**1. Introduction**

Ion-exchange has been used exactly for one century to modify the surface properties of glass; Schülze in 1913 [1] was in fact the first to demonstrate that monovalent cations contained in glass could be exchanged when a soda lime silicate glass was immersed into a bath of molten silver nitrate. During the years, ion-exchange processes were developed and industrialized for numerous applications, such as chemical strengthening of glass articles [2, 3], gradient index (GRIN) lenses [4, 5] and planar waveguides [6]; the ion-exchange properties of glass have been also used to explain the functioning of the pH glass electrode and the chemical durability of glass [7].

In the last years, ion-exchange of glass has re-acquired great interest due to the possibility to increase the strength also of three-times and to work on articles of different shapes (even curved, wavy or hollow) and with limited thickness, avoiding many of the problems associated to thermal tempering such as optical distortions of the surface and premature failure due to NiS inclusions. Several contemporary technologies and applications, which regard the modern everyday life, took fundamental advantages from the application of ionexchange to glass components such as pharmaceutical packaging, transparent lightweight armor, transparencies for private vehicles, trains and aircrafts, 3D / touch / flexible displays, photovoltaic modules [8].

Typically, an industrial ion-exchange process is performed by placing the glass components for several hours (from about 4 h even to 120 h) in a vessel containing a molten salt; in the most typical configuration sodium (or lithium) containing silicate glass is immersed into a molten potassium nitrate bath at temperatures ranging from 400°C to 500°C [9-11]. During the ion-exchange process the glass can be considered as a matrix of immobile negative

© 2012 Sglavo, licensee InTech. This is an open access chapter distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. © 2012 Sglavo, licensee InTech. This is a paper distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

groups with associated mobile cations (Na+ or Li+); the contact with liquid monovalent ioncontaining salt induces interdiffusion that can be treated with Nerst-Plank equations. After the ion-exchange process is completed, the articles are rinsed with water and dried, being immediately ready for successive use. For a given glass composition, the overall strengthening is a function of the type of invading ion (salt bath composition), bath temperature and immersion time.

In the past, no much attention has been devoted to the variation of chemical composition of the salt bath, to its influence on the ion-exchange process and resulting chemical, physical and mechanical performances. As a matter of fact, since interdiffusion depends on the concentration of the ions, one should expect that any variation in the liquid bath composition modifies the ion-exchange process. In addition, some recent results [12] pointed out a more effective ion-exchange process when the glass article is immersed in a non-pure liquid bath containing significant amount of the ion to be exchanged present in the glass.

There is therefore an increasing interest in the analysis and understanding of the influence of salt bath composition on ion-exchange process and consequent properties for silicate glasses.

In the present work soda lime silicate float glass from commercial source was considered and were subjected to ion-exchange in different KNO3 salts. The treated samples are then characterized in terms of potassium penetration profile and mechanical strength to point out the influence of the bath composition on final performances.
