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Pagani A.,National Research Council Italy | Francescon F.,Ideal Standard International | Pavese A.,National Research Council Italy | Pavese A.,University of Milan | Diella V.,National Research Council Italy
Journal of the European Ceramic Society | Year: 2010

The present investigation deals with a characterization method for fired body (cast piece) from a standard sanitary-ware industrial cycle, relying upon data mainly from optical/electron microscopy and chemical mapping. Image processing techniques have been used to reconstruct the phase-distribution throughout the body, so as to provide a phase-arrangement-sensitive description of the crystalline and amorphous components. The results so attained are compared with those from classical X-ray powder diffraction in terms of total phase-contents. The amorphous phase-content and its distribution can be determined by optical microscopy, and the modest level of precision of the phase quantification is improvable by accounting for the occurrence of voids. Residual quartz is identified by means of the backscattered electron contrast differences in images, and thereby its morphologic properties and amount are determined. The use of elemental X-ray maps allows one to attain a description of the local composition and, on the basis of some assumptions, to quantify microcrystalline mullite and also discriminating between primary versus secondary mullite. © 2009 Elsevier Ltd. All rights reserved.


Bernasconi A.,University of Milan | Marinoni N.,University of Milan | Pavese A.,University of Milan | Pavese A.,National Research Council Italy | And 2 more authors.
Ceramics International | Year: 2014

This work is focused on the study of macroscopic and microscopic properties of traditional sanitary-ware vitreous bodies as a function of feldspar flux and firing time-temperature profile, using a fixed slip formulation (50 wt.% clay, 25 wt.% quartz and 25 wt.% feldspar). Two flux particle sizes (45 and 75 μm), three flux compositions (Na-based feldspar, K-based feldspar and a mix of them) and three firing cycles with the same soaking temperature (i.e. 1240 C) have been combined to evaluate their effects on the relevant industrial properties of water absorption and thermal expansion. The micro-scale observables, phase composition and micro-morphology, have also been investigated. Despite a general similarity exhibited by the ceramic samples, qualitative and quantitative differences in terms of feldspar dissociation temperature, phase-composition and densification trends have been observed. In particular, for a fixed firing cycle, the combination of the sodium based feldspar with the smallest flux particle size leads systematically to a water absorption value that is below the 0.5 target value and to a glass amount that approaches 70 wt.%. Thermal expansion coefficients below the quartz α-β transition are found in the 6.2-6.9×10-6 C-1 range; the highest values seem to be favoured by incorporation of potassium based. © 2013 Elsevier Ltd and Techna Group S.r.l.All rights reserved.


Bernasconi A.,University of Milan | Diella V.,National Research Council Italy | Pagani A.,National Research Council Italy | Pavese A.,University of Milan | And 5 more authors.
Journal of the European Ceramic Society | Year: 2011

This work reports a study on (i) the evolution of mineral phases versus time and temperature, and (ii) some relationships between phases observed, process parameters, and macroscopic properties (thermal expansion and water absorption), in sanitary-ware vitreous bodies. These properties are relevant to satisfying the technical requirements of sanitary-ware. We have fixed the green body composition, varying some key process parameters, such as firing temperature (Tf), firing time (tf) and quartz grain size (d50); a grid of 30 Tf-tf-d50 points has been explored. We have spanned the tf-Tf space (0-80min; 1200-1280°C) using firing temperatures representative of the plateau values of the heating curve in industrial processes. X-ray powder diffraction has been used to determine the phase composition for each Tf-tf-d50 point. Scanning electron microscopy proved useful in enhancing the micro-structural characterization. Quartz d50 seems to be the process-parameter which most effectively co-relates with the thermal expansion of the glassy matrix. © 2011 Elsevier Ltd.


Bernasconi A.,University of Milan | Diella V.,National Research Council Italy | Marinoni N.,University of Milan | Pavese A.,University of Milan | And 2 more authors.
Ceramics International | Year: 2012

Two series of glazes have been produced from different combinations of the same raw materials in the range of interest for sanitary-ware applications: they are designed to allow one to get insight into network-forming and network-modifying species. Fusibility tests and hot stage microscope observations show the influence of even low differences in the starting chemical compositions on the transformation temperatures. X-ray powder diffraction, wavelength dispersion spectrometry and scanning electron microscopy prove that: (i) zircon, the most abundant crystalline phase, is homogeneously distributed and decreases by a 3% from its starting value; (ii) the glass-phase of glaze has a quasi-uniform composition. X-ray synchrotron radiation micro-tomography shows that glaze porosity is 15% by volume, and voids are prevalently not interconnected and with size up to 50 μm. The linear thermal expansion of the glass phase of glaze ranges between 6 and 7 × 10 -6 °C -1, without apparent correlation with composition. © 2012 Elsevier Ltd and Techna Group S.r.l. All rights reserved.


Pagliari L.,University of Milan | Dapiaggi M.,University of Milan | Pavese A.,University of Milan | Pavese A.,CNR Institute for the Dynamics of Environmental Processes | Francescon F.,Ideal Standard International
Journal of the European Ceramic Society | Year: 2013

Cristobalite is a common silica polymorph in ceramics, as it can crystallize in SiO2-rich systems during high temperature processes. Its occurrence in final traditional ceramic bodies remarkably affects their thermal expansion, thus playing an important role in the shrinkage upon cooling. The quartz-cristobalite transformation kinetics is investigated by in-situ isothermal X-ray powder diffraction experiments and then correlated to the average particle size (〈d〉) of the starting quartz using a model here developed. An Avrami-like rate equation, i.e. α(t)=1-exp(-k×t)n, in which the n-term is assumed to account for the dependence on the average particle size, has provided the best fitting of theoretical to experimental data, yielding activation energy values that range from 181 to 234kJmol-1, and exponential n-coefficients from 0.9 to 1.5. Ex-situ observations have demonstrated that the formation of cristobalite from quartz after 50min, 2, 4 and 6h at 1200 and 1300°C, exhibits a remarkable dependence on 〈d〉 of quartz, showing comparable behaviours in the case of 〈d〉 equal to 15.8 and 28.4μm, but significant differences for 〈d〉 of 4.1μm. The formation of cristobalite is boosted remarkably at temperature higher than 1200°C, with an increase by weight even of 500%, with respect to its content at lower temperature. The method of sample preparation (dry powder, wet powder and tablet of compressed dry powder) seems to influence the results only at temperature > 1200°C and in the case of fine powder. © 2013 Elsevier Ltd.

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