Glass strengthening via high-intensity plasma-arc heating

A high-intensity plasma-arc lamp was used to irradiate the surface of soda-lime silicate glass tiles to determine whether an increase in strength could be achieved. The lamp has a maximum power density of 3500 W/cm ², a processing area of 2 cm × 10 cm, a broad-spectrum energy distribution between 0.2 and 1.4 μm, and was controlled to unidirectionally sweep across 50 mm² tiles at a constant speed of 8 mm/s. Ring-on-ring (RoR) equibiaxial flexure and four-point unidirectional flexure testings of entire tiles were used to measure and compare uncensored and unimodal Weibull failure stress distributions of treated and untreated glass. Even under nonoptimized processing conditions, the RoR Weibull characteristic failure stress increased by approximately 25% and the four-point-bend Weibull characteristic failure stress increased by approximately 65%. Additionally, the failure stresses of the weakest samples of the heat-treated glass were significantly higher than those of the untreated glass. Strengthening was due to a fire-polishing-like mechanism. The arc-lamp heat treatment caused the location of the strength-limiting flaws in the four-point-bend tiles to change; namely, failure initiation occurred on the gauge section surface for the treated glass, whereas it occurred at a gauge section edge for the untreated glass. Arc-lamp heat treatment is attractive not only because it provides strengthening, but because it can (noncontact) process large amounts of glass quickly and inexpensively, and is a process that either a glass manufacturer or an end-user can readily use.