Glass with Hydration‐induced Compressive Stress Profiles

A novel potassium phospho-aluminosilicate composition is described that can be strengthened by water vapor to achieve deep compressive stress (CS) profiles. Water vapor treatment at (A) 85 degrees C and 85% relative humidity for 40 days results in a CS of 389 +/- 20 MPa and a compressive depth of layer (DOL) of 18 +/- 2 mu m. When treated at (B) 160 degrees C and 0.1 MPa for 7 days, a CS of 245 +/- 20 MPa and a DOL of 40 +/- 2 mu m is achieved. Glasses with hydration-induced stress profiles can provide high retained strength following flaw introduction compared with ion-exchanged soda-lime silicate glass. Sample treatment B also has an exemplary Vickers indentation cracking threshold value greater than 20 kgf. The hydration profile determined by secondary ion mass spectrometry (SIMS) is shown to closely match the stress profile for these samples. SIMS analysis also shows that the depth of water enrichment correlates well with the depletion depth of phosphorus. The high tendency towards water-induced strengthening for this new type of glass even enables self-strengthening by the generation of a near-surface CS profile following exposure to ambient conditions.