Ion exchange equilibria between glass and molten salts

It is shown that interaction between the ions undergoing ion exchange leads to a sigmoidal equilibrium curve. A negative interaction in the glass causes the ratio of concentration of the two ions to be more nearly equal to unity in the glass than it is in the molten salt. It is further shown that the Rothmund-Kornfeld parameter is a measure of the non-ideality of the system. A value of the parameter greater than unity indicates a negative interaction energy.