a PMMA (polymethyl methacrylate) tube, whose length and diameter are both 4 mm. Thus a partially-closed environment is created. There is a hole on the side wall of the tube near the working electrode to place the reference electrode. Another hole in the upper part of the tube wall connects the FI device. The volume of the injections can be controlled quantitatively by setting the speed and the duration of the rotations.

 

  1. Figure 2 is difficult to clearly appreciate the results, and the figure is too small

Answer: Figure 2 is improved.

 

  1. “the adsorptivity of NO3- ions is relatively weak, so the quantity of NO3- ions adsorbed directly onto the passive film is small and disperses generally, thus Fe3+ ions in the film increases slightly after the disturbance by the injection; “

This is your interpretation but is not readily supported by the data shown.

Answer: The “Fe3+ ions” and “Fe2+ ions” in the manuscript have been changed to Fe(III) and Fe(II) , respectively.

When the concentrations of NO3- ions and Cl- ions are the same (the concentration of NO3- ions is low, 0.02 mol/dm3), these two anions have synergistic effects on the anodic dissolution of iron. Fe(III) would change to (FeCln)3-n and then spreads into the bulk solution, which is beneficial for the pits to nucleate. Table 2 obtained from Figure 3 shows that NO3- ions promote the anodic dissolution of iron when CNO3-/CCl- = 1:1. The same conclusion can be obtained from the SEM morphology (Figure 4).

Correspondingly, this part has been modified in the manuscript.

As NO3- ions have strong oxidation characteristics, it will promote the change of Fe(II) in the passive film into Fe(III) [25, 26] (Fig. 5A stepⅠ). When CNO3- = CCl- = 0.020 mol•dm-3 in the same injections, the two anions adsorbed competitively onto the passive film. Thus Fe(III) in the film increases after the injection disturbance.

 

  1. The advantages of this electrode (the PCE) in comparison with the conventional one are as follows:

The flow injection analysis is a useful technique for the detection of various substances, such as the detection of DNA fragment, trace level of Fe, Hg, Cr, chloride and so on. In the present work, different concentrations of Cl- ions and/or NO3- ions were injected into the partially-closed environment by the flow injection (FI), which can control the quantity of the injected solution accurately. The speed and the duration of each injection can be automatically controlled by program.

Almost all of the electrochemical reactions are carried out at the electrode/electrolyte interface, so the physicochemical microenvironment at the interface is different from the bulk solution. As a result, we cannot predict the electrochemical reactions by measuring the concentrations of the bulk solution.

The primary attempt of this research is to manipulate the physicochemical microenvironment at the electrode/electrolyte interface so as to obtain more information (in a designed environment) about the composition and the stability of the passive film on the electrode surface, the condition for the formation of the passivating species and so on. The effects of the injections on the anodic dissolution processes of iron are then analyzed by comparing the anodic behavior before and after the injection perturbation.

Author Response File: Author Response.doc

Reviewer 2 Report

The paper contains the study of effects of chloride ions (Cl- ions) and nitrate ions (NO3- ions) on the anodic dissolution of Fe/0.5 mol dm-3 H2SO4 system . Investigation was carried out by the flow injection (FI) of various composition-containing solutions into the vicinity of a partially-closed electrode. Authors analyzed the effects on the electrodissolution processes. They found that at low concentration NO3- ions promotes the general corrosion of iron by creating more active sites for Cl- ions but at high concentration it inhibits the Cl- ions related corrosion.

In my opinion this paper can be interesting to readers of Metals journal. But in my opinion, the research presented is not new and was previously carried out in research centers around the world – mainly in Asia. The paper is rather clearly presented. The paper contains 5 figures and 2 tables – some figures are legible and good quality.

English of the paper is rather good and meet the requirement of the journal – in my opinion the language of the paper should be improved. I am asking for corrections by a native speaker.

 

I also find some mistakes for example:

  • Authors should correct Abstract – please describe the scientificity of the test results obtained.
  • The literature review (Introduction) is mainly based on Asian publications. For this reason, it is not possible to assess the validity and scientific novelty of the studies undertaken within paper with regard to world literature.
  • Chapter Materials and Methods – the names of the measuring equipment used should be given – model of equipment (manufacturer, city, country).
  • In the whole paper, you write the values in percent as for example 99.99% (for example: page 2, line 60) – you should write and value with unit with spaces (99.99 %).
  • In my opinion Conclusions chapter should be changed (edited). In this chapter there are no summary of all significant research results obtained by the Authors and written in the Results
  • In Figures 2 – no details are visible – please increase the size of chemical symbols and descriptions on the axes. Please describe individual drawings in the caption (A, A', B, B', C, C'). The inset to figure 4 is illegible.
  • In Figures 3 – no details are visible – please increase the size of chemical symbols and descriptions on the axes. Please describe individual drawings in the caption (A, A', B, B', C, C').
  • In Figures 4 – no details are visible – too small legends on the images (A, A', B, B', C, C') – no details are visible. Please include descriptions of individual photos under the caption for the figures – they can be found below the description for the figures.
  • Amount of references is also sufficient but some papers cited in the references (22 from all 28) are older then 10 years and 26 from all 28 are older then 5 years – Authors should include several modern papers.
  • I the list of references I found 2 papers of the Authors of reviewed paper. Are these the first studies related to this subject for the Authors?
  • Minimum 11 papers from all 28 are wrote by authors from Asia – China, Japan, India and others. I propose to add some new (from the last 5 years) publications on the production or properties of these type of materials. Authors should include several modern papers (also from Europe and America).

 

The manuscript can be accepted for publication in Metals journal after MAJOR corrections.

Author Response

Reviewer 2:

  1. Authors should correct Abstract– please describe the scientificity of the test results obtained.

Answer: The “Abstract” has been re-written as MDPI required.

 

  1. The literature review (Introduction) is mainly based on Asian publications. For this reason, it is not possible to assess the validity and scientific novelty of the studies undertaken within paper with regard to world literature.

Answer: New references have been added to the “Introduction”.

 

  1. Chapter Materials and Methods– the names of the measuring equipment used should be given – model of equipment (manufacturer, city, country).

Answer: All the names of the measuring equipment used in this study have been given.

CHI 660B analyzer (Shanghai Chenhua Instruments Co., Ltd, Shanghai, China).

Peristaltic Pump (Model BT00-600 M, Baoding Lange constant flow pump Co., Ltd, Baoding, China).

Scanning Electron Microscope (SEM, Model S-3400N, produced by Hitachi Company, Tokyo, Japan).

 

  1. In the whole paper, you write the values in percent as for example 99.99% (for example: page 2, line 60) – you should write and value with unit with spaces (99.99 %).

Answer: “99.99%” has been changed into “99.99 %”.

 

  1. In my opinion Conclusionschapter should be changed (edited). In this chapter there are no summary of all significant research results obtained by the Authors and written in the 

Answer: TheConclusions” chapter has been re-edited.

 

  1. In Figures 2 – no details are visible – please increase the size of chemical symbols and descriptions on the axes. Please describe individual drawings in the caption (A, A', B, B', C, C'). The inset to figure 4 is illegible.

Answer: Figure 2 and Figure 4 have been improved.

 

  1. In Figures 3 – no details are visible – please increase the size of chemical symbols and descriptions on the axes. Please describe individual drawings in the caption (A, A', B, B', C, C').

Answer: Figure 3 has been improved.

 

  1. In Figures 4 – no details are visible – too small legends on the images (A, A', B, B', C, C') – no details are visible. Please include descriptions of individual photos under the caption for the figures – they can be found below the description for the figures.

Answer: Figure 4 has been improved.

 

  1. Amount of references is also sufficient but some papers cited in the references (22 from all 28) are older then 10 years and 26 from all 28 are older then 5 years – Authors should include several modern papers.

Answer: Some new publications, especially in the last 5 years, have been added to the manuscript.

 

  1. I the list of references I found 2 papers of the Authors of reviewed paper. Are these the first studies related to this subject for the Authors?

Answer: The first studies related to this measurement setup (the flow injection (FI) combined with a partially-closed electrode (PCE)) have been reported in the journal of Electrochemistry Communication (M. Zeng et al., 2009). However, the contents published are quite different from the contents of this study.

The article of Zeng et al. is to design current oscillations by flow injections (only the bulk solution and water were injected), and then analyze the cause of the oscillations.

In this study, the effects of different anions on the anodic dissolution have been studied by this method for the first time. The local perturbation caused by the FI combined the PCE offers valuable information about the composition and the stability of the passive film, the anodic dissolution of the electrode and so on. Then the effects of the injections (the anions) on the anodic dissolution processes of iron are then analyzed by comparing the anodic behavior before and after the injection perturbation.

 

  1. Minimum 11 papers from all 28 are written by authors from Asia – China, Japan, India and others. I propose to add some new (from the last 5 years) publications on the production or properties of these types of materials. Authors should include several modern papers (also from Europe and America).

Answer: Some new publications, especially from Europe and America in the last 5 years, have been added to the manuscript.

 

Author Response File: Author Response.doc

Reviewer 3 Report

  1. In the Introduction, the authors consider the available data on the effect of Cl ions and NO3 ions on the anodic behavior of iron and stainless steels in both acidic and neutral solutions. Since different electrodes and solutions are considered, the effect of these ions on the corrosion process should be different. It seems to me, first of all, it is necessary to describe the known data on the influence of Cl- and NO3-ions on the corrosion behavior of iron in acids.
  2. It is not clear what purpose the authors pursue by using a partially-closed electrode (PCE). There is no comparison in the manuscript of the results obtained with a conventional electrode and a partially-closed electrode. The Conclusion states “The experimental results show that FI technique combined with PCE is an effective method to investigate the corrosion processes of metals”. However, it remains unclear: which results show the advantages of this electrode in comparison with the conventional one.
  3. The designations in Fig. 2 and 3 are poorly visible. The picture is not visible - insert in Fig. 2 A '.
  4. Fig.4. The authors write that “Ithere is no pit on the surface (Fig. 4B and 4C)”. Nevertheless, the metal surface has many defects (Fig. 4A, 4B, 4C, 4C '). The origin of these defects has not been explained.
  5. Lines 163-164. The meaning of the phrase "According to the hard and soft acids and bases (HSAB) principle [28], Fe3 + ions is hard acid, which combines with Cl- ions (hard base) readily, and then spreads into the bulk solution quickly" is not clear. Why does the formation of the [FeCln] complex affect the rate of movement of Fe3+ ions? It is also not clear what part of the total amount of Fe3 + ions will exist in the form of the [FeCln] complex.
  6. Lines 166-167. The assumption that Fe3+ ions are active / defective sites of the passive film requires a more detailed explanation and justification.
  7. Recommendation: Major Revision.

 

Author Response

Reviewer 3:

  1. In the Introduction, the authors consider the available data on the effect of Cl- ions and NO3- ions on the anodic behavior of iron and stainless steels in both acidic and neutral solutions. Since different electrodes and solutions are considered, the effect of these ions on the corrosion process should be different. It seems to me, first of all, it is necessary to describe the known data on the influence of Cl- and NO3-ions on the corrosion behavior of iron in acids.

AnswerNew references about the influence of Cl- and NO3-ions on the corrosion behavior of iron or stainless steel have been added to the “Introduction”.

 

  1. It is not clear what purpose the authors pursue by using a partially-closed electrode (PCE). There is no comparison in the manuscript of the results obtained with a conventional electrode and a partially-closed electrode. The Conclusion states “The experimental results show that FI technique combined with PCE is an effective method to investigate the corrosion processes of metals”. However, it remains unclear: which results show the advantages of this electrode in comparison with the conventional one.

Answer:

The advantages of this electrode (the PCE) in comparison with the conventional one are as follows:

The flow injection analysis is a useful technique for the detection of various substances, such as the detection of DNA fragment, trace level of Fe, Hg, Cr, chloride and so on. In the present work, different concentrations of Cl- ions and/or NO3- ions were injected into the partially-closed environment by the flow injection (FI), which can control the quantity of the injected solution accurately. The speed and the duration of each injection can be automatically controlled by program.

Almost all of the electrochemical reactions are carried out at the electrode/electrolyte interface, so the physicochemical microenvironment at the interface is different from the bulk solution. As a result, we cannot predict the electrochemical reactions by measuring the concentrations of the bulk solution.

The primary attempt of this research is to manipulate the physicochemical microenvironment at the electrode/electrolyte interface so as to obtain more information (in a designed environment) about the composition and the stability of the passive film on the electrode surface, the condition for the formation of the passivating species and so on. The effects of the injections on the anodic dissolution processes of iron are then analyzed by comparing the anodic behavior before and after the injection perturbation.

A more detailed description about the advantages and the purpose of this method is given in the “Introduction”. Besides, the details of the experimental design have been added in the “Materials and Methods”.

 

  1. The designations in Fig. 2 and 3 are poorly visible. The picture is not visible -- insert in Fig. 2 A '.

Answer: Figure 2 and Figure 3 have been improved. Figure 2A’ has been enlarged and the inserted figure has been deleted.

 

  1. In Fig.4, the authors write that “There is no pit on the surface (Fig. 4B and 4C)”. Nevertheless, the metal surface has many defects (Fig. 4A, 4B, 4C, 4C '). The origin of these defects has not been explained.

Answer: Fig.4A is the surface morphology without injection (relative uniform corrosion morphology). Fig.4 B, C and C’ are very similar to Fig. 4A. The surface defects are maybe the accumulation of corrosion products. The obvious pits are induced by chloride ions (Fig.4 A’), which are well known for their aggressive characteristics.

This explanation has been already re-edited in the manuscript.

As shown in Fig. 4A, relative uniform corrosion morphology is seen without perturbation. And no visible change of surface morphology is observed when the Cl--free solutions are injected into the vicinity of PCE (Fig. 4B and C). If the injected solution only contains Cl- ions, obvious pits appear (Fig. 4A’). But in the presence of NO3- ions in the Cl--containing injections, the corrosion behavior are quite different (Fig. 4B’ and C’).

 

  1. (Lines 163-164) The meaning of the phrase "According to the hard and soft acids and bases (HSAB) principle [28], Fe3+ ions is hard acid, which combines with Cl- ions (hard base) readily, and then spreads into the bulk solution quickly" is not clear. Why does the formation of the [FeCln] complex affect the rate of movement of Fe3+ ions? It is also not clear what part of the total amount of Fe3+ ions will exist in the form of the [FeCln]3-n

Answer: We modified Fe3+ ions to Fe(III) in the passive film. NO3- ions adsorb onto the passive film and then Fe(III) forms in the passive film for the oxidized feature of NO3- ions. In the presence of Cl- ions, Fe(III) changes into [FeCln]3-n complex on the electrode surface and spreads into the bulk solution.

This explanation has been also re-edited in the manuscript.

Thus in the presence of Cl- ions on the electrode surface, Fe(III) in the film changes into (FeCln)3-n and then spreads into the bulk solution quickly (Fig. 5A step Ⅱ and Ⅲ).

  1. (Lines 166-167) The assumption that Fe3+ ions are active / defective sites of the passive film requires and justification.

Answer:

Some references have been cited to explain the assumption. For example, the point defect model (PDM) is accepted by many researchers. A more detailed explanation has been given in the manuscript.

 

Author Response File: Author Response.pdf

Round 2

Reviewer 2 Report

The authors have properly addressed the concerns from the referee. Most of my remarks have been included in the revised document.

The authors reformatted abstract, body text and conclusions of the paper. They corrected figures (2, 3, 4), descriptions and captions of the figures – their quality is satisfying. They corrected the names of the measuring equipment.

Referring to my substantive reservations – the authors made the necessary modifications. They corrected the list of references. Authors have improved the language – language corrections are sufficient.

The manuscript can be accepted for publication in Metals journal in the current form.

Reviewer 3 Report

I have no comments

Back to TopTop