LATTICE-DEFECTS IN CALCIUM-PHOSPHATE CERAMICS - HIGH-RESOLUTION TEM ULTRASTRUCTURAL-STUDY

Ultrastructural properties of precipitated apatites were characterized before and after sintering at 900 and 1250-degrees-C using high resolution transmission electron microscopy. The apatite crystals were oriented with respect to the electron beam so that the crystals could be examined in relation to the high resolution images of the (001) and (100) planes. The ultrastructural properties were found to be affected by sintering temperature. Numerous lattice defects, including atomic vacancies, dislocations and two types of grain boundaries were observed. In addition, a new type of three-dimensional lattice defect was frequently observed in the apatites sintered at 900-degrees-C. This type of lattice defect has the character of a hexagonal parallelipiped void, probably resulting from an aggregation of atomic vacancies. Calcium phosphate ceramics (hydroxyapatite and tricalcium phosphate) prepared by precipitation and subsequent sintering to temperatures above 1100-degrees-C are presently used as bone grafts. The amount and kind of defects such as those observed in this study have significant implications on the extent of the degradation of these materials in vivo.