RESEARCH INTERESTS OF THE DIECKMANN GROUP
General Interests
The focus of the research of the Dieckmann Group is on the high temperature physical chemistry of solids. Investigated are thermodynamic and kinetic topics. One important area is the systematic investigation of the relationships between point defects and point defect-related properties in transition metal-containing ionic crystals and the kinetics of solid state reactions in related model systems. Another area of interest is high temperature reactions that have potential to be used for the in-situ fabrication of metal-ceramic microstructures, including composites. Recently, we became interested in the diffusion of ions in glasses.
Point Defects and Point Defect-Related Properties of Non-stoichiometric Oxides
The non-stoichiometry of ionic crystals is related to the presence of ionic and electronic point defects, i.e., to a component activity-dependent disorder. Our group experimentally determines values for the deviation from the stoichiometry in transition metal-containing oxides, for the diffusivity of cations and the electrical conductivity in order to investigate in detail the relationships between point defects and the transport of matter and charge. Models for these relationships are developed based on the experimental results.
Kinetics of Solid-State Reactions in Model Systems
We are interested in the kinetics and the morphology of solid-state reactions. To better understand these topics we study the relationships between transport, nucleation, reaction rates and the morphology of reaction products. Recently, our focus is on spinel formation reactions. By combining experimental results for the defect-related transport of ions in the solid phases involved in spinel formation reactions with experimental observations for the spinel formation kinetics we try to reach a detailed understanding of the reaction; this includes the type of point defects which is most important for the reaction.
High Temperature Reactions Leading to Metal-Ceramic Microstructures
Due to the interest in metal-ceramic composites our group has become interested in studying reactions which have the potential to be used for the in-situ formation of such composites. The reactions considered are partial reduction reactions and displacement reactions. We are especially interested in obtaining a better understanding of the relationships between different processing parameters, reaction rates and the microstructures obtained.
High Temperature Phase Equilibria
When required for studies of the types discussed above we also investigate phase equilibria at high temperatures. For this purpose we experimentally determine by measuring different properties as a function of thermodynamic variables, the conditions at which phases are stable and where phase transformations occur. Of interest in most cases are metal/oxide equilibria or equilibria between different oxides. Thermodynamic modeling is also performed.
Ceramic Single Crystal Growth
Ceramic single crystal growth is mainly done to obtain single crystals for investigations on the topics described above. We have also performed systematic single crystal growth of oxides, which have the potential to be used as laser materials, i.e., Cr-doped forsterite and differently doped YAG. We systematically study the relationships between the growth conditions and the crystal properties obtained. -- Some information about our ceramic single crystal laboratory can be accessed by clicking here.
Diffusion of Cations in Glasses
For several years our group is now involved in the study of the diffusion of cations in glasses and of the influence of water incorporated into glass on this diffusion. Studies were performed on the diffusion of sodium in silica in in Corning Code 1737 glass and on the influence of water on this diffusion. Currently we perform studies on the diffusion of sodium in model glasses of the system CaO-Al2O3-SiO2. The influence of the composition of the glass, the temperature, and the moisture content of the environment is investigated.
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last update: 07/06/2005