EFFECTS OF HEAT TREATMENT ON SPINELS AS DETERMINED BY VIS/NIR AND RAMAN SPECTROSCOPY AND XRD

Heat treatment is done to improve the color and clarity and, therefore, the value of gemstones. The objectives of this study include observing color and inclusion changes in pink spinels after heat treatment, and analyzing structural changes within differently colored spinels using Raman Spectroscopy and X-ray diffraction with a Paris Edinburgh Press. We expected the heat treatment to yield color changes and fading of small inclusions. Cut and polished spinels were heated to 1400C for 2 days or 850C for 3 days. Future experiments involve 800C, 750C, and 700C all for 1 week, 1500C for 4 days, and 1600C for 12 hours. To determine changes, Vis/NIR spectroscopy data were taken before and after heating. Only non-heat treated spinels were analyzed with the Paris Edinburgh Press; these XRD data show that the spinels with different colors are structurally different from one another. Raman spectroscopy was used in this study to observe structural changes in spinels that were exposed to heat. Six spinels were heated to 850C for 24 hours, six spinels were heated at 1200C for 6 hours, and the last six were heated at 1600C for 6 hours. The Raman spectroscopy data show that the six spinels exposed to 850C for 24 hours did not change structurally, but the 12 spinels exposed to 1200C or 1600C for six hours did change structurally.