Temperature‐related changes of bioapatite based on hypermineralized dolphin's bulla

The central region of the hypermineralized dolphin's bulla (ear bone), contains >95 wt% mineral with ~10 wt% structurally incorporated carbonate. The mineral‐bioapatite undergoes phase changes during heating. However, the step‐by‐step changes with increasing temperature are still unclear. Raman spectroscopy is proved to be a powerful technique in analyzing crystallographic transformation of bioapatite. The bulla was heated stepwise from 100 °C to 900 °C for the Raman analyses. Both positions and widths of Raman peaks were studied. Crystals of the bioapatite are stable up to 200 °C. From 300 °C to 600 °C, the decrystallization is a gradual process with delicate changes rather than a sharp transformation. Carbonate is depleted at ~500 °C, and then decrystallization is terminated. At temperature over 600 °C, bioapatite re‐crystallizes and is transformed to OHAp at 700 °C. The crystallinity is then gradually improved while the temperature increased to 900 °C. No phases of β‐tricalcium phosphate or calcium pyrophosphate were detected in this study.