Self-Healing Properties of Cerium-Modified Molybdate Conversion Coating on Steel
, Algirdas Selskis, Skirmante Tutliene, Monika Skruodiene, Jurgis Pilipavičius, Jurga Juodkazyte and Rimantas Ramanauskas *Round 1
Reviewer 1 Report
Authors presented the cerium-modified molybdate conversion coatings on a carbon steel. In addition, they analyzed the possible synergistic action of Ce and Mo on the protective and self-healing properties of the coatings.
Overall manuscript is well written but presentation is very poor. Author should revise the present manuscript as per the comments.
1) Abstract need to be revised thoroughly as it looks like summary.
2) Fig. 1 must be revised with spacing between title of the axis and units. What is B in the figure 1. Author should mention in the manuscript.
3) Authors must revise the Fig.4 with some different colors which will be easy to understand. In addition, add the information about peaks in the XPS in figure itself.
4) Authors should revise the Figs. 6 and 8 with different colors.
5) Conclusions need to be revise.
Author Response
Dear Editor, Dear Reviewers,
Thank you for your valuable comments and suggestions! Accordingly, the following corrections were done:
Responses to the Reviewer (I)
- Abstract need to be revised thoroughly as it looks like summary.
Abstract has been revised and this is a new version:
ABSTRACT
An environmentally friendly alternative to chromium, phosphate/molybdate and cerium-modified phosphate/molybdate conversion coatings were deposited on a carbon steel surface. Different surface analytic techniques were applied to obtain complementary information on the composition, element distribution, morphology and inner structure of the coatings in order to establish the relationship between coating properties and corrosion performance. The higher protective and stronger self-healing abilities were found for phosphate/molybdate/cerium conversion coating deposited in a sulphate-containing solution. The protective barrier strength was found to be related with certain aspects of the coating morphology such like homogeneous distribution of fine crystallites and, hence, lower number of structural defects. The self-healing ability depended on both, the composition (higher amount of Ce(IV)) and micro-structural characteristics, such as defectiveness, of the conversion layer.
- 1 must be revised with spacing between title of the axis and units. What is B in the figure 1. Author should mention in the manuscript.
The correct Figure 1 was present in .doc file (see below). Modification occurred while converting this file to .pdf format.
- Authors must revise the Fig.4 with some different colors which will be easy to understand. In addition, add the information about peaks in the XPS in figure itself.
Deconvoluted peaks in revised Fig. 4 b are shown in different colors, as well the binding energies of these peaks are indicated
- Authors should revise the Figs. 6 and 8 with different colors.
The curves in revised Figs. 6, 8 and 9 are shown in different colors.
Fig. 6.
Fig. 8
Fig. 9.
- Conclusions need to be revise.
Conclusions were revised and this is a new version:
Conclusions
A phosphate/molybdate and cerium-modified phosphate/molybdate conversion coatings were deposited on a carbon steel surface in an attempt to find correlations between their corrosion performance and morphology, micro-structure and composition. It was found that ~20 minutes were enough to achieve complete conversion process for each stage of molybdate and cerium layer deposition, while increase in process duration resulted in significant increment in the number of structural defects. The most significant influence on the properties of investigated coatings was exerted by the presence of sulphate ions in the Ce deposition solution. The latter conditions were favorable for the formation of thinner conversion layer, which had significantly lower number of structural defects and exhibited the best protective properties among all the investigated coatings.
The deposited phosphte/molybdate coatings contained Mo(VI) and Mo(IV) compounds with the molar ratio 3:2 and were detected to be incapable of self-repair, what can be attributed to a weaker oxidizing power of Mo(VI) than Ce(IV) compounds.
Modification of phosphate/molybdate coatings with Ce ions resulted in the supplement of conversion layer with a mixture of Ce(III) and Ce(IV) oxides, which was located in the outer part of the coating. The stronger self-healing ability of cerium-modified phosphate/molybdate coatings, which was deposited in sulphate-containing solution, may be attributed to both, the larger fraction of Ce(IV) in the conversion coating and the lower number of structural defects. The results obtained imply that micro-structural characteristics of investigated conversion coatings are important in determining their self-healing abilities.
Reviewer 2 Report
Evaluation of the paper “ Self-healing properties of cerium-modified molybdate conversion coating on steel”
Before first appearance in the text of acronyms please provide their details only some example : FE-SEM-FIB 10 and TEM
This is not clear, so please check and rephase “ The higher protective and stronger self-healing abilities were found for phosphate/molybdate/cerium conversion coating deposited in a sulphate-containing solution. This was attributed to higher values of both: total cerium and Ce(IV) content”
Please indicate some application!
Ok is good addition of Ce but what about its cost ???
“polished with emery paper up to grade 400” this sis a standard procedure ??? how easy will be to replicate at industrial scale?? How much roughness will generate ??
Please provide details of current and others ettup for “X-ray (EDX) spectrometer measurements
Nothing about sample preparation for TEM please provide details
Please provide some image about this casue will make the work more interesting “The increase in the conversion time up to 0.5 h led to the increase in the density of cracks in the film,”
How much error do you estimate “might be some errors in the data”
Nothing mentioned in methods section about “done by mechanical scratching with a sharp metallic needle” please provide details of load and so on
Nothing about the quantification of “higher total amount of Ce”
You say in conclusion “Among cerium-modified”…” This was attributed to the higher total amount of Ce” Please revise this paragraph cause do not make sense
Author Response
Dear Editor, Dear Reviewers,
Thank you for your valuable comments and suggestions! Accordingly, the following corrections were done:
Responses to the Reviewer (II)
- Before first appearance in the text of acronyms please provide their details only some example : FE-SEM-FIB 10 and TEM
All acronyms were explained in the manuscript at their first appearance.
Line 83: A focused ion beam scanning electron microscope (FIB-SEM) system
- This is not clear, so please check and rephase “ The higher protective and stronger self-healing abilities were found for phosphate/molybdate/cerium conversion coating deposited in a sulphate-containing solution. This was attributed to higher values of both: total cerium and Ce(IV) content”
A new version of Abstract was prepared and the mentioned paragraph was rewritten as follows:
Lines 13-17:
The higher protective and stronger self-healing abilities were found for phosphate/molybdate/cerium conversion coating deposited in a sulphate-containing solution. The protective barrier strength was found to be related with certain aspects of the coating morphology such like homogeneous distribution of fine crystallites and, hence, lower number of structural defects. The self-healing ability depended on both, the composition (higher amount of Ce(IV)) and micro-structural characteristics, such as defectiveness, of the conversion layer.
- Please indicate some application!
The area of application of Ce conversion coatings as a possible alternative to toxic chromate coatings is discussed in the Introduction of the revised manuscript: The following paragraph was added to the Introduction.
Line 23:
Steel is the most frequently used metal in various industries, however, its susceptibility to corrosion in many environments limits its application. Therefore, a wide variety of coating processes have been developed to achieve coatings with desirable properties to meet certain surface protection requirements. Chromate conversion coatings have been widely applied for corrosion protection of metals, including steel, as providing both, barrier and self-healing effects.
- Ok is good addition of Ce but what about its cost ???
Ce conversion coatings are of particular interest in the area of metal corrosion as an alternative to toxic chromate coatings. Therefore, the question of Ce compound prices is not dominant in this case. In addition, according to our knowledge, the price of metallic Ce is around eight times lower than that of metallic Mo (https://en.institut-seltene-erden-de)
- “polished with emery paper up to grade 400” this sis a standard procedure ??? how easy will be to replicate at industrial scale?? How much roughness will generate
The steel samples before deposition of conversion coating were polished with grade 400 SiC emery paper on polishing equipment Tegramin-25, which is designed for perfect and reproducible results when preparing them for SEM and TEM analysis.
The following revision in the 62 line was done: ”with polishing equipment Tegramin-25”
- Please provide details of current and others ettup for “X-ray (EDX) spectrometer measurements
The following information regarding the measurements was included: Line 86
The morphology of samples was examined using 2-3 keV energy secondary electrons, EDX spectra were obtained at 1.6 nA probe current and 20 kV high tension.
- Nothing about sample preparation for TEM please provide details
The following details on the sample preparation for TEM measurements were included:
Line 90:
A protective Pt layer of 1 μm thickness was deposited on a sample selected area of 20 μm x 3 μm before a cross-sectioning or sample preparation for TEM. A focussed Ga+ ions beam was used in the sample cutting at 30 kV. Omniprobe Model 100.7 nanomanipulator was applied for TEM lamella lift-off. Final thinning was performed on the attached to TEM grid lamella.
- Please provide some image about this casue will make the work more interesting “The increase in the conversion time up to 0.5 h led to the increase in the density of cracks in the film,”
The following SEM images (g and h) of the Fe/P-Mo-Ce1 sample, where the process of Ce deposition lasted 40 min and resulted in higher amount of structural defects appearance, were added to Fig. 2
g h
- How much error do you estimate “might be some errors in the data”
Depth profiling in the XPS measurements was realized using relatively low energy Ar+ ion beam (accelerating voltage of ca. 1.0 kV and a beam current of 20 µA cm−2). Thus possibile Ce(IV) reduction induced by Ar+ ion bombarding is minimal and Ce(III)/Ce(IV) concentration variations in the measured samples should not exceed 5%.
This information was added in line 226 of the revised manuscript: ~20±5%.
- Nothing mentioned in methods section about “done by mechanical scratching with a sharp metallic needle” please provide details of load and so on
The following information was added of the revised manuscript:
Line 70:
In order to create an artificial defect and to evaluate the self-healing ability of the investigated conversion coatings the deposited samples were manually scratched with metallic needle (the width of scratch ~ 30 µm) to expose a steel surface.
- Nothing about the quantification of “higher total amount of Ce”
The amount of Ce was evaluated by means of EDX analysis and the results are presented in Table 1. The following information was added of the revised manuscript:
Line 321:
as determined by EDX (see Table 1)
- You say in conclusion “Among cerium-modified”…” This was attributed to the higher total amount of Ce” Please revise this paragraph cause do not make sense
Conclusions were revised and this is a new version:
Conclusions
A phosphate/molybdate and cerium-modified phosphate/molybdate conversion coatings were deposited on a carbon steel surface in an attempt to find correlations between their corrosion performance and morphology, micro-structure and composition. It was found that ~20 minutes were enough to achieve complete conversion process for each stage of molybdate and cerium layer deposition, while increase in process duration resulted in significant increment in the number of structural defects. The most significant influence on the properties of investigated coatings was exerted by the presence of sulphate ions in the Ce deposition solution. The latter conditions were favorable for the formation of thinner conversion layer, which had significantly lower number of structural defects and exhibited the best protective properties among all the investigated coatings.
The deposited phosphte/molybdate coatings contained Mo(VI) and Mo(IV) compounds with the molar ratio 3:2 and were detected to be incapable of self-repair, what can be attributed to a weaker oxidizing power of Mo(VI) than Ce(IV) compounds.
Modification of phosphate/molybdate coatings with Ce ions resulted in the supplement of conversion layer with a mixture of Ce(III) and Ce(IV) oxides, which was located in the outer part of the coating. The stronger self-healing ability of cerium-modified phosphate/molybdate coatings, which was deposited in sulphate-containing solution, may be attributed to both, the larger fraction of Ce(IV) in the conversion coating and the lower number of structural defects. The results obtained imply that micro-structural characteristics of investigated conversion coatings are important in determining their self-healing abilities.
Round 2
Reviewer 1 Report
Authors revised the manuscript as per the comments. The revised manuscript can be accepted for publication.
Reviewer 2 Report
Thank you
