Quantification of Anion and Cation Release from a Range of Ternary Phosphate-based Glasses with Fixed 45 mol% P2O5

Abstract

This article reports on the use of ion chromatography (IC) to investigate extensively the release profiles of both cations and anions and characterize the relationship between composition and degradation for a ternary-based Na₂O-CaO-P₂O₅ glass system developed as biomaterials. Studies are carried out on glasses with the formula 45P₂O₅-55(xCaO-Na₂O) in deionized water, where x = 30, 35, and 40 mol%, using a cumulative release method, where the solution is changed at regular intervals.

Degradation behavior is linear with time where the degradation rate shows an initial decrease with increasing CaO content. This rate then increases with a further addition of CaO. Cation release profiles follow similar trends to the degradation rates. Anion release profiles show a decrease for the PO₄ and linear polyphosphate (P₂O₇ and P₃O₁₀) species with increasing CaO content. This decrease is attributed to the cross-linking of the Ca²⁺ ions. In contrast, the cyclic P₃O₉ anion exhibits the highest amount of anionic release, which demonstrates similar trends to the cations. These release patterns suggest that the cyclic P₃O₉ species dominate the degradation rates. The proposed mode of degradation is a hydrolysis reaction, with the cyclic metaphosphate undergoing acid/base catalysis. The pH remains constant for the 30 and 35 mol% CaO glasses, and drops to about 5.5 for the 40 mol% composition. By using a response factor, it is possible to semiquantitatively analyze the additional peaks observed in the chromatograms. Suggestions are also put forward as to the identity of some of these unidentified peaks.

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