In a Titanium Electric Heater for a 20% Zinc Sulfate Electrolyte at 60°C, How Does the Current Density from the Adjacent Plating Busbar (0.5 A/dm² vs. 2 A/dm²) Modify the Stray Current-Induced Pitting Pattern?

In zinc sulphate electroplating, stray currents from nearby busbars may polarise the titanium heater. At low current density (0.5 A/dm2) the stray currents produce scattered, shallow pits (depth 20–50 µm). Under high current density (2 A/dm²), stray currents cause concentrated, deep pits (depth 100–300 µm) along the busbar direction. The rate and localisation of pitting increases with increasing current density.

Quantitative Stray Current Density vs. Pitting

At 60°C for 500 hours in 20% ZnSO₄:

Stray Current Density (A/dm²) Pit Density (pits/cm²) Max Pit Depth (µm) Pit Pattern 0 (baseline) 0 0 None 0.5 5–20 20–50 Scattered
1.0 20-60 50-150 Moderate alignment
1.5 50–150 100–250 Aligned 2.0 100-300 150-350Highly aligned Busbar Orientation and Distance Effect

Distance from Busbar (mm) Stray Current Density (A/dm2) Pitting Severity (relative)
50 2.0–3.0 Severe 100 1.0-1.5 Moderate 200 0.3-0.5 Low 500 0.05-0.1 Negligible Stray Current Mitigation Guide

Measured Stray Current Density (A/dm^2) Recommended Action Expected Max Pit Depth (mm/year)
0.3 None <20
0.3–0.8 Plastic mesh shield heater 20-80
0.8–1.5 Move heater >300 mm from busbar 50–150 >1.5 Electrical isolation + shielding installation >150
Recommendation on Engineering

In the case of zinc sulphate electroplating, keep the titanium heater no closer than 300 mm from the busbars. Fit a perforated plastic shield around the heater to decrease stray currents. The engineer controls the stray current density to avoid severe pitting.