Synthesis and Structural Analysis of Sol Gel Derived Stoichiometric Monophasic Hydroxyapatite

Hydroxyapatite (HAP) ceramics belongs to a class of calcium phosphate-based biomaterial, which has been widely used as bone substitute for long time. In recent years, synthetic HAP has assumed substantial interest and importance due to its chemical similarity with the natural Ca phosphate mineral present in a biological hard tissue. Considering the wide applications of calcium phosphate compounds in biomedical fields, numerous HAP synthesis techniques have been developed. The most commonly used technique for the preparation of HAP is the precipitation technique, involving wet chemical reactions between the calcium and phosphate reagents under controlled temperature and pH conditions [1 5]. However, this method has some inherent disadvantages, primarily the difficult control of the pH value over 9 to avoid the formation of a Ca-deficient HAP which on sintering undergoes easy decomposition, forming tricalcium phosphates. In this respect, the sol-gel technique is an effective method for the preparation of monophasic powder due to the possibility of a strict control of the process parameters. This method offers a molecular mixing of the calcium and phosphorus which is capable of improving the chemical homogeneity. The sol-gel product characterized by nano-size dimension is an very important parameter to improve the contact and stability at the artificial/natural bone interface. Moreover, the high reactivity of the sol-gel powder allows a reduction of the processing temperature and degradation phenomena occurring during sintering. The major limitation of the sol-gel technique is linked to the possible hydrolysis of phosphates [6]. Hence, the present investigation proposes a new method to prepare a phase pure HAP powder via the sol-gel route.