Chemical durability of Na 2OCaOSiO 2 glasses in acid solutions

Abstract

The resistance of Na 2OCaOSiO 2 glasses to acid solutions has been studied. The compositions studied were Na 2O · 4SiO 2, Na 2O · x CaO · (4− x) SiO 2 and a common electrode glass containing 22.63Na 2O and 5.58 CaO, mol%. The reaction was made at 40°C for about 3 h in 1N solutions of HCl, HNO 3 and H 2SO 4. Powdered glass samples were used and the reaction was followed by analyzing the solution for soda, lime and silica. The extraction rates of each constituent were measured. The effect of acid concentration was also studied for each glass using 10 −3–10N solutions of the three acids for a fixed time. The quantity of calcium extracted increased slowly at first with increasing calcium content in the glass, but rapidly when the lime content exceeded ≈10 mol%. Above this concentration, both calcium and sodium appears to pass into solution in the same proportion in which they are present in the glass. The extraction rate was found to depend on the type and concentration of the acid used, being least in H 2SO 4 and much higher and almost equal in both HCl and HNO 3. An attempt was made to correlate the results of decomposition of the soda-lime-silica glasses to their membrane potentials in acidic solutions.