I synthesized Hydroxyapatite by wet chemical precipitation process with the help of a phosphate and calcium precursor and maintaining the pH of the solutions after mixing at different values using an alkali solution. I found that the percentage yield of hydroxyapatite varies with varying pH values while rest of the synthesis parameters were kept constant throught the synthesis process. What may be the exact reason for this variation in the yield of HA with varying pH? Thanks in advance.
Emon Barua
Have a look at the Pourbaix diagram for your system. For example, Figure 1 in the attached. This tells you which species are stable at which pH. You'll find that there's a pH region where hydroxyapatite (not upper case) is the dominant and stable species.
It is important to remember that composition of HAp may vary greatly depending on precipitation conditions. Optimal pH value of precipitation of stoichiometric HAp (Ca10(PO4)6(OH)2, molar Ca/P 1.67) is 11-12; lowering the pH may cause the deviation of Ca/P ratio due to the formation of calcium-deficient HAp Ca10-xHx(PO4)6(OH)2-x, 0
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