Composition and Phase Analysis

In the following sections we provide detailed descriptions of the techniques required for such characterization. 

Conventional chemical analysis techniques such as wet analysis or atomic absorption (AA) can provide a relatively accurate chemical composition for studying the Ca/P ratio and stoichiometric composition of HA. Energy dispersive spectroscopy (EDS), typically in conjunction with scanning electron microscopy (SEM) or transmission electron microscopy (TEM) has also been used extensively to analyze chemical composition, both quickly and directly. This technique allows the incident electron beam to be moved from one surface region to another for mapping the localized surface elemental composition and their distribution. However, low concentrations of elements are not measured accurately when using EDS. 

The reflection broadening in the XRD pattern is attributed to the contributions of the crystaUite size, microstrain and the instrument itself The crystal size D is inversely proportional to the peak breadth, according to the Scherrer s formula 

Further, it is also possible to determine the crystallographic characteristics of HA crystals from the XRD data. HA has the hexagonal crystallographic structure, where the relationship between the distance (d) of two adjacent net planes and the (hkl) Miller indices of the reflection planes, is given by [51]  

A slight shift of the diffraction peaks can be observed when some trace elements are incorporated into the HA crystal. 

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