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Effects of the Second Anodization Parameters on the Hydrophobicity and Anti-Icing Properties of Al Surface with Composite Nanopore Structure

Coatings 2023, 13(11), 1859; https://doi.org/10.3390/coatings13111859

by Bo Li^1,2, Jie Bai^1,2, Liuqing Yang^1,2, Lusong Zhang^1,2, Xu Dai³, Cheng Zhang⁴

, Xujiang Hua⁴, Tao Zhu⁴, Huiying Xiang⁴, Ruijin Liao³ and Yuan Yuan^4,*

Reviewer 1:

Dhruvi Patel

Reviewer 2: Anonymous

Reviewer 3:

Selcan Karakuş

Coatings 2023, 13(11), 1859; https://doi.org/10.3390/coatings13111859

Submission received: 21 September 2023 / Revised: 13 October 2023 / Accepted: 23 October 2023 / Published: 29 October 2023

(This article belongs to the Special Issue Durability of Transmission Lines)

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

The present manuscript, "Effects of the second anodization parameters on the hydrophobicity and anti-icing properties of Al surface with composite nanopore structure" is good and meet scientific level of publication in Coatings, MDPI. Author’s discussion in compelling and results are presented well in the context of healthy and scientific point view. The author's discussion and arguments are sufficient, clearly explained with good english written proficiency. Therefore, I think that this work can be accepted for the publication after some minor revision.

1. Where is (c) and (d) in the figure 1. There is some confusion in figure 1 and its caption here. Please correct and explain well.

2. Improve introduction explanation with novelty of work.

3. Conclusion is not so promising, discuss the novelty and future perspective.

4. Add some more literatures to support the study.

Author Response

Reviewer: 1

Comments:

Comment 1: Where is (c) and (d) in the figure 1. There is some confusion in figure 1 and its caption here. Please correct and explain well.

Answer: We are thankful to the reviewer for the careful suggestions. We have made some mistakes in the caption of figure 1. Here, we corrected this wrong description under your suggestion.

The revision details are as follows:

Page 3 (line 90): “Experimental platforms: (a) Anodization equipment; (b) Icing experimental chamber; (c) corona performance tests; (d) temperature rise tests” has been rephrased as “Experimental platforms: (a) Anodization equipment; (b) Icing experimental chamber”

Comment 2: Improve introduction explanation with novelty of work.

Answer: Thanks for your valuable suggestions. We have supplemented more contents in introduction to improve introduction explanation with novelty of work under your suggestions.

The revision details are as follows:

Page 2 (line 49): Superhydrophobicity is not completely equivalent to the anti-icing performance, and the low ice adhesion of the superhydrophobic surface is significant for the rapid deicing of overhead transmission lines [1, 2]. Therefore, it is important to study and optimize the anti-icing performance of the superhydrophobic surface.

Page 2 (line 66): Moreover, the structural design of anodized nanopores structure has been the focus of many scholars. The reported structural designs include the dendritic shape [1], bottle type [3], textured dimples [4], etc. These designed nanopores structures prepared by optimized anodization can enable the anodized film to achieve multiple functions [5, 6], including improving corrosion protection [3], expanding the lubricant capacity [4] and inhibiting the consumption of modified solvents and lubricants [1]. Therefore, the preparation of composite nanopore structures by two anodization processes can theoretically improve the anti-icing performance of traditional anodized pore structures.

Among all types of icing on transmission conductors, glaze icing could be seen as the most serious icing disaster that threatens lines and towers. Glaze icing is a phenomenon that occurs in a climate including slight cold, strong wind, rain with large diameters of water droplets, and the intersection of strong warm and cold air [2]. However, limited by experimental conditions, there are fewer studies on the anti-icing protection of conductors against glaze-icing [1, 7], while more attention is paid to the frost and condensation in the indoor room, and ice and snow in the outer environment [8-10]. Therefore, this study is also focused on the stimulated glaze-icing on conductors in the laboratory

Comment 3: Conclusion is not so promising, discuss the novelty and future perspective.

Answer: Thank you for this constructive suggestion. We have supplemented more contents in conclusion to discuss the novelty and future perspective under your suggestions.

The revision details are as follows:

Page 12 (line 376): In this study, the two-step anodizing method was used to prepare superhydrophobic Al surfaces with a composite nano-pores structure, which effectively improves the anti-icing performance of traditional anodized single nanopores structures, especially for glaze-icing protection. This study can be helpful for the further preparation of this Aluminum Conductor Steel Reinforced (ACSR). Moreover, the durability of anti-icing properties still needs further exploration.

Comment 4: Add some more literatures to support the study.

Answer: Thank you for this constructive suggestion. We have added more literatures to support the study under your suggestions.

The revision examples are as follows:

Reference:

[1] Xiang H, Yuan Y, Zhu T, Dai X, Zhang C, Gai Y, et al. A novel durable anti-icing slippery surfaces with dendritic porous structure. Mater Today Phys. 2023;35:101137.

[2] Li B, Bai J, He J, Ding C, Dai X, Ci W, et al. A Review on Superhydrophobic Surface with Anti-Icing Properties in Overhead Transmission Lines. Coatings2023.

[3] Lee J, Lee M-H, Choi C-H. Design of Robust Lubricant-Infused Surfaces for Anti-Corrosion. ACS Appl Mater Interfaces. 2022;14(1):2411-23.

[4] Qin Y, Li Y, Zhang D, Xu N, Zhu X. Wettability, durability and corrosion properties of slippery laser-textured aluminum alloy surface under water impact. Surf Coat Technol. 2020;394:125856.

[5] Liu C-Y, Biring S. Nanoplatform based on ideally ordered arrays of short straight and long beer bottle-shaped nanochannels. Microporous Mesoporous Mater. 2019;287:71-6.

[6] Lee W, Ji R, Gösele U, Nielsch K. Fast fabrication of long-range ordered porous alumina membranes by hard anodization. Nat Mater. 2006;5(9):741-7.

[7] Liu GY, Yuan Y, Liao RJ, Xiang HY, Wang L, Yu Q, et al. Robust and self-healing superhydrophobic aluminum surface with excellent anti-icing performance. Surf Interfaces. 2022;28:101588.

[8] Boinovich LB, Emelyanenko AM, Emelyanenko KA, Modin EB. Modus Operandi of Protective and Anti-icing Mechanisms Underlying the Design of Longstanding Outdoor Icephobic Coatings. ACS Nano. 2019;13(4):4335-46.

[9] Parin R, Martucci A, Sturaro M, Bortolin S, Bersani M, Carraro F, et al. Nano-structured aluminum surfaces for dropwise condensation. Surf Coat Technol. 2018;348:1-12.

[10] Irajizad P, Nazifi S, Ghasemi H. Icephobic surfaces: Definition and figures of merit. Adv Colloid Interface Sci. 2019;269:203-18.

[11] Xiang H, Yuan Y, Zhu T, Dai X, Zhang C, Gai Y, et al. Anti-Icing Mechanism for a Novel Slippery Aluminum Stranded Conductor. ACS Appl Mater Interfaces. 2023;15(28):34215-29.

[12] Dai X, Yuan Y, Liao R, Liu G, Zhang C, Huang H. Experimental Studies of a Novel Anti-Icing Aluminum Conductor With Excellent Durability and Improved Electrical Performance. IEEE Trans Power Delivery. 2023:1-12.

[13] Wang F, Lv F, Liu Y, Li C, Lv Y. Ice adhesion on different microstructure superhydrophobic aluminum surfaces. J Adhes Sci Technol. 2013;27(1):58-67.

[14] Papadopoulos C, Rakitin A, Li J, Vedeneev AS, Xu JM. Electronic Transport in Y-Junction Carbon Nanotubes. Phys Rev Lett. 2000;85(16):3476-9.

[15] Dai X, Wen C, Wu L, Liu L, Wu Y, Ding X, et al. Influences of pulse frequency on formation and properties of composite anodic oxide films on Ti-10V-2Fe-3Al alloy. Chin J Aeronaut. 2021;34(11):228-42.

Reviewer 2 Report

Comments and Suggestions for Authors

In this work, the authors have studied the effect of two-step anodization on the hydrophobicity and anti-icing properties of the aluminum surface. The authors propose that the findings of this study can help protect overhead transmission lines from ice/snow disasters, mitigating any direct economic impacts. The research is interesting, however there are several concerns/questions that must be addressed and highlighted in the manuscript before it is published online and made public.

After careful reading, I would like to offer my comments as follows.

1. The outcomes of the research study are very interesting. However, the entire research is based on a flat Al substrate. When we consider transmission lines, they exhibit a cylindrical geometry and that would certainly play a role on the hydrophobicity and anti-icing performance. Can the authors comment on the effect of substrate geometry on the performance characteristics after anodization?

Additionally, how will the microstructures formation vary from a flat geometry to the cylindrical geometry? Please highlight your comments in the manuscript.

2. Following Point 1, can the authors comment on how this two-step anodization process be scaled to fabricate the composite nanostructure on the Al overhead transmission lines, to understand the feasibility of the process proposed?

3. The authors need to provide more details on the mechanism of the composite structure formation in the two-step anodization process. In the current state, the details are lacking.

4. Since PFAS (per- and polyfluoroalkyl substances) are facing immense regulation and litigations globally due to their ability to persist in the environment and contaminate food/water sources, can the authors comment on any sustainable alternatives that could be used against heptafluorodecyltrimethoxysilane modification? Please make a note about the same in the manuscript.

Comments on the Quality of English Language

Minor editing of English language required

Author Response

Reviewer: 2

Comments:

Comment 1: The outcomes of the research study are very interesting. However, the entire research is based on a flat Al substrate. When we consider transmission lines, they exhibit a cylindrical geometry and that would certainly play a role on the hydrophobicity and anti-icing performance. Can the authors comment on the effect of substrate geometry on the performance characteristics after anodization? Additionally, how will the microstructures formation vary from a flat geometry to the cylindrical geometry? Please highlight your comments in the manuscript.

Answer: Thank you for the constructive suggestion. As you mentioned, the special geometry of the transmission line greatly affects the fabrication of the nano-pores structure. In our previous study, if this nano-pores structure prepared on Aluminum Conductor Steel Reinforced (ACSR) has a similar geometric feature as that of flat Al substrate, the hydrophobicity and anti-icing performance can also particularly improve that of bare transmission conductors [11]. However, the anti-icing behavior of the anodized ACSR is still difficult to achieve that of the flat Al plates, mainly reflected in gaps between single strands of the ACSRs, causing the easy capture of water droplets and the failure of the Cassie hydrophobic state.

For difficulties in the micro-structure formation on the cylindrical structure of the Al conductors, the processed area of the Al conductor needs to be considered to determine the electrical parameters of the anodization (current, voltage, and time, etc.). In addition, a uniform electric field needs to be provided to prepare a uniform pore structure. Otherwise, it will lead to the inconsistent applied current flowing the different areas on the ACSR surface, resulting in uneven distribution of nano-pores structure at different positions, greater fluctuations, and susceptibility to concentrated heating leading to structural damage.

In this study, preparation and anti-icing properties of composite nanopores structure were preliminarily explored on the Al plates. Recently, our group has also reported this composite nanopores structure on SLIPS film. Nevertheless, the preparation and related properties of superhydrophobic ACSRs with this composite nanopores structure need further studies in the future.

Therefore, our comments were highlighted under your suggestions.

The revision details are as follows:

Page 10 (line 321):.In particular, transmission lines with a special cylindrical geometry can significantly affect the fabrication of the composite nano-pores structure [11, 12]. In our previous studies, it was difficult to completely repeatedly prepare this nano-pores structure with a similar geo-metric feature on Aluminum Conductor Steel Reinforced (ACSR) as that of a flat Al substrate. For difficulties in the micro-structure formation on the cylindrical structure of the Al conductors, the processed area of the Al conductor needs to be considered to determine the electrical parameters of the anodization (current, voltage, time, etc.). In addition, a uniform electric field needs to be provided to prepare a uniform pore structure [11, 12]. Otherwise, it will lead to inconsistent current flowing through the different areas on the ACSR surface, resulting in uneven distribution of nano-pores structure at different positions, greater fluctuations, and susceptibility to concentrated heating leading to structural damage. After that, a closely similar micro-structure can be obtained on Al conductors, achieving the hydrophobicity and anti-icing properties. However, the anti-icing behavior of the anodized ACSR is still difficult to achieve that of the flat Al plates, mainly reflected in gaps between single strands of the ACSRs, causing the easy capture of water droplets and the failure of the Cassie hydrophobic state [1, 11].

Page 11 (line 339): In this study, preparation and anti-icing properties of superhydrophobic composite nanopores structure were preliminarily explored on the Al plates. For comparison, Table 2 provides widely-reported studies on the anti-icing superhydrophobic Al plates [1, 2, 7, 8, 13]. Obviously, anodized Al plates with composite structure in this study show low ice adhesion and long-delayed frosting time. Although the outdoor snow icing test was not performed [8], glaze icing tests show a significant improvement compared with previous studies of our group [1, 7]. Therefore, the superhydrophobic Al surface with this composite nano-pores shows profound application potential. Recently, our group has also reported this composite nanopores structure on SLIPS film. Nevertheless, the preparation and related properties of superhydrophobic ACSRs with this composite nanopores structure still need further studies in the future.

Table 2. Comparison in wettability and anti-icing properties of different superhydrophobic aluminum surfaces

Specimens with structures	Technique	Contact angle (°)	Anti-icing behavior	Ref.
Anodized Al plate with composite structure	Anodization	172	0.79 kPa; Delay frosting to 2 h; 0.1 g ice formed after 8 h of the glaze icing	This study
Acid-etched surface with FAS	Acid etching	165	0.58 kPa	[13]
Polyamide mesh structure with SiO₂ nanoparticles	Depositing	153	1.9 kPa; Delay frosting to ~18 min	[2]
Nano-texture by laser processing	Laser ablation	153	Little snow accumulated on the surface after outdoor time of 3 years	[8]
Anodized Al plate with single structure	Anodization	156	Some big glaze-ice at the top edge after 80 min	[7]
Slippery surface with dendritic structure	Anodization and SLIPS	~105	~5 kPa; 1.9 g ice formed after 3 h of the glaze icing	[1]

Comment 3: Following Point 1, can the authors comment on how this two-step anodization process be scaled to fabricate the composite nanostructure on the Al overhead transmission lines, to understand the feasibility of the process proposed?

Answer: Thank you for this careful suggestion. Similar to the precautions for the first anodization on Al overhead transmission lines, the second anodization needs to further consider the appropriate electrical parameters to form the composite nano-pores structure with a similar geometric feature. Moreover, ultrasonic cleaning with deionized water should be considered between twice anodization to ensure no phosphoric acid and impurity residue on the surface of the Al conductors. Here, we have discussed and supplemented related contents on how this two-step anodization process be scaled to fabricate the composite nanostructure on the Al overhead transmission lines.

The revision details are as follows:

Page 11 (line 337): Moreover, similar to the precautions for the first anodization on Al overhead transmission lines, the second anodization needs to further consider the appropriate electrical parameters to form the composite nano-pores structure with a similar geometric feature. Moreover, ultrasonic cleaning with deionized water should be considered between twice anodization to ensure no phosphoric acid and impurity residue on the surface of the Al conductors. Finally, superhydrophobic ACSRs with this composite nano-pores could be fabricated.

Comment 4: The authors need to provide more details on the mechanism of the composite structure formation in the two-step anodization process. In the current state, the details are lacking.

Answer: Thank you for the constructive suggestion. We have supplemented more contents in introduction to explain the designed ideas of the composite nano-pores structure. Also, more discussions on mechanisms of the composite structure formation in this study were also provided under your suggestions.

The revision details are as follows:

Page 2 (line 61): Moreover, the structural design of anodized nanopores structure has been the focus of many scholars. The reported structural designs include the dendritic shape [1], bottle type [3], textured dimples [4], etc. These designed nanopores structures prepared by optimized anodization can enable the anodized film to achieve multiple functions [5, 6], including improving corrosion protection [3], expanding the lubricant capacity [4] and inhibiting the consumption of modified solvents and lubricants [1]. Therefore, the preparation of composite nanopore structures by two anodization processes can theoretically improve the anti-icing performance of traditional anodized pore structures.

Page 11 (line 311): In all, for the prepared composite nano-pores structure, the first step of phosphoric acid anodization has a significant impact on the upper nano-pores structure. The parameter settings refer to previous research to obtain appropriate porosity and roughness to achieve good anti icing behavior [7]. Here, the concave defects of the thin barrier layer at the bottom of the nano-pores were formed by the first anodization of phosphoric acid [5, 6]. The second anodization of oxalic acid will start to dissolve from these defects, and continue to passivate to form narrower nano-pores in the lower layer [1, 4, 14]. Besides effects of the etching and passivation, the second oxidation of oxalic acid will also have a dissolution effect on the upper nano-pores formed under phosphoric acid anodization [1]. When the current density and oxidation time of the second anodization are increased, the roughness and fluctuation of the upper layer will further increase in Figure 2. Therefore, the second step of anodization process not only forms the lower layer nano-pores structure, but also has a dissolution effect on the upper layer nano-pores structure. Finally, by comparing hydrophobicity and anti-icing performance, the optimal parameters for the second anodization to prepare composite pore structures were determined.

References: