Guglielmo Macrelli is senior scientist in Isoclima SpA- R&D Department. He received his Master’s Degree (MSc) in Physics- Università Degli Studi di Bologna in 1982 working at the Bologna ENEA computational Center in the field of diffusion and transport of neutrons in matter. He has been active since 1990 in many glass science areas: ion exchange in silicate glasses, thin film optical coatings and mechanical glass properties.
He works for Isoclima SpA since 1992 and he has been involved in the development of industrial chemical strengthening plants and processes for soda-lime silicate glasses, sodium alumina-silicate glasses, and lithium alumina-silicate glasses and in the development of thin film coating on glass for heated glazing, induced transmittance solar control coatings and electrochromic coatings based on all solid state thin film inorganic layers.
He is specialist in glass strength and strengthening processes and in optical characterization of glazing He has authored a number of peer reviewed scientific papers and participated as speaker in several international conferences. He has an extended experience (more than 25 years) in glass testing and glass processing (thin film coatings, glass chemical strengthening by Ion Exchange and glass strengthening by thermal processing).
Guglielmo Macrelli is member of the American Ceramic Society
Ion Exchange an “old age” technique for high strength modern glazing applications
Isoclima SpA- Science Division, via A.Volta, 14 – Este (PD) Italy
Ion Exchange techniques are really old age. Examples can be found in the field of cultural heritage  in lustre decorations of pottery of Medieval and Renaissance typically in the Mediterranean basin. In these examples (see Figure 1 taken from ) a glazed pottery is decorated by a metal-glass nanocomposite thin layer. An ion exchange process is induced at high temperature where metal ions are exchanged for alkali ions in the glass with subsequent diffusion of the metal ions in the glazed matrix.
Figure 1 – a) Lustre prepared by Mastro Giorgio in Gubbio (Italy, 1528); b)Manises Coat of arms of Ricci Family, (Florence, Italy 1470)
Ion exchange, as a modern application in silicate glasses, is known since 1913 . A significant breakthrough in strengthening applications can be dated in last century, in the Sixties . From that time up to now Chemical Strengthening by Ion Exchange has become a widely used technology to increase glass strength. In Figure 2 some evidences of structural applications are shown ranging from transportations (aircrafts, high performance sport cars, ships), medical devices, architectural, armoured glazing to arrive to the recent huge diffusion of chemically strengthened glass components in consumer electronics devices.
Figure 2 – High strength by Ion exchange modern glazing application: Cockpit airplane windshields, high performance cars, medical devices; armoured glazing, marine glazing, consumer electronics, architectural high performance structural glazing.
Ion exchange can be understood as a thermodynamic equilibrium process at the Glass/Ion Source interface and as a kinetic transport process in the glass matrix (see Figure 3). Surface equilibrium conditions are influenced by the process parameters (temperature and process time), glass chemical composition and ion source contaminations. Interdiffusion kinetics within the glass matrix is related to the couple of exchanging ions and it depends mainly from temperature and, at a second order, by the concentration of exchanging
In ion exchange performed below the glass transition temperature, stress is generated by elastic suppression of strain. After this simple explanation some residual issues about the “anomaly” of the linear network dilation coefficient (B) remained . This issue has been recently solved ,  allowing a deeper understanding of stress build up by ion exchange at a molecular and atomistic level. For applications it is relevant the possibility to model residual stress taking into account ion exchange kinetics and stress relaxation (see Figure 4).
Predictions of residual stress profile coupled with linear fracture mechanics allow the evaluation of glass strength  and of the stability of surface flaws and cracks when exposed to applied external complex stress fields. This last issue, coupled with a deeper understanding of interrelationship between network topology, yield strengths, flaw cavitation and growth in molten glass will open the way to new perspectives in stronger glass .
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 Schulze, G; Ann.Phys.(Leipzig), 40 (1913) 335.
 Varshneya A.K., Fundamentals of Inorganic Glasses 2nd Edition – Society of Glass Technology, Sheffield, UK 2006
Wang, M.;Smedskjaer,M.M.;Mauro,J.C.;Sant,G.;Bauchy,M.;Phys.Rev.Applied;2017 Vol 8, Iss.5
 Varshneya AK, Olson GA, Kreski PK, Gupta PK.; J Non Cryst Solids. 2015;427:91-97.
Macrelli,G.; Int.J.Appl.Glass Sci.; 2018;9; 156-166
 Varshneya,A.K.; Int.J.Appl.Glass Sci.; 2018;9; 140-155