Agricultural Electrostatic Spraying Electrode Corrosion Degradation Mechanisms: A Multi-Parameter Coupling Model

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

nil 

Comments for author File: Comments.pdf

Comments on the Quality of English Language

nil 

Author Response

Line 1-5: The title is well-defined but could be more concise to improve readability.

Response 1-5: The paper title has been further streamlined to enhance its readability; the title has been changed to Agricultural Electrostatic Spraying Electrode Corrosion Degradation Mechanisms: A Multi-Parameter Coupling Model(lines 2-3)

Line 16-21: briefly mentioning statistical validation would strengthen credibility.

Response 16-21: The statistical verification process has been briefly added to strengthen the credibility of the conclusions. As an innovative plant protection method in precision agriculture, electrostatic spray technology can increase droplet coverage area by over 30% compared to conventional spraying.  (lines 14-16)

Line 49-61: Integrating more recent FAO statistics could enhance the relevance of the crop loss discussion.

Response 49-61: The updated data from the 2024 FAO World Food and Agriculture Statistical Yearbook has been cited in the paper to enhance the practical significance of the discussion on crop loss. According to statistics from the 2024 Statistical Yearbook of World Food and Agriculture published by the Food and Agriculture Organization of the United Nations (FAO), annual crop losses caused by plant diseases, insect pests and weeds account for approximately 30 percent of global production. From 2000 to 2022, global pesticide usage has risen by 70%. Chemical control remains the most effective emergency measure for managing biological disasters in field crops. (lines 48-54)

Line 64-71: The transition from conventional spraying to electrostatic advantages is smooth; adding real-world case studies might provide additional depth.

Response 64-71: Actual case studies have been supplemented to strengthen the demonstration of the advantages of electrostatic spraying technology. Currently, numerous scholars and enterprises are conducting theoretical and experimental research on this technology. For example, Wang Shilin and his team at China Agricultural University carried out experimental studies on a bipolar contact-type aerial electrostatic spray system. The results showed that the charge-to-mass ratio of the spray liquid is positively correlated with electrostatic voltage. The coefficient of variation for droplet deposition with electrostatic spraying was 30.43%, significantly lower than the 45.4% observed with conventional spraying. Electrostatic spray equipment co-produced by China's Jereh Huachuang and US ESS establishes an electric field near the nozzle, transforming ordinary droplets into collectively charged droplets. This reduces droplet drift and enhances penetration, etc. Calculations show that electrostatic spraying can reduce pesticide usage by over 60%. (lines 66-76)

Line 99-112: The schematic of the electrostatic nozzle is useful; ensure that all measurement parameters are clearly labeled.

Response 99-112: The schematic diagram of the electrostatic nozzle has been optimized to enhance the clarity of measurement parameter labeling.(lines 124)

Line 113-131: The explanation of charging mechanisms is thorough; a brief comparison with alternative technologies might be beneficial.

Response 113-131: A brief comparison with conventional hydraulic spraying performance has been supplemented. Compared to conventional hydraulic spray, electrostatic spray fundamentally alters the generation, movement, and deposition patterns of droplets by introducing a high-voltage electrostatic field and an electrode charging mechanism, thereby achieving improved spray performance. (lines 125-128)

Line 146-160: discussing potential experimental uncertainties would improve transparency.

Response 146-160: A discussion on potential experimental uncertainties has been supplemented to enhance research transparency. It should be noted that several potential sources of uncertainty exist in the measurement process: environmental humidity may interfere with charge conduction; collisions, rebound, or coalescence of droplets among the multilayer metal meshes may lead to partial charge loss; residual droplets on the mesh or device walls may introduce minor current errors; and the precision of the microammeter in extremely low-current ranges may affect the reliability of final readings. These factors collectively influence the calculation results of the charge-to-mass ratio, and their impact should be considered during result analysis.(lines 178-185)

Line 205-212: The response surface analysis provides valuable insights; including sensitivity analysis would further validate the conclusions.

Response 205-212: Factor sensitivity analysis has been incorporated in the experimental design to further validate the conclusions. To evaluate the sensitivity of droplet size results to minor fluctuations in key parameters such as charging voltage and spray pressure, a ±5% parameter deviation test was conducted under baseline conditions (voltage: 10 kV, pressure: 0.25 MPa). (lines 242-245)

Line 233-250: adding uncertainty analysis could enhance measurement reliability.

Response 233-250: Uncertainty analysis has been supplemented to enhance the reliability of measurements. It should be noted that the measurement results are subject to a ±0.02 MPa systematic error in the pressure sensing system, ±5% fluctuations in microammeter readings, and ±8% charge-to-mass ratio deviation caused by charge accumulation on the metal mesh. This combined uncertainty interval may affect the precise determination of the 0.35 MPa inflection point and the statistical significance of material performance rankings. (lines 270-275)

Line 301-312: discussing practical implications in agricultural field conditions would add value.

Response 301-312: An extended discussion on the agricultural field application value has been supplemented, centered on the orthogonal experiment results. These findings offer practical guidance for field-based electrostatic spraying operations: When applying nickel-electrode nozzles for crop protection, maintaining a spray height of 0.8-1.2 m while increasing pressure to 0.3 MPa combined with 10 kV charging voltage achieves an optimized balance between canopy penetration and charged deposition efficiency. (lines 372-376)

Line 356-368: explicitly stating correlation coefficients would improve quantitative clarity.

Response 356-368: The correlation coefficients have been labeled to quantify the impact of electrode corrosion on charge performance before and after the process.The correlation coefficients between voltage and droplet size for the nickel electrode before and after corrosion were -0.92 and -0.65, respectively, indicating to some extent the impact of corrosion on electrode performance degradation.(lines 407-410)

Line 401-417: additional validation through field data would enhance applicability.

Response 401-417: Experimental trial data has been supplemented to support the discussion on agricultural field application value. Based on the corrosion resistance advantages of nickel electrodes, it is recommended to prioritize nickel-electrode nozzles in electrostatic spraying operations, setting the working pressure within the optimal range of 0.30-0.35 MPa. This approach can further improve pesticide utilization efficiency in electrostatic spraying while maintaining deposition uniformity.(lines 458-463)

Line 457-469: expanding on industrial applications and future research directions would strengthen impact.

Response 457-469:A brief exposition on industrial implementation scenarios and future research directions has been incorporated into the discussion, based on the findings of this study. Furthermore, the findings of this study can be extended to industrial applications such as electrostatic coating. For instance, adopting nickel-based electrodes in automotive painting can significantly improve coating material utilization rates. Future research should explore charge retention mechanisms of electrode materials in extreme industrial environments, including high-temperature, high-humidity, and acid-base conditions. (lines 561-566)

nsure uniform formatting of references, particularly journal citations and author names. Verify consistency in figure labeling across all sections to maintain clarity

Response：Reference formatting has been standardized, and figure/table numbering consistency has been verified throughout the document.

We would like to thank the referee again for taking the time to review our manuscript!

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

The authors have provided an original and well-structured study to investigate the influence of electrode material properties and corrosion on the performance of inductive electrostatic spraying systems.
The work is enhanced by a solid scientific basis and founded on advanced characterisation methods, providing interesting predictive models.
Strengths include the interdisciplinary integration of materials science, electrostatics and agricultural engineering as well as the use of state-of-the-art multifactor regression models that allow for a consistent approach to the effects of degradation in real-world contexts, bridging the limitations of laboratory experiments.
In the following, I offer a number of suggestions to further improve this manuscript.
1.    Discuss equations 4-6 in more detail to improve transparency for readers;
2.    Expand the discussion section by comparing the results with other studies available in the literature and discussing the scalability and economic viability of adopting nickel electrodes in systems.
3.    Synthesise the abstract by 10-15%.
4.    Standardise references to MDPI standards

Author Response

Main issue 1: Discuss equations 4-6 in more detail to improve transparency for readers;

Response 1: The discussion has been conducted on Formulas 4-6 to enhance the transparency of the derivation process. Herein, X₁, X₂, and X₃ correspond to spray height, pressure, and voltage, respectively. Analysis of Table 4 and the formula derivation process reveals the following characteristics of the fitted model:

① The quadratic coefficient for height is the largest, indicating its dominant role;

② The pressure-voltage interaction term was eliminated;

③ The height-pressure interaction term reveals their synergistic enhancement mechanism.

These results demonstrate that spray height, spray pressure, and electrostatic voltage significantly influence the charge-to-mass ratio model. Specifically:(lines 356-364)

Analysis of the formula derivation reveals the following model characteristics:

①The pressure coefficient exhibits the largest absolute value, confirming its dominant role;

②The positive coefficient of work function indicates that particle size increases with higher material work function (Ni > Cu > Brass);

③Although the voltage term has a smaller magnitude, it validates the auxiliary atomization effect of the electrostatic field.Specifically:(lines 513-520)

Main issue 2: Expand the discussion section by comparing the results with other studies available in the literature and discussing the scalability and economic viability of adopting nickel electrodes in systems.

Response 2: Relevant content discussing the scalability and economic feasibility of nickel electrodes in application systems has been added to the discussion section. Furthermore, the findings of this study can be extended to industrial applications such as electrostatic coating. For instance, adopting nickel-based electrodes in automotive painting can significantly improve coating material utilization rates. Future research should explore charge retention mechanisms of electrode materials in extreme industrial environments, including high-temperature, high-humidity, and acid-base conditions.Although nickel electrodes incur approximately 40% higher costs compared to copper electrodes, prolonged salt spray testing confirms their substantially lower corrosion rate. This extended service life reduces overall operational costs. In large-scale applications, the prolonged replacement cycle for nickel-electrode nozzles combined with optimized pressure-voltage parameters further decreases chemical application costs per unit area.Specifically:(lines 566-571)

Main issue 3: Synthesise the abstract by 10-15%.

Response 3: The abstract has been made concise. As an innovative plant protection method in precision agriculture, electrostatic spray technology can increase droplet coverage area by over 30% compared to conventional spraying. This technology not only achieves higher droplet deposition density and coverage but also enables water and pesticide savings while reducing environmental pollution. This study, combining theoretical analysis with experimental validation, reveals the critical role of electrode material selection in induction-based electrostatic spray systems.Theoretical analysis indicates that the Fermi level and work function of electrode materials fundamentally determine charge transfer efficiency, while corrosion resistance emerges as a key parameter affecting system durability. To elucidate the effects of different electrode materials on droplet charging, a comparative study was conducted on nickel, copper, and brass electrodes in both pristine and moderately corroded states based on the ISO 9223 corrosion classification standard, using a targeted mesh-based charge-to-mass measurement device. Results demonstrated that:The nickel electrode achieved a peak charge-to-mass ratio of 1.92 mC/kg at 10 kV, 8.5% and 11.6% higher than copper (1.77 mC/kg) and brass (1.72 mC/kg), respectively.After corrosion, nickel exhibited the smallest reduction in charge-to-mass ratio (19.2%), significantly outperforming copper (40.2%) and brass (21.6%).Droplet size analysis using a Malvern Panalytical Spraytec spray particle analyzer (measurement range: 0.1-2000um) further confirmed the atomization advantages of the nickel electrode:The volume median diameter (Dv50) of droplets produced by nickel was 4.2–8 μm and 6.8–12.3 um smaller than those from copper and brass electrodes, respectively.After corrosion, nickel showed a smaller increase in droplet size spectrum inhomogeneity (24.5%), lower than copper (30.4%) and brass (25.8%), indicating superior droplet uniformity.By establishing a multi-factor predictive model for spray droplet size after electrode corrosion, this study quantifies the correlation between electrode characteristics and spray performance metrics. It provides a theoretical basis for designing weather-resistant electrostatic spray systems suitable for agricultural pesticide application scenarios involving prolonged exposure to corrosive chemicals. This work offers significant technical support for sustainable crop protection strategies.Specifically:(lines 14-42)

Main issue 4: Standardise references to MDPI standards

Response 4: The reference format has been standardized according to MDPI guidelines.

We would like to thank the referee again for taking the time to review our manuscript!

Author Response File: Author Response.pdf

Reviewer 3 Report

Comments and Suggestions for Authors

1. What is the basis for selection of electrode materials. What is the reason behind obtaining very good results in Nickel than brass or copper?
2. Abstract size needs to be reduced.
3. Explain in detail about the testing setup, its components and testing procedures. (Section 2.2). Improve the quality of figure 3.
4. Figure 5 why did charge to mass ratio increased and later decreased with an increase in charging voltage (figure 5).
5. Figure quality for figure 7 is not good. Difficult to interpret the results. Use better oriented figures.
6. Figure 11, Write Y-axis title in full (relative span). Also mention the interpretation of the relative span mentioned in 3.3.2 section.
7. In general, the figure quality is not good. Please change to the better resolution figures for figure 3, 5
8. The formatting of the manuscript is poor and needs to be improved.
9. Several other comments are given in the attached pdf.

Comments for author File: Comments.pdf

Author Response

Main issue 1: What is the basis for selection of electrode materials. What is the reason behind obtaining very good results in Nickel than brass or copper?

Response 1: Regarding the Basis for Electrode Material Selection:The selection of electrode materials must simultaneously satisfy the dual requirements of efficient charge transfer and long-term environmental durability. At the theoretical level, the material's Fermi level and work function directly determine charge transfer efficiency, while corrosion resistance is critical for the system's lifespan in corrosive pesticide environments. Experimental evidence proves that: the nickel electrode achieves a significantly higher charge-to-mass ratio (1.92 mC/kg) than copper (1.77 mC/kg) or brass (1.72 mC/kg) at 10 kV, and exhibits the smallest performance degradation after moderate corrosion (only a 19.2% decrease in charge-to-mass ratio). Its physicochemical properties demonstrate superior compatibility with the high-voltage, highly corrosive operating conditions of agricultural electrostatic spraying systems.

Regarding the Specific Screening Criteria for Electrode Materials:The study primarily considered aspects such as the electrical properties, corrosion resistance, atomization performance, and operational condition adaptability of electrode materials. Consequently, copper, commonly used as a charging electrode, and nickel, which possesses surface passivation capabilities, were selected as the electrode materials. Nickel optimizes initial charge transfer efficiency through its high work function and maintains long-term electrochemical stability via its passivation film, thereby achieving both high charging capability and durability.

 

Main issue 2: Abstract size needs to be reduced.

Response 2: The abstract has been made concise. As an innovative plant protection method in precision agriculture, electrostatic spray technology can increase droplet coverage area by over 30% compared to conventional spraying. This technology not only achieves higher droplet deposition density and coverage but also enables water and pesticide savings while reducing environmental pollution. This study, combining theoretical analysis with experimental validation, reveals the critical role of electrode material selection in induction-based electrostatic spray systems.Theoretical analysis indicates that the Fermi level and work function of electrode materials fundamentally determine charge transfer efficiency, while corrosion resistance emerges as a key parameter affecting system durability. To elucidate the effects of different electrode materials on droplet charging, a comparative study was conducted on nickel, copper, and brass electrodes in both pristine and moderately corroded states based on the ISO 9223 corrosion classification standard, using a targeted mesh-based charge-to-mass measurement device. Results demonstrated that:The nickel electrode achieved a peak charge-to-mass ratio of 1.92 mC/kg at 10 kV, 8.5% and 11.6% higher than copper (1.77 mC/kg) and brass (1.72 mC/kg), respectively.After corrosion, nickel exhibited the smallest reduction in charge-to-mass ratio (19.2%), significantly outperforming copper (40.2%) and brass (21.6%).Droplet size analysis using a Malvern Panalytical Spraytec spray particle analyzer (measurement range: 0.1-2000um) further confirmed the atomization advantages of the nickel electrode:The volume median diameter (Dv50) of droplets produced by nickel was 4.2–8 um and 6.8–12.3 um smaller than those from copper and brass electrodes, respectively.After corrosion, nickel showed a smaller increase in droplet size spectrum inhomogeneity (24.5%), lower than copper (30.4%) and brass (25.8%), indicating superior droplet uniformity.By establishing a multi-factor predictive model for spray droplet size after electrode corrosion, this study quantifies the correlation between electrode characteristics and spray performance metrics. It provides a theoretical basis for designing weather-resistant electrostatic spray systems suitable for agricultural pesticide application scenarios involving prolonged exposure to corrosive chemicals. This work offers significant technical support for sustainable crop protection strategies.Specifically:(lines 14-42)

Main issue 3: Explain in detail about the testing setup, its components and testing procedures. (Section 2.2). Improve the quality of figure 3.

Response 3: 

The experimental methodology has been refined, with detailed specifications of the test apparatus configuration provided. Discussions on potential experimental uncertainties have been supplemented to enhance research transparency, and the image quality of Figure 3 has been improved. The droplet charge-to-mass ratio measurement experiments for electrostatic spraying were conducted at the College of Plant Protection Machinery, HARDI Factory, Heilongjiang Bayi Agricultural University. The charge-to-mass ratio of the electrostatic spray droplets was measured using a dedicated charge-to-mass ratio testing system. As illustrated in Figure 3, the system comprises an electrostatic spray test bench, a target grid droplet collection device, a microcurrent meter, a timer, and a computer.

The liquid charging current was monitored using a Yidie EST121 digital microcurrent meter (±0.5% accuracy). The collector, positioned beneath the nozzle, is a target grid box designed to capture droplets in real-time while acquiring their charge. The three-dimensional structure of the target grid collection device is shown in Figure 3. Constructed from stainless steel, the device integrates a three-layer brass mesh with decreasing aperture sizes (top to bottom) to ensure precise current measurement and prevent liquid accumulation on the metal grids. Current signals from the bottom electrode are transmitted to a precision ammeter. The microcurrent meter processes these signals and uploads the data to a current recording application on the computer for storage and analysis.

It should be noted that several potential sources of uncertainty exist in the measurement process: environmental humidity may interfere with charge conduction; collisions, rebound, or coalescence of droplets among the multilayer metal meshes may lead to partial charge loss; residual droplets on the mesh or device walls may introduce minor current errors; and the precision of the microammeter in extremely low-current ranges may affect the reliability of final readings. These factors collectively influence the calculation results of the charge-to-mass ratio, and their impact should be considered during result analysis.Specifically:(lines 162-185)

 

Main issue 4: Figure 5 why did charge to mass ratio increased and later decreased with an increase in charging voltage (figure 5). Figure quality for figure 7 is not good. Difficult to interpret the results. Use better oriented figures. Figure 11, Write Y-axis title in full (relative span). Also mention the interpretation of the relative span mentioned in 3.3.2 section.

Response 4: A brief analysis has been performed on why the mass-to-charge ratio initially increases then decreases with rising charging voltage. When the charging voltage reaches 12 kV, the charge-to-mass ratio of droplets exhibits a moderate decline with further voltage increases. This phenomenon occurs because at 12 kV:①Rayleigh limit constraints on droplet charging become significant;②Breakdown threshold of humid air is lowered, impairing charge transfer efficiency.Electrode corrosion substantially exacerbates the decline in charge-to-mass ratio. (lines 297-301)。The clarity of Figure 7 has been enhanced; the non-standard labeling issues in Figure 11 have been corrected; and a quantitative interpretation of how charging voltage affects spray droplet size distribution has been supplemented.

Main issue 5:In general, the figure quality is not good. Please change to the better resolution figures for figure 3, 5

Response 5: The manuscript format has been optimized and figure/table resolutions have been enhanced.

 

We would like to thank the referee again for taking the time to review our manuscript!

Author Response File: Author Response.pdf

Reviewer 4 Report

Comments and Suggestions for Authors

The article is well organized and has 28 references. The structure of this paper consists of four main parts - Introduction, description of the experiment, Results and Conclusion. Thus, this paper is experimental in nature - which in my opinion is appropriate for such a topic. In general, the topic of this article is suitable for the chosen Journal - however, it is largely multidisciplinary, at the junction of electrical engineering and material science.

The disadvantages of this article include its narrow specificity and limited practical applicability in agriculture.

To improve this article

[page 1, line 31] please fix mc/kg -> mC/kg

[page 5, line 167] please fix (q/m) -> (C/kg) or something like that

[page 5, line 172-174] please fix “10kV” -> “10_kV”, etc.

[page 5, line 188] please fix Table1 -> Table_1

[page 7, line 261-262] please fix kv -> kV

[page 8, line 292] please fix “mc/kg” -> “mC/kg”

[page 8, line 304] please fix “Table2” -> “Table_2”

[page 10, line 334, 341, 346, 347] please add space “ “

[page 10, line 331] please fix “mc/kg” -> “mC/kg”

[page 4, line 144, 162] please add space “ “ into Figure2, Figure 3

[page 15, line 471] please fix Table6 -> Table_6, + fix content of the Table

Overall, I support this article after minor revision.

Author Response

1. page 1, line 31: please fix mc/kg -> mC/kg

The issue has been modified in the article.（line 27-28）.

2.page 5, line 167: please fix (q/m) -> (C/kg) or something like that

The issue has been modified in the article.（line 193)

3.page 5, line 172-174：please fix “10kV” -> “10_kV”, etc.

The issue has been modified in the article.（line 198-199)

4.page 5, line 188:please fix Table1 -> Table_1.

The issue has been modified in the article.（line 215）

5.page 7, line 261-262: please fix kv -> kV

The issue has been modified in the article.（line 298-299）

6.page8, line292:please fix “mc/kg” -> “mC/kg”

The issue has been modified in the article. (line 330)

7.page 8, line 304: please fix “Table2” -> “Table_2”

The issue has been modified in the article. (line 343)

8.page 10, line 334, 341, 346, 347: please add space “ “

The issue has been modified in the article.

9.page 10, line 331：please fix “mc/kg” -> “mC/kg”

The issue has been modified in the article. （line 373）

10.page 4, line 144, 162: please add space “ “ into Figure2, Figure 3

The issue has been modified in the article.（line 161 and line 188）

11.page 15, line 471: please fix Table6 -> Table_6, + fix content of the Table.

The issue has been modified in the article.（line 534）

 

We would like to thank the referee again for taking the time to review our manuscript!

Author Response File: Author Response.pdf

Round 2

Reviewer 3 Report

Comments and Suggestions for Authors

Authors have mostly done good job with revision.