Transformation of bentonite from natural calcium bentonite to sodium bentonite induced by the addition of sodium.
During this process, calcium bentonite looses its calcium ions and adsorbs double the amount in sodium ions. The quantity of accumulated ions is a quality characteristic and is measured as equivalent mass (mval) per 100 g of clay. Under-activation or over-activation has a negative influence on mechanical properties of the molding material. Creeping over-activation of the entire system must be particularly taken into account when ions transfer from the water glass-bonded core into the bentonite-bonded molding material system (s. active bentonite).