Physico-chemical Methods for the Identification of Microcristalline Basic Calcium 135 



specific area of the intermediary product is 130±10m-/g according to the electron 

 micrograph. The suspension of the amorphous product in water leads to crystalline 

 material of hydroxyapatite X-ray diffraction patterns with the same pH-curve as the 

 HA. The Ca/P ratio of the amor- 

 phous product is the same as the 

 one for its water suspension at any 

 time and pH, and also the same 

 as that for the end product of the 

 uninterrupted Hayek synthesis. 

 TG- and DTA-curves of the a- 

 morphous product are very dif- 

 ferent to those of HA (Fig. 3). The 

 characteristic temperatures are now 

 100 ''C, 170 '-'C and 300 '-'C, re- 

 presenting waterlosses of about 

 8 moles (adsorbed water), 1.8 and 

 0.2 — 0.3 moles. The total waterloss 

 up to 1000 °C is 3.2 to 3.3 moles. 

 The DTA-curve corresponds with 

 the TG-curve except for one exo- 

 thermic peak at 680 C. 



These curves resemble those of 

 a mixture of TCPH and OCP, 

 which are shown in Fig. 4. X-ray 

 analysis shows that the product re- 

 mains amorphous up to 600 °C. At 

 650 '^C the reflexes of the r/-TCP 

 appear thus corresponding to the 

 exothermic peak of the DTA. At 

 650 C we can observe the X-ray 

 pattern of /j-TCP. Therefore, we c 

 can state that the amorphous pro- 

 duct is a mixture of TCPH and 

 OCP. If we consider the pH of : 

 the intermediary step as the end- 

 pH, we find according to equation 

 (1) a Ca/P ratio about 1.84. The 

 discrepancy in the experimental 

 value can be explained by surface 

 adsorption of Ca'-*. This shows us that global chemical analyses are unsufficient to 

 determine the real nature of hydroxyapatites. In aqueous suspension the amorphous 

 product is hydrolized and the pH decreased. 



400 600 800 °C 



:urves of amorphous product 



200 

 Fig. 



400 



600 800 °C 



ics of OCP 



HA 



III. Conclusions 



is formed in two distinct steps: formation of the amorphous product then 



hydrolization to the final HA. TCPH is formed directly as shown by X-ray dif- 

 fraction patterns which are crystalline from the very beginning. The synthesis can be 



