Investigation of thermal parameters and crystallisation in a ternary CaO-Na2O-P2O5-based glass system

This paper presents the results of a study of the thermal properties of a r ange of phosphate-based glasses in the system CaO-Na2O-P2O5. The glasses ha d a fixed P2O5 content of 45 mol% and the CaO:Na2O ratio was varied. The gl asses 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 phas e that is probably calcium rich. In the middle compositional region. multip le 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. F rom this data, it is evident that the NaPO3 forms via a bulk nucleation mec hanism and that Na4Ca(PO3)(6) forms via surface nucleation. The factors con trolling this precipitation process are discussed and ionic radius as a con trolling factor is hypothesised. (C) 2001 Elsevier Science Ltd. All rights reserved.