Vitrification of β-tricalcium phosphate in sodium aluminoborophosphate glass and the effect of Ga3+ substitution

• Up to 80 wt% β-Ca3(PO4)2 can be vitrified in sodium aluminoborate glass.
• Multinuclear 1D NMR identifies the different sites occupied by the cations.
• Q21 and Q30 phosphate glass species are replaced by Q00.
• Devitrification to β-Ca3(PO4)2 with Na+ substituting on Ca(4) and Al3+/Ga3+ on Ca(5).
• Ga3+ substitution is preferred over Al3+ substitution.

Sodium calcium aluminoborophosphate glasses (some containing Ga3+) simulate interactions at the interface between β-tricalcium phosphate crystal waste hosts (β-TCP and β-TC(Ga)P) and sodium aluminoborophosphate (NABP) glass encapsulant. 31P NMR and Raman spectroscopies show progression from Na+ charge-balanced, mixed QAlP=Q21+Q30 in the NABP base glass, to Ca2+ charge-balanced, Q00 dominated structure, eventually inhibiting vitrification above 80 wt% addition of β-TCP or β-TC(Ga)P. 27Al NMR shows [Al(PO4)n] species with dominant n=4 and 11B NMR shows the 4-coordinated boron fraction in NABP falls from 0.7 to 0.1 on addition of the crystal hosts. Devitrification of glasses with 60–70 wt% crystal additions shows that Na+ and Al3+ from the encapsulant substitute for ∼20% of Ca2+ in the β-TCP phase formed from the β-TCP:NABP glasses whilst ∼85% of Ga3+ resubstitutes into β-TCP from the β-TC(Ga)P:NABP glasses. This demonstrates the preference for Ga3+ substitution over Al3+ in the Ca(5) site.

NABP encapsulant, loaded with up to 80 wt% Ga3+-doped β-TCP, can be roller-quenched to form a glass which is recrystallisable with 85% reclamation of Ga3+ by the TCP.Figure optionsDownload as PowerPoint slide