INFLUENCE OF THE MIXED ALKALI EFFECT ON THE CHEMICAL DURABILITY OF Na2O-TiO2-SiO2 GLASSES.

the influence of the mixed alkali effect on the chemical durability of Na//2O-TiO//2-SiO//2 glasses during substitution of K//2O for Na//2O in 21Na//2O-26TiO//2-53SiO//2 glasses was investigated. The best chemical durability was found at K//2O/Na//2O equals 2. 5 where the minimum was close to K** plus ions of larger size. It was shown that the water corrosion process of the system was predominantly controlled by both the mobility and the exchange function of K** plus ions resulting in the generation of a titanium-rich and silicon-rich layer at the surface. The mixed alkali effect can therefore be applied to lower the rate of water corrosion and increase chemical durability so that optical glasses with higher chemical durability can be obtained.