Caratterizzazione chimico-mineralogica e tecnologica di materiali naturali zeolitizzati e scarti industriali da impiegare per la realizzazione di ceramici tradizionali e ceramici avanzati

The experiments performed in this work made it possible to collect positive indications concerning the possibilities of the thermal transformation of natural zeolitized materials and powder-like industrial wastes into ceramics. The structural evolution at temperatures higher than 1000 °C results in the thermal collapse of the structure of the zeolitic components which gives rise to prevailingly amorphous products. Scant crystals of phases exhibiting high thermal stability, such as feldspar, augite and quartz, are dispersed in such amorphous matrix which is mostly composed of silica, alumina and iron oxide. The thermal treatment brings to final products similar to traditional ceramics characterised by good densification and good mechanical properties but also evidenced some difficulties and problems which require further reflections. Nevertheless the high values of linear shrinkages recorded in this work seem to strongly hinder the thermal transformation of this powder-like waste into ceramics. However, an attempt of obtaining lower linear shrinkages was performed by preventive thermal treatment aimed at evolving part of zeolitic water; Ba- and K-exchange of starting materials resulting in celsian and leucite crystallization; mixing of this by-product with powder-like waste exhibiting higher dimensional stability, such as those deriving from quartz-feldspar-kaolinite sands for glass production.