2024/08/28 by Gehrke, Eckhard, Ullner, Christian, Hähnert, Manfred
#660
paper · doi:10.34657/14143
The crack growth on silicate glasses of the systems x Na2O - (100-x) SiO2, x Na2O - 11 Αl2O3 - (89-x) SiO2, x Na2O - 11 B2O3 - (89-x) SiO2, x Na2O - 7 CaO - (93-x) SiO2 and x Na2O - 17 CaO - (83-x) SiO2 as well as on two commercial glasses (soda-lime-silica and sodium borosilicate glass) in water, acids and bases has been studied. In alkali oxide containing silicate glasses the crack-growth mechanism is based on a stress-stimulated splitting of siloxane bridges due to attack of both hydroxide ions (dominant in NaOH) and molecular water (dominant in LiOH). Real network dissolution with a rate like the crack-growth velocity (occurring in hydrofluoric acid or in water on extremely leachable glasses) leads to a plateau-like region of the crack growth. The threshold of crack growth in alkali-containing glasses is caused by alkali leaching forming a surface-near glass layer with modified mechanical properties within the cracks. Therefore, this threshold is enhanced with increasing pH value of the medium. The two commercial multicomponent glasses behave in a similar way like the investigated model glasses. The crack-growth curves indicate that the failure risk decreases in the order base, water, acid as well as with increasing concentrations of base or acid.