Glasses For The Preparation Of Gradient Index Lenses In The Na20-Al203-B203-Si02 System - Hydrolytic Durability, Thermal And Optical Properties

Glasses in the system Na20-Al203-B203-Si02 were melted from the raw materials and studied with respect to their chemical durability, their crystal growth velocities, their refractive index and dispersion, their glass transition temperature and their thermal expansion coefficient. With increasing Na20 concentration, the crystal growth velocity increases and the chemical durability decreases. Equimolar substitution of B203 for Si02 results in a decrease in both the chemical durability and in crystal growth velocities. Optimum glass compositions to produce gradient index lenses should possess B203 concentrations of around 12.5 to 15 mol% and molar Al203 concentrations some percent larger than the Na20 concentration. In these glasses, nonbridging oxygen does not occur.