The thickness of an electroplated zinc layer is directly related to the plating time, following Faraday's laws of electrolysis. Here’s how they are connected:
Author: Robby
The thickness of an electroplated zinc layer is directly related to the plating time, following Faraday's laws of electrolysis. Here’s how they are connected:
Plating Time (t):
Longer plating time = thicker zinc deposit.
The relationship is linear under constant current density and efficiency.
Current Density (i):
Higher current = faster deposition (but excessive current can cause poor quality).
Cathodic Efficiency (η):
Not all current contributes to plating (some is lost to side reactions like hydrogen evolution).
Typical zinc plating efficiency: 70–95% depending on bath chemistry.
Electrochemical Equivalent (Z):
For zinc, Z ≈ 0.0202 g/Ah (grams per amp-hour).
The thickness (d) of the zinc coating can be calculated using:
d=M⋅i⋅t⋅ηn⋅F⋅ρ×104(in microns, μm)d=n⋅F⋅ρM⋅i⋅t⋅η×104(in microns, μm)
Where:
M = Molar mass of zinc (65.38 g/mol)
i = Current density (A/dm²)
t = Plating time (hours)
η = Cathodic efficiency (decimal, e.g., 0.9 for 90%)
n = Number of electrons in reaction (Zn²⁺ + 2e⁻ → Zn, so n = 2)
F = Faraday’s constant (96,485 C/mol)
ρ = Density of zinc (7.14 g/cm³)
Simplified Formula:
For practical purposes, in a standard zinc sulfate or cyanide bath:
d≈8.2×i×t×η(μm)d≈8.2×i×t×η(μm)
*(Example: At 2 A/dm² for 30 min (0.5 h) with 85% efficiency → d ≈ 8.2 × 2 × 0.5 × 0.85 ≈ 7 μm)*
Initial Adhesion: Very short times may lead to non-uniform nucleation.
Limitations: Beyond a certain thickness, roughness or dendrites may form.
Agitation & Temperature: Affect deposition rate and quality.
For precise control, measure thickness using:
Micrometer (before/after plating)
X-ray fluorescence (XRF)
Magnetic or eddy current gauges