Complex thermal kinetic study of calcium phosphate biomaterial CaHPO4 using the asymmetric deconvolution approach

The complex dehydroxylation kinetics of calcium phosphate biomaterial CaHPO4 was investigated using non-isothermal thermogravimetry/differential thermal analysis and multi-peak fitting method, under air flow at different heating rates. The overlapped kinetic curves were separated into two independent steps by the asymmetric Fraser-Suzuki function and the thermal characteristics with kinetic parameters were determined. For each step, the activation energy E alpha was evaluated using model-free isoconversional methods of differential Friedman (Fr) and, integral Ozawa-Flynn-Wall and Kissinger-Akahira-Sunose (KAS). The E-alpha calculations showed close values for integral methods by comparison with results of the differential Fr. The best fit of experimental kinetic curves was achieved by considering the KAS activation energy and Johnson-Mehl-Avrami (JMA(n)) as the adequate function model with a nucleation-growth mechanism. Both dehydroxylation steps of biomaterial were attributed to the microstructure heterogeneity including two kinds of particle size and shape as was confirmed by dynamic light scattering analysis and SEM microscopy.

Automated summary

The complex dehydroxylation kinetics of calcium phosphate biomaterial CaHPO4 were investigated using non-isothermal thermogravimetry/differential thermal analysis and multi-peak fitting method. The overlapped kinetic curves were separated into two independent steps and the best fit of experimental kinetic curves was achieved by considering the appropriate function model and kinetic parameters. The study also confirmed the correlation between the dehydroxylation steps and the microstructure heterogeneity of the biomaterial through dynamic light scattering analysis and SEM microscopy.