High-temperature transformation of bioapatite to β-tricalcium phosphate: Structural and isotopic changes in cortical bone up to 1400 °C

This study explores the structural and isotopic transformations of cortical bone bioapatite exposed to high temperatures (700–1400 °C) under oxidising conditions. Using a controlled experimental setup, modern bovine bone samples were burned at 100 °C intervals for 4 h and analysed using Fourier Transform Infrared Spectroscopy in attenuated total reflectance mode (FTIR-ATR) to evaluate crystallinity (IRSF) and carbonyl-to-carbonate (C/C) ratios. Complementary stable isotope analysis (δ13C and δ18O) of bioapatite carbonates provided additional insight into volatile loss and thermally induced changes. Results show an increase in crystallinity between 700 and 800 °C, followed by a decline at higher temperatures, complete carbonate loss at 1200 °C, and evidence of structural reorganisation. At 1300–1400 °C, FTIR spectra confirm a phase transition from bioapatite to β-tricalcium phosphate (β-TCP). Isotopic measurements were viable up to 1100 °C, beyond which carbonates were no longer detectable. Periosteal and endosteal regions exhibited consistent δ13C offsets, particularly at lower temperatures. These transitions reflect sintering-related phenomena and underscore the potential of thermally treated bone as an alternative to synthetic materials in biomedical applications. This work provides novel insights into the thermal behaviour of natural bioapatite and introduces an integrated FTIR-isotope approach with implications across forensic, archaeological, and biomaterial sciences.