AUTHOR=Rampf Markus , Dittmer Marc , Ritzberger Christian , Höland Wolfram 

TITLE=Controlled Parallel Crystallization of Lithium Disilicate and Diopside Using a Combination of Internal and Surface Nucleation

JOURNAL=Frontiers in Materials

VOLUME=3

YEAR=2016

URL=https://www.frontiersin.org/journals/materials/articles/10.3389/fmats.2016.00047

DOI=10.3389/fmats.2016.00047

ISSN=2296-8016

ABSTRACT=<p>In the mid-twentieth century, Dr. Donald Stookey identified the importance and usability of nucleating agents and mechanisms for the development of glass-ceramic materials. Today, a number of various internal and surface mechanisms as well as combinations thereof have been established in the production of glass-ceramic materials. In order to create new innovative material properties, the present study focuses on the precipitation of CaMgSi<sub>2</sub>O<sub>6</sub> as a minor phase in Li<sub>2</sub>Si<sub>2</sub>O<sub>5</sub>-based glass-ceramics. In the base glass of the SiO<sub>2</sub>–Li<sub>2</sub>O–P<sub>2</sub>O<sub>5</sub>–Al<sub>2</sub>O<sub>3</sub>–K<sub>2</sub>O–MgO–CaO system, P<sub>2</sub>O<sub>5</sub> serves as nucleating agent for the internal precipitation of Li<sub>2</sub>Si<sub>2</sub>O<sub>5</sub> crystals, while a mechanical activation of the glass surface by means of ball milling is necessary to nucleate the minor CaMgSi<sub>2</sub>O<sub>6</sub> crystal phase. For a successful precipitation of CaMgSi<sub>2</sub>O<sub>6</sub>, a minimum concentration of MgO and CaO in the range between 1.4 and 2.9 mol% in the base glasses was determined. The nucleation and crystallization of both crystal phases takes place during sintering a powder compact. Dependent on the quality of the sintering process, the dense Li<sub>2</sub>Si<sub>2</sub>O<sub>5</sub>–CaMgSi<sub>2</sub>O<sub>6</sub> glass-ceramics show a mean biaxial strength of up to 392 ± 98 MPa. The microstructure of the glass-ceramics is formed by large (5–10 μm) bar-like CaMgSi<sub>2</sub>O<sub>6</sub> crystals randomly embedded in a matrix of small (≤1 μm) plate-like Li<sub>2</sub>Si<sub>2</sub>O<sub>5</sub> crystals arranged in an interlocking manner. While there is no significant influence of the minor CaMgSi<sub>2</sub>O<sub>6</sub> phase on the strength of the material, the translucency of the material decreases upon precipitation of the minor phase.</p>