Effect of boron oxide on the microstructure of mullite-based glass-ceramic glazes for floor-tiles in the CaO–MgO–Al2O3–SiO2 system

• Published in: Journal of the European Ceramic Society 2006-01, Vol.26 (12), p.2285-2292
• Main Authors: Torres, F J, de, Sola E R, Alarcon, J
• Format: Article
• Language: English
• ISSN: 0955-2219
• DOI: 10.1016/j.jeurceramsoc.2005.04.020

The effect of increasing replacement of Al2O3 by B2O3 in a parent glass on the sintering and further crystallisation of mullite was investigated. The composition of the parent glass was chosen in the mullite primary phase field of the CaO-MgO-Al2O3-SiO2 quaternary system. Glass powder pellets were heated under standard (10 C/min and 2 h of hold time) and fast (25 C/min and 5 min of hold time) heatings at different temperatures from 700 to 1190 C. Sintering of B2O3-containing glasses took place in the range between 850 and 1050 C. XRD showed that mullite formed as unique crystalline phase for glasses containing amounts of B2O3 larger than 6 wt%. For lower amounts of boron oxide, cordierite was formed as secondary crystalline phase. Quantitative determination of mullite by Rietveld analysis indicated that the higher amount of mullite present in the glass-ceramic fast heated at 1160 C was 19.5 wt% for the glass containing 9 wt% of B2O3. The final microstructure of the glass-ceramic glazes showed the presence of well shaped, long acicular mullite crystals dispersed within the residual glassy phase. Results of glass-ceramic glazes when applied as slurry and under industrial heating conditions indicated promising mechanical properties. 20 refs.