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Leoben, Austria

The University of Leoben, in the town of Leoben, Austria, is the country's university for mining, metallurgy and materials. It was founded on 4 November 1840, as the Steiermärkisch-Ständische Montanlehranstalt in Styria, Austria's mining region. In 1848 Peter Tunner relocated the university to the nearby town of Leoben, where it is still located today. That year the university had a mere 48 students enrolled. Wikipedia.

Vollath D.,NanoConsulting | Fischer F.D.,University of Leoben
Progress in Materials Science

Based on the definition of fluctuation in connection to phase transformations, structural fluctuations are spontaneous transitions from an equilibrium phase to a non-equilibrium phase, followed by a back-transformation into the equilibrium phase, criteria for the fluctuation of isolated single particles and ensembles of nanoparticles are developed. It is important to realize that, in case of ensembles, the probability for fluctuation depends on the number of transformed particles. Especially the latter criteria are deduced from a statistical model describing fluctuation processes. Furthermore, this statistical model leads to the conclusion that the equilibrium state of fluctuation processes is characterized by a minimum of the free enthalpy. Interestingly, this equilibrium state is independent of the character of the nanoparticles either being conventional particles or ones characterized by indistinguishability. A detailed thermodynamic analysis, studying isothermal and adiabatic processes, of the behavior of a single isolated particle and an ensemble under isothermal and adiabatic conditions allows formulating a set of seven theorems. In the adiabatic case, the calculations indicate the existence of bistability or hysteresis in the temperature range of transformation. Experimentally, these phenomena are well documented, however, in most cases, attributed to activation phenomena. As a result of this study, at least connected to nanoparticles, the interpretation of these experiments needs thorough examination. Furthermore, a complete or partial adiabatic enclosure of the specimen, which is in experimental reality unavoidable, causes a shift of the transformation temperatures. This result enforces a new view on phase diagrams, especially on those for nanoparticles. © 2011 Elsevier Ltd. All rights reserved. Source

Fritz-Popovski G.,University of Leoben
Journal of Applied Crystallography

An extension of the indirect Fourier transformation method for two-dimensional small-angle scattering patterns is presented. This allows for a model-free investigation of real-space functions of oriented structures. The real-space function is built from two-dimensional basis functions. The Fourier transformed basis functions are approximated to the scattering pattern. The solution to this problem in reciprocal space can be used to compute the corresponding real-space functions. These real-space functions contain information on size, shape, internal structure and orientation of the structures studied. Information on structures that are oriented in different distinct directions can be partly separated. The applicability of the technique is demonstrated on simulated data of oriented cuboids and on two experimental data sets based on the nanostructure of spruce normal wood. © 2013 International Union of Crystallography Printed in Singapore - all rights reserved. Source

Fischer F.D.,University of Leoben | Svoboda J.,Academy of Sciences of the Czech Republic
Progress in Materials Science

Diffusion of elements and vacancies is embedded in the framework of continuum mechanics and thermodynamics. The evolution equations for the site fractions of the substitutional and interstitial elements as well as the vacancies are derived. Each possible activity of vacancies, from no to non-ideal and ideal sources and sinks for vacancies, is taken into account. Manning's theory is implemented considering the vacancy wind effect. Furthermore, the role of a stress state is rigorously treated and shows its different influence on substitutional and interstitial elements as well as on vacancies. The reader is provided by the full set of diffusion equations for each kind of vacancy activity. Physically most relevant types of boundary condition, representing closed system with different activities of vacancies at its surface, are studied in detail. The theoretical framework is demonstrated by two illustrative examples emphasizing the interaction of bulk diffusion with an internal phase interface and/or the surface of the system expressed by contact conditions taking into account the properties of the interface or the surface. © 2013 Elsevier Ltd. All rights reserved. Source

Svoboda J.,Academy of Sciences of the Czech Republic | Fischer F.D.,University of Leoben
Acta Materialia

A rigorous concept for diffusion of hydrogen is presented that allows for the role of trapping and/or hydrostatic stress. Nonlinear partial differential equations for the concentration of freely diffusing hydrogen in the lattice and for the total concentration of hydrogen both in the lattice and traps are derived. A generalized chemical diffusion coefficient can be deduced and is compared with reported relations from the literature. Simulation results are presented for different amounts of traps and their different energetic levels (depths), both for hydrogen concentration profiles and the total amount of hydrogen in the case of charging or discharging a cylindrical specimen. A significant charging/discharging asymmetry occurs for high hydrogen concentrations and high amounts of traps of sufficient depth. Comparisons of the chemical diffusion coefficient with experimental results from the literature are also presented. © 2011 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved. Source

The new two-dimensional indirect Fourier transformation converts small-angle scattering patterns obtained by means of area detectors into two-dimensional real-space functions. These functions contain identical information to the scattering patterns, but many parameters related to the microstructure can be obtained directly from them. The size and shape of the microstructures are mainly reflected in the contours of the real-space functions. Their height can be used to get information on the internal architecture of the microstructures. The principles are demonstrated on nanostructured silica biotemplated by spruce wood. © 2015 International Union of Crystallography. Source

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