Key Takeaways & Executive Findings
- •• • At 6 g/L TiN, the coating achieved 743.62 HV microhardness, a 120 μm thickness, and grain sizes of 67.28 nm (Ni) and 35.84 nm (TiN), directly extending the service life of copper electrode plates by resisting abrasive wear from pesticide slurries and mechanical cleaning. • • The corrosion current density dropped to 6.07×10−9 A/cm2 with Ecorr at −0.23 V vs. SCE, and 24 h salt spray produced only minor pits without spalling; this order-of-magnitude reduction in corrosion rate prevents conductivity loss and droplet distribution drift in humid field conditions. • • Interfacial contact resistance reached a minimum of 6.4 mΩ·cm2, ensuring efficient charge transfer for electrostatic droplet charging; this low resistance is critical because even small increases in contact resistance reduce charging efficiency and pesticide deposition uniformity. • • The maximum contact angle of 132.82° at 6 g/L TiN creates a hydrophobic surface that reduces droplet adhesion and delays electrochemical corrosion, addressing the persistent problem of liquid film formation that accelerates degradation of copper plates in spray systems.
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Abstract
Electrostatic spraying improves pesticide deposition by charging droplets, but copper electrode plates undergo electrochemical corrosion and surface oxidation in humid, weakly acidic, pesticide-laden environments, reducing conductivity and charge transfer efficiency. Ni-TiN nanocoatings with varying TiN concentrations were electrodeposited on T2 copper cathodes using a nickel anode at a cathode-to-anode area ratio of 1:2 and 60 mm electrode gap. TiN nanoparticles averaged 43 nm. Scanning electron microscopy, energy-dispersive spectroscopy, transmission electron microscopy, X-ray diffraction, microhardness testing, contact angle measurement, electrochemical workstation, and salt spray testing characterized the coatings. TiN addition refined the cellular Ni structure, reduced porosity, and produced only face-centered cubic Ni and TiN phases without intermetallic or oxide impurities. At 6 g/L TiN, the coating reached 120 μm thickness, 743.62 HV microhardness, Ni and TiN average grain sizes of 67.28 nm and 35.84 nm, corrosion potential of −0.23 V versus SCE, corrosion current density of 6.07×10−9 A/cm2, interfacial contact resistance of 6.4 mΩ·cm2, and contact angle of 132.82°. After 24 h continuous salt spray, only minor pits appeared without spalling or loosening. The results demonstrate that optimized TiN concentration enhances corrosion resistance, hardness, hydrophobicity, and electrical conductivity, providing a reference for protecting electrostatic spray nozzle copper plates.
1. Introduction
Electrostatic spraying systems rely on copper electrode plates to inductively charge pesticide droplets, improving deposition on crop surfaces and reducing drift. However, these plates operate continuously in humid, weakly acidic environments laden with agrochemicals. Copper's intrinsic susceptibility to electrochemical corrosion and surface oxidation leads to conductivity decay, charge transfer inefficiency, and uneven droplet distribution. Existing commercial approaches, such as bare copper or simple metallic coatings, fail to simultaneously provide corrosion resistance, hydrophobicity, and low interfacial contact resistance. The result is frequent maintenance, inconsistent spray performance, and increased pesticide waste.
This study addresses the bottleneck by electrodepositing Ni-TiN nanocomposite coatings on T2 copper plates. The protocol systematically varies TiN nanoparticle concentration to control grain refinement, porosity, and phase purity. At an optimized TiN concentration of 6 g/L, the coating achieves a unique combination of high microhardness (743.62 HV), low corrosion current density (6.07×10−9 A/cm2), low interfacial contact resistance (6.4 mΩ·cm2), and high hydrophobicity (contact angle 132.82°). These metrics directly counter the failure mechanisms of bare copper, offering a scalable electrodeposition route for durable electrostatic spray nozzle plates.
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LIU Hongyuan, LI Yufei, LI Qiang, HU Jun, LI Qingda (2026). Preparation of Ni-TiN Nanocomposite Coatings and Their Application to Copper Electrode Plates for Electrostatic Spray Nozzles. Surface Technology (表面技术). https://doi.org/10.16490/j.cnki.issn.1001-3660.2026.10.006
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Frequently Asked Questions
What is the primary failure mechanism of bare copper electrode plates in electrostatic spray nozzles, and how does the Ni-TiN coating mitigate it?
Bare copper undergoes electrochemical corrosion and surface oxidation in humid, weakly acidic pesticide environments, leading to conductivity loss and uneven droplet charging. The Ni-TiN coating reduces corrosion current density to 6.07×10−9 A/cm2 and shifts corrosion potential to −0.23 V vs. SCE, effectively blocking corrosive media. The hydrophobic surface (contact angle 132.82°) further reduces droplet adhesion, delaying electrolyte film formation.
Why is 6 g/L TiN identified as the optimal concentration, and what happens at lower or higher concentrations?
At 6 g/L, TiN nanoparticles promote heterogeneous nucleation and pin grain boundaries, yielding a dense coating with 743.62 HV hardness, 120 μm thickness, and minimal porosity. Lower concentrations provide insufficient TiN adsorption on the cathode, weakening grain refinement and increasing porosity. Higher concentrations may cause agglomeration, leading to uneven distribution and deteriorated mechanical and corrosion properties.
How does the interfacial contact resistance of 6.4 mΩ·cm2 compare to bare copper, and why is this metric critical for electrostatic spraying?
Bare copper typically exhibits higher contact resistance due to oxide formation. The Ni-TiN coating maintains a continuous conductive nickel matrix with dispersed TiN nanoparticles, optimizing electron transport pathways. A low contact resistance of 6.4 mΩ·cm2 ensures efficient charge transfer to droplets, which is essential for achieving high deposition efficiency and uniform spray coverage.
What is the long-term durability of the Ni-TiN coating under continuous salt spray, and what does this imply for field service life?
After 24 h continuous salt spray testing, the coating showed only minor pits with no spalling or loosening. This indicates strong adhesion and corrosion resistance. In field conditions, such performance suggests a significant extension of service life compared to bare copper, reducing maintenance frequency and downtime for electrostatic spray systems.
Can this electrodeposition process be scaled up for industrial production of copper electrode plates, and what are the key control parameters?
The process uses standard electrodeposition with a T2 copper cathode, nickel anode, cathode-to-anode area ratio of 1:2, and 60 mm electrode gap. Key control parameters include TiN concentration (optimized at 6 g/L), current density, and bath agitation to prevent nanoparticle agglomeration. The use of 43 nm TiN nanoparticles and conventional equipment supports scalability, though uniform dispersion and continuous filtration are critical for consistent coating quality.
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