Effect of P2O5 content in two series of soda lime phosphosilicate glasses on structure and properties – Part II: Physical properties
Introduction
There is some controversy as to the role of P2O5 in soda lime phosphosilicate glass structure, bioactivity and bone mineralization. The Hench model [1], [2] predicts that the presence of phosphate is required in the implant material. However, this model does not predict the bioactivity of some glass compositions which do not contain phosphate [3] and neglect the network connectivity of the glass [4], [5], [6]. The Hench model also assumes congruent dissolution, which is not possible as these glasses phase separate into a phosphate rich and silicate rich phase as shown in part I. The phosphate phase will degrade in the presence of water at a much higher rate than the silicate phase. This phase separation results in orthophosphate groups () in the phosphate phase which are charge balanced by alkali and alkaline earth cations. This has the effect of reducing the number of non-bridging oxygens in the silicate phase resulting in higher connectivity.
Part I of this study examined the structure of two series of bioglasses with varying phosphate contents using solid state MAS-NMR spectroscopy. The purpose of the second part of the study is to use more conventional characterization techniques to validate the NMR findings and assess properties important for processing promising compositions. Glass densities were measured to compare experimental values to calculated values from glass network connectivities based on glass composition (Doweidar’s model [7], [8]) and using network connectivities obtained from fitting of the 29Si MAS-NMR data. Thermal expansion coefficients were obtained from dilatometry and values compared to calculations using the Appen model [9]. Thermal expansion coefficients are important to characterize, particularly for applications which may involve coatings. If bioactive glass compositions can be identified with thermal expansion coefficients matched to metals typically used in prosthetic implants (or preferably slightly higher than the metal so the glass is in compression), this could provide an important component to the next generation of biomedical devices. Characteristic temperatures were observed using differential thermal analysis (DTA) to examine the effect of phosphate addition on the glass transition temperature and devitrification behavior. The working range, Tx–Tg, is an important parameter in various applications such as viscous flow sintering (coatings) and fiber drawing. Finally, X-ray diffraction, on amorphous and again on subsequently heat treated samples, was used to investigate if any crystallites were present, and if so how this might relate to the structure of the devitrified material to the parent glass.
Section snippets
Glass melting
Details of glass melting can be found in part I of this paper (REF). Glasses for thermal expansion coefficient (TEC) measurements and density were remelted from the frit described above for 30 min and cast into preheated (≈Tg–10 °C) graphite moulds and annealed in an electric furnace overnight. The rod shaped samples formed were cut into sections of 6 mm in diameter and 25 mm in length using a slow speed diamond saw. The ends of these rods were ground flat using SiC abrasive paper. It should be
Density
Fig. 1, Fig. 2 show the density measurements for the glasses from series I and II, respectively.
The plots also show the density values calculated using Doweidar’s model [7], [8] which assumes a binary distribution of silicate Qn species. All glass compositions were normalized to exclude the phosphate content, and all fell in the 33 ⩽ xt ⩽ 50 mol% region (where xt is the total modifier mol%), therefore the Qn distribution was Q3 and Q2 in the binary distribution model. The relative proportions of the
Conclusions
The modified Doweidar model, taking into account the effect of the P2O5 not entering the glass network, seems to provide a closer fit to experimental density values. The densities of series I increased and series II decreased with P2O5 addition. Theoretical thermal expansion coefficients (Appen) also showed a relatively good match to experimental values. This can be explained by the increase in the amount of the separate phosphate phase with P2O5 addition which contains weaker P–O bonds
Acknowledgements
MDO and SW would like to thanks EPSRC (Grant No. EP/C549309/1) and Imperial College London for funding this work. MDO would like to thank Dr. Steve Skinner for useful discussions on Rietveld refinement.
References (14)
J. Non-Cryst. Solids
(1998)J. Non-Cryst. Solids
(1999)- et al.
J. Non-Cryst. Solids
(2005) - et al.
J. Non-Cryst. Solids
(2000) - et al.
J. Non-Cryst. Solids
(2000) J. Am. Ceram. Soc.
(1991)
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