Zinc
Zinc anodes are also commercially available in two alloys, one for use in soils and the other for seawater applications. Zinc may undergo rapid intergranular corrosion at temperatures above 120°F (50°C). At temperatures above 130°F (50°C) and particularly in the presence of carbonates, zinc can passivate and the potential of the passive film can become more noble than steel, leading to corrosion of the steel.
Zinc is particularly useful in sea-water applications where its low driving potential against steel is insufficient to cause damage to most paints and enables the current output to vary with demand; thus, it is to some extent self-controlling. Zinc anodes do not normally evolve hydrogen nor is there a risk of thermite sparking.
High-purity zinc anodes are used in soil and fresh water environments in the form of ribbons and rods primarily. Grounding cells or structure grounding applications also commonly use high-purity zinc anodes. Applications requiring AC mitigation or safety grounding mats at test stations may use zinc ribbons.
Zinc grounding cells employ two or four zinc rods spaced very close together, but insulated from physical contact, and placed in a special chemical backfill.
MIL-A-18001K or ASTM B418 Type I– for salt water and brackish water use.
ASTM B418 Type II– high purity for underground and fresh water use.
Chemical Composition
| Element | US-Mil-A-18001K | ASTM B418 Type II | Zinc Alloy, Zn-Al-Mg (Elevated temperature) |
|---|---|---|---|
| Content % | |||
| Aluminium AL | 0.10-050 % | 0.005 % max | 0.10 – 0.28 % |
| Cadmium Cd | 0.025-0.07% | 0.003 % max | 0.001 % max |
| Iron Fe | 0.005% Max | 0.0014 % max | 0.004 % max |
| Copper Cu | 0.005% Max | 0.002 max % | 0.001 % max |
| Lead Pb | 0.006% Max | 0.003% Max | 0.006% Max |
| Magnesium Mg | – | – | 0.03 – 0.18% |
| Other | 0.10% max total | 0.10% max total | 0.10% max total |
| Zinc Zn | Remainder | Remainder | Remainder |
Electrochemical Properties
| Element | US-Mil-A-18001K | ASTM B418 Type II | ||
|---|---|---|---|---|
| Open voltage (-V) | -1.10 V | |||
| Closed voltage (-V) | -1.05 V | |||
| Capacity (A.h/kg) | 780 A.h/kg min | |||
| Efficiency (%) | 90 % min | |||
| Consumption rate (kg/A-y) | 11.90 kg/A-y | |||
| Consumption rate (kg/A-y) | seawater and blackish water (T<50°C) | soil and fresh water | ||
| Zinc Alloy, Zn-Al-Mg ( Elevated temperature) |
||||
| Temperature | 20°C | 45°C | 60°C | 80°C |
| Closed voltage (-V) | -1.03 V | -1.03 | -0.97 | -0.95 |
| Capacity (A.h/kg) | 780 A.h/kg | 750 A.h/kg | 690 A.h/kg | 670 A.h/kg |
All weights in kilograms.All dimensions in millimetres.
Lermetal anodes height and width are standard design widely used in the industry market.
Our Cathodic Protection Engineer and foundry can customise owner’s and buyer’s requirements upon request.
Zinc anode for tidal gate
Zinc anode for jetty
