Abstract
The effect of pH variation in starting solution on the characteristics of hydroxyapatite precipitates and powder prepared by the wet method was investigated. Hydroxyapatite precipitates was agglomerated, the average agglomerated particle size was decreased in the range from 2 to 6${\mu}{\textrm}{m}$ with increasing pH values in starting solution. The aspect ratio of rod-shaped hydroxyapatite particle was rapidly increased at pH 11 and 11.5. The maximum specific surface area, 91.1$m^2$/g, was at pH 10.5. Dried powder prepared at high pH values contained more minutes CO2 than that prepared at low pH values. The poor crystallinity was maintained up to $600^{\circ}C$ regardless of the pH values in starting solutions. However, the second phase or high crsytalline hydroxypatite phase appeared above 80$0^{\circ}C$. In pH 9.5 and pH 10, $\beta$-whitlockite transformed to $\alpha$-whitlockite at 120$0^{\circ}C$, while in pH 10.5-11.5, hydroxyapatite phase was maintained up to 120$0^{\circ}C$.