Effect of fly ash on the physico-chemical and mechanical properties of a porcelain composition

The ceramic industry is one of the largest consumers of natural raw materials but has also the capacity and potential to make significant contributions in solving environmental problems by consuming solid rejects of various industries. In a traditional triaxial porcelain composition quartz was fully substituted by fly ash. The effect of this substitution and subsequently firing the specimens at different temperatures (1100-1300 degrees C) were investigated by measuring related properties. Optimum properties were obtained with the specimen having 30% fly ash. Requirement of feldspar was found to be reduced to 20%. The flexural strength of the porcelain body reached a maximum value of 72.3 MPa at 1300 degrees C while the apparent porosity value reached almost zero. There was around 20% increase in flexural strength in comparison to that of the conventional triaxial body. Higher proportion of feldspar above 20% resulted in narrowing the vitrification range. Mullite content was found to increase with increasing proportion of fly ash. SEM studies revealed the presence of alpha-quartz and secondary mullite needles embedded in a glassy matrix. Extensive cracking around the quartz grains was also observed. Intense interlocking of fine mullite needles was found to be responsible for development of higher flexural strength in fly ash incorporated porcelain body. A composition has been proposed where fly ash as high as 30% can be accommodated. Thus, an alternative use of an otherwise waste material is proposed, which can be converted into economic benefit and at the same time offering a possible solution to problems so far as environmental and waste disposal are concerned. (C) 2010 Published by Elsevier Ltd and Techna Group S.r.l