Univ.-Prof. Dr. Volker Kahlenberg
Applied mineralogy and crystallography
The activities of the group are at the interface between applied and basic research. The focus is on materials development and characterization of solids used in industrial high-temperature processes. These include, for example, products from the steel, ceramic, glass, binder and refractory industries, which, in addition to high-tech applications, play a direct or indirect role in many areas of everyday life (bricks, sanitary ceramics, tiles, etc.). A particular focus of our research is on in-situ measurements using various X-ray diffraction methods to study the production and use of crystalline solids under conditions as close to process conditions as possible, up to 1500 °C. Furthermore, influences of the crystalline structure on the changes in properties can be tracked directly.
In-situ powder X-ray diffraction study on the high-temperature behavior of the silicate-based ion exchanger Na[Si2O4(OH)]·3H2O
The Diffraction Center West, which has been developed by the working group over many years, and the equipment available there represent a distinctive resource in Austria for the investigation of single crystals and polycrystalline samples with the objective of obtaining information about their crystal structures using X-ray diffraction. The emphasis is on oxidic compounds, which are of particular significance for our own field of research. The center's diverse sample environments permit investigations of materials' behavior under a range of non-ambient conditions, including high or low temperatures, elevated pressures, variable humidity, and reactive gas atmospheres. The center's pool of devices is optimized for specific applications and collectively cover a vast range of applications, which are utilized intensively by numerous LFU and external partners.
Phase triangle in the ternary system Na2O-CaO-SiO2
The interpretation of the high-temperature behavior of silicate materials is essentially based on precise knowledge of the respective phase diagrams. Surprisingly, however, this data is lacking for a large number of “simple” three- or four-component systems. In the course of our recent investigations, we have worked on a series of systems for the first time, proven the existence of new phases, and corrected the results of older studies. In addition to carrying out syntheses in the numerous furnaces available in our labs - also combining it with thermoanalytical experiments (DTA-TG-MS, DSC) - the results can be compared with thermodynamic modeling calculations using software packages such as FactSage.
Experimental (left) und theoretically predicted (right) single-crystal diffraction pattern of the iron- ore sinter phase SFCA-III. The pattern can be explained with an oriented intergrowth of two different polytypes.
A comprehensive understanding of the crystal structure is indispensable in elucidating the physicochemical properties of crystalline solids. Our extensive experience has demonstrated that, particularly in industrially relevant systems, rapid reaction processes can frequently result in the formation of intricate structural phenomena, including polytypism, polysomatism, twinning, and modulated structures. The successful description of such complex systems requires a high degree of specialized crystallographic knowledge, which is available in the working group and makes us a valued cooperation partner at the national and international levels.