Abstract
In the mid-19th 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 CaMgSiO6 as a minor phase in Li2Si2O5 based glass-ceramics. In the base glass of the SiO2-Li2O-P2O5-Al2O3-K2O-MgO-CaO system P2O5 serves as nucleating agent for the internal precipitation of Li2Si2O5 crystals while a mechanical activation of the glass surface by means of ball milling is necessary to nucleate the minor CaMgSi2O6 crystal phase. For a successful precipitation of CaMgSi2O6 a minimum ratio of MgO and CaO in the range between 1.4 mol% 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 Li2Si2O5-CaMgSi2O6 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 CaMgSi2O6 crystals randomly embedded in a matrix of small (≤ 0.5 µm) plate like Li2Si2O5 crystals arranged in an interlocking manner. While there is no significant influence of the minor CaMgSi2O6 phase on the strength of the material, the translucency of the material decreases upon precipitation of the minor phase.
Highlights
In the 1950s, Dr Donald Stookey succeeded in the production of the first glass-ceramic of the lithium disilicate type worldwide (Stookey, 1959; Höland and Beall, 2012)
The concentration of MgO and CaO in the base glasses increases from glasses A to D
The extension of the chemical composition of the base glass by certain amounts of MgO and CaO is the prerequisite for the precipitation of CaMgSi2O6 as a minor crystal phase in Li2Si2O5 glass-ceramics
Summary
In the 1950s, Dr Donald Stookey succeeded in the production of the first glass-ceramic of the lithium disilicate type worldwide (Stookey, 1959; Höland and Beall, 2012). Stove tops and kitchenware belong to the most famous applications of glass-ceramics just as telescope mirrors, the nosecones of spaceships, and dental prostheses (Höland and Beall, 2012). In light of this wide field of applications for Donald Stookey’s invention, the impact of his work on the technological progress of humankind becomes obvious and has his research motivated and driven the mind and work of a huge number of scientists in various fields of research ever since. Besides enhancing the mechanical strength and machinability of glasses, the precipitation of certain crystal phases helped to control a number of different material properties including optical and electrical properties of glass matrix materials (Beall, 1971, 2014; Mauro et al, 2013)
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