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

The central region of the hypermineralized dolphin's bulla (ear bone), contains >95wt% mineral with 10wt% 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 degrees C to 900 degrees C for the Raman analyses. Both positions and widths of Raman peaks were studied. Crystals of the bioapatite are stable up to 200 degrees C. From 300 degrees C to 600 degrees C, the decrystallization is a gradual process with delicate changes rather than a sharp transformation. Carbonate is depleted at 500 degrees C, and then decrystallization is terminated. At temperature over 600 degrees C, bioapatite re-crystallizes and is transformed to OHAp at 700 degrees C. The crystallinity is then gradually improved while the temperature increased to 900 degrees C. No phases of -tricalcium phosphate or calcium pyrophosphate were detected in this study. Copyright (c) 2015 John Wiley & Sons, Ltd.