High-quality ultralong hydroxyapatite nanowhiskers grown directly on titanium surfaces by novel low-temperature flux coating method

Idiomorphic, one-dimensional (1-D), and high-quality hydroxyapatite (HAp) nanocrystals were successfully, directly, and densely grown on a Ti substrate at the relatively low temperature of 300 °C using a KNO ₃-LiNO ₃ flux coating method. The grown HAp crystals have a 1-D shape with a very high aspect ratio (much larger than 100) and an average size of 3250 × 25 nm (length × width). The ultralong 1-D crystals grown at 300 °C were identified as highly crystalline HAp by their X-ray diffraction (XRD) patterns, which clearly displayed the four characteristic lines of HAp between 31.5° and 34.5°. Additionally, high-resolution transmission electron microscopy (HRTEM) images demonstrated that these ultralong whiskers were high-quality because point and line defects were not observed. From the energy-dispersive X-ray spectroscopy (EDS) analysis, major components were homogeneously distributed in the HAp whiskers. In addition, the effects of holding temperature and starting composition on the forms and average sizes of the grown HAp whiskers were investigated.