Inhomogeneous glass surfaces resulting from rapid forming operations - evidence from differential corrosion

A chemical compositional heterogeneity develops on glass surfaces which have experienced rapid expansion/stretching - as during the press or press/blow process used in forming. A differential etching technique using HF and HBF4 is developed to demonstrate that such heterogeneities occur on the surface of commercial articles such as soda-lime silicate tumblers. Comparison with articles exposed to aggressive conditions in a well-characterized dishwasher reveals that similar corrosion patterns appear in both cases - as alternatively corroded/non-corroded regions arranged as striations running vertically along the tumbler. Analysis of these striae by imaging ellipsometry and interferometry indicates that they consist of ridges 50-150 nm high in relief with a width and repeat distance of 0.05-0.15 mm. This pattern is in qualitative agreement with a recent physical modeling study and suggests that the ridges arise from durable low alkali glass which is at the surface of the gob/parison before the press/blow and which has been striated by less durable, high alkali glass from the interior of the gob. Under corrosive conditions, the alkali-rich glass dissolves away to leave behind the durable ridge. (C) 2004 Elsevier B.V. All rights reserved.