Glasses from the quaternary glass system K2O-Na2O-CaO-P2O5 were produced by standard glass forming techniques. The compositions were limited by fixing the P2O5 at 45 mol%, fixing the CaO content at ...either 20, 24 or 28 mol%. The K2O and Na2O made up the residual varying from 0 to 25 mol% K2O. General trends showed that with increasing CaO content, the glasses showed a decrease in solubility as expected. For a single system of fixed CaO content, with increasing K2O content, there was an increase in solubility. This was seen at all three CaO contents. All the glasses showed an initial increase in pH followed by a gradual decrease with time and this was accounted for by the initial release of Na+ ions into solution. For the ion release curves, for all fixed CaO contents, the glass with 0 mol% K2O showed the lowest Ca2+ release. This was accounted for as being due to the low solubility compared to the K2O containing glasses. The Na+ release appeared anomalous, as it was higher than all the K2O containing glasses. Even though the glasses with 0 mol% K2O showed the lowest solubility, the amount of Na+ contained in the glass was high, hence the high levels of release.
This paper presents the results of a study of the thermal properties of a range of phosphate-based glasses in the system CaO-Na2O-P2O5. The glasses had a fixed P2O5 content of 45 mol% and the ...CaO:Na2O ratio was varied. The glasses were produced and ground and their thermal properties measured using a Setaram differential thermal analyser (DTA). Initial data showed that for the high Na2O containing glass, NaPO3 forms and a second unidentified phase that is probably calcium rich. In the middle compositional region, multiple phases precipitated out and were identified as NaPO3 and Na4Ca(PO3)6. For the high CaO content glasses, Na4Ca(PO3)6 was the only phase formed. Further studies were carried out to examine whether the phases were bulk or surface nucleating, by grinding the samples to different particle sizes. From this data, it is evident that the NaPO3 forms via a bulk nucleation mechanism and that Na4Ca(PO3)6 forms via surface nucleation. The factors controlling this precipitation process are discussed and ionic radius as a controlling factor is hypothesised.
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