Conductometric Study of Precursor Compound Formation during Wet-Chemical Synthesis of Nanocrystalline Hydroxyapatite

摘要

Conductometry was employed to study the phase evolution of calcium phosphate compounds during the wet-chemical synthesis of hydroxyapatite (HA).Calcium hydroxide and orthophosphoric acid were used to prepare HA at various temperatures ranging from 30 to 95 deg C.The electrical conductivity and pH of the reaction mixture were measured at regular intervals of time during acid addition,and the rate of change of conductivity was used to decipher the end point of the reaction.Our previous studies have shown that the end product of this reaction route yields mildly carbonated crystalline HA.The trend of the change in conductivity with time was similar at all temperatures.The conductivity curves were divided into three regions based on the variation in slope of the curves.The slope of the curves decreased with increasing temperatures in the first two regions,and the slope is greater in the second region than in the first.From the conductivity and pH measurement results,the possible precursor phase was identified and it had the composition Ca_3(PO_4)_2.The kinetics of phase transformation was also analyzed and compared to previous work.The similarities between this work and the traditionally adapted experimental work for phase formation and transformation kinetics are highlighted,and the novelty in the current work is discussed.