Performance of SiO₂-TiO₂-RO-R'₂O System of Glass for Sapphire Filling

Sapphire, ruby, diamond, emerald and golden emerald are the five most precious stones in the world. The resources of sapphire are depleting because of continuous mining. Madagascar sapphire has gradually been recognized since 1990s. Madagascar sapphire is almost in commercial grade, and very little in gem grade depending on the color and purity. High refractive index lead glass is widely used in gemstone filling as a filler material. However, long-term use of lead glass will cause adverse factors to human health. Therefore, the aim of this paper is to discover a type of lead-free high refraction glass as a sapphire filling material. A new glass system is designed and prepared for sapphire filling in this work. The glass system is SiO₂-TiO₂-RO-R'₂O with different molar ratios of Na₂O/K₂O (R represents alkaline earth and R' represents alkali). Different properties of this new glass system are studied such as physical performance (density and refractive index), thermal performance (glass-transition temperature T_g and recrystallization temperature T_x), thermal stability and skeleton structure of the glass. The effects of these factors on the performance of glass are also discussed. According to the current results, the density and refractive index meet the requirement of sapphire filling when n(Na⁺):n(K⁺)=2:3 in this glass system. Meanwhile, its thermal stability is very high and the filling process does not cause crystallization easily. Therefore, such type of glass can be used as a sapphire filling material.