EXPERIMENTAL STUDY ON TECHNOLOGY OF HIGH TEMPERATURE HEAT TREATMENT OF SHANDONG SAPPHIRE UNDER OXIDATION

How to modify colour of blue sapphires from Shandong is the experiment′s target. According to the sample′s colour and diaphaeity under strong light source and natural light, sapphires can be further divided into blue black, dark blue and blue . Among them dark blue sapphire and blue sapphire have well colour modified effect after heat treatment. The main equipment for heat treatment is boxy zirconia ultra high temperature electric furnace. It adopts ZrO₂ heater element and 1800℃ high temperature furnace heating system which consists of main heating and auxiliary heating systems. The main parameters for heat treatment of sapphires include the acquisitively sustained time at the highest temperature, the velocity of step up and step down temperature during heat treatment, chemical reagent contacted with gems, the chemical property and gas pressure of the atmosphere. Two kinds of effective colour modifying technology have been attained by adjusting a series of parameters:(1) the technology of partial step up pressure and high temperature heat treatment; (2) the technology of multi circulation heat treatment under open system. The preceding method possesses better effect than the later, but each has its own characteristics.