Characterisation of the dissolution of phosphate-based glasses via vapour sorption

Abstract

Event Abstract Back to Event Characterisation of the dissolution of phosphate-based glasses via vapour sorption Shiva Naseri1, William C. Lepry1, Maziar Shah Mohammadi1, Kristian E. Waters1 and Showan Nazhat1 1 McGill University, Department of Mining and Materials Engineering, Canada Introduction: Phosphate-based glasses (PGs) have been studied for wide range of biomedical applications attributable to the ability to control their degradation rates through their chemistry[1]. The flexibility in ionic doping allows for their tunable dissolution properties[2]. Herein, the potential of dynamic vapour sorption (DVS) in analysing the dissolution and potential reactivity of PGs was investigated. Materials and Methods: Melt-derived PGs of the composition 50P2O5-40CaO-xSiO2-(10 − x)TiO2, where x = 7, 5, 3, and 0 (mol%)[3] were sieved between 38 and 45 μm to give a specific surface area of 0.1243±0.0014 m2/g as measured by BET. A DVS Intrinsic (Surface Measurements Systems Ltd., UK) instrument was used to examine the aqueous interactions of the PGs. The mass change (± 0.1 µg) of 50 mg of particles at 37±0.05 °C was measured when: 1) the relative humidity (RH) was increased stepwise at 5% up to 90% then back down to 0% while the relative mass change was measured either when equilibrium (dm/dt < 0.002 %/min) was reached or after a maximum of 4 h; 2) the particles were exposed to 90% RH for 24 h, followed by 0% RH for another 24 h. PG dissolution rates were determined through immersion in deionized water (DIW) up to 28 days at 37 °C[3]. Differential thermal analysis was performed to identify the glass transition temperature (Tg)[3]. SEM, ATR-FTIR, NMR and XRD were used to analyse the morphological and structural changes of the PG particles as a consequence of exposure to DVS. Results: The sorption phase of all compositions indicated an initial small increase in mass up to 65% RH followed by a dramatic increase in mass up to 90% RH (Figure 1a). The inflection point in mass increase may be explained by deliquescence phenomena[4],[5]. Figure 1b shows the correlation between dissolution rate, Tg and inflection points. The sorption kinetics of PGs was investigated by direct exposure to 90% RH for 24 h and followed by exposure to 0% RH for a further 24 h (Figure 2a). Figure 2b indicates an exponential correlation between PG composition and rates of mass change, as well as mass change at 24 h (end of sorption phase) and 48 h (end of desorption phase). Discussion: PGs with higher silica content, demonstrated an increase in the rate of mass change, percentage increase in mass, and total sorption at 90% RH in both DVS methods. It is expected that by replacing silica with titania the PGs become more stable and consequently less reactive with vapour due to the formation of the stronger Ti-O-P bonds. Additionally, it can be seen that Tg increases by replacing silica with titania due to the crosslinking effect of the TiO2 and Ti-O-P bond formation. Conclusions: The short-term aqueous interactions of PG particles via DVS were analysed and correlated with glass structure and longer term dissolution in DIW. DVS may be a promising technique for the rapid, accurate and quantitative measurement of the reactivity of glasses. Funding of NSERC, CFI, Quebec MEIE, and McGill University Faculty of Engineering Gerald Hatch Faculty Fellowship are gratefully acknowledged. WCL (MEDA) and SN (Werner Graupe International Fellowships/MEDA) are partially supported by McGill’s Faculty of Engineering.