Glass - Back to the Future!



Presenting Author:
Vincenzo Sglavo
<vincenzo.sglavo@unitn.it>

article posted 13 April 2016


Vincenzo M Sglavo
University educacon: “Laurea cum laude” in Materials Engineering (University of Trento, Italy, 1988)

Appointments:
Associated Professor of Materials Science and Technology (Faculty of Engineering - Department of Industrial Engineering, University of Trento, Italy, 1999 to date)

Adjunct Professor (Materials Research InsKtute, The Pennsylvania State University, USA, 2001)

Post Doctoral Fellow (Department of Materials Science and Engineering, The Pennsylvania State University, USA, 1993-1994)

Researcher (Department of Materials Engineering, University of Trento, Italy, 1989-1999)#






Effect of salt impurities on the chemical strengthening of float glass by ion-exchange

Vincenzo M. Sglavo* & Hamid Hassani
Dipartimento di Ingegneria Industriale, Università degli Studi di Trento, Via Sommarive, 9 - I-38123 Trento (Italy)


Chemical strengthening of glass by ion-exchange process has gained notable interest during the last years because of its flexibility in reinforcing glass components of different geometry and thickness and the possibility to obtain very high mechanical performances. Several variables like glass composition, molten bath composition, temperature and time can affect the efficiency of the ion-exchange process. During a typical industrial process, sodium atoms contained in the glass are substituted by potassium ions diffusing from the molten salt. An interesting aspect regards the poisoning of the bath after each process and its enrichment in sodium. In addition, the presence of several impurities in the bath can influence the ion-exchange efficiency. In the present work, the effect of variable sodium concentration in the molten bath and of typical impurities present in KNO3 commercial salts on the performances of the strengthened glass was analyzed. Soda-lime-silicate float glass samples were subjected to ion-exchange. The flexural strength was measured by a ring-on-ring test method, the compressive stress was determined by optical methods and the surface chemical composition of the glass was analyzed by Energy Dispersion X-ray Spectroscopy (EDXS). The results point out that the residual stress decreases in a non linear and monotonic fashion as a function of the sodium content within the bath; the same is for the potassium surface concentration potassium and the flexural strength. The presence of some specific impurities like Ca and H2O also appear to be detrimental for the ion-exchange process efficiency. Possible solutions for reactivating non-efficient bath are also discussed.