Measurement of stress build‐up of ion exchange strengthened lithium aluminosilicate glass

Abstract

A recently developed nondestructive method was used to investigate the stress buildup in chemically strengthened lithium aluminosilicate glass. We utilized an updated version of the gradient scattered light method, which now enables more precise determination of the depth coordinates, recovering a more detailed stress profile around the knee. The main motivation of the work was to characterize and optimize the development of the knee-shaped breaking point in stress profile in lithium aluminosilicate glass prepared by the Saunders-Kubichan method of one-step strengthening in a mixture of KNO 3 +NaNO 3 molten salt bath. In the industry, a two-step process is still commonly used to build such a stress profile; the one-step strengthening will simplify the process as well as save the cost. Compared to previous studies, which used a destructive method based on transmitted light photoelasticity, we found that in the samples ion exchanged for 24 hours, the knee-shaped breaking points were situated two times deeper whereas the case depths were 28% shallower. The measured stress profiles were validated by stress equilibrium and by comparison to Na + ion concentration profiles. K E Y W O R D S glass, ion exchange, polarization, refractive index, scattering 2408 | HÖDEMANN Et Al. How to cite this article: Hödemann S, Valdmann A, Paemurru M, et al. Measurement of stress build-up of ion exchange strengthened lithium aluminosilicate glass.

Mechanical, thermal, and structural investigations of chemically strengthened Na2O–CaO–Al2O3–SiO2 glasses

“…The surface RCS of the CS glass monoliths, σ s , were determined using SCALP-05, a scattered light polariscope equipment from GlasStress Ltd. It is a well-described method to determine RCS in glass, see (Hödemann et al, 2016;Sun et al, 2019;Hödemann et al, 2020). The measurement depth was 0.75 mm, the stress optic coefficient (ΔC) was assumed to be constant, ΔC = 2.72 TPa −1 , and the refractive index (RI) was assumed to be 1.52 for x = {0, 4, 8, 12} and 1.53 for x = {16, 20} where x is the Al 2 O 3 content; q.v., Section 2.1, and Table 1.…”