M.Sc. Laura Briese | Institute for Non-Metallic Materials, Clausthal University of Technology | Germany
Dr. rer. nat. Susanne Selle | Fraunhofer Institute for Microstructure of Materials and Systems IMWS | Germany
Dr. rer. nat. Christian Patzig | Fraunhofer Institute for Microstructure of Materials and Systems IMWS | Germany
Prof. Joachim Deubener | Institute for Non-Metallic Materials, Clausthal University of Technology | Germany
Prof. Thomas Höche | Fraunhofer Institute for Microstructure of Materials and Systems IMWS | Germany
Metal nanocrystals embedded in a glass matrix are called “metal nanocluster composite glasses” (MNCG) and exhibit interesting properties, appealing for many different applications like new display materials or optical switches. Especially transition metal nanocrystals as nickel are promising candidates for many MNCG applications as they show strong magnetic behavior interesting for data storage or magnetic resonance contrast media. The magnetic properties however strongly depend on the size of the nanocrystals which need to be tailored for the specific application. A well-suited method for the nickel nanocrystal synthesis is a hydrogen gas flow treatment of a NiO containing base glass at temperatures above Tg, where H2 reduces the Ni2+ species to metallic nickel. Both, time and temperature were found to influence the crystal population. However, also the glass structure plays a distinct role for the final crystal size distribution. To study the compositional effect, different borosilicate glasses were prepared. After the hydrogen gas treatment the nanocrystal-bearing layer was analyzed using X-ray diffraction, transmission electron microscopy as well as X-ray microscopy to obtain information on the microstructure. Depth-dependent size distributions of Ni nanocrystals are discussed on basis of the silicon-to-boron ratio and the type of the network modifier in the glasses.
Crystallization sequence in TiO2-nucleated glass ceramics with quartz solid solution, keatite solid solution and cordierite as main crystalline phases
Dr. rer. nat. Oliver Hochrein | SCHOTT AG, Mainz | Germany
Prof. Joachim Deubener | TU Clausthal | Germany
Sixteen glass samples belonging to the lithium-magnesium-aluminosilicate system were obtained by variously mixing keatite solid solution and cordierite endmember compositions; TiO2 oxide was added as a nucleating agent. Their crystallization sequence was subsequently analyzed by differential scanning calorimetry and X-ray diffraction. It was possible to observe that seed former phases and nucleation efficiency were strongly influenced by the Li2O/(Li2O+MgO) and Al2O3/(Al2O3+SiO2) ratios of the base glasses. Metastable crystallization of high quartz solid solution occurred in all analyzed specimens, but the persistency of this phase was again dependent from the composition of the samples. Further heat treatment invariably induced the formation of cordierite and/or keatite solid solution in the samples: the mechanism of this phase transition and the final microstructure of the samples displayed noticeable differences throughout the studied compositional field.