Glass - Back to the Future!



Presenting Author:
Wolfram Höland
<wolfram.hoeland@ivoclarvivadent.com>

article posted 06 June 2016


Wolfram Höland
Born in 1952.
Study of chemistry at the Friedrich Schiller University, Jena, Germany, from 1970 to 1977
Degree in chemistry in 1974
Doctoral thesis on solid state reactions of glass raw materials at the Friedrich Schiller University in 1978
Habilitation thesis on the development of new glass-ceramics at the Friedrich Schiller University in 1985
University lecturer at the Friedrich Schiller University in 1986
Professor of glass chemistry at the Friedrich Schiller University from 1989 to 1991
Research chemist in ceramics, glasses and glass-ceramics at IVOCLAR Ltd., Principality of Liechtenstein, since autumn 1991
Head of the r&d glass chemistry and ceramics department at IVOCLAR Ltd. 1993-2002
Head of fundamental research on glass and ceramics at IVOCLAR VIVADENT AG, since 2003
Representative of Liechtenstein in the ICG (International commision on glass/ the world glass society) since 1994
Chairman of TC 7 (technical committee 7, glass-ceramics) of the ICG (International commission on glass) 1995-2004
156 scientific publications; 75 patents; co-editor of seven textbooks (including three monographs)
Monographs:

W. Höland, G.H. Beall. Glass-ceramic technology, The American Ceramic Society, Westerville, OH, USA (2002) and second edition, Wiley (2012)
W. Höland, Glaskeramik,vdf, UTB; Zurich, Switzerland and Stuttgart, Germany, 2006







Nanophase formation in the process of nucleation and crystallisation of glass-ceramics

Wolfram Höland, Christian Ritzberger, Marc Dittmer and Markus Rampf
Ivoclar Vivadent AG, R&D, Bendererstr. 2, Li-9494 Schaan, Principality of Liechtenstein


The nucleation process is the driving force to develop glass-ceramics with tailor made properties. The authors show different chemical systems which allowed a controlled formation of nanophases to develop glass-ceramics with very special properties.

Based on a precipitation of an amorphous nano-sized phosphate in the SiO2-Al2O3-K2O-Li2O-P2O5 system, it was possible to precipitate Li2Si2O3 and Li2Si2O5 crystals in the glass-ceramic. Detailed microstructure studies imply that the interface between the phosphate phase and the SiO2 rich glass matrix acts as the nucleation center of the lithium silicate crystal phases. The final result is a glass-ceramic with preferred translucency, high toughness and high strength.

Based on the knowledge of such phase formation processes including nano-sized phases in amorphous or nano-crystalline condition, the authors often applied “twofold” nucleation and crystallisation processes to develop glass-ceramics. “Twofold” nucleation and crystallisation demonstrates the formation of two different nucleation processes to precipitate two chemically different crystal phases within a glass-ceramic. Applying such processes in multicomponent chemical systems, different properties could be combined within new types of products. The following two examples demonstrate this phenomenon.

At first: Nano-sized phase formation was studied in the SiO2-Al2O3-K2O-Li2O-P2O5-CaO-F system. Applying the twofold nucleation and crystallisation processes, it was possible to develop a Li2Si2O5 – Ca5(PO4)3F glass-ceramic with preferred translucency.

Second: The incorporation of Cs2O in lithium silicate glasses extended the chemical nature of the glass to the SiO2-Al2O3-K2O-Li2O-P2O5-Cs2O system. Controlling the nano-phase formation within such a system, Li2Si2O5 and CsAlSi5O12 crystals were precipitated in the glass-ceramic. The different phase formation cycles allowed the control of the mechanical and thermal properties in a tailor made manner.