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Modelling and simulation of the mechanical properties of YSZ/Al2O3 composites: a preliminary study
No full textIn recent years, a model based on the Voronoi tessellation and the random electrical networks (EN) has been developed to simulate the influence of the microstructure on the electrical properties of polycrystalline ionic conductor composites and encouraging results have been obtained. By the same approach, the elastic modulus of yttria-stabilized cubic zirconia (YSZ)/Al2O3 has been tentatively simulated exploiting the analogy between the electrical and mechanical dynamic responses. A random network constituted of discrete elastic elements (springs) was used to sketch the mechanical behaviour of these polycrystalline composites. Preliminary results and remarks are presented and discussed
A random resistor model to forecast the electrical properties of crystalline ionic conductor composites
No full textA model able to forecast the electrical properties of crystalline composites is presented. Systems having both insulating and ionic conducting phases were simulated taking into account the relative size and distribution of the particles. The model works through three steps: a suitable digital image-based representation of the material microstructure, its conversion into a 3-D electrical network and the impedance calculation. The polycrystalline microstructure of the matrix was generated using the Voronoi tessellation and the insulating phase was successively distributed along intergranular positions by a Montecarlo method. The simulated digital image was converted in a network of cubes and their edges substituted with discrete circuits. Such a procedure was pet formed by well defined rules; so the bulk and the grain boundary electrical behaviour of the different phases was reproduced. The electrical network thus attained was solved via a transfer-matrix method and the complex impedance spectra obtained. The model might be used to tailor the composites in order to obtain the best compromise between its electrical properties and microstructure
How to forecast the electrical behaviour of ionic conductor composites ?
No full textThe theoretical models that might be used to forecast the electrical behaviour of ionic conductor composites for application in SOFCs are reviewed. A comparison of the different models is performed and comparative analysis of their power is presented on the basis of a case simulation (YSZ (7,54 mol%Y2O3)-Al2O3 (5 wt%) composite). The lack of systematic experimental works makes a wide comparison with the theoretical results very difficult, so the real power of the models can not yet be fully assessed and only introductory considerations are tentatively given. Nevertheless from the preliminary results, it seems possible to affirm that Electrical Network Models are able to better sustain the simulation of the electrical properties of YSZ-Al2O3 composites. Certainly many other improvements have to be done before ENMs became confident tools for tailoring "ab initio" the electrical properties of two phase mixtures
The evolution of cement paste hydration process by impedance spectroscopy
No full textImpedance spectroscopy (I.S.) measurements were carried out on ordinary portland cement paste, cured in 100% relative humidity environment, at different temperatures. The results collected during 28 d show that the electrical conductivity decreases to an almost constant value. The higher the curing temperature the shorter is the time necessary to obtain the quasi-steady-state conditions. A thermally activated conduction mechanism in cement paste was observed. The possibility of using I.S. (a non-destructive and in-situ technique) to follow the evolution of the cement paste hydration process was validated by traditional techniques (X-ray diffraction and thermogravimetry). Very good agreement was obtained
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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