Influence of Ta2O5 addition on the crystallisation behaviour of a bioactive glass (AP40).

DTA, x-ray diffraction (XRD) and SEM were employed to study crystn. of AP40 and RKKP glassy materials. Wt. compns. of both glasses are very close to the Ilmaplant parent glass: SiO2=44·00; CaO=32·16; MgO=2·84; CaF2=5·00; Na2O=4·60; K2O=0·20; P2O5=11·20 for AP40 and SiO2= 43·84; CaO=31·93; MgO=2·79; CaF2=4·94; Na2O=4·55; K2O=0·19; P2O5=10·27; Ta2O5=0·99; La2O3=0·50 for RKKP. Crystd. AP40 and RKKP consist of wollastonite and fluoroapatite nanocrystals, not larger than 500 nm. Wollastonite crystallizes by a mechanism of surface nucleation. Crystn. is preceded by glass-in-glass phase sepn. into phosphate and silicate glassy phases. The glass-in-glass phase sepn. is finer in RKKP. The exptl. results suggest that Ta2O5, present only in the RKKP glass compn., catalyzes the nucleation of the phosphate glassy phase