Corrosion Protection Evaluation of Mild Steel: The Role of Hybrid Materials Loaded with Inhibitors
Round 1
Reviewer 1 Report
The manuscript appears to be nicely written at the first glimpse but when reading it in more details serious flaws are observed. Firstly, application of inhibitors with nanocontainers is designed for coatings, there is no need to use nanoncontainers in solution where inhibitor can be dissolved anyway! Secondly ATT has been examined as corrosion inhibitor by other researchers so authors should have addressed literature findings. Thirdly, as nanocontainers also adsorb on steel surface they may also provide some inhibiting effect which is not evaluated in this work. On page 2 authors explain the motivation for their work and test parameters that will be examined in the work but it appears that very little of the announced has been actually conducted (only one type of inhibitor and steel is examined). Thus the overall quality of this paper is not sufficiently for manuscript publication in this journal.
Specific comments:
From the EDS results on mild steel Figure 6 it is concluded that there is no oxide layer on the steel surface. Taking in account sample preparation described in 2.2., exposure to NaOH solution should result in oxide formation
"All the electrochemical characterizations were conducted in a pH range from 6.92 to 7.74."- what was the reason of pH variation?
There is no need for Figure 2 when everything is already presented in Table 2.
Figure 10- there is no unit for impedance modulus. There is something wrong with EIS data for blank sample. Phase angle values are too low. When presenting EIS data both experimental and fitted data should be presented.
There is no explanation how Cdl was calculated.
Author Response
Response to Reviewer #1 comments
Dear Editor,
Below follows a detailed list of answers (in red) to the Reviewer’s constructive comments together with the changes that we have made in the manuscript.
Point 1: The manuscript appears to be nicely written at the first glimpse but when reading it in more details serious flaws are observed. Firstly, application of inhibitors with nanocontainers is designed for coatings, there is no need to use nanoncontainers in solution where inhibitor can be dissolved anyway!
Response 1: The authors agree with the Reviewer’s comment that application of inhibitors with nanocontainers is designed for coatings. However, the motivation for this work is the assessment of the corrosion behavior of mild steel in the presence of potential corrosion inhibitor 5-amino-1,3,4-thiadiazole-2-thiol (ATT) loaded into hybrid material. The authors wanted to first evaluate the potential inhibitive effect of ATT loaded into nanocontainers on mild steel without any obstruction of the inhibitor action by the coating. Our future plans include studies on the corrosion protection of coatings containing (CexTiyOz) nanocontainers loaded with ATT that will be applied onto several metal alloys.
Point 2: Secondly ATT has been examined as corrosion inhibitor by other researchers so authors should have addressed literature findings.
Response 2: The authors would like to thank the Reviewer for his comment. Additional references have been placed in the introduction part addressing the evaluation of ATT as corrosion inhibitor in metal alloys, in the presence of either acid environments or NaCl electrolytes (Yang et al. Applied Surface Science 255 (2008) 2994-2999; Bentiss et al. Journal of Electroanalytical Chemistry 803 (2017) 125-134; Kartsonakis et al. Corrosion Science 112 (2016) 289-307; Sethuraman et al. Materials Today Communications 14 (2018) 27-39; Solmaz et al. Colloids and Surfaces A: Physicochem. Eng. Aspects 312 (2008) 7-17).
Point 3: Thirdly, as nanocontainers also adsorb on steel surface they may also provide some inhibiting effect which is not evaluated in this work.
Response 3: This type of studies will be included in our future plans, where evaluation of empty nanocontainers of ceramic nanocontainers (including nanocontainers of CexTiyOz) on the corrosion protection of mild steel, black steel and hot dip galvanized steel will be conducted in acid, neutral and basic corrosive environments.
Point 4: On page 2 authors explain the motivation for their work and test parameters that will be examined in the work but it appears that very little of the announced has been actually conducted (only one type of inhibitor and steel is examined). Thus, the overall quality of this paper is not sufficiently for manuscript publication in this journal.
Response 4: The text related to motivation has been revised according to the Reviewer’s comment.
Point 5: From the EDS results on mild steel Figure 6 it is concluded that there is no oxide layer on the steel surface. Taking in account sample preparation described in 2.2., exposure to NaOH solution should result in oxide formation
Response 5: The text 2.2 was revised and the sentence “All the substrates were abraded again with SiC paper up to 5μm grain size (P4000) prior their use in the electrochemical characterizations. All the aforementioned cleaning procedure is necessary in order the removal of oils, grease, and caked-on dirt; removal of scale and oxide films by pickling.” was added. The absence of oxide formation on the surface of the steel is ascribed to the abrading process.
Point 6: "All the electrochemical characterizations were conducted in a pH range from 6.92 to 7.74."- what was the reason of pH variation?
Response 6: The reason for the pH variation, roughly 0.82, can be ascribed due to the residence time of the distilled water (after the distillation process) until it is used for the preparation of the electrolyte solutions. As the time elapses, more carbon dioxide from the environment is absorbed, which is hydrolyzed making the distilled water more acidic.
Point 7: There is no need for Figure 2 when everything is already presented in Table 2.
Response 7: Figure 2 was omitted.
Point 8: Figure 10- there is no unit for impedance modulus. There is something wrong with EIS data for blank sample. Phase angle values are too low. When presenting EIS data both experimental and fitted data should be presented.
Response 8: Figure 9 (former Figure 10) was revised. Both experimental and fitted EIS data are presented. The authors agree that the phase angle degrees for the blank samples are not very negative. The obtained results can be attributed to the rapid corrosion onset of the blank samples.
Point 9: There is no explanation how Cdl was calculated.
Response 9: The Cdl is calculated by equation (2): “Taking into account the aforementioned Equation (2), the Cinh and Cdl parameters were determined (Table 5).”.
Reviewer 2 Report
The authors present a study on the corrosion behavior of a protected mild-steel with a composite material. Several characterization techniques are performed and described properly, and finally, a model of the possible mechanism of corrosion inhibition is proposed.
Here are some observations:
-The introduction needs to be checked for grammar and clarity.
-On the analysis, the peaks as identified by the authors in the XRD pattern correspond to: "TiO2 anatase (89-4921, syn), Ti0.936O2 rutile (89-0554,syn), cerium (38-0765), Ce11O20 cerium oxide (89-8435), CeO2-x cerium oxide (49-1415) and Ce2TiO5 cerium titanium oxide (49-1606)."
I will assume to find only CeTiO peaks when it is mentioned that the "nanocontainers are of high purity".
It seems that the resulted material are phases of TiO2 and CeO2 separately but not the formation fo CeTiO. Can the authors explain this? In such case you would have a mix of TiO2 and CeO2.
-It is not clear (or maybe I missed it) in the text how the nanocomposite is applied to the surface of the steels. Can the authors provide a brief description or a reference that explains how the steels are coated and if this coverage uniform?
-It is not discussed what it is the role of the TiO or CeO2 or CeTiO in the corrosion effect? Are these compounds gone after the exposure to NaCl?
Comments for author File: 
Comments.pdf
Author Response
Response to Reviewer #2 comments
Dear Editor,
Below follows a detailed list of answers (in red) to the Reviewer’s constructive comments together with the changes that we have made in the manuscript.
Point 1: The authors present a study on the corrosion behavior of a protected mild-steel with a composite material. Several characterization techniques are performed and described properly, and finally, a model of the possible mechanism of corrosion inhibition is proposed. Here are some observations: The introduction needs to be checked for grammar and clarity.
Response 1: The introduction part has been revised in respect of grammar and clarity.
Point 2: -On the analysis, the peaks as identified by the authors in the XRD pattern correspond to: "TiO2 anatase (89-4921, syn), Ti0.936O2 rutile (89-0554,syn), cerium (38-0765), Ce11O20 cerium oxide (89-8435), CeO2-x cerium oxide (49-1415) and Ce2TiO5 cerium titanium oxide (49-1606)."
I will assume to find only CeTiO peaks when it is mentioned that the "nanocontainers are of high purity".
It seems that the resulted material are phases of TiO2 and CeO2 separately but not the formation fo CeTiO. Can the authors explain this? In such case you would have a mix of TiO2 and CeO2.
Response 2: The part related to XRD discussion was revised: “Considering the aforementioned types, it maybe remarked that the produced nanocontainers consist of phases cerium titanium oxide together with cerium oxide and titanium oxide. This result can be assigned to the different reactivity of the inorganic precursors of TTIP and Ce(NO3)3 during their hydrolysis and condensation reactions.”
Point 3: -It is not clear (or maybe I missed it) in the text how the nanocomposite is applied to the surface of the steels. Can the authors provide a brief description or a reference that explains how the steels are coated and if this coverage uniform?
Response 3: The steels are not coated with nanocontainers. The loaded nanocontainers were added into the electrolytic solution (NaCl 3.5 wt.%). As the immersion time of the mild steel into the electrolytic solution (corrosive environment) elapses, the inhibitor is released from the nanocontainers and is adsorbed onto the steel surface. The corresponding part of the text was revised as following: “For this purpose, mixtures of loaded nanocontainers in a corrosive environment of NaCl 3.5 wt.% solutions were used. The solutions of NaCl 3.5 wt.% were prepared with distilled water. The loaded nanocontainers were added into the electrolytic solution (NaCl 3.5 wt.%). As the immersion time of the mild steel into the electrolytic solution (corrosive environment) elapses, the inhibitor is released from the nanocontainers and is adsorbed onto the steel surface. Taking into account the TGA results denoting that the CexTiyOz nanocontainers are ~ 32 wt.% loaded with ATT (Figure 2) as well as the low solubility of ATT corrosion inhibitor in water (0.5 mg/100g), the content of loaded nanocontainers in NaCl solution was 0.050 w/v in order saturated solutions of ATT to be obtained.” Moreover, the reference “Kartsonakis et al. Journal of Nanoscience and Nanotechnology Vol. 10, 1–9, 2010” was added to the text, explaining the procedure.
Point 4: --It is not discussed what it is the role of the TiO or CeO2 or CeTiO in the corrosion effect? Are these compounds gone after the exposure to NaCl?
Response 4: The CexTiyOz nanocontainers are used as the corrosion inhibitor ATT carriers. The nanocontainers remain into the NaCl solution. The ATT is released from the nanocontainers as the immersion time elapses. However, in our future plans, studies on the evaluation of empty nanocontainers of ceramic nanocontainers (including nanocontainers of CexTiyOz) on the corrosion protection of mild steel, black steel and hot dip galvanized steel will be conducted in acid, neutral and basic corrosive environments.
Round 2
Reviewer 1 Report
Authors have added new sentence in introduction part: „Furthermore, black steel does not contain any carbon“ – as far as I know black steel has low carbon content but it is not zero.
Page 2: „They found that ATT was performed a perfect inhibition efficiency“ what would be a perfect inhibition efficiency?
„The main goal of the presented study is to discern which inhibitors perform best at the aforementioned corrosion process restriction.“ ; “The originality and novelty of the present research rests upon type of corrosion inhibitors studied that are loaded into hybrid materials, on the corrosion behaviour of mild steel.“ – As stated in first review, only one inhibitor was studied so this cannot be the main goal of this work.
Author Response
Dear Editor,
Below follows a detailed list of answers (in red) to the Reviewer’s constructive comments together with the changes that we have made in the manuscript.
Reviewer #1
Point 1: Authors have added new sentence in introduction part: „Furthermore, black steel does not contain any carbon“– as far as I know black steel has low carbon content but it is not zero.
Response 1: The authors thank the Reviewer for his recommendation that is right; the sentence was omitted.
Point 2: Page 2: “They found that ATT was performed a perfect inhibition efficiency” what would be a perfect inhibition efficiency?
Response 2: The sentence was revised.
Point 3: „The main goal of the presented study is to discern which inhibitors perform best at the aforementioned corrosion process restriction.“ ; “The originality and novelty of the present research rests upon type of corrosion inhibitors studied that are loaded into hybrid materials, on the corrosion behaviour of mild steel.“ – As stated in first review, only one inhibitor was studied so this cannot be the main goal of this work.
Response 3: Both sentences were rephrased according to the Reviewer’s comments.
Reviewer 2 Report
If you could improve more the quality and presentation of Fig. 2 and Fig. 4, that would be better.
Author Response
Dear Editor,
Below follows a detailed list of answers (in red) to the Reviewer’s constructive comments together with the changes that we have made in the manuscript.
Reviewer #2
Point 1: If you could improve more the quality and presentation of Fig. 2 and Fig. 4, that would be better.
Response 1: Both Fig. 2 and Fig. 4 were revised in order their quality and presentation to be improved.
