In fact, the magnesium rod in the electric water heater mainly protects the inner container and heating tube of the water heater. The principle of protection is called cathodic protection principle, but it actually applies the principle of primary battery.
There are a lot of free metal ions in tap water. In the absence of external interference, these metal ions will take away the free electrons of iron, that is, the heating rod, causing corrosion and rust of the heating rod, causing hidden dangers. Adding magnesium rod, the active type of magnesium metal is better than that of iron, and it is easier to lose free electrons, thus protecting the heating rod well. In fact, the magnesium rod is protecting the heating rod even if it sacrifices itself.
Extended data
Function of magnesium rod in water heater
In the water heater, the magnesium rod is installed in the middle of the metal liner. When the enamel coating on the surface of the metal liner is completed, the enamel shields the metal liner, and the insulation resistance between the magnesium rod and the metal liner can reach more than 2 m Ω, and the output current of the magnesium (rod) anode is almost zero. However, when there is a local crack in the enamel liner, a small resistance is formed between the magnesium anode and the metal liner by water, and the magnesium anode starts to output current, and the current flows to the exposed metal liner to produce a polarization film, which repairs the damaged enamel and insulates the gold domain liner from corrosion. Because magnesium anode consumes itself when outputting current, it is called sacrificial anode method.
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