Differences in densification behaviour of K- and Na-feldspar-containing porcelain bodies

Porcelain bodies fabricated from triaxial mixtures of clay, quartz and feldspar with different amounts of Na2O and K2O were investigated to study their densification behaviour on thermal treatment at which the bodies achieve full vitrification. The high temperature dilatometric study has shown a distinct behaviour in their densification rate. The degree of vitrification of the densified samples and samples separately heated at different temperatures was determined by measuring the shrinkage, bulk density (BD), percent water absorption (%WA) and flexural strength. It was found that Na-rich feldspar containing body composition achieve full vitrification at lower temperature compared to K-rich feldspar containing composition with improved flexural strength. Differential thermal analysis-thermogravimetric analysis (DTA-TGA) confirms similar reaction steps for both the compositions up to 1000 degreesC, beyond which feldspar forms eutectic melt and starts reacting. As the purity of raw materials has a strong influence on the colour of the fired bodies, the bodies were also subjected to colour measurement and their differences in whiteness also compared, and is discussed in this paper. The scientific and technological importance of such vitrified porcelain products has also been touched upon, highlighting their industrial application. (C) 2003 Elsevier Science B.V. All rights reserved