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CERAMIC MATERIALS BASED ON HIGH AMOUNTS OF INDUSTRIAL WASTESE

Emilia Karamanova, Alexander Karamanov

Abstract

The production of tiling and building ceramics is based mainly on the traditional system clay-silica-feldspar. However, in recent decades it has been demonstrated that some of these raw materials can be successfully replaced by various industrial wastes. Because of the high feldspars price a significant part of these studies was based on the usage of different alternative “amorphous” fluxes (as glass culets, TV cathode ray tubes, basaltic tuffs and others). Unfortunately, the addition of similar materials in amounts, higher than 10-15 wt %, leads to an increase of the amorphous phase in ceramics, which decreases their mechanical properties. However, if an industrial waste with appropriate chemical composition is combined with clay materials, in some cases it is possible to eliminate entirely the feldspars, as well as to obtain ceramics with higher crystallinity and improved mechanical properties; this intriguing result is possible when controlled re-crystallization processes is taking place during the sintering and cooling steps. In the present work author’s results with similar ceramics, based on 70 wt % metallurgical slags and on 60 wt % bottom ashes from municipal solid waste incinerator (MSWI) are summarised. The sintering is studied by dilatometry, while the crystallization process – by DTA-TG and XRD analysis. The structures of the final samples (both surface and fractures) and morphology and compositions of the formed crystal phases are characterized with SEM coupled with EDS. The open and closed porosities are evaluated by water absorption and density measurements with gas pycnometer. The results elucidate that the new ceramics are characterised with low open (0.5-5.0 vol %) and relatively high closed (10-20 vol%) porosities, as well as with 40-60 wt % crystallinity. The observed structures and phase compositions are untypical for the traditional ceramics and are comparable to those of the glass-ceramics from industrial wastes, which however are produced by a more complicated and more expensive technology cycle.

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DOI resolver: doi.org/10.5593/sgem2021/4.1/s18.27

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