Lithium-Cobalt Glass for Sapphire

Abstract

Sapphire was improved by filling lithium-cobalt glass. Cobalt concentration in lithium glass is 0.1-2 wt%. The sapphires with glass were heated by an electric furnace at 1100 °C for 1-5 hours. Physical properties of the stone before and after treatment were investigated by measuring refractive index and specific gravity. Stones were investigated the inclusion and fissure by a gem microscope. Reflectance spectrum was analyzed by UV-visible spectrophotometer and color changes were referenced by CIEL*a*b* system. Fluorescence was examined with a UV Lamp. Experimental results of heated sapphire treatment with lithium-cobalt glass found that the refractive index (RI) decreased from 1.76 - 1.77 to 1.53 - 1.55 and the specific gravity (SG) decreased from 3.95 - 4.00 to 3.37 – 3.40. Cause of these results is that the refractive index and specific gravity of lithium-cobalt glass are lower than of sapphires. The cobalt in glass filled in fissure of sapphires is cause of blue color appeared in crack. The orange-red fluorescence appeared in both short wave and long wave of UV. For analysis of trace elements by the UV-visible spectrophotometer range 300-800 nm, cobalt peak appeared at wavelength 530 nm while iron peak and another peak of improved sapphire in all conditions were found at wavelength 488 nm and 750 nm, respectively. The height of peak at 750 nm depended on the amount of cobalt. The color of improved sapphire was closed to blue color when compared with sapphire before improvement.