Surface alteration of zinc ultraphosphate glass in humid air at 140 degrees C

A mechanism for the alteration of zinc ultraphosphate glass by humid air at 140 degrees C is presented. The glass was prepared by melting a H3PO4-ZnO batch at 900 degrees C for one hour, its composition is 54.6(+/-1.5)P2O5-34 .2(+/-0.5)ZnO-11.2(+/-0.4)H2O. H-1 and P-31 nuclear magnetic resonance show s that water adsorption occurs and simultaneaously leads to the formation o f monophosphoric (H3PO4) and diphosphoric (H4P2O7) acids. The surface condu ctivity data are consistent with the formation on the glass surface of an a cidic solution of phosphates. The thermogravimetric data shows that this so lution reaches equilibrium with the atmospheric water, that decreases the a dsorption rate of water, (C) 1999 Elsevier Science B.V. All rights reserved .