Time: 01:40 p.m.
Place: Materials Day 2013, Ruhr-Universität Bochum, Bochum, Germany
Herbert Gleiter, Karlsruhe Institute of Technology, Karlsruhe, Germany
Modern technology is based on the fact that the properties of crystalline solids can be controlled by modifying their atomic structure (e.g. by structural phase transformations or by introducing lattice defects) and/or by varying their chemical composition (e.g. by alloying). Comparable structural/chemical modifications of today's glasses are not possible because their atomic structures and their chemical compositions are controlled by the structures/compositions of the corresponding rapidly cooled melts at the glass transition temperature.
Nano-glasses are a new class of non-crystalline solids. They differ from todays glasses by their microstructure that resembles the microstructure of poly-crystals. In fact, they consist of nm-sized regions with melt-quenched glassy structures connected by interfacial regions, the structure of which is characterized (in comparison to the corresponding melt-quenched glass) by (1) a reduced (up to about 15%) density, (2) a reduced (up to about 20%) number of nearest neighbor atoms and (3) a different electronic structure. If these glassy regions have different chemical compositions, multi-phase nanoglasses result that consist e.g of nm-sized ionic SiO2 and metallic PdSi regions In other words, it is the attractive novel feature of nanoglasses that they open the way to generate solids with new non-crystalline atomic and new electronic structures as well as with new chemical compositions that differ from the atomic and the electronic structures as well as the chemical compositions of the glasses available today. Due to their new kind of atomic, electronic and chemical structures, the properties of nano-glasses may be modified by (1) controlling the size of the glassy regions (i.e. the volume fraction of the interfacial regions) and/or (2) by varying their chemical compositions. Nano-glasses exhibit new properties, e.g. a Fe90Sc10 nano-glass is (at 300 K) a strong ferromagnet whereas the corresponding melt-quenched glass is paramagnetic. Moreover, nano-glasses were noted to be more ductile, biocompatible, and catalytically more active than the corresponding melt-quenched glasses.
In the past, the understanding and utilization of crystalline materials such as metals, semiconductors, ceramics etc. resulted in specific periods within the development of mankind such as the iron age, the bronze age etc. All of these periods are characterized by the fact that new properties of new materials permitted new technologies to be developed. Today, we seem to be in a comparable situation for materials with non-crystalline structures. In fact, nanoglasses seem to open the way to a world of new non-crystalline materials with controllable atomic, electronic and chemical structures and new properties. Hence, by analogy to the developments based on crystalline materials in the past (such as the iron age, the bronze age etc.), nanoglasses may permit the development of an age of new technologies based on utilizing the new properties of nanoglasses.
A prerequisite for a development of this kind (a kind of “glass age”) is, however, that one succeeds in developing economic methods for producing large quantities of nanoglasses.