A sacrificial anode is a type of cathodic protection system that is made of a metal alloy that has a higher "active" voltage (a more negative electrochemical potential) than the metal structure it protects (the cathode). The potential difference between the two metals means that corrosion of the sacrificial anode material takes precedence over the protected structure, which effectively prevents oxidation reactions on the protected metal structure. In addition to the anode and cathode, two other conditions must exist for a sacrificial anode to work. The flow of electrons from the anode to the material it protects must have a loop (the usual path is physical contact) and an electrolyte (water, humidity) to transfer the electrons.
Chemical composition of aluminum anode
| Types | Zn | In | Cd | Sn | Mg | Si | Ti | Impurities, not more than | Al |
| Si | Fe | Cu |
| Al-Zn-In-Cd | 2.5-4.5 | 0.018-0.050 | 0.005-0.02 | — | — | — | — | 0.1 | 0.15 | 0.01 | Balance |
| Al-Zn-In-Sn | 2.2-5.2 | 0.020-0.045 | — | 0.018-0.035 | — | — | — | 0.1 | 0.15 | 0.01 | Balance |
| Al-Zn-In-Si | 5.5-7.0 | 0.025-0.035 | — | — | — | 0.10-0.15 | — | 0.1 | 0.15 | 0.01 | Balance |
| Al-Zn-In-Sn-Mg | 2.5-4.0 | 0.020-0.050 | — | 0.025-0.075 | 0.50-1.00 | — | — | 0.1 | 0.15 | 0.01 | Balance |
| Al-Zn-In-Mg-Ti | 4.0-7.0 | 0.020-0.050 | — | — | 0.50-1.50 | — | 0.01-0.08 | 0.1 | 0.15 | 0.01 | Balance |
Electrochemical performance of aluminum anode
| Performance, types, indicators | Open circuit potential
-V(SCE) | Working potential
-V(SCE) | Actual capacitance A · h/kg | Current efficiency
% | condition |
| Ordinary aluminum alloy anode | 1.10-1.18 | 1.05-1.12 | ≥2400 | ≥85 | Corrosion products are easy to fall off and dissolve evenly on the surface. |
| High-efficiency aluminum alloy anode | 1.10-1.18 | 1.05-1.12 | ≥2600 | ≥90 |
| Highly activated aluminum alloy anode | 1.45-1.50 | 1.40-1.45 | ≥2080 | ≥70 |
