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    There are many types of sacrificial anode materials to choose from, such as magnesium and magnesium alloys, zinc and zinc alloys, aluminum alloys, etc. Among them, magnesium sacrificial anode materials can provide a potential of approximately-1.75V, zinc about -1.1V, and industrial pure aluminum about -0.8V. In practical operation, the selection of sacrificial anodes should be comprehensively considered based on the potential provided by each material, the surrounding environment in contact with the metal, and the required magnitude of the protective current.

I. Soil Medium Requirements for Sacrificial Anodes

II. Soil is a complex system composed of gaseous, liquid, and solid substances. The composition of these three states changes with factors such as temperature, climate, and season, leading to variations in soil resistivity, redox potential, pH value, salt content, etc., making the assessment of soil corrosiveness extremely complex. As a commonly used reference indicator, Table 5-1 provides the standard for evaluating soil corrosiveness based on soil resistivity.

The grounding resistance of the anode is related to soil resistivity, and it changes annually. To avoid such variations and reduce grounding resistance, the anode in the soil should be surrounded with backfill material. In addition to limiting the formation of surface films and preventing electro-osmotic dehydration, such backfill material ensures uniform current output and uniform consumption of the material. The latter is mainly due to the gypsum content in the backfill material, while bentonite and diatomaceous earth help retain moisture. Adding sodium sulfate can reduce the resistivity of the backfill material. The composition includes: gypsum powder, bentonite, diatomaceous earth, sodium sulfate.

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