OPTICAL TRANSMISSIVITY CHANGES OF THIN HYDROXYAPATITE SHEETS ON HEATING

Thin hydroxyapatite sheets, consisting either of superfine hydroxyapat ite particles or particles increased in size by hydrothermal treatment , have been fabricated by a modified pressure casting procedure. The s heets were fairly well transparent after their fabrication and drying. On heating to 1000 degrees C the samples of superfine particles becam e opaque while the samples of hydrothermally treated gels remained ess entially transparent. By measuring the optical transmissivity of sheet preforms during their constant rate heating it is possible to determi ne the temperature interval in which the transition or partial transit ion between the transparent and the opaque state takes place. Dilatome tric measurements show an expansion of samples above 1000 degrees C, w hich is undoubtedly connected with creation of pores. Pore creation ma y be the reason also for the decrease of the transmissivity of specime ns above ca. 750 degrees C.