Synthesis of hydroxyapatite-based powders by mechano-chemical method and their sintering

Ceramic hydroxyapatite (HA) is on the way to one of the most promising and diversified materials for employment in surgery, thanks to its good characteristics of biocompatibility and bioadaptability. The main and probably unique deficiency of these materials obtained by traditional methods consists in its weak mechanical resistance, that does not allow their use when even low loading is involved To improve the mechanical properties of HA-based ceramic bodies additions are normally necessary. In this paper the authors propose a method to prepare powders and composite ceramic bodies with a matrix comprising HA. The powders are produced by the utilization of a simple and economic mechano-chemical method. The composite ceramic bodies are easily obtained by simple firing of the powders at a suitable temperature (1250 degrees C). The powders, after sintering, give products that show a flexural strength of more than 100 MPa in standard samples. This value is significantly higher than that usually attainable with present commercially available powders (60 MPa). The transformation in the components (HA and beta-tricalcium phosphate) of the composite ceramic arises from the nature of the powders, consisting of highly defective HA. The mechano-chemical process is described together with the employed procedures specifically followed for reactive milling of starting powders. The preparation conditions of defective HA powders and properties acquired through such a method are reported. By this method an intimate mixing of beta-tricalcium phosphate (beta-TCP) inside the HA matrix is obtained that easily allows the preparation of ceramic bodies with reproducible properties, with no necessity for additions and mixing procedures, that could lead to inhomogeneity.