Glass - Back to the Future!

Presenting Author:
Arun K Varshneya

article posted 18 April 2016

Arun Varshneya is a Sheffield glass technology department alumnus. After securing his B.Sc.Tech with honors in glass technology in 1965 at “Elmfield”, he migrated to the US to get his MS and PhD under the advisorship of the late Professor Alfred R. Cooper. He worked at the Ford Scientific Laboratories and GE Lighting Business Group before joining Alfred University as a professor of glass science and engineering. Varshneya co-founded his entrepreneurship company “Saxon Glass Technologies, Inc.” in 1996 and continues to be its CEO. The company delivers glass chemical strengthening service particularly for the pharma glass packaging, armor, and mobile phones. Arun is the solo author of the textbook, “Fundamentals of Inorganic Glasses”, now in its second edition published by the Society of Glass Technology. He is the author/co-author of nearly 150 publications of which roughly 20 are devoted to glass chemical strengthening. Arun is also the author of the 13-page article on “Industrial Glass” in Encyclopaedia Britannica. He is a 2014 Distinguished Life Member of the American Ceramic Society, recipient of the 2007 President’s Award of the International Commission on Glass and a Fellow of the Society of Glass Technology.

Recent Advances in the Chemical Strengthening of Glass

Arun K. Varshneya
Saxon Glass Technologies, Inc., Alfred NY 14802 USA;

After lying somewhat dormant for good reasons, the glass chemical strengthening technology has seen rapid advances within the last decade since its initial discovery in 1962. The key developments have been triggered by the need for the greatly increased drop resistance for thin flat glass covers used in personal mobile electronic communication devices. Primary advance has been the highly controlled manufacture of glass as thin as ~0.5 mm without the need for grinding and polishing. Glass is produced by “fusion overflow”, “down-draw” or by the “float” processes. Cover glasses are processed routinely to 600 -1,000 MPa surface compression with a depth-of-layer from 25 to 60 microns. Potential reduction in the warp of a thin substrate after ion exchange, long term maintenance of the molten salt bath, understanding of the beneficial compressive stress buildup and control of its relaxation are additional recent advances in the technology. It is understood that a sodium containing glass does not acquire its potassiated compositionally equivalent as-melted (“CEAM”) structure instantly after ion exchange. Elastic and delayed elastic deformations transform it to the usually observed “stuffed” state which relaxes by viscous flow to the CEAM structure over much longer time, or at a higher temperature (Figure 1). Compression due to suppressed deformations may build up essentially instantly, however, pico- and nano-second relaxations cause a rapid loss of the beneficial compression eventually achieving the CEAM structure (Figure 2). After a brief discussion of the dormancy, this presentation intends to highlight the recent advances in glass strengthening that promise a bright future for a variety of glass products; the science of many being a Turner legacy.

Figure 1 : Deformations during Na+ ↔ K+ ion exchange stuffing of glass

Figure 2: Buildup and relaxation of the beneficial compression