Galvanic Compatibility
The compatibility of two different metals may be predicted by consideration of their "Anodic Index". This parameter is a measure of the electrochemical voltage that will be developed between the metal and gold. To find the relative voltage of a pair of metals it is only required to substract their Anodic Indexes.
For normal environments, such as storage in warehouses or non-temperature and humidity controlled environments, there should not be more than 0.25 V difference in the "Anodic Index". For controlled environments, in which temperature and humidity are controlled, 0.50 V can be tolerated. For harsh environments, such as outdoors, high humidity, and salt environments, there should be not more than 0.15 V difference in the "Anodic Index". For example; gold - silver would have a difference of 0.15V being acceptable
Often when design requires that dissimilar metals come in contact, the galvanic compatibility is managed by finishes and plating. The finishing and plating selected facilitates the dissimilar materials being in contact and protect the base materials from corrosion.
| Metal | Index (V) |
|---|---|
| Most Cathodic | |
| Gold, solid and plated, Gold-platinum alloy | -0.00 |
| Rhodium plated on silver-plated copper | -0.05 |
| Silver, solid or plated; monel metal. High nickel-copper alloys | -0.15 |
| Nickel, solid or plated, titanium an s alloys, Monel | -0.30 |
| Copper, solid or plated; low brasses or bronzes; silver solder; German silvery high copper-nickel alloys; nickel-chromium alloys | -0.35 |
| Brass and bronzes | -0.40 |
| High brasses and bronzes | -0.45 |
| 18% chromium type corrosion-resistant steels | -0.50 |
| Chromium plated; tin plated; 12% chromium type corrosion-resistant steels | -0.60 |
| Tin-plate; tin-lead solder | -0.65 |
| Lead, solid or plated; high lead alloys | -0.70 |
| 2000 series wrought aluminum | -0.75 |
| Iron, wrought, gray or malleable, plain carbon and low alloy steels | -0.85 |
| Aluminum, wrought alloys other than 2000 series aluminum, cast alloys of the silicon type | -0.90 |
| Aluminum, cast alloys other than silicon type, cadmium, plated and chromate | -0.95 |
| Hot-dip-zinc plate; galvanized steel | -1.20 |
| Zinc, wrought; zinc-base die-casting alloys; zinc plated | -1.25 |
| Magnesium & magnesium-base alloys, cast or wrought | -1.75 |
| Beryllium | -1.85 |
| Most Anodic |
Read more about this topic: Lasagna Cell
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