Structures and dissolution behaviors of MgO–CaO–P2O5–Nb2O5 glasses

Abstract MgO–CaO–P2O5–Nb2O5 glasses with the substitution of MgO for CaO consisting predominantly of meta-, pyro-, and orthophosphate groups were prepared using a melt-quenching method, and their structures and dissolution behaviors were investigated. Magnesium in the metaphosphate compositions was shown to act as a modifier oxide and coordinate phosphate groups. Magnesium in the pyro- and/or orthophosphate compositions was shown to act as a network former and to form P–O–Mg bonds, which crosslink short phosphate groups. The chemical durability of the metaphosphate glasses increased with increasing the substitution of MgO for CaO because magnesium exhibits a larger field strength than calcium. However, the durability of the pyro- and/or orthophosphate glasses decreased with increasing the MgO content: P–O–Mg bonds weakened the glass network structure and induced hydrolysis.