Effect of different chemical treatments on hydroxyapatite formation of carbon fibers reinforced carbon and SiC dual matrices composites

In this study, the carbon fibers reinforced carbon and SiC dual matrices (C/C-SiC) composites with 3D needle-punched structure were fabricated by liquid silicon infiltration (LSI). This work focused on the effects of different chemical treatments (aqueous of HF/HNO3, aqua regia and CaCl2 solution) on apatite formation under biomimetic condition. Samples were characterized by scanning electron microscopy (SEM), electron probe microanalysis (EPMA), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), fourier transform infrared spectroscopy (FTIR) and so on. The ability of hydroxyapatite formation was evaluated by simulated body fluid (SBF) immersion test. The formation mechanism of apatite layer grown on modified C/C-SiC composites was also revealed. The results showed that modified sample surfaces were consisted of groups OH, COOH or/and Ca2+ ions. These negatively functional groups attracted surrounding Ca2+ ions to form and anchor the nucleus. The Ca2+ ions contributed to the apatite nucleation and proliferation by increasing apatite saturation. The SBF results showed that a homogeneous precipitation layer of apatite formed on C/C-SiC after about two weeks under the combined actions of aqua regia and CaCl2. This suggested treatments of aqua regia and CaCl2 solution led to positive results in terms of apatite formation of modified C/C-SiC compared to the native C/C-SiC material.