An Investigation of the
Chemical Synthesis and High-Temperature Sintering Behavior
Calcium Hydroxyapatite (HA)
Tricalcium Phosphate (TCP)

    * A. Cüneyt TAS, et. al., Journal of Materials Science: Materials in Medicine, Vol. 8, pp. 91-96 (1997).  (®download PDF)
    *A. Cüneyt TAS, Patent No: TR 1995 01422B, Turkish Patent Institute, Ankara, Turkey.


The experimental conditions for the synthesis of sub-micron, spherical particles of calcium hydroxyapatite [Ca10(PO4)6(OH)2] (HA) and tricalcium phosphate [Ca3(PO4)2] (TCP) were investigated by using a process of chemical co-precipitation from the aqueous solutions of calcium nitrate and di-ammonium hydrogen phosphate salts. The precipitation process employed was also found to be suitable for the production of sub-micron HA/TCP composite powders in situ. Pure HA and TCP powders synthesized were found to be stable even at 1300°C in air for prolonged heating times. Bioceramic sample characterization was achieved by powder X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDXS), and density and surface area measurements. Crystallographic analyses of HA powders were performed by the Rietveld method on the collected powder XRD data.

The SEM micrograph below (Click on the figure areas to display the pics:) shows a close-up of our HA pellets
(50 MPa uniaxial pressure) after sintering in an air atmosphere
at 1200°C for 6 hours.


The below micrograph also belongs to a similar HA sample
as above, but this time viewed at a lower magnification....
These uniaxially pressed HA samples were "translucent."

The below photograph clearly shows the "cracks" that may be visible
upon heating the samples of TCP (tricalcium phosphate) above
1200°C... TCP phase is known to undergo a polymorphic transformation
at around 1180°C, and the significant volume change accompanied
by this transformation causes cracks to develop in the
microstructure. Additions of Mg (about 2 to 10 at%) into the
Ca-sites of TCP may be helpful in reducing the extent of such cracks..
Sinterability of TCP powders were also much lower than those of HA.


Researchers: Erdal Sahin, Nezahat Kivrak, Oguz Yigiterhan, N. Ozgur Engin, Serra Çagatay, Alp Sehirlioglu, and A. Cuneyt Tas (1994-1997).