Sintering and crystallization behaviour of glass frits made from silicate wastes

Sintering and crystallisation of glass powders obtained front vitrified silicate residues are investigated. The residues considered were ashes derived from the combustion of municipal wastes, glass cullet and feldspar waste, which were mixed in different proportions to result in SiO2 contents >46 wt%. By means of shrinkage measurements using heating microscopy, sintering was found to start at about 750degreesC for all mixtures investigated and to be completed in a very short temperature interval of between 100 and 150degreesC, depending on the composition. Crystallisation took place during the final sintering stage. By means of particle size analysis, linear shrinkage, water absorption and density measurements coupled with x-ray diffraction analysis and scanning electron microscopy, it was found that dense glass ceramic materials can be obtained from powders of average particle size <45 mum. The incinerator fly ash appears to be more suitable than incinerator grate ash for obtaining dense glass ceramics by the powder route developed here.