Seawater Cooling Water System Zinc Alloy Sacrificial Anode

Zinc anodes were among the earliest anodes used, first employed by Davy in 1824. Early failures of zinc anodes were mainly due to iron content exceeding standards, leading to passivation of the zinc anode. Therefore, iron content must be controlled below 0.0014%. With 0.4% aluminum and 0.15% cadmium, the allowable iron content can reach 0.005%. In environments containing carbonates, bicarbonates, and salts, the surface of the zinc anode becomes passivated, causing the zinc anode potential to become more positive. The higher the temperature, the more pronounced this effect. In environments containing sulfates and chlorides, zinc anodes do not passivate. Even if the zinc anode has already passivated, adding gypsum powder (containing sulfate ions) around the zinc anode can rapidly reduce the potential to -1.10V (CSE).

High-purity zinc anodes can be used in soil environments with resistivity less than 20 Ω·m or in freshwater. Zinc alloy sacrificial anodes are mostly used in seawater environments. The electrode potential is -1.10V (CSE), with a driving voltage of 0.25V. At temperatures above 49°C, intergranular corrosion occurs; above 54°C, the electrode potential of the zinc anode becomes positive, and its polarity with steel reverses—the zinc becomes the cathode and is protected, while the steel becomes the anode and corrodes. Therefore, zinc anodes are generally used in environments below 49°C and must be used with backfill. Zinc alloy anodes can be used as grounding batteries or structural grounding. Zinc strips can be used for AC interference grounding of pipelines and equalizing grids in valve chambers. The current efficiency of zinc anodes is not significantly affected by output current density.

Zinc alloy sacrificial anodes possess excellent electrochemical performance, performing well in seawater and other media containing chloride ions, with strong self-regulating capability for current output. They are mostly used in soil environments with resistivity less than 20 ohm·meters or in seawater environments.