Improved Uniformity Properties and Corrosion Resistance of Zinc–Nickel Composite Coating Enhanced by Nano-SiO₂

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

This study examined the use of nano-SiO₂ particles in the electroplating of Zn alloy composite coatings to prevent the corrosion of low carbon steel substrates. The study's findings have the potential to enhance corrosion resistance and surface uniformity, which are critical for applications in industries such as automotive and construction.

 

The paper concluded that the most effective concentration of nano-SiO₂ for enhancing the corrosion resistance and structural uniformity of Zn-Ni coatings was 3 wt%.

 

Coatings that contained 3 wt% SiO₂ concentration exhibited the lowest corrosion current density (5.762 × 10⁻⁶ A/cm²), which was considerably superior to coatings that did not contain nano-SiO₂.

 

The polarization resistance (Rp) was increased by 3 wt% nano-SiO₂ in electrochemical experiments, as evidenced by Tafel plots and electrochemical impedance spectroscopy (EIS), reaching 2282 Ω•cm².

 

The corrosion efficacy was reduced by the presence of excessive SiO₂ (>5 wt%), which resulted in surface roughness and potential microcracks.

 

The grain size was reduced, the coating surface was smoothed, and surface defects such as micropores were eradicated by the addition of nano-SiO₂ as demonstrated by SEM and AFM.

A nano-SiO₂ structure that was distinctly regular was achieved at a concentration of 3 wt%. However, nanoparticle aggregation occurred at higher concentrations (e.g., 10 wt%), resulting in uneven and irregular surfaces.

 

The corrosion resistance of samples containing 3 wt% nano-SiO₂ was most notably enhanced by the formation of a stable passivation layer by Zn coatings.

The investigation encompasses an extensive array of assessments. A comprehensive evaluation of both structural and electrochemical properties is included in the use of SEM, AFM, and EIS.

 

The pervasive use of ZN coatings in industries that necessitate corrosion-resistant materials renders them of industrial significance. The investigation furnishes critical information that facilitates the optimization of electroplating procedures, thereby ensuring that they are consistent with industry standards.

 

-The validity of the results is substantiated by the specific data presentation, which includes tables and figures. For instance, Nyquist and Bode plots exhibit a strong correlation with corrosion resistance measurements.

 

The following are a few of the deficiencies that deserve inclusion in the manuscript:

 

-The study does not include information on corrosion resistance in long-term experiments, as it focuses on the corrosion resistance period. The study is not deficient in that it does not include salt spray test results that could last for weeks or months.

 

- When nano-SiO₂ concentrations exceed 5 wt%, the coating's efficacy is compromised by agglomeration and microcracks. Nevertheless, it does not propose any remedies to mitigate particle agglomeration. It would be more suitable to incorporate solutions to this circumstance into the study.

 

- Small laboratory-scale samples were electroplated with nano SiO₂ onto Zn. It is necessary to provide information regarding the method's scalability for larger industrial components while ensuring a uniform distribution of nano-SiO₂.

 

– In order to guarantee uniform nano-SiO₂ distribution on larger surfaces during industrial-scale production, it is necessary to provide recommendations on how to reduce particulate agglomeration at higher concentrations.

 

- Is it possible to sustain the enhanced corrosion resistance that was observed in the short term when subjected to severe environments, such as marine or chemical atmospheres, for an extended period of time?

 

- Is it possible to resolve the aggregation issues that are observed at elevated SiO₂ concentrations by substituting nano-SiO₂ with nanoparticles like Al₂O₃ or TiO₂? Can articles that contain Al₂O₃ or TiO₂ nanoparticles be compared? Is it possible to enhance corrosion resistance?

 

Nano-SiO₂ is an appealing additive due to its widespread availability and relatively low cost. Nevertheless, the cost-benefit analysis of incorporating 3% nano-SiO₂ into large-scale applications is not yet available. The cost-benefit analysis must be conducted.

 

The industrial applicability of the coating will remain uncertain in the absence of long-term testing. It would be more beneficial for researchers to incorporate the results of industrial applications of ZN into this subject.

 

The study concluded that the most effective concentration for corrosion resistance was 3 wt% nano-SiO₂. However, the paper does not comprehensively investigate the compromises between cost, mechanical strength, and corrosion protection at various concentrations.

 

- Will mechanical properties, such as bond strength and hardness, diminish at a concentration of 3 wt% nano-SiO₂ despite an increase in corrosion resistance? In what manner will the transformation transpire? For a thorough assessment of a material, it is necessary to evaluate its electrochemical stability in conjunction with its mechanical performance.

 

 

English and grammar

 

-The complexity and length of certain sentences render them challenging to comprehend. The intelligibility of the sentences will be enhanced by either shortening them or dividing them into smaller, more comprehensible sentences.

 

- Paragraphs that are superfluous in length are augmented by the repetition of certain phrases. It is possible to enhance the manuscript's conciseness by consolidating the redundant information.

 

Passive voice is permissible in scientific writing; however, excessive use may diminish the text's appeal. For the sake of lucidity, it may be advantageous to convert certain sentences to active voice.

 

- It is suitable for publication; however, it requires further refinement to ensure grammatical consistency, clarity, and conciseness. A native English-speaking editor who specializes in scientific publications is advised to conduct a professional language review or proofreading prior to submission. This enhances the paper's overall legibility and guarantees that it adheres to rigorous academic standards.

 acceptable with minimal modifications.

Comments on the Quality of English Language

 

 

English and grammar

 

-The complexity and length of certain sentences render them challenging to comprehend. The intelligibility of the sentences will be enhanced by either shortening them or dividing them into smaller, more comprehensible sentences.

 

- Paragraphs that are superfluous in length are augmented by the repetition of certain phrases. It is possible to enhance the manuscript's conciseness by consolidating the redundant information.

 

Passive voice is permissible in scientific writing; however, excessive use may diminish the text's appeal. For the sake of lucidity, it may be advantageous to convert certain sentences to active voice.

 

- It is suitable for publication; however, it requires further refinement to ensure grammatical consistency, clarity, and conciseness. A native English-speaking editor who specializes in scientific publications is advised to conduct a professional language review or proofreading prior to submission. This enhances the paper's overall legibility and guarantees that it adheres to rigorous academic standards.

 

 

 

 

 

Author Response

【Response】Thanks very much for the reviewer’s suggestion. We have already accepted the suggestion.

Lines 403-421：“To further verify the long-term corrosion resistance of the ZN-SiO₂ composite coating, a salt spray test was conducted. The results indicate that the ZN coating containing 3 wt% nano-SiO₂ exhibits superior corrosion resistance compared to both the ZN coating without nano-SiO₂ and the coating with a higher concentration of nano-SiO₂.

Specifically, a 3 wt% nano-SiO₂ coating exhibited the best corrosion resistance. In contrast, coatings without nano-SiO₂ or with higher SiO₂ concentrations demonstrated localized corrosion and delamination of the coating. These findings align with the electrochemical impedance spectroscopy and Tafel analysis we provided, confirming that a 3 wt% nano-SiO₂ concentration optimally enhances the uniformity and compactness of the coating, thereby improving its ability to withstand prolonged exposure in corrosive environments.

The results of the salt spray test corroborated the previously provided electrochemical data and demonstrated the stability of the proposed coating under marine or industrial-like conditions. This long-term performance further underscores the potential industrial applications of the ZN composite coating with an optimal nano-SiO₂ content.”

Type of  coating	Time to 5% red rust (hours)
no SiO2	216
3 % SiO2	384
5 % SiO2	336

 

 

The revision has been modified.

- When nano-SiO₂ concentrations exceed 5 wt%, the coating's efficacy is compromised by agglomeration and microcracks. Nevertheless, it does not propose any remedies to mitigate particle agglomeration. It would be more suitable to incorporate solutions to this circumstance into the study.

【Response】Thanks very much for the reviewer’s suggestion. We have already accepted the suggestion.

Lines 226-233 “When the concentration of nano-SiO₂ exceeds 5 wt%, particle agglomeration and the formation of micro-cracks in the coating are observed, negatively impacting the uniformity and performance of the coating. To address these challenges, potential strategies include surface modification of nano-SiO₂ using silane coupling agents, the introduction of dispersants such as PVA into the electroplating solution, and the application of ultrasonic agitation during the electrodeposition process. These methods aim to enhance the dispersibility of nanoparticles and will be further explored in future research to optimize the performance of the coating.”

Thank you for highlighting the need to address particle agglomeration at higher nano-SiO₂ concentrations. We agree that proposing solutions to mitigate this issue would improve the study's practicality and applicability. To this end, we have incorporated a discussion on potential remedies into the manuscript.

The revision has been modified.

- Small laboratory-scale samples were electroplated with nano SiO₂ onto Zn. It is necessary to provide information regarding the method's scalability for larger industrial components while ensuring a uniform distribution of nano-SiO₂.

【Response】Thanks very much for the reviewer’s suggestion. We have already accepted the suggestion.

– In order to guarantee uniform nano-SiO₂ distribution on larger surfaces during industrial-scale production, it is necessary to provide recommendations on how to reduce particulate agglomeration at higher concentrations.

【Response】Thanks very much for the reviewer’s suggestion. We have already accepted the suggestion.

- Is it possible to sustain the enhanced corrosion resistance that was observed in the short term when subjected to severe environments, such as marine or chemical atmospheres, for an extended period of time?

【Response】Thanks very much for the reviewer’s suggestion. We have already accepted the suggestion.

Lines 415-418：“The results of the salt spray test corroborated the previously provided electrochemical data and demonstrated the stability of the proposed coating under marine or industrial-like conditions. This long-term performance further underscores the potential industrial applications of the ZN-SiO₂ coating with an optimal nano-SiO₂ content.” 

- Is it possible to resolve the aggregation issues that are observed at elevated SiO₂ concentrations by substituting nano-SiO₂ with nanoparticles like Al₂O₃ or TiO₂? Can articles that contain Al₂O₃ or TiO₂ nanoparticles be compared? Is it possible to enhance corrosion resistance?

【Response】Thanks very much for the reviewer’s suggestion. We have already accepted the suggestion.

Our group is conducting experiments on nano-Al₂O₃ and nano-TiO₂ as electroplating additives. When the concentration is higher, nanoparticle aggregation occurs. To solve the problem of nanoparticle aggregation, different systems will add different additives. Relatively speaking, they all improve the corrosion resistance. Different materials have different optimal values. Similarly, there are many influencing factors, such as the particle size of the nanoparticles. The particle size of the TiO₂ nanoparticles we obtained is different from that of SiO₂.

Nano-SiO₂ is an appealing additive due to its widespread availability and relatively low cost. Nevertheless, the cost-benefit analysis of incorporating 3% nano-SiO₂ into large-scale applications is not yet available. The cost-benefit analysis must be conducted.

 

The industrial applicability of the coating will remain uncertain in the absence of long-term testing. It would be more beneficial for researchers to incorporate the results of industrial applications of ZN into this subject.

 

The study concluded that the most effective concentration for corrosion resistance was 3 wt% nano-SiO₂. However, the paper does not comprehensively investigate the compromises between cost, mechanical strength, and corrosion protection at various concentrations.

 

- Will mechanical properties, such as bond strength and hardness, diminish at a concentration of 3 wt% nano-SiO₂ despite an increase in corrosion resistance? In what manner will the transformation transpire? For a thorough assessment of a material, it is necessary to evaluate its electrochemical stability in conjunction with its mechanical performance.

【Response】Thanks very much for the reviewer’s suggestion. We have already accepted the suggestion. 

English and grammar

 

-The complexity and length of certain sentences render them challenging to comprehend. The intelligibility of the sentences will be enhanced by either shortening them or dividing them into smaller, more comprehensible sentences.

 

- Paragraphs that are superfluous in length are augmented by the repetition of certain phrases. It is possible to enhance the manuscript's conciseness by consolidating the redundant information.

 

Passive voice is permissible in scientific writing; however, excessive use may diminish the text's appeal. For the sake of lucidity, it may be advantageous to convert certain sentences to active voice.

 

- It is suitable for publication; however, it requires further refinement to ensure grammatical consistency, clarity, and conciseness. A native English-speaking editor who specializes in scientific publications is advised to conduct a professional language review or proofreading prior to submission. This enhances the paper's overall legibility and guarantees that it adheres to rigorous academic standards.

 acceptable with minimal modifications.

【Response】Thanks very much for the reviewer’s suggestion. We have already accepted the suggestion. 

 

 

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

57 – garnered – gathered?

114 - TEA was added to make Ni2+ fully complex – is it correct wording?

Fig. 1 – The text in the plots is too small, and the SEM images lack callouts indicating the objects mentioned in the text (e.g., particles, micro-pores, nodular grains, etc.).

Fig. 1 and Fig. 2 – These figures present the same row of samples but use different sizes and scales, making comparison difficult.

Fig. 3 – This figure shows a ~10 µm agglomerated SiO2 particle, and the authors state that nano-SiO2 particles are accumulated on the surface of the 10 wt% sample. However, there is no evidence of such particles in Fig. 2, so it remains unclear whether Fig. 3 can be a good representation of the sample as a whole. Additional larger-scale images would be helpful to assess the distribution of such particles.

Fig. 5 – According to the authors, the plated coatings are characterized by agglomerated nano-sized granular crystallites. However, while both surfaces exhibit a granular structure, Fig. 5d shows fewer grains with a less dense distribution compared to Fig. 5b. Additionally, Fig. 5c reveals that the sample surface is covered with parallel grooves, but their origin is not explained. It is unclear whether these grooves were already present on the pristine sample surface or emerged during the deposition process. Although the authors mention that the surface roughness increases in the 10 wt% sample, no numerical data is provided.

Author Response

57 – garnered – gathered?

【Response】 Thanks very much for the reviewer’s suggestion. We have already accepted the suggestion. 58-“gathered”.

114 - TEA was added to make Ni2+ fully complex – is it correct wording?

【Response】Thanks very much for the reviewer’s suggestion. We have already accepted the suggestion. TEA was added to form a stable complex with Ni²⁺ ions.

 

Fig. 1 – The text in the plots is too small, and the SEM images lack callouts indicating the objects mentioned in the text (e.g., particles, micro-pores, nodular grains, etc.).

【Response】Thank you for your detailed feedback on the figures. We have revised the figures to address the concerns as follows:

Lines 189-191:“Square frames (a2) highlight micro-pores, dashed circles (a2) indicate irregular particles, triangular frames (c2) mark nodular grains. ”

Fig. 1 and Fig. 2 – These figures present the same row of samples but use different sizes and scales, making comparison difficult.

【Response】Thanks very much for the reviewer’s suggestion. We have already accepted the suggestion.

Fig. 1 and Fig. 2: Consistent scales and sample layouts have been applied to improve comparability.

Fig. 3 – This figure shows a ~10 µm agglomerated SiO₂ particle, and the authors state that nano-SiO₂ particles are accumulated on the surface of the 10 wt% sample. However, there is no evidence of such particles in Fig. 2, so it remains unclear whether Fig. 3 can be a good representation of the sample as a whole. Additional larger-scale images would be helpful to assess the distribution of such particles.

【Response】Thank you for your comments on Fig. 3 and the observation of representative agglomerated SiO₂ particles. However, the area depicted in Fig. 3 represents multiple regions examined during the study period. Furthermore, the morphological characteristics observed in Fig. 2, such as increased surface roughness and the emergence of nodular grains, confirm the presence of particle agglomeration at higher concentrations of nano-SiO₂.We acknowledge this as a limitation of the current study, and it is imperative to acquire a larger scale of images in future research to provide a more comprehensive assessment of particle distribution. We appreciate your suggestions, which will guide the refinement of subsequent studies.

 

Fig. 5 – According to the authors, the plated coatings are characterized by agglomerated nano-sized granular crystallites. However, while both surfaces exhibit a granular structure, Fig. 5d shows fewer grains with a less dense distribution compared to Fig. 5b. Additionally, Fig. 5c reveals that the sample surface is covered with parallel grooves, but their origin is not explained. It is unclear whether these grooves were already present on the pristine sample surface or emerged during the deposition process. Although the authors mention that the surface roughness increases in the 10 wt% sample, no numerical data is provided.

【Response】Thank you for your detailed feedback on the figures. We have revised the figures to address the concerns as follows:

1. Particle structure: Compared with Fig. 5b, the particle distribution density in Fig. 5d is lower, which is caused by the agglomeration of 5wt% nano-SiO₂ particles, in contrast to the uniform grain distribution observed at 3wt% sample.
2. Parallel grooves: The parallel grooves visible in Fig. 5c are due to the substrate pre-treatment process, such as mechanical polishing, rather than the electrodeposition process itself. We hope these clarifications and explanations can address your concerns and deepen your understanding of coating morphology characteristics.

 

Author Response File: Author Response.pdf

Reviewer 3 Report

Comments and Suggestions for Authors

The authors are commended on their methodical experimentation and presentation of data. A suggestion would be to add a brief note on the performance of the modified substrate with respect to commercially available alternatives, to better emphasize the effectiveness of the modifying strategy. Furthermore, some up-to date references, can also enhance overall value of the presented data. 

Author Response

【Response】Thanks very much for the reviewer’s suggestion. We have already accepted the suggestion.

At the end of the main text, we added” Correspondingly, it can be foreseen that compared with traditional commercially available ZN alloys, ZN composite alloys with adding appropriate amounts of nano-SiO₂ will have better corrosion resistance.”

Author Response File: Author Response.pdf

Round 2

Reviewer 2 Report

Comments and Suggestions for Authors

1. Parallel grooves: The parallel grooves visible in Fig. 5c are due to the substrate pre-treatment process, such as mechanical polishing, rather than the electrodeposition process itself. We hope these clarifications and explanations can address your concerns and deepen your understanding of coating morphology characteristics.

In this case, the sample preparation process should be described in more detail. The article states: "The roughness observed in these regions is significantly elevated, indicating potential particle aggregation or uneven dispersion phenomena." However, the increased roughness of the 5 wt% sample appears to be more related to the initial roughness of the sample rather than the properties of the coating. It is unclear why the samples were polished differently, resulting in varying initial roughness.

I would like to mention again a quite similar article related to Zn-Ni coatings enhanced with SiO2 nanoparticles written by Tuaweri et al.: https://www.researchgate.net/publication/275575694_Corrosion_Resistance_Characteristics_of_Zn-NiSio2_Composite_Coatings However, this article is not present in the list of references. Additionally, the results obtained by the authors are in contradiction to the results of the Tuaweri group. It would be valuable to analyse differences between the both studies and the obtained results.

Author Response

【Response】Thanks very much for the reviewer’s suggestion. We have already accepted the suggestion.

The lines 162-164 in the manuscript: “Before electroplating, the low-carbon steel sheet is polished with 400#，800# and 1000# sandpaper, successively. Then it was cleaned thoroughly with anhydrous ethanol, acetone, and DI water for 3 minutes, respectively.” So the detailed description of the sample preparation process had been described before. We agree that the parallel grooves observed in Fig. 5c may be influenced by the substrate pre-treatment process, particularly mechanical polishing rather than electroplating processes, which can also be determined through small-scale SEM images in Fig.1c1&c2. Hence, the observed increase in roughness in the 5 wt% sample is primarily attributed to particle aggregation and uneven dispersion during electrodeposition, rather than initial substrate roughness. We will improve the mechanical polishing method the next step.

Thank you again.

 

I would like to mention again a quite similar article related to Zn-Ni coatings enhanced with SiO2 nanoparticles written by Tuaweri et al.: https://www.researchgate.net/publication/275575694_Corrosion_Resistance_Characteristics_of_Zn-NiSio2_Composite_Coatings However, this article is not present in the list of references. Additionally, the results obtained by the authors are in contradiction to the results of the Tuaweri group. It would be valuable to analyse differences between the both studies and the obtained results.

【Response】

The 14th reference (Tuaweri, T.J.; Jombo, P.P.; Okpala, A.N. Corrosion Resistance Characteristics of Zn-Ni/SiO2 Composite Coatings. Deleted Journal 2014, 3, 1–12) is present in manuscript. Also, in the introduction, it is mentioned that “Extensive research has explored this topic using both acidic and alkaline plating solutions [2,4,7-17].” Because Tuaweri et al. reported the composite coatings were produced from acid sulphate Zn-Ni/SiO₂ baths made from pH 2.0-2.5. This is very different from our work, as our samples were prepared in an alkaline plating solution, especially pH 12.0. Moreover, in order to maintain the integrity of nano-SiO₂, our experiment was conducted at room temperature (25±2℃). As is well known, pH value has a significant impact on electroplating, so there has not been much discussion in our work.

Thank you again.

 

 

Author Response File: Author Response.docx