Physical and chemical changes to commercial sodium phosphate glasses after aging or dynamic vapor sorption

Commercial sodium phosphate glasses are used as reference materials for polyphosphate chain length analysis. Water can spontaneously hydrolytically degrade the characteristic polyphosphate P-O-P bond, and reduce the polyphosphate chain length. XRD, Raman spectroscopy, and SEM were used to characterize glasses stored for two weeks, six months and >10 years, and three commercial sodium phosphate glasses after controlled water vapor adsorption and desorption. Rapid water vapor absorption was measured above 50 % relative humidity. The chain length distribution for a dissolved commercial sodium phosphate glass with an average chain length of 45 P O 3 − units was analyzed with polyacrylamide gel electrophoresis. A distribution of linear polyphosphates, interrupted with a population spike of ∼13 P O 3 − units, trimetaphosphate rings, and orthophosphates were identified. ³¹ P-MAS NMR suggested that the linear polyphosphate population spike could be the product of large ring polyphosphate scission upon dissolution. This study confirms the importance of dry storage for chain length reference phosphate glasses.