The pH value is an important factor that influences the
precipitation of apatite phase from aqueous solutions. Previous
studies [23] showed that to control the pH variation from acid to
basic range was favorable to the development of whisker-like pure
HAp because the acid condition led to the formation of the
whisker-like precursor octacalcium phosphate (OCP). When pH
values were raised, OCP was transformed into HAp and the
whisker-like morphology kept. Thus, the influence of pH value
upon the FHAp precipitation was systematically investigated with
the expectation for long FHAp whiskers. The phase composition
during the pH variation was shown in Fig. 6. At a pH value of 4,
the resultant phase was CaF2. When the pH values were raised,
CaF2 formed in the acid range was transformed into FHAp, but did
not develop the whisker-like morphology