Effect of the glass composition on the chemical durability of zinc-phosphate-based glasses in aqueous solutions

The chemical durability of glasses with the composition 40P2O5–55ZnO–1Ga2O3–4Ag2O and 41P2O5–51ZnO–8Ga2O3 (mol%) was studied by measuring the rates of aqueous dissolution in neutral, acidic and alkaline aqueous solutions and discussed as a function of the glass composition. The change in the pH of the solutions as a function of the immersion time of the samples was used to study the dissolution mechanism. Using XRD and SEM/EDXA, we showed that the dissolution in deionized (DI) water and HCl consists of the leaching of the phosphate chains into the medium along with (i) the formation of a hydrated layer with the composition Zn2P2O7·3H2O and also of AgCl agglomerates when immersed in HCl and (ii) a leaching out of P, Ga and Ag when immersed for more than 180 min in DI water and for more than 60 min in HCl. The dissolution in NaOH–Na2CO3 consists of a net consumption of the OH− along with the formation of layers of Zn3(PO4)2·(H2O)4 and Zn(H2PO2)2·H2O with no apparent diffusion of P, Ga and Ag when immersed for as long as 240 min. Increasing the Ga2O3 concentration in zinc-phosphate glass at the expense of Ag2O lowers the dissolution rate when immersed in DI water, HCl and NaOH–Na2CO3 probably due to a reinforcement of the glass network.

The chemical durability of glasses with the composition 40P2O5–55ZnO–1Ga2O3–4Ag2O (Ag-containing) and 41P2O5–51ZnO–8Ga2O3 (Ag-free) was studied in DI water, HCl and NaOH–Na2CO3 solutions. The chemical durability was found to depend on the solution pH and of the glass composition. Increasing the Ga2O3 content leads to a higher ratio of Q1/(Q1+Q2) species indicating that it shortens the phosphate chains. Gallium is thought to connect the phosphate groups reinforcing the glass network. Consequently, probably due to its weaker network, the Ag-containing glass exhibits a faster dissolution rate when immersed in DI water, HCl and NaOH–Na2CO3 aqueous solution.Figure optionsDownload as PowerPoint slideHighlights
► Leaching of the phosphate chains with the formation of a hydrated layer when immersed in neutral and acidic solutions.
► Consumption of the OH− with the formation of Zn3(PO4)2·(H2O)4 and Zn(H2PO2)2·H2O layer when immersed in alkaline solution.
► Decrease of the dissolution rate with an increase of the Ga2O3 concentration at the expense of Ag2O in zinc-phosphate glass.