Influence of mineralogy and particle size on the technological properties of ball clays for porcelain stoneware tiles

The influence of the mineralogical and granulometric characteristics of ball clays on the technological properties of ceramic tiles was investigated with special reference to porcelainized stoneware production. The raw materials currently used by the tilemaking industry are fine-grained clays consisting mainly of kaolinite, quartz, illite and randomly interstratified illite/smectite, with occasional smectite. The particle size distribution affects in particular the plasticity and the size changes of tiles during processing, the finest fraction (<0.2 ?m) being the most effective. The mineralogical composition has a relevant effect on the mechanical properties and pressing behaviour: smectite and interstratified I/S play a prevalent role, together with the structural order of kaolinite and illite. Sintering is to a large extent conditioned by the amount of fluxing components (i.e. feldspars, illite, iron oxyhydroxides, etc.) while the firing shrinkage is also related to the powder compressibility.