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Whiston, United Kingdom

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.

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