High-potential alloy , M1– provides a higher driving voltage than the standard alloy.
Magnesium anodes used in cathodic protection applications in soil are sometimes supplied
prepackaged with a prepared backfill material in a cloth or cardboard container. The special backfill
prevents direct soil contact to reduce localized corrosion of the anode, prevents passivation of
the anode caused by reactions with soil salts, provides a low-resistivity environment around the
anode, and expands when wet to fill the hole and eliminate air voids. The most common backfill
material contains 75% hydrated gypsum, 20% bentonite clay, and 5% sodium sulfate.