article posted 21 March 2016
Christian Bocker conducts research at the Otto-Schott-Institut ...
Nano crystallisation in glass ceramics affected by liquid/liquid phase separation in non-isochemical systems
Christian Bocker1, Thomas Höche2, Christian Patzig2, Changgui Lin1 & Christian Rüssel1
1 Otto-Schott-Institut, University Jena, Germany
2 Fraunhofer Institute for Microstructure of Materials and Systems, Halle, Germany
In recent years a mechanism has been described for nano crystallisation in non-isochemical systems which imply the formation of a diffusion barrier which hinders furthers crystal growth or coarsening. In some glasses liquid/liquid phase separation in the melt occurs already with the addition of minor concentrations, for instance rare earths or fluorides. In dependence of the size one refers to clusters (few nanometres) or liquid/liquid phase separation (usually larger than 100 nm). The growth mechanism of these non-isochemical phases is described in first models and is similar to nano crystallisation whereas the composition might change in phase separation droplets in dependence of the temperature. Further studies concern the combination of these effects, i.e. phase separation and the resulting crystallization. Also in phase separated glass systems a nano crystallisation can be observed. The formation as well as distribution of the crystallites is determined by the previous phase separation structure. The characterization of these complex structures is challenging and can be simplified by the separation of the particles from the matrix, for instance using extraction replica methods.