Preparation and characterization of sol-gel derived glasses in the ternary Na2O-Al2O3-P2O5 system

The development of a new sol-gel synthesis route to organic free Na2O-Al2O3-P2O5 xerogels is reported. These xerogels contain P2O5 up to 67.5 mole% and Al2O3 up to 20 mole% and could be melted to homogeneous glasses in air at significantly lower temperatures than those applied using the conventional melting method. This sol-gel route was investigated using different analytical tools. DTA/TG analysis indicated that neither organic residues nor sodium nitrate residues were present in the dried gels. FTIR spectroscopy showed the presence of all characteristic phosphate groups and bonds in the dried gels, especially the P=O and the P-O-P bonds. Solid-state 31P MAS NMR revealed the formation of Q2 chain-like polyphosphates of variable polymerisation degrees in the dried gels. Characterisation of the prepared glasses showed that their properties agreed very well with those glasses prepared by the conventional melting method. 25 refs.