Crystallization characteristics of La2O3-containing glasses for glass ionomer cement

Glasses with general formula 4.5SiO2 ⋅ 3Al2O3 ⋅ 1.5P2O5∙(2.5 − x)CaO ⋅ xLa2O3 ⋅ 2.5CaF2 (x = 0.0–1.0) for glass ionomer cement have been prepared by conventional melting and water quenching. The influence of substitution of La2O3 for CaO on glass transition temperature (Tg), setting time and crystallization was studied. An increase in La2O3/CaO ratio shifted Tg to higher temperature. Fluorapatite (Ca5(PO4)3F), mullite (3Al2O3 ⋅ 2SiO2), lanthanum aluminum silicate solid solution, and anorthite (CaO ⋅ Al2O3 ⋅ 2SiO2) were identified by XRD in the heat-treated materials; then, their formation was dependent on glass composition and heat-treatment temperature. After heat-treating at 750 °C with glass samples of La2O3/CaO = 0, 0.25 (molar ratio), only fluorapatite phase was precipitated; however, anorthite was additionally formed at 950 and 1050 °C. With further increasing La2O3/CaO ratio and/or heat-treatment temperature, lanthanum aluminum silicate solid solution existed as the major phase.

► A new type of glass-ionomer cement containing lanthanum was prepared.
► The crystallization of the ionomer glasses has been reported.
► The lanthanum calcium silicate phase capture fluorapatite components in its structure.
► The La2O3/CaO replacement in glasses led to improve the microstructure.