A reverse “S-type” mixed alkali effect of structural variations and correlated water resistance of Na2O/K2O-CaO-Al2O3-B2O3-SiO2 glasses with equal weight substitutions of Na2O by K2O

In glass factory, the substitution of Na 2 O by K 2 O is often on an equal weight base. This work investigated such a substitution in a Na 2 O/K 2 O-CaO-Al 2 O 3 -B 2 O 3 -SiO 2 pharmaceutical packaging glass. After measuring the concentrations of leached ions in and pH of the water resistance test solutions, a reverse “S-type” mixed alkali effect (MAE) on the water resistance of glass was revealed. The glass with 1wt% and 4.2wt% K 2 O exhibited the worst and best water durability, respectively. The FTIR and Raman spectroscopic results demonstrated the variations of Q 2 and [BO 3 ] with K 2 O/(Na 2 O+K 2 O) ratios also exhibited a reverse “S-shaped” trend, which is in good agreement with the water resistance results. Moreover, the ion leaching ratios were in the sequence of B > Si > Al > Na > K, aligning with the ion radius. The results suggest the need for a comprehensive understanding of MAE when designing pharmaceutical packaging glasses compositions based on the weight percentages.